Dielectric Modes in Antiferroelectric and Ferroelectric Liquid Crystals in a Pure Enantiomeric Version and a Racemic Mixture.

The dielectric properties of synclinic (ferroelectric SmC*) and anticlinic (antiferroelectric SmCA*) smectic liquid crystals composed of molecules of one chiral version (S) are presented and compared with properties of racemic mixture (R, S), showing SmC and SmCA phases. The racemic mixture completely loses its ferroelectric and antiferroelectric properties. Surprisingly, only one dielectric mode observed in the antiferroelectric SmCA* phase disappeared in the dielectric response of the racemic SmCA phase. Additionally, we observed that in the SmC phase, seen in the racemic mixture, the weak dielectric mode (named the X mode) is detected, which seems to be the continuation of the PL mode existing in the racemic SmCA. Moreover, this mode in the racemic SmC has nothing to do with the Goldstone mode, typical for the SmC* phase. This paper describes in detail the real and imaginary parts of dielectric permittivity in smectic phases for the enantiomer and racemate with and without a DC field, compares the properties of the X and PL modes, and discusses the full scheme of dielectric modes in enantiomer and racemate.

Synthesis and Characterization of New Chiral Smectic Four-Ring Esters.

Orthoconic antiferroelectric liquid crystals (OAFLCs) represent unique self-organized materials with significant potential for applications in photonic devices due to their sub-microsecond switching times and high optical contrast in electro-optical effects. However, almost all known OALFCs suffer from low chemical stability and short helical pitch values. This paper presents the synthesis and study results of two chiral AFLCs, featuring a four-ring structure in the rigid core and high chemical stability. The mesomorphic properties of these compounds were investigated using polarizing optical microscopy and differential scanning calorimetry. Spectrometry and electro-optical studies were employed to estimate the helical pitch, tilt angle, and spontaneous polarization of the synthesized compounds and the prepared mixtures. All studied compounds exhibit enantiotropic chiral smectic mesophases including the SmA*, the SmC*, and a very broad temperature range of the SmCA* phase. Doping top-modern antiferroelectric mixture with synthesized compounds offers benefits such as increased helical pitch and tilt angle values without significantly influencing spontaneous polarization. This allows the prepared mixture to be regarded as an OAFLC with high optical contrast, characterized by an almost perfect dark state. These valuable physicochemical and optical properties suggest significant potential of studied materials for practical applications.

Decontamination Effect of Hypochlorous Acid Dry Mist on Selected Bacteria, Viruses, Spores, and Fungi as Well as on Components of Electronic Systems.

This publication presents the effect of hypochlorous acid dry mist as a disinfectant on selected bacteria, viruses, spores, and fungi as well as on portable Microlife OXY 300 finger pulse oximeters and electronic systems of Raspberry Pi Zero microcomputers. The impact of hypochlorous acid on microbiological agents was assessed at concentrations of 300, 500, and 2000 ppm of HClO according to PN-EN 17272 (Variant I). Studies of the impact of hypochlorous acid fog on electronic components were carried out in an aerosol chamber at concentrations of 500 ppm and 2000 ppm according to two models consisting of 30 (Variant II) and 90 fogging cycles (Variant III). Each cycle included the process of generating a dry mist of hypochlorous acid (25 mL/m3), decontamination of the test elements, as well as cleaning the chamber of the disinfectant agent. The exposure of the materials examined on hypochlorous acid dry mist in all variants resulted in a decrease in the number of viruses, bacteria, spores, and fungi tested. In addition, the research showed that in the variants of hypochlorous acid fogging cycles analyzed, no changes in performance parameters and no penetration of dry fog of hypochlorous acid into the interior of the tested medical devices and electronic systems were observed.

Optimization of Liquid Crystalline Mixtures Enantioseparation on Polysaccharide-Based Chiral Stationary Phases by Reversed-Phase Chiral Liquid Chromatography.

