(360f) Adsorption of Star Polymers to Fluid Interfaces

Star polymers and similar nanoparticulate brushes can be effective and efficient emulsifiers and foaming agents. When environmentally responsive polymer arms are incorporated in the star polymers, the resulting emulsions can be rendered environmentally responsive. These attributes suggest possibly advantageous application potential for star polymers in commercial formulations, yet little is understood about their fundamental interfacial characteristics and quantitative structure/activity relationships are only beginning to emerge for this novel class of surface active materials. This presentation considers adsorption of a variety of star polymers at fluid interfaces, including air/water interfaces and two types of oil/water interfaces, one representing a poor solvent / water interface and the other a good solvent / water interface. Interfacial tension reduction and dynamic dilatational elastic modulus are measured by pendant drop tensiometry methods, and the extent of adsorption is independently determined by ellipsometry. Both large, multi-arm star polymers and smaller star polymers containing 14 polymer arms per star are examined. For the latter, variants are considered where the arms are block copolymers that present nonionic blocks, weakly cationic pH-responsive blocks, and/or zwitterionic blocks. Star polymer morphology and composition have strong effects on interfacial packing and the resulting interfacial tension reduction and dilatational elasticity characteristics. Differences in the latter may correlate with emulsifying and/or foaming effectiveness for different star polymers.