Abstract
The adsorption of ethoxylated surfactants on differently sized polystyrene nanoparticles was followed by microcalorimetric titration. Titration allowed three phases of the adsorption process to be distinguished: (a) a first, exothermic phase due to hydrophobic interaction of surfactant and particle surface; (b) a second endothermic phase due to interfacial micelle formation; and (c) a third exothermic phase due to molecular rearrangements in the adsorption layer. The driving force for the adsorption of poloxamer and poloxamine block copolymers is the interfacial micelle formation signifying that it is a mainly entropy-driven process. A third phase of molecular rearrangement could only be detected for high molecular weight poloxamers. Nonyl- and dinonylphenols (Antarox CO and DM series) with short polyethoxy chains adsorb by hydrophobic interaction via a single-phase process, whilst long-chain derivatives exhibit all three phases. The thiicker adsorption layers on small latex particles could be attributed to promotion of interfacial micelle formation.
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