Enantioseparation of nineteen liquid crystalline racemic mixtures obtained based on (R,S)-2-octanol was studied in reversed-phase mode on an amylose tris(3-chloro-5-methylphenylcarbamate) (ReproSil Chiral-MIG) and a cellulose tris(3,5-dichlorophenylcarbamate) (ReproSil Chiral-MIC). These polysaccharide-based chiral stationary phase (CSP) columns for High-Performance Liquid Chromatography (HPLC) were highly effective in recognizing isomers of minor structural differences. The mobile phase (MP), which consists of acetonitrile (ACN)/water (H2O) at different volume ratios, was used. The mobile phases were pumped at a flow rate of 0.3, 0.5, or 1 mL·min-1 with a column temperature of 25 °C, using a UV detector at 254 nm. The order of the elution was also determined. The chromatographic parameters, such as resolution (Rs), selectivity (α), and the number of theoretical plates, i.e., column efficiency (N), were determined. The polysaccharide-based CSP columns have unique advantages in separation technology, and this study has shown the potential usefulness of the CSP columns in separating liquid crystalline racemic mixtures belonging to the same homologous series.

The Influence of the Molecular Structure of Compounds on Their Properties and the Occurrence of Chiral Smectic Phases.

We have designed new chiral smectic mesogens with the -CH2O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics.

Crystallization kinetics of (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy)but-1-oxy]-2-fluorobenzoate.

Chiral liquid crystalline compounds belonging to the homologous series of (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[m-(2,2,3,3,4,4,4-heptafluorobutoxy)alk-1-oxy]-2-fluorobenzoates show various behaviors on cooling depending on the length of the CmH2m chain. The homologue with m = 2 crystallizes, while for m = 5, 6, 7, and presumably also for m = 3, the glass of the anticlinic smectic CA* phase is formed. The previous results for m = 4 suggest that this homologue may also be a glassformer. This paper presents the study of the crystallization kinetics for the compound with m = 4 in isothermal conditions (by polarizing optical microscopy) and for the 5-40 K min-1 cooling rates (by differential scanning calorimetry). Microscopic observations enable estimation of the energy barrier for nucleation, which equals 409 kJ mol-1. The threshold cooling rate necessary for complete vitrification of the smectic CA* phase, obtained by extrapolating the enthalpy change during crystallization to zero, is equal to 81 K min-1 or 64 K min-1 for the linear and parabolic fits, respectively. The structural studies by X-ray diffraction show that crystal phases have lamellar structures both in the pristine sample and after crystallization from the melt but with different layer spacing. A weak relaxation process is detected in the sample after melt crystallization, revealing the presence of the conformational disorder. The dynamic glass transition temperature of the SmCA* phase, estimated from the relaxation time of the PH process (as the α-relaxation time could not be registered in a wide enough temperature range), is 244 K.

A Siamese neural network framework for glass transition recognition.

A Siamese neural network, which is a deep learning technique, was applied to investigate phase transitions based on polarising microscopic textures of liquid crystals like: antiferroelectric smectic CA* phase and its glass, smectic I phase and its glass, and smectic G and its glass. It is an example of a subtle transition without significant structural changes, where textures above and below the glass transition temperature are similar. The Siamese neural network could distinguish textures of the chosen liquid crystal phases from a glass of that phase. This publication provides details of the Siamese neural network and its implementation based on three different convolutional neural networks has been tested.

Impact of carbon quantum dots on self-assembly and dielectric relaxation modes of a room temperature tri-component fluorinated antiferroelectric liquid crystal mixture.

We investigated the impact of carbon quantum dots (CQDs) of sizes ∼2-5 nm in a room temperature tri-component fluorinated antiferroelectric liquid crystal (AFLC) mixture. The synthesised CQDs have been characterised by high-resolution transmission electron microscopy and X-ray diffraction spectroscopy. An increase in the transition temperature and enthalpy to the isotropic liquid phase indicates stabilization of the AFLC mixture in the presence of CQDs. The dielectric studies have been carried out in the frequency range of 1 Hz-40 MHz under the planar anchoring conditions of the molecules. An appreciable increase in the permittivity, dielectric strength, and conductivity has been observed owing to the existence of sp2/sp3 hybridization in the CQDs which form a strong coupling and develop a dipolar ordering in the systems. Various relaxation frequencies were increased with the incarceration of CQDs in the AFLC mixture. Overall, the different studies suggest that the doped CQDs are very well settled in between the host molecules without disturbing the molecular ordering of the hosts. Such results are encouraging and reveal the potential applicability of the CQD doped systems to produce highly efficient tuneable optical devices and other multifaceted applications.

Vitrification of the smectic CA* phase and kinetics of cold crystallization investigated for a fluorinated compound with a chiral centre based on (S)-(+)-3-octanol.

