Swelling behaviour of PNIPAM-polyisoprene core-shell microgels at surface

Abstract

Poly(N-isopropylacrylamide) (PNIPAM)-based microgels covered with hydrophobic but water-permeable shell were used for modification of a hydrophilic substrate with the aim to provide a ‘contraphilic’ wetting behaviour, namely, to make the surface more hydrophobic in water environment (polar medium) than in dry state in air (non-polar medium). Bottom-up approach has been applied for a stepwise preparation of a structured two-component surface. Loosely packed microgels self-organised into quasiperiodic arrays were chemically grafted to the hydrophilic, functionalised substrate. Afterwards, a surface-initiated polymerisation of isoprene was performed selectively from microgels making them hydrophobic. The surface was found to be water-sensitive, as observed by in situ AFM measurements. The surface fraction of the hydrophobic component increased from 13% in the dry state up to 25% in water due to swelling of the microgels. However, small contraphilic effect was recorded by water contact angle measurements because of a moderate lateral swelling of the core-shell microgels and due to a fast swelling of the microgels already upon the measurements.