Conformation of Poly(styrene sulfonate) Layers Physisorbed from High Salt Solution Studied by Force Measurements on Two Different Length Scales

Abstract

The conformation of poly(styrene sulfonate) (PSS) layers physisorbed from 1 M NaCl is determined by force measurements and imaging on two length scales. With colloidal probe technique steric forces as predicted for neutral grafted brushes are observed. On decrease and increase of the NaCl concentration, the grafting density remains constant, yet the brush thickness swells and shrinks reversibly with the salt concentration with an exponent of -0.3. At low salt conditions, the brush length amounts to 30% of the contour length, a behavior known for polyelectrolyte brushes and attributed to the entropy of the counterions trapped in the brush. Between a PSS layer and a pure colloidal silica sphere, the same steric forces are observed, and additionally at large separations (beyond the range of the steric repulsion) an electrostatic force is found. A negatively charged AFM tip penetrates the brush--a repulsive electrostatic force between the tip and surface is found, and single chains can be imaged. Thus, with the nanometer-sized AFM tip, the flatly adsorbed fraction of the PSS chains is seen, whereas the micrometer-sized colloidal probe interacts with the fraction of the chains penetrating into solution.

Effects of Reactive Oxygen Species on Single Polycation Layers

“…Moreover single chains or brush building events after radical attack can be excluded. 8 Furthermore, XPS measurements find no evidence for additional ion adsorption onto the PEI layer in consequence of the radical attack (Tables 1 and 2 in the Supporting Information). This indicates that the decreased surface potential/charge density after radical attack is caused by a Based on the constant Debye length and consequently the constant range of electrostatic force, we observe that the magnitude of the electrostatic repulsion reduces after radical attack.…”

Probing effects of polymer adsorption in colloidal particle suspensions by light scattering as relevant for the aquatic environment: An overview

“…Direct evidence for such conformational transitions is currently not available for polymer films adsorbed to colloidal particles. However, such conformational changes on planar substrates are well documented with the quartz crystal microbalance or direct force measurements (Block and Helm, 2008;Sedeva et al, 2010;Porus et al, 2012a). For example, adsorbed poly(lysine) and poly(vinyl amine) films adsorbed on silica surfaces from solutions containing high levels of salt would swell substantially upon decrease of the salt level.…”

Dynamic Compression of in Situ Grown Living Polymer Brush: Simulation and Experiment

“…Regarding the force of interaction, f , for the geometry of a grafted plane and a spherical body of radius R at distance D between the surfaces can be described by a slightly modified equation [74][75][76][77],…”