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 technological development.
Mechanism of Microbubble-GO Attachment
In this study, an ionic liquid (IL) of imidazolium chloride , namely 1-dodecyl-3-methylimidazolium chloride ([C 12mim]Cl) at various concentrations from 100 ppm to 8000 ppm was used as a binding surfactant to bridge microbubbles and GO. The mechanism of microbubble-GO attachment studied in this research included the electrostatic interactions of microbubble-GO, the hydrophobic attraction of microbubble-GO, the contact angle of microbubble-GO, and Gibbs free energy of a microbubble-GO system.
The results showed that the optimal microbubble-GO attachment (highest contact angle and most negative Gibbs free energy) occurred at 350 ppm [C 12 mim]Cl, at which GO reached an isoelectric point (IEP – zeta potential .)(ZP) of GO is 0 mV). Since GO reached maximum hydrophobicity at IEP, it was concluded that microbubble-GO attachment is dominated by hydrophobic attraction with insignificant electrostatic interactions.
Qualitative analysis also confirmed the successful attachment and production of the GO-coated microbubbles in 350 ppm[C 12 mim]Cl. In addition, a single microbubble in 100 ppm[C 12 mim]Cl, where maximum electrostatic attraction forces between microbubbles and GO are expected, was also analyzed qualitatively. Here, the attachment of GO to the microbubbles was not significantly observable, further proving the dominance of hydrophobic attraction.
In another note, the amount of GO bound to a microbubble in 350 ppm[C 12mim]Cl was also successfully quantified by the UV-Vis method, where GO exhibited an absorption peak centered at 233 nm. The results of this study demonstrated the importance of hydrophobic attraction for microbubble-particle attachment, especially for microbubble-GO attachment and the successful synthesis of GO-coated microbubbles for various applications.