Mechanical unfolding of collapsed macromolecules with linear and comb-like architectures

Authors: Alexey Polotsky, Anna Ivanova, Oleg Borisov, and Tatiana Birshtein

Abstract: Recent advances of experimental techniques have made it possible to manipulate individual molecules and macromolecules and study their properties. This concerns, in particular, the mechanical properties of macromolecules — by using the atomic force microscope, optical or magnetic tweezers, it is possible to stretch individual macromolecules and investigate the response of the macromolecule to applied deformation or extensional force. This allows not only to obtain information about the mechanical properties, but also to get an insight into the conformational structure of the polymers under study. In the present talk, we discuss the results of theoretical studies of mechanical unfolding of macromolecules in the position clamp mode, i.e. when the macromolecule deformation is kept fixed or controlled.
We consider three systems:

- linear homopolymer chain collapsed in a poor solvent,
- comb-like homopolymer collapsed in a poor solvent,
- amphiphilic comb-like copolymer with a solvophilic backbone and solvophobic side chains.

Using self-consistent field modeling and analytical arguments we demonstrate that force-extension behaviour of these systems is very non-trivial and, in the case of comb-like macromolecules, can demonstrate rather complex oscillatory, or "sawtooth" patterns.

[1] A.A. Polotsky, M.I. Charlaganov, F.A.M. Leermakers, M. Daoud, O.V. Borisov and T.M. Birshtein. Mechanical Unfolding of a Homopolymer
Globule Studied by Self-Consistent Field Modeling. Macromolecules, 2009, 42, №14, 5360 5371.
[2] A.A. Polotsky, M. Daoud, O.V. Borisov, T.M. Birshtein. A Quantitative Theory of Mechanical Unfolding of a Homopolymer Globule. Macromolecules, 2010, 43, №3, 1629-1643.
[3] A.A. Polotsky, T.M. Birshtein, A.A. Mercurieva, F.A.M. Leermakers,
O.V. Borisov. Unfolding of a comb-like polymer in a poor solvent: translation of macromolecular architecture in the force–deformation spectra. Soft Matter 2017, 13, №48, 9147-9161.
[4] A.S. Ivanova, I.V. Mikhailov, A.A. Polotsky, A.A. Darinskii, T.M. Birshtein, O.V. Borisov. Cascades of unfolding transitions in amphiphilic molecular brushes. J. Chem. Phys. 2020, 152, №8, 081101.