Avtar S. Matharu

Liquid crystals for holographic optical data storage

A tutorial review is presented to inform and inspire the reader to develop and integrate strong scientific links between liquid crystals and holographic data storage, from a materials scientists viewpoint. The principle of holographic data storage as a means of providing a solution to the information storage demands of the 21st century is detailed. Holography is a small subset of the much larger field of optical data storage and similarly, the diversity of materials used for optical data storage is enormous. The theory of polarisation holography which produces holograms of constant intensity, is discussed. Polymeric liquid crystals play an important role in the development of materials for holographic storage and photoresponsive materials based on azobenzene are targeted for discussion due to their ease of photo-reversion between trans- and cis-states. Although the final polymer may not be liquid crystalline, irradiation can induce ordered domains. The mesogens act in a co-operative manner, enhancing refractive indices and birefringences. Surface relief gratings are discussed as a consequence of holographic storage. Cholesteric polymers comprising azobenzene are briefly highlighted. Irradiation causing cis-trans-isomerisation can be used to control helix pitch. A brief mention of liquid crystals is also made since these materials may be of future interest since they are optically transparent and amenable to photo-induced anisotropy.

The significance of D-amino acids in soil, fate and utilization by microbes and plants: review and identification of knowledge gaps

BackgroundD-amino acids are far less abundant in nature than L-amino acids. Both L- and D-amino acids enter soil from different sources including plant, animal and microbial biomass, antibiotics, faeces and synthetic insecticides. Moreover, D-amino acids appear in soil due to abiotic or biotic racemization of L-amino acids. Both L- and D-amino acids occur as bound in soil organic matter and as “free“ amino acids dissolved in soil solution or exchangeably bound to soil colloids. D-amino acids are mineralized at slower rates compared to the corresponding L-enantiomers. Plants have a capacity to directly take up “free“ D-amino acids by their roots but their ability to utilize them is low and thus D-amino acids inhibit plant growth.ScopeThe aim of this work is to review current knowledge on D-amino acids in soil and their utilization by soil microorganisms and plants, and to identify critical knowledge gaps and directions for future research.ConclusionAssessment of “free“ D-amino acids in soils is currently complicated due to the lack of appropriate extraction procedures. This information is necessary for consequent experimental determination of their significance for crop production and growth of plants in different types of managed and unmanaged ecosystems. Hypotheses on occurrence of “free“ D-amino acids in soil are presented in this review.

Thermosetting resin based on epoxidised linseed oil and bio-derived crosslinker.

Thermosetting resins were synthesised from epoxidised linseed oil (ELO) in combination with a bio-derived diacid cross linker (Pripol 1009) in the presence of amine catalysts (triethylamine (TEA), 1-methylimidazole (1-MeIm), 2-methylimidazole (2-MeIm), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP), yielding a 99.5% bio-derived, highly flexible transparent film, with significant water resistance. It was demonstrated that the mechanical and thermal properties of the resulting films were significantly influenced by the type of amine catalyst selected. The use of catalysts significantly enhanced the mechanical properties of the films; tensile strength improved by up to 545% (DMAP), Youngs modulus improved by up to 422% (2-MeIm) and elongation at break improved by 14–84%. An infrared spectroscopic study coupled with simultaneous thermal analysis and modulated differential scanning calorimetry (MDSC) was undertaken in an attempt to elucidate the curing mechanism. Epoxide ring opening is clearly evidenced by infrared spectroscopy and the studies suggest that DMAP probably aids crosslinking between ELO and Pripol 1009 via epoxide ring opening, followed by etherification, due to its good nucleophilicity. The optimum DMAP catalyst loading giving the highest value of Youngs modulus was determined at 1% with respect to the total resin weight. Higher concentrations of DMAP (5% wt) decreased the Youngs modulus.

Applications of nanoparticles in biomass conversion to chemicals and fuels

Biorefineries are facilities that process biomass into fuels, power and value-added chemicals and with the increasing population and depleting petroleum reserves they are fast becoming more important to society. The technology required to process a wide variety of biomass types can be highly complex due to potentially unknown, varying or difficult to breakdown chemical structures within them. One of the prospective routes to a successful biorefinery, that can treat a wide range of biomass and produce products with good selectivity, is the use of nanoparticles as heterogeneous catalysts. The potential of nanoparticles to catalyse and modify chemical processes, thereby influencing both the nature of the products and their distribution is seen as highly promising. In this publication, we aim to give an overview of the use of a range of nano-catalysts and nano-enzymatic supports for greener biorefinery processing. Finally, future prospects of greener routes to nanoparticle production and their integration into biomass are discussed.

Opportunity for high value-added chemicals from food supply chain wastes

With approximately 1.3 billion tonnes of food wasted per annum, food supply chain wastes (FSCWs) may be viewed as the contemporary Periodic Table of biobased feedstock chemicals (platform molecules) and functional materials. Herein, the global drivers and case for food waste valorisation within the context of global sustainability, sustainable development goals and the bioeconomy are discussed. The emerging potential of high value added chemicals from certain tropical FSCW is considered as these are grown in three major geographical areas: Brazil, India and China, and likely to increase in volume. FSCW in the context of biorefineries is discussed and two case studies are reported, namely: waste potato, and; orange peel waste. Interestingly, both waste feedstocks, like many others, produce proteins and with the global demand for vegetable proteins on the rise then proteins from FSCW may become a dominant area.

