Deformation of isotropic and anisotropic liquid droplets dispersed in a cellulose liquid crystalline derivative

Abstract

In this work we study the strain-induced deformation of both isotropic and anisotropic liquid droplets dispersed in a liquid crystalline cellulose matrix. We have produced two types of acetoxypropylcellulose (APC) solid films one with a droplet dispersion of the commercial liquid crystal E7 from Merck, and another with a droplet dispersion of silicone oil. To produce the solid films a solution of APC (60%wt) in dimethylacetamide (DMAc) with 15%wt of either the commercial nematic liquid crystal E7 or the silicone oil was prepared. After homogenization the phase separated solutions were submitted to a shear flow mechanical field and casted onto a Teflon plate. We performed mechanical uniaxial stress-strain tests in the free standing films recording continuously the strain and images of the deformed droplets. The mechanical tests were carried out using a mini stress-strain testing machine apparatus and an Olympus optical polarizing microscope with an attached CCD camera. The images obtained from the mechanical tests for each value of the imposed strain were then analyzed comparing the images of deformed droplets with those of the undeformed ones, extracting in this way the local strain field. The droplet deformation data obtained show, as expected, significant differences in the local strain field when stretching parallel and perpendicular to the initial shear direction. No significant differences were found in the local strain fields obtained from the silicone oil and the E7 droplets films. The local strain fields variation with the imposed strain are compared with the predictions of the theory developed for nematic elastomers by Warner and Terentjev (Liquid crystal elastomers. Clarendon Oxford Press, Oxford, 2003).

Liquid crystalline cellulosic elastomers: free standing anisotropic films under stretching

“…Five independent successful measurements were performed with the longest dimension of the sample parallel or perpendicular to the casting shear direction. The features (not the values) of the stress/strain curves obtained were similar to those from other APC and HPC already reported in the literature (Borges et al 2001;Almeida et al 2009). …”

“…Their different preparation methods generate materials with different mechanical, optical, thermal and structural properties (Siqueira et al 2010). Because of this, cellulose derivative have been widely used as reinforcing agents in bio and nano composites (Liu et al 2011;Siqueira et al 2010), electro-optical displays materials (Godinho et al 1998;Almeida et al 2002;Costa et al 2007), local strain sensor (Almeida et al 2009) and biocarrier.…”

From Cellulosic Based Liquid Crystalline Sheared Solutions to 1D and 2D Soft Materials

“…The features (not the values) of the stress/strain curves obtained were similar to those from other APC and HPC already reported in the literature for isotropic and anisotropic cellulose derivatives [ 59 , 60 , 61 ].…”

Design, synthesis, and characterization of a combined main-chain/side-chain liquid-crystalline polymer based on ethyl cellulose

“…The liquid crystalline behavior of cellulose derivatives has since aroused much interest in the field of liquidcrystalline polymers (Bhadani and Gray 1983;Isogai et al 1984;Pawlowski et al 1987;Yamagishi et al 1988;Chen et al 1992;Jiang and Huang 1993;Shaikh et al 1999;Huang et al 2007;Godinho et al 2009;Almeida et al 2009). During recent decades, several studies reported the introduction of the bulky and rigid mesogenic substituents on the cellulose backbone as side groups (Terbojevich et al 1999;Wu et al 2002Wu et al , 2003Wu et al , 2004Granström et al 2009).…”