Green Assembly of Covalently Linked BiOBr/Graphene Composites for Efficient Visible Light Degradation of Dyes.

A novel high-performance BiOBr@graphene (BiOBr@G) photocatalyst with a new assembly structure had been demonstrated using a facile hydrothermal method through chemical bonding of reduced graphene oxide and structure-defined BiOBr flakes for improving charge separation and transfer performance, which were first synthesized at room temperature in immiscible solvents without corrosive acids. The prepared samples were characterized, and the BiOBr@G composite realized an efficient assembly portfolio of graphene and BiOBr flakes with defined structures, verified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman and X-ray photoelectron spectroscopy (XPS), in which BiOBr flakes were covalently linked with the assembled graphene sheets through the Bi-C bond. This composite exhibited remarkable visible light absorbance and efficient photoinduced charge splitting characteristics in comparison with those of pure BiOBr, as established by DRS absorption, photoluminescence radiation, and photocurrent study. Hence, a very small amount (5 mg) of the BiOBr@G composite displayed a complete photodegradation effect on the rhodamine B dye under only 15 min of visible light excitation, which was three times faster than that of pure BiOBr and extremely superior to that of commercial P25. This was probably ascribed to the well-defined BiOBr structure itself, elevated light absorbance, and Bi-C chemical bond inducing quick charge separation and transfer in the BiOBr@G composite. Additionally, investigations on the photocatalytic mechanism displayed that the photogenerated holes in the BiOBr valence band and derivative superoxide radicals played vital roles in the photodegradation of RhB dyes, as reinforced by the electron spin resonance method, where the covalent linking of BiOBr and graphene served as an effective pathway for charge transportation.

Self-assembly of carbon nanotube/graphitic-like flake/BiOBr nanocomposite with 1D/2D/3D heterojunctions for enhanced photocatalytic activity.

A self-assembled nanocomposite of lamellar BiOBr covalently bonded with conductive network of dispersive one-dimensional carbon nanotubes (1D CNT) and two-dimensional reduced graphitic-like flakes (2D GF) had been in situ constructed using one-pot facile solvothermal technique. Through self-assembly, BiOBr/CNT/GF (BiOBr/CG) displayed three-dimensional architectures in which a strong interfacial contact interaction and covalent banding between BiOBr nanostructures and CNT/GF network appeared. Furthermore, visible-light-driven catalytic activity of BiOBr/CG for RhB dye degradation was superior to that of pure BiOBr or BiOBr/C. Interestingly, the photodegradation activity of the BiOBr/CG nanocomposite could be improved further by subsequent facile annealing treatment, in which the annealed BiOBr/CG-DS had degraded almost 97.9% of RhB dye within only 100 min of visible-light irradiation. Moreover, analysis of the photodegradation mechanism revealed that the repression of electron-hole recombination in the nanocomposites, with sufficient covalent interfacial contact with CNT/GF as effective electron collecting and transferring system, were responsible for the outstanding photocatalytic performance. This effect, in turn, led to the continuous generation of O2- and OH reactive oxygen species for the degradation of RhB dye, which was verified by active species trapping and ESR spectra.

Paper-like flexible optically isotropic liquid crystal film for tunable diffractive devices.

We have demonstrated a paper-like diffractive film in which nano-structured liquid crystal droplets are embedded in elastomeric monomer incorporated polymer matrix by polymerization induced phase-separation. The film with voltage-tunable phase grating exhibits an optically isotropic phase with high transparency and an effective chromatic diffraction for an incident white light with sub-millisecond switching time. In addition, the proposed diffractive film is exhibiting excellent chemical stability against organic and inorganic solvents. In this paper, the diffraction properties of test films depending on incident polarization direction, wavelength, and spatial dispersion are characterized. Easy processing and optically isotropic nature of the film imparts potential applications to flexible electro-optic devices that can be widely implemented in wearable photonics.

Measuring ambulation with wrist-based and hip-based activity trackers for children with cerebral palsy.

