Microfluidic Synthesis of Colloidal Silica

Abstract

We demonstrate the design, fabrication, and operation of microfluidic chemical reactors for the synthesis of colloidal silica particles. Two reactor configurations are examined: laminar flow reactors and segmented flow reactors. We analyze particle sizes and size distributions and examine their change with varying linear flow velocity and mean residence time. Laminar flow reactors are affected by axial dispersion at high linear velocities, thus leading to wide particle size distributions under these conditions. Gas is used to create a segmented flow, consisting liquid plugs separated by inert gas bubbles. The internal recirculation created in the liquid plugs generates mixing, which eliminates the axial dispersion effects associated with laminar flow reactors and produces a narrow size distribution of silica nanoparticles.

Emulsification in a microfluidic flow-focusing device: effect of the viscosities of the liquids

“…Since the generation of droplets with a predictable and reproducible size and size distribution determines their potential applications (including the synthesis of polymer colloids), several research groups have explored various aspects of the process of emulsification (Seo et al 2005a;Xu et al 2005;Zhang et al 2006;Cygan et al 2005;El-Ali et al 2005;Garstecki et al 2005a;Hudson et al 2005;Jensen and Lee 2004;Khan et al 2004;Song et al 2003;Zheng and Ismagilov 2005;Zheng et al 2003) . It has been observed that the size of droplets is controlled by the design of the microfluidic device (Sugiura et al 2002a, b;Tan et al 2006), the properties of liquids, and the rates of flow of two immiscible phases (Cramer et al 2004;GananCalvo 1998;Ganan-Calvo and Gordillo 2001;Garstecki et al 2004Garstecki et al , 2005aGarstecki et al , 2005bGarstecki et al , 2006Thorsen et al 2001;Serra et al 2007;Tice et al 2003;Ward et al 2005).…”

The pressure drop along rectangular microchannels containing bubbles

“…The ability to predict how a bubble or droplet [5][6][7] will move through a microfluidic device, in the presence or absence of surfactant, is important for a number of current and emerging applications in which bubbles are used to enhance mixing, [8][9][10] to facilitate chemical reactions, 11,12 or to serve as tools for logic-based computations. 13 As microfluidic devices grow in complexity, the number of possible paths that bubbles can take through the devices will grow to accommodate parallel processes or multiple functionalities that employ multiple bubbles on one chip.…”

“…15,16 The bubbles that we measured were longer than the width of the channel and were hydrodynamically isolated-that is, they were separated from each other by a distance greater than the height of the channel-because lab-on-a-chip devices that employ bubbles most frequently use such long, isolated bubbles. 9,12 The pressure drop added by isolated bubbles surrounded by a liquid that contains surfactant, and moving at speeds typical of those in microfluidic devices, has not previously been investigated experimentally for channels of rectangular crosssection; rectangular channels are the common configuration for most microfluidic channels made using photolithographic or soft-lithographic methods. Ratulowski and Chang, Stebe et al, and Park have examined the effect of surfactant on the pressure drop due to bubbles in cylindrical channels.…”

Challenges and Innovations in Reaction Engineering

“…Let us look now at some of their other advantages such as: (1) high surface-to-volume ratios and, due to small dimensions, enhanced mass and heat transfer coefficients by one to two orders of magnitude, (2) laminar flow conditions and low pressure drop but ability to make residence time distribution (RTD) narrow by introduction of another phase, (3) controllable RTD and back mixing, (4) high volumetric productivity, (5) low manufacturing and operating costs, (6) increased safety due to small amount of material, and (7) scaleup in parallel (scale out). The MIT group of Klavs Jensen, among others, has recognized the importance of being able to manipulate multiphase systems in micro reactors and they have shown that 258 M. P. Dudukovic one can get competitive performance for various reactions and separations and in material synthesis (Jensen, 2001;Losey et al, 2001;De Mas et al, 2003;Khan et al, 2004). The achieved performance of the micro reactor depends on the level of understanding of the chemical system and the ability to manipulate micro reactor design so as to meet the reaction contacting requirements best.…”