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The surface wetting or coating of materials by polymers is crucial for designing functional interfaces and various industrial applications. However, the underlying mechanisms remain elusive. In this study, the wetting behavior of hydroxyl-terminated polybutadiene (HTPB) on a quartz surface was systematically investigated using computer simulation methods. A notable tip-dominant surface adsorption mode of HTPB was identified, where the hydroxyl group at the end of the polymer chain binds to the surface to initiate the wetting process. Moreover, it was found that with the increase in the degree of polymerization (e.g., from DP = 10 to 30), spontaneous adsorption of HTPB becomes increasingly difficult, with a three-fold increase in the adsorption time. These results suggest a competition mechanism between enthalpy (e.g., adhesion between the polymer and the surface) and entropy (e.g., conformational changes in polymer chains) that underlies the wetting behavior of HTPB. Based on this mechanism, two strategies were employed: altering the degree of polymerization of HTPB and/or regulating the amount of interfacial water molecules (e.g., above or below the threshold amount of 350 on a 10 × 10 nm2 surface). These strategies effectively modulate HTPB's surface wetting process. This study provides valuable insights into the mechanisms underlying the surface adsorption behavior of HTPB and offers guidance for manipulating polymer wetting processes at interfaces. [ABSTRACT FROM AUTHOR]

The adsorption of cationic water-soluble polymers onto negatively charged porous wood pulp fibers is an essential aspect of papermaking. Adsorption data can be displayed as a direct plot of the amount adsorbed, Γ, versus the amount of polymer added or as an isotherm plot showing the amount adsorbed versus the residual unadsorbed polymer. In either data presentation, the analysis is more transparent if the units of each axis are the same (e.g., mg/g or meq/g), giving dimensionless slopes. Values for Γmax, ΓI, fI, and Γme can be extracted from many isotherms where: Γmax is the maximum capacity of the fibers to adsorb polymer; ΓI is the y-axis isotherm intercept and gives the maximum dose that can be fully adsorbed; fI is the slope of the direct plot at ΓI, and fI is the mass fraction of the added polymer that can access interior (pore) surfaces; and, Γme is the saturated amount of polymer adsorbed on exterior surfaces. Additionally, the molecular weight distribution of the adsorbing polymer in conjunction with the adsorption isotherm can be used to estimate the molecular weight distributions of adsorbed polymer on interior and exterior fiber surfaces as functions of the polymer dose. [ABSTRACT FROM AUTHOR]

The surface wetting or coating of materials by polymers is crucial for designing functional interfaces and various industrial applications. However, the underlying mechanisms remain elusive. In this study, the wetting behavior of hydroxyl-terminated polybutadiene (HTPB) on a quartz surface was systematically investigated using computer simulation methods. A notable tip-dominant surface adsorption mode of HTPB was identified, where the hydroxyl group at the end of the polymer chain binds to the surface to initiate the wetting process. Moreover, it was found that with the increase in the degree of polymerization (e.g., from DP = 10 to 30), spontaneous adsorption of HTPB becomes increasingly difficult, with a three-fold increase in the adsorption time. These results suggest a competition mechanism between enthalpy (e.g., adhesion between the polymer and the surface) and entropy (e.g., conformational changes in polymer chains) that underlies the wetting behavior of HTPB. Based on this mechanism, two strategies were employed: altering the degree of polymerization of HTPB and/or regulating the amount of interfacial water molecules (e.g., above or below the threshold amount of 350 on a 10 × 10 nm2 surface). These strategies effectively modulate HTPB’s surface wetting process. This study provides valuable insights into the mechanisms underlying the surface adsorption behavior of HTPB and offers guidance for manipulating polymer wetting processes at interfaces.

This communication describes an initial study into the interaction of solution polyvinylpyrrolidone (PvP) with electrode-supported monolayers of dioleoyl phosphatidylcholine (DOPC). Experiments were carried out in phosphate buffered saline (PBS) at pH 7.4, and solutions were screened on a DOPC-coated microfabricated Hg/Pt electrode in flow cell. The effect of the PvP interaction on the form of rapid cyclic voltammograms (RCV) was recorded at 40 Vs−1. It was found that the PvP-DOPC interaction is strongly dependent on PvP chain length. For shorter chain lengths, the interaction is linearly related to PvP concentration whereas at longer chain lengths, the interaction is Langmuirean; however, the interaction RCV in all cases is representative of adsorption. Both the affinity constant, K2, and the limit of detection (LoD) are extracted from these plots, and these values are inversely related to each other. Plots of log K2 and –log LoD versus the monomer segment number (PvPm) fit a two-term equation consisting of a power term and an exponential term. Plots of (log K2)/PvPm versus PvPm are near reciprocal showing that there is 'looping' of the chains on the DOPC surface during the adsorption process. The results fit a model of entropically driven adsorption at short chain lengths and enthalpically driven adsorption at longer chain lengths the latter assumedly due to non-covalent interactions between the PvP chains on the DOPC surface. [ABSTRACT FROM AUTHOR]

