Prediction of Droplet Diameter for Microchannel Emulsification

Recently, we proposed microchannel (MC) emulsification, a novel method for making monodisperse emulsions using a microfabricated channel array. The previous study demonstrated that droplet size is affected by MC geometry. This study proposes a model for the prediction of droplet diameter based on the droplet formation mechanism and on experimental observation. The MC structure used in this study is composed of a narrow channel and a terrace. The terrace is a microfabricated slitlike shape, on which the dispersed phase inflates to a disklike shape. The MC geometry is defined in terms of two variables, terrace length ( L ) and MC depth ( H ). First, the relationship between droplet diameter and MC geometry was investigated experimentally. Experimental observation suggests that the dispersed phase, which is within the detachment length ( A ) from the terrace end, detaches and forms a droplet. The droplet volume was estimated from the volume of the dispersed phase that detaches from the terrace during this process. This volume was calculated using a detachment length parameter, A, assuming the dispersed phase on the terrace to be disk-shaped. Experimental observation and regression analysis indicate that A is independent of L . The prediction curves were fitted by regression analysis as functions of L, using fitting parameters A for each H . The values of A obtained by regression analysis were linearly correlated with H . The prediction curve, which is expressed by two variables L and H, was obtained. The prediction model was correlated with the experimental data. The mean percentage deviation of the calculated values from experimental results was 5.4%. The prediction curve was corrected using the corrected MC depth. The final form of the corrected prediction curve shows a mean percentage deviation from experimental results of 4.6%.