AIM: To assess the accuracy of consumer available wrist-based and hip-based activity trackers in quantitatively measuring ambulation in children with cerebral palsy (CP). METHOD: Thirty-nine children (23 males, 16 females; mean age [SD] 9y 7mo [3y 5mo]; range 4-15y) with CP were fitted with trackers both on their wrist and hip. Each participant stood for 3 minutes, ambulated in a hallway, and sat for 3 minutes. The number of steps and distance were recorded on trackers and compared to manually counted steps and distance. Pearson correlation coefficients were determined for the number of steps during ambulation from each tracker and a manual count. Mean absolute error (MAE) and range of errors were calculated for steps during ambulation for each tracker and a manual count and for distance for each tracker and hallway distance. RESULTS: For the number of steps, a weak inverse relationship (r=-0.033) was found for the wrist-based tracker and a strong positive relationship (r=0.991) for the hip-based tracker. The MAE was 88 steps for the wrist-based and seven steps for the hip-based tracker. The MAE for distance was 0.06 miles for the wrist-based and 0.07 miles for the hip-based tracker. INTERPRETATION: Only the hip-based tracker provided an accurate step count; neither tracker was accurate for distance. Thus, ambulation of children with CP can be accurately quantified with readily available trackers. WHAT THIS PAPER ADDS: Consumer available activity trackers accurately measure ambulation in children with cerebral palsy (CP). The hip-based tracker is more accurate than the wrist-based tracker for children with CP. The hip-based Fitbit activity tracker accurately measures step counts of children with CP during ambulation.

MEDICIÓN DE LA AMBULACIÓN CON RASTREADORES DE ACTIVIDAD DE MUÑECA Y CADERA PARA NIÑOS CON PARÁLISIS CEREBRAL: OBJETIVO: Evaluar la precisión de los rastreadores de actividad basados ​​en la muñeca y en la cadera disponibles para el consumidor en la medición cuantitativa de la ambulación en niños con parálisis cerebral (PC) METODO: Treinta y nueve niños (23 varones, 16 mujeres; edad media [DS] 9 años y 7 meses [3 años y 5 meses]; rango 4-15 años) con PC fueron equipados con rastreadores en su muñeca y cadera. Cada participante se paró durante 3 minutos, caminó por un pasillo y se sentó durante 3 minutos. La cantidad de pasos y la distancia se registraron en los rastreadores y se compararon con los pasos y la distancia contados manualmente. Los coeficientes de correlación de Pearson se determinaron para el número de pasos durante la ambulación de cada rastreador y un conteo manual. El error absoluto medio (MAE) y el rango de errores se calcularon para los pasos durante la ambulación y la distancia del pasillo para cada rastreador y para el conteo manual. RESULTADOS: Para el número de pasos, se encontró una relación inversa débil (r = -0.033) para el rastreador ubicado en la muñeca y una relación positiva fuerte (r = 0.991) para el rastreador ubicado en la cadera. El MAE fue de 88 pasos para la muñeca y siete pasos para el rastreador de la cadera. El MAE para la distancia fue de 0.06 millas para la muñeca y 0.07 millas para el rastreador ubicado en la cadera. INTERPRETACIÓN: Solo el rastreador ubicado en la cadera proporcionó un conteo de pasos preciso; ninguno de los rastreadores era preciso para la distancia. Por lo tanto, la deambulación de los niños con PC se puede cuantificar con precisión con rastreadores fácilmente disponibles.