The adsorption mechanism of different polymers containing ionic polyamino acids monomers in the chain structure at the solid–liquid interface was investigated. Initially, the influence of molecular weight and solution pH on simple polyamino acids (poly(L-aspartic acid) and poly(L-lysine) binding was determined. Considering the obtained dependencies, the polymer adsorption layer conformation was proposed in the systems containing block copolymers (both diblock and symmetrical triblock) consisting of polypeptide as well as poly(ethylene glycol) fragments. The presented studies focused on the application of two experimental methods. The polymer adsorption was carried out using the batch method and the adsorbate concentration was determined spectrophotometrically. Then, the turbidimetric measurements were taken. The analysis of the obtained results showed that the adsorption process of block copolymers depends on two factors. Firstly, the solution pH determines both the nature of the interactions of the copolymer structural units with the solid surface and the conformation of the polypeptide chains. The second parameter influencing the adsorption layer structure is the ratio of the lengths of both blocks. Introducing a short PEG fragment into the polymer main chain may improve the polymer adsorption properties by increasing the number of interactions with the adsorbent surface. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations that examine the partitioning of dilute solutions of ring or linear chains into a slit pore using two chain models, the random‐walk (RW) model and the self‐avoiding walk (SAW) model are presented. The partitioning coefficients K for the ring and the linear chains at the surface interaction both under the critical adsorption point (CAP) and above the CAP are compared. In both chain models, K for the ring remains larger than K for the linear chains. The ring chain crosses over the point K = 1 at a weaker surface interaction than the linear chain. When extrapolated to infinite chain length, the cross‐over point for the ring and linear chain becomes the same (within statistical errors) for the RW model but remains different for the SAW model. The density profiles of the ring within the pore reveal the development of humps near the wall as the surface interaction crosses over the CAP. The excluded volume interaction in the SAW model additionally impacts the partitioning of chains in a solution consisting of a binary mixture of ring and linear chains and makes the K values in a binary mixture differ from the monodispersed solutions. [ABSTRACT FROM AUTHOR]

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Adsorption of a single AB random copolymer (RC) chain onto homogeneous and inhomogeneous ab surfaces with a regular periodic pattern is studied theoretically. For the averaging over disorder in the RC sequence, the constrained annealed approximation, known as the Morita approximation is employed. A general scheme for constructing the Morita approximation of an arbitrary order m is proposed; it is based on representation of the RC monomer sequence as a Markov chain of overlapping (m –1)-ads. The problem is solved within the framework of the generating functions approach for the two-dimensional partially directed walk model of the polymer on a square lattice. Temperature dependences of various adsorption characteristics are obtained. The accuracy of the Morita approximation is assessed by comparison with the numerical results for RC with quenched sequences obtained by the transfer matrix approach. It is shown that for RC adsorption on a homogeneous surface for AB -copolymers with adsorbing A and neutral B blocks, it is sufficient to use the Morita approximation of second or third order. If the non-adsorbing B block is repelled from the surface, then a higher order of the approximation (5th–6th) is required. An important indicator of validity of the Morita approximation is the entropy: if the order of the approximation is not high enough, the entropy becomes negative in the low-temperature regime which means that the Morita approximation is wrong in this order. In the case when the surface is periodically inhomogeneous, the Morita approximation works worse and very high orders are required, which can be beyond the computational capabilities. Moreover, the Morita approximations become degenerate: approximations of two or more consecutive orders give the same result. [ABSTRACT FROM AUTHOR]

Polymers play an important role in hybrid enhanced oil recovery (EOR), which involves both a polymer and low-salinity water. Because the polymer commonly used for low-salinity polymer flooding (LSPF) is strongly sensitive to brine pH, its efficiency can deteriorate in carbonate reservoirs containing highly acidic formation water. In this study, polymer efficiency in an acidic carbonate reservoir was investigated experimentally for different salinity levels and SO42- concentrations. Results indicated that lowering salinity improved polymer stability, resulting in less polymer adsorption, greater wettability alteration, and ultimately, higher oil recovery. However, low salinity may not be desirable for LSPF if the injected fluid does not contain a sufficient number of sulfate (SO42-) ions. Analysis of polymer efficiency showed that more oil can be produced with the same polymer concentration by adjusting the SO42- content. Therefore, when river water, which is relatively easily available in onshore fields, is designed to be injected into an acidic carbonate reservoir, the LSPF method proposed in this study can be a reliable and environmentally friendly method with addition of a sufficient number of SO4 2-ions to river water. [ABSTRACT FROM AUTHOR]

Biomimetic actuators are typically constructed as functional bi- or multilayers, where actuating and resistance layers together dictate bending responses upon triggering by environmental stimuli. Inspired by motile plant structures, like the stems of the false rose of Jericho (Selaginella lepidophylla), we introduce polymer-modified paper sheets that can act as soft robotic single-layer actuators capable of hygro-responsive bending reactions. A tailored gradient modification of the paper sheet along its thickness entails increased dry and wet tensile strength and allows at the same time for hygro-responsiveness. For the fabrication of such single-layer paper devices, the adsorption behavior of a cross-linkable polymer to cellulose fiber networks was first evaluated. By using different concentrations and drying procedures fine-tuned polymer gradients throughout the thickness can be achieved. Due to the covalent cross-linking of polymer with fibers, these paper samples possess significantly increased dry and wet tensile strength properties. We furthermore investigated these gradient papers with respect to a mechanical deflection during humidity cycling. The highest humidity sensitivity is achieved using eucalyptus paper with a grammage of 150 g m−2 modified with the polymer dissolved in IPA (~13 wt%) possessing a polymer gradient. Our study presents a straightforward approach for the design of novel hygroscopic, paper-based single-layer actuators, which have a high potential for diverse soft robotic and sensor applications. [ABSTRACT FROM AUTHOR]

