title: Effects of pH and ionic strength on the stability of nanobubbles in aqueous solutions of alpha-cyclodextrin.
abstract: Formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules is a spontaneous process. Using a combination of laser light scattering (LLS) and zeta-potential measurements, we investigated the effects of salt concentration and pH on their stability in alpha-cyclodextrin (alpha-CD) aqueous solutions. Our results reveal that the nanobubbles are unstable in solution with a higher ionic strength, just like colloidal particles in an aqueous dispersion, but become more stable in alkaline solutions. The zeta-potential measurement shows that the nanobubbles are negatively charged with an electric double layer, presumably due to adsorption of negative OH- ions at the gas/water interface. It is this double layer that plays a critical dual role in the formation of stable nanobubbles in aqueous solutions of water-soluble organic molecules, namely, it not only provides a repulsive force to prevent interbubble aggregation and coalescence but also reduces the surface tension at the gas/water interface to decrease the internal pressure inside each bubble.
authors: Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
authors: Fan
authors: F
authors: Jin
authors: Junfang
authors: J
authors: Li
authors: Xiaodong
authors: X
authors: Ye
authors: Chi
authors: C
authors: Wu