Evaporative Deposition of Surfactant-Laden Nanofluid Droplets over a Silicon Surface

Abstract

Morphologies of evaporative deposition, which has been widely applied in potential fields, were induced by the competition between internal flows inside evaporating droplets. Controlling the pattern of deposition and suppressing the coffeering effect are essential issues of intense interest in the aspects of industrial technologies and scientific applications. Here, evaporative deposition of surfactant-laden nanofluid droplets over silicon was experimentally investigated. A ring-like deposition was formed after complete evaporation of sodium dodecyl sulfate (SDS)-laden nanofluid droplets with an initial SDS concentration ranging from 0 to 1.5 CMC. In the case of initial SDS concentrations above 1.3 CMC, no cracks were observed in the ring-like deposition, indicating that the deposition patterns of nanofluid droplets could be completely changed and cracks could be eliminated by sufficient addition of SDS. With the increase of the initial concentration of hexadecyl trimethylammonium bromide (CTAB), the width of the deposition ring gradually decreased until no ring-like structure was formed. On the contrary, with the increase of the initial Triton X-100 (TX-100) concentration, the width of the deposition ring gradually increased until a uniform deposition was generated. Moreover, when the initial TX-100 concentration was high, a "tree-ring-like" pattern was discovered. Besides, morphologies of evaporative pattern due to the addition of surfacants were qualitatively analyzed.

Inhibiting Cracks in Latte Droplets

“…50 Increasing surfactant concentration over the surfactant critical micelle concentration (CMC) is favorable to achieve uniform crack-free deposits. 35 Here, the presence of Marangoni flows could be one reason for fewer crack deposits from the latte droplets compared to the coffee droplets. The invariant latte surface tension to the fraction of milk (from ϕ milk = 20−100%), indicating that all latte solutions are over the CMC concentration.…”

“…It is worthwhile to note that surfactant-induced flows may counteract capillary flows inside an evaporating water droplet and cause uniform deposit patterns (Marangoni effect) . Increasing surfactant concentration over the surfactant critical micelle concentration (CMC) is favorable to achieve uniform crack-free deposits . Here, the presence of Marangoni flows could be one reason for fewer crack deposits from the latte droplets compared to the coffee droplets.…”

“…Crack formation is one of the interesting complex phenomena that occur during evaporation, essential in disease diagnosis , and useful to determine the mechanical properties of printable bioinks for biofabrication approaches. − Cracks emerge when the residual local stress inside the evaporating colloidal droplets reaches the local strength limits; as a result, cracking releases the internal stress. − Typically, capillary pressures produced by fluid menisci between colloidal particles on the top of the coating are responsible for cracking as a process of abrupt air and water exchanges. − Adding polymer molecules into solvents and absorbing them on colloidal particles or filling pores between particles can suppress the capillary pressures and modify the resultant deposit structures after evaporation. , The printable bioinks have been limited to developing technologies using polymer-based materials: for instance, a biocompatible material printable under physiological circumstances . In other words, the limitation refers to a trade-off between biocompatibility and printability in most polymeric materials. ,, In this situation, crack prevention without the addition of polymers is a challenging task.…”

Geometrically-controlled evaporation-driven deposition of conductive carbon nanotube patterns on inclined surfaces

“…30 While thermal Marangoni flow in pure water droplets at room temperature is not well understood yet, 31,32 the presence of surfactants can have a strong impact on the flow and contact line deposition. [33][34][35] However, the physics of the problem is very complicated in such a way that different types of surfactants can have different effects on the interfacial flow of evaporating sessile droplets. 36 It was shown that insoluble surfactants do not produce Marangoni vortices, 37 but soluble surfactants can drive considerable recirculation.…”

Deposition Patterns of Evaporating Sodium Alginate Sessile Droplets Cross‐Linked by Calcium Chloride

“…The interplay between capillary and Marangoni flows in evaporating droplets of complex fluids such as polymer solutions or colloidal suspensions leads to the formation of unique patterns. [33][34][35][36] These morphological patterns of drying bio-colloidal droplets can be utilized in biomedical applications and medical diagnosis. [37] Pathak et al [38] investigated the effect of salt concentration in the aqueous solution of bovine serum albumin on the patterns left by evaporating sessile droplets.…”