Crust Effect on Multiscale Pattern Formations in Drying Micelle Solution Drops on Solid Substrates

Abstract

Spherical micelles of a polystyrene-b-poly(dimethylsiloxane) (PS-b-PDMS) diblock copolymer with the number-average molecular weight of 193 000 g/mol for PS and 39 000 g/mol for PDMS were obtained by using n-dodecane or n-octane as the selective solvent for the PDMS block. The drying process of micelle solution drops with relatively high polymer concentration on solid substrates and the resultant drying patterns were studied using optical microscopy and atomic force microscopy. The drying drops exhibited an inner solution "cap" connecting with an outer gelled "foot" through a transition zone. A crust was first formed on the surface of the transition zone and remained on the top of the foot region. An inhomogeneous stress perpendicular to the radial direction within the crust, which was due to the solvent evaporation accompanied by the receding of the solution cap, induced regular 45 degrees -tilted stripes (pleats) in the transition zone and main radial cracks in the foot region. The stripes and cracks have periods of a few and tens of microns, respectively. Concave micelle "bricks" were also observed between cracks. In addition to micelle close packing, these patterns demonstrate that drying micelle solution drops may provide a potential means to manipulate fine and multiscale structures for technological applications.

Buckling and collapse during drying of a single aqueous dispersion of casein micelle droplet

“…Compared to the loss of mass for water, the caseins showed a similar tendency during stages 1 and 2 despite a slight difference due to the water holding capacity of caseins. One interesting point is the apparent onset of gelation, as indicated by the occurrence of a gelled foot (Goor et al, 2012;Ma et al, 2004;Fig. 4.…”

Self-assembly in evaporated polymer solutions: Influence of the solution concentration

“…Applications of micro-scaled relieves obtained under evaporation of polymer solutions as biomedical interfaces has been discussed intensively as well [4,5]. It was demonstrated that under particular conditions, intensive evaporation of the solution gives rise to ordered self-assembled patterns on a length scale significantly exceeding molecular dimensions [6][7][8][9][10][11][12][13][14]. Similar patterns were observed under evaporation of volatile liquids [15,16].…”

“…For film thickness less than about 100 nm (thin layers) effective molecular interactions between the liquid layer surface and the substrate dominate all other forces (like thermocapillarity or gravity) and thus determine the film stability and patterning under dewetting [17][18][19]. For evaporated films of a thickness above 100 nm thermocapillarity forces become dominant, resulting in instability caused by the Marangoni convection [6][7][8][9][10][11][12]15,16,[20][21][22][23][24][25]. However, when evaporation is present thermocapillarity represents only one of several destabilizing mechanisms: vapor recoil, differential evaporation (dependence of the evaporation rate on the thickness of the film) and, sometimes, solutocapillarity, all contribute to the development of interfacial instability and as a result exert an influence on the pattern's makeup [26].…”

On the mechanism of patterning in rapidly evaporated polymer solutions: Is temperature-gradient-driven Marangoni instability responsible for the large-scale patterning?

“…Evaporation-induced self-assembled patterns were observed in different systems, including soluble silica introduced into ethanol/water solvent, aqueous solutions of colloidal nanoparticles and polymer solutions [3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Evaporation-driven patterns demonstrate a large variety of scales, starting from the nanoscale up to large-scale patterns of 10-100 lm .…”