A simple approach for coffee-ring suppression yielding homogeneous drying patterns of ZnO and TiO2 nanoparticles

Ioana Marica; Maria Stefan; Sanda Boca; Alexandra Falamaş; Cosmin Farcău

doi:10.1016/j.jcis.2022.12.113

A simple approach for coffee-ring suppression yielding homogeneous drying patterns of ZnO and TiO₂ nanoparticles

J Colloid Interface Sci. 2023 Apr:635:117-127. doi: 10.1016/j.jcis.2022.12.113. Epub 2022 Dec 21.

Authors

Ioana Marica¹, Maria Stefan¹, Sanda Boca², Alexandra Falamaş¹, Cosmin Farcău³

Affiliations

¹ Molecular and Biomolecular Physics Department, National Institute for Research and Development of Isotopic and Molecular Technologies, 67-103 Donat, 400293 Cluj-Napoca, Romania.
² Institute for Interdisciplinary Research in Bio-Nano-Sciences, Babes-Bolyai University, 42 T Laurian, 400271 Cluj-Napoca, Romania; Molecular and Biomolecular Physics Department, National Institute for Research and Development of Isotopic and Molecular Technologies, 67-103 Donat, 400293 Cluj-Napoca, Romania.
³ Molecular and Biomolecular Physics Department, National Institute for Research and Development of Isotopic and Molecular Technologies, 67-103 Donat, 400293 Cluj-Napoca, Romania. Electronic address: cfarcau@itim-cj.ro.

PMID: 36580694
DOI: 10.1016/j.jcis.2022.12.113

Abstract

Evaporation-induced self-assembly in colloidal droplets is a method for organising nanoparticles on substrates, with various resulting patterns. The coffee-ring pattern is among the most common ones, but its non-uniformity limits its applicability, which led to efforts for developing coffee-ring suppression strategies. Considering the wide applicability of ZnO and TiO₂ nanoparticles, there is a high demand for practical means to deposit them as uniform films. Here, we present a simple approach for obtaining highly uniform thin films of ZnO and TiO₂ nanoparticles by drop-coating in ambient conditions, without using surfactants or other surface chemistry modifications. Disc-like films were obtained via a restricted evaporation achieved by covering the droplets with a lid during drying, seconded by the relatively high sedimentation rate of these nanoparticles. To better understand the assembly mechanism, the influence of suspension concentration, type and temperature of the substrate, droplet volume, colloid type, and evaporation rate were studied. The method allows preparing disc-like nanoparticle films with a good control over their diameter and thickness, onto different kinds of substrates (glass, Si, polyethylene terephthalate, polystyrene). By fabricating both two-dimensional lattices and custom disc patterns we highlight the versatility of this drop-coating method and its potential for, e.g., automatized serial production processes.

Keywords: Coffee-ring suppression; Colloidal self-assembly; Drop coating; Evaporation rate; Nanoparticles; Sedimentation; Thin films; Titanium dioxide; Zinc oxide.