Controlling nanoparticle template morphology: effect of solvent chemistry
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Controlling nanoparticle template morphology: effect of solvent chemistry Maria M. Cortalezzi1, Vicki Colvin2 and Mark R. Wiesner1. 1 Energy and Environmental Systems Institute, Rice University, 6100 Main St. MS-317, Houston, TX 77005, USA. 2 Department of Chemistry, Rice University, 6100 Main St. MS-60, Houston, TX 77005, USA.
ABSTRACT Porous solids were obtained from self-assembled deposits of silica nanoparticles used as templates to form 3-D porous membranes. The effect of the solvent chemistry on the morphology of the deposits was investigated. The parameters of interest are surface tension and ionic strength of the solvent, due to electrostatic and capillary interactions. Deposits of nanoparticles of different sizes were obtained for a variety of conditions. The deposits were imaged using SEM and showed distinctive structures for each of the solvent chemistries. The phenomenon is consistent with the DVLO theory and calculations of capillary interaction energy.
INTRODUCTION There is general consensus that the utility of a porous material depends on the internal pore diameter, the pore size distribution, and morphology [1]. Traditional methods for the fabrication of porous materials such as stretching, track-etching, or phase inversion can produce membranes with one dimensional channel structures and have very little control over the pore size distribution [2]. The unavailability of methods for producing materials with uniform sub micrometer pores [3] and, more specifically, a gap in preparation methods of porous materials in the 10-100 nm range [4] have been recognized. Porous solids can be created from colloidal crystal templates, or more generally, from deposits of nanoparticles onto substrates. The voids in the deposits can be filled with a polymeric or inorganic material and upon etching of the nanoparticles, a porous material with a threedimensional structure is formed. The template-derived process provides the means to fabricate porous membranes that have well defined and well controlled pore sizes with completely interconnected pores, and to design the morphology of the pore structure to the nanosize scale. Template based porous materials have gained much attention lately because they can be prepared in a wide variety of materials, pore sizes and pore structures. The method has been described as powerful, inexpensive and controllable, holding promise for the formation of advanced new materials [5]. The deposition of colloidal particles may occur by different mechanisms: gravity sedimentation from dispersions, filtration, centrifugal sedimentation, sedimentation in capillaries, colloidal solutions spun coated onto surfaces, or capillary forces. We have used the selfassembly technique by capillary forces because it provides precise control of the thickness of the film through particle size and concentration in solution [6]. Previous work has shown that particle size, particle concentration, meniscus height, solvent evaporation rate, and shape of liquid surface have an important effect on colloid
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