Monday 10 January 2022

Simone Napolitano
Polymer and Soft Matter Dynamics, Experimental Soft Matter and Thermal Physics (EST), Université libre de Bruxelles (ULB), Brussels, Belgium
Irreversible adsorption: new insights on molecular mobility, thermodynamics and interfacial interactions
Online. Please visit the link.

Irreversibly adsorbed polymer layers represent an intriguing class of novel nanomaterials with unexpected properties, strongly deviating from what observed in unbounded polymer melts. Importantly, tuning the thickness of the adsorbed layer, an operational parameter equivalent to the number of chains adsorbed on a unit surface, allows modifying the performance of polymer coatings without affecting the interfacial chemistry.

Here, we discuss on the physics behind the formation of irreversibly adsorbed layers onto solid substrate. By analyzing the outcome of experiments and simulations, we show how changes in thermal energy and interaction potential affect the equilibrium and the nonequilibrium components of the kinetics. We find that the adsorption process is thermally activated, and the activation energy (EA) depends on the adsorbing substrate. EA is comparable to that of local non-cooperative processes (10’s kJ/mol) for polymers deposited on silicon oxide, while on aluminum oxide it reaches values typical of the structural process (100’s kJ/mol). We identify a universal linear relation between the growth rates at short and long adsorption times, suggesting that the monomer pinning mechanism is independent of surface coverage, while the progressive limitation of free sites significantly limits the adsorption rate. Finally, we show how that the adsorption kinetics is altered by the occurrence of a kinetic trap at large interfacial interactions. We discuss on the role of chain reorganization leading to an effective increase in the number of molecules adsorbed per unit surface.

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