Molecular insight into the reversible dispersion and aggregation of graphene utilizing photo-responsive surfactants

Abstract

Reversible dispersion and aggregation of graphene with photo-stimuli response have exhibited enormous potential in electrochemical and biomedical fields owing to its green and efficient characteristics. However, the molecular mechanism of photo-controllable dispersibility of graphene is still limited. Herein, the reversible dispersion and aggregation of graphene in the existence of photo-responsive surfactant (2-(4-(4-butylphenyl)diazenylphenoxy) ethyltrimethylammonium bromide, AzoTAB) is investigated by molecular dynamics simulation. Analysis of structural features indicates that the adsorption configurations of trans-AzoTAB and cis-AzoTAB show different evolutions with increasing concentration. At high surfactant concentrations, exceed trans-AzoTAB molecules move away from the graphene surface and generate second adsorption layer, while cis-AzoTAB molecules prefer to lift a benzene ring to obtain an “L-shaped” configuration, which responsible for the larger saturated adsorption capacity of cis-AzoTAB molecules. Subsequently, the potential of mean force (PMF) provides comprehensive direct evidence for the influence of adsorption configurations on the dispersibility of graphene. It is observed that the transition between the π-π stacking structure formed by three trans-AzoTAB layers and the “L-shaped” configuration of cis-AzoTAB molecules can achieve the reversible dispersion and aggregation processes of graphene. Thus, the photoisomerization of AzoTAB triggered by exposure to UV/visible light could be utilized to realize reversible dispersion and aggregation of graphene.