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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.

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.

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

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

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 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.

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.

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.

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.

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.

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.

International audience; Adhesion forces between tungsten spherical microparticles and tungsten substrates with different roughnesses have been measured using the Atomic Force Microscopy (AFM) colloidal probe technique. Mean roughnesses of the tungsten substrates were measured by AFM and were ranked in three categories i.e. nanoscale, sub-microscale and microscale roughnesses. Experimental Hamaker constant of 37 ± 3.5 × 10 −20 J has been obtained using a spherical tungsten particle of 10.5 µm in radius and a tungsten substrate with nanoscale root-mean-square roughness of rms = 11.5 nm. It was shown that larger roughness of the order rms = 712 nm induces a two order of magnitude decrease on the adhesion of tungsten microparticles compared to a smooth tungsten surface with nanoscale roughness. Comparison with the van der Waals-based adhesion force model of Rabinovich which integrates the roughness of surfaces showed good agreement with experimental pull-off forces even when roughness of the substrate is close to the micrometer range. In such case, measurements have shown that dependency of adhesion force with particle size (in the micrometer range) has a secondary influence compared to the roughness of surfaces.

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.

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...

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.

The accurate determination of Hamaker constant of humus is the basis for understanding the colloidal behavior of humus in environment. However, the determination of the Hamaker constant of humus is still a challenge because of its low value in Hamaker constant. In this study, a method for determining the Hamaker constant of humus with dynamic light scattering (DLS) technique has been established. Firstly, the Hamaker constants of the mixture colloids of “humic acid (HA) + montmorillonite (Mont, with known high Hamaker constant)” with different HA/Mont ratios were determined by DLS technique. Secondly, the mathematic relationship of the Hamaker constant (A) of the mixture colloid and HA content (y with percentage) was established, and it was A = 13.32 × 10−20 y−0.507 J. From which, finally, the Hamaker constant of HA (when y = 100) was obtained and it was 1.29 × 10−20 J. The validity of the obtained Hamaker constant of HA was confirmed by the comparison of the calculated CCC by adopting the obtained Hamaker constant of HA and the experimentally determined CCC by DLS. The established method in this study can be applied to the Hamaker constant determination of other nano-sized organic materials by DLS.

We propose a computational scheme to evaluate Hamaker constants, $A$, of molecules with practical sizes and anisotropies. Upon the increasing feasibility of diffusion Monte Carlo (DMC) methods to evaluate binding curves for such molecules to extract the constants, we discussed how to treat the averaging over anisotropy and how to correct the bias due to the non-additivity. We have developed a computational procedure for dealing with the anisotropy and reducing statistical errors and biases in DMC valuations, based on possible validations on predicted $A$. We applied the scheme to cyclohexasilane molecule, Si$_6$H$_{12}$, used in 'printed electronics' fabrications, getting $A \sim 105 \pm 2$ [zJ], being in plausible range supported even by other possible extrapolations. The scheme provided here would open a way to use handy {\it ab initio} evaluations to predict wettabilities as in the form of materials informatics over broader molecules., The manuscript was revised according to review comments

The aim of this paper is to present a method for predicting the effect of temperature on contact angles and wetting transitions for n-alkanes on PTFE. The analysis is based on the effect of temperature on two closely related phenomena, which are critical in the determination of contact angles: intermolecular forces and the thickness of an adsorbed film in the region adjacent to the three-phase contact. Considering solely van der Waals forces, it is possible to reproduce the experimental temperature dependence of contact angles. At low temperature values, contact angles show a small and linear decrease with temperature. For higher temperature values, substantially larger decreases are exhibited by the more volatile alkanes. In the case of n-octane, a single transition from partial to total wetting is found at 443K. This transition, which arises from the vanishing of the effective Hamaker constant at 430K, is characterized by a surface specific heat exponent close to one, indicating the existence of a first order wetting transition. For the less volatile alkanes, the contact angle decrease is progressively less pronounced as the volatility decreases in such a way that for n-hexadecane the contact angle remains approximately constant throughout the temperature range under study.

