Droplet Based Microfluidics for Synthesis of Mesoporous Silica Microspheres
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1272-KK08-02
Droplet Based Microfluidics for Synthesis of Mesoporous Silica Microspheres Nick J. Carroll,1 Svitlana Pylypenko,2 Amber Ortiz,1 Bryan T. Yonemoto,1 Ciana Lopez,1 Plamen B. Atanassov,2 David A. Weitz,3 and Dimiter N. Petsev1* 1
Department of Chemical and Nuclear Engineering and Center for Biomedical Engineering, University of New Mexico, Albuquerque, New Mexico 87131 2
Center for Emerging Energy Technologies, University of New Mexico, Albuquerque, New Mexico 87131 3
School of Engineering and Applied Sciences, Department of Physics, Harvard University, Cambridge, Massachusetts 02138
ABSTRACT Herein we present methods for synthesizing monodisperse mesoporous silica particles and silica particles with bimodal porosity by templating with surfactant micelle and microemulsion phases. The fabrication of monodisperse mesoporous silica particles is based on the formation of well-defined equally sized emulsion droplets using a microfluidic approach. The droplets contain the silica precursor/surfactant solution and are suspended in hexadecane as the continuous oil phase. The solvent is then expelled from the droplets, leading to concentration and micellization of the surfactant. At the same time, the silica solidifies around the surfactant structures, forming equally sized mesoporous particles. We show that hierarchically bimodal porous structures can be obtained by templating silica microparticles with a specially designed surfactant micelle/microemulsion mixture. Oil, water, and surfactant liquid mixtures exhibit very complex phase behavior. Depending on the conditions, such mixtures give rise to highly organized structures. A proper selection of the type and concentration of surfactants determines the structuring at the nanoscale level. Tuning the phase state by adjusting the surfactant composition and concentration allows for the controlled design of a system where microemulsion droplets coexist with smaller surfactant micellar structures. The microemulsion droplet and micellar dimensions determine the two types of pore sizes.
INTRODUCTION Emulsification of a polymer precursor followed by execution of the polymer chemistry within emulsion droplet reactors provides a facile and versatile method for producing microparticles. Not surprisingly, if a liquid-to-solid chemical reaction proceeds to completion within these drops, the resultant solid particles will possess the shape of the droplets.1, 2 Microfluidic flowfocusing devices (MFFDs) provide a straightforward and robust approach to the formation of highly monodisperse emulsion drops.3 It has been demonstrated that microfluidic-generated drops can function as both morphological templates and chemical reactors for the synthesis of monodisperse polymer 4-6 and biopolymer 7 particles.
An appealing feature to engineer into emulsion-polymerized particles is porosity. Particles with well-defined pore morphology are essential for many areas of modern technology. Potential applications include catalysis 8, 9 and electrocatalysis,10 chromatography,11 and drug d
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