A Neutron Reflectivity Study of Poly(N-isopropylacrylamide) at the Air−Water Interface with and without Sodium Dodecyl Sulfate

The properties of poly(N-isopropylacrylamide) (polyNIPAM) at the air/water interface, with and without sodium dodecyl sulfate (SDS), were measured by neutron reflectivity and surface tension. Below the lower critical solution temperature (LCST), polyNIPAM adsorbs at the air/water interface to give a thin (δ ∼ 1.5 nm) layer with a low water content approximately equal to phase-separated polyNIPAM above the LCST. Above the LCST the adsorbed polymer layer increases by a factor of 10 approximately equal to the effective diameter of a single phase-separated polymer chain (a globule). Polymer-bound SDS lowers the density of adsorbed polyNIPAM because of electrostatic effects.