O. D. Velev*, T. A. Jede, R. F. Lobo and A. M. Lenhoff
Nature, vol. 389, p. 447-448, 1997
Materials and methods
The monodisperse latex suspensions of amidine (positively charged) and sulphate (negatively charged) latices were obtained from IDC (USA). The latices were diluted with deionised water or with HTAB solution to 0.1 vol% and then filtered for 2 hours through 25 mm diameter polycarbonate membranes with pore size of 0.1 mm (Poretics Inc., USA). The slow filtration requires a small pressure drop across the membrane – typically not higher than 5 kPa. With positively charged latices, the HTAB was added to the original latex suspension at a concentration of 0.02 M. To prevent coagulation in the case of negatively charged particles, the latex layer was deposited first and then washed with HTAB solution for 20 mins. The excess unadsorbed surfactant within the latex layers was removed by a quick wash with deionised water (less than 60 s).
A 1 M Si(OH)4 aqueous solution was prepared by mixing of 38 g of tetramethyl orthosilicate (Aldrich, 98+%) with 250 ml of 0.02 M NaOH. This solution was stirred, filtered and diluted 2´ with water before addition to the colloidal crystal films. The latex/silica deposits were dried in a vacuum oven for 30 mins at 50oC and then heated in a programmable furnace (Centurion VPM) at 450oC for 4 hours with an initial temperature increase of 1oC/min.
The optical observations were carried out on an Olympus BH2 microscope in transmitted illumination. The samples for SEM were covered with a thin Au film by vacuum sputtering and observed using a JEOL JXA-840 scanning electron microscope. The original latex crystals were observed at acceleration voltages < 10 kV because of the sample degradation in the beam. The silica samples were stable even at accelerating voltages higher than 40 kV.
* If you are interested in additional information or in collaboration,
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Department of Chemical Engineering, University of Delaware,
Newark, Delaware 19716 USA
© Copyright 1997, Velev, Jede, Lobo & Lenhoff
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