The adsorption mechanism of different polymers containing ionic polyamino acids monomers in the chain structure at the solid–liquid interface was investigated. Initially, the influence of molecular weight and solution pH on simple polyamino acids (poly(L-aspartic acid) and poly(L-lysine) binding was determined. Considering the obtained dependencies, the polymer adsorption layer conformation was proposed in the systems containing block copolymers (both diblock and symmetrical triblock) consisting of polypeptide as well as poly(ethylene glycol) fragments. The presented studies focused on the application of two experimental methods. The polymer adsorption was carried out using the batch method and the adsorbate concentration was determined spectrophotometrically. Then, the turbidimetric measurements were taken. The analysis of the obtained results showed that the adsorption process of block copolymers depends on two factors. Firstly, the solution pH determines both the nature of the interactions of the copolymer structural units with the solid surface and the conformation of the polypeptide chains. The second parameter influencing the adsorption layer structure is the ratio of the lengths of both blocks. Introducing a short PEG fragment into the polymer main chain may improve the polymer adsorption properties by increasing the number of interactions with the adsorbent surface.

[Display omitted] • Hybrid nanofluid with carbonized ZIF-67 reduced polymer adsorption and boosted oil recovery. • Polymer improved nanofluid stability at 75 °C, confirmed by UV–Vis, lasting over 7 days. • Polymeric nanofluid formed Winsor Type III emulsions and altered wettability to mixed-wet. • Core flooding showed 45.8 % tertiary oil recovery improvement in carbonate rocks at 75 °C. • Injectivity analysis shows high-permeability cores (≥290 mD) ideal for hybrid floodings. Traditional nanoparticle and polymer-based enhanced oil recovery methods face challenges such as nanoparticle agglomeration and polymer adsorption, particularly at elevated reservoir temperatures. This study introduces hybrid polymeric nanofluids, combining carbonized Zeolitic Imidazolate Framework-67 (ZIF-67) with sulfonated copolymers to address these issues. Viscosity tests were conducted at 25 °C, 50 °C, 75 °C, and 90 °C, revealing a 39.67 % increase in viscosity at 90 °C, attributed to electrostatic and hydrogen bond interactions. For subsequent analyses—stability, adsorption, and core flooding—75 °C was selected as the representative high reservoir temperature. Stability assessments, confirmed via UV–Vis spectroscopy, demonstrated nanofluid durability over at least seven days. Carbonized ZIF-67 reduced polymer adsorption on rock surfaces, enhancing oil recovery and reducing environmental impact. Dynamic core flooding experiments showed a 45.8 % improvement in oil recovery by the hybrid nanofluid on carbonate rock samples. The hybrid nanofluid increased RF and RRF, improving the mobility ratio and redirecting flow to lower-permeability zones, reducing unswept oil and enhancing macroscopic sweep efficiency. Winsor Type III emulsification during the post-flooding phase of polymer-nanoparticle injection significantly improved trapped oil mobilization. Reduced contact angles from 170° to 100° altered the wettability, enhancing oil recovery. Carbonized ZIF-67 nanoparticles increased viscous forces, reduced capillary forces, and minimized polymer adsorption. The polymeric nanofluid achieved a capillary number of 1.0 × 10−3, two orders higher than that of polymer alone, resulting in superior performance. Injectivity optimization showed shear rates of 15.9 s−1 in 1700 mD cores and 79.8 s−1 in 80 mD cores, causing pressure drops of 15 psi and 1200 psi, respectively. This highlights injectivity challenges in 80 mD cores, while cores ≥ 290 mD are ideal for our polymer-nanoparticle hybrid applications. [ABSTRACT FROM AUTHOR]

Selective aggregation can be used to improve the collection of fine valuable mineral particles often lost in industrial separation processes. This approach might be applicable to flocculate fine copper mineral particles such as chalcopyrite. It is hypothesised that the polymeric flocculant charge type will influence selectivity between chalcopyrite and waste minerals. This work investigates the use of charged anionic (APAM) and cationic (CPAM) polyacrylamides to selectively aggregate negatively charged chalcopyrite from its common waste (quartz). The interaction of the polymers with the mineral's surfaces as well as its flocculation capability were investigated through adsorption isotherms, turbidity tests, and in-situ aggregate size measurement. Furthermore, the ability to selectively aggregate and recover the valuable chalcopyrite from a quartz mixture by sedimentation was assessed. The results indicated that both charged polymers can be used to aggregate fine chalcopyrite particles, however, CPAM is non-selective towards the valuable mineral, as it also aggregates quartz. CPAM has a stronger affinity for both minerals, probably due to charge-charge interaction adsorption mechanisms, whereas APAM adsorption was lower, and more likely to be driven by hydrogen bonding. The interaction of APAM with quartz was limited probably because its highly negatively charged surface tends to repel the anionic polymer. Finally, the recovery of the chalcopyrite by sedimentation separation improved when using both polymers, but higher recoveries were obtained when using APAM. [Display omitted] • Fine CuFeS 2 particles were aggregated using anionic and cationic polyacrylamides. • Only APAM is selective towards CuFeS 2 , while CPAM also flocculates quartz. • Polymer charge affects the adsorption mechanism and affinity to both minerals. • Aggregate size and structure were studied with a novel image analysis technique. • Recovery of CuFeS 2 by sedimentation separation was improved with polymer addition. [ABSTRACT FROM AUTHOR]

