MULTIPLE EMULSION FORMATION IN CROSS-SHAPED MICROCHANNEL USING ALTERNATIVE DROPLET GENERATION TECHNIQUE

Jiro Shimamura, Yuto Yokoyama, Hiroyuki Moriguchi, Toru Torii Graduate School of Frontier Science, The University of Tokyo, Japan

ABSTRACT We produced several types of multiple emulsion in one chip by controlling the wetting property of the Cross-shaped

microchannel with Octadecyltrichlorosilane (OTS) and UV irradiation. The number of inner droplet was controlled flex-ibly by changing flow rate both in sheath-flow and alternative generation. Spherical and nonspherical polymer beads con-taining inner droplets were also produced. This technique would be expected to use for various field of encapsulation.

KEYWORDS: Alternative generation, Monodisperse, Polymer beads, Seath-flow generation, Surface-modification

INTRODUCTION The production of highly- functional emulsion is required in the field of drug delivery system or functional food. �

We had produced various kinds of droplets in microchannels (MC) [1], such as Janus droplet for electronic paper [2] and double emulsions with one process in a single glass chip [3]. A double emulsion encapsulating two different kinds of re-agents is expected to use as a test reagent in which encapsulated-regent react mutually and functional food. Therefore the flow condition and phenomena in the Cross-shaped MC (CS) was examined when a difference between two dispersed-phases flow rate (ΔDF) was applied, varying the continuous-phase flow rate (CF) to get a flow scheme of monodisperse droplet formation. The micro-PIV analysis was also executed. The double emulsion was produced in one chip by modi-fying surface properties in a CS structured MC.

EXPERIMENTAL We produced multiple emulsion by sheath-flow and alternative generation (Figure 1). The MC was fused silica with

rectangular cross section to make O/W and W/O/W emulsions (Figure 2 (a)). Glass micro-syringes with syringe pumps were used to keep a constant flow rate.

Flow images were captured using a high-speed camera. To make the multiple emulsions, the hydrophobic junction and hydrophilic junction were in the same MC by controlling the wetting property with OTS and UV irradiation (heating glace chip at 120oC) (Figure 2 (b-c)). The W/O/W emulsion was produced, inner fluid was water, middle fluid, decane (CRS75-1wt %) or 1,6-hexanediol diacrylate (CRS75-1wt%, DAROCUR1173-1wt%) and outer fluid, PVA solution (2wt %).

Figure 1. Schematic illustration of microchannel for producing multiple emulsions.

Figure 2. Glass chip and the Surface modification of Glass chip.(a) Glass MC to produce O/W emulsion (right) and W/O/W multiple emulsion (left). (b-c) Surface modification on a glass chip by UV irradiation. (Glace chip was heated at 120oC).

978-0-9798064-3-8/µTAS 2010/$20©2010 CBMS 1820 14th International Conference onMiniaturized Systems for Chemistry and Life Sciences

3 - 7 October 2010, Groningen, The Netherlands

RESULTS AND DISCUSSION Figure 3 shows the flow regime model of the two-phase flow as a function of the Continuous flow rate (CF) and dif-

ference flow rate (ΔDF). In figure 3, the flow regime model has several droplet formation patterns. In CS construction, two dispersed flow rate (DF) affect each other, generating O/W emulsion droplets dependently.

By heating the glass chip on a hot plate, the UV irradiation times were reduced dramatically (Figure 4). The surface temperature of MC had relative to reduction of contact angles. In this studies, the multiple emulsions were produced in a single glass chip by controlling the wetting property of the MC with OTS and UV irradiation (glace chip was heated at 120oC).

We investigated the scheme of monodisperse droplet formation by sheath-flow and by alternative generation (Figure 1). The relation between flow rate and numbers of inner droplets by sheath-flow is shown in Figure 5. By sheath-flow generation, numbers of inner droplets were possible to be controlled from 0 between 2 (Figure 5). And by alternative generation, those were controlled from 0 between 4 (Figure 6).

Moreover the W/O/W emulsions encapsulating two different kinds of substances were produced when a� difference flow rate (ΔDF) was applied (Figure 7). Resulting that the several types of multiple Emulsions were produced and those emulsions were encapsulated stably by UV irradiation (Figure 6).

Figure 3. Flow regime model of drop-by-drop for-mation as a function of the CF and ΔDF in CS (O/W emulsion).

Figure 4. Relation between irradiation time and con-tact angle by changing heating temperature of glass chip.

Figure 5. The production of W/O/W emulsion by sheath-flow generation (left) and Relation between flow rate and num-bers of inner droplets by Sheath-flow generation (x-y-z axis) (right).

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Figure 6. The production of W/O/W emulsion by alternative generation (left) and production of several types of W/O/W emulsion capsules (right). (a)-(c) The diacrylate droplets were polymerizationed by UV irradiation.

Figure 7. W/O/W multiple emulsions encapsulating two different kinds of substances. (CF=2.0ml/h, DF1=3.0ml/h, DF2=2.0ml/h, ΔDF=1.0ml/h) (a-b) The flow model and actual image of W/O/W emulsion production when a difference between two dispersed-phases flow rate was applied. (c) Overall view of the MC for producing double emulsion.

CONCLUSION By heating the glass chip on a hot plate, the UV irradiation times for surface modification were reduced dramatically .

Controlling the wetting property of the CS with OTS and UV irradiation, the W/O/W multiple emulsions encapsulating two different kinds of substances were produced successfully. This technique would be expected to use for various field of encapsulation.

REFERENCES: [1] T. Nisisako, T. Torii, and T. Higuchi , Droplet formation in a microchannel network , Lab on a Chip, 2, pp. 24-26

(2002) [2] T. Nisisako, T. Torii, and T. Higuchi , Novel microreactors for functional polymer beads, Chemical Engineering

Journal, 101(1-3), pp. 23-29 (2004) [3] S. Okushima, T. Nisisako, T. Torii, and T. Higuchi , Controlled Production of Monodisperse Double Emulsions by

Two-Step Droplet Breakup in Microfluidic Devices, Langmuir , 20, pp. 9905-9908 (2004)

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