Change in interfacial behavior by variation of amphiphilic nanosheets/anionic surfactant ratio using dynamic tensiometry

Abstract

Nanoparticles/surfactant interplays can robustly manipulate interfacial properties, while it is still unclear how their interactions affect interface behavior. This research recap unprecedented research for determination of dynamics of adsorption and dynamic surface properties of amphiphilic sheet-like nanoparticles in anionic surfactant mixtures and generalizing their characteristics in industrial and macroscopic applications by controlling microscopic active mechanism, particularly tuning foam properties and controlling its behavior. Amphiphilic nanosheets are surface-active particles which tend to self-assemble at the air-water interface. In this study, a system of an anionic surfactant (sodium dodecylsulfate (SDS)) and an amphiphilic nanoparticle (Graphene oxide (GO)) is studied at different ratios. It appears that there is a critical value for the minimum number of surfactants per nanosheets (> 160) to make the amphiphilic nanoparticle more hydrophilic. The results set out that below this critical ratio, the amphiphilic nanoparticles are partially hydrophobic and they are surface-active enough to be adsorbed considerably at the air-water interface. The nanoparticle adsorption causes an increase in surface elasticity and a decrease in surface tension (ST). As SDS/GO ratio increases, GO particles are heavily surrounded by SDS molecules rendering them hydrophilic particles. The hydrophilic GO particles start traveling back into the bulk, drastically decreasing elasticity and increasing the ST. When SDS concentration approaches the pure SDS critical micelle concentration (CMC), there appears that some of GO/SDS complexes are still on the air-water interface to slow down the dynamics of ST. The presence of GO/SDS complexes at the interface also decreases ST to lower values compared to the pure SDS near the CMC. The hydrophilic transition of GO nanoparticles is also confirmed by ζ potential and DLS measurements. This suggests a simple way to tune foam properties and behavior by selecting proper nanoparticle/surfactant ratio.