In Situ Observation of Ca2+ Diffusion-Induced Superstructure Formation of a Rigid Polyanion

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• 作者：Zi Liang Wu ; Riku Takahashi ; Daisuke Sawada ; Md. Arifuzzaman ; Tasuku Nakajima ; Takayuki Kurokawa ; Jian Hu ; Jian Ping Gong
• 刊名：Macromolecules
• 出版年：2014
• 出版时间：October 28, 2014
• 年：2014
• 卷：47
• 期：20
• 页码：7208-7214
• 全文大小：420K
• ISSN：1520-5835

文摘

Diffusion of multivalent metallic ions into aqueous solution of rigid, negatively charged macromolecules of high concentration is an effective approach to prepare macroscopically anisotropic hydrogels. However, the mechanism for superstructure formation is still not clear. By observing the mixing process of a small drop of CaCl₂ solution with solution of a rigid polyanion, poly(2,2鈥?disulfonyl-4,4鈥?benzidine terephthalamide) (PBDT), under the polarizing optical microscope, the diffusion profile of Ca²⁺ and detailed anisotropic gelation process of PBDT are revealed. Diffusion of Ca²⁺ into the surrounding PBDT solution immediately induces the formation of physical liquid crystalline (LC) gel with concentric alignment of PBDT. The thickness d of this region increases with diffusion time t, obeying the diffusion law d 鈭?t^1/2. A thin ring of constant width (鈭?00 渭m) with radial alignment of PBDT appears at the diffusion/reaction front, ahead of the concentric alignment region. When two drops of CaCl₂ fluxes meet, their outside thin rings interact with each other and the PBDT in this contacting region orients 卤45掳 to the midline of the two drops. From these observations, we rationally contend that the internal stress induced by the contraction of gel phase is responsible for the ion diffusion-induced PBDT orientations. This structure formation mechanism gives insight into other diffusion-directed anisotropic gelation systems.