The effect of ionisation of silica nanoparticles on their binding to nonionic surfactants in oil-water system: an atomistic molecular dynamic study

In this study, the adsorption of nonionic surfactant, triethylene glycol monododecyl ether (C12E3), on a surface of silica nanoparticle (NP) has been studied with variation in the degree of ionisation (DI) of silica NP using all-atom molecular dynamic simulations in hexadecane-water system. Hydrogen bonding is found to be responsible for the adsorption of C12E3 on NP, particularly at low DI. We observe that with increasing DI of NP, the amount of adsorption of C12E3 on NP reduces, which is negligible beyond DI approximate to 0.5. The decrease in the adsorption with increasing DI is due to the decrease in the number of hydrogen bonds formed by the silica NP with surfactant molecules. Potential of mean force (PMF) profiles indicate attractive interactions between NP and C12E3 for DI <0.5, and for larger DI depletion effect is observed. This work explains the unusual effect of nonionic surfactant on interfacial tension in the presence of silica particles as observed in recent experiments. [GRAPHICS] .