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%.