A Short Review on the Rheology of Twist Grain Boundary-A and Blue Phase Liquid Crystals

Topological defects are important in determining the properties of physical systems and are known varyingly depending on the broken symmetry. In superfluid helium, they are called vortices; in periodic crystals, one refers to dislocations; and in liquid crystals, they are disclinations. The defects and the inter-defect interaction in some highly chiral liquid crystals stabilize some intermediate complex phases such as Blue Phases (BPs) and Twist Grain Boundary-A (TGBA) phases. The defect dynamics of these phases contributes to the rheological properties. The temperature range of these intermediate phases usually are very small in pure liquid crystals; consequently, a detailed experiment has been difficult to achieve. However, the temperature range could be enhanced significantly in multicomponent systems. In this review article, we discuss some recent experimental progress made in understanding the rheological properties of the wide-temperature-range TGBA and BP liquid crystals

A Short Review on the Rheology of Twist Grain Boundary-A and Blue Phase Liquid Crystals

Topological defects are important in determining the properties of physical systems and are known varyingly depending on the broken symmetry. In superfluid helium, they are called vortices; in periodic crystals, one refers to dislocations; and in liquid crystals, they are disclinations. The defects and the inter-defect interaction in some highly chiral liquid crystals stabilize some intermediate complex phases such as Blue Phases (BPs) and Twist Grain Boundary-A (TGBA) phases. The defect dynamics of these phases contributes to the rheological properties. The temperature range of these intermediate phases usually are very small in pure liquid crystals; consequently, a detailed experiment has been difficult to achieve. However, the temperature range could be enhanced significantly in multicomponent systems. In this review article, we discuss some recent experimental progress made in understanding the rheological properties of the wide-temperature-range TGBA and BP liquid crystals

Rheological studies on liquid-crystal colloids prepared by dispersing spherical microparticles with homeotropic surface anchoring

<p>We report rheological studies on the liquid-crystal colloids prepared by dispersing silica microparticles with homeotropic surface anchoring in 8CB liquid crystal. In nematic colloids, a shear-thickening behaviour is observed in low shear rate region. The apparent yield stress of both the nematic and smectic-A (SmA) phases increases with increasing volume fraction of particles . The critical strain amplitude (, i.e., crossover of and ) in SmA colloids decreases significantly with increasing . The frequency-dependent storage modulus of SmA colloids show a power-law behaviour and the loss modulus exhibits a shallow minimum. The optical rheomicroscopy shows that the nematic colloids form a network structure which are stretched and broken at high shear rate. When the temperature is decreased to SmA phase, the networks collapse showing regions of high-density particles. The variation of storage modulus with indicates that the SmA colloids response is dominated by defects.</p

Controlled Crystallization of Acetazolamide from Aqueous Polymeric Solutions for Enhancing Dissolution Rate: Application of Statistical Moment Theory and Molecular Docking

515-521Presence of additives in crystallization process in a controlled manner can lead to different crystal morphologies which could have a favourable impact on drug dissolution rate. Four different hydrophilic polymers (methylcellulose, hydroxypropyl methylcellulose, polyvinyl alcohol, and carboxymethyl cellulose) were used for the controlled crystallization of acetazolamide (ACZ) by solvent evaporation technique. Crystal imperfections of ACZ occurred in the lattice of growing crystal when crystallized from aqueous polymeric solution and evaluated using both the traditional Full Width at Half Maximum (FWHM) () and statistical mean value of the XRD peak width (). Crystal imperfection has brought about significant improvement in the dissolution of newly produced acetazolamide crystals. ACZ crystal produced in presence of Hydroxypropyl methylcellulose (AHPMC) showed crystal imperfection to the maximum extent and also the greatest dissolution of the drug was noticed from AHPMC compared to other crystals. Statistical mean value of the peak width of XRD data as the error-free technique has been utilized successfully for estimating crystallite properties of acetazolamide crystallized from ethanol as solvent and aqueous polymeric solution as anti-solvent. Crystallite properties using traditional Full Width Half Maxima method and the error-free Statistical Moment Analysis were compared. This controlled crystallization technique could be utilized in the design and development of formulation for improved solubility and bioavailability of the drug

Synthesis and characterization of novel ABA-type azobenzene-containing tri-block copolymers from telechelic polystyrene

