Self-Assembly and Morphological Patterns in Drying Droplets of Bio-colloids

Pal, Anusuya

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Self-Assembly and Morphological Patterns in Drying Droplets of Bio-colloids

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Understanding the drying evolution and morphological patterns of the colloidal fluids is very important and relevant to many industrial processes, pharmaceutical products, medical and forensic applications. This evolutionary process might look very straightforward; however, it is well accepted in the droplet community that the underlying physics is hard to comprehend. The final depositing patterns depend on several factors, including the solute particles' properties, nature of the solvent, geometry, substrate, environmental conditions, etc. The biological colloids (proteins, blood, etc.) attracted many researchers' significant attention due to the local self-assembling interactions between the constituent particles. This dissertation's principal thrust is to explore how and why different patterns are generated when these bio-colloids' native/initial properties vary as the droplets are dried under uniform conditions (surface, humidity, temperature, droplet diameter, etc.). In this work, the hierarchical complexity is systematically altered from one-component to multi-component systems. The findings of this dissertation reveal a unique drying pattern for (i) different globular proteins (the simplest hierarchical structure) with and without the bulk liquid crystals (LCs), and (ii) the whole human blood (the most complex hierarchical structure). These drying droplets' interfacial and self-assembling behavior are thoroughly examined using optical and scanning electron microscopic imaging, along with noble image processing protocols and contact angle measurements. Additionally, various statistical tests are employed to quantify a broad set of image data. The experimental work establishes the following outcomes- (i) the protein drying droplets confirms that the protein-protein interactions over the protein-substrate interactions play a substantial role in determining the morphological patterns, (ii) the LCs' texture are influenced by different protein droplets indicating that these bulk unaligned LCs are not always randomly distributed, and (iii) the experiments on the whole human blood approve that a concentration-driven phase transition may evolve in the bio-colloidal solution containing a large number of interacting components. Additionally, the effects of the saline water and the various substrate-controlled temperatures on the drying evolution and their resulting deposition patterns are examined in this dissertation. This work concludes that a series of simple experiments can track complex physical behavior unveiling new insights into the physics of pattern formation in a symmetric drying droplet.

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