scholarly journals Effect of Shear Rate on the Orientation and Relaxation of a Vanillic Acid Based Liquid Crystalline Polymer

Polymers ◽  
2018 ◽  
Vol 10 (9) ◽  
pp. 935 ◽  
Author(s):  
Gijs de Kort ◽  
Nils Leoné ◽  
Eric Stellamanns ◽  
Dietmar Auhl ◽  
Carolus Wilsens ◽  
...  

In this study, we report on the visco-elastic response during start-up and cessation of shear of a novel bio-based liquid crystal polymer. The ensuing morphological changes are analyzed at different length scales by in-situ polarized optical microscopy and wide-angle X-ray diffraction. Upon inception of shear, the polydomain texture is initially stretched, at larger strain break up processes become increasingly important, and eventually a steady state texture is obtained. The shear stress response showed good coherence between optical and rheo-X-ray data. The evolution of the orientation parameter coincides with the evolution of the texture: the order parameter increases as the texture stretches, drops slightly in the break up regime, and reaches a constant value in the plateau regime. The relaxation of the shear stress and the polydomain texture showed two distinct processes with different timescales: The first is fast contraction of the stretched domain texture; the second is the slow coalescence of the polydomain texture. The timescale of the orientation parameter’s relaxation matched with that of the slow coalescence process. All processes were found to scale with shear rate in the tested regime. These observations can have far reaching implications for the processing of liquid crystal polymers as they indicate that increased shear rates during processing can correspond to an increased relaxation rate of the orientation parameter and, therefore, a decrease in anisotropy and material properties after cooling.

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1134
Author(s):  
Bo Seok Song ◽  
Jun Young Lee ◽  
Sun Hwa Jang ◽  
Wan-Gyu Hahm

High-speed melt spinning of thermotropic liquid crystalline polymer (TLCP) resin composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-napthoic acid (HNA) monomers in a molar ratio of 73/27 was conducted to investigate the characteristic structure development of the fibers under industrial spinning conditions, and the obtained as-spun TLCP fibers were analyzed in detail. The tensile strength and modulus of the fibers increased with shear rate in nozzle hole, draft in spin-line and spinning temperature and exhibited the high values of approximately 1.1 and 63 GPa, respectively, comparable to those of industrial as-spun TLCP fibers, at a shear rate of 70,000 s−1 and a draft of 25. X-ray diffraction demonstrated that the mechanical properties of the fibers increased with the crystalline orientation factor (fc) and the fractions of highly oriented crystalline and non-crystalline anisotropic phases. The results of structure analysis indicated that a characteristic skin–core structure developed at high drafts (i.e., spinning velocity) and low spinning temperatures, which contributed to weakening the mechanical properties of the TLCP fibers. It is supposed that this heterogeneous structure in the cross-section of the fibers was induced by differences in the cooling rates of the skin and core of the fiber in the spin-line.


2002 ◽  
Vol 80 (8) ◽  
pp. 1162-1165 ◽  
Author(s):  
B Henrissat ◽  
G K Hamer ◽  
M G Taylor ◽  
R H Marchessault

A series of dodecyl 1-thio-β-D-glycosides has been synthesized and characterized (DSC, NMR, CP MAS, X-ray diffraction) as possible new marking materials with liquid-crystalline properties. These compounds undergo solid to liquid crystal phase transitions at various temperatures, which depend on the nature of the carbohydrate part of the structure. Their liquid-crystalline phases show extreme shear thinning behaviour.Key words: liquid crystal, powder X-ray diffraction, phase transition, thioglycoside, solid-state NMR, marking material


1990 ◽  
Vol 45 (7) ◽  
pp. 1084-1090 ◽  
Author(s):  
Klaus Praefcke ◽  
Bernd Kohne ◽  
Andreas Eckert ◽  
Joachim Hempel

Six S,S-dialkyl acetals 2a-f of inosose (1), tripodal in structure, have been synthesized, characterized and investigated by optical microscopy and differential scanning calorimetry (d.s.c.). The four S,S-acetals 2c-f with sufficiently long alkyl chains are thermotropic liquid crystalline; 2 e and 2 f are even dithermomesomorphic. Each of these four inosose derivatives 2c-f exhibits monotropically a most likely cubic mesophase (MI); in addition 2e and 2f show enantiotropically a hexagonal mesophase (Hx) with a non-covalent, supramolecular H-bridge architecture. Whereas the nature of the optically isotropic mesophase MI needs further clarification the stable high temperature mesophase Hx of 2 e and 2 f has been established by a miscibility test using a sugar S,S-dialkyl acetal also tripodal in structure and with a Hx phase proved by X-ray diffraction, but in contrast to 2 with an acyclic hydrophilic part. Similarities of structural features between the Hx-phases of 2e and 2f as well as of other thermotropic and lyotropic liquid crystal systems are discussed briefly.


