Following a previous work investigating the flow-induced crystallization (FIC) of polybutylene terephthalate/polytetrahydrofuran (PBT/PTHF) multiblock copolymers under steady shear, we propose here to deal with the case of large amplitude oscillatory shear (LAOS). For this purpose, we focus on a single copolymer ($\overline{M_w}=50\mathrm{kg}\mathrm{mo}{\mathrm{l}}^{-1}$) made, in average, of a sequence of nine soft and eight hard segments. We show unambiguously that LAOS accelerates the polymer crystallization when increasing (i) the frequency from 0.5 up to 50 rad s⁻¹ (at a constant strain amplitude of 100%) or (ii) the strain amplitude from 10 to 300% (at a constant frequency of 2.5 rad s⁻¹). Based on this data, we demonstrate that high oscillatory shear rates have similar effects as the steady shear rate regarding the gelation time, i.e., that frequency- and strain amplitude-related effects are secondary. We carefully analyze the stress response through Fourier-transform decomposition that emphasizes the rich rheological behavior of our material during its liquid-to-solid phase transition. With the help of x-ray scattering experiments (ex situ SAXS and WAXS), we then propose a global scenario rationalizing the whole set of rheological observations based on the copolymer structure. In parallel, we propose to use a recent model that we developed to simulate the stress response in the case of steady shear-promoted FIC and adapt it to the case of LAOS. Remarkably, our model, which is based on modified Doi–Edwards equations only, provides good qualitative agreement with the data when varying the strain amplitude or the frequency. Furthermore, it is found to predict quantitatively the gelation time of the system.

中文翻译：

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大振幅振荡剪切下多嵌段共聚物的流致结晶：实验与模型

在先前的研究中，在稳态剪切作用下研究了聚对苯二甲酸丁二醇酯/聚四氢呋喃（PBT / PTHF）多嵌段共聚物的流动诱导结晶（FIC），我们在此提出了应对大振幅振荡剪切（LAOS）的方法。为此，我们专注于单一共聚物（$\overline{{\mathrm{中号}}_w}=50\mathrm{公斤}\mathrm{莫}{\mathrm{升}}^{-\mathrm{1个}}$）平均由9个软分段和8个硬分段组成。我们清楚地表明，当（i）频率从0.5增加到50 rad s ^-1（在100％的恒定应变幅度下）或（ii）应变幅度从10到300％（在a不变时）时，LAOS会加速聚合物的结晶。 2.5 rad s ^-1的恒定频率）。基于此数据，我们证明，关于胶凝时间，高振荡剪切速率与稳定剪切速率具有相似的效果，即，与频率和应变幅度相关的影响是次要的。我们通过傅里叶变换分解仔细分析应力响应，该分解强调了我们的材料从液相到固相转变过程中丰富的流变行为。借助X射线散射实验（易地SAXS和WAXS），然后我们提出了一个全球性的情况下理顺一整套基于共聚物结构的流变意见。同时，我们建议使用我们开发的最新模型来模拟稳定剪切促进的FIC情况下的应力响应，并将其适应于LAOS的情况。值得注意的是，我们的模型仅基于修正的Doi–Edwards方程，在改变应变幅度或频率时，与数据具有良好的定性一致性。此外，发现定量地预测系统的胶凝时间。