| Abstract
| - The paper describes a study for the determination of the phase behavior of a self-assembling dilute aqueous cetyltrimethylammonium bromide (CTAB) and dodecyl benzene sulfonic acid (HDBS) system using flow in microchannels.The diffusional length scales of ∼10−100 μm and volumes on the order of a few tens of nanoliters allow fastcomposition and temperature homogeneity compared to “bulk” experiments, where characteristic volumes and lengthscales are on the order of milliliters and centimeters, respectively. Fluorescence emission of a polarity-sensitivefluorophore was used with the surfactants for phase characterization. To demonstrate the validity of the new approach,the critical micelle concentrations (cmc) for CTAB and HDBS were first shown to agree with the cmc obtained inthe literature under bulk conditions. Subsequently, the microstructures of dilute (less than 0.8 wt % total surfactant)aqueous mixtures of CTAB and HDBS were examined. The range of desired concentrations and accurate flow dilutionsof the samples were achieved by imposing controlled pressure gradients across the channel network. Marked changesin slopes of fluorescence emission intensity versus composition were used to demarcate phase boundaries. A seriesof microstructures ranging from mixed micelles (M), vesicles (V), and giant vesicles (GV) was observed in the ternaryCTAB/HDBS/water system. Experimental data from the microfluidic method was found to be consistent with theresults obtained from bulk phase experiments using fluorescence, turbidity, dynamic light scattering, and cryogenictransmission electron microscopy.
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