Adsorption of a single homopolymer chain with bending stiffness onto a heterogeneous regular stripe-patterned surface consisting of adsorbing and non-adsorbing stripes is studied theoretically in the framework of the lattice model and the generating functions approach. The stiffness is introduced by assigning a statistical weight to a trans -isomer (a straight segment) with respect to a gauche -isomer (a kink). The temperature is taken as the main control parameter since it affects both the strength of the monomer units’ attraction to the adsorbing stripes and the chain stiffness. It is shown that the adsorption transition temperature is a non-monotonic function on the bending energy having a minimum. The position of this minimum depends on the stripes’ width and only slightly deviates from zero bending energy. Temperature dependences of the main conformational and thermodynamic characteristics of the adsorbed chain are obtained. It is demonstrated that in most of the studied cases the adsorption is accompanied by the chain localization on a single adsorbing unit stripe and the chain stiffness enhances this effect. [ABSTRACT FROM AUTHOR]

This review is the third part of a series of reviews on hydrophobization of lignocellulosic materials, a relevant topic nowadays, due to the need to replace fossil fuel-based materials. The review provides an overview of the hydrophobization of lignocellulosic materials by polymer adsorption, and both chemical and radiation-induced grafting of polymers. While adsorbed polymers are only attached to the surfaces by physical interactions, grafted polymers are chemically bonded to the materials. Radiation-induced grafting is typically the most environmentally friendly grafting technique, even though it provides little control on the polymer synthesis. On the other hand, controlled radical polymerization reactions are more complex but allow for the synthesis of polymers with elaborated architectures and well-defined properties. Overall, a wide range of contact angles can be obtained by polymer adsorption and grafting, from a slight increase in hydrophobicity to superhydrophobic properties. The choice of modification technique depends on the end-use of the modified material, but there is a clear trend towards the use of more environmentally friendly chemicals and processes and the grafting of polymers with complex structures. [ABSTRACT FROM AUTHOR]

For application as an aqueous ink, a low-acid-value and poorly water-soluble amphiphilic block copolymer was successfully converted into an aqueous solution with a concentration of ≤ 5 wt%. This was achieved via neutralization with an alkaline solution after the preparation of a highly concentrated solution of the highly viscous alcohol. When cyan and magenta inks were prepared in aqueous solutions via this method, the pigment dispersibility was improved and the viscosity of each ink was reduced. In traditional ink preparation approaches, the pigments, polymers, and additives are often mixed and dispersed together, but the importance of dissolving polymers in advance has been confirmed in this study. Zeta potential measurements of the pigments showed that a more negative potential led to a more dispersible ink, likely due to a greater electrostatic repulsion closely related to the adsorption of dispersants. The development of highly concentrated aqueous polymer dispersion solutions of poorly water-soluble block copolymers has enabled more precise analysis between polymer structures and dispersion mechanisms for thick pigment dispersions, including zeta potential estimation to study adsorption and rheological dispersion characteristics. In general, the design of polymer dispersants is determined by ink tests, and the results are always affected by polymer solubility. This paper therefore demonstrates the possibility of widening the scope of polymer design for inks through improving polymer solubility. [Display omitted] • Aqueous inks were formed from insoluble block polymers with low acid values. • Concentrated 5 wt% aqueous solutions of water-insoluble polymers were simply prepared by pre-solution. • Cyan and magenta inks were obtained with improved pigment dispersibilities. • This demonstrates the possibility of widening the scope of polymer design for inks. [ABSTRACT FROM AUTHOR]

