The Effect of Hydrophilic Bentonite Nanoclay on the Thermogelation Properties of Poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) Triblock Copolymer Aqueous Solutions

• Published in: Journal of macromolecular science. Physics 2015-03, Vol.54 (3), p.316-328
• Main Authors: Ioan, Livia, Teodorescu, Mircea, Stǎnescu, Paul O., Drăghici, Constantin, Zaharia, Anamaria, Sârbu, Andrei, Stoleriu, Stefania
• Format: Article
• Language: English
• Subjects: bentonite; block copolymer; composite hydrogel; poly(ethylene glycol); poly(N-isopropylacrylamide); thermosensitivity
• ISSN: 0022-2348; 1525-609X
• DOI: 10.1080/00222348.2015.1010419

The effect of hydrophilic bentonite addition on the thermogelation properties of aqueous solutions of poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) (PNIPAM-PEG-PNIPAM) triblock copolymers of various compositions and molecular weights was investigated. Dynamic rheometry and differential scanning calorimetry (DSC) measurements showed that increasing concentrations of clay added to 20 wt.% polymer aqueous solutions caused a decrease of the temperature at which the viscosity starts increasing, while the temperature corresponding to the maximum endothermic effect due to the PNIPAM chain dehydration remained practically unchanged. The storage modulus, G′, increased with clay concentration for shorter PNIPAM chain triblock copolymers, while an opposite situation occurred in the case of the block copolymer with the longest PNIPAM block. For bentonite concentrations above 1 wt.%, G′ was larger than the viscous modulus, G″, at temperatures higher than the phase separation temperature, indicating a predominantly elastic character of the resulting composite hydrogels. These findings were explained through the presence of polymer-clay interactions occurring mainly through the PEG blocks.