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Hypothesis Analytical expressions for calculating Hamaker constant (HC) and van der Waals (VDW) energy/force for interaction of a particle with a solid water interface has been reported for over eighty years. This work further developed novel analytical expressions and numerical approaches for determining HC and VDW interaction energy/force for the particle approaching and penetrating air-water interface (AWI), respectively. Methods The expressions of HC and VDW interaction energy/force before penetrating were developed through analysis of the variation in free energy of the interaction system with bringing the particle from infinity to the vicinity of the AWI. The surface element integration (SEI) technique was modified to calculate VDW energy/force after penetrating. Findings We explain why repulsive VDW energy exists inhibiting the particle from approaching the AWI. We found very significant VDW repulsion for a particle at a concave AWI after penetration, which can even exceed the capillary force and cause strong retention in water films on a solid surface and at air-water-solid interface line. The methods and findings of this work are critical to quantification and understanding of a variety of engineered processes such as particle manipulation (e.g., bubble flotation, Pickering emulsion, and particle laden interfaces).

Blocking non-specific binding of fluorescent biomolecules in single-molecule detection is one of the most important approach to minimize the background noise. Polyethylene glycol (PEG) and its derivatives are the most frequently-used self-assembled monolayers (SAMs) for surface passivation because they are particularly effective at reducing the adsorption of a majority of fluorescent biomolecules. Most studies about mechanism focus only on biomolecules themselves and sparse literature exists examining the interactions between commercial fluorophores and organosilane SAMs. The objective of this study was studying the interactions between fluorescein isothiocyanate (FITC) and PEG SAMs in solutions with different ionic strengths. Total internal reflection microscopy (TIRM) was utilized for quantitative analysis of the interactions. In low ionic strength solution, strong electrostatic attractions between PS-silica-FITC particles and PEG500 SAMs were detected even though both bodies were negatively charged. The origin of the attractive force was the charge correlations between the heterogeneous surfaces. In high ionic strength, the electrostatic attractions were completely screened, only left with the van der Waals attractions between the PS-silica-FITC particles and PEG SAMs. Due to the polarizability of FITC molecule, Hamaker constant was enlarged and the measured attractive forces depended on the thickness of PEG SAMs. The phenomenon can be explained by the mechanism of biomolecular resistance, including steric repulsion and hydration shell. The energy penalty of a small molecule is much less than that of a large biomolecule while penetrating into the PEG layers. This work reveals that the PEG SAMs not only fail to prevent the non-specific binding of FITC molecules, but also attract the fluorophores through van der Waals interactions.

Since the middle of the 20th century inorganic and polymer nanomaterials have been increasingly appearing in everyday life. Starting from the phenomenal discoveries of the Toyota Central Research team in the 1990s until today, nanomaterials are used as a reinforcement agent for polymer matrices improving their mechanical, thermal or chemical properties. Consequently, nanofillers led to the significant expansion of polymers applicability. However, it is of great importance to better understand the nature and mechanisms behind these phenomena. The aim of current thesis is focused on boehmite and boehmite-based materials with regard to its unique nature of intermolecular interactions. Unlike many other nanomaterials, boehmite particles are characterized by repelling each other. On the other hand, it shows high attraction with diverse materials including polymers. This provides good ground for the development of outstanding boehmite-based nanocomposites. In this work, the nature of interactions for boehmite-boehmite and boehmite-polymer was studied. A hypothesis in the thesis states that the size of the nanocrystallites, the distances between the γ-AlOOH layers in the boehmite, or/and its surface modification affect intermolecular interactions. To confirm this theory, a range of comprehensive techniques and methods has been applied. The first part of the research was focused on growth of boehmite nanocrystals large enough for targeted investigation. It is worth mentioning, that even though this material is nanocrystalline by structure, the synthesis of boehmite with the crystals larger than 50 nm is a tremendous challenge. Nevertheless, boehmite particles of about 200 nm in crystalline size (abbreviated ACNO) has been achieved in this work. To further characterize materials of focus Small- and Wide-angle X-ray Scattering (SAXS and WAXS) analysis, X-ray Photoelectron Spectroscopy (XPS), Electron Energy Loss Spectroscopy (EELS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Raman Spectroscopy have been used. The particular attention was given to the studies of intermolecular interactions. For this purpose, an advanced Atomic Force Microscopy (AFM) method has been applied, for which custom-made AFM probe was developed. Geological boehmite, ACNO and commercial boehmite (HP14) with various surface modifications of the last were compared. The Hamaker constant for these materials was successfully determined and the plasmonic behavior of the boehmite was studied. Further studies were focused on boehmite-polymer interactions. State-of-the-art 3D microfabrication technique, such as Multiphoton Lithography (MPL), was used to prepare polymer and nanocomposites, based on ACNO boehmite and SZ2080 photoresist. Meanwhile investigating pristine photoresist, an interesting phenomenon of strong but fading adhesion of the polymer microstructures to the AFM tip was discovered. For this purpose, ageing experiments of 3D microstructure sample was performed by means of AFM, XPS and SEM. As a result, time-dependent behavior of SZ2080 was described. This study provides important information for the material science community using MPL printing technique. Nanocomposites based on SZ2080 photoresist and 2 wt% of different types of boehmite as nanofiller prepared by MPL technique, were designed with regard to abovementioned results on long-time behavior. SEM, Intermodulation AFM (ImAFM) and Nanoscale Thermal Analysis (NanoTA) were performed to study the effect of the nanomaterial on the change of topography, Young’s modulus, glass transition temperature, stiffness and energy dissipation. The nanocomposite exhibited different mechanical properties compared to the pure polymer and the nanofiller. Moreover, the inhibition phenomenon of boehmite nanoparticles embedment on photoresist side polymerization, during storage was observed. However, this aspect needs further investigation. This thesis is devoted to a comprehensive thorough study of the interactions between nanoparticles that repel each other, meanwhile attract to other materials. The findings of this thesis bring many answers to currently unexplored questions like estimating Hamaker constant of repulsive materials and the complexity of its nature. Based on the outcome of this work many engineering guidelines for the use of nanocomposites and their design can be gathered., Seit Mitte des 20. Jahrhunderts tauchen anorganische und polymere Nanomaterialien immer häufiger im täglichen Leben auf. Seit den phänomenalen Entdeckungen des Toyota Central Research Teams in den 1990er Jahren bis heute werden Nanomaterialien als Verstärkungsmittel für Polymermatrices verwendet, um deren mechanische, thermische oder chemische Eigenschaften zu verbessern. Folglich haben Nanofüllstoffe zu einer erheblichen Erweiterung der Anwendungsmöglichkeiten von Polymeren geführt. Es ist jedoch von großer Bedeutung, die Natur und die Mechanismen hinter diesen Phänomenen besser zu verstehen. Die vorliegende Arbeit befasst sich mit Böhmit und auf Böhmit basierenden Materialien im Hinblick auf die einzigartige Natur der intermolekularen Wechselwirkungen. Im Gegensatz zu vielen anderen Nanomaterialien zeichnen sich Böhmitpartikel dadurch aus, dass sie sich gegenseitig abstoßen. Auf der anderen Seite zeigt es eine hohe Anziehungskraft auf verschiedene Materialien, einschließlich Polymere. Dies bietet eine gute Grundlage für die Entwicklung hervorragender Nanokomposite auf Böhmitbasis. In dieser Arbeit wurde die Art der Wechselwirkungen von Böhmit-Böhmit und Böhmit-Polymer untersucht. Eine Hypothese in dieser Arbeit besagt, dass die Größe der Nanokristallite, die Abstände zwischen den γ-AlOOH-Schichten im Böhmit oder/und seine Oberflächenmodifikation die intermolekularen Wechselwirkungen beeinflussen. Um diese Theorie zu bestätigen, wurde eine Reihe umfassender Techniken und Methoden angewandt. Der erste Teil der Forschung konzentrierte sich auf das Wachstum von Böhmit-Nanokristallen, die groß genug für eine gezielte Untersuchung waren. Obwohl dieses Material von seiner Struktur her nanokristallin ist, stellt die Synthese von Böhmit mit Kristallen von mehr als 50 nm eine enorme Herausforderung dar. Dennoch wurden in dieser Arbeit Böhmitpartikel mit einer Kristallgröße von etwa 200 nm (abgekürzt ACNO) hergestellt. Zur weiteren Charakterisierung der Materialien wurden Klein- und Weitwinkel-Röntgenstreuungsanalysen (SAXS und WAXS), Röntgenphotoelektronenspektroskopie (XPS), Elektronenenergieverlustspektroskopie (EELS), Transmissionselektronenmikroskopie (TEM), Rasterelektronenmikroskopie (SEM) und Raman-Spektroskopie eingesetzt. Besonderes Augenmerk wurde auf die Untersuchung der intermolekularen Wechselwirkungen gelegt. Zu diesem Zweck wurde eine fortschrittliche Methode der Rasterkraftmikroskopie (AFM) angewandt, wobei eine maßgeschneiderte AFM-Sonde entwickelt wurde. Verglichen wurden geologischer Böhmit, ACNO und kommerzieller Böhmit (HP14) mit verschiedenen Oberflächenmodifikationen des letzteren. Die Hamaker-Konstante für diese Materialien wurde erfolgreich bestimmt und das plasmonische Verhalten des Böhmits wurde untersucht. Weitere Studien konzentrierten sich auf die Wechselwirkungen zwischen Böhmit und Polymer. Modernste 3D-Mikrofabrikationstechniken wie die Multiphotonenlithografie (MPL) wurden zur Herstellung von Polymer- und Nanokompositen auf der Grundlage von ACNO-Böhmit und SZ2080-Photoresist eingesetzt. Bei der Untersuchung von unbehandeltem Fotolack wurde das interessante Phänomen einer starken, aber nachlassenden Haftung der Polymermikrostrukturen an der AFM-Spitze entdeckt. Zu diesem Zweck wurden Alterungsexperimente an 3D-Mikrostrukturproben mit Hilfe von AFM, XPS und SEM durchgeführt. Als Ergebnis wurde das zeitabhängige Verhalten von SZ2080 beschrieben. Diese Studie liefert wichtige Informationen für die Materialwissenschaft, die die MPL-Drucktechnik einsetzt. Nanokomposite auf der Basis von SZ2080-Photoresist und 2 Gew.-% verschiedener Böhmit-Typen als Nano-Füllstoff, die mit der MPL-Technik hergestellt wurden, wurden im Hinblick auf die oben genannten Ergebnisse zum Langzeitverhalten entwickelt. SEM, Intermodulations-AFM (ImAFM) und thermische Analyse im Nanomaßstab (NanoTA) wurden durchgeführt, um die Auswirkungen des Nanomaterials auf die Veränderung der Topografie, des Elastizitätsmoduls, der Glasübergangstemperatur, der Steifigkeit und der Energiedissipation zu untersuchen. Das Nanokomposit wies im Vergleich zum reinen Polymer und zum Nanofüllstoff unterschiedliche mechanische Eigenschaften auf. Außerdem wurde das Phänomen der Einbettung von Böhmit-Nanopartikeln in die Polymerisation auf der Fotolackseite während der Lagerung beobachtet. Dieser Aspekt muss jedoch weiter untersucht werden. Diese Arbeit widmet sich einer umfassenden Untersuchung der Wechselwirkungen zwischen Nanopartikeln, die sich gegenseitig abstoßen, während sie sich zu anderen Materialien anziehen. Die Ergebnisse dieser Arbeit liefern viele Antworten auf bisher unerforschte Fragen wie die Abschätzung der Hamaker-Konstante von abstoßenden Materialien und die Komplexität ihrer Natur. Auf der Grundlage der Ergebnisse dieser Arbeit können viele technische Richtlinien für die Verwendung von Nanokompositen und deren Design erstellt werden.