<div><p>The telechelic polystyrene (tPS) was used as a macro-reversible addition fragmentation chain transfer (RAFT) agent to prepare the ABA-type tri-block copolymers (TBCs), poly{4-[4-(11-acryloyloxyundecyloxy)phenylazo]benzonitrile}-<i>b</i>-polystyrene-<i>b</i>-poly{4-[4-(11-acryloyloxyundecyloxy)phenylazo]benzonitrile} [poly(AUPAB)-<i>b</i>-PS-<i>b</i>-poly(AUPAB)] with 4-[4-(11-acryloyloxyundecyloxy)phenylazo]benzonitrile (AUPAB) as a monomer by the RAFT polymerization process. The poly(AUPAB) was used as a reference to probe the role of polystyrene block in poly(AUPAB)-<i>b</i>-PS-<i>b</i>-poly(AUPAB) macromolecular chain. The TBCs were characterized by spectral techniques, thermal analysis, and polarizing optical microscopic studies and compared the results with individual blocks, poly(AUPAB), and tPS. The TBCs exhibited higher thermal stability and liquid crystal–isotropic phase transition peak temperature (<i>T</i>_LC-I), and glass transition temperature (<i>T</i>_g) values compared to the poly(AUPAB). TBC <i>T</i>_LC-I value was dependent on the AUPAB wt% in macromolecular chain. Furthermore, the acquired results by optical microscopy suggest that after incorporation of the polystyrene block in acrylate-based pendant azobenzene polymer chain resulted in lower domain size of focal conic texture, which is characteristic of smectic-A liquid crystalline phase compared to the homopolymer. The photophysical properties of the TBCs were similar to those of the poly(AUPAB). Microphase-separated nano-segregation was observed in annealed thin films of TBCs.</p></div

Synthesis and characterization of novel ABA-type azobenzene-containing tri-block copolymers from telechelic polystyrene

<div><p>The telechelic polystyrene (tPS) was used as a macro-reversible addition fragmentation chain transfer (RAFT) agent to prepare the ABA-type tri-block copolymers (TBCs), poly{4-[4-(11-acryloyloxyundecyloxy)phenylazo]benzonitrile}-<i>b</i>-polystyrene-<i>b</i>-poly{4-[4-(11-acryloyloxyundecyloxy)phenylazo]benzonitrile} [poly(AUPAB)-<i>b</i>-PS-<i>b</i>-poly(AUPAB)] with 4-[4-(11-acryloyloxyundecyloxy)phenylazo]benzonitrile (AUPAB) as a monomer by the RAFT polymerization process. The poly(AUPAB) was used as a reference to probe the role of polystyrene block in poly(AUPAB)-<i>b</i>-PS-<i>b</i>-poly(AUPAB) macromolecular chain. The TBCs were characterized by spectral techniques, thermal analysis, and polarizing optical microscopic studies and compared the results with individual blocks, poly(AUPAB), and tPS. The TBCs exhibited higher thermal stability and liquid crystal–isotropic phase transition peak temperature (<i>T</i>_LC-I), and glass transition temperature (<i>T</i>_g) values compared to the poly(AUPAB). TBC <i>T</i>_LC-I value was dependent on the AUPAB wt% in macromolecular chain. Furthermore, the acquired results by optical microscopy suggest that after incorporation of the polystyrene block in acrylate-based pendant azobenzene polymer chain resulted in lower domain size of focal conic texture, which is characteristic of smectic-A liquid crystalline phase compared to the homopolymer. The photophysical properties of the TBCs were similar to those of the poly(AUPAB). Microphase-separated nano-segregation was observed in annealed thin films of TBCs.</p></div

The neglected continuously emerging Marburg virus disease in Africa: A global public health threat

Abstract Background and Aim Severe viral hemorrhagic fever (VHF) is caused by Marburg virus which is a member of the Filoviridae (filovirus) family. Many Marburg virus disease (MVD) outbreaks are reported in five decades. A major notable outbreak with substantial reported cases of infections and deaths was in 2022 in Uganda. The World Health Organisation (WHO) reported MVD outbreak in Ghana in July 2022 following the detection of two probable VHF patients there. Further, the virus was reported from two other African countries, the Equatorial Guinea (February 2023) and Tanzania (March 2023). There have been 35 deaths out of 40 reported cases in Equatorial Guinea, and six of the nine confirmed cases in Tanzania so far. Methods Data particularly on the several MVD outbreaks as reported from the African countries were searched on various databases including the Pubmed, Scopus, and Web‐of‐science. Also, the primary data and reports from health agencies like the WHO and the Centers for Disease Control and Prevention CDC) were evaluated and the efficacy reviewed. Results Chiroptera in general and bat species like Rousettus aegyptiacus and Hipposideros caffer in particular are natural reservoirs of the Marburg virus. MVD‐infected nonhuman primate African fruit‐bat and the MVD‐infected humans pose significant risk in human infections. Cross‐border viral transmission and its potential further international ramification concerns raise the risk of its rapid spread and a potential outbreak. Occurrence of MVD is becoming more frequent in Africa with higher case fatality rates. Effective prophylactic and therapeutic interventions to counter this deadly virus are suggested. Conclusion In the face of the lack of effective therapeutics and preventives against MVD, supportive care is the only available option which contributes to the growing concern and disease severity. In view of the preventive approaches involving effective surveillance and monitoring system following the “One Health” model is extremely beneficial to ensure a healthy world for all, this article aims at emphasizing several MVD outbreaks, epidemiology, zoonosis of the virus, current treatment strategies, risk assessments, and the mitigation strategies against MVD