Kinetics and Energetics of Solute Segregation in Granular Block Copolymer Microstructures
Kinetics and Energetics of Solute Segregation in Granular Block Copolymer Microstructures
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DOI：
10.1021/acs.macromol.8b02044
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发表时间：
2018-12-25
期刊：
影响因子：
5.5
通讯作者：
Bockstaller, Michael R.
中科院分区：
文献类型：
--
作者：
Lee, Bongjoon;Bleuel, Markus;Bockstaller, Michael R.
结合电子成像和晶粒映射以及超小和小角度中子散射，分析了层状聚（苯乙烯-b-异戊二烯）共聚物晶界区域内氘化聚苯乙烯（d-PS）的偏析动力学。溶质偏析仅限于大角度晶界（即，取向差超过阈值的晶粒之间的边界）。发现 d-PS 的积累在高角度边界上是均匀的，在边界区域内达到约 52 vol% 的溶质平衡局部浓度。这被解释为 d-PS 分离的结果，使得边界区域中受扰动的链构象得以松弛，从而减少了存储在高角度边界中的弹性应变能。使用连续层变形模型估算弹性应变能，并将其与通过分析晶界三联结处的二面角确定的实验（相对）边界张力进行比较。麦克莱恩型界面吸附模型被证明可以定量捕获边界区域内溶质积累的动力学和程度。该模型表明，偏析速率对溶质的迁移率敏感，而大角度晶界内溶质的极限浓度则由晶界缺陷的能量决定。这些结果为解释嵌段共聚物共混体系中的结构粗化过程提供了基础，与原始的嵌段共聚物类似物相比，通常发现嵌段共聚物共混体系会产生更多颗粒状的微观结构（具有更小的晶粒尺寸），并为缺陷的策略性修饰工艺的开发提供信息，从而使基于嵌段共聚物的材料具有新的功能。
The segregation kinetics of deuterated polystyrene (d-PS) within the grain boundary regions of a lamellar poly(styrene-b-isoprene) copolymer is analyzed using a combination of electron imaging and grain mapping as well as ultrasmall and small-angle neutron scattering. Solute segregation is limited to high-angle grain boundaries (that is, boundaries between grains having misorientations that exceed a threshold value). The accumulation of d-PS is found to be uniform across high-angle boundaries, reaching an equilibrium local concentration of solute within the boundary regions of about 52 vol %. This is interpreted as a consequence of d-PS segregation enabling the relaxation of perturbed chain conformations in the boundary regions, thus reducing the elastic strain energy that is stored in high-angle boundaries. The elastic strain energy is estimated using a continuum layer deformation model and compared to the experimental (relative) boundary tension that is determined by analysis of dihedral angles at grain boundary triple junctions. A McLean-type interface adsorption model is demonstrated to quantitatively capture both the kinetics and the extent of solute accumulation within boundary regions. The model reveals that the rate of segregation is sensitive to the mobility of the solute while the limiting concentration of solute within high-angle boundaries is determined by the energy of grain boundary defects. The results provide a basis for the interpretation of structure coarsening processes in block copolymer blend systems that are often found to result in more granular microstructures (featuring smaller grain sizes) as compared to the pristine block copolymer analogues and inform the development of processes for the strategic decoration of defects to enable new functionalities in block copolymer-based materials.