Transverse cylindrical microdomain orientation in an LC diblock copolymer under oscillatory shear
Transverse cylindrical microdomain orientation in an LC diblock copolymer under oscillatory shear
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DOI：
10.1021/ma991155y
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发表时间：
1999-11-02
期刊：
影响因子：
5.5
通讯作者：
Thomas, EL
中科院分区：
文献类型：
--
作者：
Osuji, C;Zhang, YM;Thomas, EL
许多研究人员已经研究了通过剪切层状和圆柱形微区嵌段共聚物的定向微区形态的发展，并且发现观察到的取向取决于诸如温度（特别是接近ODT）、应变振幅、应变速率、机械对比度、链结构和分子量等变量。1-10这方面的工作有很好的评论。图11，12对于层流和圆柱体，三种不同的取向是可能的，即平行、垂直和横向，在每种情况下，通过圆柱体长轴和层流重复矢量相对于流动和流动梯度方向的取向来区分。已发现层状系统的加工条件导致所有三种类型的取向以及混合取向。[11]在经受稳定和振荡剪切的圆柱形微区形成螺旋-螺旋嵌段共聚物中，平行取向，其中圆柱体长轴沿着流动方向对齐，是迄今为止观察到的压倒性取向，[3，5，9]，唯一的例外是Gronski等人，他们发现了LC二嵌段共聚物垂直取向的圆柱体，这是由于LC介晶的氰基端基与振荡剪切池的玻璃表面的强垂面锚定。10在这里，我们报告了横向圆柱体取向的选择，圆柱体长轴沿着涡度方向对齐，通过液晶（LC）二嵌段共聚物在LC范围内经受大幅度振荡剪切，以及随后在LC相的热清除后快速转变为平行圆柱体取向。研究的材料是80 000 g/mol苯乙烯、介晶官能化异戊二烯二嵌段共聚物，表示为P（S-b-ILC）27/53，含有27 000 g/mol的聚苯乙烯嵌段和53 000 g/mol的聚异戊二烯-LC嵌段。PS的体积分数为0.34，导致在本体中形成六边形填充的圆柱体。异戊二烯嵌段使用聚合物类似化学改性，如在其他地方详述的13，以产生偶氮苯侧基液晶二嵌段共聚物，如图1中示意性描绘的。我们还研究了PI-LC均聚物（MW）78 000）。两种材料均形成层间距为31 μ m且介晶间距为4-5 μ m的近晶A LC介晶相。PI-
The development of oriented microdomain morphologies by shearing lamellar and cylindrical microdomain block copolymers has been studied by many researchers, and observed orientations were found to depend on such variables as temperature (in particular proximity to ODT), strain amplitude, strain rate, mechanical contrast, chain architecture, and molecular weight. 1-10 Good reviews of work in this area are available. 11, 12 For lamellae and for cylinders, three distinct orientations are possible, viz. parallel, perpendicular, and transverse, discriminated by the orientation of the cylinder long axes and lamellar repeat vector with respect to the flow and flow gradient directions in each case. Processing conditions of lamellar systems have been found that lead to all three types of orientation as well as mixed orientations. 11In cylindrical microdomain forming coil-coil block copolymers subjected to steady and oscillatory shear, parallel orientation, in which the cylinder long axes are aligned along the flow direction, is the overwhelming orientation observed to date, 3, 5, 9 with the sole exception of Gronski et al., who found cylinders in the perpendicular orientation for an LC diblock copolymer due to strong homeotropic anchoring of the cyano end groups of the LC mesogens to the glass surfaces of the oscillatory shear cell. 10 Here, we report on the selection of the transverse cylinder orientation, with cylinder long axes aligned along the vorticity direction, by a liquid crystalline (LC) diblock copolymer subjected to large amplitude oscillatory shear within the LC regime, and a subsequent rapid transition to the parallel cylinder orientation upon the thermal clearing of the LC phase. The material investigated is an 80 000 g/mol styrene, mesogen-functionalized isoprene diblock copolymer, denoted P (S-b-ILC) 27/53, containing a polystyrene block of 27 000 g/mol and a polyisoprene-LC block of 53 000 g/mol. The volume fraction of PS is 0.34, leading to the formation of hexagonally packed cylinders in the bulk. The isoprene block was modified using polymer analogous chemistry as detailed elsewhere13 to produce an azobenzene side-group liquid crystal diblock copolymer, depicted schematically in Figure 1. We also studied the PI-LC homopolymer (MW) 78 000). Both materials formed smectic A LC mesophases with a layer spacing of 31 Å and intermesogen distance of 4-5 Å. The PI-