One of the most intriguing properties of rod-like polymers is the ability to form a nematic phase. Among a broad variety of external stimuli to promote the isotropic (I)-nematic (N) transition, a shear-induced nematic phase represents one of the most fascinating phenomena in polymer physics. Here, after reviewing some relevant findings on quiescent and shear-induced nematics, we present the novel shear-induced isotropic-nematic transition exhibited by poly(ether ether ketone) (PEEK) melts of various chain lengths. The key factor is the significant rigidity of the PEEK chain that makes it a rod-like polymer. The molecular weight (M_w) dependence of the zero-shear viscosity (${\eta }_0$) of PEEK in the isotropic phase, follows the Doi-Edwards theoretical prediction for rod-like polymers in the entangled regime; ${\eta }_0\sim M_w^6$. The shear-induced I-N transition manifests in the apparent shear viscosity dependence on the shear rate (flow curves) with three regimes: I) an isotropic response with no measurable birefringence at low shear rates, II) an I-N transition with an isotropic-nematic biphase, two steady state values of apparent viscosity and mild birefringence at intermediate shear rates, and III) a continuous nematic phase with strong birefringence at high shear rates with $\eta \sim {\dot{\gamma }}^{-1/2}$. Additionally, the observed threshold shear rates for regimes II and III for the four PEEK samples were used to construct a dynamic phase diagram of PEEK at 370°C, revealing that such a transition is stress-controlled.

棒状聚合物最吸引人的特性之一是能够形成向列相。在促进各向同性（I）向列（N）过渡的各种外部刺激中，剪切诱导的向列相代表了聚合物物理学中最引人入胜的现象之一。在这里，在回顾了有关静态和剪切诱导的向列相的一些相关发现之后，我们提出了各种链长的聚醚醚酮（PEEK）熔体表现出的新型剪切诱导的各向同性-向列相变。关键因素是PEEK链的坚固性，使其成为棒状聚合物。分子量（中号_瓦特）的零剪切粘度的依赖性（${\eta }_0$）在各向同性相中的PEEK遵循Doi-Edwards对缠结态棒状聚合物的理论预测; ${\eta }_0〜{\mathrm{中号}}_w^6$。剪切诱导的IN转变表现为表观剪切粘度取决于剪切速率（流动曲线）的三种状态：I）在低剪切速率下无可测双折射的各向同性响应； II）各向同性向列双相的IN转变，在中等剪切速率下具有表观粘度和中等双折射的两个稳态值，以及III）在高剪切速率下具有强双折射的连续向列相$\eta 〜{\dot{\gamma }}^{-\mathrm{1个}/2}$。此外，使用观察到的四个PEEK样品的II和III阈值阈值剪切速率来构建370°C下PEEK的动态相图，表明这种转变是受应力控制的。