Nematic Property Research Articles

Carboxylated cellulose nanocrystals with chiral nematic property from cotton by dicarboxylic acid hydrolysis

Carboxylated cellulose nanocrystals (CNCs) were produced from cotton linter using a mixture of a dicarboxylic acid (maleic acid or succinic acid) and its corresponding anhydride with or without catalyst in acetic acid as solvent. The low solubilities of these dicarboxylic acids can ease chemical recovery and decrease environmental impact (especailly maleic acid is a U.S. FDA approved indirect food additive (21CFR175-177)) and capital costs compared with the conventional concentrated sulfuric acid hydrolysis for producing CNCs. The dicarboxylic-acid-produced CNCs (DC-CNCs) contained surface carboxyl groups of approximately 0.5 mmol/g, with ranges of dimensions of 50–150 nm in diameter and 50–700 nm in length. Birefringence was observed in the DC-CNC suspensions above critical concentrations. However, fingerprint texture was only observed in the DC-CNC suspensions produced with catalyst p-toluenesulfonic acid. Scanning electron microscopy images of the cross section of DC-CNC films revealed a periodic ordered multilayer structure. DC-CNCs were also produced using recycled dicarboxylic acids.

Mechanical forces in cell monolayers.

In various physiological processes, the cell collective is organized in a monolayer, such as seen in a simple epithelium. The advances in the understanding of mechanical behavior of the monolayer and its underlying cellular and molecular mechanisms will help to elucidate the properties of cell collectives. In this Review, we discuss recent in vitro studies on monolayer mechanics and their implications on collective dynamics, regulation of monolayer mechanics by physical confinement and geometrical cues and the effect of tissue mechanics on biological processes, such as cell division and extrusion. In particular, we focus on the active nematic property of cell monolayers and the emerging approach to view biological systems in the light of liquid crystal theory. We also highlight the mechanosensing and mechanotransduction mechanisms at the sub-cellular and molecular level that are mediated by the contractile actomyosin cytoskeleton and cell-cell adhesion proteins, such as E-cadherin and α-catenin. To conclude, we argue that, in order to have a holistic understanding of the cellular response to biophysical environments, interdisciplinary approaches and multiple techniques - from large-scale traction force measurements to molecular force protein sensors - must be employed.

Mesomorphism dependence on molecular rigidity and flexibility

A novel homologous series of liquid crystalline properties is synthesized and studied with a view to understand the effect of molecular structure on its thermotropic properties. Novel homologous series consisted of thirteen homologs. All the homologs are enantiotropically smectogenic with absence of nematic property even in the monotropic condition. Textures of the homologs as observed through an optical hot stage polarizing microscopy. The mesophase temperature range vary minimum from 6.0°C to a maximum 37.0°C at the methyloxy and propyloxy derivatives of a series respectively with its thermal stability (Sm–I) 127.0°C. Transition curves of a phase diagram behaved in normal manner. Odd–even effect is observed for Sm–I transition curve.

Molecular structural flexibility dependence of mesomorphism through ortho-substituted bromo group

ABSTRACTA novel series of liquid crystal (LC) materials of Schiff's bases viz. RO-C6H4‒CH˭CH‒COO‒C6H4‒N˭CH‒C6H4‒Br (ortho) is synthesized and studied with a views to understanding and establishing the effect of molecular structure on liquid crystal properties and to provide novel thermotropic LC material to the scientific and technological community of research interest. The novel series consists of thirteen members (C1 to C8, C10, C12, C14, C16 & C18). All the members of a series are enantiotropic liquid crystals. Smectic (C10‒C18) and nematic (C1‒C18) property commence from C10 and C1 homologue respectively. Transition temperatures and the textures of homologues were determined using a polarizing optical microscope (POM) equipped with a heating stage. Transition curves Cr-M, Sm-N and N-I of a phase diagram behaved in normal manner. Odd–even effect is absent for Sm-N transition curve, but it is present for N-I curve. Sm-N transition curve is extrapolated to C8 and C6 nonsmectogenic homologues to determine and predict their latent ability for exhibition of smectic property. Analytical and spectral data confirms the molecular structures of homologues. Thermal stabilities of smectic and nematic are 85.4°C and 130.1°C °C whose upper and lower total mesophase length vary from 58.0°C to 06.0°C at the C10 and C1 = C5 = C6 homologue, respectively. Textures of nematic phase are threaded or Schlieren and smectic phase are of type A or C. LC properties of present novel series are compared with structurally series known series. Thus, present novel series is predominantly nematogenic and partly smectogenic with middle ordered melting type and considerable total mesophase length range.

