Conformational Behaviour of Comb‐Like Poly(4‐vinylpyridinium) Salts and their Complexes with Surfactants in Solution and on a Flat Surface

Abstract

We synthesised P4VP bromides with octyl and dodecyl pendant groups; the bromide anions in these polymer salts were further substituted with dodecylsulfate or bis(2‐ethylhexylsuccinate) anions. Direct SFM visualisation of the original P4VP chains, of the macromolecular salts and of their complexes, showed that the attachment of the pendant groups and especially the complexation with the surfactants promotes stretching of the macromolecules while adsorbing on mica substrate. On the other hand, viscosimetry showed that in solution (chloroform) the comb‐like chains and their complexes with dodecylsulfate had more compact conformations than those of the original P4VP. The scaling exponents describing the correlation between the contour length and the end‐to‐end distance of the adsorbed macromolecules were found to be ca. 3/4, which is indicative of 2D self‐avoiding walk statistics.magnified image

Scanning Force Microscopy as Applied to Conformational Studies in Macromolecular Research

“…According to our experience, the achievable precision of n measurements is characterised by a few percent of the relative error, provided sufficiently large statistics is accumulated. [159,160] Yet, when interpreting the results of experimental SFM investigations one should not forget about the possibility of incorrect determination of the const parameter because of not sufficiently high spatial resolution of the microscope. It means that the stiffness of a polymer chain may be estimated incorrectly (overestimated).…”

“…We systematically developed the methodology to determine the n-exponent in the SFM research on single macromolecules. Recently, we have tested our methodology on several model systems, [159,160] see also other results to be discussed below. The first and most revealing system was a set of polymer chains of the same type but with some structural difference.…”

“…It was demonstrated, that both initial P4VP chains and their hydrophobically modified derivatives can be routinely visualised using SFM. [159] The conformation of the adsorbed macromolecules with different numbers of side chains per a monomer was somewhat different. This difference could clearly be perceived just by looking at the SFM micrographs.…”

“…As such a system we selected a set of poly-4-vinylpyridine macromolecules modified up to different degrees with hydrophobic side chains. [159] For single polyvinylpyridine molecules it was known before from the literature that they are among a few examples of flexible chain macromolecules, which can be routinely visualised by SFM when adsorbed on a mica substrate. One of the reasons of convenience for the visualisation may be related to the stability of the adsorbed macromolecules on the substrate due to electrostatic interaction.…”

“…[171] Our model set of the P4VP-samples included initial (unmodified) P4VP chains as well as the same chains after hydrophobic modification with different grades. [159,172] The number of hydrophobic side chains was increasing in the series: zero, one, two, three, as a result of different types of hydrophobic modification applied. The introduced side chains decrease interaction of macromolecules with a substrate (mica) and increase their effective rigidity as a whole upon adsorption.…”