Wettability of amphiphilic poly(amido amine) (PAMAM) dendrimers on quartz: Effect of electrostatic and hydrophobic interaction

Wettability of amphiphilic poly(amido amine) (PAMAM) dendrimer on quartz surfaces was studied as a function of structure differences. The dependence of contact angle on concentration presented various tendencies with the increase of hydrophobic chain length, in which, maximum value of -log C curve occurred only for QPAMC(16) with more hydrophobicity. However, slightly changes were observed in the tendency of contact angle versus concentration specifically for QPAMC(12), with large contact angle value emerged instead, indicating a large hydrophobic group density on quartz surface differing from that of traditional surfactants. In addition, the amphiphilic dendrimer with long hydrophobic chain has obvious ability to alter the wettability of oil-wet surfaces.Quantitative and qualitative descriptions of the adsorption were investigated to explore the wettability nature. Significant morphological differences in QPAMC(m) were observed after adsorption on quartz, which transformed from spherical micelles into hemimicelles for QPAMC(8) induced by the affinity of molecules onto the surface, however, regularly spherical aggregates tended to form for QPAMC(12) and QPAMC(16), and the size and thickness have dependence of bulk concentration. The results indicated that the affinity of head group and the self-association driven by the chain length for amphiphilic dendrimers revealed synergistic effect both in adsorption and wetting properties. [GRAPHICS] .