Self-assembly of colloidal sulfur particles influenced by sodium oxalate salt on glass surface from evaporating drops

Abstract

Evaporation of sessile droplets containing colloidal particles induces outward flow within the drop, which produces the well-known ''coffee-ring'' effect or a dense ring-like deposition along the perimeter. In this work, the formation of a self-assembled structure during drying of microlitre drops on the glass surface, containing colloidal sulfur particles (synthesized in situ by the reaction of oxalic acid and sodium thiosulphate), is investigated experimentally with help of optical microscopy. Our results show that the particles are self-assembled into a tree-like structure after the evaporation of liquid drops taken from the reaction mixture. The sulfur particles alone cannot form similar self-assembly structures in pure water, but the sodium oxalate salt present in the reaction mixture helps to form the tree-like structure. The structure formation is also influenced by evaporative flux inside the liquid drop, and capillary and van der Waals attractive forces between the particles. The different parameters such as particle size, particle and salt concentration, acid to thiosulphate ratio, drop volume and addition of surfactants strongly influences the structure formation.

Self-assembly of colloidal sulfur particles on a glass surface from evaporating sessile drops: influence of different salts

“…Citric acid mediated particles also give a uniform deposit of sulfur particles in the drop area without any visible self-assembled pattern at the drop periphery. Now similar to our previous work 38 it can be concluded that the resultant salts formed along with the sulfur particle suspension because of the reaction between sodium thiosulphate and various acids which play a major role in the formation of the self-assembled pattern (as shown in Fig. 2 and Fig.…”

“…In our previous publication 38 we reported the formation of treelike or fractal self-assembled structures of sulfur nanoparticles from the evaporated sessile drops. In that study, the particles were synthesized by an oxalic acid catalyzed reaction of sodium thiosulfate, and it was explained that the sodium oxalate present in the reaction mixture plays a key role in the formation of self-assembled structures.…”

“…The ratios giving the best structures for each of the acids were found out after careful experimentation according to the methodology followed in our previous work. 38…”

“…35 Most recently our previous work highlights the role played by the resultant salt of the reaction, sodium oxalate, in guiding the self-assembly of sulfur particles according to the crystal structure of the salt. 38 This work is primarily concerned with the self-assembly of colloidal sulfur particles in the presence of different salts that was formed during the chemical reaction. It has been found that the fractal structure formation by colloidal sulfur particles during evaporation of the drop is highly dependent on the type of salt present in the media.…”

Bénard–Marangoni Dendrites upon Evaporation of a Reactive ZnO Nanofluid Droplet: Effect of Substrate Chemistry

“…In general, the solvent evaporation dynamics proximal to the surface and at the dewetting front is affected by the surface wettability by the dispersion, and in turn the substrate surface chemistry. Upon evaporation of a droplet of radius R with a contact angle  on the substrate at the three-phase contact line, the evaporating flux J(r) at a distance r from droplet center scales as J(r) ∝ (R − r)λ, where λ = ( − 2)/(2 − 2)(51). This indicates that the evaporation flux prominent in the coffee ring formation mechanism is similar on all the three substrates, due to the similar initial pinned CA values and those for the nano/microfluids.…”