MEDINDO A DEAMBULAÇÃO COM RASTREADOR DE ATIVIDADE POSICIONADO NO PUNHO E QUADRIL COMERCIALMENTE DISPONÍVEL EM CRIANÇAS COM PARALISIA CEREBRAL: OBJETIVO: Avaliar a precisão de rastreadores de atividade posicionados no punho e quadril, disponíveis para o consumidor, para mensurar qualitativamente a deambulação em crianças com paralisia cerebral (PC). MÉTODO: Trinta e nove crianças (23 meninos, 16 meninas; média da idade [DP] 9 anos e 7 meses [3 anos e 5 meses]; amplitude 4-15 anos) com PC foram equipados com rastreadores em punho e quadril. Cada participante permaneceu em pé durante 3 minutos, andando em um corredor, e sentado por 3 minutos. O número de passos e distância foram registrados nos rastreadores e comparados com os passos e distância medidos manualmente. Coeficientes de correlação de Pearson foram determinados para o número de passos durante a deambulação para cada rastreador e a contagem manual. O Erro Médio Absoluto (EMA) e variância de erros foram calculados para os passos durante a deambulação para cada rastreador e a contagem manual e para a distância de cada rastreador e a distância do corredor. RESULTADOS: Para o número de passos, uma relação inversa fraca (r=-0,033) foi encontrada entre o rastreador do punho e uma relação positiva forte (r=0,991) para o reastreador do quadril. A EMA foi de 88 passos para o rastreador do punho e sete passos para o rastreador do quadril. A EMA para a distância foi de 0,06 milhas (9,66km) para o rastreador do punho e 0,07 milhas (11,26km) para o rastreador do quadril. INTERPRETAÇÃO: Somente o rastreador do quadril forneceu a contagem precisa dos passos; nenhum rastreador foi preciso para a distância. Assim, a deambulação em crianças com PC pode ser quantificada com precisão com os rastreadores atualmente disponíveis.

Facile synthesis of carbon nanotubes covalently modified with ZnO nanorods for enhanced photodecomposition of dyes.

Utilizing a one-pot solvothermal procedure novel one-dimensional zinc oxide-carbon nanotube nanohybrids (ZnCT) were synthesized in alcohol-alkali solution, free of catalytic assistance. The ZnCT hybrids were prepared through covalent modification of zinc oxide nanorods (ZnO NRs) with functionalized carbon nanotubes (f-CNTs). The morphology and microstructure of as-prepared ZnCT hybrids were characterized by scanning electron microscopy (SEM), powder X-ray diffraction, Raman, X-ray photoelectron and UV-vis absorption spectroscopies. SEM images of the ZnCT hybrids indicated that the ZnOethanol NRs grew longer along the vertical radial (0 0 0 1) surface and aggregated to a lesser extent than the analogous ZnOmethanol NRs. Photodegradation analysis showed that the off-white ZnCTethanol hybrid with ascendant UV-visible light absorption had displayed superior photocatalytic activity towards Rhodamine B (RhB) dyes than either pure ZnOethanol, ZnOmethanol NRs or ZnCTmethanol hybrid, among which the photocatalytic activity of ZnOethanol NRs was better than that of ZnOmethanol NRs. Raman and X-ray photoelectron spectroscopy analyses confirmed a strong interaction between f-CNTs and ZnOethanol NRs in ZnCTethanol hybrid, in which Zn ions were chemically bonded to negatively charged oxygen-containing groups at the graphene-like surface of f-CNTs. The enhanced separation lifetime of the photogenerated electron-hole observed by surface photovoltage and photocurrent measurements of the ZnCTethanol hybrid was attributed to the efficient covalent linking of ZnOC and close contact configuration between the f-CNTs and ZnOethanol NRs. Further controlled photodegradation and electron spin resonance (ESR) analyses revealed that the photodegradation of RhB dyes resulted from photogenerated holes, and radical species, such as O2-, OH-, which were formed in-situ. Details of the photocatalytic mechanism were also explored herein.

Fast response and transparent optically isotropic liquid crystal diffraction grating.

We have demonstrated an electrically tunable less polarization sensitive and fast response nanostructured polymer dispersed liquid crystal (nano-PDLC) diffraction grating. Fabricated nano-PDLC is optically transparent in visible wavelength regime. The optical isotropic nature was increased by minimizing the liquid crystal droplet size below visible wavelength thereby eliminated scattering. Diffraction properties of in-plane switching (IPS) and fringe-field switching (FFS) cells were measured and compared with one another up to four orders. We have obtained a pore-type polymer network constructed by highly interlinked polymer beads at which the response time is improved by strong interaction of liquid crystal molecules with polymer beads at interface. The diffraction pattern obtained by transparent nano-PDLC film has several interesting properties such as less polarization dependence and fast response. This device can be used as transparent tunable diffractor along with other photonic application.

