Gurumurthy Hegde

Periodic anchoring condition for alignment of a short pitch cholesteric liquid crystal in uniform lying helix texture

Due to flexoelectricity, a cholesteric liquid crystal unidirectionally aligned in a sandwich cell, with its helix lying parallel to the confining cell substrates, exhibit a flexoelectro-optic response when subjected to an electric field applied perpendicular to the helix axis. The clarity of the flexoelectro-optic response is dependent on the quality of the uniformly lying helix texture of the cholesteric which often is difficult to achieve. Herein, a method for alignment of a short pitch cholesteric in such a texture by means of a periodic surface anchoring condition with periodicity matching that of the cholesteric liquid crystal is described.

Synthesis and photoswitching properties of bent-shaped liquid crystals containing azobenzene monomers

Three novel bent-shaped monomers, namely 1,3-phenylene bis-{4-[4-(n-allyloxyalkyloxy)phenylazo]benzoate} 5a–c, containing azobenzene as side arms, resorcinol as central units and terminal double bonds as polymerisable functional groups were synthesised and characterised. The mesophase behaviour was investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurements and it was found that all three compounds display SmAintercal mesophases. These bent-shaped molecules exhibit strong photoisomerisation behaviour in solutions in which trans to cis isomerisation takes about 50 seconds whereas the reverse process takes almost 31 hours.

Activated carbon nanospheres derived from bio-waste materials for supercapacitor applications – a review

Supercapacitors are perfect energy storage devices; they can be charged almost instantly and release energy over a long time. They can be charged multiple times with minimal degradation in performance. Supercapacitor performance is determined by the composition of the electrode and advanced configurations. In this review, we compare the performance of different electrode materials which are obtained from biowaste based precursors. Our main interest in this review is to study the supercapacitor properties using carbon based spherical natured particles well known as carbon nanospheres. Carbon based electrodes, particularly bio-waste activated carbon nanospheres, have gained interest due to their excellent energy storage ability. In this paper, Activated Carbon Nanospheres derived from several bio-waste materials are reviewed on the basis of their cyclic voltammograms, specific capacitances, surface areas, electrolytes used and fabrication process.

Fast liquid crystal light shutter

By proper assembling and electronic driving of two parallel single nematic liquid crystal cells with planar and vertical alignment of the liquid crystal molecules, respectively, arranged in a double cell, fast switching between bright and dark states, back and forth, is achieved. The switching rise and fall time of the device corresponds to the switching rise time of the cells from the relaxed to the switched state. The simultaneous transition of the cells from the switched to the relaxed state, however, remains optically hidden from the observer due to the optical compensation effect during this transition.

High performance supercapacitor using catalysis free porous carbon nanoparticles

Very high supercapacitance values are obtained using catalyst free porous carbon nanoparticles (PCNs). The obtained PCNs have a porous structure with fine particles 35 nm in size. The specific capacitance of PCNs is 343 F g −1 and 309 F g −1 at 5 mV s −1 and 0.06 A g −1 , respectively. PCNs shows a high cyclic stability of about 90% and high columbic efficiency of 95% over 2500 cycles at 1 A g −1 . Impedance spectra show low resistance of PCNs, supporting their suitability for supercapacitor electrode application.

Azo containing thiophene based prop-2-enoates for photoalignment of a nematic liquid crystal

The ability of suitably derived prop-2-enoates from 3-(thiophen-2-yl)- and 3-(thiophen-3-yl)-prop-2-enoic acid and appropriately fluorinated and non-fluorinated 4-[(4-alkoxyphenyl)diazenyl]phenols to promote excellent photoalignment of a bulk commercial nematic liquid crystal is reported. The performed study showed that the photoalignment of the liquid crystal is influenced by the number and disposition of fluoro-substituents and the position of attachment of the terminal thiophene moiety, either 2- or 3-substituted, in the molecular structure of the alignment material. Inclusion of a lateral fluoro-substituent(s) induces an excellent photoalignment whereas the non-fluorinated counterpart tends to give an unsatisfactory alignment. 3-Substituted thiophenes give a better photoalignment than their 2-substituted isomeric counterparts. A prototype display, which contains an alignment layer made from one of the proposed materials, possessing good alignment ability, is presented in order to demonstrate the application potential of these materials in LCDs.

Exploring the mesomorphic potential of 2,4-disubstituted thiophenes: a structure–property study

The synthesis and mesomorphic properties of 25 novel esters derived from 4-substituted thiophene-2-carboxylic acids and either (S)-1-methylheptyl 4-hydroxybenzoate or (S)-1-methylheptyl 4′-hydroxybiphenyl-4-carboxylate are described. A structure–property relationship has been deduced, and mesogenic properties are found to be dependent on the total number of rings in the molecular core and the nature of the substituent in the 4-position of the thiophene ring. Four-ring systems have greater thermal stability and are more likely to form mesophases than their three-ring counterparts. A 1,4-phenylene substituent in the 4-position of the thiophene ring (Series I and II) gives better thermal properties than does a 2,5-thienyl substituent (Series III and IV). A rationale is suggested in terms of conjugative effects that may be important in mesophase thermal stability. A preliminary molecular modelling study (B3LYP/6–31G(d)) reveals that 2,4-disubstituted systems offer a slight preference for a folded geometry structure compared with their 2,5-counterparts. Homologues (nu2009=u20097–10,12) in Series II show an interesting chiral phase behaviour between the SmA and SmC* ferrielectric phase, tentatively assigned SmX*, which then gives a SmC* antiferroelectric phase. Textures have been characterised by thermal polarising microscopy using a conventional glass slide cover-slip and free-standing film. Although the SmX* phase has still to be fully characterised, this is the first reported occurrence of such a phase in 2,4-thiophene systems.

