Cho Sangwon, Seo Youngwook P, Seo Yongsok
RIAM, Department of Materials Science and Engineering, College of Engineering, Seoul National University, Kwanakro 1, Kwanakku, Seoul 08826, Korea.
ACS Omega. 2022 Jan 18;7(4):3341-3347. doi: 10.1021/acsomega.1c05497. eCollection 2022 Feb 1.
In this work, we investigated the effect of a change in the molecular structure and ensuing molar mass change of a matrix polymer (polyamide 6, Ny 6) on droplet deformation of a dispersed thermotropic liquid crystalline polymer (TLCP, a poly(ester amide)) in shear flow. This study focuses on a total capillary number (the sum of the shear capillary number and the elasticity capillary number) and the viscosity ratio between the TLCP and Ny 6, for the morphological development and mechanical performance of TLCP/Ny 6 blends. In contrast to Ny 6, which has a lower melt viscosity than the TLCP melt, a modified Ny 6 (m-Ny 6) with . 2 orders higher melt viscosity than that of Ny 6 at a shear rate of 1 s was found to facilitate the deformation of the TLCP phase. A total capillary number was defined to characterize the viscoelasticity effect on droplet deformation in the blend system. The first normal stress difference obtained from the viscosity curve using Steller's method was used for the evaluation of the elasticity capillary number. The total capillary number for the Ny 6 blend was far less than the critical capillary number and was insufficient for the dispersed TLCP droplets to be deformed. The shear capillary number of the m-Ny 6 blend was greater than the critical capillary number but was still insufficient for droplet deformation into fibril shapes. The total capillary number, including the elastic capillary number, was sufficiently greater than the critical capillary number for deformation of the dispersed TLCP droplets. Morphological observations and a comparison with the theoretical work confirmed the importance of the viscoelasticity of the melt in the immiscible Ny 6/TLCP blends for composite fabrication in shear flow. Both the high viscosity and the first normal stress difference of m-Ny 6 promote the deformation and fibrillation of the dispersed TLCP droplets.
在本研究中，我们探究了基体聚合物（聚酰胺6，Ny 6）的分子结构变化及随之而来的摩尔质量变化对分散的热致液晶聚合物（TLCP，一种聚（酯酰胺））在剪切流中液滴变形的影响。本研究聚焦于总毛细管数（剪切毛细管数与弹性毛细管数之和）以及TLCP与Ny 6之间的粘度比，以研究TLCP/Ny 6共混物的形态发展和力学性能。与熔体粘度低于TLCP熔体的Ny 6不同，发现在剪切速率为1 s时，熔体粘度比Ny 6高2个数量级的改性Ny 6（m-Ny 6）有利于TLCP相的变形。定义了一个总毛细管数来表征共混体系中粘弹性对液滴变形的影响。使用斯特勒方法从粘度曲线获得的第一法向应力差用于评估弹性毛细管数。Ny 6共混物的总毛细管数远小于临界毛细管数，不足以使分散的TLCP液滴变形。m-Ny 6共混物的剪切毛细管数大于临界毛细管数，但仍不足以使液滴变形为原纤形状。包括弹性毛细管数在内的总毛细管数足够大于临界毛细管数，以使分散的TLCP液滴变形。形态观察以及与理论工作的比较证实了熔体的粘弹性在不相容的Ny 6/TLCP共混物用于剪切流复合制造中的重要性。m-Ny 6的高粘度和第一法向应力差都促进了分散的TLCP液滴的变形和原纤化。