Dynamic Response of Graphitic Flakes in Nematic Liquid Crystals: Confinement and Host Effect.

Electric field-induced reorientation of suspended graphitic (GP) flakes and its relaxation back to the original state in a nematic liquid crystal (NLC) host are of interest not only in academia, but also in industrial applications, such as polarizer-free and optical film-free displays, and electro-optic light modulators. As the phenomenon has been demonstrated by thorough observation, the detailed study of the physical properties of the host NLC (the magnitude of dielectric anisotropy, elastic constants, and rotational viscosity), the size of the GP flakes, and cell thickness, are urgently required to be explored and investigated. Here, we demonstrate that the response time of GP flakes reorientation associated with an NLC host can be effectively enhanced by controlling the physical properties. In a vertical field-on state, higher dielectric anisotropy and higher elasticity of NLC give rise to quicker reorientation of the GP flakes (switching from planar to vertical alignment) due to the field-induced coupling effect of interfacial Maxwell-Wagner polarization and NLC reorientation. In a field off-state, lower rotational viscosity of NLC and lower cell thickness can help to reduce the decay time of GP flakes reoriented from vertical to planar alignment. This is mainly attributed to strong coupling between GP flakes and NLC originating from the strong π-π interaction between benzene rings in the honeycomb-like graphene structure and in NLC molecules. The high-uniformity of reoriented GP flakes exhibits a possibility of new light modulation with a relatively faster response time in the switching process and, thus, it can show potential application in field-induced memory and modulation devices.

Comparative studies on field-induced stretching behavior of single-walled and multiwalled carbon nanotube clusters.

We demonstrate distinct entanglement of single-walled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT) clusters in nematic liquid crystal medium using scanning electron microscopy technique and the entanglement influence on electric field-induced stretching phenomena of the said clusters in the same medium under optical microscopy investigation. The observed stretching threshold field for MWCNT clusters is found to be higher than the SWCNT counterpart caused by the interplay between attractive field-induced dipolar interaction of intercarbon nanotube (CNT) bundles and the distinct degree of entanglement of neighboring CNT bundles. Subsequently observed different tensile elasticity modulus results for different CNT kinds also confirm different CNT bundle entanglement and attractive dipolar interaction between adjacent CNT bundles in CNT clusters are responsible for distinct stretching threshold field behavior.

Elongation of discotic liquid crystal strands and lubricant effects.

After a short review on the physics of pulled threads and their mechanical properties, the paper reports and discusses the strand elongation of disordered columnar phases, hexagonal or lamella-columnar, of small molecules or polymers. The mechanical properties appear to be relevant to the length of the columns of molecules compared to the thread length, instead of the usual correlation length. If, taking the entanglement effect into account, the column length is short, the strand exhibits rather fluid-like properties that may even look nematic-like at the macroscopic scale. The Plateau-Rayleigh instability breaks the thread shortly thereafter. However, because the hydrodynamic objects are the columns instead of the molecules, the viscosity is anomalously large. The observations show that the strands in the columnar phases are made of filaments, or fibrils, which are bundles of columns of molecules. This explains the grooves and rings, which are observed on the antenna or bamboo-like strand profiles. On pulling a strand, the elongation stress eventually exceeds the plasticity threshold, thus breaking the columns and the filaments. As a result, cracks, more exactly, giant dislocations are formed. These change the strand thickness by steps of different birefringence colors. Interestingly, the addition of a solute may drastically change the effective viscosity of the columnar phase and its mechanical properties. Some solutes, such as alkanes, exhibit lubricant and detangling properties, whereas others such as triphenylene, are antilubricant.

Dynamic electro-optic response of graphene/graphitic flakes in nematic liquid crystals.

