Relaxation Properties of Pressure-sensitive Adhesives upon Withdrawal of Bonding Pressure

Relaxation properties of pressure-sensitive adhesives (PSA) have been studied with the squeeze-recoil tester used in the regime of parallel-plate dilatometer under conditions imitating the removal of compressive force in the course of adhesive bond formation. The relaxation properties of PSAs are compared with their adhesive behavior measured using the 180-Deg Peel Test. Two classes of PSAs are considered: 1) conventional rubbery adhesives based on the mixtures of styrene-isoprene-styrene (SIS) block copolymer with a tackifier resin and a plasticizer, and butyl rubber plasticized with low-molecular-weight polyisobutylene, and 2) hydrophilic PSAs composed of the blends of high-molecular-weight poly(N-vinyl pyrrolidone) (PVP) with oligomeric polyethylene glycol (PEG). By comparing the adhesive and relaxation behaviors of different PSAs, the relaxation criteria for pressure-sensitive adhesion have been stated. Relaxation behavior of the examined PSAs demonstrates two values of retardation time: the shorter retardation time of 10–70?sec and the longer time of 300–660?sec. These times can be associated, respectively, with small- and large-scale mechanisms of strain recovery. By comparing the relaxation and adhesive properties of PVP-PEG blend (which involves the formation of a hydrogen-bonded network through both terminal hydroxyl groups in PEG short chains) with the properties of covalently crosslinked copolymers of vinyl pyrrolidone (VP) with PEG-diacrylate and comb-like VP copolymers with PEG-monomethacrylate, the contributions of covalent crosslinking and H-bonding network have been characterized.     

A New Field-Compatible Methodology for the Collection and Analysis of Fungal Fragments

A field-compatible collection system was developed and tested for the collection and analysis of fungal fragments. The new collection system consists of two types of Sharp-Cut cyclone samplers (PM _2.5 and PM _1.0 ) and an after-filter. Fungal particles are collected into three size fractions: (1) spores ( > 2.5 μ m); (2) a fragment-spore mixture (1.0–2.5 μ m); and (3) submicrometer-sized fragments ( < 1.0 μ m). The system was laboratory-tested using polystyrene latex (PSL) particles and particulate matter aerosolized from sporulating Aspergillus versicolor and Stachybotrys chartarum cultures. In addition to the particle count measured with direct-reading instruments, the (1 → 3)- β -D-glucan content in each size fraction was determined with the Limulus Amebocyte Lysate (LAL) assay.

Experiments conducted with PSL particles showed that the 50% cut-off values of the two cyclone samplers under the test conditions were 2.25 μ m and 1.05 μ m, respectively. No particle bounce onto the after-filter was observed when the total particle number entering the collection system was kept below 1.6 × 10 ⁸ . The (1 → 3)- β -D-glucan assay of samples aerosolized from both fungal species suggested that surface area is an important factor for determining the (1 → 3)- β -D-glucan content in the entire size-range of particles.

In conclusion, the new methodology is a promising tool for separating and analyzing fungal fragment samples.     

Enhancement of Surfactants in Nanoparticles Produced by an Electrospray Aerosol Generator

Electrospray aerosol generators (EAGs) disperse conducting solutions into air, promptly neutralize the particles to remove the excess charge, and evaporate the residual solvent with a dry air flow. For solutions containing multiple solutes, the particles may become enhanced in the more surface-active solutes. The extent of the enhancement was estimated for nanoparticles electrosprayed from a solution containing NaCl and surfactant sodium dodecyl sulfate (SDS) mixed in a 9:1 weight ratio. A tandem particle mobility analyzer was used to quantify the hygroscopic growth factor (GF). The relative fractions of NaCl and SDS in the particles were estimated from the measured GFs assuming that NaCl and SDS take up water independently of each other. The nanoparticles were considerably enhanced in SDS relative to the starting solution, with the NaCl:SDS weight ratio increasing with the distance from the EAG electrified capillary tip to the neutralizer, and reaching ～1:1 at the longest distances probed. The enhancement in SDS likely occurred during particle fission events as particles traveled from the capillary to the neutralizer. This study has practical ramifications for aerosol nanotechnology and aerosol-assisted drug delivery, which rely on EAG as an instrument of choice for nanoparticle generation.

