Molecular orientation, "Region I" shear thinning and the cholesteric phase in aqueous hydroxypropylcellulose under shear

Hongladarom, K.; Burghardt, Wesley R.

doi:10.1007/s003970050089

Cited by 32 publications

(23 citation statements)

References 27 publications

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“…According to Ref. 31 So, one can conclude that loading HPC/PEG with 5% of different clays in our case does not change the LC structure of the matrix.…”

Section: Optical Polarizing and Transmission Electron Microscopysupporting

confidence: 61%

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Morphology and rheology of composites based on anisotropic polymer matrix and different clays

Vasilyev

Makarova

Ребров

et al. 2011

J of Applied Polymer Sci

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Structure and rheological properties of hybrids with polymer matrix and layered silicates as filler were studied. Solution containing 60% wt of hydroxypropylcellulose (HPC) in oligomeric polyethyleneglycol (PEG) was used as a matrix. The peculiarity of this study is that the matrix depending on temperature can form different phase states including liquid-crystalline (LC). So, a possibility of coexistence and superposition of different ordered structures can be realized at different temperatures. Three different fillers were used: natural Namontmorillonite (MMT) and organoclays obtained by treating MMT with surfactants varying in polarity of their molecules. Depending on the type of clay, materials with different morphology can be obtained. X-ray data showed that PEG intercalates all types of clay used whereas penetration of HPC macromolecules into clay galleries during mixing does not occur. Clay modified with more polar surfactant should be treated as the most convenient material to be intercalated by PEG. Rheological studies (included steady-state and dynamic shear properties in a wide temperature range) demonstrate that composites are viscoplastic materials and the yield stress is observed already at 5% fillers loading. The level of the yield stress depends on the phase state of the matrix being induced by the superposition of structures formed by clay particles as well as by the LC phase (if it exists). The same conclusion can be made on the base of linear oscillatory measurements because the existence of the LC phase and/or the presence of filler lead to a pseudo solid-like behavior of a system as whole.

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“…According to Ref. 31 So, one can conclude that loading HPC/PEG with 5% of different clays in our case does not change the LC structure of the matrix.…”

Section: Optical Polarizing and Transmission Electron Microscopysupporting

confidence: 61%

“…According to Ref. 31, it is a reliable indicator of the cholesteric LC phase. Thin films (∼ 100 μm) of HPC/PEG in crossed polarizers are colored in gray gradations [Fig.…”

Section: Resultsmentioning

confidence: 99%

Morphology and rheology of composites based on anisotropic polymer matrix and different clays

Vasilyev

Makarova

Ребров

et al. 2011

J of Applied Polymer Sci

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“…The sample was sheared to a partially unwound state which then relaxed to a ground-state CLC configuration with a uniform helical axis perpendicular to the shear direction, as also observed in other studies of HPC-based LCs [21][22][23][24][25]. The equilibrium pitch p ≈ 350 nm [21][22][23][24][25] and "layer" periodicity [26] p/2 ≈ 175 nm allow for optical exploration of elastic distortions due to colloidal particles much larger than p/2. The LC cells were constructed from 170 μm thick glass plates optimized for high-resolution imaging and laser manipulation when using microscope objectives with high numerical aperture.…”

mentioning

confidence: 95%

Active Shape-Morphing Elastomeric Colloids in Short-Pitch Cholesteric Liquid Crystals

et al. 2013

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Active elastomeric liquid crystal particles with initial cylindrical shapes are obtained by means of soft lithography and polymerization in a strong magnetic field. Gold nanocrystals infiltrated into these particles mediate energy transfer from laser light to heat, so that the inherent coupling between the temperature-dependent order and shape allows for dynamic morphing of these particles and well-controlled stable shapes. Continuous changes of particle shapes are followed by their spontaneous realignment and transformations of director structures in the surrounding cholesteric host, as well as locomotion in the case of a nonreciprocal shape morphing. These findings bridge the fields of liquid crystal solids and active colloids, may enable shape-controlled self-assembly of adaptive composites and light-driven micromachines, and can be understood by employing simple symmetry considerations along with electrostatic analogies.

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“…The variation in shape and intensity of the reflection peak, as well as the position of the l max , in the reflection spectra of the sheared (E-CE)C/AA cholesteric LC solution, indicates that the cholesteric order with the planar texture is gradually regained during the relaxation. Hongladarom and Burghardt have also found that the selectively reflected light of an HPC cholesteric solution becomes more intense with increasing relaxation time by measuring the birefringence and flow visualization [6].…”

Section: Relaxation Behaviourmentioning

confidence: 97%

“…There are three representative deformations [1], i.e. splay-bend-twist deformation when the helix axis is along the shearing direction, splay-bend deformation when the helix axis is along the velocity gradient direction [2][3][4][5][6], and the twist deformation when the helix axis is along the vortex axis of the shearing [7,8]. Secondly, the rheological properties and deformation behaviour of the cholesteric phase are markedly changed depending on different shearing histories and rates [9].…”

Section: Introductionmentioning

confidence: 99%

Relaxation Processes in sheared films of ethyl-cyanoethyl cellulose cholesteric liquid crystalline solutions

Wang¹

2003

Liquid Crystals

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The relaxation processes in sheared films of ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) cholesteric liquid crystalline (LC) solutions were studied by polarizing optical microscopy (POM) and UV-Vis spectrophotometry. Under shearing normal to the helix axis and above the critical shear rate, the planar texture arrangement of the (E-CE)C/AA cholesteric LC solution was destroyed and transformed to the nematic phase. Observed by POM, the banded texture formed quickly following the cessation of the shear, but it was unstable and disappeared after several minutes. The reflection spectrum of the sheared (E-CE)C/AA cholesteric LC solution film was recorded as a function of relaxation time. It was found that the selective reflection property was lost under the shear, but the shape of the reflection spectrum recovered quickly with cessation of the shear, and the reflection peak in the spectrum became sharper with time, returning to the original form before shearing. A proposed model of the structural transformation during the relaxation was confirmed by additional optical measurement and transmission electron microscopy.

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Molecular orientation, "Region I" shear thinning and the cholesteric phase in aqueous hydroxypropylcellulose under shear

Cited by 32 publications

References 27 publications

Morphology and rheology of composites based on anisotropic polymer matrix and different clays

Morphology and rheology of composites based on anisotropic polymer matrix and different clays

Active Shape-Morphing Elastomeric Colloids in Short-Pitch Cholesteric Liquid Crystals

Relaxation Processes in sheared films of ethyl-cyanoethyl cellulose cholesteric liquid crystalline solutions

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