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We investigate the shear surface rheology of a thermosensitive polymer, PNIPAM (poly(N-isopropylacrylamide)), adsorbed at the air−water interface using an interfacial stress rheometer. This polymer is characterized by a lower critical solution temperature, LCST, of 32 °C; i.e., PNIPAM chains undergo a coil to globule transition as the temperature is increased above the LCST. We measure a spectacular increase in the surface shear elasticity and viscosity of PNIPAM layers as a function of the temperature around the LCST due to an increase in the amount of adsorbed species as the solvent quality decreases for PNIPAM chains. Moreover, the layers undergo a transition from a Newtonian liquidlike state to an elastic state due to an increase in intermolecular entanglements. We also show that the heating protocols have a strong influence on the rheological properties of the layers. In particular, we show that when the solutions are continuously heated from ambient temperature to well above the LCST, PNIPAM chains ...

Spreading at the air−solution interface, of poly(dimethylsiloxane) (PDMS), a widely used ingredient in commercial antifoaming agents, depends strongly on the type of surfactant dissolved in solution. To isolate which polymer−surfactant interactions control the process, we measure surface pressure isotherms for PDMS on a wide variety of surfactant solutions. Moreover, we directly probe the influence of electrostatic forces by addition of a 1:1 electrolyte to the solutions. Although surfactant type, anionic, cationic, or nonionic, and level of charge play only a minor role, the length of the surfactant tail can control the PDMS spreading behavior. For the homologous series of alkyltrimethylammonium bromides, a critical carbon chain length of 14 is found, above which PDMS displays “complete” wetting behavior. However, shorter chain lengths can induce a metastable condition of “pseudopartial” wetting. We utilize both two dimensional polymer scaling concepts and generalized spreading coefficients to rationaliz...