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首页> 外文期刊>Journal of Applied Polymer Science >Thermal Transitions of Poly(vinyl alcohol) Hydrogel Sensed by a Fluorescent Probe
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Thermal Transitions of Poly(vinyl alcohol) Hydrogel Sensed by a Fluorescent Probe

机译：荧光探针感测的聚乙烯醇水凝胶的热转变

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Fluorescence from the fluorescein molecule has been used to study of phase transition processes in five poly(vinyl alcohol)(PVA) hydrogels in the temperature range 75-350 K. These hydrogels were prepared with PVA with molecular weight = 124,000-186,000, 99+% hydrolyzed, by repeated freezing-thawing cycles in five compositions: 9.9, 11.1, 13.3, 16.5 and 20.9 PVA w/w %. Plots of total fluorescence intensity versus temperature, normalized with the fluorescence signal at 75 K, and of the emission wavelength maximum versus temperature indicated that the dynamic of the guest deactivation was dependent on the hydrogel thermal transitions. These thermal transition processes were compared to three model systems: uranine (fluorescein di-sodium salt) in water, fluorescein in water/ethanol (85%/15% v/v), and fluorescein/PVA homopolymer, Small spectral shifts were obtained for these model systems over the entire temperature range attributed to the hot hand effect. Nevertheless, larger spectral shifts were obtained for hydrogels, indicating that shifts of the chemical dissociation equilibrium was occurring in this last case. Slope changes of both intensity and wavelength maximum plots versus temperature occurred at the same temperature values, and we attributed the onset of of hydrogel thermal transition as the sol-gel transition occurring at T≌ 370 K; at 320 K we observed the glass transition temperature of PVA plasticized by water molecules; at T ≌ 240 ± 5 K we attributed the melting point of water molecules bonded to the PVA chains (freezable bond molecules); at T ≌ 270 ± 5 K we observed the melting point of free water molecules (bulk water and, at 135-145 K the water glass transition.
机译：来自荧光素分子的荧光已用于研究温度范围为75-350 K的五种聚乙烯醇（PVA）水凝胶中的相变过程。这些水凝胶由分子量为124,000-186,000、99 +的PVA制备通过重复冷冻-融化循环，在5种组合物中水解9.9％，11.1、13.3、16.5和20.9PVA w / w％。总荧光强度与温度的关系图，已用75 K的荧光信号进行了归一化，最大发射波长与温度的关系图表明，客体失活的动力学取决于水凝胶的热转变。将这些热转变过程与三种模型系统进行了比较：水中的尿素（荧光素二钠盐），水/乙醇中的荧光素（85％/ 15％v / v）和荧光素/ PVA均聚物，获得了较小的光谱位移这些模型系统在整个温度范围内归因于热手效应。然而，对于水凝胶，获得了较大的光谱位移，这表明在最后一种情况下发生了化学离解平衡的位移。在相同的温度值下，强度和波长最大值图的斜率变化均发生在温度下，我们将水凝胶热转变的发生归因于溶胶-凝胶转变发生在T≌370 K处。在320 K下，我们观察到水分子增塑的PVA的玻璃化转变温度。在T≌240±5 K时，我们将键合到PVA链上的水分子（可冻结键分子）的熔点归因于此;在T≌270±5 K时，我们观察到游离水分子（散装水的熔点，在135-145 K时，水玻璃化转变温度）。

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