Thermally Tunable Dynamic and Static Elastic Properties of Hydrogel Due to Volumetric Phase Transition.

Yuqi Jin,Teng Yang,Shuai Ju,Arup Neogi,Tae-Youl Choi,Haifeng Zhang

doi:10.3390/polym12071462

Abstract

The temperature dependence of the mechanical properties of polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) hydrogel was studied from the static and dynamic bulk modulus of the material. The effect of the temperature-induced volumetric phase transition on Young’s Modulus, Poisson’s ratio, and the density of PVA-PNIPAm was experimentally measured and compared with a non-thermo-responsive Alginate hydrogel as a reference. An increase in the temperature from 27.5 to 32 °C results in the conventional temperature-dependent de-swelling of the PVA-PNIPAm hydrogel volume of up to 70% at the lower critical solution temperature (LCST). However, with the increase in temperature, the PVA-PNIPAm hydrogel showed a drastic increase in Young’s Modulus and density of PVA-PNIPAm and a corresponding decrease in the Poisson’s ratio and the static bulk modulus around the LCST temperature. The dynamic bulk modulus of the PVA-PNIPAm hydrogel is highly frequency-dependent before the LCST and highly temperature-sensitive after the LCST. The dynamic elastic properties of the thermo-responsive PVA-PNIPAm hydrogel were compared and observed to be significantly different from the thermally insensitive Alginate hydrogel.

Highlights

Hydrogels were first discovered in 1894 [1] as a cross-linked polymer that swells in water [2].The pH and temperature-sensitive phase transition effect of poly N-iso-propylacrylamide hydrogel were observed due to the hydrophobic bond formation [3]
The first part of the experiments demonstrates the temperature-dependent low strain-rate mechanical tests compared to the static mechanical properties as well as the density changes in the thermally tunable PVA-PNIPAm hydrogel and thermally insensitive Alginate hydrogels
The mechanical properties of temperature-sensitive PVA-PNIPAm hydrogel change rapidly from 28 to 34 ◦ C, which can be used as a trigger in various ultrasonic applications

Summary

Introduction

Hydrogels were first discovered in 1894 [1] as a cross-linked polymer that swells in water [2].The pH and temperature-sensitive phase transition effect of poly N-iso-propylacrylamide hydrogel were observed due to the hydrophobic bond formation [3]. Hydrogels were first discovered in 1894 [1] as a cross-linked polymer that swells in water [2]. Around the 1970s, polyethylene oxide (PEO) drew more attention due to its abundance and higher variations in terms of molecular weight [5]. This led to the study of volumetric phase transition in hydrogel [6] by temperature [7], light [8], ionic strength [9], and pH [10]. PVA-PNIPAm hydrogel has a clear phase transition between 30 and 35 ◦ C, which is called lower critical solution temperature (LCST).

Methods

Results

Conclusion