Encapsulation of Bromothymol Blue into a Polysiloxane Network Matrix in Presence of Surfactants

Bromothymol blue (BTB) pH indicator was encapsulated into polysiloxane network using the sol-gel process. Transparent monolithic disks of entrapped BTB were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox LA, GLA) surfactant. Ultraviolet visible spectra showed that the encapsulated BTB retains its structure in terms of its response to pH. The kinetic studies reveal that there was a faster response to pH in the case of GLA surfactant than in the case of CTAB. It is found that the co-entrapment of cationic surfactant CTAB or zwitterionic surfactant GLA with TEOS has shifted the equilibrium of the BTB to the ionized form due to the electrostatic interaction between the surfactant and the BTB anion and therefore the base form becomes more pronounced (e.g., shift from yellow to red) than that of sol-gel matrix without surfactant.