Restricted meniscus convective self-assembly

• Published in: Journal of colloid and interface science Vol. 344; no. 2; pp. 315 - 320
• Main Authors: Chen, Kai, Stoianov, Stefan V., Bangerter, Justin, Robinson, Hans D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.04.2010
• Subjects: Coatings; Colloidal crystal; Diffusion rate; Drying; Evaporation; Humidity; Nanospheres; Reduction; Relative humidity; Self assembly; Wetting film; Self-assembly; Wetting film; Nanospheres; Evaporation; Colloidal crystal; Humidity
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2010.01.010

A variant of convective self-assembly for thin colloidal crystal is introduced, with growth speeds twice those of the conventional technique. The scaling of growth speed with humidity is also investigated. Convective (or evaporation-induced) self-assembly is a standard technique for depositing uniform, poly-crystalline coatings of nanospheres across multiple square centimeters on the timescale of minutes. In this paper, we present a variation of this technique, where the drying meniscus is restricted by a straight-edge located approximately 100 μm above the substrate adjacent to the drying zone. Surprisingly, we find this technique to yield films at roughly twice the growth rate compared to the standard technique. We attribute this to differing rates of diffusion of vapor from the drying crystal in the two cases. We also investigate the crystal growth rate dependence on ambient relative humidity and find, contrary to some previous reports, that the growth rate depends strongly on the humidity. We introduce a model which indicates that while the length of the drying zone may increase with humidity, this alone cannot compensate for the simultaneous reduction in evaporation rate, so a lower humidity must always lead to a higher growth speed. Comparing the model to our experimental results, we find that the length of the drying zone is constant and mostly independent of parameters such as humidity and surface tension.