The purpose of this work is a quantitative determination of the effective interaction potential, upon distance, between inert nanoparticles or (parallel or crossed) nanopores which are inserted in a bilayer-membrane. The expected effective pair-potential is the sum of a repulsive part and an attractive one. The expression of this repulsive part that originates from the thermal fluctuations of the host bilayer-membrane, was put in evidence in some recent experiments using Synchrotron Small-angle X-ray scattering, and has a Gaussian form, with an amplitude and a range that depend essentially on the density of the nano-inclusions (nanoparticles or nanopores). The amplitude is simply the contact energy between the nano-inclusions, and the second represents the in-plan correlation length that measures the membrane fluctuations extent. The attractive part is the usual van der Waals attractive potential. First, we construct the expression of the effective pair-potentials. Second, we rigorously study their classification with respect to the relevant parameters of the problem, which are the geometric dimensions of the nano-inclusions (their radius, ratio aspect of the parallel nanopores, angle between crossed nanopores), their density and the Hamaker constant. In particular, we show the existence of a special value of the nano-inclusion density (critical coagulation density), at which a coagulation regime takes place. Below this critical density, the pair-potential presents an energy barrier that prevents the coagulation of the nano-inclusions, and above, such a potential is completely attractive. Finally, we emphasize that the achieved classification may serve to studying the structure and thermodynamics of these nano-inclusions, as a two-dimensional model fluid system.

The removal of heavy metals from drinking water has attracted great interest in water purification technology. In this study, a biocompatible Polyaniline (PANI) polymer filled with TiO2 and ZnO nanoparticles (NPs) is considered as an adsorbent of cadmium iodide from water. Theoretical investigation of the van der Waals (vdW) interactions deduced from the Hamaker constant calculated on the basis of Lifshitz theory was presented. It was found that the surface energy as well as the work of adhesion between water and PANI/NPs across air increases with an increasing volume fraction of the TiO2 and ZnO nanoparticles. Consequently, an increase in the Laplace pressure around the cavities/porosities was found, which leads to the enhancement of the specific contact surface between water and PANI/NPs. On the other hand, for the interactions between CdI2 particles and PANI/NPs surface across water, we show that the interactions are governed principally by the attractive London dispersion forces. The vdW energy and force increase proportionally with the augmentation of the volume fraction of nanoparticles and of the radius of the CdI2 particle. Particularly, the PANI/TiO2 has been proved to be a better candidate for adsorption of cadmium iodide from water than PANI/ZnO.

Understanding the cake structure during filtration is important to minimizing fouling and reducing cleaning operation. Here, a Monte Carlo model is proposed to investigate the effect of Hamaker constant, zeta potential, particle size, ionic strength and applied pressure on the profile of the particle volume fraction of the cake structure. A scaling relationship between the local deposit solid volume fraction and various operation conditions in the micro-scale is presented. This result can be well explained by a force balance model based on the two simple particle distributions. Combining this scaling relationship and a developed force accumulation and transfer model allows a better determination of the reversibility of the deposit layer, and also provides insight into selecting appropriate cleaning strategies.

Despite its considerable practical importance, the deposition of real Brownian particles transported in a channel by a liquid, at small Reynolds numbers, has never been described at a comprehensive level. Here, by coupling microfluidic experiments, theory, and numerics, we succeed in unravelling the problem for the case of straight channels at high salinity. We discover a broad regime of deposition (the van der Waals regime) in which particle–wall van der Waals interactions govern the deposition mechanism. We determine the range of existence of the regime, for which we calculate the concentration profiles, retention profiles, and deposition kinetics analytically. The retention profiles decay as the inverse of the square root of the distance from the entry, and the deposition kinetics are given by the expression S≈(A2.1kTξL)1/2, where S is a dimensionless deposition function, A is the Hamaker constant, and ξL is a dimensionless parameter characterizing fluid flow properties. These findings are well support...

The van der Waals force between dielectric plates comprising ultrathin conducting films was calculated by employing two models. In the first model, the ultrathin dielectric film was modeled as a dielectric plate of a small thickness, and the Lifshitz theory was applied. In the second model, an ultrathin dielectric film was modeled as a plasma sheet, which is an infinitesimally thin fluid carrying mass and charge. For each model, the interacting force was considered to be a function of the separation gap between the films, and the difference in the force-distance relationships of two was discussed.

