Probing molecular interactions at polymer/substrate interfaces from gel friction experiments

phd offer 2024-2027

Sciences and Engineering of Soft Matter (SIMM),
UMR 7615
Adress : ESPCI – 10 rue Vauquelin – 75231 Paris Cedex 05
Chair : Etienne Barthel
Supervisors : Émilie Verneuil, Antoine Chateauminois

Contacts : ou
https://www.simm.espci.fr/-Matiere-Molle-Hors-Equilibre-.html

application deadline : April 15th 2024

(left) Schematics of the friction experiment between a glass sphere and a gel: velocity V and normal load Fn are imposed and the friction force Ft is measured (right) Physical model : polymer chains from the gel adsorbed. Once bound to the substrate, chains are stretched as substrate is translated at velocity V until they detach at some point, and relax.This macroscopic experiment allows to measure the molecular parameters characterizing this dissipative mechanism : adsorption energy and polymer elasticity.

Abstract

Describing the dynamics of polymers near solid surfaces is of great relevance to mechanics, adhesion, friction, or flows at interfaces as they set the boundary conditions and, from these, the whole dynamic response of polymeric soft matter systems. However, direct information on polymer/substrate interactions can be challenging to obtain. Indeed, the polymer dynamics at interfaces strongly couples polymer/substrate interactions and polymer/polymer interactions in the bulk.

In order to isolate the polymer/substrate interactions, we have developed dedicated friction experiments where a spherical glass probe slides on swollen polymer networks, often called gels. In such dilute systems, we found that measurements of the velocity dependence of the friction force allows to measure the polymer/substrate interaction energy as well as the surface density of adsorption sites [1]. For that purpose, experimental results were analyzed within the framework of a novel theoretical model which is based on the assumption that energy is dissipated at the sliding interface from the pinning, stretching and subsequent depinning of polymer chains of the gel surface on the glass substrate.

Within the framework of this project we aim at a better description of the interaction potential between gel polymer chains and glass surface from the exploration of the overlooked low velocity regime. In the literature, experimental data and theoretical models developed within the context of single molecule force spectroscopy [2,3] suggest that this low velocity regime could provide new information regarding the strength, lifetime, and energetic details of molecular interactions at the sliding interface. We will explore this regime while playing with the physical-chemistry of the interface. For that purpose, the physical-chemistry of the glass probe will be modified by grafting mixtures of various silanes. In addition, grafting of gel molecules with different physico-chemical properties (polyelectrolytes, chain length…) at the surface of the bulk hydrogel will allow to tune molecular interactions at the interface.

Profile and required skills

We are seeking a candidate with experimental skills and a background in physics or physical-chemistry. A knowledge in soft matter physics and/or physical-chemistry of surfaces will be appreciated.

References
1. L. Ciapa, L. Olanier, Y. Tran, C. Frétigny, A. Chateauminois & E. Verneuil, Friction through molecular adsorption at sliding interfaceof hydrogels: theory and experiments, submitted to Soft Matter
2. Friddle, R. W., Noy, A. & De Yoreo, J. J. Interpreting the widespread nonlinear force spectra of intermolecular bonds. Proc. Natl. Acad. Sci. U.S.A. 109, 13573–13578 (2012).
3. Friddle, R. W., Podsiadlo, P., Artyukhin, A. B. & Noy, A. Near-Equilibrium Chemical Force Microscopy. J. Phys. Chem. C 112, 4986–4990 (2008)
 

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