Observation of Large Nematic Domain in Suspension of Nano-Plate

 

Observation of large nematic domain in suspension of nano-plates

Zhengdong Cheng, Abhijeet Shinde

Concentration dependent liquid crystalline phase transitions in aqueous suspensions of plate-like nanoparticles are of interest to scientists^{1, 2} and engineers³. From metastable suspension, nematic tactoids nucleate, grow and settle due to gravity. As the time passes, gravity keeps compressing the nematic tactoids thus increasing their concentration.  tactoids with different orientations merge and develop a uniform domain spanned over the entire suspension except the top isotropic phase. Role of gravity in the formation of the large domain is investigated. It is also found that growth of the domain is faster in suspensions containing low aspect ratio (thickness/size) nano-plates. Alignment of nanoplates in the large domain is studied using polarized optical microscope, circular dichroism and synchrotron X-ray.

Figure. Cross polarizer observations of vertical tube containing suspension of nano-plates of same concentration but at different times. (a) Isotropic (dark) and Nematic (colorful) phases separation observed in suspension 1 day after its preparation. Different colors in nematic phase appear due to different orientations of nematic tactoids. (b) After 70 days, large domain developing near side wall and bottom of the tube. (c) Large domain with some defects developed in the suspension after 160 days. Directions of polarization in polarizer and analyzer are indicated with lines ‘P' and ‘A' respectively. Gravity is vertically downwards and is indicated by arrow ‘g'.

                                            

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