The topographical features on the individual particles in a powder and the surfaces with which they interact affect the powder adhesion. An experimental and modelling framework called the Enhanced Centrifuge Method (ECM) maps particle and surface properties onto 'effective' Hamaker constant distributions that describe the van der Waals (vdW) adhesion between a powder and a surface. The ECM was used to study the adhesion between polystyrene powder and silica surfaces to exemplify the 'effective' Hamaker constants quantify the effects of particle and surface properties on adhesion. Silica surfaces were polished to alter their surface roughness profiles to reveal levels of roughness in which the adhesion was controlled by either the powder or surface properties. This study revealed surface roughness height descriptions are inadequate descriptors of adhesion, and instead the frequency of roughness peaks to the particle size must be considered. This result was verified using an existing particle adhesion simulator.

In this study, a novel technique based on adaptive fading extended Kalman filter for atomic force microscopy is proposed to directly estimate the topography of a sample surface without needing any control system. While in conventional imaging techniques, the scanning speed or the bandwidth is limited due to a relatively large settling time, the method proposed in this research is able to address this issue and estimate the topography throughout transient oscillation of the microcantilever. With this aim, an estimation process using an adaptive fading extended Kalman filter (augmented with forgetting factor) as the system observer is designed and coupled with the system dynamics to obtain sample topography. Obtained results demonstrate that the sample height is estimated by this algorithm with high accuracy and a relatively high scanning speed. Moreover, the observer is able to identify the topography and Hamaker constant simultaneously. Therefore, the presented approach can compensate for the low scanning speed of the classical imaging method as well as eliminate the need for a closed-loop controller.

Hypothesis: As a fluid approaches three phase coexistence, adsorption may take place by the successive formation of two intervening wetting films. The equilibrium thickness of these wetting layers is the result of a delicate balance of intermolecular forces, as dictated by an underlying interface potential. The van der Waals forces for the two variable adsorption layers may be formulated exactly from Dzyaloshinskii-Lifshitz-Pitaevskii theory, and analytical approximations may be derived that extent well beyond the validity of conventional Hamaker theory. Calculations: We consider the adsorption equilibrium of water vapor on Silver Iodide where both ice and a water layers can form simultaneously and compete for the vapor as the triple point is approached. We perform numerical calculations of Lifshitz theory for this complex system and work out analytical approximations which provide quantitative agreement with the numerical results. Findings: At the three phase contact line between AgI/water/air, surface forces promote growth of ice both on the AgI/air and the water/vapor interfaces, lending support to a contact nucleation mode of AgI in the atmosphere. Our approach provides a framework for the description of adsorption at three phase coexistence, and allows for the study of ice nucleation efficiency on atmospheric aerosols., Accepted Manuscript

The paper is a theoretical study of mechanically activated processes in tribocontact, which lead to the formation of a lubricating film between rubbing bodies. The adhesive aspect of tribofilm formation is considered using the condition of the mechanical activation of the friction surface. This condition is satisfied when the adhesion energy becomes greater than the cohesion energy. The Hamaker constant is used to describe not only the adhesive interaction during friction, but also the amount of matter transferred when the mechanical activation condition is met. It is shown that the adhesive effect decreases with the second power of the distance from the friction surface. A relationship is derived that relates tribological characteristics to the Hamaker constant as the fundamental characteristic of the material. It is shown how the friction coefficient in the steady-state regime depends on the counterbody material and the antifriction transfer film material. Numerical results are compared to experimental data.

