Morphogenesis of polycrystalline dendritic patterns from evaporation of a reactive nanofluid sessile drop

Dendritic surface patterns from Bénard‐Marangoni instabilities upon evaporation of a reactive ZnO nanofluid droplet: A fractal dimension analysis

“…One of the well-defined cells is shown in Figure 1c. These cells, similar to the BM flow pattern observed during the evaporation of polystyrene/toluene solution [14], were identified as solidified manifestations of Bénard-Marangoni (BM) convection cells [3]. The occurrence of the BM instabilities and flows may be gauged by the Marangoni number, B, which considers the counter balancing effects of the surface tension and the viscous force in a liquid film [18], and it also depends on solvent physical parameters such as thermal diffusivity, dynamic viscosity, temperature gradient, thermal conductivity, density, and specific heat capacity.…”

“…They attributed different BM cell sizes to the fluctuations in the local fluid viscosity induced by the variation in the local particle concentration during the evaporation. Here, the varying BM cell sizes  BM ~ 200 -800 μm suggest that the BM flows were triggered at different droplet thickness d or thinning stages during the evaporation, which maybe attributed to the inhomogeneities in the concentration of particle and molecular species in situ generated from ZnO dissolution[3,5].In contrast, drying of the nano/microfluid droplets from the commercially acquired ZnO nanopowder(Figure 1d-f)and ZnO powder(Figure 1g-i)left the substrate surface covered with dense, fibrous structures intercalated with ZnO nano/microcrystal residues, as shown in the insets in…”

“…The EISA process based on reactive ZnO nano/microfluids can result in a plethora of hierarchical surface patterns composed of fibres or dendrites [3,[5][6]. For instance, the dendritic patterns triggered by Bénard-Marangoni (BM) instabilities [7][8] were analogous to the foliage of red algae, Spanish dagger, or spider plant [3]. To go beyond such a descriptive account and to seek understanding of the correlation between the surface pattern and the underpinning physical parameters, here we perform fractal dimension (FD) analysis of the surface patterns.…”

Crystallization from Thin Films on a Hot Plate: A New Approach of Solid Surface Pattering

“…When crystallization takes place on a solid substrate the single-crystals appear as a collection of many isolated or partially clusterized similar crystals, only their size and numer varying. Sometime, when the solutions are highly diluted, dendritic shapes are obtained (small and flat single-crystals bonded in fractal like structures) (Figure 1(b)) [22] [35]. These dendritic self-assembled crystals are hardly reproducible (at least as shape).…”

Facile Fabrication of Multifunctional ZnO Urchins on Surfaces

“…Several fabrication methods of ZnO nanostructured surfaces have been reported [21][22][23][24][25][26][27][28], such as hydrothermal synthesis, laser ablation, sputtering, thermal decomposition, evaporation induced self-assembly [29,30], and the sol-gel technique. Various ZnO nanostructures that have been reported include one-dimensional (1-D) morphologies such as nanowires [31][32][33], nanofibers [29,30], nanorods [34][35][36][37], micro-dendrites [38,39], and nanotubular structures [40][41][42][43][44], as well as 3-D architectures such as flowers/urchins [45][46][47][48][49][50], tetrapods/jack-like [51,52], and hedgehogs [53]. The 3-D nanostructures with enhanced surface area may be used as substitutes for 1-D nanostructure arrays with enhanced functionalities, but their fabrication requires either sophisticated instrumentation or elevated temperatures (and thus high energy input).…”