We present a theoretical calculation of the dispersive interaction of mesoporous Au sponges. The ability to manipulate the dielectric function of the sponge by varying its porosity is applied to the calculation of the Hamaker constant using Lifshitz theory and the near radiative heat transfer properties. By using an effective medium approximation the dielectric function of the mesoporous sponge is calculated. As the porosity increases, our calculations show that the Hamaker constant decreases significantly. This is also used to calculate the van der Waals force between a gold nanoparticle and a gold mesoporous sponge as a function of the porosity. Also, using the fluctuating electrodynamics formalism, the change in the local electromagnetic density of states in the near field is calculated. As an application, the near field radiative heat absorbed by a SiC nanoparticle at a fixed distance from a Au sponge is calculated for different values of the porosity. The maximum heat transfer is achieved for high po...

In this work, 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) with an average crystal size of 300 nm was prepared by bead milling to examine the effect of pH and ionic strength on the Zeta potential. The results showed that nanoRDX has no isoelectric point within the entire range studied (2

Nanosized activated carbons (NACs) are emerging as a new class of engineered nanomaterials, but their colloidal stability governing the fate and transport in aquatic environments has not yet been evaluated. We have characterized four representative NAC materials and examined their colloidal stability and early-stage aggregation kinetics under various water chemistry conditions. The results showed that these NAC particles had intensity-weighted hydrodynamic diameters (Dh) and number-weighted averaged diameters (Dn) of approximately 200 and 100 nm, respectively, and that their aggregation kinetics exhibited both reaction- and diffusion-limited regimes in the presence of monovalent (NaCl) or divalent (CaCl2) salt with distinct critical coagulation concentrations (CCC), indicating that their colloidal stability under the tested aqueous conditions was consistent with the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The fitting of the aggregation kinetics with predictions based on DLVO theory yielded the Hamaker constant of 2.1–2.7 × 10−20 J (ACWC, aqueous medium). The study demonstrated that NACs may be relatively stable under typical freshwater chemistry conditions, suggesting their potential applications as reactive agents for remedy of contaminated water and soil systems where long-time suspension of introduced particles is desired. The observed strong colloidal stability may also indicate high possibility of NACs being nanosized pollutants in natural and engineered environmental systems.

Understanding nanomaterial (NM) stability is required for an adequate interpretation of ecotoxicological test outcomes, fate and behavior studies, to generate parameters (such as critical coagulation concentration, CCC; and attachment efficiency, α) for environmental fate models, and for comparison among different studies. Numerous studies measured CCC and α for different types of NMs with a major focus on investigating the effect of ionic strength, ion valency and natural organic matter, with fewer studies investigating the effect of NM and other medium properties. Consequently, wide discrepancies can be found in the literature among the reported CCC and α values, even for NMs of the same composition and properties. In this context, the aim of this review is to investigate the dependence of NM aggregation kinetic parameters (e.g. CCC and α) on NM and medium physicochemical properties and to rationalize the differences observed among different studies, where possible. We found that various material and medium physicochemical properties need to be considered to predict NM aggregation behavior. Some trends were observed and rationalized based on theoretical studies and data available in the literature. For charge stabilized NMs with constant zeta potential, NM stability (CCC) decreases with the increase in Hamaker constant, increase in NM size, increase in buffer (carbonate and phosphate) concentration, increase in temperature, and light irradiation. The CCC increase with counterion complexation. For sterically stabilized NMs, the CCC increases with the increased surface coverage by the capping agent molecules and completely coated NMs do not aggregate even in high ions strength medium (e.g. seawater). These results highlight the significant role of NM and medium properties in influencing the environmental stability and fate of NMs, and will help refine NM fate models and improve our understanding of NM uptake and toxicity.

In this paper, the behavior of the C60 colloidal species in acetonitrile in the presence of electrolytes is considered. The properties of the negatively charged fullerene aggregates change markedly in the presence of even low concentrations of electrolytes, such as NaClO4, Ca(ClO4)2, Ba(ClO4)2, La(ClO4)3, La(NO3)3, HClO4, N(n-C4H9)4ClO4, n-C16H33N(CH3)3ClO4, and n-C16H33NC5H5ClO4. The coagulation kinetics was studied using the Fuchs function, W. The values of the critical coagulation concentration in concert with the ζ values allowed attempting to estimate the Hamaker constant for C60 using the DLVO approach. The interaction of the C60 aggregates with electrolytes results not only in coagulation, but in some cases also in overcharging. The peculiarities of these processes are studied via the UV- and visible spectroscopy, dynamic light scattering, electrophoretic titrations, and monitoring of the particles size variations with time.

