Surfactant effect on production of monodispersed microspheres by microchannel emulsification method

Super‐monodispersed oil‐in‐water (O/W) microspheres (MS) were produced using a microchannel (MC) emulsification technique. To investigate the effect of the surfactant on the behavior of the O/W‐MS formation, the MS size and its distribution, various surfactants were used for the MC emulsification process. An MC plate with 8.9 μm equivalent diameter was employed. It was found that the super‐monodispersed O/W‐MS production depends on the type of surfactant used. When nonionic and anionic surfactants were used, supermonodispersed O/W‐MS were produced, and the average droplet diameter was about 30 μm with a standard deviation less than 1 μm. For cationic surfactants, the super‐monodispersed O/W‐MS production was not successful, especially for the case where hydrophobic surfactant was dissolved in the oil phase. The results indicated that it is very important to maintain the hydrophilicity of the MC surface during the MC emulsification process. It is considered that the hydrophilic group of the anionic and nonionic surfactant was repulsed from the negatively charged MC surface so that the hydrophilicity of the MC surface was maintained. Otherwise, adsorption of the positively charged group of the cationic surfactant occurred on the MC surface which improved wetting of the MC surface and deteriorated the MC emulsification process. The analysis was supported by contact angle measurement.