1. Single macromolecules as probes for pressure and friction in fluid monolayers
Sergei S. Sheiko, UNC Chapel Hill, PRF# AC7
Our research program develops a molecular-level understanding of polymer spreading through visualization of individual molecules during flow.
We demonstrated that single brush molecules could be used as sensors of film pressure and friction in flowing polymer films.1 Flow-induced conformational changes were compared with static films by generalizing the Flory theorem for structurally asymmetric mixtures of brushes and chains of the same chemical structure.2 We anticipate the utilization of such miniature sensors for probing flow properties on nanometer length scales, which would impact fluidics, lubrication, and surface coatings.
Generalized Flory theorem. We experimentally verified the Flory theorem for structurally asymmetric polymer mixtures that predicts three conformational regimes of a brush-like macromolecule embedded in a melt of linear chains.
2 Phys. Rev. Lett. 99, (2007)
Molecular pressure sensors. Single brush molecules change conformation during flow. (a) Molecules are coiled in the vicinity of liquid reservoir where the pressure is high, while they get extended upon approaching the film edge (b,c). The visualized pressure gradient gives the friction coefficient between the melt and substrate. 1 Adv. Mat. 19, 2930 (2007).