Physico-thermal properties of pure liquids are important fundamental information for process engineering calculations. Data of these properties are tabulated for many substances. Predictive, yet phenomenological, equations for these data have been proposed in literature. In this paper correlations for molar volume, Hamaker constant, shear viscosity, surface tension, specific heat capacity, and thermal conductivity are proposed that are based on physical reasoning and on the corresponding states principle, CSP. Hence, it is primarily the critical data and the molar mass of the substances that go into the correlations. Some of the correlations require knowledge of the acentric factor and of the boiling and melting temperatures. The given correlations predict the tabulated physico-thermal data well over a wide temperature range. Furthermore, predictive correlations for the critical volume, critical pressure, and the critical compressibility factor are proposed. These correlations are calibrated by parameters...

In order to minimize the effects of surface roughness and deformation, a new method for estimating the Hamaker constant, A, of solids using the approach-to-contact regime of an atomic force microscope (AFM) is presented. First, a previous “jump-into-contact” quasi-static method for determining A from AFM measurements is analyzed and then extended to include various AFM tip-surface force models of interest. Then, to test the efficacy of the “jump-into-contact” method, a dynamic model of the AFM tip motion is developed. For finite AFM cantilever-surface approach speeds, a true “jump” point, or limit of stability, is found not to appear, and the quasi-static model fails to represent the dynamic tip behavior at close tip-surface separations. Hence, a new “quasi-dynamic” method for estimating A is proposed that uses the dynamically well-defined deflection at which the tip and surface first come into contact, dc, instead of the dynamically ill-defined “jump” point. With the new method, an apparent Hamaker const...

Powder behavior affects a wide variety of industries due to the use of solids in processing and manufacturing. As such, the prediction of powder behavior is advantageous to these industries and particle scale measurements that allow prediction of powder behavior can be very beneficial. The centrifuge technique was utilized experimentally with silica particles adhered to stainless steel to characterize the adhesion of the silica powder. To describe the observed adhesion force distributions, a simulated powder with a realistic size distribution, but assumed to be comprised of smooth spheres, was conceived. The adhesion between the real powder and the stainless steel was modeled using the idealized powder and assuming a simple sphere-flat plate adhesion model. During the model validation, an effective Hamaker constant distribution that allowed the simulated adhesion of the smooth spheres to match the experimentally-observed adhesion was developed. The effective Hamaker constant distribution captured the effects of the roughness and shape variations in the individual particle within the powder, and these effects were linked to the measured particle size distribution of the powder.

ZnO nanowires were bent on amorphous SiO2 and SiN substrates in an ambient atmosphere using optical nanomanipulation. The kinetic friction between the nanowires and substrate was determined from the bent shape of the nanowires. The kinetic friction force per unit area, i.e. frictional shear stress, for the ZnO/SiO2 and ZnO/SiN nanowire/substrate systems being measured were 1.05 ± 0.28 and 2.08 ± 0.33 MPa, respectively. The surface roughness and the Hamaker constant of SiO2 and SiN substrates had significant effect on the frictional stresses.

The aim of the present study was to check the influence of the Hamaker constant (A(h)) on the calculated critical thickness of foam films. It was done by a comparison between the experimental data of the critical thickness and the theoretically obtained data with different values of (A(h)), which take part in the equations of Radoev, Scheludko, Manev, and Vrij. We calculated the latter for film thicknesses from 15 to 70 nm based on several equations. We used the experimental data of hcr (average value of critical thickness and measured once, in the place of a spot appearance) for foam films stabilized by non-ionic surfactant n-dodecyl-&beta, D-maltoside (C12G2) or by cationic surfactant n-dodecyl trimethylammonium bromide (C12TAB), as measured by the interferometric method. The foam films were produced from solutions with surfactant concentration at CMC (Critical Micelle Concentration) in the presence of 0.1 M NaBr. For films of C12G2, the best correspondence was found between measured hcr (in the spot) and calculated ones by the RShM equation using effective A(h) (introduced by Coons et al.) or Vassilieff&rsquo, s values, but with a correction for the added electrolyte. For films stabilized by C12TAB, a difference between the measured and theoretically calculated hcr was found, which was probably due to the nature of the surfactant. Nevertheless, this difference was smallest when calculated hcr values were obtained with data for Aeff (h) and Vassilieff&rsquo, s A(h) constant, respectively.

