Abstract:
The time variation of the morphology, weight, temperature, and integral mechanical properties of drying drops of biological fluids are investigated with the aim of defining more exactly the mechanism of self-organization in the drops. Test fluids in experiments are distilled water, a physiological salt solution (0.9 wt.% NaCl), a solution of bovine serum albumin (BSA) in water, and a solution of BSA (7 wt.%) in the physiological solution. It is shown that the variation of the weight of the drying drops can be described by a sloping straight line with two slightly nonlinear portions at the beginning and at the end of the drying process. The earlier nonlinear portion correlates with a more rapid fall of the temperature, which slows down and stabilizes as a saturated vapor layer forms over the drop. The later nonlinear portion in the drop weight variation is associated with the retardation of water diffusion through the solidifying medium. The temperature variation of the drops is a superposition of endothermal (water evaporation) and exothermal (salt crystallization and gelation) phase transitions. Phase transitions may change the mechanical properties of the drying drops, which can be detected by the method of acoustic impedancemetry.
Fulltext:
PDF file (1124 kB)
