均聚物球的力学解折叠理论：力钳模式下的全有或全无转变与位置钳模式下的相共存
Theory of mechanical unfolding of homopolymer globule: all-or-none transition in force-clamp mode vs phase coexistence in position-clamp mode
摘要：
本文从理论上研究了由柔性均聚物长链在贫溶剂中坍缩形成的小球在拉伸力f（力钳模式）或拉伸变形D（位置钳模式）作用下的平衡机械展开。我们的分析，像所有以前的分析这个问题，表明小球的行为在两种模式的扩展本质上是不同的。在力钳模式中，随着施加的力的增加，发生机械展开的小球没有分子内微相分离，并在一定的阈值的拉力的小球展开作为一个整体（“全或无”过渡）。阈值力的值和链端之间的距离的相应跳跃随着溶剂质量的劣化和/或聚合度的增加而增加。在位置钳模式下，通过球状和扩展微相的分子内微相共存发生球状展开，然后发生突然的解开过渡。在微相分离制度的反作用力表现出一个“异常”的减少与增加扩展。力-夹模式和位置-夹模式的变形曲线比较表明，在弱和强拉伸下，两种模式的曲线重合，在中间拉伸范围内观察到差异。另一种展开的情况是典型的短球：在这两种模式的扩展，他们不断展开，没有跳跃或分子内的微相共存，通过一系列均匀拉长的配置。
英文摘要：
Equilibrium mechanical unfolding of a globule formed by long flexible homopolymer chain collapsed in a poor solvent and subjected to an extensional force f (force-clamp mode) or extensional deformation D (position-clamp mode) is studied theoretically. Our analysis, like all previous analysis of this problem, shows that the globule behaves essentially differently in two modes of extension. In the force-clamp mode, mechanical unfolding of the globule with increasing applied force occurs without intramolecular microphase segregation, and at certain threshold value of the pulling force the globule unfolds as a whole ("all-or-none" transition). The value of the threshold force and the corresponding jump in the distance between the chain ends increase with a deterioration of the solvent quality and/or with an increase in the degree of polymerization. In the position-clamp mode, the globule unfolding occurs via intramolecular microphase coexistence of globular and extended microphases followed by an abrupt unraveling transition. Reaction force in the microphase segregation regime demonstrates an "anomalous" decrease with increasing extension. Comparison of deformation curves in force and position-clamp modes demonstrates that at weak and strong extensions the curves for two modes coincide, differences are observed in the intermediate extension range. Another unfolding scenario is typical for short globules: in both modes of extension they unfold continuously, without jumps or intramolecular microphase coexistence, by passing a sequence of uniformly elongated configurations.
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