[Display omitted] Polymer and small molecules are often used to modify the wettability of mineral surfaces which facilitates the separation of valuable minerals such as molybdenum disulfide (MoS 2) from gangue material through the process of froth flotation. By design, traditional methods used in the field for evaluating the separation efficacy of these additives fail to give proper access to adsorption kinetics and molecule conformation, crucial aspects of flotation where contact times may not allow for full thermodynamic equilibrium. Thus, there is a need for alternative methods for evaluating additives that accurately capture these features during the adsorption of additives at the solid/liquid interface. Here, we present a novel method for preparing MoS 2 films on quartz crystals used for Quartz Crystal Microbalance with Dissipation (QCM-D) measurements through an electrochemical deposition process. The resulting films exhibit well-controlled structure, composition, and thickness and therefore are ideal for quantifying polymer adsorption. After deposition, the sensors can be annealed without damaging the quartz crystal, resulting in a phase transition of the MoS 2 from the as-deposited, amorphous phase to the 2H semiconducting phase. Furthermore, we demonstrate the application of these sensors to study the interactions of additives at the solid/liquid interface by investigating the adsorption of a model polymer, dextran, onto both the amorphous and crystalline MoS 2 surfaces. We find that the adsorption rate of dextran onto the amorphous surface is approximately twice as fast as the adsorption onto the annealed surface. These studies demonstrate the ability to gain insight into the short-term kinetics of interaction between molecules and mineral surface, behavior that is key to designing additives with superior separation efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] Solid-state polymer adsorption offers a distinct approach for surface modification. These ultrathin, so-called Guiselin layers can easily be obtained by placing a polymer melt in contact with an interface, followed by a removal of the non-adsorbed layer with a good solvent. While the mechanism of formation has been well established for Guiselin layers, their stability, crucial from the perspective of materials applications, is not. The stability is a trade-off in the entropic penalty between cooperative detachment of the number of segments directly adsorbed on the substrate and consecutively pinned monomers. Experimental model systems of Guiselin layers of polystyrene (PS) on silicon wafers with native oxide layer on top were employed. The stability of the adsorbed layers was studied as a function of PS molecular weight and polydispersibility by various microscopic and spectroscopic tools as well as quasi-static contact angle measurements. Adsorbed layers from low molecular weight PS were disrupted with typical spinodal decomposition patterns whereas high molecular weight (>500 kDa) PS resulted in stable, continuous layers. Moreover, we show that Guiselin layers offer an enticing way to modify a surface, as demonstrated by adsorbed PS that imparts a hydrophobic character to initially hydrophilic silicon wafers. [ABSTRACT FROM AUTHOR]

Biomimetic actuators are typically constructed as functional bi- or multilayers, where actuating and resistance layers together dictate bending responses upon triggering by environmental stimuli. Inspired by motile plant structures, like the stems of the false rose of Jericho (Selaginella lepidophylla), we introduce polymer-modified paper sheets that can act as soft robotic single-layer actuators capable of hygro-responsive bending reactions. A tailored gradient modification of the paper sheet along its thickness entails increased dry and wet tensile strength and allows at the same time for hygro-responsiveness. For the fabrication of such single-layer paper devices, the adsorption behavior of a cross-linkable polymer to cellulose fiber networks was first evaluated. By using different concentrations and drying procedures fine-tuned polymer gradients throughout the thickness can be achieved. Due to the covalent cross-linking of polymer with fibers, these paper samples possess significantly increased dry and wet tensile strength properties. We furthermore investigated these gradient papers with respect to a mechanical deflection during humidity cycling. The highest humidity sensitivity is achieved using eucalyptus paper with a grammage of 150 g m−2 modified with the polymer dissolved in IPA (~13 wt%) possessing a polymer gradient. Our study presents a straightforward approach for the design of novel hygroscopic, paper-based single-layer actuators, which have a high potential for diverse soft robotic and sensor applications.

We examine the critical cracking thicknesses of as‐dried colloidal TiO2 suspensions containing water‐soluble polymeric additives, above which cracks spontaneously propagate. In contrast to common observations, the critical cracking thickness increases in a nonlinear, stepwise manner as increasing the concentration of the polymeric additive in the suspension. The critical thickness diverges when the polymer content increases above a certain threshold. We demonstrate that the first and second critical cracking thickness increments are attributable to the onset of polymer adsorption and a subsequent transition in the conformations of the adsorbing polymer chains, respectively. The critical thickness profiles with respect to normalized polymer adsorption amounts at different particle diameters converged into a single master curve. These results illustrate nontrivial evaporation processes in which the various roles of polymeric additives delay cracking into thicker films. [ABSTRACT FROM AUTHOR]

The adsorption of nonionic polymers to cellulose is of large importance both in the plant cell wall during synthesis and for the development of sustainable materials from wood. Here, the thermodynamics of adsorption of the polysaccharide xyloglucan (XG) to both native and chemically modified cellulose with carboxyl groups was investigated using molecular dynamics simulations. The free energy of adsorption was calculated as the potential of mean force between an XG oligomer and model cellulose surfaces in a range of temperatures from 298 K to 360 K. It was found that the adsorption near room temperature is an endothermic process dominated by the entropy of released interfacial water molecules. This was corroborated by quantitative assessment of the absolute entropy per water molecule both at the interface and in the bulk. In the case of native cellulose, the adsorption became exothermic at higher temperatures, while the relatively strong interactions between water and the charged groups of the oxidized cellulose impede such a transition. The results also indicate that the extraction of strongly associated hemicelluloses would be facilitated by low temperature. [ABSTRACT FROM AUTHOR]

Monolayer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te) have attracted much attention for use in electronic and optical applications. Due to their sensitivity to gases, the surface of these materials has been protected by coating with polymers such as polyethyleneimine (PEI). However, the effects of such coating layers on the electronic and optical properties of MX2 are not well understood. In this work, density functional theory calculations are used to study the effects of adsorption of PEI on monolayer MX2 substrates based on the electronic and optical properties before and after PEI adsorption. The results show that the bandgap of the substrate decreases significantly upon PEI adsorption, while the optical spectra show only slight modification with a decrease of intensity at short wavelengths around 300 nm. The results also indicate that PEI adsorption results in n-type doping states in MX2 but does not deteriorate the optical properties in the visible range. [ABSTRACT FROM AUTHOR]

