Abstract Temperature dependence of cross-linked poly(N-isopropylacrylamide) (PNIPAAm) gels in particle microgel and macrogel forms with different densities of crosslinking was studied by fluorescence measurements of 8-anilino-1-naphthalene sulfonic acid (ANS) doped into the hydrogels. The experiments for each sample were carried out for some weeks, by making sure that equilibrium was established at each temperature. The fluorescence intensity ratio of ANS at 460 and 540 nm was found to be useful as a measure of the polarity of the environment around ANS molecules in a gel. The results indicate that the environment of PNIPAAm chains in macrogel and microgel forms of different crosslinking densities are the same. Fluorescence depolarization of ANS first clarified that, after volume phase transition, the collapsed state of PNIPAAm gels is unlike a polymer film, but has free spaces where ANS can rotate freely because of the water molecules escaping from the PNIPAAm chains. The information of these free spaces produced by desorption of water molecules would be useful in the processing and utilization of PNIPAAm particle gels.

中文翻译：

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使用荧光探针技术澄清巨凝胶和微凝胶形式的聚（N-异丙基丙烯酰胺）水凝胶的内部微环境

摘要 通过对掺入水凝胶中的 8-苯胺基-1-萘磺酸 (ANS) 进行荧光测量，研究了具有不同交联密度的颗粒微凝胶和大凝胶形式的交联聚（N-异丙基丙烯酰胺）（PNIPAAm）凝胶的温度依赖性。 . 通过确保在每个温度下建立平衡，对每个样品进行了数周的实验。发现 ANS 在 460 和 540 nm 处的荧光强度比可用作凝胶中 ANS 分子周围环境极性的量度。结果表明，不同交联密度的巨凝胶和微凝胶形式的PNIPAAm链的环境是相同的。ANS 的荧光去极化首先阐明，在体积相变之后，PNIPAAm 凝胶的塌陷状态与聚合物薄膜不同，但由于水分子从 PNIPAAm 链中逸出，因此 ANS 可以在其中自由旋转。这些由水分子解吸产生的自由空间的信息将有助于 PNIPAAm 颗粒凝胶的加工和利用。