The viscosity-radius relationship for concentrated polymer solutions
The viscosity-radius relationship for concentrated polymer solutions
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DOI：
10.1038/s41598-018-36596-6
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发表时间：
2019-01-24
影响因子：
4.6
通讯作者：
Dunstan, Dave E.
中科院分区：
文献类型：
--
作者：
Dunstan, Dave E.
高分子物理学的一个关键假设是无规链聚合物在流动中延伸。最近的实验证据表明，高分子链压缩库埃特流的方式与预期相反。在这里，缩放参数和文献中的实验证据被用来确定粘度η和链回转半径R-G之间的关系。发现粘度-回转半径关系为η，类似于R-G（m（（gamma）over dot）），其中m（（gamma）over dot）是取决于特定聚合物-溶剂体系和剪切速率的粘度-温度关系的幂律指数，（gamma）over dot。的粘度示出的是一个幂律函数的半径，并随着半径减小的条件下，链是理想的无规行走在浓溶液中。此外，这种关系与聚合物流变学中广泛观察到的粘度-温度和粘度-剪切速率行为一致。延伸的假设与这些观察结果不一致，因为它要求链的尺寸随着温度的升高而增加。因此，剪切稀化是随着剪切速率增加半径减小的结果，如R-G类似于（gamma）/点（-n/m（（gamma）/点）），其中n是幂律指数。此外，热膨胀系数决定了对不同聚合物体系测量的幂律指数的变化。n的典型值使得能够拟合线圈尺寸行为的测量减小。此外，聚合物链延伸以降低粘度的概念意味着增加链尺寸导致粘度降低。该假设将要求粘度随着线圈半径的减小而增加，这是简单地非物理的。
A key assumption of polymer physics is that the random chain polymers extend in flow. Recent experimental evidence has shown that polymer chains compress in Couette flow in a manner counter to expectation. Here, scaling arguments and experimental evidence from the literature are used to determine the relationship between the viscosity, eta, and chain radius of gyration, R-G. The viscosity-radius of gyration relationship is found to be eta similar to R-G(m((gamma)over dot)) where m((gamma)over dot) is the power law exponent of the viscosity-temperature relationship that depends on the specific polymer-solvent system and the shear rate, (gamma)over dot. The viscosity is shown to be a power law function of the radius, and to decrease with decreasing radius under conditions where the chains are ideal random walks in concentrated solution. Furthermore, this relationship is consistent with both the widely observed viscosity-temperature and viscosity-shear rate behavior observed in polymer rheology. The assumption of extension is not consistent with these observations as it would require that the chains increase in size with increasing temperature. Shear thinning is thus a result of a decreasing radius with increasing shear rate as R-G similar to (gamma)over dot(-n/m((gamma)over dot)) where n is the power law exponent. Furthermore, the thermal expansion coefficients determine the variation in the power law exponents that are measured for different polymer systems. Typical values of n enable the measured reduction in coils size behavior to be fitted. Furthermore, the notion that polymer chains extend to reduce the viscosity implies that an increasing chain size results in a reduced viscosity is addressed. This assumption would require that the viscosity increases with reducing coil radius which is simply unphysical.