Photoinduced anisotropy in a family of amorphous azobenzene polyesters for optical storage

We investigate parameters associated with optical data storage in a variety of amorphous side-chain azobenzene-containing polyesters denoted as E1aX. The polyesters possess a common cyano-substituted azobenzene chromophore as a side chain, but differ in their main-chain polyester composition. Seventeen different polymers from the E1aX family divided into four classes, depending on the type of the main-chain substituent (one-, two-, and three-ring aromatic or alicyclic) have been thoroughly investigated. Various parameters characterizing the photoinduced birefringence in these materials, such as the response time, thermal and light stability, and long-term stability under ambient light at room temperature have been measured. Each of these parameters is quantitatively represented and therefore it is possible to make a clear comparison between the properties of the polymers. The results indicate that the long-term stability at ambient temperature is closely related to the thermal stability of the photoinduced birefringence. A strong correlation has also been found between the response time and the stability of the induced anisotropy toward illumination with unpolarized white light. One of the classes of E1aX polymers characterized by two-ring aromatic substituent in the main chain is a good candidate for optical data storage media. A recording energy of approximately 2 J/cm2 is sufficient to induce high refractive-index modulations of deltan = 0.13 in these materials, which is retained even at elevated temperatures (>130 degrees C). Long-term stability of greater than one year for the induced anisotropy has also been achieved.

Electrically commanded surfaces for nematic liquid crystal displays

Electrically commanded surfaces (ECS) is a liquid crystal display concept whereby the switching of the alignment layer, which is driven by an electric field applied across the layer, is further transferred to the bulk liquid crystal material via elastic forces. This work presents the electro-optic response of a sandwich cell with alignment layer made of siloxane-based ferroelectric liquid crystal polymer, representing the ECS. The bulk liquid crystal material of choice was an in-house nematic mixture comprising fluorinated liquid crystalline compounds with negative dielectric anisotropy (Delta-epsilon < 0). We report a distinct linear electro-optic response, arising from the field-induced in-plane switching of the nematic which in turn is mediated by the ECS.

Laterally fluorinated liquid crystals containing the 2,2′‐bithiophene moiety

The synthesis and systematic evaluation of the influence of lateral mono‐, di‐ and tetra‐fluorination of the terminal phenyl ring on mesomorphic properties in seven novel series of suitably fluoro‐substituted 5‐n‐alkyl‐5′‐(4‐n‐decyloxyphenyl)‐2,2′‐bithienyls is reported. Compared with their non‐fluorinated parent counterparts, lateral fluorination eliminates high order smectic phases and reduces thermal stability, to reveal compounds exhibiting a selection of nematic, smectic A and smectic C phase types. As the number of fluoro‐substituents increases from one to two, mesophase thermal stability drops drastically; the disposition of the second fluoro‐substituent is important. Across‐axis disposition is more detrimental than along‐axis. However, complete fluorination does not destroy mesophase formation. Indeed, tetrafluorophenyl compounds are more stable than certain 3,5‐ and 2,6‐difluoro compunds. The extrapolated birefringence for members of a series of 5‐n‐alkyl‐5′‐(2,3‐difluoro‐4‐n‐decyloxyphenyl)‐2,2′‐bithienyls is approximately 0.21.

New insights into the curing of epoxidized linseed oil with dicarboxylic acids

The effect of systematically increasing chain length of a series of linear α,ω-dicarboxylic acids (DCAs) from C6 to C18 diacids and a cyclic diacid, Pripol 1009F, on thermal and mechanical properties of the resultant epoxy thermosets derived from epoxidized linseed oil (ELO) are reported. Different techniques including differential scanning calorimetry (DSC), solvent extraction, FT-IR, NMR, dynamic mechanical analysis (DMA), tensile tests and thermogravimetric analysis (TGA) are used in this study. The results indicated that the obtained epoxy resins were highly crosslinked polymers with only a small fraction of low molecular weight soluble materials. The glass transition temperature (Tg), tensile strength, Youngs modulus, elongation at break and toughness decreased while the thermal stability increased with respect to increasing chain length of DCAs. Interestingly, strain hardening was only observed for adipic acid (C6) sample for which the best mechanical properties observed.

From waste to wealth using green chemistry

The availability of chemically rich food supply chain waste (FSCW) gives it considerable potential as a resource for the manufacture of chemicals including materials and fuels. By applying clean chemical technologies to the extraction and conversion of molecules from FSCW, we can aim to produce genuinely green and sustainable products to help meet the legislative and consumer-oriented demands of a sustainable society. Low-temperature microwave (MW) processing is a particularly powerful technology to achieve this aim and is shown to be effective for several different high-volume, geographically diverse biomass types.