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首页> 外文期刊>Journal of Applied Polymer Science >A Framework for Morphological Evolution vis-a-vis Phase Transitions in Polymer Solutions
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A Framework for Morphological Evolution vis-a-vis Phase Transitions in Polymer Solutions

机译：聚合物溶液中相变的形态演化框架

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When a polymer crystallizes from solution,it is well known that the resulting morphology depends on whether any liquid-liquid phase separation (LLPS) has preceded crystallization. In addition to the dense morphology that results when crystallization occurs directly from a homogeneous solution, at least three other distinctly different morphologies are produced if crystallization follows LLPS.Although much work has been reported in this regard, a framework that can relate the path that a process might follow across a phase diagram to the consequent morphology is lacking. We report here the fundamental elements of a simple thermodynamic framework that serves to identify the driving forces that produce these different morphologies. It is based on identification of the nucleating phase, if any, in LLPS and coupling it with the domain in which nucleation of crystallization occurs. The essential elements of the framework for morphological evolution are demonstrated by relating the sequence of phase transitions to the morphology which can result in the crystallized polymer when a polymer solution is cooled from a homogeneous state at a high temperature. Four distinctly different morphologies are shown to evolve,depending on whether crystallization occurs (a) directly from a homogeneous solution (dense); (b) following binodal liquid-liquid phase separation, LLPS, with nucleation of the polymer-rich phase (GMP—globular microporous); (c) following spinodal LLPS (FMP—fibrillar microporous); or (d) following binodal LLPS with nucleation of the solvent-rich phase (CTMP—cell-tunnel microporous). An improtant implication of the framework is that a predictable sequence of "dense -> GMP -> PMP -> CTMP -> dense" morphologies has to arise with increase in overall polymer concentration is such solutions. The framework also serves to identify conditions, such as passage through specific temperature/concentration regions in the phase diagram, that would increase the likelihood of forming mixed or coexisting morphologies. However,it is still necessary to develop appropriate kinetic models to predict sizes of the morphological components within each of the four morphologies.
机译：当聚合物从溶液中结晶时，众所周知，所得的形态取决于是否在结晶之前进行了任何液相-液相分离（LLPS）。除了直接从均质溶液中结晶而产生的致密形态外，如果遵循LLPS进行结晶，还会产生至少三种其他截然不同的形态。尽管在这方面已有许多工作报道，但可以将框架与过程可能会贯穿相图，从而导致缺少形态。我们在这里报告了一个简单的热力学框架的基本元素，该框架可用于识别产生这些不同形态的驱动力。它基于对LLPS中成核相（如果有）的识别，并将其与发生结晶成核的域耦合。通过将相变的顺序与形态相关联来证明形态演化框架的基本要素，当在高温下将聚合物溶液从均质状态冷却时，形态可导致结晶的聚合物。显示出四种明显不同的形态，这取决于是否直接从均质溶液（致密）中发生结晶; （b）在二项式液-液相分离法（LLPS）之后，富聚合物相（GMP-球状微孔）成核; （c）在旋节线的LLPS（FMP-原纤维微孔）之后;或（d）在Binodal LLPS之后，富溶剂相（CTMP-细胞隧道微孔）成核。该框架的重要意义在于，随着此类溶液中总聚合物浓度的增加，必须出现可预测的“致密-> GMP-> PMP-> CTMP->致密”形态。该框架还用于识别条件，例如通过相图中特定的温度/浓度区域，这会增加形成混合或共存形态的可能性。然而，仍然有必要开发适当的动力学模型来预测四种形态中每种形态的形态成分的大小。

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