Nanoplastics (NPs) derived from degradation of macroplastics and microplastics possess potential threat to aquatic biota and human health. Their fate and transport in aquatic systems are mainly governed by aging processes and aggregation behavior. In this study, we simulated plastic aging process using UV-irradiation and compared the aggregation kinetics of fresh versus aged polystyrene NPs (PSNPs) under aqueous conditions. The results showed that fresh PSNPs had strong negative surface charge and exhibited both reaction- and diffusion-limited aggregation regimes, in agreement with classic Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. Divalent electrolytes were 10–15 times more effective in inducing PSNP aggregation than monovalent electrolytes. The aging process inhibited PSNP aggregation in NaCl solutions by increasing the negative charge on PSNP surface and the organic matter content in solution, while promoted PSNP aggregation in CaCl2 solutions due to interactions between Ca2+ and carboxyl groups formed on aged PSNP surface. Such distinct behaviors were consistent with characterizations by contact angle measurements, potentiometric titration, total organic carbon (TOC) analysis, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Hamaker constants obtained from DLVO fitting decreased from 3.5 × 10−21 J for fresh PSNPs to 1.5 × 10−21 J for aged PSNPs. This study indicated that UV-irradiation plays a vital role in governing the fate, transport, and potential hazards of PSNPs in aquatic environments.

In this study, we present theoretical and experimental data on the interaction forces between starch and particles of hematite and quartz as well as their implications for flotation and aggregation. The individual Hamaker constant for starch acting through vacuum, A 11 , was calculated, and its value, 6.27 × 10−20J, demonstrates the highly hydrophilic character of gelatinized starch. The Hamaker constants for quartz/water/starch and for hematite/water/starch, A 132 , were also calculated, and these values were 6.07 × 10−21J and 17.90 × 10−20J, respectively. It was confirmed that starch strongly adsorbs onto hematite, whereas on quartz, starch may adsorb onto only silicon surface sites. In fact, AFM images of quartz surfaces showed non-adsorbed areas or areas with a thin layer of starch that certainly do not interfere in subsequent adsorption by the collector (etheramine). The interaction energies between gelatinized starch and the hematite and quartz surfaces were estimated based on DLVO theory at pH 10.5 and a constant ionic strength (10−3 mol.L−1 NaCl). The repulsion electrostatic energy was higher for the quartz-starch system than for the interactions between hematite and starch. The calculated total energy of interaction between quartz and starch revealed that there is no possibility of aggregation for the individual colloids of starch and quartz particles. On the other hand, spontaneous adhesion between the colloids and hematite particles was confirmed by DLVO theory.

The fast-growing production and application of carbon nanotube (CNT) materials in a variety of industrial products inevitably lead to their release to wastewater and surface water. CNT would experience oxidization in wastewater treatment plant due to the presence of large amount of disinfectants, such as H2O2 and O3, which in turn affects the environmental fates and risks of CNT. In this study, oxidized CNT materials (O-CNTs) were prepared by treating CNT with H2O2/UV and O3 (denoting as H2O2-CNT and O3-CNT, respectively). A variety of characterizations indicated that oxygen containing groups were generated on CNT surface upon the oxidation, and the O/C ratio increased in the order of pristine CNT

We quantitatively link the macroscopic phase behavior of protein solutions to protein–protein interactions based on a coarse-grained colloidal approach. We exploit the extended law of corresponding states and apply the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory in order to infer the second virial coefficient b2, an integral measure of the interaction potential, from the phase behavior, namely, cloud-point temperature (CPT) measurements under conditions favoring protein crystallization. This determination of b2 yields values that quantitatively agree with the results of static light scattering (SLS) experiments. The strength of the attractions is quantified in terms of an effective Hamaker constant, which accounts for van der Waals attractions as well as non-DLVO forces, such as hydration and hydrophobic interactions. Our approach based on simple lab experiments to determine the CPT in combination with the DLVO theory is expected to facilitate further biophysical research on protein–protein interaction...

Contrary to numerous studies on the stability of fullerene aqueous colloidal solutions in the presence of electrolytes, the corresponding issue for the organosols was until recently almost unexplored. In this article, the state of C60 in methyl alcohol and the regularities of the coagulation of colloidal solution in this solvent were examined in the presence of electrolytes. Alcosols with a fullerene concentration of 4 × 10–6 M were prepared by the dilution of the C60 saturated solution in toluene by methanol. The ca. 300 nm-sized aggregates possess a negative electrokinetic potential value, ζ = −37 ± 8 mV. To determine the critical coagulation concentrations, CCC, the size increase of the species was followed up using the dynamic light scattering method. The analysis of the coagulation in terms of the Fuchs function, W, was accompanied by zeta potential monitoring. The consideration of the data for 1:1 electrolytes NaClO4 and N(n-C4H9)4ClO4 allows a rough estimate of the Hamaker constant of fullerene–ful...