Copyright 2012 American Association for Aerosol Research     

Techniques for Dispersion of Microorganisms into Air

ABSTRACT

Many commercially available devices initially developed for dispersion of biologically inert particles have been adopted for aerosolization of microoganisms in laboratory settings. However, these dispersion devices are not always adequate for microbial particles, as they do not simulate natural release into air. Wet dispersion methods are appropriate for viruses and most bacteria, whereas dry methods are more suitable for most fungal and actinomycete spores. Characteristics of the resulting aerosol are dependent on the dispersing shear forces and the sensitivity and agglomeration of the tested microorganisms. Consequently, each microbial group may need a specific dispersion technique. The following devices have been developed and tested in this study: the bubbling aerosol disperser, the agar-tube disperser, and the swirling-flow disperser. Testing included the evaluation of both physical and microbiological characteristics of aerosolized microorganisms. Each of the dispersers has shown several advantages over commercially available ones. When used for the dispersion of bacteria from the liquid suspension, the bubbling aerosol disperser was found to produce considerably fewer amounts of microbial fragments and much lower levels of microbial metabolic injury than the commercially available Collison nebulizer. Fungal spores dispersed from their colonies by the agar-tube disperser were found to have a more stable aerosol concentration and a lower fraction of agglomerates than achievable by conventional powder dispersion. The swirling-flow dispersion technique was used for aerosolization of actinomycetes because the agar-tube disperser could not provide a stable concentration of these spores due to their smaller size. The tests have shown that new methods minimize the changes of properties of the microorganisms during their aerosolization in the laboratory.     

Design and Collection Efficiency of a New Electrostatic Precipitator for Bioaerosol Collection

We have developed and tested a new bioaerosol sampler in which airborne microorganisms are collected by electrostatic means. In this sampler, 2 ionizers charge the incoming particles if they carry insufficient electric charge for efficient collection. The organisms are then subjected to a precipitating electric field and are collected onto 2 square agar plates positioned along the flow axis. Tests with nonbiological NaCl particles versus B. subtilis var. niger (BG) spores and vegetative cells have shown that airborne microorganisms are collected more efficiently than nonbiological particles, even when the microorganisms have first passed through an electric charge neutralizer with no additional charging applied. The difference was attributed to the natural charges contained in cell membranes or spore coats of the microorganisms. Charge-neutralized BG spores and vegetative cells were collected at 4 L/min with efficiencies close to 80%, depending on the precipitation voltage, versus 50-60% for NaCl test particles. When incoming BG spores were charged with positive ions and then collected by a precipitating voltage of + 1,300 V, about 80% of the incoming spores were collected and more than 70% of incoming spores formed colonies. These experiments with BG spores have also indicated that there were no significant particle losses inside the sampler. The collection efficiency of biological and nonbiological particles increased to 90-100% when the particles were externally charged and the precipitating voltage was increased to more than - 4,000 V. It has also been shown that the aerosolized BG spores (used as anthrax simulants for bioaerosol sensors) carry a net negative electric charge. Thus the collection efficiency depends on the polarity of the electric field applied across the agar plates. These findings indicate that the collection of airborne microorganisms is possible by electrostatic precipitation without prior electric charging if the microorganisms already carry electric charges. These are usually high immediately after their release into the air.     

Enhancement of the Performance of Low-Efficiency HVAC Filters Due to Continuous Unipolar Ion Emission

Our novel concept utilizing continuous emission of unipolar ions, which has been recently proven to enhance the efficiency of facepiece respirators, was applied to conventional HVAC filters. Laboratory study demonstrated that the air ion emission in the vicinity of a low-efficiency HVAC filter significantly improves its performance. For example, the collection efficiency of two commercial HVAC filters challenged with 1μm PSL particles jumped from 5–15% (measured with no ion emission) to 40–90% (when the ion output rate was ～ 10¹² e^?/sec). The enhancement effect depends on the filter type and, generally, on the distance from the ion emitter to the filter surface. The results were explained as follows. The air ions with high mobility are deposited on the fibers forming a macroscopic electric field, which shield out some incoming unipolarly charged particles due to repelling forces. The field estimate has shown that this explanation is feasible. The enhancement effect seems to have a good potential to be employed in industrial and residential ventilation systems as it enhances the aerosol collection efficiency of a low-efficiency HVAC filter while not affecting its pressure drop.     