Mesomorphism Dependence on Cis-Trans Configuration and Varying Terminal/Lateral Group

A chalconyl trans vinyl ester homologous series of thermotropic liquid crystals RO-C6H4-CH=CH-COO-C6H4-CH=CH-CO-C6H3 (OCH3)2 meta-para is synthesized and studied with a view to understand and establish the relation between molecular structure and mesomorphism or mesomorphic behaviors. Novel homologous series consists of thirteen homologues (C1 to C18). First five (C1 to C5) homologues are nonmesogenic. Rest of the homologues (C6 to C18) homologues is mesogenic. Monotropically smectogenic character appears from C6 to C10 homologue and C12 to C18 homologues are enantiotropically smectogenic. Nematogenic property is totally absent throughout a series. Textures of smectic phase are of the type smectic A or C. Transition curves of a phase diagram behaved in normal manner. Analytical, spectral and thermal data supports the molecular structures of homologues. Odd-even effect is observed for Sm-I/I-Sm transition curve. Thermal stability for smectic is 93.7 °C and the mesomorphic phase lengths from enantiotropic homologues for smectic from minimum to maximum is 6.0 °C to 28.0 °C at the C12 and C18 homologue respectively. Series is smectogenic without exhibition of nematic property. The group efficiency order on the basis of thermal stability is derived; from comparative study of present series and analogous series.

Mesomorphism Dependence on Cis-Trans Configuration and Varying Terminal/Lateral Group

A chalconyl trans vinyl ester homologous series of thermotropic liquid crystals RO-C6H4-CH=CH-COO-C6H4-CH=CH-CO-C6H3(OCH3)2meta-para is synthesized and studied with a view to understand and establish the relation between molecular structure and mesomorphism or mesomorphic behaviors. Novel homologous series consists of thirteen homologues (C1to C18). First five (C1to C5) homologues are nonmesogenic. Rest of the homologues (C6to C18) homologues is mesogenic. Monotropically smectogenic character appears from C6to C10homologue and C12to C18homologues are enantiotropically smectogenic. Nematogenic property is totally absent throughout a series. Textures of smectic phase are of the type smectic A or C. Transition curves of a phase diagram behaved in normal manner. Analytical, spectral and thermal data supports the molecular structures of homologues. Odd-even effect is observed for Sm-I/I-Sm transition curve. Thermal stability for smectic is 93.7 °C and the mesomorphic phase lengths from enantiotropic homologues for smectic from minimum to maximum is 6.0 °C to 28.0 °C at the C12and C18homologue respectively. Series is smectogenic without exhibition of nematic property. The group efficiency order on the basis of thermal stability is derived; from comparative study of present series and analogous series.

Dependence of mesomorphism on tail group in combination with a lateral methoxy group

ABSTRACTA novel homologous series of esters with a lateral methoxy group and terminal n-heptyl cinnamate group was synthesized and studied to investigate mesomorphic behavior in relation to structure. The twelve membered series consists of methoxy to pentyloxy derivatives that are nonmesomorphic and the rest of the homologs as smectegenically mesomorphic, including C6 and C7 monotropic smectic and C8 to C16 enantiotropic smectic without exhibition of any nematic property. The textures of smectogenic mesophases are focal conic fan shaped or batonates of the type smectic-A or Schlieren-C. An odd-even effect is exhibited by the Sm–I transition curve in the phase diagram. The Cr–Sm and Sm-I transition curves behave in a normal manner. Transition temperatures and textures were determined on an optical polarizing microscope, equipped with a heating stage. Some representative members were characterized by IR, H1NMR, mass spectra, and elemental analysis. Analytical data support the molecular structures of the homologs. Mesomorphic properties of the present novel series are compared with the structurally similar known series. The present series is smectogenic only, whose thermal average stability is 89.8°C and of a middle-ordered melting type.

First report of charge-transfer induced heat-set hydrogel. Structural insights and remarkable properties.

The remarkable ability of a charge-transfer (CT) complex prepared from a pyrene-based donor (Py-D) and a naphthalenediimide-based acceptor (NDI-A) led to the formation of a deep-violet in color, transparent hydrogel at room temperature (RT-gel). Simultaneously, the RT-gel was diluted beyond its critical gelator concentration (CGC) to obtain a transparent sol. Very interestingly, the resultant sol, on heating above 70 °C, transformed into a heat-set gel instantaneously with a hitherto unknown CGC value. Detailed studies revealed the smaller globular aggregates of the RT-gels fuse to form giant globules upon heating, which, in turn, resulted in heat-set gelation through further aggregation. The thermoresponsive property of Py-D alone and 1 : 1 Py-D : NDI-A CT complex was investigated in detail which revealed the hydrophobic collapse of the oxyethylene chains of the CT complex upon heating was mainly responsible for heat-set gelation. Thixotropy, injectability, as well as stimuli responsiveness of the RT-gels were also addressed. In contrast, heat-set gel did not show thixotropic behavior. The X-ray diffraction (XRD) patterns of the xerogel depicted lamellar packing of the CT stacks in the gel phase. Single crystal XRD studies further evidenced the 1 : 1 mixed CT stack formation in the lamellae and also ruled out orthogonal hydrogen bonding possibilities among the hydrazide unit in the CT gel although such interaction was observed in a single crystal of NDI-A alone. In addition, a Ag(+)-ion triggered metallogelation of NDI-A and nematic liquid-crystalline property of Py-D were also observed.

