A Comparative Study of the Phase Separation of a Nematic Liquid Crystal in the Self-assembling Drying Protein Drops
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.209
A Comparative Study of the Phase Separation of a Nematic Liquid Crystal in the Self-assembling Drying Protein Drops Anusuya Pal1, Amalesh Gope2, and Germano S. Iannacchione1 1 Order-Disorder Phenomena Laboratory, Department of Physics, Worcester Polytechnic Institute, Worcester, MA, 01609, USA
2
Department of English and Foreign Languages, Tezpur University, Tezpur, Assam, 784028, India
ABSTRACT
The drying process, self-assembly of the proteins and the phase separation of a thermotropic liquid crystal (LC) from an initial aqueous solution represent a rich area of study. A focus of this work is to compare the behavior of two different proteins, bovine serum albumin [BSA] and lysozyme [Lys] in the ternary system through optical microscopy. During the drying process, the intensity profile shows three regimes in the presence of LC whereas no intensity variation is observed in its absence in both protein drops. The striking outcome is the presence of an umbilical defect of [+1] strength in every domain near the edge of BSA drop, whereas, each domain has a central dark region surrounded by a bright region in the dried Lys drop. Finally, the crack spacing in the dried Lys drop is reduced in the presence of LC whereas, no significant difference is found in the dried BSA drop.
INTRODUCTION Pattern formation in drying drops has the potential in many technological applications including printing, microfluidics, medical diagnostics and forensics [1]. To date, majority of the drying experiments explored the drying process of various polymers, nanoparticles, proteins, biological fluid, etc. [2,3]. Of late, the findings of drying droplets attracted the attention of the liquid crystal (LC) communities. For example, in a recent study, a lyotropic LC (a dye Sunset Yellow FCF or SSY) is examined in which distinct LC phases are observed during the drying process [4]. In another study, the self-assembly of a thermotropic LC, i.e. 5CB (4-cyano-4'-pentyl-
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biphenyl) is studied as a drying drop in a surfactant-stabilized system. And, the radial and bipolar orientations of 5CB are observed when transiting from chaotic to organized patterns [5]. This paper will report the drying process of the ternary system at the morphological level. The samples were prepared using two well-studied, water soluble proteins, bovine serum albumin (BSA) and lysozyme (Lys), dissolved in de-ionized water with a small fraction of a thermotropic, nematic LC. The LC (5CB) is partially soluble in water but incompatible with proteins when water is absent. The core findings of this paper include a temporal study that provides a qualitative description of BSA particles and the LC droplets during the drying process. The intensity profile of BSA-LC and Lys
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