In the current study, mathematical models were developed to predict the transient concentration and size distribution of inclusions in a two-strand continuous casting tundish. The collision and growth of inclusions were considered. The contribution of turbulent collision and Stokes collision was evaluated. The removal of inclusions from the top surface was modeled by considering the properties of inclusions and the molten steel, such as the wettability, density, size, and interfacial tension. The effect of composition of inclusions on the collision of inclusions was included through the Hamaker constant. Meanwhile, the effect of the turbulent fluctuation velocity on the removal of inclusions at the top surface was also studied. Inclusions in steel samples were detected using automatic SEM Scanning so that the amount, morphology, size, and composition of inclusions were achieved. In the simulation, the size distribution of inclusions at the end steel refining was used as the initial size distribution of inclusions at tundish inlet. The equilibrium time when the collision and coalescence of inclusions reached the steady state was equal to 3.9 times of the mean residence time. When Stokes collision, turbulent collision, and removal by floating were included, the removal fraction of inclusions was 16.4 pct. Finally, the removal of solid and liquid inclusions, such as Al2O3, SiO2, and 12CaO·7Al2O3, at the interface between the molten steel and slag was studied. Compared with 12CaO·7Al2O3 inclusions, the silica and alumina inclusions were much easier to be removed from the molten steel and their removal fractions were 36.5 and 39.2 pct, respectively.

Cohesive Hamaker constants of solid materials are measured via optical and dielectric properties (i.e., Lifshitz theory), inverse gas chromatography (IGC), and contact angle measurements. To date, however, a comparison across these measurement techniques for common energetic materials has not been reported. This has been due to the inability of the community to produce samples of energetic materials that are readily compatible with contact angle measurements. Here we overcome this limitation by using physical vapor deposition to produce thin films of five common energetic materials, and the contact angle measurement approach is applied to estimate the cohesive Hamaker constants and surface energy components of the materials. The cohesive Hamaker constants range from 85 zJ to 135 zJ across the different films. When these Hamaker constants are compared to prior work using Lifshitz theory and nonpolar probe IGC, the relative magnitudes can be ordered as follows: contact angle > Lifshitz > IGC. Furthermore, the dispersive surface energy components estimated here are in good agreement with those estimated by IGC. Due to these results, researchers and technologists will now have access to a comprehensive database of adhesion constants which describe the behavior of these energetic materials over a range of settings.

This study reveals a promising feature of graphene encapsulating process to significantly enhance the mutually inclusive tensile strength and ductility of aluminium based composites using the semi-solid powder forming process. It was corroborated based on van der Waals–Casimir interaction free energy that graphene sheets have an unprecedented capacity to manipulate the Hamaker constant of SiC nanoparticles, prompting formation of nano/micro-sized grains. Authenticating by the strengthening model, fractographic observations have also demonstrated the unique functionality of graphene sheets in strengthening via grain refining, thermally enhanced dislocations, shear-lag, geometrically necessary dislocations, crack bridging and fibre pull out mechanisms.

The objective of this work was to investigate the effect of precipitating environment on asphaltene precipitation such as, precipitant (n-alkanes: C5, C7, C9, C12, C14), asphaltene concentration, and temperature. A combination of gravimetric and spectroscopic techniques was used for the detection and quantification of asphaltene precipitation. By measuring the absorbance of the supernatant fluid with UV–vis spectrometer after centrifugation, the contents of precipitated asphaltenes were obtained by difference method. We found that at high n-alkane concentrations (>70% by volume), the precipitated asphaltenes decrease with increasing the carbon number of n-alkanes, while at low n-alkane concentrations ( C5 > C12 > C9 > C7. As asphaltene concentration increases the yield of precipitated asphaltenes increase, especially variation of asphaltene states from nano-aggregates to clusters lead to more serious precipitation. The stability of asphaltenes decreases with temperature elevating when the volume ratios of n-heptane/toluene are 4:6, 5:5, or 6:4. However, at higher ratio of n-heptane/toluene (7:3) the opposite effect occurs. Based on the view that the property of precipitated asphaltenes is diverse when diluting with different concentration of n-heptane, this bizarre phenomenon was investigated from the perspective of difference in asphaltene property. To verify this opposite effects, three sub-fractions of asphaltenes (SA1, SA2, and SA3) were extracted to investigate temperature effects.The experimental results show that SA3 (more soluble) become more stable at higher temperature while SA1 and SA2 (less soluble) were both destabilized with increasing temperature.