Thin polymeric coatings are commonly used for altering surface properties and modulating the interfacial performance of materials. Possible contributions from the substrate to the interfacial forces and effects are, however, usually ignored and are not well understood, nor is it established how the coating thickness modulates and eventually eliminates contributions from substrates to the van der Waals (vdW) interfacial force. In this study we quantified, by colloid-probe atomic force microscope (AFM) and by theoretical calculations, the interfacial vdW contributions from substrates acting through ethanol plasma polymer (EtOHpp) coatings of a range of thicknesses on Au and Si bulk materials. In approach force curves against EtOHpp-coated Au substrates the magnitude of the vdW force decreased as the EtOHpp coating thickness increased to 18 nm and then plateaued with further increases in coating thickness, providing direct evidence for a contribution to the total interfacial vdW force from the Au substrate acting through thin coatings. The experimental observations accord with theoretical calculations of the thickness dependence of Hamaker coefficients derived from rigorous simulation using the Lifshitz theory. In addition, the measured forces agree well with theoretical predictions including correction for finite roughness. Thus, our experimental and theoretical results establish how the thickness of polymer thin film coatings modulates the total interfacial vdW force and how this can be used to tune the net vdW force so as to either contain a large substrate contribution or arise predominantly from the polymeric overlayer. Our findings enable rational design of coating thickness to tailor interfacial interactions and material performance. Refereed/Peer-reviewed

Mounting the atomic force microscope (AFM) probe on the gripper of the robotic nanoscale manipulators system enables the combination of the AFM and scanning electron microscope (SEM). The AFM–SEM-based method of determining Hamaker constant for carbon nanotube (CNT) and AFM cantilever in the vacuum condition of SEM, which is completed through a robotic nanoscale manipulators system, is presented for the first time. During Hamaker constant determining experiment, the elastic force is measured utilising integrated AFM–SEM imaging technique through detecting the deflection of AFM cantilever that actually equals van der Waals adhesion force. The van der Waals attraction force between CNT and AFM cantilever is calculated through the modelling of a cylindrical nanotube and a flat gold-coated surface. The experiment results indicate that Hamaker's constant measured are comparable to typical values published by previous researchers, being of the order of 100 zJ, which indicates that the present approach is valid and reliable.

In this study a theoretical study is carried out on the binary collision of round-sided disks (RSD) suspended in a Newtonian fluid under a simple shear flow. RSD is composed of a disk part and a half-torus part which circumscribes the side of the disk. The diameter of the disk is fixed at 2 µm while the thickness and the half-torus size are varied so that the aspect ratio varies from 0.13 to 0.288. The liquid viscosity is changed from 0.01 to 1 Pa·s. The hydrodynamic force and van der Waals force with the Hamaker constant of 1.06 × 10−20 J are considered in tracking the position and the orientation of each particle. The Brownian motion is considered to be negligible. The collision of two particles initially separated by sufficiently a long distance is considered and the kinetic constant of coagulation is obtained by considering the presence of collision, the orientations of two particles and the flux of liquid flow. The result shows that the kinetic constant of coagulation is reduced to approximately 1/4 of the kinetic constant of non-interacting particles by the hydrodynamic interaction when the viscosity is 1 Pa·s. As collision modes, side-side and side-edge are considered. Side-side mode is found to be the dominant mode of collision for differing aspect ratio and differing viscosity of the liquid. The dominance of the side-side collision mode implies the formation of two-dimensional flocs in the shear flow.

In this study a theoretical study is carried out on the collision of two rod-like particles suspended in Newtonian fluid under a shear flow. The length of the particle is fixed at 2 µm while the diameter is varied so that the aspect ratio (length/diameter) varies from 1 to 20. Liquid viscosity is changed from 0.01 to 1 Pa·s. The Brownian motion is considered to be negligible. Both hydrodynamic and van der Waals interactions are included in tracking the position and the orientation of each particle. The Hamaker constant is fixed at 1.06 × 10−20 J. The result shows that the kinetic constant of coagulation is reduced to approximately 40% of the value for the non-interacting particles when the viscosity is 1 Pa·s. As collision modes, face-edge, side-side, side-edge and edge-edge are considered. The side-edge mode is most frequently observed in the given range of aspect ratio.

In this paper, a simulation model for frequency modulation atomic force microscopy (FM-AFM) operating in constant amplitude dynamic mode is presented. The model is based on the slow time varying function theory. The mathematical principles to derive the dynamical equations for the amplitude and phase of the FM-AFM cantilever-tip motion are explained and the stability and performance of its closed-loop controller to keep the amplitude at constant value and phase at 90° is analysed. Then, the performance of the theoretical model is supported by comparison of numerical simulations and experiments. Furthermore, the transient behaviour of amplitude, phase and frequency shift of FM-AFM is investigated and the effect of controller gains on the transient motion is analysed. Finally, the derived FM-AFM model is used to simulate the single molecule/nanoscale force spectroscopy and study the effect of sample viscosity, stiffness and Hamaker constant on the response of FM-AFM.

The initial development and preliminary validation of improvements to an existing approach-to-contact atomic force microscopy (AFM) method for determining the Hamaker constant, A, of solid material...

Recent experiments report that slowly sheared noncolloidal particle suspensions unexpectedly exhibit rate(ω)-dependent complex viscosities in oscillatory shear, despite a constant relative viscosity in steady shear. Using a minimal hydrodynamic model, we show that van der Waals attraction gives rise to this behavior. At volume fractions φ=20-50%, the complex viscosities in both experiments and simulations display power-law reductions in shear, with a φ-dependent exponent maximum at φ=40%, resulting from the interplay between hydrodynamic, collision, and adhesive interactions. Furthermore, this rate dependence is accompanied by diverging particle diffusivities and pronounced cluster formations after repeated oscillations. Previous studies established that suspensions transition from reversible absorbing states to irreversible diffusing states when the oscillation amplitude exceeds a φ-dependent critical value γ0,φc. Here, we show that a second transition to irreversibility occurs below an ω-dependent critical amplitude, γ0,ωc≤γ0,φc, in the presence of weak attractions.

We study a conceivable two-fluid system with a layer of one fluid between a solid support and a semi-infinite layer of the other fluid in which the molecular van der Waals (vdW) forces act like gravity in well-studied cases with similar spatial arrangements. The solid support consists of two layers so that vdW forces are, similar to the gravity systems (GS), finite at the solid–fluid interface. In this Part 1, we focus on the Young–Laplace (YL) equilibrium drops of the “light” liquid with a zero angle between the solid–fluid and fluid–fluid interfaces and compare them with the YL drops in the analogous GS. We point out that there is essentially just a single GS, in contrast to a continuum of vdW systems corresponding to different values of a dimensionless Hamaker constant (DHC). We find that when the latter is above a certain threshold value, the YL drop volume cannot exceed a certain terminal value, just as it is known to be the case for GS. In contrast, in vdW systems with the smaller DHC, the YL drops may have arbitrarily large volumes, which is a major difference from GS. We introduce a certain “non-classical particle” kinetic energy and a corresponding generalized phase plane. These “energy” considerations predict interfaces with vertical tangents, which are in an excellent agreement with equilibrium drop interfaces found by numerical continuation methods. For small DHC, numerical simulations on a neutral-wave-long interval confirm the lubrication-approximation evolutions from initially flat films toward the—perpetually approached—equilibrium YL drops of the same volume. We point out that the evolution for larger DHC may be approached by the boundary integral methods suitable for the Stokes flows, which we will further investigate in the future Part 2 of this work.

