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Background: Face masks, also referred to as half masks, are essential to protect healthcare professionals working in close contact with patients with COVID-19-related symptoms. Because of the Corona material shortages, healthcare institutions sought an approach to reuse face masks or to purchase new, imported masks. The filter quality of these masks remained unclear. Therefore, the aim of this study was to assess the quality of sterilized and imported FFP2/KN95 face masks. Methods: A 48-minute steam sterilization process of single-use FFP2/KN95 face masks with a 15 minute holding time at 121°C was developed, validated and implemented in the Central Sterilization Departments (CSSD) of 19 different hospitals. Masks sterilized by steam and H2O2 plasma as well as new, imported masks were tested for particle filtration efficiency (PFE) and pressure drop in a custom-made test setup. Results: The results of 84 masks tested on the PFE dry particle test setup showed differences of 2.3±2% (mean±SD). Test data showed that the mean PFE values of 444 sterilized FFP2 face masks from the 19 CSSDs were 90±11% (mean±SD), and those of 474 new, imported KN95/FFP2 face masks were 83±16% (mean±SD). Differences in PFE of masks received from different sterilization departments were found. Conclusion: Face masks can be reprocessed with 121 °C steam or H2O2 plasma sterilization with a minimal reduction in PFE. PFE comparison between filter material of sterilized masks and new, imported masks indicates that the filter material of most reprocessed masks of high quality brands can outperform new, imported face masks of unknown brands. Although the PFE of tested face masks from different sterilization departments remained efficient, using different types of sterilization equipment, can result in different PFE outcomes. [ABSTRACT FROM AUTHOR]

Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro- 9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10-2 electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems. [ABSTRACT FROM AUTHOR]

In this study, polycarbonate (PC) and polystyrene (PS) are subjected to plastic deformation by means of cold rolling and the resulting variation of the free volume and its subsequent time evolution after rolling is investigated by means of positron annihilation lifetime spectroscopy (PALS). The value of the long lifetime component that is attributed to the decay of ortho-positronium (τo-Ps) and its intensity (Io-Ps) are used to characterize, respectively, the size and the concentration of the free-volume holes. In addition to the PALS experiments, the effect of plastic deformation on the dynamic tensile modulus is investigated. The PALS results show that both for well-aged PC and PS an increase of τo-Ps and a decrease of Io-Ps occur upon plastic deformation. During the subsequent aging, τo-Ps tends to return to the value assumed before plastic deformation, while Io-Ps remains constant with time. These results corroborate the idea of an amorphous-amorphous transition, rather than that of a “mechanical rejuvenation” as proposed in the past to explain the ability of plastic deformation to reinitiate physical aging. Finally, a linear relation between the size of the free-volume holes and the dynamic tensile modulus is found, which suggests that the stiffness of amorphous glassy polymers is fully determined by their nanoscopic structure. [ABSTRACT FROM AUTHOR]

We have studied the molecular orientational order and director kinetics of the nematic phase formed by dissolving poly-p-phenylene-terephthalamide (PPTA) in sulphuric acid using deuterium NMR spectroscopy. Measurements were made on standard polymer samples using deuterated sulphuric acid and with deuterated PPTA in normal H2SO4. The influence of temperature and polymer concentration on the quadrupolar splittings which reflect the orientational order of the solvent and the solute are reported. The biphasic gap, between the nematic and the isotropic phase, for an 8.84%(w/w) solution was found to be about 10 °C. The influence of polymer concentration on the orientational order of the polymer solute is consistent with the predictions of a modified Maier–Saupe theory. By measuring the time dependence of the spectra the kinetics of field-induced director reorientation has been studied. The reorientation process from a multidomain sample to a uniform director alignment can be adequately described using an approach in which the different domains are decoupled. [ABSTRACT FROM AUTHOR]

In this paper, refractometry is used for characterization of the adhesion between bitumen and aggregates. The main purpose of this paper is to find whether preferential adsorption occurs and can be demonstrated in pure and undiluted road-construction bitumen. For this, bitumens from different crudes with different penetration grades and six bitumens with different penetration grades from the same crude are examined in a refractometer. The measurements give indices of refraction of the different bitumens at the bitumen-aggregate interface. In this paper, it is concluded that the indices of refraction are strongly related to the penetration of the bitumens. Clear preferential adsorption was not found from the refractometric measurements at this stage. It is suggested that a change in the composition of the bulk of the bitumen results in a similar change in composition at the aggregate surface. [ABSTRACT FROM AUTHOR]