• Size-based characterisation helped to understand how EPS flocculate particles. • Different EPS fractions showed different adsorption kinetics and binding affinities. • Optical reflectometry revealed site-blocking effect in mixed EPS. • Mixed EPS flocculated particle mixtures better than the high-MW EPS fraction. Microbial extracellular polymeric substances (EPS) produced from wastewater are generally heterodispersed, which is expected to influence their flocculation performances and mechanism, particularly in mixed particle systems. The different molecular weight (MW) fractions should contribute to the overall adsorption affinity and flocculation mechanism of EPS in single and dual clay systems. EPS harvested from bioreactors were size-fractionated into high, medium and low MW fractions (HMW, MMW, LMW, respectively). The harvested mixed EPS and its fractions were characterised by diverse analytical techniques coupled with optical reflectometry to investigate the role of each EPS fraction in the overall flocculation mechanism of EPS in kaolinite and montmorillonite clay systems. In single clay systems, both the harvested mixed EPS and the HMW-EPS fraction showed comparable flocculation performances. However, mixed EPS proved to be more efficient than the HMW-EPS fraction for dual clay flocculation. Site blocking effects were observed in mixed EPS: the LMW and MMW EPS first adsorbed to the surface due to higher diffusivities and faster mass transfer to the interface, while the HMW-EPS were slowly transported but were attached to the surface irreversibly and stronger than the LMW/MMW-EPS. We propose from this, a mixed EPS adsorption mechanism: extended anionic polymer tails in solution, thereby enhancing particle flocculation. [ABSTRACT FROM AUTHOR]

Carbonate rock strengthening using chemical techniques is a strategy to prevent excessive fines migration during oil and gas production. We provide herein a study of the adsorption of three types of hydrolysed polyacrylamide (HPAM) of different molecular weight (F3330S, 11–13 MDa; F3530 S, 15–17 MDa; F3630S, 18–20 MDa) onto calcium carbonate (CaCO3) particles via spectrophotometry using a Shimadzu UV-2600 spectrometer. The results are compared to different adsorption isotherms and kinetic models. The Langmuir isotherm shows the highest correlation coefficient (R2 > 0.97) with equilibrium parameters (RL) ranging between 0 and 1 for all three HPAMs, suggesting a favorable monolayer adsorption of HPAM onto CaCO3. The adsorption follows pseudo-second order kinetics, indicating that the interaction of HPAM with CaCO3 is largely dependent on the adsorbate concentration. An adsorption plot reveals that the amount of HPAM adsorbed onto CaCO3 at equilibrium increases with higher polymer molecular weight; the equilibrium adsorbed values for F3330S, F3530S and F3630S are approximately 0.24 mg/m2, 0.31 mg/m2, and 0.43 mg/m2, respectively. Zeta potential analysis shows that CaCO3 has a zeta potential of +12.32 mV, which transitions into negative values upon introducing HPAM. The point of zero charge (PZC) is observed at HPAM dosage between 10 to 30 ppm, in which the pH here lies between 9–10.

Clays are not only ubiquitous in nature, but they are also used in huge quantities in a broad range of industrial applications, such as thixotropic drilling fluids, ore pelletizers, waste disposal sealants, or fillers in polymer nanocomposites. In order to model environmental processes or to design new materials on a rational base, it is of prime importance to determine and possibly modify the interfacial properties of clay platelets at the solid/electrolyte interface. In this context, the fundamental question rises how far the stoichiometric interlayer charges as determined by the composition of the silicate layer correlates with the diffuse double-layer properties. Here, this question is addressed by means of a series of purposely synthesized sodium 2:1 layered silicates with defined composition and hence interlayer charge densities, respectively. Platelets of layered silicates of large enough diameter to perform AFM colloidal probe measurements were produced by melt synthesis. For comparison also, a natural muscovite mica has been included in this study. The diffuse layer properties in electrolyte solution have been determined by direct force measurements using the colloidal probe AFM technique and by electrokinetic measurements, respectively. We find that the diffuse layer potential decreases with increasing interlayer charge of the 2:1 layered silicates. This counterintuitive finding is attributed to ion adsorption and was further corroborated by determining the quantitative adsorption of polyelectrolytes, namely poly(amidoamine) dendrimers. [ABSTRACT FROM AUTHOR]

