The interaction between liquid-liquid dispersion covered with polymer-surfactant complexes has been in investigated. The polymer used for our investigations is poly(vinyl alcohol) and the surfactants were sodium dodecyl sulfate, cetyltrimethylammonium bromide and tetradecyltrimethylammonium bromide, and nonyl phenol ethoxylate (NP10). It has been found that the magnitude and the onset of repulsive forces increase dramatically during the association process. The onset of association depends on the nature of surfactant and interfacial properties of the emulsion droplet. The force profiles follow an exponential scaling with a characteristic decay length equal to the Rg of the polymer, irrespective of the surfactant concentration. No associative behavior has been observed in the presence of nonionic surfactant (NP10). The experimental observations suggest that in the presence of charged surfactant molecules or micelles, the neutral polymer chains at the interface are converted into partial polyelectrolytes, where the charges on the chain repel each other and the electrostatic repulsion collectively leads to chain stretching, which would provide better stability to the colloidal particles.

We provide experimental evidence for stretching and collapse of neutral polymer layers, already adsorbed at an oil-in-water interface, due to its interaction with surfactants. Upon stretching, the first interaction length (2L(0)) follows a power law dependence on surfactant concentration ( proportional, variant C(x)(s), where x approximately 0.5 for cationic surfactants) and collapses in the presence of salt, as a relatively weak power law (C(-y)(s), where y=0.17), in good agreement with brush length decay for polyelectrolyte brushes.

Precise control of crystal orientation, and specifically the exposed surface, is critical for the engineering of heterostructures. Here, using CoPt as a model system, we explore the energetics to expose suitable facets to promote the required heterostructure formation. Different heterostructures are grown ranging from core/shell structure, diffused interface, dumbbell structured dimers, and embedded island structures wherein these hybrids are fabricated via micro/macrolevel facet-selective growth. The reaction conditions used to achieve such diversity starting from the same seed offer insights into the growth mechanisms of these heterostructures. Such a microscopic understanding of surface chemistry paves the way for the design of new heterostructures with exciting properties.

No abstract

No abstract