NDLI: Thermal analyses of poly(N-isopropylacrylamide) in aqueous solutions and in nanocomposite gels

Content Provider	Springer Nature Link
Author	Haraguchi, Kazutoshi Xu, Yingjia
Copyright Year	2012
Abstract	The coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPA) prepared by free-radical redox polymerization in aqueous solutions and its nanocomposite (NC) gels were investigated by differential scanning calorimetery. The lower critical solution temperatures (LCST) of aqueous solutions of PNIPA of different molecular weights were not significantly affected by molecular weight (M w: 0.19 × 106−4.29 × 106 g × mol−1) or polymer concentration (1−10 wt%), although the enthalpy of transition increased with molecular weight, at M w (<1.2 × 106 g × mol−1). The glass-transition temperature of PNIPA in the dried state also remained constant (138 °C), regardless of molecular weight. On the other hand, the enthalpy of the coil-to-globule transition of PNIPA in NC gels consisting of a PNIPA/clay network decreased with increasing clay concentration (C clay), while the onset temperature (≡LCST) was almost constant, regardless of C clay. The PNIPA chains in NC gels could be classified into the following three types: P-1, which exhibits a normal LCST transition, similar to that of linear PNIPA; P-2, exhibiting restricted transition at higher temperatures as a result of interactions with the clay; and P-3, which does not undergo that transition because of stronger restrictions. It was found that the proportion of P-3 increases with increasing C clay. However, some P-1 and P-2 was still observed, even in NC gels with high C clay. That the transition to the hydrophobic globular state was restricted by interactions with the clay was confirmed by measurements on PNIPA after removal of the clay from NC gels.
Starting Page	1627
Ending Page	1636
Page Count	10
File Format	PDF
ISSN	0303402X
Journal	Colloid and Polymer Science
Volume Number	290
Issue Number	16
e-ISSN	14351536
Language	English
Publisher	Springer-Verlag
Publisher Date	2012-06-07
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Poly(N-isopropylacrylamide) Coil-to-globule transition Nanocomposite Hydrogel Clay Glass transition Food Science Physical Chemistry Soft and Granular Matter, Complex Fluids and Microfluidics Polymer Sciences Characterization and Evaluation of Materials
Content Type	Text
Resource Type	Article
Subject	Colloid and Surface Chemistry Materials Chemistry Physical and Theoretical Chemistry Polymers and Plastics

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