Deuteration-Induced Volume Phase Transition Temperature Shift of PNIPMAM Microgels.

Marian Cors,Lars Wiehemeier,Thomas Hellweg,Julian Oberdisse

doi:10.3390/polym11040620

Abstract

The effect of deuteration on the volume phase transition (VPT) temperature of poly (N-isopropylmethacrylamide) (pNIPMAM) microgels in aqueous suspension is determined via IR spectroscopy and size measurements by photon correlation spectroscopy (PCS). We study the effect of a hydrogenated and a deuterated solvent (H2O/D2O), and of the hydrogenated and (partially) deuterated monomer. Deuteration of the monomer or copolymerization with deuterated monomers shifts the volume phase transition temperature (VPTT) by up to 8.4 K to higher temperatures, in good agreement with known results for pNIPAM microgels. Moreover, the shape of the swelling curve is found to depend on deuteration, with the highest deuteration leading to the sharpest VPT. Finally, the quantitative agreement between FTIR spectroscopy and PCS evidences the spatial homogeneity of the microgel particles. Our results are rationalized in terms of the effect of deuteration on hydrogen bonding. They shall be of primary importance for any experimental measurements close to the VPT involving isotopic substitution, and in particular contrast variation small angle neutron scattering.

Highlights

Acrylamide-based microgels are colloidal gels in the size range of some 10 nm to one micrometer [1].The particle structure consists of a cross-linked polymer network of acrylamides, usually swollen by water
We have recently described the procedure of Fourier transform infrared (FTIR) spectroscopy of microgels in a dedicated article [53]
In this article we present a study of the deuteration-induced changes of the swelling behavior of pNIPMAM-based microgels

Summary

Introduction

The particle structure consists of a cross-linked polymer network of acrylamides, usually swollen by water. These kind of microgels show reversible shrinking and swelling as a function of external stimuli, for example temperature [1,2]. This property makes them suitable in various kinds of applications like drug delivery [3,4,5,6,7], photonic crystals [8] and photonic structures [9], micro and nanoreactors [10,11,12,13], smart surface coatings [14,15], and sensors [16,17].

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