Strain-induced matrix and droplets anisotropic deformation in liquid crystalline cellulose dispersed liquid crystal films

Filip, Daniela; Costa, I.; Figueirinhas, J. L.; Godinho, M. H.

doi:10.1163/156855406777408539

Cited by 4 publications

(3 citation statements)

References 22 publications

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“…It is also known that polymer chains align during the PDLC film stretching process and this promotes subtle changes in the liquid crystal alignment in the droplets as a result of the polymer alignment induced by the tensile strain [23]. Uniaxially stretched anisotropic phase separated polymer films were recently obtained from APC and their optical [24] and mechanical properties [25] have been studied.…”

Section: Introductionmentioning

confidence: 99%

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

Costa¹,

Almeida²,

Filip³

et al. 2006

Opto-Electronics Review

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In this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (∼60 μm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introducted in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.

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Section: Introductionmentioning

confidence: 99%

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

Costa¹,

Almeida²,

Filip³

et al. 2006

Opto-Electronics Review

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“…We relate our morphological observations with the surface alignment of the liquid crystal on the cellulosic matrix used in the method proposed in literature by Mori et al [9]. Previously [19], for the composite material with nematic droplets, we investigated the effects of the mechanical stretching on the liquid-crystalline polymer orientation surrounding droplets of low molecular weight liquid crystal. Applying elongation along the shear direction produces an increased alignment on the polymeric matrix while a deep molecular reorientation is taking place in perpendicular direction.…”

Section: Resultsmentioning

confidence: 96%

“…Normally, in this type of device, the cholesteric liquid crystal is confined in elliptical shaped droplets, dispersed in an isotropic matrix [17,18]. In this system we use freestanding films and the displayed colours are obtained as a function of the temperature and the mechanical strain imposed with the advantage of using a cellulose liquid-crystalline matrix which can allow for different optical behaviours depending on the direction of stretching [19].…”

Section: Introductionmentioning

confidence: 99%

Mechanically activated cholesteric polymer dispersed liquid crystals

Ferreira¹,

Almeida

Costa³

et al. 2007

Liquid Crystals

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In this paper we deal with a cellulose derivative cholesteric dispersed liquid crystal (CCDLC) with mechanically tuneable optical properties. The composite is formed with a matrix of acetoxypropylcellulose with embedded micrometric and submicrometric droplets of a cholesteric mixture. Polarizing optical microscopy and atomic force microscopy (AFM) measurements performed on the system are reported and it is shown that the wavelength of the reflected light can be changed by a temperature variation and it is also changeable through a mechanical deformation. The pitch of the deformed droplets can be measured from AFM photographs and compared with the wavelength reflected by the CCDLC composite material.

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

et al. 2009

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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).

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Strain-induced matrix and droplets anisotropic deformation in liquid crystalline cellulose dispersed liquid crystal films

Cited by 4 publications

References 22 publications

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

Mechanically activated cholesteric polymer dispersed liquid crystals

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

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