Interaction and Structure of Surfaces Coated by Poly(vinyl amines) of Different Line Charge Densities

Abstract

Interactions between preadsorbed films of poly(vinyl amine) (PVA) of two different line charge densities on silica substrates were studied with the colloidal probe technique based on the atomic force microscope (AFM). The preadsorbed films were prepared by adsorption of PVA from a pH 4 solution without any added salt. The highly charged PVA adsorbs in a flat configuration and in laterally heterogeneous layers, while the more weakly charged PVA analog adsorbs in thicker and more homogeneous films. As revealed by reflectivity measurements, such preadsorbed PVA films are stable in polyelectrolyte-free solutions. However, force measurements with the colloidal probe reveal that their interactions depend strongly on the ionic strength. Upon approach, interactions are dominated by electrostatic diffuse layer overlap forces. Both PVA films have very similar diffuse layer charge densities of about 1.5 mC/m2. Since these values are substantially lower than what would be expected from the total charge of the adsorbed polyelectrolytes measured by reflectivity, we infer that coadsorption of anions represents the principal mechanism in charge neutralization. Upon retraction, the adhesion between the films is dominated by bridging forces due to single polymer chains. Such bridging adhesion becomes progressively important with increasing ionic strength, whereby their range and frequency increase. The work of adhesion due to bridging is about 0.3 mN/m. At low ionic strengths, the films behave differently. While the highly charged PVA shows unspecific adhesion at small distances, the more weakly charged PVA analog shows few adhesion events occurring at long distances.

Stability of negatively charged latex particles in the presence of a strong cationic polyelectrolyte at elevated ionic strengths

“…The role of co-adsorbed chloride ions becomes even more prominent with increasing ionic strength. This charge neutralization scenario seems to be relatively general for the adsorption of strongly charged polyelectrolytes to oppositely charged substrate, as similar conclusions were reached for other systems [48,49].…”

A silica/PVA adhesive hybrid material with high transparency, thermostability and mechanical strength

“…However, using silica/PVA to obtain an adhesive interfacial surface may be difficult, due to the requirements of chemical reactions and heating. 17 In order to obtain strong adhesion at room temperature by spreading a droplet of silica/ PVA nanoparticle adhesive onto a surface under stress, a good dispersion of SiO 2 at an appropriate concentration in PVA is required. Obtaining the correct balance is still a key issue, 18 because an excessive content of silica particles will lead to drawbacks such as opaqueness, cracking, deformation, phase separation and easy breakage following heating.…”

Large Mechanical Response of Single Dendronized Polymers Induced by Ionic Strength

“…A larger mechanical response of synthetic polymers could be obtained by modifying their stiffness. Although the persistence length of linear polyelectrolytes as measured by light scattering can be tuned substantially through the ionic strength of the surrounding aqueous medium,16 no substantial change in chain elasticity was observed 10. 11 This surprising feature was explained by a scale dependence of the measured persistence length 17.…”

“…The mechanical properties of individual dendronized polymers were probed by atomic force microscopy (AFM) in force spectroscopy mode 5. 10, 12, 18, 24 This technique measures the stretching force of a polymer chain bridging the AFM tip and the substrate (Figure 2). Dendronized polymers grafted onto the AFM tip are likely to attach covalently to the substrate upon contact between the tip and the substrate.…”