Coating Regimes for Controlled Convective Assembly of Monolayered Nanoparticle Films

Convective assembly with controlled evaporation and controlled substrate withdrawal (i.e. in a dip-coating configuration) is well-accepted as a facile method for deposition or coating of colloidal films. The interplay of bulk particle concentration, substrate withdrawal rate, and to a lesser degree evaporation control (by controlled laminar gas flow similar in configuration to air-knife), are shown to mediate film thickness at the thick multilayer regime. At the thinner film regime, the concept of ``thickness'' must be recast in terms of ``coverage'' of discrete patterned films with void spaces. Even in situations where particle coverage is in excess of that required for complete single-layer coverage, resultant films are often discrete and patterned. We discuss, therefore, the identification of coating windows for which the method can achieve uninterrupted monolayers with a close-packed structure by tuning bulk particle concentration and substrate withdrawal rate.