South African women and children remain at the centre of the human immunodeficiency virus (HIV) pandemic, and maternal well-being plays a critical role in child health. In this study, we evaluated the impact of the paediatric visit on the determination of antiretroviral therapy (ART) eligibility in mothers using Alere Pima™ Analyser (Pima™) testing as an adjunct to routine care. Fifty-two mothers who had failed to obtain routine CD4 screening were enrolled during the paediatric visit at Tygerberg Children’s Hospital between November 2011 and May 2012. Clinical staging assessments and parallel standard CD4 cell count testing were performed. Finger-prick samples for the Pima™, and simultaneous venous samples for reference flow cytometry, were obtained. The Pima™ identified 37% of mothers as meeting ART eligibility versus 35% using the reference flow cytometry method. An additional 4% of mothers were identified using World Health Organization clinical staging only. The sensitivity of the Pima™ was 89%, specificity 91%, and positive and negative predictive values 84% and 94%, respectively. These results indicate that the paediatric HIV care visit can provide a valuable additional intervention opportunity to identify mothers in need of ART, with point-of-care CD4 technologies being used as a meaningful adjunct in screening for ART eligibility. [ABSTRACT FROM AUTHOR]

Structure and rheological properties of hybrids with polymer matrix and layered silicates as filler were studied. Solution containing 60% wt of hydroxypropylcellulose (HPC) in oligomeric polyethyleneglycol (PEG) was used as a matrix. The peculiarity of this study is that the matrix depending on temperature can form different phase states including liquid-crystalline (LC). So, a possibility of coexistence and superposition of different ordered structures can be realized at different temperatures. Three different fillers were used: natural Na-montmorillonite (MMT) and organoclays obtained by treating MMT with surfactants varying in polarity of their molecules. Depending on the type of clay, materials with different morphology can be obtained. X-ray data showed that PEG intercalates all types of clay used whereas penetration of HPC macromolecules into clay galleries during mixing does not occur. Clay modified with more polar surfactant should be treated as the most convenient material to be intercalated by PEG. Rheological studies (included steady-state and dynamic shear properties in a wide temperature range) demonstrate that composites are viscoplastic materials and the yield stress is observed already at 5% fillers loading. The level of the yield stress depends on the phase state of the matrix being induced by the superposition of structures formed by clay particles as well as by the LC phase (if it exists). The same conclusion can be made on the base of linear oscillatory measurements because the existence of the LC phase and/or the presence of filler lead to a pseudo solid-like behavior of a system as whole. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The focus of this study is on incorporating pendant sulfonate groups along the backbone of a liquid crystalline polyester (LCPE) with the aim to improve the dispersion of single wall carbon nanotubes (SWNTs) and nanodiamonds (NDs). Two LCPE matrices, one sulfonated (LCPE-S) and one nonsulfonated reference polymer (LCPE-R), were successfully synthesized via a melt condensation method using aromatic and aliphatic AB, AA, and BB-type monomers. Upon the introduction of SWNT and ND particles, the glass transition temperature ( Tg) of the sulfonated LCPE increased from 21.5 °C to 41.0 °C and 41.9 °C, for SWNTs and NDs, respectively. When sulfonate groups were absent, a decrease in Tg was observed. The storage modulus ( E′) followed a similar trend, i.e., E′ increased from 1.3 GPa to 5.2 GPa and 3.4 GPa, upon the addition of NDs and SWNTs. The LCPE-S showed a lower thermal stability due to the loss of sulfonate groups, i.e. the 5% weight loss temperature ( T [ABSTRACT FROM AUTHOR]

We report the synthesis and properties of a homologous series of asymmetric, mesogenic derivatives of 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). Benzyloxy (BnO-), alkoxy benzoate ester derivatives BnO-ODBP-Ph-O-Cn, where n = 4, 5, 6, 7, 8, 9, 12, were studied by 2H-NMR, X-ray diffraction and polarising microscopy in order to ascertain if the lower temperature nematic phases exhibited biaxiality. Deuterium nuclear magnetic resonance (NMR) of labelled probes in these asymmetric mesogens does not show evidence of biaxiality. The absence of biaxiality is discussed in terms of the statistical non-linearity of these asymmetric ODBP mesogens. [ABSTRACT FROM AUTHOR]

In the present work we relate the microstructure of a distinct type of short fiber reinforced blends (SFRBs) to their melt rheology. These systems consist of polyamide-6 (PA6) and short glass fiber (GF) reinforcement dispersed in a polyethylene (PE) matrix. An appropriate choice of the components, their interfacial characteristics, and the processing route led to the formation of a continuous network, percolating throughout the matrix. The network consisted of fibers (GF) “welded” together by bridges of the dispersed phase material (PA6). A strong strain softening of the melts of the SFRBs was observed at strain amplitudes below 3%, which was absent for their binary equivalents with the same fiber loading and no second thermoplastic component. Based on the specific microstructure of the blends, a model is proposed that accounts for their strain softening behavior. The model considers the “capillary” forces acting between the fibers participating in the network. These capillary forces arise from the deformation of the PA6 bridges “welding” the fibers together. We propose that the macroscopic deformation process produces points of locally concentrated and magnified deformation. The deformation at these points is sufficient to produce the strain softening of the system. The three parameters that appear in the model have a clear physical meaning. The theoretical results are in good qualitative agreement with the experiments. [ABSTRACT FROM AUTHOR]

