Thermoresponsive Core Polystyrene-Shell NIPAm Microgels

Abstract

We report the investigation of a colloidal crystal array (CCA) of thermoresponsive colloidal core-shell microgels prepared via the emulsion polymerization method using polystyrene (PS) as a hard core and N,N,-methylene(bisacrylamide) (BIS) as a cross-linker with acrylic acid (AA) as a co-monomer with a soft-shell morphology. In this work, PS/NIPAm colloidal core-shell microgels were prepared and characterized by Atomic Force Microscopy (AFM), particle size analyzer, and reflectance measurements. In situ measurement of reflectance with varying temperatures was carried out from 25° to 45°C using a special setup assembly with a temperature controller attached to the sample stand of the reflectance measurement instrument. PS core and PNIPAm shell morphology was confirmed by AFM analysis. The effect of varying mole of N-isopropylacrylamide (NIPAm) from 2.1 to 8.3 mmol while keeping the shell monomer ratio constant on the reflectance and particle size measurements with respect to temperature was investigated. The particle size increased as the NIPAm molar proportion was increased from 2.1 to 8.3 mmol. As expected, using more NIPAm led to an increase in the particle size and a thicker shell. A general trend was observed in the variation of reflectance wavelength peak decreasing with increase in temperature, allowing these novel CCA of PS/NIPAm microgels to be a potential core-shell microgel candidate for chemical sensor applications and optically tunable materials.