The formation of glass of the anticlinic high-tilted smectic CA* phase even at low cooling rates (≥2 K min-1) is reported for (S)-4'-(1-ethylhexyloxycarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pentyl-1-oxy]benzoate. The kinetics of crystallization is investigated via differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The temperature region of the largest crystallization rate, the activation energy of cold crystallization and the energy barrier of nucleation are determined. The coupling of the characteristic crystallization time with the α-relaxation time is studied. A high fragility index equal to 139 is obtained for this glassformer. Comparison with a very similar glassforming compound, with the chiral centre based on (S)-(+)-2-octanol instead of (S)-(+)-3-octanol, is presented.

Extracting Group Velocity Dispersion values using quantum-mimic Optical Coherence Tomography and Machine Learning.

Quantum-mimic Optical Coherence Tomography (Qm-OCT) images are cluttered with artefacts - parasitic peaks which emerge as a by-product of the algorithm used in this method. However, the shape and behaviour of an artefact are uniquely related to Group Velocity Dispersion (GVD) of the layer this artefact corresponds to and consequently, the GVD values can be inferred by carefully analysing them. Since for multi-layered objects the number of artefacts is too high to enable layer-specific analysis, we employ a solution based on Machine Learning. We train a neural network with Qm-OCT data as an input and dispersion profiles, i.e. depth distribution of GVD within an A-scan, as an output. By accounting for noise during training, we process experimental data and estimate the GVD values of BK7 and sapphire as well as provide a qualitative GVD value distribution in a grape and cucumber. Compared to other GVD-retrieving methods, our solution does not require user input, automatically provides dispersion values for all the visualised layers and is scalable. We analyse the factors affecting the accuracy of determining GVD: noise in the experimental data as well as general physical limitations of the detection of GVD-induced changes, and suggest possible solutions.

Investigation of Chiral Smectic Phases and Conformationally Disordered Crystal Phases of the Liquid Crystalline 3F5FPhH6 Compound Partially Fluorinated at the Terminal Chain and Rigid Core.

Complementary methods are applied to investigate the phase transitions and crystallization kinetics of the liquid crystalline compound denoted as 3F5FPhH6. Two crystal phases are confirmed, and one of them is the conformationally disordered (CONDIS) phase. Complexity of the melt crystallization process is revealed by the analysis with Friedman's isoconversional method. The melt crystallization of 3F5FPhH6 shows different mechanisms depending on temperature, which is explained by the relation between the thermodynamic driving force and the thermal energy of translational degrees of freedom. The studied compound crystallizes even during fast cooling (30 K/min), unlike similar compounds with different fluorosubstitutions of the benzene ring, which form the smectic glass for moderate cooling rates. The tendency to vitrification of the smectic phase decreases apparently with the decreasing stability width of the SmCA* phase and the increasing relaxation time of the collective relaxation process in this phase, at least for homologues differing from 3F5FPhH6 only by the type of fluorosubstitution.

Static Permittivity and Electro-Optical Properties of Bi-Component Orthoconic Antiferroelectric Liquid Crystalline Mixtures Targeted for Polymer Stabilized Sensing Systems.

The behavior of two newly formulated bi-component orthoconic antiferroelectric liquid crystalline (OAFLC) systems, i.e., the Compound A + Compound B mixture system and Compound C + Compound B mixture system has been discussed in light of temperature and concentration dependencies of helical pitch length, spontaneous polarization, relaxation time, bulk viscosity, and the anchoring energy strength coefficient, together with static dielectric permittivity (ε) and dielectric anisotropy. Compound A + Compound B mixtures possess spontaneous polarization between 190-340 nC.cm-2 and fast relaxation times between 190-320 µs in the smectic antiferroelectric SmCA* phase at room temperature. Compound C + Compound B mixtures also have a spontaneous polarization in the range of 190-280 nC.cm-2 and relaxation times in the range of 190-230 µs at room temperature. Most of the mixtures have a helical pitch below one micrometer in the SmCA* phase. These advanced mixtures show a broad temperature range of the antiferroelectric SmCA* phase, fast switching of molecules under an applied electric field, negative dielectric anisotropy and a short helical pitch, confirming the advantage of designing new polymer-stabilized OAFLC that is targeted for novel application in sensing devices, utilizing the fast responsive electro-optical modulation elements.

Comparative study of electrooptic, dielectric, and structural properties of two glassforming antiferroelectric mixtures with a high tilt angle.