Fibrinogen (Fg) self-assembly is sensitive to the physicochemical properties of an environment like pH and ionic strength. These parameters tune the direction and strength of noncovalent physical driving forces determining protein intermolecular interactions. The attraction-repulsion balance in intermolecular interactions of the multidomain protein Fg at pH values 3.5, 7.4, and 9.5 and varying ionic strengths of the water medium has been analyzed by the complex diffusive approach, proposed by us previously. The concentration dependence of protein collective diffusion was analyzed within the phenomenological approach, based on the frictional formalism of nonequilibrium thermodynamics proposed by H. Vink. The analysis of protein diffusion data has shown the fundamental difference in the physical nature and direction of interaction forces between protein molecules at different conditions. The paired interaction potential of protein molecules was characterized in terms of second virial coefficients and Hamaker constants within the Deryaguin-Landau-Verwey-Overbeek theory and the "porous" colloid particle model. Our results indicated the maximum Hamaker constant and dominance of the van der Waals attraction between Fg molecules at pH 7.4. The increase in pH up to 9.5 results in the zero values of the second virial coefficient and Hamaker constant, corresponding to the full reciprocal compensation for electrostatic repulsion and van der Waals attraction. In the acidic medium (pH 3.5), the strong electrostatic repulsion substantially exceeds the van der Waals attraction. A high ionic strength is characterized by a significant decrease of all intermolecular interactions, which is expressed in almost zero values of virial coefficients and the Hamaker constant. Thus, it is experimentally shown that the physiological conditions of the Fg environment (pH 7.4 and slight ionic strength) provide a high probability for peak physical attraction between fibrinogen molecules, which is used in nature to facilitate blood clotting.

This study is to establish computational fluid dynamics (CFD) simulations of disordered fibrous filters under unfavorable conditions to investigate the effects of chemical and physical factors on filtration performance. We employed a discrete phase model (DPM) to track individual particles, and user-defined functions were implemented to consider the particle deposition to the collector surface via interception and interaction energy. During the DPM process, calculations based on interactional and fluid hydrodynamic effects were proceeded for all injected individual colloids. The results of filtration and collision efficiencies of the single collectors obtained by our CFD simulations showed a very good agreement with the existing expressions and data, accurately predicting the trends of particle deposition and reentrainment. After the validation of the developed particle tracking method, the disordered fibrous filters with randomly distributed monodisperse fibers were studied. The results showed that the reentrainment of deposited particles was enhanced with increasing fluid velocity and solid volume fraction and decreasing fiber size due to the hydrodynamic effects. Moreover, the combined effect with ionic strength, Hamaker constant and zeta potential determined particle deposition behavior by altering particle/filter interactions. The developed simulation method for predicting filtration performance does not contain any free parameters or empirical factors.

This article seeks to demonstrate a direct and simplified correlation between the measurement of the wettability and the agglomeration potency of the inclusion particles in liquid ferrous alloy. The established methodology has been validated by the agreement between the calculated coagulation coefficient of Al2O3 particles and the experimental data in the open literature. Subsequently, the coagulation coefficient of Al2O3, MgO, and Ti2O3 particles in ferrous alloy melts was evaluated quantitatively by the proposed method using the actual experimental data of contact angle and surface tension. Meanwhile, the effect of the matrix composition has been investigated by comparing the Hamaker constant and coagulation coefficient between Ti2O3/pure iron and Ti2O3/low-carbon steel systems. It is noted that the change of coagulation coefficient associated with the contact angle is caused by the formation of a new phase at the oxide/metal interface at the high temperature. The present work aims to provide a deep understanding of the connection between inclusion motion behavior in the liquid alloy and the high temperature interfacial phenomenon.

Making a nanoparticle (NP) approach and interact with a plasma membrane (PM) through the receptor-ligand interaction is key for applications like targeted drug delivery, cellular imaging, and theranostics. In this paper, we show that the van der Waals (vdW) interactions dominate the electrostatics ensuring that a gold NP approached the PM more spontaneously as compared to a silica NP. The negative σ (charge density) of a PM induces a negative electrostatic potential at the surface of the approaching gold NP and the silica NP; however, there is very little difference between these induced values due to a small electric double layer at the physiological salt concentration (c∞). Hence there is very little difference in the electrostatic repulsion between the two cases, while the PM-NP vdW attraction is much more for the gold NP as a result of a larger Hamaker constant. Therefore, in comparison to the gold NP, the silica NP would (a) undergo a promotion of the specific adhesion and a prevention of the non-specific adhesion simultaneously for a larger σ − c∞ phase space including the physiological conditions, (b) necessitate a larger length of the ligands to trigger spontaneous receptor-ligand interactions, and (c) require a larger driving force for force-driven receptor-ligand interactions.

A physically substantiated ionic-electrostatic model of the wedge pressure by Deryagin, modified for definition of the water retentivity of natural and artificial colloidal dispersions with a variable moisture content (soils, grounds, clay minerals, wood, caustobioliths, synthetic polymeric hydrogels), is considered. In this model, the relation between the moisture content and dispersivity (effective specific area) of a colloidal system serves as a phase variable. For the first time, with the use of the sorption-equilibrium, moisture-thermodesorption, and equilibrium-centrifugation methods, wedge-pressure isotherms, representing the dependence of the thermodynamic moisture potential (specific Gibbs energy) of a material on the mass fraction of moisture in it, were obtained for materials different in genesis and dispersivity, whose thermodynamic moisture potential varies in absolute value within the wide range 0.1–260 kJ/kg, and the wedge pressure of colloid-bonded disperse systems was quantitatively estimated with regard for the variable factors (temperature, composition, liquid-phase concentration) of the aggregative stability of their colloidal complex determining the phenomenon of dynamics of the dispersivity and water retentivity of such systems. A methodology of calculating the effective specific area of a material by the slope of its wedge-pressure isotherms, constructed at the logarithmic scale, is proposed as an alternative to the standard Brunauer–Emmett–Teller method. The new method is close to the traditional one in the specific area of a material obtained with them, but the method proposed differs favorably from the standard method by the temperature invariance and the possibility of calculating the energy of interphase interactions in the material with the use of the generalized Hamaker constant.

Atomically heterogeneous systems, which are created by low energy (0.5 keV) inert gas ion irradiation on metallic surfaces exhibit wetting properties that are characteristically different from those containing physical or patchwise chemical heterogeneities. The wetting properties of such systems are dictated by modification of intermolecular forces by near-surface implanted impurities, leading to a modified effective Hamaker constant. In the present study, special attention is devoted to look at the wetting hysteresis of such systems. It is found that the contact angle is almost a constant in the advancing mode and a finite hysteresis is observed during the receding process, which is believed to arise from liquid retention in the receding mode. We conclude that the nanoscale roughness and the atomic-scale heterogeneities induce negligible pinning and in the receding mode, the solid exhibits a modified effective Hamaker constant which is dependent on the probe liquid. In the advancing mode, however, the effective Hamaker constant is independent of the liquid and depends only on the solid and the embedded ionic species. The evidence of liquid retention has been further validated by a model involving the effective enhancement of surface free energy due to coverage of a thin liquid film.

