Shape and structure recovery of an LCP droplet under a large step strain : observation and stress calculation

• Published in: Rheologica acta Vol. 46; no. 7; pp. 921 - 932
• Main Authors: MACAUBAS, Paulo H. P, KAWAMOTO, Hideo, TAKAHASHI, Masaoki, OKAMOTO, Kenzo, TAKIGAWA, Toshikazu
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.08.2007; Springer Nature B.V
• Subjects: Applied sciences; Cellulose and derivatives; Droplets; Exact sciences and technology; Liquid crystal polymers; Liquid crystals; Mathematical analysis; Natural polymers; Optical microscopy; Physicochemistry of polymers; Recovery; Shear strain; Texture; Viscosity; Dimethylsiloxane polymer; Polymer blends; Shear flow; Experimental study; Droplet; Heterogeneous mixture; Interface structure; Hydroxypropylcellulose Polymer blend Liquid crystalline polymer Poly-domain structure Interface tensor; Domain structure; Liquid crystal polymers; Banded structure; Cellulose derivatives; Cellulose(hydroxypropyl); Lyotropic state; Computing method; Cellulose ether; Recovery (properties)
• ISSN: 0035-4511; 1435-1528
• DOI: 10.1007/s00397-007-0175-x

Shape recovery of a droplet of liquid crystalline polymer (LCP) hydroxypropylcellulose in a matrix of poly(dimethyl siloxane) subjected to a step shear strain has been studied via optical microscopy. Just after application of a large strain, the LCP droplet shape is flat ellipsoid, and then the droplet takes cylindrical shape and band texture perpendicular to the flow direction appears. The band texture fades away before emergence of poly-domain structure. In the final process with the shape of spheroid, poly-domain structure recovers very slowly. Except for the final process, the shape change is identical with that of isotropic droplet at strains smaller than 3, when the LCP viscosity in Region II is taken as an equivalent viscosity for normalization. For a 20:80 blend, the excess relaxation modulus is calculated based on the Doi-Ohta theory, taking account of the distribution of droplet size and compared with experimental modulus data.