Dependence of Mesomorphism on Molecular Rigidity

A novel smectogenic homologous series of twelve homologues synthesized and studied with a view to understand and establish the effect of molecular structure on liquid crystal properties (LC) and LC behaviors of thermotropic homologues. First (C1) to last (C16) member of a series exhibited only enantiotropically smectogenic property without showing nematic property which is absent even in the monotropic condition. Transition and melting temperature including textures of homologues were determined by an optical polarizing microscopy equipped with a heating stage, texture of a smectic phase are of the type A or C. Smectogenic phase length ranger between 5.1°C to 22.6°C. Smectic-Isotropic (Sm-I) thermal stability is 153.55°C. Analytical, spectral and thermal data supported molecular structures of homologues. LC behaviors of present novel series are compared with the structurally similar homologous series. Transition curves viz. Cr-Sm and Sm-I transition curves of a phase diagram behaved in normal manner.

Dependence of Mesomorphism on Molecular Rigidity

A novel smectogenic homologous series of twelve homologues synthesized and studied with a view to understand and establish the effect of molecular structure on liquid crystal properties (LC) and LC behaviors of thermotropic homologues. First (C1) to last (C16) member of a series exhibited only enantiotropically smectogenic property without showing nematic property which is absent even in the monotropic condition. Transition and melting temperature including textures of homologues were determined by an optical polarizing microscopy equipped with a heating stage, texture of a smectic phase are of the type A or C. Smectogenic phase length ranger between 5.1°C to 22.6°C. Smectic-Isotropic (Sm-I) thermal stability is 153.55°C. Analytical, spectral and thermal data supported molecular structures of homologues. LC behaviors of present novel series are compared with the structurally similar homologous series. Transition curves viz. Cr-Sm and Sm-I transition curves of a phase diagram behaved in normal manner.

Synthesis and Study of Novel Liquid Crystalline Homologous Series: 4-(4′-n-Alkoxy Benzoyloxy)-3-Methoxy Phenyl azo-3″, 4″ Dichlorobenzenes

The synthesis and mesomorphic properties of a new homologous series of azomesogens, 4-(4′-n-alkoxy benzoyloxy)-3-methoxy phenyl azo-3″,4″ dichlorobenzene is detailed. The first four members of the series are nonmesomorphic, and the other eight members are smectogenic in character. The smectic mesophase, which is exhibited montropically, commences from the pentyl to the hexadecyl derivatives. The usual odd-even effect is observed in the isotropic-smectic transition curve. The isotropic-smectic transition curve behaves in a normal manner. The smectic mesophase shows a focal conic fan shaped texture of the smectic A type. An important feature of the series is the absence of the nematic property. The thermal stability and mesomorphic characteristic are compared with two structurally similar homologous series.

Mesomorphic behaviour of 4-benzoyloxybenzoic acid and its binary mixture with 4-acetoxybenzoic acid

The nematic liquid crystalline property of 4-benzoyloxybenzoic acid (BBA) was observed by polarizing microscopy and X-ray diffraction. The structure of the hydrogen-bonded BBA dimer was verified by FT-IR, and the axial ratio (l / d) of the rod-like molecule was calculated to be 5.8, which is large enough to exhibit a liquid crystalline phase. The mesophase was stable at 240 C. At higher temperatures, for example, 270 C, the trans -esterification side reaction occurred. The binary phase diagram of BBA and 4-acetoxybenzoic acid shows the eutectic temperature at 175 C.

Observation of Phase Separation Process in the Binary Mixture of Nematic and Isotropic Polymers

We investigated the phase separation process in the binary mixture of the semi-rigid thermotropic liquid crystalline polymer and the flexible polymer. By raising temperature, an initially homogeneous mixture undergoes the phase separation. Utilizing the nematic property of one component, we were able to observe this segregation process by means of a polarizing microscope under crossed polarizers. We found a new mechanism to explain the coalescence of droplets in the latest stage.

Derivation and Application of an Algorithm for the Numerical Calculation of the Local Orientation of Nematic Liquid Crystals

Abstract Starting from a relaxation equation for the alignment tensor, an algorithm is derived which allows the numerical calculation of the dynamic and static behavior of the director field n with the correct nematic symmetry property, where n and - n are equivalent. As a first application, a two-dimensional problem is treated where the typical nematic defects with half-integer winding numbers only occur when the algorithm with the correct nematic symmetry property is used. Furthermore, the method is applied to the static and dynamic behavior of a Frederiks cell with strong and weak anchoring.