Vitrification of the antiferroelectric smectic-C_{A}^{*} phase is reported for the orthoconic mixture W-1000 and its new derivative W-356. The crystallization is not observed even upon slow cooling and the cold crystallization on subsequent heating is also absent. Molecular dynamics in the smectic phases of both mixtures is investigated down to 173 K and the fragility parameters are determined from the temperature behavior of the α-process. X-ray diffraction is applied to compare the structural parameters of W-356 and W-1000 as well as to study the structural changes during the glass transition of the Sm-C_{A}^{*} phase. The evolution of the smectic layer order within the Sm-C_{A}^{*} glass is reported, while the correlation length of the short-range order in the smectic layers is shown to be almost constant below the glass transition temperature. Electrooptic properties of W-356: spontaneous polarization, tilt angle and switching time are determined and compared with these of W-1000. The observed differences between the properties of W-356 and W-1000 might be explained by the dimer formation of components with the -C≡N terminal group, present only in the W-356 mixture, and by the different structure of the aromatic molecular core in one of the W-356 components.

Broadband-excitation-based mechanical spectroscopy of highly viscous tissue-mimicking phantoms.

Standard rheometers assess mechanical properties of viscoelastic samples up to 100 Hz, which often hinders the assessment of the local-scale dynamics. We demonstrate that high-frequency analysis can be achieved by inducing broadband waves and monitoring their media-dependent propagation using optical coherence tomography. Here, we present a new broadband wave analysis based on two-dimensional Fourier transformation. We validated this method by comparing the mechanical parameters to monochromatic excitation and a standard oscillatory test data. Our method allows for high-frequency mechanical spectroscopy, which could be used to investigate the local-scale dynamics of different biological tissues and the influence of diseases on their microstructure.

Investigation of crystallization kinetics and its relationship with molecular dynamics for chiral fluorinated glassforming smectogen 3F5HPhH6.

The phase transitions, crystallization kinetics and molecular dynamics of (S)-4'-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pent-1-oxy] benzoate (3F5HPhH6) are investigated by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The vitrification of the antiferroelectric hexatic phase is observed for cooling rates ≥5 K min-1 and the fragility index determined from dielectric data is mf ≈ 90. Two regimes of non-isothermal cold crystallization are distinguished using the Kissinger and Augis-Bennett methods in the heating rate ranges of 1-5 K min-1 (larger activation energy) and 8-20 K min-1 (lower activation energy). The correlation between the time of non-isothermal cold crystallization (using isothermal approximation) and relaxation time of the α-process is determined. The obtained coupling coefficient ξ ≈ 0.7 and temperature dependence of the crystallization rate Z from the Ozawa model imply a mainly diffusion-controlled cold crystallization below 275 K. The Avrami exponents n and Ozawa exponents nO determined for isothermal melt crystallization and non-isothermal cold crystallization, respectively, weigh in favour of two- rather than three-dimensional crystal growth. The transition between crystal phases is observed on heating, with a lower activation energy for 1-3 K min-1 than for 5-20 K min-1 rates.

Modification of AFLC Physical Properties by Doping with BaTiO3 Particles.

In this paper, for the first time, the influence of the BaTiO3 particles on the antiferroelectric liquid crystalline phase was shown. Low concentrations and two different sizes of BaTiO3 particles (nano- and submicroparticles) were used. It was found that admixture of the ferroelectric particles causes a decrease in the concentration of free ions in the liquid crystal matrix. Despite the small amount of admixture, a decrease in spontaneous polarization, switching time and rotational viscosity, was observed, while the tilt angle of molecules and the smectic layer thickness did not change. It turns out that BaTiO3 particles have a very large impact on the dielectric spectra not only in the antiferroelectric phase but also in the ferroelectric and paraelectric phases of the polymorphic mixture studied. The dopants affect also the complex conductivity. In this paper, we explain why some properties are modified by BaTiO3 particles and others are not.

Effectiveness of Lactobacillus reuteri DSM 17938 for the Prevention of Nosocomial Diarrhea in Children: A Randomized, Double-blind, Placebo-controlled Trial.

