CONFIGURATIONS AND DYNAMICS OF REAL CHAINS .2. INTERNAL VISCOSITY
CONFIGURATIONS AND DYNAMICS OF REAL CHAINS .2. INTERNAL VISCOSITY
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DOI：
10.1021/ma50005a042
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发表时间：
1981-01-01
期刊：
影响因子：
5.5
通讯作者：
GANAZZOLI, F
中科院分区：
文献类型：
--
作者：
ALLEGRA, G;GANAZZOLI, F
张力沿着聚合物链的分子内传递只能通过旋转重排发生，这是内部粘度的起源。这被解释为对沿着链的构型运动传播的阻力，这是由骨架键周围的旋转障碍引起的。弛豫机制通过行波阻尼发生，如在线性力近似内，每个简正模态都有两个不同的弛豫时间。其中较大的一个包含随简正模坐标而增加的内部粘度贡献，这与目前的假设基本一致。该理论还纳入了现实的二次分子内势，与本系列的第一篇论文类似（Allegra, G.; Ganazzoli, F. J. Chem. Phys. 1981, 74, 1310）。通过适当选择键旋转弛豫的特征时间 r0，可以近似再现通过实验发现的聚苯乙烯的复数模量。动态结构因子通常与单一时间指数的偏离甚至比不存在内粘度时更加显着。选择聚合物的实际立体化学结构发挥作用的 Q 范围 (0.1< Q= 4ir sin (0/2)/< 0.4 Á-1) 并忽略流体动力相互作用效应，我们表明，根据为 r0 选择的特定值，近似幂律 t1/2Q'3= 常数通过 d— 3 进行相干散射验证，以及 ß 在 2.4 和~ 3 之间进行非相干散射验证。 （t1/2=半峰时间宽度）。因此，引用的论文中提出的建议，即不需要调用流体动力相互作用来解释在此 Q 范围内接近 3 的 ß 值，这一建议得到了证实。该理论还预测，即使在理想的没有外部摩擦力的情况下，弛豫时间也会出现类似劳斯的谱。此外，与 Fixman 的计算机模拟结果一致，链松弛的初始速率与内粘度无关。
Intramolecular transmission of tensile force along a polymer chain can only occur via rotational rearrangements, which is the origin of internal viscosity. This is interpreted as the resistance to the propagation of configurational motionsalong the chain, caused by the rotational barriers around skeletal bonds. The relaxation mechanism occurs via traveling waves damping off as Within the linear force approximation, each normal mode is characterizedby two distinct relaxation times. The larger of them contains an internal viscosity contribution increasing with the normal mode coordinate, in essential agreement with what is currently assumed. A realistic, quadratic intramolecular potential is also incorporated in the theory, proceeding in analogy with the first paper of this series (Allegra, G.; Ganazzoli, F. J. Chem. Phys. 1981, 74, 1310). With a suitable choice of the characteristic time r0 for bond-rotation relaxation, the complex modulus experimentally found for polystyrene is approximately reproduced. The dynamic structure factor departs in general from a single time exponential even more dramatically than in the absence of internalviscosity. Selecting a Q range where the actual stereochemical structure of the polymer comes into play (0.1< Q= 4ir sin (0/2)/< 0.4 Á-1) and ignoring the hydrodynamic interaction effects, we show that the approximate power law t1/2Q'3= constant is verified with d— 3 for coherent scattering and with ß between 2.4 and~ 3 for incoherent scattering, depending on the particular value chosen for r0 (t1/2= half-peak time width). Hence the suggestion proposed in the quoted paper that hydrodynamic interaction need not be invoked toexplain a value of ß close to 3 in this Q range is confirmed. The theory also predicts a Rouse-like spectrum of the relaxation times even in the ideal absence of external friction forces. Furthermore, in agreement with Fixman’s computer simulation results, the incipient rate of chain relaxation is independent of internal viscosity.