The sorption of water vapor in Kapton® (polyimide) films has been investigated with a new method, dielectric sorption analysis (DSA). The technique is based on high-resolution time-resolved capacitance measurements performed during exposure of an organic coating to humidified nitrogen. The basis of the method is described together with experimental details related to the capacitance measurement, long-term stability, reproducibility, and other characteristics of the setup. The technique allows the determination of the sorption/desorption and diffusion characteristics of a coating on a time scale varying from seconds to days. Mass transport properties derived from complementary weight measurements are in good agreement with the DSA results. Real-time monitoring of the moisture sorption in organic coatings demonstrates the potential of the technique in the field of nondestructive coating inspection and testing. [ABSTRACT FROM AUTHOR]

Preliminary molecular dynamics simulations of the nematic phase of 4-n-pentyl-4′-cyanobiphenyl are described. The simulations include all molecular degrees of freedom. The influence of the molecular dipole moment is investigated by comparing simulations with and without a charge distribution on the molecules. Inclusion of the charge distribution is found to lead to a slight broadening of the orientational distribution function, in qualitative agreement with Raman measurements of the orientational order parameters. [ABSTRACT FROM AUTHOR]

The article focuses on implication of molecular dynamics simulation in switching 5CB dipole synthesis. The study highlights the establishment of molecular density (MD) of liquid crystals which describe usable in developing model system. The author believes that the atomic detail MD simulations in liquid crystallization establish orientational effect of dipole moment, and the dipole-induced reaction and MD simulations shows electric properties in the model system.

Two series of discotic liquid crystals, one based on metal-free and the other on copper containing phthalocyanine (Pc) as the central core and eight peripherally n-alkoxy groups (C6–C12) as substituents have been synthesized and their mesomorphic properties and structural parameters have been determined. These compounds represent a series totally devoid of polymorphism, the mesophase in all cases being Dho. In the solid state an orthorhombic two dimensional lattice with four molecules per unit cell and a presumably tilted stacking is present, while in the mesophase the planes of the molecules are on average perpendicular to the direction of the stacks. The aggregation behaviour of the C8, C10 and C12 homologues was studied as a function of solvent polarity and of concentration. The electrical properties of the copper complexes of the n-dodecoxy and n-octoxy derivatives have been determined by means of complex impedance spectroscopy and compared with those of the non-mesogenic CuPc. [ABSTRACT FROM AUTHOR]

A theory of the tensile strength of oriented polymer fibres is presented. From an analysis of the observed fracture envelope it is shown that the criterion for fracture of the fibre is either a critical shear stress or a critical shear strain. Owing to the chain orientation distribution in the fibre, the initiation of fracture is likely to occur in domains whose symmetry axes have orientation angles in the tail of this distribution. By considering the fibre as a molecular composite, the tensile strength is calculated as a function of the modulus. The results are compared to the observed values of PET, POK, cellulose II, PpPTA, PBO and PIPD fibres. In addition, the relation between the ultimate strength and the chain length distribution is investigated. By using the critical shear strain as a fracture criterion in the Eyring reduced time model, relations are derived for the fibre strength as a function of the load rate, as well as for the lifetime under constant load. Moreover, this model predicts the dependence of the strength on the temperature. The theoretical relations are compared to the experimental results on PpPTA fibres. [ABSTRACT FROM AUTHOR]

In this study, the binary phase diagram of two triphenylene derivatives is investigated by using differential scanning calorimetry (DSC), optical polarizing microscopy (OPM), and wide-angle x-ray scattering (WAXS). The triphenylene derivatives studied are based on hexa-alklyoxy-triphenylene. One compound in the binary mixture HAT6 has six symmetrical hexyloxy tails each containing six carbon atoms. The other compound, HAT6-C10UC6, has one asymmetrical tail bearing a urea functionality at a specific distance from the aromatic core. The introduction of this asymmetrical H-bonding unit into the structure results in a complete disruption of liquid crystallinity while a “pseudo re-entrant” phenomenon is observed in the binary mixture phase diagram. [ABSTRACT FROM AUTHOR]

Presents a small-angle neutron scattering investigation of rigid polyelectrolytes under shear. Applications of rigid-rod synthetic molecules; Methodology used to study the analysis; Discussion of polymerization; Sample preparation and conditioning of polymers.

We use an elastomer as infill material for a photonic crystal. As a result of the thermal-expansion-induced strongly negative thermal optical coefficient, this material is highly suitable for thermal tuning of the transmission of a cavity. This is demonstrated by global infilling of a hole-type silicon photonic crystal slab and global thermal tuning. In the temperature range 20-60 °C the cavity peak shows a pronounced elastomer-induced blue shift of 2.7 nm, which amply overcompensates the red shift arising from the thermo-optic property of the silicon. These results qualify the elastomer for tuning by local optical heating. [ABSTRACT FROM AUTHOR]