Arabidopsis thaliana Plants with Different Levels of Aliphatic- and Indolyl-Glucosinolates Affect Host Selection and Performance of Bemisia tabaci

Generalist insects show reduced selectivity when subjected to similar, but not identical, host plant chemical signatures. Here, we produced transgenic Arabidopsis thaliana plants that over-express genes regulating the aliphatic- and indolyl- glucosinolates biosynthetic pathways with either a constitutive (CaMV 35S) or a phloem-specific promoter (AtSUC2). This allowed us to examine how exposure to high levels of aliphatic- or indolyl-glucosinolates in homogenous habitats (leaf cage apparatus containing two wild-type or two transgenic leaves) and heterogeneous habitats (leaf cage apparatus containing one wild-type and one transgenic leaf) affects host selection and performance of Bemsia tabaci, a generalist phloem-feeding insect. Data from homogenous habitats indicated that exposure to A. thaliana plants accumulating high levels of aliphatic- or indolyl-glucosinolates negatively affected the performance of both adult females and nymphs of B. tabaci. Data from heterogeneous habitats indicated that B. tabaci adult females selected for oviposition plants on which their offspring perform better (preference-performance relationship). However, the combinations of wild-type and transgenic plants in heterogeneous habitats increased the period of time until the first choice was made and led to increased movement rate on transgenic plants, and reduced fecundity on wild-type plants. Overall, our findings are consistent with the view that both performance and selectivity of B. tabaci decrease in heterogeneous habitats that contain plants with closely-related chemical signatures.     

Differential Activity of Plasma and Vacuolar Membrane Transporters Contributes to Genotypic Differences in Salinity Tolerance in a Halophyte Species,Chenopodium quinoa

Halophytes species can be used as a highly convenient model system to reveal key ionic and molecular mechanisms that confer salinity tolerance in plants. Earlier, we reported that quinoa (Chenopodium quinoa Willd.), a facultative C3 halophyte species, can efficiently control the activity of slow (SV) and fast (FV) tonoplast channels to match specific growth conditions by ensuring that most of accumulated Na⁺ is safely locked in the vacuole (Bonales-Alatorre et al. (2013) Plant Physiology). This work extends these finding by comparing the properties of tonoplast FV and SV channels in two quinoa genotypes contrasting in their salinity tolerance. The work is complemented by studies of the kinetics of net ion fluxes across the plasma membrane of quinoa leaf mesophyll tissue. Our results suggest that multiple mechanisms contribute towards genotypic differences in salinity tolerance in quinoa. These include: (i) a higher rate of Na⁺ exclusion from leaf mesophyll; (ii) maintenance of low cytosolic Na⁺ levels; (iii) better K⁺ retention in the leaf mesophyll; (iv) a high rate of H⁺ pumping, which increases the ability of mesophyll cells to restore their membrane potential; and (v) the ability to reduce the activity of SV and FV channels under saline conditions. These mechanisms appear to be highly orchestrated, thus enabling the remarkable overall salinity tolerance of quinoa species.     

二氧化碳管道意外泄漏减压过程的断裂控制研究进展

管道是二氧化碳捕集、利用和封存（carbon capture, utilization, and storage,CCUS）技术产业链中输运大量二氧化碳（CO₂）的最优方式,但其在运行中具有意外泄漏风险。本文从实验和计算机模拟两个方面综述了国内外开展CO₂管道泄漏减压、断裂扩展的研究进展,分析了相态、管材、埋地条件等初始状态对裂纹扩展规律的影响。阐述了状态方程、杂质因素、理论模型对开展实验和模拟计算研究的影响。归纳了适用于建立减压波预测模型的状态方程,开展流固耦合研究的理论方法和模拟仿真软件,设计CO₂输运管道参考的技术文档。总结了当前CO₂管道泄漏减压、断裂扩展控制研究方面需深入研究的科学问题,展望了亟待开展的研究内容,包括构建多元混合物状态方程在三相点、相间线的计算模型;探究裂纹裂间处CO₂热物性质与裂纹断裂扩展的耦合关系;建立管道止裂准则,开发、优化CO₂输运管道专用止裂器。