Experimental investigation of deposition patterns of citric acid modified magnetic nanofluids droplet affected by substrate temperatures.

Over the past decades, complex deposition patterns after the evaporation of particle-laden droplets spark intense interest in interpreting the formation of deposition patterns due to their numerous applications in biomedicine, ink-jet printing, biopsy, etc. This work experimentally studies the formation of deposition patterns during evaporation of the magnetic nanofluid (MNF) droplet stands on a smooth glass/hydrophobic surface at different substrate temperatures. A CCD camera mounted on the microscopy is used to capture the process of droplet evaporation. An infrared camera is applied to quantify the temperature distribution along the vapour-liquid interface of the evaporating droplet. Additionally, 3 μm sized microbeads are applied to track the flow motion of the solute inside for different temperatures. The evaporation of sessile droplets has been conducted by controlling substrate temperature, which ranges from 10 °C to 70 °C. The experimental results show that there are three distinct patterns with the increasing temperature, namely a uniform pattern, a typical 'coffee ring' pattern, and a dual ring pattern. The experimental results show that Marangoni flow becomes essential for the formation of a secondary ring pattern with increasing substrate temperatures. This study shows that controlling substrate temperature is an efficient and simple method to control the formation of the sessile droplet. [ABSTRACT FROM AUTHOR]