The scenario of released nanoparticles from consumer products into the environment especially natural waters has become a great concern nowadays. Assessing their aggregation and stability under environmental conditions is important in determining their fate and behavior in natural waters. The aggregation behavior of selected nanoparticles (iron oxide and alumina) was investigated at variable concentrations of humic acid (5, 10, 50 mg/L), and pH variation in solution. Dynamic light scattering was used to measure their z-average hydrodynamic diameter and zeta potential. Derjaguin-Landau-Verwey-Overbeak (DLVO) theory was used to explain the thermodynamic interactions between two particles. Then, the stability was evaluated by assessing their aggregation. The increasing of humic acid concentrations enhanced aggregation of iron oxide and alumina nanoparticles, particularly at low pH levels. The maximum aggregation was found in pH below the point of zero charge (PZC) due to electrostatic destabilization and electrostatic stabilization that took place at pH above the point of zero charge. Meanwhile, at pH point of zero charge, nanoparticles were coated with negative humic acid charged. From this study, properties of nanoparticles (size, surface charge, Hamaker constant) and environmental condition (humic acid concentration, pH) have their specific roles to control the fate and behavior of nanoparticles in environmental media.

Atomic force microscopy (AFM) is a device that is used for not only high-resolution imaging but also used for measuring forces. It is possible to quantify the surface density change for both colloid and nano probe as well as silica surface. By changing the quantity of ions within a potassium chloride solution, it then becomes possible to evaluate the quantity of ions that attach themselves to AFM colloid probe, nano probe and silica samples. In this study, the force was measured between AFM probes and silica surface in different ionic concentrations. Two different types of AFM probe were used: a colloid probe with a radius of 500 nano-meters and a nano probe with a radius of 10 nano-meters. This study is focused on measuring how the force magnitude, especially electrical double layer force, varied between the two types of probes by changing ionic concentrations. For all test trials, the results agreed with the electrical double layer theory. Although the micron probe was almost an exact match for all ranges, the nano probe was closest within its short-range forces. This is attributed to the formula use when analyzing the electrical double layer force. Because the formula was originally calculated for the micron probe, the shape and size of the nano probe created too many variables for an exact match. Along with quantifying the forces, this experiment allowed for an observation of Van der Waals force making it possible to calculate the Hamaker constant. Conclusively, all results show that the obtained surface charge density increases as the ionic concentration increases. In addition, through the comparison of the results obtained from the nano-sized probe and the micron-sized probe, it was concluded that nano size probe mapped higher surface charge density above the silica surface than the micron-sized probe under the same conditions.

Soot nanoparticles (SNPs) undergo aging processes in aqueous systems, altering their physicochemical properties and affecting their fate and transport. This study investigated the aging effects via ultraviolet irradiation on aggregation kinetics of SNPs in water. The results showed that, compared to fresh SNPs, those irradiated for 1 day aggregated more easily in NaCl and CaCl2 solutions, with reduction of critical coagulation concentrations by 72% and 40%, respectively. Similar phenomena were found in additional six electrolyte solutions, and SNPs irradiated for > 3 days had no measurable difference in aggregation rate. The aggregation-enhancement of irradiated SNPs was more prominent at low electrolyte concentrations and pH > 4. However, in the presence of macromolecules, irradiated SNPs could be stabilized against aggregation via steric hindrance with strength of bovine serum albumin > humic acid > alginate > fulvic acid, whereas alginate further destabilized aged SNPs via calcium bridging. The fitted Hamaker constant increased from 7.8 × 10−20 (fresh) to 1.2 × 10−19 J (7-day irradiated), suggesting that decarboxylation during irradiation may weaken electrical repulsion and enhance van der Waals attraction, promoting aggregation. These results demonstrated the vital role of UV-induced aging in fate and transport of SNPs in wet environments.

Copper oxide films hold substantial promise as anti-stiction coatings in micro-electromechanical (MEMS) devices and with shrinking dimensions on the nanometre scale on nano electromechanical (NEMS) devices. The Hamaker constant will play a very significant role in understanding stiction and tribology in these devices. We used an approximate but sufficiently accurate form of the Lifshitz theory using the multiple oscillator model to calculate the Hamakers constant of symmetric copper oxide thin films based on experimentally obtained dielectric data in the wavelength range 190-850 nm using spectroscopic ellipsometry. We also used the Tabor–Winterton approximation (TWA) and Surface energy measurements to determine the Hamaker constant. There was better agreement in the Hamaker constant values obtained by the limited Lifshitz theory and TWA approach than with the Surface energy approach. The difference is explained through the influence of surface roughness on the surface energy using extensions of the stochastic KPZ growth model and the Family-Vicsek scaling relation and rigorous treatment of the Cassie-Baxter and Wenzel models as optimisations of a surface free energy functional linking roughness and surface tension. The dominance of the Cu2O phase in the films and of the London dispersion force on the surface of the films was previously confirmed by FTIR Cu(I)–O vibrational mode observation and XPS Cu 2p3/2 binding energy peak and its fitted satellites. The use of the limited Lifshitz theory and ellipsometry data would seem to provide a suitable best first approximation for determining the Hamaker constant of predominantly dispersive anti-stiction coatings in technologically important MEMS/NEMS devices.

In this paper, a new multi-frequency excitation method based on combination resonance is introduced to enhance the non-contact atomic force microscopy performance. In combination resonance, excitation frequencies are selected so that summation/subtraction of excitation frequencies is close to the natural frequencies of the microcantilever. Due to the nonlinear nature of this method, the probe response to excitation is very sensitive to change in tip-sample forces. This could be used to generate high-resolution compositional mapping and topographical images of the surface. The present study reveals that both amplitude and phase shift of the combination resonance are sensitive to change in parameters such as Hamaker constant, damping coefficient, Young’s modulus and tip-sample initial distance. It is observed that because of high sensitivity to Hamaker constant a small change in the surface material leads to considerable variations in amplitude and phase shift. This sensitivity is employed to improve compositional mapping of the surface materials. It is also found out that the response amplitude in the combination resonance is very sensitive to change in the tip-sample initial distance. This sensitivity may be used to reduce the vertical noise and increase image resolution, especially in environments with low quality factors. Overall, using this technique the image contrast increases significantly and high resolution compositional mapping of surfaces is achieved.

The investigation and subsequent understanding of the interactions of nanomaterials with components of their surrounding media is important to be able to evaluate both potential use cases as well as potential risks for human health and for the environment. To investigate such interactions, asymmetrical flow field-flow fractionation (AF4) is an interesting analytical tool. This statement grounds on the fact that interactions of the analyte with the membrane and with components of the eluent are crucial for the retention behavior of the analyte within the field-flow fractionation (FFF) channel. Therefore, the investigation of the retention behavior provides an insight in the nature of the interactions between analyte, membrane and eluent. Within this publication, the influence of the composition of the eluent on the retention behavior of aqueous dispersions of two model analytes is investigated. Eluents with different types of salts and surfactants and eluents with different salt concentrations were prepared and the influence of the composition of these eluents on the retention behavior of polystyrene and polyorganosiloxane particles was compared. Three main trends were observed: Elution times increase with increasing electrolyte concentration; when comparing different electrolyte anions, the retention time increases the more kosmotropic the anion is; when comparing different electrolyte cations, the retention order depends on the surfactant. Additional dynamic light scattering (DLS) measurements were conducted to verify that the differences in retention times are not caused by actual differences in particle size. Instead, the differences in elution time can be correlated with the concentration and with the chao-/kosmotropicity of the added electrolyte ions. Therefore, AF4 proves to be sensitive to subtile changes of interaction forces on the level of Coulomb and van der Waals forces. The experimentally gathered elution times were used to develop a model describing the retention behavior, based on an enhanced version of the standard AF4 model: By introducing particle-medium-membrane interactions in the standard AF4 model via the respective Hamaker constants, the calculation of retention times was possible. The congruence of the calculated with the experimental retention times confirmed the validity of the simulation.