Synthesis and liquid crystalline behaviour of substituted (E)-phenyl-4-(phenyldiazenyl) benzoate derivatives and their photo switching ability

ABSTRACT Azobenzene derivatives containing phenyl/4-halogen-phenyl 4-{(E)-[4-(pent-4-en-1-yloxy)phenyl]diazenyl}benzoate group with different electronegative substituent (H, F, Cl, Br and I) at other end was synthesised. These azo-based benzoate derivatives have been characterised by FTIR, 1H-NMR, 13C-NMR, elemental analyser, POM and UV-Vis spectroscopy. Photosaturation at 358 nm obtained after 82 s of UV irradiation and the longest thermal back relaxation time of 45 h recorded by UV-Vis. The azo derivative could be possible photolock under UV light, as observed by the improved thermal back relaxation time. The resulting photolockable chain of azobenzene might prove valuable in the development of optical device application. These azobenzene moieties also exhibit liquid crystalline behaviour with respect to the halogen substitution as an electron withdrawing group shows that strong structure property relationship exists among them. GRAPHICAL ABSTRACT

A facile and green strategy for the synthesis of Au, Ag and Au Ag alloy nanoparticles using aerial parts of R. hypocrateriformis extract and their biological evaluation

A facile and green strategy is reported here to synthesize gold (Au), silver (Ag) and gold-silver (Au-Ag) alloy nanoparticles (NPs) through bio-reduction reactions of aqueous corresponding metal precursors mediated by extracts of aerial parts of R. hypocrateriformis, which act as both reducing and stabilizing agents, under microwave irradiation. UV-vis spectrophotometer, XRD, FT-IR, FESEM/TEM, TGA and EDAX analysis were used to characterize the obtained NPs. The formation of NPs is evident from their surface plasmon resonance peak observed at λmax=∼550, 450 and 500nm for Au, Ag and Au-Ag alloy NPs respectively. XRD pattern revealed that fcc structure, while FT-IR spectra signify the presence of phytochemicals adsorbed on NPs. Such a biofunctionalized NPs were characterized by their weight loss, 30% due to thermal degradation of plant phytochemicals observed in TG analysis. The spherical shape of Au, Ag and Au-Ag alloy NPs (∼10-50nm) is observed by FE-SEM/TEM images. EDAX analysis confirms the expected elemental composition. Moreover, these NPs showed enhanced antimicrobial, antioxidant, and anticancer activities, though it is more pronounced for Au-Ag alloy NPs, which is due to the combining effect of phytochemicals, Au and Ag metals. Thus, the biosynthesized NPs could be applied as effective growth inhibitors for various biomedical applications.

Polyvinyl Alcohol/Polysaccharide Hydrogel Graft Materials for Arsenic and Heavy Metal Removal

Water pollution from arsenic and some other heavy metals has been reported all over the world. The goal of this investigation is to develop different polysaccharides–polyvinyl alcohol (PVA) hydrogel graft materials for the removal of toxic and carcinogenic arsenic (As) species as well as a series of heavy metals (Mn2+, Cr2+, Fe3+, Ni2+, Cu2+ and Pb2+) from contaminated water. Hydrogels were developed with PVA and PVA/polysaccharide (as blended materials) using a γ-ray irradiation technique and then characterized by Fourier transform infrared (FTIR) and gravimetric methods. The absorbed dose of γ-radiation was optimized to obtain good gelation, and some important physical parameters such as gel fraction, degree of swelling and water absorption kinetics of the synthesized hydrogels were also investigated. The optimum absorbed dose of 30 kGy gave a gel fraction of about 98% in the PVA/corn starch (CS) hydrogel. The developed hydrogels have the capability to make chelates, which are utilized for the removal of arsenic and heavy metals. The absorption of arsenic and heavy-metal ions from the respective aqueous solution by the chelating functionalized gels has been assessed by atomic absorption spectrophotometry (AAS). The calculated maximum amount of iron and arsenic removal capacities of 37u2006075 and 22u2006112 mg kg−1, respectively, were found for the PVA/CS hydrogel. We also found that polysaccharide (PS) analogues showed affinities toward the metal ions to a considerable extent in the following order: Fe3+ > Mn2+ > Cu2+ >. The results obtained from this study indicate that the functionalized hydrogels show a good chelating tendency and are suitable for water treatment.