Adsorption of weak polyelectrolytes onto charged nanoparticles, and concurrent effects such as spatial partitioning of ions may be influenced by details of the polyelectrolyte structure (linear or star–like) and size, by the mobility of the nanoparticle surface charge, or the valence of the nanoparticle counterions. Ionization and complexation of weak polyelectrolytes on spherical macroions with monovalent and divalent countrions has been studied with constant–pH Monte Carlo titrations and primitive electrolyte models for linear and star–like polymers capable, also, of forming charged hydrogen bonds. Nanoparticles surface charge has been represented either as a single colloid–centered total charge (CCTC) or as surface–tethered mobile monovalent spherical charges (SMMSC). Differences in the average number of adsorbed polyelectrolyte arms and their average charge, and in the relative amount of macroion counterions (m–CI's) released upon polymer adsorption are found between CCTC and SMMSC nanoparticles. The amount of the counterions released also depends on the polymer structure. As CCTC adsorbs a lower number of star–like species arms, the degree of condensation of polymer counterions (p–CI's) onto the polyelectrolyte is also substantially higher for the CCTC colloid, with a concurrent decrease of the osmotic coefficient values. [ABSTRACT FROM AUTHOR]

Polymers adsorbed on nanoparticles (NPs) are important elements that determine the dispersion of NPs in polymer nanocomposite (PNC) films. While previous studies have shown that increasing the number of adsorbed polymers on NPs can improve their dispersion during the drying process, the exact mechanism remained unclear. In this study, we investigated the role of adsorbed polymers in determining the microstructure and dispersion of NPs during the drying process. Investigation of the structural development of NPs using the synchrotron vertical-small-angle X-ray scattering technique revealed that increasing polymer adsorption suppresses bonding between the NPs at later stages of drying, when they approach each other and come in contact. On the particle length scale, NPs with large amounts of adsorbed polymers form loose clusters, whereas those with smaller amounts of adsorbed polymers form dense clusters. On the cluster length scale, loose clusters of NPs with large amounts of adsorbed polymers build densely packed aggregates, while dense clusters of NPs with small amounts of adsorbed polymers become organized into loose aggregates. The potential for the quantitative control of NP dispersion in PNC films via modification of polymer adsorption was established in this study.

The first experimental evidence of polymer adsorption in natural carbonates obtained from streaming potential measurements is presented. The surface probing of the Estaillades core was realized in a highly saline environment with I ~ 3 M similar to formation water naturally found in some oil reservoirs, which are typical target for enhanced oil recovery (EOR) by Smart Water Injection Methods (SWIM) and Hybrid SWIM. A highly sensitive setup with an exceptional signal-to-noise ratio even at high salinity, allowing to discriminate voltage fluctuations below 0.1 mV, was used to probe the streaming potential coupling coefficient. The injection of partially hydrolyzed polyacrylamide Flopaam 3130S was followed by chase flooding with formation water for several pore volumes, to assure that any changes measured after the polymer flooding are due to the retained polymer. We show that the streaming potential coupling coefficient changes sign after polymer adsorption. This result not only is an unambiguous evidence for polymer adsorption but has implications on chemical EOR scenarios that need to consider wettability changes due to inversion of surface charge. [ABSTRACT FROM AUTHOR]

Two grades of chitosan [chitosan 30000 g mol−1 (N-chitosan 30) and 250000 g mol−1 (N-chitosan 250)] were functionalized by the Kabachnik–Fields reaction. To obtain the highest phosphonic ester grafting rate (55% and 40% for the N-chitosan 30 and N-chitosan 250, respectively), the pH must be kept constant during the reaction (pH=5). Then, a partial hydrolysis of the ester functions was carried out in HCl medium to generate phosphonic acid functions up to 25% and 20% for the N-chitosan 30 and N-chitosan 250, respectively. It was shown that the grafting of phosphonic acids on chitosan significantly reduced the dynamic viscosity. Afterwards, electrochemical impedance measurements were performed in an aqueous solution (pH=5) in the presence of either N-chitosans or P-chitosans (3 wt.%). The two native N-chitosans were little adsorbed onto the carbon steel surface and the corrosion protection was low. In contrast, the impedance results in the presence of the 30000 g mol−1 phosphorylated chitosan (P-chitosan 30) evidenced the beneficial effect of grafted phosphonic acid on its adsorption on the steel surface. The lower efficiency of the 250000 g mol−1 (P-chitosan 250) was attributed to its high molecular weight which made difficult the interactions between the phosphonic groups and the metallic surface. [ABSTRACT FROM AUTHOR]

Molecular simulations (Dissipative Particle Dynamics - DPD) were used to quantify the effect of polymer adsorption on the effective shear viscosity of a semi-dilute polymer solution in microchannel Poseuille flow. It is well known that polymer depletion layers develop adjacent to solid walls due to hydrodynamic forces, causing an apparent wall slip and reduced effective viscosity (increased total flow rate). We found that depletion layers also developed in the presence of hydrodynamically rough adsorbed layers on the wall. Polymer-polymer (steric) repulsion between flowing and adsorbed polymer expanded the depletion layer compared to no-adsorption cases, and the effective viscosity was reduced further. Desorption occurred for higher shear rates, reducing the repulsion effect and shrinking the depletion layers. A phenomenological algebraic model for the depletion layer thickness, including a shear modified adsorption isotherm, was developed based on the simulation data. The depletion layer model can be used together with the effective viscosity model we developed earlier. [ABSTRACT FROM AUTHOR]

