Mechanical unfolding of a homopolymer globule: applied force vs applied   deformation
  We propose the quantitative mean-field theory of mechanical unfolding of a globule formed by long flexible homopolymer chain collapsed in poor solvent and subjected to an extensional force We show that with an increase in the applied force the globule unfolds as a whole without formation of an intermediate state. The value of the threshold force and the corresponding jump in the distance between chain ends increase with a deterioration of the solvent quality and / or with an increase in the degree of polymerization. This way of globule unfolding is compared with that in the D-ensemble, when the distance between chain ends is imposed. 
Alexey A. Polotsky, Elizaveta E. Smolyakova, Oleg V. Borisov, and   Tatiana M. Birshtein
cond-mat.soft cond-mat.stat-mech