Stabilization of Liquid Interface and Control of Two-Phase Confluence and Separation in Glass Microchips by Utilizing Octadecylsilane Modification of Microchannels

Abstract

We demonstrated a liquid/liquid and a gas/liquid two-phase crossing flow in glass microchips. A 250-microm-wide microchannel for aqueous-phase flow was fabricated on a top glass plate. Then, as a way to utilize the surface energy difference for stable phase confluence and separation, a 250-microm-wide microchannel for organic-phase (or gas-phase) flow was fabricated on a bottom glass plate and the wall was chemically modified by octadecylsilane (ODS) group. The top and bottom plates were sealed only by pressure. A microchannel pattern was designed so that the two phases made contact at the crossing point of the straight microchannels. The crossing point was observed with an optical microscope. Results showed that the ODS modification of the microchannel wall clearly improved stability of the interface between the two fluids. Pressure difference between fluids was measured and the interface of water and nitrobenzene was stable for the pressure difference from +300 Pa to -200 Pa. The pressure drop in a countercurrent flow configuration was also estimated, and the pressure difference required to realize the counter current flow was less than the allowable pressure range. Finally, we discussed the advantages of utilizing this approach.

Microflow Systems for Chemical Synthesis and Analysis: Approaches to Full Integration of Chemical Process

“…Therefore, novel MUOs taking these issues into account are needed. Kitamori et al have developed MUOs for various purposes, such as mixing and reaction [4,5], phase confluence and separation [6][7][8][9][10][11][12][13][14][15][16][17], solvent extraction [18], gas/liquid extraction [19][20][21][22], solid-phase extraction and reaction on surfaces [23][24][25][26][27][28][29][30][31][32][33][34], heating [35][36][37][38][39], cell culture [40][41][42][43][44], and ultrasensitive detection [45][46][47][48][49][50][51][52]…”

“…Some groups have proposed selective chemical surface modification to change surface-free energy for stabilization of the multiphase microflows [7,11,14,15,[66][67][68][69][70]. Figure 6b illustrates the shape of the liquid-liquid interface in a microchannel with chemically patterned surfaces.…”

Integration of Chemical and Biochemical Analysis Systems into a Glass Microchip

“…We have investigated the stabilization of the interface and control of the liquid confluence and separation by utilizing a chemical modification of the microchannel wall. 22 In this method, the microchannel for organic solvent flow was modified by surface coupling of the octadecylsilane (ODS) group, while the microchannel for aqueous flow had a bare glass surface. In order to demonstrate the effectiveness of this method, twophase crossing flow was performed.…”

Interfacial Phenomena and Fluid Control in Micro/Nanofluidics

“…43 While volume effects such as buoyancy dominate in laboratory-scale experiments because of the density differences between phases, surface effects such as capillary pressure and wetting often govern fluid properties in microfluidic systems. 24,[44][45][46] To effectively design micro-/nanofluidic systems for accommodating micro-and nanofluidic behavior, it is crucial to understand the surface effects in such a system.…”

“…5, was investigated. [44][45][46][98][99][100][101] When half of the microchannel wall is hydrophobically modified while the other half remains hydrophilic, fluid 1 (aqueous) and fluid 2 (organic or gas) tend to flow along the hydrophilic and hydrophobic portions of the wall, respectively. Furthermore, the liquid interface is pinned at the boundary between the hydrophilic/hydrophobic areas, and the control conditions drastically change.…”