Graphene oxide (GO)-coated microbubbles in imidazolium-based ionic liquid

This study presents the feasibility of coating microbubbles with graphene oxide (GO), a transpiring material that has since attracted intensive research in both fundamental science and technology developments. In this study, an imidazolium chloride ionic liquid (IL), namely 1-dodecyl-3-methylimidazolium chloride ([C12mim]Cl) at various concentrations from 100 ppm to 8000 ppm was used as the binder surfactant to bridge microbubbles and GO. The mechanism of microbubble-GO attachment studied in this research included microbubble-GO electrostatic interactions, microbubble-GO hydrophobic attraction, microbubble-GO contact angle and Gibb's free energy of a microbubble-GO system. Results showed that the optimum microbubble-GO attachment (highest contact angle and most negative Gibb's free energy) occurred at 350 ppm [C12mim]Cl in which GO achieved isoelectric point (IEP – zeta potential (ZP) of GO is at 0 mV). Since GO gained maximum hydrophobicity at IEP, it was inferred that microbubble-GO attachment was dominated by hydrophobic attraction with insignificant electrostatic interactions. Qualitative analysis further confirmed the successful attachment and production of the GO-coated microbubble in 350 ppm[C12mim]Cl. Besides that, a single microbubble in 100 ppm[C12mim]Cl at which maximum attractive electrostatic forces are anticipated between microbubbles and GO was also analysed qualitatively. Here, GO attachment onto the microbubble was not significantly observable, thus further proving the dominance of hydrophobic attraction. On a different note, the amount of GO attached onto a microbubble in 350 ppm[C12mim]Cl was also successfully quantified using UV–Vis method at which GO possessed an absorption peak centered at 233 nm. The outcomes of this study demonstrated the significance of hydrophobic attraction for microbubble-particle attachments particularly for microbubble-GO attachment and successful synthesis of GO-coated microbubbles for various applications.