Investigation of morphology and volume phase transition of supramacromolecular microgels by NMR spectroscopy and quartz crystal microbalance

Abstract

Microgels have a wide range of applications, from catalysis to biomedical applications such as drug delivery in dispersion, or as surface‐attached materials to improve the biocompatibility of implants or as anti‐fouling coatings. The first aim of this work is to understand the morphology of the supramacromolecular, tannic acid (TA) crosslinked microgels using two‐dimensional 1H NMR spectroscopy, and relaxometry. The second aim is to study the volume phase transition (VPT) of TA‐crosslinked microgels with different crosslinker densities in dispersion using NMR. In this context, 1H high‐resolution NMR spectroscopy is used in combination with the two‐state model and the Boltzmann sigmoidal function to determine thermodynamic quantities of the VPT, such as temperature (Tt), width of transition (ΔTt), and change in entropy (ΔS). Third, surface‐deposited microgels are characterized in terms of their VPT using a quartz crystal microbalance (QCM‐D) to study the properties of these microgels for applications where they are used as coatings. Finally, the Tt of microgels supramolecular crosslinked with TA are compared with microgels covalently crosslinked with N,N′‐methylenebisacrylamide (BIS) in dispersion, using NMR, and deposited on a surface, using QCM‐D. For this purpose temperature‐responsive poly(N‐vinylcaprolactam) and poly(N‐isopropylacrylamide) microgels crosslinked with the plant‐derived polyphenol TA or BIS are used.