Unfolding of a comb-like polymer in a poor solvent : Translation of macromolecular architecture in the force-deformation spectra

A numerical self-consistent field modeling approach was employed to study the mechanical unfolding of a globule made by comb-like polymers in a poor solvent with the aim of unraveling how the macromolecular architecture affects the shape of the single-molecule force-deformation curves. We demonstrate that the dependence of the restoring force on the imposed extension of the main chain of the comb-like polymer exhibits a characteristic oscillatory shape in the intermediate deformation range. Theoretical arguments are developed that enable us to relate the shape of the patterns on the force-deformation curves to the molecular architecture (grafting density and length of the side chains) and interaction parameters. Thus, the results of our study suggest a new approach for the determination of macromolecular topology from single-molecule mechanical unfolding experiments.</p

Wetting of a polymer brush, a system with pronounced critical wetting

We consider a polymer brush composed of units of type P, at a solid substrate S in an incompatible binary A/L solvent mixture. At A/L coexistence the film thickness of the wetting component A depends mainly on the second virial coefficient AP of polymer-polymer contacts in an A-rich phase: with increasing AP the film thickness jumps from a microscopic to a mesoscopic value and then continues to grow proportionally to AP. The film grows smoothly without bounds when the fluid interface is further out than the segments of the brush chains can reach. This escape of the A-L interface from the brush coincides with the (second-order) wetting transition and occurs at . Substrates covered by a polymer brush are excellent surfaces to measure critical wetting because the wetting behavior can be tuned independently from the short-range interactions of the solvents with the solid substrate. For relatively thin brushes, van der Waals contributions can seriously modify these predictions. However, as the brush thickness is proportional to the chain length N, the relative contribution of these forces can be tuned; i.e., for a sufficiently large brush height the (long-range) van der Waals forces can be ignored. The wetting scenario has been elaborated by a numerical self-consistent-field theory for inhomogeneous polymer systems

Adhesion-induced fingering instability in thin elastic films under strain

In this study, thin elastic films supported on a rigid substrate are brought into contact with a spherical glass indenter. Upon contact, adhesive fingers emerge at the periphery of the contact patch with a characteristic wavelength. Elastic films are also pre-strained along one axis before the initiation of contact, causing the fingering pattern to become anisotropic and align with the axis along which the strain was applied. This transition from isotropic to anisotropic patterning is characterized quantitatively and a simple model is developed to understand the origin of the anisotropy