Meeting Abstract

P2.114  Saturday, Jan. 5  Coffee-ring formation by melanosomes with high aspect ratios SRINIVASAN, A.*; GATTO, R.; SHAWKEY, M.D.; University of Akron, Ohio as180@zips.uakron.edu

Small particles suspended in water sometimes aggregate around the edge of drying drops, forming so-called “coffee rings.” Recent research suggests that this phenomenon is limited to low aspect ratio particles. However, these results were obtained using a single type of synthetic material (polystyrene), and thus the observed limitation may be due to the constraints of the material itself rather than aspect ratio per se. Therefore, tests using additional materials with varying aspect ratios are needed. We performed dewetting experiments using droplets containing melanin-containing organelles (melanosomes) that vary extensively in aspect ratio. We used melanosomes from three avian species, pigeon Columba livia, red-winged blackbird Agelaius phoeniceus and peacock Pavo cristatus, with aspect ratios ~ 4, 5.5 and 7.2 respectively. In a series of experiments, we varied surface tension, pH level, speed of evaporation and concentration of melanosomes to determine under what conditions these particles may form rings. Contrary to previous experiments with high AR polystyrene particles, all three types of melanosomes formed rings when suspended in deionized water. Similar to previous experiments with low AR particles, ring assembly was inhibited by low pH and high surface tension of the suspension liquid, strengthened by high pH and low surface tension, and unaffected by melanosome concentration. These results demonstrate that ring formation is not always limited by aspect ratio and that some biological materials may have properties that make them particularly prone to self-assembly.