Effects of surface treatment and storage conditions of silicon microchannel emulsification plates on their surface hydrophilicity and preparation of soybean oil-in-water emulsion droplets

A major problem of microchannel (MC) emulsification that enables producing monodisperse emulsions is difficulty in stably producing monodisperse emulsions using silicon MC array plates stored for a long period of time. The purpose of this study was to analyze the effects of storage conditions of silicon MC array plates on their surface properties and MC emulsification. To make the MC array plate surfaces hydrophilic, they were treated by oxygen plasma. Each silicon plate was then stored in air, nitric acid, or Milli-Q water at different temperature. The change in the hydrophilicity of the MC array plate surface was monitored with contact angle measurement. Hydrophilic property of the plasma treated MC array plate was better kept by storing in a hydrophilic medium with a low concentration of positively charged hydrogen ions which could be supported by the zeta-potential data of MC array plates and dynamic contact angle results. We also clarified that monodisperse food-grade O/W emulsions are produced using a MC array plate with a static contact angle below a critical value.