Microphase Structure of Poly(N-isopropylacrylamide) Hydrogels As Seen by Small- and Wide-Angle X-ray Scattering and Pulsed Field Gradient NMR

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• 作者：Krisztina Lszl ; Armel Guillermo ; Andrei Fluerasu ; Abdellatif Moussad ; Erik Geissler
• 刊名：Langmuir
• 出版年：2010
• 出版时间：March 16, 2010
• 年：2010
• 卷：26
• 期：6
• 页码：4415-4420
• 全文大小：778K
• 年卷期：v.26,no.6(March 16, 2010)
• ISSN：1520-5827

文摘

Above the lower critical solution temperature T_c (ca. 34 °C), poly(N-isopropylacrylamide) hydrogels become weakly hydrophobic and undergo microphase separation. Macroscopic deswelling, however, is extraordinarily slow, the out-of equilibrium state of the gel being conserved for many days. In this article the structure of the microphase-separated state above T_c is probed by small-angle X-ray scattering and by pulsed field gradient NMR of the protons of water, both in the water phase and in the polymer-rich phase. Above T_c the gel comprises two microphases, separated by smooth interfaces. The cavities occupied by the water phase form a connected network. The diffusion rate of the water molecules in this phase varies from one cavity to another and can be described by a Gaussian distribution. Water molecules belonging to the polymer-rich phase are also mobile, but their self-diffusion coefficient D is greatly diminished. Absence of compartmentalization of the water phase implies that the slow deswelling rate of the gel is not due to trapping of the water phase.