Electric field induced dynamic reorientation phenomenon of graphene/graphitic flakes in homogeneously aligned nematic liquid crystal (NLC) medium has been demonstrated by optical microscopy. The flakes reorient from parallel to perpendicular configuration with respect to boundary plates of confining cells for an applied field strength of as low as tens of millivolt per micrometer. After field removal the reoriented flakes recover to their initial state with the help of relaxation of NLC. Considering flake reorientation phenomenon both in positive and negative dielectric anisotropy NLCs, the reorientation process depends on interfacial Maxwell-Wagner polarization and NLC director reorientation. We propose a phenomenological model based on electric field induced potential energy of graphitic flakes and coupling contribution of positive NLC to generate the rotational kinetic energy for flake reorientation. The model successfully explains the dependence of flake reorientation time over flake shape anisotropy, electric-field strength, and flake area. Using present operating scheme it is possible to generate dark field-off state and bright field-on state, having application potential for electro-optic light modulation devices.

Electric-field induced elastic stretching of multiwalled carbon nanotube clusters: a realistic model.

The oscillating electric-field induced stretching phenomenon of multiwalled carbon nanotube (MWCNT) clusters in liquid crystal medium demonstrates distinct threshold behaviour under optical microscopic investigation. The optimum field required for the initiation of MWCNT cluster stretching is found to depend on their length in the field-off state. The phenomenon has been explained in light of a classical theoretical model assuming MWCNT agglomerates as a single electric dipole. The spring constant and induced charge obtained by fitting the formulated theoretical model show good agreement with previous reports, hence establish the proposed dipolar reorientation mechanism of MWCNT clusters induced by the electric field.

High performance transflective liquid crystal display associated with fringe-field switching device.

The outdoor readability of the most popular portable liquid crystal display (LCDs) viz. fringe field switching has been addressed both in single and dual cell gap transflective devices. The devices use dual orientation, such as, homogeneous alignment in transmissive (T) part and 64° twisted alignment in reflective (R) part. The dark states of the proposed devices are achieved by controlling phase retardation in T part and polarization rotation in R part and the white state is realized by rotating optic axis of liquid crystal and removing phase retardation in T and R parts, respectively. The devices show high light efficiency without requiring any optical compensation films, exhibiting strong potential for portable display applications.

The StrataTest® human skin model, a consistent in vitro alternative for toxicological testing.

Three-dimensional in vitro skin models provide an alternative to animal testing for assessing tissue damage caused by chemical or physical agents and for the identification and characterization of agents formulated to mitigate this damage. The StrataTest® human skin model made with pathogen-free NIKS® keratinocyte progenitors is a fully-stratified tissue containing epidermal and dermal components that possesses barrier function as determined by measurements of electrical impedance. Independent batches of skin tissues responded consistently to known chemical irritants even after refrigerated storage for up to 7 days. Reactive oxygen species (ROS) were detected after exposure of skin tissues to ozone, cigarette smoke or ultraviolet (UV) irradiation. Pretreatment with the antioxidant parthenolide-depleted (PD)-Feverfew extract prevented cigarette smoke-induced or UV irradiation-mediated increases in ROS. Interleukin (IL)-1α and IL-1 receptor antagonist (IL-1RA) secretion increased in a dose dependent manner following UV irradiation but cytokine release was abrogated by pretreatment with a UVA/UVB sunscreen. Similarly, immunohistochemical detection showed increased thymidine dimer formation in UV-irradiated skin tissue that was prevented with sunscreen pretreatment. These results demonstrate that the StrataTest® human skin model is broadly applicable to a wide range of in vitro toxicological assays.

Viewing angle controllable liquid crystal display with high transmittance.

All conventional viewing angle switchable liquid crystal displays with pixel division have drawback in light efficiency because the sub-pixel that controls viewing angle does not transmit the incident light at normal direction. In this paper, we propose new viewing angle controllable homogeneously aligned liquid crystal display in which the pixel is composed of red, green, blue, and white pixels. The colored pixels are driven by fringe-field switching and the white pixel is driven by complex field. In wide-viewing angle mode, the liquid crystal (LC) directors in all pixels rotate in plane, contributing to high transmittance. In narrow-viewing angle mode, the LC directors in color pixels rotate in plane for light transmission while the LC directors in white pixel can rotate or tilt upward by simultaneous fringe and vertical electric field. The high tilted LC directors generate light leakage in oblique directions which can be utilized for viewing angle control and also transmission at normal direction for image expression. The proposed device overcomes the long standing problem of transmittance sacrifice in the conventional devices.