Optimization of miniemulsion process using different solvents

Miniemulsions are heterophase systems consisting of small, stable and narrowly distributed droplets in a continuous phase [1]. Recently this system shows a high potential for different biocatalytic reactions, as environmentally friendly reaction media consisting 80% of water [2]. The other important factor is enormous interfacial area, readily available for interfacial catalysis. The systems are obtained using high shear force, in particular, ultrasound. For a typical oil-in-water miniemulsion, an oil phase (e.g. substrates), a hydrophobic agent (e.g. hexadecane), an emulsifier (usually nonionic surfactant), and water are homogenised to obtain monodisperse droplets in the size range up to 500 nm[1,2]. The objective of present work was to obtain a stable miniemulsion system through optimization of conditions of ultrasonication using different solvents (oil phase). The effect of six solvents (hexane, cyclohexane, isooctane, decane, hexadecane and acetonitrile) on miniemulsion stability was explored. In order to establish a reproducible dispersion procedure, power and amplitude of ultrasonication was varied and it´s relation with the droplet size was observed. The influence of the ultrasonication time was also evaluated on miniemulsion stability. Droplet size and distribution factor were characterized by dynamic light scattering. The results show that the particle size varied between 320 and 630 nm, except for the systems with the cyclohexane in which a higher size was obtained. The best result was achieved with 50% of amplitude and 30W of power using hexane as a solvent. The phase separation was observed for the cyclohexane and acetonitrile miniemulsion systems. It could be due to the droplet size (cyclohexane) or acetonitrile hydrophilic character.