Hydrogen bonded liquid crystals thesis

Accordingly, preferred species for use as the hydrogen donor mesogen are those containing carboxylic acids, phenols, amides, and alcohols.

US5139696A - Hydrogen-bonded liquid crystal complexes - Google Patents

The other reason for the deviation between the theoretical and experimental values may be due to electron cloud of non-polar solvent benzene affecting the dipole moment value of the solute system in experimental case [11, 25, and 26]. In each of these cases, the lowering of the melting point is merely an application of Raoult's law and the "stabilization" only results from a depression of the melting point; no intermolecular forces such as hydrogen-bonding are involved.

The present trend is of liquid mixtures leading to formation of hydrogen bonding in the system due to solute-solvent interactions. Accordingly, it is an object of the present invention to develop new mesogenic materials which have increased mesophase to isotropic transition temperatures.

We find that intermolecular contrast appears only when the short-range tip-sample force gradient, ; any long-ranged attractive electrostatic contribution to the maxima observed at the expected hydrogen-bond positions is not detectable within the accuracy of our measurements.

It is a further object to develop new mesogenic materials having increased mesophase stability as compared to any of the components utilized to produce them. These and still further objects will be apparent from the ensuing description of the invention.

The strength of a hydrogen bond is related to the particular atoms to which both of the hydrogen bond-forming atoms is attached. Basic hydrolysis of 13 afforded macromolecule 14, which precipitated upon neutralization of the basic cleavage medium. By starting with mesogens having the appropriate hydrogen bond-forming structures, a hydrogen bond may be formed between the two different mesogens which bond will be essentially along the long axes of each mesogen to produce a new mesogenic complex having an extended mesophase and an elevated nematic to isotropic transition temperature.

The amount of literature on hydrogen bonding is, unsurprisingly, voluminous, given its central importance in so many scientific fields, including biochemistry and biomaterials 6organic synthesis 7and, of particular relevance to this paper, crystal engineering and self-assembly at surfaces 8.

The general, common molecular feature of such compounds is an elongated, narrow molecular framework, which usually is depicted as a rod or cigar-shaped entity. Conclusions The synthesis of three new main chain noncentrosymmetric hydrogen bonded macromolecules incorporating alkanol, alkanoic acid, and aniline donors is described.

One of the physical parameters used for conformational analysis of any resultant structure is the net dipole moment [6]. The liquid mixtures in the present study are useful for hydrogen bonding formation with liquid crystals [12] which eventually affect the dipole moment and relaxation time.

It should be noted that Schroeder does not even consider mixtures of different compounds, let alone suggest an interaction therebetween. The resultant new mesogenic complexes so produced exhibit mesogenic behavior not only over an expanded temperature range than both of the parent compounds, but also at a higher temperature than for either compound individually.

Relatively weak intermolecular hydrogen bonding is present in macromolecules 10, 11, and Hamiltonian quantum mechanical calculations such as AM1, PM3 and MNDO optimized converged geometry operation is performed by using Spartan Modeling software for both pure and binary systems of alkyl p-hydroxy benzoates and isopropanol.

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The average relaxation times are calculated from their respective Cole-Cole [23] plots. The excess dipole moment value is a qualitative index for the presence of a hydrogen bond between nHB and IPA.

Selected papers on this subject: Macromolecules 11 and 14 both possess enantiotropic crystal crystal transitions in addition to melting and crystallization temperatures, while macromolecule 10 only has melting and crystallization phase transitions. The theoretical values of dipole moments for individual compounds and solute mixtures are given in tables 2 and 3.

In STHM, the experimental observable is, however, the junction conductance and, particularly for small tip-sample separations, there is a complex relationship between this observable and the tip-sample force. Siva Sankara Reddy, K. Dielectric dispersion studies of polar liquids such as alcohols, benzoates and their binary mixtures were carried out to determine the nature of interaction that exist between the molecules due to hydrogen bonding dipole moment and the relaxation behavior phenomena.

Intriguingly, and before the publication of the DFM results, it had been discovered that the very high spatial resolution attained in DFM could also be achieved in STM by similar functionalisation of the tip and operation at small tip-sample separations 151617Wiegel, Supramolecular main chain liquid crystalline polymers and networks with competitive hydrogen bonding: The extent of the dissociation will determine the amount of mesogenic complex which can be formed by hydrogen bonding.

Nonetheless, images of this type are routinely acquired owing, we believe, to the ease with which NTCDI molecules are transferred from the surface to the tip apex.

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Interestingly, the dipole moments show alternation along the series with even numbers having higher dipole moments than the odd neighbours. More particularly, it relates to novel nematic and smectic mesogens which are produced by the hydrogen bonding of two different mesogens essentially along the long axes of the mesogenic portions of each.

Search articles by author. Synthesis of Macromolecules The synthesis of macromolecule 10 is shown in Scheme 1. The forces responsible for such interactions cannot be studied when such molecules are isolated.

A hydrogen bond is considered sufficiently along the long axes to be within the scope of the present invention if the resultant new mesogenic complex exhibits a mesophase to isotropic transition temperature which is higher than that of both of the starting mesogens Preferably the hydrogen bond is formed between terminal hydrogen donor and acceptor groups so as to produce the longest possible new mesogenic complex.

Examples of suitable families of starting mesogens include, but are not limited to, Schiff bases, diazo compounds, azoxy compounds, stilbenes, tolans, esters, biphenyls, and terphenyls. Fretchet, Supramolecular liquid crystalline complexes exhibiting room temperature mesophases and electro-optic effects.

The system obeys nearly Debye and non-Debye type relaxations for the low and high frequency regions. Wolf, Synthesis and characterization of noncentrosymmetric Hydrogen bonded liquid crystalline polymers [Ph.

Mapping the force field of a hydrogen-bonded assembly

Of course, the extent of dissociation must be limited by the stochiometry of the mesogens. Ph.D. Thesis, University of Ottawa () Hydrogen‐bonded liquid crystals built from hydrogen‐bonding donors and acceptors Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridyl moieties.

Department of Chemistry

Crystals liq. Crystals, [Taylor & Francis Online]. Halogen-bonded Liquid Crystals and Co-crystals: non-mesomorphic precursors bind to one another via a halogen bond between an electron-poor iodide and an electron-rich nitrogen.

The resulting complexes are found to have liquid crystal properties. Depending upon the length of the chain, type of bonding and the functional groups present in the hydrogen bonded liquid crystals exhibit a rich variety of phase polymorphism and hence the physical properties of the hydrogen bonded liquid crystals are correlated with their molecular structure.

The thermotropic hydrogen-bonded liquid crystal 4-n-hexylbenzoicacid (6BA), in which 6BA molecules form a cyclic dimer (6BA) 2 by two hydrogen bonds between carboxylic acids (Chart 1a), exhibits a nematic liquid crystal phase in the temperature range between.

Hydrogen-bonded liquid crystals. Novel mesogens incorporating nonmesogenic bipyridyl compounds through complexation between hydrogen-bond donor and acceptor moieties. Takashi Kato, Jean M. J. Frechet, Paul G. Wilson, Takeshi Saito, Toshiyuki Uryu, Akira Fujishima, Chihiro Jin. work on the structural characterization of hydrogen-bonded co-crystals which exhibit liquid phases, we have prepared compounds of 4-alkoxybenzoic acid–1,2-bis(pyridinyl).

Hydrogen bonded liquid crystals thesis
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