BACKGROUND: Multiple studies of probiotics used to prevent nosocomial diarrhea have provided conflicting results. The effects likely depend on the probiotic strain and/or dosage. The aim of this study was to assess the effectiveness of Lactobacillus reuteri DSM 17938 (L. reuteri; daily dose of 1 × 10 colony forming units) for preventing nosocomial diarrhea in children. METHODS: We conducted a multicenter, randomized, double-blind, placebo-controlled trial in 184 children, 1-48 months of age, admitted to the hospital for reasons other than diarrhea. A computer-generated randomization scheme was used to allocate participants to receive either L. reuteri (n = 91) at a daily dose of 1 × 10 colony forming units, for the duration of hospitalization, or an identical appearing placebo (n = 93). Patients, study personnel and data analysts were blinded to assignment. The primary outcome was the occurrence of nosocomial diarrhea (≥3 loose or watery stools in 24 hours that occurred >72 hours after admission). Analysis was by intention-to-treat. RESULTS: Baseline characteristics were similar in the 2 groups. Nosocomial diarrhea occurred in 13 (7.1%) children. No difference was found between the L. reuteri and the placebo groups (7/91 vs 6/93, respectively; relative risk: 1.19; 95% confidence interval: 0.43-3.27). There was also no difference between the L. reuteri and placebo groups for any of the secondary outcomes, including adverse effects. Rotavirus vaccination status had no effect on the results. CONCLUSION: L. reuteri in the dosage regimen used was not effective in preventing nosocomial diarrhea in children.

The efficacy of Lactobacillus reuteri DSM 17938 in infants and children: a review of the current evidence.

UNLABELLED: We aimed to systematically evaluate evidence on the effectiveness of Lactobacillus reuteri DSM 17938 (L. reuteri) for treating and preventing diseases in infants and children. MEDLINE and the Cochrane Library were searched in December 2013, with no language restrictions, for relevant randomized controlled trials (RCTs) and meta-analyses. The search was updated in April 2014. One systematic review and 14 RCTs met the inclusion criteria. The use of L. reuteri may be considered in the management of acute gastroenteritis as an adjunct to rehydration. There is some evidence that L. reuteri is effective in reducing the incidence of diarrhea in children attending day care centers. There is no evidence of effectiveness of L. reuteri in preventing nosocomial diarrhea in children. The administration of L. reuteri is likely to reduce crying time in infants with infantile colic in exclusively or predominantly exclusively breast-fed infants, but not in formula-fed infants. More studies are needed. Preliminary data suggest that L. reuteri may be effective in the prevention of some functional gastrointestinal disorders, such as colic and regurgitation. This innovative approach needs further evaluation by an independent research team. Preliminary evidence provides a rationale for further assessing the efficacy of L. reuteri for treating functional constipation or functional abdominal pain. However, it is too soon to recommend the routine use of L. reuteri for these conditions. There are no safety concerns with regard to the use of L. reuteri in nonimmunocompromised subjects. There are also data to support the safety of using L. reuteri in preterm infants. CONCLUSION: Our results precisely define current evidence on the effects of the administration of L. reuteri DSM 17938 to the pediatric population.

Gelatin tannate for treating acute gastroenteritis: a systematic review.

Gelatin tannate (GT) is a complex of tannic acid, which possesses astringent, antibacterial, and anti-inflammatory properties, and a protective gelatin. It is increasingly being marketed as an antidiarrheal drug. Our aim was to review data on the effectiveness of GT in treating acute gastroenteritis (AGE) in children and adults. The MEDLINE, EMBASE, and the Cochrane Library databases were searched in July 2013, with no language restrictions, for controlled clinical trials. Additional references were obtained from reviewed articles. Two trials met the inclusion criteria. In adults, one randomized controlled trial involving 40 subjects (mean age: 43±13 years) found that, compared with placebo, GT may be more effective at reducing some symptoms of AGE in the first 48 h after initiation of treatment. In children, one poor quality study (no randomization and no blinding) involving 211 children (mean age: 2.5±2.4 years) reported some beneficial effect of GT at 12 h after initiation of treatment. None of the studies evaluated the effect of GT on the primary outcome measures for this review such as stool output, duration of diarrhea, admission to hospital, duration of hospital stay, and (in children) weight gain after rehydration. Currently, there is no evidence to support the use of GT for treating AGE in children and only sparse evidence to support the use of GT in adults. Further well-designed trials, with sufficient power, adequate follow-up periods, and clinically relevant outcome measures, are needed. These include stool volume, duration of diarrhea, admission to hospital, duration of hospital stay, weight gain after rehydration, and adverse effects.