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Nonlinear responses of carbon black-filled polymer solutions to forced oscillatory shear
Journal of Non-Newtonian Fluid Mechanics ( IF 3.1 ) Pub Date : 2020-05-28 , DOI: 10.1016/j.jnnfm.2020.104319
Wentao Xiong , Xiaorong Wang

Systematic rheometric measurements are carried out to explore the nonlinear responses of carbon black-filled polyisoprene/squalene solutions with the polymer concentrations ϕ in the matrix ranging from the coil overlapping state (ϕ =ϕ*) to the melt state (ϕ =1). At the coil overlapping state, when ϕ <<1, the system typically shows the classic nonlinearity, where the storage modulus G’ decreases as strain amplitude γ0 increases and the resulting stress responses are distorted and deviated from normal sinusoidal waves. At the melting state when ϕ = 1, the system displays a new nonlinearity, where the stress responses to forced oscillatory shear are surprisingly sinusoidal regardless the reduction of G’ as the strain amplitude is increased. Between the two states when ϕ*< ϕ <1, the system exhibits an anomalous and complex nonlinear rheological behavior throughout a wide range of polymer concentrations. The ratio of the third to the first harmonics (I3/I1) in the stress responses first decreases rapidly reaching a minimum when ϕ ≈ 0.1, then increases to a maximum when ϕ ≈ 0.3, after which it decreases again as ϕ approaches the melt state. Lowering the test frequency shifts horizontally the minimum and the maximum in I3/I1 vs ϕ to the right. Increasing strain amplitude intensifies this anomalous behavior. Remarkably, the restoration of broken filler network in the polymer/solvent media also displays the corresponding minimum and maximum values. The quasi-sinusoidal or linear dynamic response in a system that has a strain-dependent modulus is apparently due to the restoration of broken filler network requiring longer than the time scale of a typical dynamic perturbation.



中文翻译:

炭黑填充聚合物溶液对强迫振荡剪切的非线性响应

系统的流变测量进行了探索碳黑填充的聚异戊二烯/角鲨烯与聚合物浓度的溶液的非线性响应φ在基质中,从所述线圈重叠状态(φ  = φ* ),以熔融状态(φ = 1)。在线圈重叠的状态下,当φ  << 1,该系统典型地示出了经典的非线性,其中储能模量G”为应变振幅减小γ 0增加,并且所得到的应激反应被扭曲,并从正常正弦波偏离。在熔融状态时,φ= 1时,系统显示出新的非线性,其中,当应变幅度增大时,无论G'的减小如何,对强迫振荡剪切的应力响应都令人惊讶地呈正弦曲线。当ϕ * < ϕ <1时,在两种状态之间,系统在很宽的聚合物浓度范围内都表现出异常和复杂的非线性流变行为。应力响应中三次谐波与一次谐波的比率(I 3 / I 1)首先迅速下降,当ϕ≈0.1时达到最小值 ,然后在ϕ≈0.3时增大到最大值,此后又随着ϕ减小。接近熔化状态。降低测试频率会在右侧将I 3 / I 1 vs ϕ中的最小值和最大值水平移动。应变幅值的增大会加剧这种异常行为。值得注意的是,聚合物/溶剂介质中破碎的填料网络的恢复也显示出相应的最小值和最大值。具有应变相关模量的系统中的准正弦或线性动态响应显然是由于恢复破碎的填充网络所需的时间比典型动态扰动的时间范围长。

更新日期:2020-05-28
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