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Equilibrium mechanical unfolding of a globule formed by long flexiblehomopolymer chain collapsed in a poor solvent and subjected to an extensionalforce f (force-clamp mode) or extensional deformation D (position-clamp mode)is studied theoretically. Our analysis, like all previous analysis of thisproblem, shows that the globule behaves essentially differently in two modes ofextension. In the force-clamp mode, mechanical unfolding of the globule withincreasing applied force occurs without intramolecular microphase segregation,and at certain threshold value of the pulling force the globule unfolds as awhole ("all-or-none" transition). The value of the threshold force and thecorresponding jump in the distance between the chain ends increase with adeterioration of the solvent quality and/or with an increase in the degree ofpolymerization. In the position-clamp mode, the globule unfolding occurs viaintramolecular microphase coexistence of globular and extended microphasesfollowed by an abrupt unraveling transition. Reaction force in the microphasesegregation regime demonstrates an "anomalous" decrease with increasingextension. Comparison of deformation curves in force and position-clamp modesdemonstrates that at weak and strong extensions the curves for two modescoincide, differences are observed in the intermediate extension range. Anotherunfolding scenario is typical for short globules: in both modes of extensionthey unfold continuously, without jumps or intramolecular microphasecoexistence, by passing a sequence of uniformly elongated configurations.

Theory of mechanical unfolding of homopolymer globule: all-or-none transition in force-clamp mode vs phase coexistence in position-clamp mode