Adsorption of charged and neutral polymer chains on silica surfaces: The role of electrostatics, volume exclusion, and hydrogen bonding

Abstract

We develop an off-lattice (continuum) model to describe the adsorption of neutral polymer chains and polyelectrolytes to surfaces. Our continuum description allows taking excluded volume interactions between polymer chains and ions directly into account. To implement those interactions, we use a modified hard-sphere equation of state, adapted for mixtures of connected beads. Our model is applicable to neutral, charged, and ionizable surfaces and polymer chains alike and accounts for polarizability effects of the adsorbed layer and chemical interactions between polymer chains and the surface. We compare our model predictions to data of a classical system for polymer adsorption: neutral poly(N -vinylpyrrolidone) (PVP) on silica surfaces. The model shows that PVP adsorption on silica is driven by surface hydrogen bonding with an effective maximum binding energy of about 1.3 k B T per PVP segment at low pH. As the pH increases, the Si-OH groups become increasingly dissociated, leading to a lower capacity for H bonding and simultaneous counterion accumulation and volume exclusion close to the surface. Together these effects result in a characteristic adsorption isotherm, with the adsorbed amount dropping sharply at a critical pH. Using this model for adsorption data on silica surfaces cleaned by either a piranha solution or an O 2 plasma, we find that the former have a significantly higher density of silanol groups.

Polymer Molecular Weight Dependence on Lubricating Particle–Particle Interactions

“…4 seem to correspond to conformations where the PVP chains are lying flat or nearly flat on the substrate (PVP chain width previously reported to be ~ 1 nm). 39 This likely polymer orientation on the substrate is also justified by the low dissipation values, although it is worth noting that the dissipation of the 8 kDa PVP film is four times smaller than the higher molecular weight PVPs, signifying increased film stiffness by the lowest molecular weight PVP. highlighting potential conformational changes of the PVP molecules on silica during the adsorption process (rinse-off data not included).…”

Nonlinear electrophoresis in the presence of dielectric decrement

“…However, when dielectric decrement effects are added, we cannot proceed analytically for the calculation of both q and w and we have to rely on numerical integrations to estimate these quantities from relations (34) and (35).…”

“…Hence, more accurate approaches based on the Carnahan-Starling equation of state for a bulk monodisperse hard-sphere liquid have been proposed [33], notably to investigate polyelectrolyte adsorption on charged interfaces [34,35] and sedimentation [36]. An extensive discussion on the structure of the EDL can be found in the article of Giera et al [37], which compares molecular dynamics simulations with local-density approximations.…”

White paper on the future of plasma science for optics and glass

“…Practical technological challenges and barriers seem to be partly determined by a lack of data on the non‐linear properties of glasses, the temperature limitations of glass composites, a lack of understanding of the surface structure, surface chemistry and surface interactions with other materials at the molecular level, limited processes for online coatings, and a lack of substitutes for toxic glass components . Consequently, research and development activities will aim to improve or develop key enabling technologies and products, such as: Cost‐effective optically non‐linear glasses and graded index glasses; Improved processes for glass substrates used in thin film applications; Non‐oxide glasses with advanced compositions; Glasses with ultraviolet and infrared transparent characteristics; Alkali‐resistant systems for concrete reinforcement; Processes and compositions for smart window products; Improved processing methods for solar lenses, mirrors, and photovoltaic cells; Systems for controlled release of fertilizers, herbicides, insecticides, and pest control, or for the encapsulation of various types of hazardous waste in glass; Economical processes for the high‐speed coating of glass; Compositions with reactive surfaces for bio‐applications and sensor applications; Compositions with passive surfaces that can be used to maintain the strength of glass; Increased understanding of glass‐surface interactions through experimental and theoretical surface research …”