Conformation of End-Tethered PNIPAM Chains in Water and in Acetone by Neutron Reflectivity

Abstract

Poly(N-isopropylacrylamide) is perhaps the most well-known member of the class of temperature responsive polymers. It has a lower critical solution temperature (LCST) in water at about 32 °C. This very sharp transition (∼5 °C) is attributed to alterations in the hydrogen-bonding interactions of the amide group. In this work we investigated the conformation of end-tethered PNIPAM chains at the interface of silicon with D2O and d-acetone using neutron reflection. End-tethered PNIPAM layers were prepared utilizing the interaction between COOH-terminated PNIPAM and OH-terminated self-assembled monolayers (“method A”) and also by polymerizing N-isopropylacrylamide monomers from the silicon surface (“method B”). Reflectivity data from the protonated layers in deuterated water were obtained using a liquid cell over a range of temperature from 10 to 55 °C. For method A, PNIPAM molecular weights of 33K and 220K were examined. In D2O, we observed very limited change in the conformation of the tethered chains as the...