Crystals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 652
Author(s):  
Rony Saha ◽  
Chenrun Feng ◽  
Alexey Eremin ◽  
Antal Jákli

We present small-angle X-ray scattering, polarized optical microscopy and electric current measurements of a sulfur-containing bent-core liquid crystal material for characterization of the layer and director structures, thermally and electrically driven transitions between antiferroelectric and ferroelectric structures and switching properties. It was found that the material has polarization-modulated homochiral synclinic ferroelectric (SmCsPFmod), homochiral anticlinic antiferroelectric (SmCaPA) and racemic synclininc antiferroelectric (SmCsPA) structures that can be reversibly switched between each other either thermally and/or electrically. High switching polarization combined with softness of the liquid crystalline structure makes this compound a good candidate for applications in high-power capacitors and electrocaloric devices.


2019 ◽  
Vol 43 (1-2) ◽  
pp. 67-77 ◽  
Author(s):  
Adil A Awad ◽  
Al-Ameen Bariz OmarAli ◽  
Ahmed Jasim M Al-Karawi ◽  
Zyad Hussein J Al-Qaisi ◽  
Samer Ghanim Majeed

{1-[4-( n-Alkoxy)]-2-(4’-decyloxy)benzylidene}hydrazines ( n-alkoxy = O(CH2) nH, n = 1–9, 12, 16 or 18), an asymmetrical series of 1,2-disubstituted hydrazines, were prepared in a simple two-step procedure as a part of our continuing work in evaluating hydrophobic azine compounds as photoluminescent liquid crystalline materials. The compounds were characterized spectroscopically and their liquid crystalline behaviour and luminescent properties were evaluated using polarized light optical microscopy, differential scanning calorimetry and X-ray powder diffraction techniques. The studies revealed that all of these compounds are liquid crystalline materials exhibiting photoluminescent properties in the crystalline and liquid crystal states.


2001 ◽  
Vol 11 (4) ◽  
pp. 188-196 ◽  
Author(s):  
Katsuhiko Araki ◽  
Takeshi Kitano ◽  
Berenika Hausnerova

Abstract The rheological properties of thermotropic liquid crystalline polymer (LCP) and its carbon fiber (CF) and carbon black (CB) filled composites in molten state were measured using a cone-plate rheometer. The measurements of the CF/LCP and CB/LCP melts were performed with carbon fiber contents of 5, 10 and 20 wt %, and carbon black contents of 1.5, 3, 5, 10 and 20 wt %. As expected, steady shear viscosity of the LCP, CF/LCP and CB/LCP melts in a low shear rate region (0.1 to 1 s-1) decreased with an increase of temperature and increased with rise of filler content. In shear rate region of 1 to 50 s-1, the LCP melt showed a unique viscosity behaviour with maximum and minimum values. The CF/LCP and CB/LCP melts showed disappearance of such a unique viscosity behaviour with an increase in the CF (CB) content and an increase of temperature. CB filler had a more pronounced effect on the disappearance of the unique viscosity behaviour in comparison with CF. Regarding apparent yield stress, the CF/LCP melts gave the same value as pure LCP, the CB/LCP melts showed an increase of yield with a rise of the filler content. In addition, the first normal stress difference of the LCP and CF/LCP melts are smaller than yield stress values, although the rate of increase with shear rate is higher in case of normal stress difference than in case of yield. The results of the dynamic shear oscillatory flow measurements of CF and CB based compounds at 300˚C showed that both, the storage and loss moduli are more affected by carbon black filler. Complex viscosity values of the LCP and CF/LCP melts showed no such unique complex flow pattern as observed in the case of steady shear viscosity.


Author(s):  
Morgan Chen ◽  
Nicole Evers ◽  
Chris Kapusta ◽  
Joe Iannotti ◽  
Anh-Vu Pham ◽  
...  

We present the development of a hermetic shield packaging enclosure for RF microelectromechanical system switches (MEMS) using Liquid Crystal Polymer (LCP). A cavity formed in LCP has been laminated, at low temperature, onto a Si MEMS switch to create a hermetically sealed package. The hermetically sealed enclosure is a stack-up layer of the multi-layer organic chip-on-flex system-on-a-package (SOP). The entire SOP hermetically sealed package has a total insertion loss of ∼0.5 dB at X-band. E595 outgas tests demonstrate that the LCP package is reliable and hermetically protects the MEMS switch.


e-Polymers ◽  
2006 ◽  
Vol 6 (1) ◽  
Author(s):  
Noelle Wrubbel ◽  
Helmut Ritter ◽  
Knud Reuter ◽  
Alexander Karbach ◽  
Doris Drechsler

Abstract3,4-Ethylenedioxythiophene derivatives with aromatic, in most cases mesogenic, side groups were synthesized and their liquid crystal behaviour was characterized. These monomers were polymerized oxidatively to charged, electrically conductive polythiophenes. X-ray and atomic force microscopy studies were performed. Films of theses polythiophenes achieved via in situ polymerization were prone to a significant increase of the conductivity by annealing.


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