Folding property of di-block polyampholytes

Abstract

1.1. Monolayers of polyvinyl benzoic acid (P.V.B.A.), of poly ortho- vinyl pyridine, and poly para- vinyl pyridine as well as of copolymers containing varying proportions of vinyl benzoic acid (V.B.A.) and 2-vinyl pyridine (2-V.P.) were investigated. These polymers were spread on the air-water interface of buffer solutions of constant ionic strength and of various pH values, and their surface pressure and potentials were measured.2.2. The measured surface potentials and pressures of poly 4-vinyl pyridine (4 P.V.P.) were smaller than the corresponding potentials and pressures of poly 2-vinyl pyridine (2 P.V.P.) at the same surface concentration. From these results it was concluded that there is a higher probability for the trans- than for the cis-configuration of the pyridine residues in the polymeric chain.3.3. In the case of polyvinyl benzoic acid and the polyampholytes, strong intermolecular forces are evident. As a result, equilibrium pressure values were reached very slowly after a certain surface area was established. The forces acting in the case of P.V.B.A. are due to hydrogen bonds and, in the case of the polyampholytes, in the neighborhood of the isoelectric point, are due to both hydrogen bonds and electrostatic attraction of oppositely charged monomeric residues.4.4. The pH of the solution has only negligible influence on the surface pressures and potentials of 2-P.V.P. and 4-P.V.P. until a pH value is reached where the film starts to dissolve. At this point both the pressure and the potential drop suddenly. The influence of pH is more pronounced in the case of P.V.B.A. and is quite striking in the case of polyampholyte films. The contractive forces prevent the dissolution of the hydrophilic units in the surface. They are balanced by repulsive forces which arise from the net charge of the surface film.