Solution and solid liquid interfacial behavior of hydrophobically modified polymers, polymer surfactant, and dual polymers

Hydrophobically modified water soluble polymers constitute a novel class of polymers that are finding important applications in various industries owing to their unique structural combination of both surfactants and polyelectrolytes. These polymers show interesting aggregation/association behavior in the bulk solution phase and behave as modifiers at various interfaces. However, a systematic investigation or a thorough understanding of the properties of these polymers is lacking. In the current work, the solution and solid/liquid interfacial properties of poly (maleic acid/octyl vinyl ether) (PMAOVE) and poly (vinyl caprolactam) (PVCAP) have been systematically studied regarding hydrophobic aggregation, solution viscosity, adsorption on solids, effect on colloid stability, and their complexation with surfactants.; The long, flexible alkyl groups on PMAOVE enable the polymer to form intra-molecular hydrophobic microdomains both in aqueous solutions and at solid/liquid interfaces. In contrast, no such aggregation occurs with PVCAP due to its bulky and rigid hydrophobes. However, the exposure of large hydrophobic surfaces of the polymer to aqueous environment makes the system inherently unstable. This has two consequences. First, PVCAP shows a much reduced phase transition temperature. Second, as a means to reduce the exposed hydrophobic surface and thereby minimize the system free energy, PVCAP complexes with both anionic (sodium dodecylsulfate) and cationic (dodecyltrimethylammonium bromide) surfactants, as well as PMAOVE, through hydrophobic effects. Strikingly unexpected adsorption behavior has been observed with these complexes at solid/liquid interfaces.; The structural differences between PMAOVE and PVCAP also have significant consequences for their interfacial properties. The adsorption of PMAOVE at the alumina/water interface was found not to induce significant hydrophobic interactions between the alumina particles, while the PVCAP/silica system shows reversible flocculation or stabilization upon shift in pH or temperature. The latter observation has been explained by hydrophobic interactions in addition to the classical DLVO forces.; By carrying out a systematic experimental study as well as theoretical modelling, the structure-conformation relationship of representative HM polymers, the current research provides a deep insight into the factors governing the properties of hydrophobically modified polymers.