Surface characterization of poly(4-vinylpyridine) quaternized with tetradecyl bromide: Effect of the degree of quaternization

The surface behavior of poly(4-vinylpyridine) quaternized with tetradecyl bromide (P4VPC₁₄) as function of the quaternization degree was studied. The percentage of vinylpyridine moieties quaternized was found to be 35 to 75%. Surface pressure-area isotherms (π-A) at the air-water interface were determined. The polymer monolayers show particular shapes at different quaternization degrees. In order to get information about the hydrophobicity degree of the polymeric systems, the surface energy (SE), and their dispersion and polar contributions, γ_D and γ_P respectively, measurements of the contact angle (CA) with water, bromobenzene, and cis-decalin were performed. The results obtained are dependent on the quaternization percentage of the functionalized polymers. At high quaternization degree, hysteresis in the π-A diagrams was observed. The change in the P4VPC₁₄ molecular organization in the monolayer was also investigated during the compression and expansion processes. During these processes the monolayer was monitored by Brewster angle microscopy (BAM). For several cycles, all compression curves and all expansion curves showed a common intersection point. We have tried to describe the P4VPC₁₄ molecular organization at the air-water interface by molecular dynamic simulation (MDS). The results are also discussed in terms of the effect of the counterions and water on the stability of the system over the more packed region.