Human/humanized IgG4 antibodies have reduced effector function relative to IgG1 antibodies, which is desirable for certain therapeutic purposes. However, the developability and biophysical properties for IgG4 antibodies are not well understood. This work focuses on the head-to-head comparison of key biophysical properties, such as self-interaction and viscosity, for 14 human/humanized, and chimeric IgG1 and IgG4 S228P monoclonal antibody pairs that contain the identical variable regions. Experimental measurements showed that the IgG4 S228P antibodies have similar or higher self-interaction and viscosity than that of IgG1 antibodies in 20 mM sodium acetate, pH 5.5. We report sequence and structural drivers for the increased viscosity and self-interaction detected in IgG4 S228P antibodies through a combination of experimental data and computational models. Further, we applied and extended a previously established computational model for IgG1 antibodies to predict the self-interaction and viscosity behavior for each antibody pair, providing insight into the structural characteristics and differences of these two isotypes. Interestingly, we observed that the IgG4 S228P swapped variants, where the CH3 domain was swapped for that of an IgG1, showed reduced self-interaction behavior. These domain swapped IgG4 S228P molecules also showed reduced viscosity from experiment and coarse-grained simulations. We also observed that experimental diffusion interaction parameter (kD) values have a high correlation with computational diffusivity prediction for both IgG1 and IgG4 S228P isotypes. Abbreviations: AHc, constant region Hamaker constant; AHv, variable region Hamaker constant; CDRs, Complementarity-determining regions; CG, Coarse-grained model; CH1, Constant heavy chain 1; CH2 Constant heavy chain 2; CH3 Constant heavy chain 3; chgCH3 Effective charge on the CH3 region; CL Constant light chain; cP, Centipoise; DLS, Dynamic light scattering; Fab, Fragment antigen-binding; Fc, Fragment crystallizable; Fv, Variable domaing; (r) Radial distribution function; H1 CDR1 of Heavy Chain; H2 CDR2 of Heavy Chain; H3 CDR3 of Heavy Chain; HVI, High viscosity index; IgG1 human immunoglobulin of IgG1 subclass; IgG4 human immunoglobulin of IgG4 subclass; kD, Diffusion interaction parameter; L1 CDR1 of Light Chain; L2 CDR2 of Light Chain; L3 CDR3 of Light Chain; mAb, Monoclonal antibody; MD, Molecular dynamics; PPI Protein–protein interactions; SCM, Spatial charge map; UP-SEC, Ultra-high-performance size-exclusion chromatography; VH, Variable domain of Heavy Chain; VL, Variable domain of Light Chain

It is proposed to apply thermodynamic criteria when choosing a filler in paint formulations - critical surface tension, Hamaker constant. The values of the critical surface tension of a liquid (ethanol solutions with different water content) at the interface with a solid (different fillers) are calculated. The energy of interaction between the filler particles was estimated by the value of the Hamaker constant. Determined that microcalcite has a higher critical surface tension, compared to other fillers. It is shown that when calcite is used as a filler, the inter particle interaction is enhanced. It was found that the use in sol silicate paints as a filler of calcite contributes to obtaining a higher cohesive strength of coatings due to an increase in the contribution of dispersion forces. Based on the study, the numerical values of the Hamaker constant and the critical value of the surface tension of various fillers were obtained. It allowed makes it possible to choose the optimal type of filler. It has been established that there is a linear relationship between the value of the interaction energy between the filler particles (Hamaker constant) and the tensile strength of the coatings. A mathematical model of cohesive strength is obtained depending on the value of the Hamaker constant.

The low-temperature transportation, a process of gathering and transportation at ultrahigh water content, can incline the energy consumption and elevate the efficiency of the surface gathering system. Here we found that there is the risk of wall sticking of heavy oil in the low-temperature transportation.In this work, a theoretical model of boundary condition for heavy oil in low-temperature transportation based on DLVO theory was proposed to predict the wall sticking occurrence temperature. The outcomes of modeling results had a good agreement in comparison with experiment results (error values: 0.1°C~1.5°C).Moreover, the interaction mechanism of wall sticking was correlated well with the Hamaker constant, radius of oil droplets, Ζeta potential, and Debye length.

Deposition of engineered nanoparticles onto porous media from flowing suspensions is important for soil and groundwater quality. The deposition mechanism is controlled by interaction forces between particles and collectors. We investigated the origin and magnitude of opposing forces between silver and mica surfaces (representing nanosilver and sand grains) in solutions relevant to agricultural soils with direct measurements using a surface force apparatus. Solutions of variable NaNO3, Ca(NO3)2, and humic acid (HA) concentrations were used to differentiate individual contributing forces and quantify surface properties. The measured Hamaker constant for silver-water-mica was consistent with Lifshitz theory. Our results indicate that HA forms an adsorbed surface layer, but its charge, thicknesses, compressibility, and mass are significantly larger on mica than silver. Ca2+ primarily reduced the differences between the initially adsorbed HA layer properties on each surface, making them more similar. Force-distance profiles indicate that, when silver-mica systems were exposed to HA, osmotic-steric, electrostatic, and van der Waals forces dominate. Soft particle theory was deemed inappropriate for this system. Derjaguin's approximation was utilized to translate force measurements into interaction energy between nanosilver particles and mica collectors. We propose attachment efficiency estimates from measured surface properties, which suggest high particle mobility when nanosilver is applied to HA-rich agricultural soils with modest ionic strength.

The investigation and subsequent understanding of the interactions of nanomaterials with components of their surrounding media is important to be able to evaluate both potential use cases as well as potential risks for human health and for the environment. To investigate such interactions, asymmetrical flow field-flow fractionation (AF4) is an interesting analytical tool. This statement grounds on the fact that interactions of the analyte with the membrane and with components of the eluent are crucial for the retention behavior of the analyte within the field-flow fractionation (FFF) channel. Therefore, the investigation of the retention behavior provides an insight in the nature of the interactions between analyte, membrane and eluent. Within this publication, the influence of the composition of the eluent on the retention behavior of aqueous dispersions of two model analytes is investigated. Eluents with different types of salts and surfactants and eluents with different salt concentrations were prepared and the influence of the composition of these eluents on the retention behavior of polystyrene and polyorganosiloxane particles was compared. Three main trends were observed: Elution times increase with increasing electrolyte concentration; when comparing different electrolyte anions, the retention time increases the more kosmotropic the anion is; when comparing different electrolyte cations, the retention order depends on the surfactant. Additional dynamic light scattering (DLS) measurements were conducted to verify that the differences in retention times are not caused by actual differences in particle size. Instead, the differences in elution time can be correlated with the concentration and with the chao-/kosmotropicity of the added electrolyte ions. Therefore, AF4 proves to be sensitive to subtile changes of interaction forces on the level of Coulomb and van der Waals forces. The experimentally gathered elution times were used to develop a model describing the retention behavior, based on an enhanced version of the standard AF4 model: By introducing particle-medium-membrane interactions in the standard AF4 model via the respective Hamaker constants, the calculation of retention times was possible. The congruence of the calculated with the experimental retention times confirmed the validity of the simulation.

In this paper, based on the theoretical provisions of the theory of molecular interaction, the results of testing the algorithm proposed by the authors are presented for calculating the Hamaker constant as a characteristic of the dispersion interaction based on experimental data obtained during the study of a composition of fine powders of basalt and polymineral sand. The concept of the Hamaker analog constant is introduced; the method of determining and calculating it is based on a number of assumptions. The desired constant was calculated based on the measured equilibrium angles of wetting the surface of the dispersed material with liquids with known surface tension values. Water solutions of ethanol with different volume concentrations of the organic component were used as such liquids. For the correct application of water-alcohol systems in the proposed method, the physical and chemical constants of the water-ethanol system are calculated. It was found that the change in the structure of the powder composition allows controlling the intensity of the van der Waals interaction in the mixture, which is quantified by the value of the Hamaker constant. This fact makes it possible to select restoration (repair) construction compositions that are characterized by an increased affinity to the main material. The proposed experimental approach and algorithm for calculating the van der Waals interaction constant in fine powder systems can be used for compiling an informational reference database.