Many types of manufacturing processes involve powders and are affected by powder behavior. During the development of new powder processes, it is common that only very small quantities of powder are available. It is highly desirable to implement tools that allow the behavior of bulk powder to be predicted based on the behavior of these small quantities. If the powder can be well-characterized, it is possible to improve the processing performance. In this work, an enhancement of the centrifuge technique was proposed as a means of powder characterization by using specially designed substrates with hemispherical indentations within the centrifuge. Simulations of the centrifuge technique were performed to test the viability of applying this enhancement experimentally. These simulations predicted the percentage of particles remaining as a function of centrifuge rotational speed, indentation size, and particle size, for spherical silica particles against indented substrates made from silicon. Particles that are smaller than an indentation complement that indentation, leading to an increase in the adhesion force. In comparison, particles that are larger than an indentation have a smaller relative adhesion force. These two types of particle–indentation interactions generate a unique set of residual adhering percentage (RAP) curves that can be used to determine the particle size distribution and Hamaker constant of the system. These simulation results for the specifically-designed substrates demonstrate the capability of the enhanced centrifuge technique for advanced powder characterization.

Author(s): Gilbert, B; Comolli, LR; Tinnacher, RM; Kunz, M; Banfield, JF | Abstract: Clay swelling, an important phenomenon in natural systems, can dramatically affect the properties of soils and sediments. Of particular interest in low-salinity, saturated systems are osmotic hydrates, forms of smectite in which the layer separation greatly exceeds the thickness of a single smectite layer due to the intercalation of water. In situ X-ray diffraction (XRD) studies have shown a strong link between ionic strength and average interlayer spacing in osmotic hydrates but also indicate the presence of structural disorder that has not been fully described. In the present study the structural state of expanded smectite in sodium chloride solutions was investigated by combining very low electron dose, highresolution cryogenic-transmission electron microscopy observations with XRD experiments. Wyoming smectite (SWy-2) was embedded in vitreous ice to evaluate clay structure in aqua. Lattice-fringe images showed that smectite equilibrated in aqueous, low-ionic-strength solutions, exists as individual smectite layers, osmotic hydrates composed of parallel layers, as well as disordered layer conformations. No evidence was found here for edge-to-sheet attractions, but significant variability in interlayer spacing was observed. Whether this variation could be explained by a dependence of the magnitude of long-range cohesive (van der Waals) forces on the number of layers in a smectite particle was investigated here. Calculations of the Hamaker constant for layer-layer interactions showed that van der Waals forces may span at least five layers plus the intervening water and confirmed that forces vary with layer number. Drying of the disordered osmotic hydrates induced re-aggregation of the smectite to form particles that exhibited coherent scattering domains. Clay disaggregation and restacking may be considered as an example of oriented attachment, with the unusual distinction that it may be cycled repeatedly by changing solution conditions.

We studied turbulent coagulation rates of well-characterized carboxyl-terminated latex particles as a function of pH at different KCl concentrations. The negative charge of the studied particles increases and thus develops the electrical double layer repulsion with increasing pH. The pH-dependent coagulation rate was analyzed on the basis of the trajectory analysis with the Derjaguin, Landau, Verwey, and Overbeek theory using the solution of non-linear Poisson–Boltzmann (PB) equation under the charge regulation boundary condition, in which the electrostatic boundary conditions such as surface potential depends on surface separation distance. It should be noted that this is the first attempt to compare the calculated results with the experimental data of the effect of surface charge on turbulent coagulation rates. The calculation using the trajectory analysis can well describe the experimental data. However, to obtain the good agreement between the experimental data and the calculation, we need to decrease the Hamaker constant A H with increasing KCl concentration. The dependence of A H on salt concentration is probably ascribed to the fact that the origin of the van der Waals attraction is essentially electrostatic dipole–dipole interaction between molecules. That is, we consider that the van der Waals attraction is increasingly screened by the charge of ions with increasing salt concentration.