This study investigates pattern formation during evaporation of water-based nanofluid sessile droplets placed on a smooth silicon surface at various temperatures. An infrared thermography technique was employed to observe the temperature distribution along the air-liquid interface of evaporating droplets. In addition, an optical interferometry technique is used to quantify and characterize the deposited patterns. Depending on the substrate temperature, three distinctive deposition patterns are observed: a nearly uniform coverage pattern, a "dual-ring" pattern, and multiple rings corresponding to "stick-slip" pattern. At all substrate temperatures, the internal flow within the drop builds a ringlike cluster of the solute on the top region of drying droplets, which is found essential for the formation of the secondary ring deposition onto the substrate for the deposits with the "dual-ring" pattern. The size of the secondary ring is found to be dependent on the substrate temperature. For the deposits with the rather uniform coverage pattern, the ringlike cluster of the solute does not deposit as a distinct secondary ring; instead, it is deformed by the contact line depinning. In the case of the "stick-slip" pattern, the internal flow behavior is complex and found to be vigorous with rapid circulating flow which appears near the edge of the drop.

The formation of patterns after the evaporation of colloidal droplets deposited on a solid surface is an everyday natural phenomenon. During the past two decades, this topic has gained broader audience due to its numerous applications in biomedicine, nanotechnology, printing, coating, etc. This paper presents a detailed review of the experimental studies related to the formation of various deposition patterns from dried droplets of complex fluids (i.e., nanofluids, polymers). First, this review presents the fundamentals of sessile droplet evaporation including evaporation modes and internal flow fields. Then, the most observed dried patterns are presented and the mechanisms behind them are discussed. The review ends with the categorisation and exhaustive investigation of a wide range of factors affecting pattern formation.

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