No abstract

The use of selective interactions between conjugated polymers and single‐walled carbon nanotubes has emerged as a promising method for the separation of nanotubes by electronic type. Although much attention has been devoted to investigating polyfluorenes and their ability to disperse semiconducting carbon nanotubes under specific conditions, other polymer families, such as poly(2,7‐carbazole)s, have been relatively overlooked. Poly(2,7‐carbazole)s have been shown to also preferentially interact with semiconducting carbon nanotubes, however a detailed investigation of polymer parameters, such as molecular weight, has not been performed. We have prepared seven different molecular weights of a poly(2,7‐carbazole), from short chain oligomers to high molecular weight polymers, and have investigated their effectiveness at dispersing semiconducting single‐walled carbon nanotubes. Although all polymer chain lengths were able to efficiently exfoliate carbon nanotube bundles using a mild dispersion protocol, only polymers above a certain threshold molecular weight (Mn ∼ 27 kDa) were found to exhibit complete selectivity for semiconducting nanotubes, with no observable signals from metallic species. Additionally, we found the quality of separation to be strongly dependent on the ratio of polymer to carbon nanotube. Contrary to previous reports, we have found that an excess of poly(2,7‐carbazole) leads to incomplete removal of metallic carbon nanotubes. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2510–2516

Precise silicone networks are difficult to prepare from multiple starting materials because of poor spatial control over crosslinkl ocation, competing side reactions, and incompatible catalysts among other reasons. We demonstrate that cure processes catalyzed by B(C 6 F 5 ) 3 (the Piers-Rubinsztajn reaction) and platinum-catalyzed hydrosilylation are perfectly compatible,a nd can be used in either order.I ti sp ossible to perform three different, selective, sequential reactions in the same potu sing H-terminated silicones as chain extenders in all cases to give explicit networks. Eugenol, ar eadily available aromatic compound, acts as at rifunctional crosslinker (HO,M eO, HC= CH 2 ), each functional group of which can be induced to undergo selectiver eaction. With platinum catalysis, the reaction of SiH groups with alkenes is fastest, while B(C 6 F 5 ) 3 catalyzes reaction at phenolsm uch faster than methoxybenzene. Thus, av ariety of H-terminated telechelic siloxanes can be used to form chain extended polymers or elastomers or foams in whicht he morphology of the material and its constituent parts can be manipulated at will.As with most polymers, the current paradigm for the preparation of silicone polymers, including elastomers, should involve enhanced synthetic control such that desired properties can be attained. Structural control, however,isnot ahallmark of silicone elastomers. The three commercialc ure mechanisms normally utilized are radical, moisture cure (room-temperature vulcanization RTV), and platinum-catalyzed hydrosilylation (PtHSi).[1] Radical cure leads to irreproducible, random networks. In selected cases,m oisture cure allows the controlled incorporation of two different silicone polymers through the use of telechelic crosslinkers;more complex structures are difficult to attain. However, network errors occur when competitive hydrolysisl eads to loss of spatialc ontrolo fc rosslinks at ag iven silicon atom (Scheme 1A).Platinum-catalyzed crosslinking (PtHSi), the most common route to high-quality siliconee lastomers, utilizes the combination of telechelic silicones with pendant functional chains.U nfortunately,t he absolutec oncentration of functional groups on ag iven chain and their relative locations along the chain cannotb er eadily controlled (Scheme 1B). The resulting networks reflect the specific batch of pendant-functional polymers used. It is, therefore, difficult to reproducibly preparep recise networks from commercial materials.It is possible to create networks containing av ariety of silicone precursors in as omewhat controlledm anner by using ac ombinationo fo rthogonal cure technologiess elected from silicone and organic chemistry;d ual cure systemst hat combine any of the cure technologiesn oted above with amine/ epoxy, [2] cationic epoxy polymerization, [3] thiol-ene click, [4] or azide/alkyne click [5] allow complex network materials to be prepared. Most of thesep rocesses, however,s till suffer from random placement of crosslinking groups along as ilicone backbone.T...

The objective of this study was to characterize commercially-available cotton fabrics to determine their suitability as materials for construction of cloth masks for personal and public use to reduce infectious disease spread. The study focused on cottons because of their widespread availability, moderate performance and they are recommended for inclusion in home-made masks by international health authorities. Fifty-two cottons were analyzed by electron microscopy to determine fabric characteristics and fabric weights. Sixteen fabrics were selected to test for breathability and to construct 2-ply cotton masks of a standard design to use in quantitative fit testing on a human participant. Cotton mask fitted filtration efficiencies (FFEs) for 0.02–1 μm ambient and aerosolized sodium chloride particles ranged from 40 to 66% compared with the mean medical mask FFE of 55±2%. Pressure differentials across 2-ply materials ranged from 0.57 to > 12 mm H2O/cm2 on samples of equal surface area with 6 of 16 materials exceeding the recommended medical mask limit. Models were calibrated to predict 2-ply cotton mask FFEs and differential pressures for each fabric based on pore characteristics and fabric weight. Models indicated cotton fabrics from 6 of 9 consumer categories can produce cloth masks with adequate breathability and FFEs equivalent to a medical mask: T-shirt, fashion fabric, mass-market quilting cotton, home décor fabric, bed sheets and high-quality quilting cotton. Masks from one cloth mask and the medical mask were re-tested with a mask fitter to distinguish filtration from leakage. The fabric and medical masks had 3.7% and 41.8% leakage, respectively. These results indicate a well fitted 2-ply cotton mask with overhead ties can perform similarly to a disposable 3-ply medical mask on ear loops due primarily to the superior fit of the cloth mask which compensates for its lower material filtration efficiency.

Public health agencies have recommended the community use of face masks to reduce the transmission of airborne diseases like COVID‐19. Virus transmission is reduced when masks act as efficient filters, thus evaluating mask particle filtration efficiency (PFE) is essential. However, the high cost and long lead times associated with purchasing turn‐key PFE systems or hiring certified laboratories hampers the testing of filter materials. There is a clear need for “custom” PFE test systems; however, the variety of standards that prescribe (medical) face mask PFE testing (e.g., ASTM International, NIOSH) vary widely in their protocols and clarity of guidelines. Herein, the development is described of an “in‐house” PFE system and method for testing face masks in the context of current standards for medical masks. Pursuant to the ASTM International standards, the system uses an aerosol of latex spheres (0.1 µm nominal size) with particle concentrations upstream and downstream of the mask material measured using a laser particle analyzer. PFE measurements are obtained for a variety of common fabrics and medical masks. The approach described in this work conforms to the current standards for PFE testing while providing the flexibility to adapt to changing needs and filtration conditions.