The Derjaguin approximation (DA) relates the force between curved surfaces to the interaction free energy between parallel planes. It is typically derived by considering the direct interaction between the bodies involved, thus treating the effect of an intervening solvent implicitly by a rescaling of the corresponding Hamaker constant. Here, we provide a generalization of DA to the case of a molecular medium between the bodies, as is the case in most applications. The derivation is based on an explicit statistical-mechanical treatment of the contribution to the interaction force from a molecular solvent using a general expression for intermolecular and molecule-surface interactions. Starting from an exact expression for the force, DA is arrived at by a series of well-defined approximations. Our results show that DA remains valid in a molecular solvent as long as (i) the surface-molecule interactions are of a much shorter range than the radius R of the sphere and (ii) the density correlation length in the solvent is smaller than R. We then extend our analysis to the case where a phase transition occurs between the surfaces, which cannot easily be covered using a statistical-mechanical formalism due to the discontinuous change in the density of the medium. Instead, using a continuum thermodynamic description, we show that this phase transformation induces an attractive force between the bodies and that the force between curved surfaces can be related to the free energy in the corresponding planar case, in accordance with DA.

Force profiles between pairs of silica particles in concentrated aqueous solutions of a monovalent salt are measured using atomic force microscopy (AFM). Under such conditions, the double layer forces are negligible, and the profiles are dominated by van der Waals dispersion forces at larger distances. Heat treatment of the particles strongly influences the strength of dispersion forces. The dispersion force between the particles heated at 1200 °C was strongly attractive, and was characterized by a Hamaker constant of 2.4 × 10−21 J. This value is in good agreement with the current best theoretical estimate of the Hamaker constant for silica across water. For untreated particles, however, the dispersion force is much weaker and the Hamaker constant is 7 × 10−23 J. The Hamaker constant can be continuously tuned by adjusting the heating temperature between 1000 and 1200 °C. Such substantial variations of the Hamaker constant are caused by moderate differences in surface roughness on the nanoscale. The root mean square (RMS) of the roughness correlates inversely with the Hamaker constant, whereby the particles treated at 1200 °C have an RMS value of 0.63 nm, while the untreated particles have an RMS value of 2.5 nm. Other effects that could influence the Hamaker constant, such as changes in the degree of crystallinity, porosity, and shape of the particles, could be excluded.

Layered heterojunctions have been widely used as two-dimensional (2D) semiconductors with unique electronic and optical properties recently. However, the force interactions in layered heterojunctions have been seldom studied. In this study, we propose a simple method to fabricate a graphene layer probe (GLP) to measure the force interactions in layered heterojunctions by atomic force microscope (AFM). The graphene layer probe was formed by attaching a multilayer graphene nanoflake onto a silica microsphere that had been glued to the AFM cantilever under an optical microscope. The frictional, normal, and adhesive forces between the graphene layer probe and four different 2D layered materials (HOPG, h-BN, MoS2, and WS2) were measured. Superlubricity was achieved at these layered heterojunctions with friction coefficients varying from 0.0005 (GLP/HOPG) to 0.003 (GLP/WS2). The variations of friction, adhesion, and van der Waals (vdW) interaction were consistent with the variations of the interlayer shear stress, the surface energy of the composed 2D layered materials, and the Hamaker constant of the heterojunctions, respectively. The good agreement between the measurements and theories confirms that this method is reliable for the fabrication of graphene or other 2D layered material probes and can be widely used for layered heterojunction measurements.

We present a theoretical calculation of the changes in the Hamaker constant due to the anomalous reduction of the static dielectric function of water. Under confinement, the dielectric function of water decreases from a bulk value of 79 down to 2. If the confining walls are made of a dielectric material, the Hamaker constant reduces almost by 90\%. However, if the confinement is realized with metallic plates, there is little change in the Hamaker constant. Additionally, we show that confinement can be used to decreases the Debye screening length without changing the salt concentration. This, in turn, is used to change the Hamaker constant in the presence of electrolytes., Comment: 6 figures

Under ambient conditions, surfaces are rapidly modified and contaminated by absorbance of molecules and a variety of nanoparticles that drastically change their chemical and physical properties. The atomic force microscope tip–sample system can be considered a model system for investigating a variety of nanoscale phenomena. In the present work we use atomic force microscopy to directly image nanoscale contamination on surfaces, and to characterize this contamination by using multidimensional spectroscopy techniques. By acquisition of spectroscopy data as a function of tip–sample voltage and tip–sample distance, we are able to determine the contact potential, the Hamaker constant and the effective thickness of the dielectric layer within the tip–sample system. All these properties depend strongly on the contamination within the tip–sample system. We propose to access the state of contamination of real surfaces under ambient conditions using advanced atomic force microscopy techniques.

This study reveals an unprecedented capacity of flake graphene sheets in manipulating semi-solid deformation of aluminium matrix nanocomposites by restricting the grain growth of the nanograins during the reheating process to significantly enhance (173%) the yield strength of the fabricated composites. The graphene sheets with onion shape have also shown the unique capability in alleviating the agglomeration of SiC nanoparticles, attributed to the manipulated Hamaker constant of these particles as a result of wrapping graphene sheets. A devised mathematical approach has authenticated, for the first time, the effect of wrapping graphene sheets on subtle adjusting the Hamaker constant of SiC nanoparticles to stimulate engulfment of these nanoparticles within solidifying matrix rather than agglomeration at grain boundaries. This, therefore, has resulted in diminishing the porosity and stimulating multi-scaled micro/nano grains, thereby significantly enhancing the tensile properties of the fabricated composites.

Graphene is a honeycomb hexagonal two-dimensional (2D) crystal nanomaterial with a thickness of only 0.334 nm. It has been widely used and studied because of its ultra-thin 2D nano-characteristics and excellent electrical, thermal, optical, and mechanical properties. With the continuous in-depth study of graphene, the liquid-phase dispersion of graphene has also achieved breakthroughs. This review summarizes the research progress of the liquid-phase exfoliation mechanism, exfoliation method, stable dispersion mechanism, and dispersion method of graphene in recent years. The research situations of the Hamaker constant theory in exfoliation mechanism and Hansen solubility coefficient theory in stable dispersion mechanism are mainly discussed. The shortcomings of the research are summarized and analyzes the graphene liquid phase dispersed in the important challenge in the future. The stable dispersion method of graphene is also summarized. In the future, the π-π interaction will be the most potential method for studying graphene stabilization.

A simple and accurate closed-form expression for the Hamaker constant that best represents experimental surface force data is presented. Numerical comparisons are made with the current standard least squares approach, which falsely assumes error-free separation measurements, and a nonlinear version assuming independent measurements of force and separation are subject to error. The comparisons demonstrate that not only is the proposed formula easily implemented it is also considerably more accurate. This option is appropriate for any value of Hamaker constant, high or low, and certainly for any interacting system exhibiting an inverse square distance dependent van der Waals force. Refereed/Peer-reviewed

We have measured the diffusion coefficients, D, of aqueous micelles formed by cetyltriethyl-, cetyltripropyl- and cetyltributyl-ammonium bromides (CTEABr, CTPABr and CTBABr, respectively) and cetyltriethyl- and cetyltripropyl-ammonium hydroxides (CTEAOH and CTPAOH, respectively) by dynamic light scattering (DLS) at several temperatures from 15 to 55 °C and a range of surfactant (0.01–0.05 M) and salt (0.02–0.06 M NaBr; 0.05–0.3 M NaOH) concentrations. From values of D, we derived the respective fractional ionization values of micellar surfaces. For surfactants with bromide counterion we obtained fits of the diffusivity data using the linear interaction/DLVO approach, thus yielding estimates of the micellar hydrodynamic radius, Rh, and the micellar fractional ionization, α, which ranged from 0.26 to 0.35. For CTEAOH and CTPAOH, the fits appeared to be poorly sensitive to changes in the London-Van der Waals interactions, as expressed by the Hamaker constant, and only a large fractional ionization could account for the observed diffusivities.