Abstract In the present study, spontaneous imbibition experiments, steady-state permeability measurements, and numerical simulation were integrated to quantify the changes in the effective water permeability, capillary pressure, and water relative permeability curves due to the polymer adsorption of the spontaneously imbibed fracturing fluid. The effect of the nonionic surfactant and core bedding plane on the fluid spontaneous imbibition volumes were also investigated. The researchers considered the impact of the spontaneous imbibition of a friction reducer fluid in tight sand and shale core samples. Three comparative systematic spontaneous imbibition experiments were conducted for each of the core samples using brine, anionic friction reducer fluid, and brine again. The core sample water permeability before and after the imbibition experiment was measured using a constant rate steady-state permeability apparatus. The polymer adsorption from the spontaneously imbibed fracturing fluid significantly reduced the brine spontaneous imbibition volumes in tight sand samples and in shale samples, though to a lesser degree. Moreover, the effective water permeability was decreased because of the polymer adsorption effect. Therefore, the polymer adsorption during hydraulic fracturing reduces the fluid leak-off into the formation and also the fluid flowback. The nonionic surfactant increased the fluid spontaneous imbibition volumes in both tight sand and shale samples. Thus, adding a nonionic surfactant to the friction reducer pad fluid during hydraulic fracturing leads to enhance both of the fluid leak-off and fluid flowback. The results also showed that the effect of polymer adsorption on the imbibition rates is less when the rock-fluid contact surface is parallel to the bedding plane. The imbibition potentials and imbibition capillary pressure curves were calculated before and after polymer adsorption. The polymer adsorption led to a slight increase in the capillary pressure; moreover, the tight sand samples had higher capillary pressure than the shale samples. The imbibition water relative permeability curves were calculated using ECLIPSE commercial simulator. The polymer adsorption significantly reduces the water relative permeability curves for tight sand samples and in less degree for shale samples. Highlights • Polymer adsorption reduces fluid loss into the formation and fluid flowback. • Adding surfactant to the slickwater fluid increases its leak-off into and flowback. • Polymer adsorption impact is less when the flow is orthogonal to the bedding plane. • Polymer adsorption has a slight effect on the imbibition capillary pressure. • Polymer adsorption effect on the Krw is higher for tight sand than for shale samples. [ABSTRACT FROM AUTHOR]

• The binding mechanism of alginate and chitosan on montmorillonite surface was investigated. • pH and order of addition affected the properties of the polyelectrolyte complex. • Intercalation of chitosan followed by alginate formed the complex within the interlayer space of montmorillonite. • Thermal stability of the complex was discussed. The use of alginate@chitosan-based polyelectrolyte complexes (PEC) in encapsulation process is common due to the electrostatic interactions between the two oppositely charged biopolymers. However, the incorporation of montmorillonite (Mt) particles in the complex formation for improving the encapsulation efficiency as well as the physicochemical properties of PEC remains a challenge due to the competitive polymer–polymer and polymer-nanoparticle interactions. This study aimed to investigate the binding mechanism of alginate and chitosan through layer-by-layer approach in the presence of montmorillonite nanoparticles as a function of pH and the addition order of the components. Various techniques were employed to examine the formation of the alginate@chitosan PEC on the surface of Mt, such as zeta potential, conductivity and turbidity measurements. The characterization of the different PEC systems was performed using Fourier Transformed Infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicate that the formation of the complex is pH-dependent. The highest intercalation of the complex was observed when chitosan was added first at a lower pH, while the intercalation was reduced at neutral pH. Additionally, the thermal stability of PEC was enhanced in the presence of montmorillonite, and was dependent on both pH and the order of addition of the biopolymers. This study provides a new understanding of the complex formation mechanism between alginate and chitosan in the presence of montmorillonite nanoparticles, showing that the combination of biopolymer-based PEC with clay particles can potentially provide a low-cost, more stable and effective nanocomposite for encapsulation and delivery of active agents. [ABSTRACT FROM AUTHOR]

Polymer coatings of nanometric thickness are about to enter in everyday life as part of a wide range of applications such as protective layers, stimuli-responsive membranes or as components of flexible electronics devices. In the past 30 years, these polymer nanomaterial systems have been at the center of research interest due to the opportunities to control relevant material properties like the phase transition temperature, viscosity, permeability, or thermal expansion by variation of the film thickness. One of the key factors responsible for the deviation from bulk behavior is known as 1D confinement that describes the increasing impact of interfacial layers when reducing film thickness. This review provides a comprehensive discussion of the role of the free surface at the boundary with air and the interfacial layer in proximity of a supporting substrate on the crystallization of thin polymer films. First, the dynamics of polymers near the free surface and its impact on the crystallization of films is discussed. Subsequently, the effect of solid substrates on crystallization in thin films is elaborated, including the formation of irreversible adsorption layers, alteration of crystalline structure and the kinetics of crystallization. Subsequently, the competition between surface and interface effects on the formation of ordered structures in thin polymer films is discussed. A perspective on challenges and opportunities in the field of thin film crystallization is provided to inspire future research and development in the field. This review thus provides an up-to-date analysis of current understanding of crystallization of polymer glasses under 1D confinement, aimed at supporting the manipulation and control of the properties of polymer-based nanodevices. [Display omitted] [ABSTRACT FROM AUTHOR]