Deuteration-Induced Volume Phase Transition Temperature Shift of PNIPMAM Microgels

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.

Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications

“…Contrast matching through the solvent and employing isotopic substitution of either shell or core monomers enables studying the monomers selectively in SANS, and thereby gives access to independent measurements of their monomer density profiles. One should note that deuteration causes small differences in swelling, as published by us for p(NIPMAM) [60], but its impact remains negligible far from the VPTT. We add that although small-angle scattering is not the only technique to observe microgels [78][79][80], it is indeed very powerful due to the possibilities of deuteration allowing differentiating core and shell polymer, in bulk suspensions, without fluorescence labelling.…”

“…Berndt et al synthesized the shell with p(NIPAM) and its VPTT of ca. 33°C [60,90,91,93,94]; thus, the linear region is larger in our case, extending from ca. 20 to 45°C.…”

“…These experiments have been set up to verify the spatial structure of the core embedded in a shell. We have based these measurements on the NIPMAM core monomer used by Berndt et al (VPTT ≈ 45°C) [18,60,83,[90][91][92], but have taken NNPAM monomer (VPTT ≈ Fig. 3 a Shell model of average microgel particle indicating moves of groups of monomers between shells.…”

“…Reprinted with permission from reference [59]. Copyright 2018 American Chemical Society 23°C) [60] for the shell synthesis, thereby generating the linear swelling. Berndt et al synthesized the shell with p(NIPAM) and its VPTT of ca.…”

Injectable Hydrogels: A Review of Injectability Mechanisms and Biomedical Applications

“…Above the volume phase transition temperature (VPTT), the nanogel aggregates and surrounds cells in a 3D manner, mimicking the native microenvironment[57]. The VPTT is a specific temperature at which thermo-sensitive polymers experience a drastic change in their degree of swelling (or de-swelling), resulting in change in the size of microgels and nanogels[58]. Oppositely-charged PLGA-based nanoparticles were prepared by coating the particles with either polyvinylamine or poly(ethylene-co-maleic acid) to induce positive or negative charges, respectively.…”