Rheological properties of acetoxypropylcellulose in the thermotropic chiral nematic phase
Rheological properties of acetoxypropylcellulose in the thermotropic chiral nematic phase
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DOI：
10.1080/10587259508033502
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发表时间：
1995-01-01
影响因子：
--
通讯作者：
Navard, P
中科院分区：
文献类型：
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作者：
Cidade, MT;Leal, CR;Navard, P
在Martins(1)最近提出的LC聚合物连续介质理论框架下，对两种不同分子量的乙酰氧基丙基纤维素（APC）热致液晶（LC）样品在120℃、剪切速率在0.01 ~ 10 s（-1）之间的流变行为进行了实验数据分析。黏度eta（gamma over dot）在研究的剪切速率gamma over dot范围内显示出强烈的剪切变薄，在剪切速率约为0.1-0.2 s（-1）时具有犹豫，这取决于分子量，而第一正应力差N-1（gamma over dot）仅显示正值，随着剪切速率gamma over dot而增加，在剪切速率更高的数量级时具有犹豫，即约1- 2,2 s(-1)，也取决于分子量。随着分子量的增加，流动函数的犹豫点向较低的剪切速率偏移。对于小和中等的伽马过点，高分子量样品的剪切粘度大于低分子量样品的相应粘度，但在高伽马过点时，这种模式是相反的，交叉点在伽马近似为1.5 s（-1）。第一个正常应力差的分子量依赖性遵循类似的模式。所有这些观察都可以用马丁斯的理论来解释。由该理论导出的eta（γ / dot）和N-1（γ / dot）的表达式与实验数据非常吻合，因此可以估计一些基本的粘弹性参数。
Experimental data for the rheological behavior of two thermotropic liquid crystalline (LC) samples of acetoxypropylcellulose (APC) with different molecular weights, at 120 degrees C, and in shear rates between 0.01 and 10 s(-1), are presented and analyzed in the framework of the continuum theory for LC polymers recently proposed by Martins(1). The viscosity eta(gamma over dot) shows a strong shear thinning in the range of shear rates gamma over dot studied, with an hesitation at shear rates of about 0.1-0.2 s(-1), depending on the molecular weight, and the first normal stress difference N-1(gamma over dot) shows only positive values, increasing with shear rate gamma over dot, with an hesitation at shear rates of an order of magnitude higher, i.e. about 1-2, s(-1), also depending on the molecular weight. The hesitation points of the flow functions are displaced towards lower values of the shear rate, with increasing molecular weight. For small and intermediate gamma over dot the shear viscosity of the higher molecular weight sample is greater than the corresponding viscosity for the lower molecular weight sample, but this pattern is reversed at higher gamma over dot, the crossover point being at gamma approximate to 1.5 s(-1). The molecular weight dependence of the first normal stress difference follows a similar pattern. All these observations can be interpreted by Martins' theory. The expressions for eta(gamma over dot) and N-1(gamma over dot) derived from this theory fit very well to the experimental data, therefore allowing for some fundamental viscoelastic parameters to be estimated.