We propose a simple analytical model to investigate transient nonequilibrium effects during the formation and growth of 2D islands at the interface between a solid substrate and a fluid which contains freely diffusing adsorbable molecules. The model describes a sequence of processes: fast and uniform adsorption of isolated molecules which form an ideal 2D gaslike phase; migration along the fluid-solid interface; nucleation and growth of a 2D condensed phase in the interfacial region. The results clearly indicate the existence of critical values of adhesion energy at which the growth of two-dimensional clusters is maximum. On approaching the thermodynamic equilibrium we recover the standard behavior where the amount of adsorbed molecules steadily increases with the molecule-substrate adhesion energy. The transient anomalous behavior is the result of the competition between local surface concentration (which increases with the adhesion energy) and surface diffusion (which, in a jump diffusion picture, decreases with the adhesion force). The model has been extended to the case of two different adsorbed species which have nonideal mixing in the condensed phase. Transient anomalies were found when the minority component has a stronger adhesion energy than the more abundant one. The theory might qualitatively explain certain puzzling features observed in the adsorption of single proteins or mixtures of proteins onto flat substrates with different hydrophobicity. (C) 1998 American Institute of Physics. [S0021-9606(98)50747-7].

Unusual nonequilibrium effects during the growth of two-dimensional crystals at the solid-fluid interface

RAUDINO, Antonio
1998

Abstract

We propose a simple analytical model to investigate transient nonequilibrium effects during the formation and growth of 2D islands at the interface between a solid substrate and a fluid which contains freely diffusing adsorbable molecules. The model describes a sequence of processes: fast and uniform adsorption of isolated molecules which form an ideal 2D gaslike phase; migration along the fluid-solid interface; nucleation and growth of a 2D condensed phase in the interfacial region. The results clearly indicate the existence of critical values of adhesion energy at which the growth of two-dimensional clusters is maximum. On approaching the thermodynamic equilibrium we recover the standard behavior where the amount of adsorbed molecules steadily increases with the molecule-substrate adhesion energy. The transient anomalous behavior is the result of the competition between local surface concentration (which increases with the adhesion energy) and surface diffusion (which, in a jump diffusion picture, decreases with the adhesion force). The model has been extended to the case of two different adsorbed species which have nonideal mixing in the condensed phase. Transient anomalies were found when the minority component has a stronger adhesion energy than the more abundant one. The theory might qualitatively explain certain puzzling features observed in the adsorption of single proteins or mixtures of proteins onto flat substrates with different hydrophobicity. (C) 1998 American Institute of Physics. [S0021-9606(98)50747-7].
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.11769/10003
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