In this work, we apply lubricated squeezing to perform planar extension of styrene-butadiene rubbers (SBRs) and illustrate how large step-strained SBR undergo chain relaxation. When the imposed step strain is moderate or the stepwise planar extension is imposed sufficiently slowly, the stress relaxation is spatially uniform. Upon a large stepwise extension imposed over a period much shorter than the overall chain relaxation time, the strained SBR undergo spatially inhomogeneous molecular relaxation, plausibly due to localized chain disentanglement that results from the molecular force imbalance. As a manifestation of localized elastic yielding, the SBR specimen appears wrinkled upon unloading in the middle of stress relaxation. In situ birefringence measurements confirm that uneven chain relaxation is ongoing during stress relaxation that involves keeping the sample height H fixed after squeezing from the initial height H0 to H. Thus, localized chain relaxation is shown to take place even in the presence of geometrical constraint, i.e., the absence of any free surface or meniscus. In comparison, homogenous stepwise deformation was found to result in nonquiescent relaxation for simple shear and filament breakup for uniaxial melt stretching.

中文翻译：

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在没有自由表面的情况下，由逐步平面延伸引起的缠结聚合物熔体的非均匀链松弛

在这项工作中，我们应用润滑挤压来执行丁苯橡胶 (SBR) 的平面拉伸，并说明大阶跃应变的 SBR 如何进行链松弛。当施加的阶梯应变适中或施加足够缓慢的阶梯平面延伸时，应力松弛在空间上是均匀的。在比总链弛豫时间短得多的时间内进行大的逐步延伸后，应变的 SBR 经历空间不均匀的分子弛豫，这可能是由于分子力不平衡导致的局部链解缠结。作为局部弹性屈服的一种表现，SBR 试样在应力松弛过程中卸载时出现皱纹。原位双折射测量证实在应力松弛期间不均匀的链松弛正在进行，这涉及在从初始高度 H0 挤压到 H 后保持样品高度 H 固定。因此，即使存在几何约束，局部链松弛也会发生，即，没有任何自由表面或弯液面。相比之下，发现均匀的逐步变形会导致单轴熔融拉伸的简单剪切和长丝断裂的非静态松弛。