Reactive blending is an efficient method for synthesizing polymer blends. Industrially, this process is carried out in extruders, where the reacting polymers and the generated copolymer are subjected to high shear stresses. The dynamics of the process, and the resulting morphology is dictated by a coupling of the hydrodynamic forces in the extruder, the thermodynamic interactions between species, and the reaction kinetics on a complex interfacial manifold. We use phase-field simulations to quantify the evolution of the reactive blending process under an external shear flow. Specifically, we consider a model system of two homopolymers of equal length, which react via an end-coupling reaction to form a diblock copolymer of double the length. We compare the morphology development in two different initial geometries of the homopolymers—a cylindrical thread and a drop of one homopolymer in a matrix of the second. We investigate the effect of flow strength, measured by the shear rate, and reaction kinetics, quantified by a Damkohler number, on the progress of the reaction and morphology development. Cylindrical threads are susceptible to breakup via the Rayleigh capillary instability. We demonstrate that this instability can be suppressed by imposing shear along the direction of the thread and increasing the extent of the reaction. The reaction rate in this geometry is unaffected by shear imposed along the cylinder axis. Drops deform significantly under an imposed flow, eventually stretching to long cylindrical threads for sufficient shear rates. In the case of drops, shear stresses enhance the reaction rate by deforming the drop, enabling more homopolymers to come in contact at the expanded interface. We show that shear stresses significantly impact the morphology development and reaction dynamics in reactive polymer blending.

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反应性聚合物共混形态发展的相场模拟

反应共混是合成聚合物共混物的有效方法。在工业上，该过程在挤出机中进行，其中反应聚合物和生成的共聚物受到高剪切应力。该过程的动力学以及由此产生的形态由挤出机中的流体动力、物种之间的热力学相互作用以及复杂界面歧管上的反应动力学的耦合决定。我们使用相场模拟来量化外部剪切流下反应混合过程的演变。具体来说，我们考虑了两个等长均聚物的模型系统，它们通过末端偶联反应反应形成双倍长度的二嵌段共聚物。我们比较了均聚物两种不同初始几何形状的形态发展——圆柱形螺纹和一种均聚物在第二种基质中的一滴。我们研究了流动强度（通过剪切速率测量）和反应动力学（通过达姆科勒数量化）对反应进程和形态发展的影响。圆柱形螺纹容易因瑞利毛细管不稳定性而断裂。我们证明，可以通过沿螺纹方向施加剪切力并增加反应程度来抑制这种不稳定性。这种几何结构中的反应速率不受沿圆柱轴施加的剪切力的影响。液滴在施加的流动下显着变形，最终拉伸成长圆柱形线以获得足够的剪切率。在滴的情况下，剪切应力通过使液滴变形来提高反应速率，使更多的均聚物能够在膨胀的界面处接触。我们表明，剪切应力显着影响反应性聚合物共混中的形态发展和反应动力学。