Linear viscoelasticity of disordered polystyrene-polyisoprene block copolymer based layered-silicate nanocomposites
Linear viscoelasticity of disordered polystyrene-polyisoprene block copolymer based layered-silicate nanocomposites
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DOI：
10.1021/ma992091u
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发表时间：
2000-05-16
期刊：
影响因子：
5.5
通讯作者：
Krishnamoorti, R
中科院分区：
文献类型：
--
作者：
Ren, JX;Silva, AS;Krishnamoorti, R
研究了一系列插层纳米复合材料的熔融态线性粘弹性能。该纳米复合材料基于短无序聚苯乙烯-聚异戊二烯二嵌段共聚物和不同量的二甲基双十八烷基铵改性蒙脱土。线性动态振荡模量和应力松弛模量在定量上一致，并且表明在短时间内纳米复合材料的松弛基本上不受层状硅酸盐的存在的影响。然而，在长时间（或相当低的频率）下，混合体表现出显着改变的粘弹性行为。硅酸盐负载量超过 6.7 wt% 的杂化物表现出类伪固体行为，类似于之前剥离的末端束缚纳米复合材料研究中观察到的情况。根据简单的现象学论证，长时间行为归因于随机取向的各向异性硅酸盐片堆叠的存在，并形成无法完全松弛的渗透网络结构。这些论点得到了大振幅振荡剪切定向这些纳米复合材料并增加其液体特性的能力的进一步支持。
The melt-state linear viscoelastic properties for a series of intercalated nanocomposites are examined. The nanocomposites are based on a short disordered polystyrene-polyisoprene diblock copolymer and varying amounts of dimethyldioctadecylammonium modified montmorillonite. The linear dynamic oscillatory moduli and the stress relaxation moduli are in quantitative agreement and suggest that at short times the relaxation of the nanocomposites is essentially unaffected by the presence of the layered-silicate. However, at long times (or equivalently low frequency), the hybrids exhibit dramatically altered viscoelastic behavior. Hybrids with silicate loadings in excess of 6.7 wt % exhibit pseudo-solidlike behavior, similar to that observed in previous studies of exfoliated end-tethered nanocomposites. On the basis of simple phenomenological arguments, the long time behavior is attributed to the presence of anisotropic stacks of silicate sheets randomly oriented and forming a percolated network structure that is incapable of relaxing completely. These arguments are further supported by the ability of large-amplitude oscillatory shear to orient these nanocomposites and to increase their liquidlike character.