Glass transition behavior of clay aerogel/poly(vinyl alcohol) composites
Glass transition behavior of clay aerogel/poly(vinyl alcohol) composites
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DOI：
10.1021/ma0611826
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发表时间：
2006-09-19
期刊：
影响因子：
5.5
通讯作者：
Schiraldi, David A.
中科院分区：
文献类型：
--
作者：
Bandi, Suneel;Schiraldi, David A.
在聚合物/粘土纳米复合材料中，分散粘土的尺寸和形态是决定复合材料宏观性能的关键。粘土可以通过冷冻干燥过程转化为气凝胶结构，其密度从2.35 g/cm降低到0.05 g/cm(3)。这些粘土气凝胶的形态类似于纸牌屋的结构。以聚乙烯醇（PVOH）为基体聚合物，制备了低质量分数（0.5 ~ 4 wt %）的粘土和粘土气凝胶复合材料。研究了粘土/ PVOH复合材料的玻璃化转变温度（Tg）行为与粘土和粘土气凝胶在聚合物基体中的粒径、负载和分散性的关系。动态力学分析和差示扫描量热法测量的Tg的趋势是相似的，粘土和粘土气凝胶在1 wt %负载时都达到最大值，然后随着填料含量的增加而下降。虽然趋势是相似的，但在4 wt %的粘土复合材料下，Tg的下降幅度要比相同负载的粘土气凝胶大得多。与中尺度粘土气凝胶相比，纳米级粘土气凝胶具有更好的分散性和与聚合物的界面相互作用，在较低的质量分数下增强了聚合物的结晶度，在较高的质量分数下增加了聚合物的自由体积。Tg的相对变化被认为是两种相互竞争的影响的结果：(i)表面相互作用增强了界面（降低了链迁移率）和（ii）由于聚合物链的体结晶度较低而增加了界面自由体积（增加了链迁移率）。
In polymer/ clay nanocomposites, the size and morphology of the dispersed clay are crucial in determining the macroscopic composite properties. Clay can be converted into an aerogel structure through a freeze- drying process which results in a reduction of its density from 2.35 to 0.05 g/cm(3). The morphology of these clay aerogels resembles a house of cards structure. Low weight fraction ( 0.5- 4 wt %) composites of clay and clay aerogel with a poly( vinyl alcohol) ( PVOH) matrix polymer were prepared. Glass transition temperature ( Tg) behaviors of clay/ PVOH composites were investigated as a function of size, loading, and dispersion of clay and clay aerogel in the polymer matrix. The trends in Tg measured from both dynamic mechanical analysis and differential scanning calorimetry are similar, exhibiting a maximum value at 1 wt % loading for both clay and clay aerogel and then decreasing with additional filler content. Although the trends are similar, the drop in Tg at 4 wt % clay composite is considerably larger than that for a similar loading of clay aerogel. In comparison with the mesoscale clay aerogel, the nanoscale clay shows better dispersion and higher interfacial interaction with the polymer, which enhances polymer crystallinity at lower weight fractions and increases polymer free volumes at higher weight fractions. The relative changes in Tg are proposed to be the result of two competing effects: ( i) surface interaction which strengthens the interface ( decreasing chain mobility) and ( ii) enhanced interfacial free volume due to the lower bulk crystallinity of polymer chains ( increasing chain mobility).