On the basis of thermodynamic concept on competitive interphase interactions, the idea is forwarded about the ionic-electrostatic mechanism of water retention capacity and aggregative stability of fine solid particles in soil physical systems. The author applies modern data on the nanostructure of colloidal disperse complex of soil physical systems in the gel form, i.e., in the form of noncapillary two-phase system of resistant to aggregation particles separated by solvate layers. Disputable questions are discussed about the role of surface energy and hydration of cations in water retention as well as about the relationship between the matrix (disjoining) and the osmotic water pressures. The fundamental ionic-electrostatic model of water retention capacity is analyzed for the colloidal-disperse bodies in the areas of sorptive and film water on the water retention curve (WRC) in the form of interaction between thermodynamic potential (disjoining pressure), water content, and dispersity (effective specific surface area) of the solid phase. On the basis of this model, the potential dependence is shown between the dispersity and the mobile thermodynamic factors (i.e., temperature, charge, and concentration of ions in the electrical double layer), and the method of estimating the effective specific surface area from the WRC is proposed as an alternative to the commonly adopted BET method. For standard conditions, under which the dispersed system with monomolecular liquid layer maintains its aggregative stability, the specific surface area is calculated according to the WRC slope (the angle coefficient in semi-logarithmic coordinates) and the value of the effective size of water molecules. Simultaneously with the dispersity assessment from the WRC, the energy indices of interphase interactions— the generalized Hamaker constant and the surface tension at the solid–liquid interphase—are determined.

Hypothesis Surface effects arising from roughness and deformation can negatively affect the results of AFM contact experiments. Using the non-contact portion of an AFM deflection curve is therefore desirable for estimating the Hamaker constant, A, of a solid material. A previously validated non-contact quasi-dynamic method for estimating A is revisited, in which the cantilever tip is now always represented by an “effective sphere”. In addition to simplifying this previous method, accurate estimates of A can still be obtained even though precise knowledge of the nanoscale geometric features of the cantilever tip are no longer required. Experiments The tip’s “effective” radius of curvature, Reff, is determined from a “calibration” step, in which the tip’s deflection at first contact with the surface is measured for a substrate with a known Hamaker constant. After Reff is known for a given tip, estimates of A for other surfaces of interest are then determined. Findings An experimental study was conducted to validate the new method and the obtained results are in good agreement with predictions from the Lifshitz approximation, when available. Since Reff accounts for all geometric uncertainties of the tip through a single fitted parameter, no visual fitting of the tip shape was required.

The Hamaker constant is an important material parameter for both the description of particle interaction and the prediction of colloidal stability. Existing methods based on the classic Derjaguin–Landau–Verwey–Overbeek theory ignore the Hofmeister effects and would derive flawed results. In this article, approaches to the estimation of the Hamaker constant with and without consideration of the Hofmeister effects were, respectively, suggested, where the Hamaker constant was obtained on the basis of the mathematic relationship between electrostatic repulsive and van der Waals attractive interaction at the critical coagulation concentration (CCC) by using the dynamic light scattering technique. It indicated that the montmorillonite particles aggregation kinetics in the presence of Li+, K+, and Cs+ exhibited remarkable Hofmeister effects and the CCC values show: Li+ (277.2 mM) > K+ (80.3 mM) > Cs+ (27.2 mM). Without consideration of Hofmeister effects, completely distinct Hamaker constants for the same materi...

Hypothesis The energy loss experienced by an electron while moving through a solid is determined by the optical properties of the surrounding. Hence, quantitative Reflection Electron Energy Loss Spectroscopy (REELS) should allow the determination of optical data required for the calculation of Hamaker coefficients using Lifshitz theory. This approach might improve the accuracy of calculated Hamaker coefficients and should also enable to harness the unique capabilities of REELS to analyse nanostructured surfaces and thin-films with great spatial resolution and surface sensitivity. Experiments REELS spectra of a survey of insulating polymers and of metal-like Ti0.23Al0.32N0.44 (TiAlN) were measured, the complex dielectric functions determined and the corresponding Hamaker coefficients across vacuum and water calculated. The sensitivity of the quantification procedure towards typical systematic errors was investigated. For polystyrene the results were comparatively analysed using vacuum ultraviolet spectroscopy (VUV). Findings The accuracy especially of the non-retarded vacuum Hamaker constants of the polymers was increased when compared to VUV reflectance spectroscopy due to the higher spectral range of REELS. Furthermore, a new correction procedure for the intricate case of unresolved inelastic losses in the REELS spectrum, such as encountered in the case of TiAlN, could be developed using spectroscopic ellipsometry as a complementary mean.

Diamond-like-carbon (DLC) is a promising material for tribological applications such as hard disk, automotive, machine tool, and aerospace coatings. We performed in-situ transmission electron microscopy (TEM) and molecular dynamics (MD) studies of nanoscale single-asperities made of tetrahedral amorphous carbon (ta-C, a type of DLC with high strength) contacting single-crystal diamond, to understand the factors controlling adhesion. Visualization of the contacts in TEM enabled us to correlate the asperity's geometry and the adhesion measurements. MD simulations allowed the atomic-scale mechanisms of adhesion to be elucidated and correlated with the TEM observations. Experimentally-determined pull-in forces show less scatter than pull-off forces. The magnitude of the pull-in forces is consistent with adhesion arising from van der Waals (VDW) interactions, allowing us to estimate the ta-C/diamond Hamaker constant. MD simulations with the AIREBO potential confirmed that including VDW interactions leads to less scatter in adhesive forces in approach than in separation. MD simulations with the REBO+S potential demonstrate that the large scatter in pull-off forces observed experimentally arises from the complex nature of covalent bonding between substrate and tip, influenced by the local energy landscape, hydrogen coverage, and the number of repeated contact events. The scatter in pull-off force also tends to decrease with increasing roughness.

Atomic force microscopy (AFM) was used to characterize the attractive force, adhesive force and adhesion energy between an AFM probe tip and nanometric soot particle generated by a premixed methane/oxygen flame. Different attractive force distributions were found when increasing the height above burner (HAB), with forces ranging from 1.1–3.5 nN. As the HAB was increased, the average attractive force initially increased, briefly decreased, and then underwent a gradual increase, with a maximum of 2.54 nN observed at HAB = 25 mm. The mean adhesive force was 6.5–7.5 times greater than the mean attractive force at the same HAB, and values were in the range of 13.5–24.5 nN. The adhesion energy was in the range of 2.0–5.6 × 10 −17 J. The variations observed in the average adhesion energy with increasing HAB were different from those of the average adhesion force, implying that the stretched length of soot particles is an important factor affecting the average adhesion energy. The Hamaker constants of the soot particles generated at different HABs were determined from AFM force-separation curves. The average Hamaker constant exhibited a clear correlation with the graphitization degree of soot particles as obtained from Raman spectroscopy.