Thermoreversible Changes in Aligned and Cross-Linked Block Copolymer Melts Studied by Two Color Depolarized Light Scattering
Thermoreversible Changes in Aligned and Cross-Linked Block Copolymer Melts Studied by Two Color Depolarized Light Scattering
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通过两种颜色去偏振光散射研究对齐和交联嵌段共聚物熔体的热可逆变化
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发表时间：
2012
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通讯作者：
N. Balsara
中科院分区：
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作者：
Jeffrey D. Wilbur;E. Gomez;M. Ellsworth;B. A. Garetz;N. Balsara
描述了用于创建可以在弱对准状态和强对准状态之间重复循环的样本的过程。聚（苯乙烯-b-异戊二烯）嵌段共聚物样品首先剪切对齐，然后使用高能电子束交联。平均每条链具有超过1.0个交联的样品显示出它们的初始排列状态的几乎完全恢复，即使在高于未交联嵌段共聚物的有序-无序转变温度的20个加热循环之后。每个链具有1.1个交联的样品，其显示在加热时超过90%的对齐损失和在冷却时几乎100%的对齐恢复，提供了可逆的对齐到未对齐转变的最佳实例。具有较低交联密度的样品在加热时表现出不可逆的取向损失，而具有较高交联密度的样品在加热时表现出小于90%的取向损失。通过我们称为双色去偏振光散射（TCDLS）的技术来量化对齐，该技术是用于确定嵌段共聚物中的有序状态的传统去偏振光散射实验的扩展。通过小角X射线散射和透射电子显微镜定性确认了我们对TCDLS数据的解释。
A procedure for creating samples that can be repeatedly cycled between weakly aligned and strongly aligned states is described. Poly(styrene-b-isoprene) block copolymer samples were first shear-aligned and then cross-linked using a high energy electron beam. Samples with more than 1.0 cross-links per chain on average showed almost complete recovery of their initial alignment state even after 20 cycles of heating above the order–disorder transition temperature of the un-cross-linked block copolymer. Samples with 1.1 cross-links per chain, which showed over 90% loss of alignment on heating and almost 100% recovery of alignment on cooling, provided the best example of a reversible aligned-to-unaligned transition. Samples with lower cross-linking densities exhibited irreversible loss of alignment upon heating, while those with higher cross-linking densities exhibited less than 90% loss of alignment upon heating. Alignment was quantified by a technique that we call two color depolarized light scattering (TCDLS), an extension of the traditional depolarized light scattering experiment used to determine the state of order in block copolymers. Qualitative confirmation of our interpretation of TCDLS data was obtained by small-angle X-ray scattering and transmission electron microscopy.