Filtering
facepiece respirators (FFRs) protect wearers from inhalation
of fine particulates and help prevent transmission of airborne viruses.
Here, an FFR material is produced by successive deposition of contact
drawn poly(ethylene oxide) (PEO) fibers. Fibers are formed by immersing
an array of pins in a highly viscous precursor solution of PEO and
then rapidly removing the pins such that polymer entanglement occurs,
forming multiple liquid bridges that rapidly dry as they extend. Tunable
filtration is achieved by varying the number of PEO fiber elongation
cycles. Placing the PEO textiles between two woven cotton cloths provides
structural support and additional filtration capacity, achieving a
maximum filtration efficiency of 95% with a corresponding initial
pressure drop of 281 Pa. The entrapment of silver nanoparticles in
the PEO fibers imparts virucidal properties to PEO-based textiles,
as demonstrated by inactivation of a human coronavirus HCoV-OC43 and
influenza A virus inoculum. The ability to tune filtration efficiency
to application needs and provide advanced function through entrapment
of active materials represents a versatile tool for limiting exposure
to airborne particulates and pathogens.
The effect of particles on the behavior of polymers in solution is important in a number of important phenomena such as the effect of "crowding" proteins in cells, colloid-polymer mixtures, and nanoparticle "fillers" in polymer solutions and melts. In this Letter, we study the effect of spherical inert nanoparticles (which we refer to as "crowders") on the diffusion coefficient and radius of gyration of polymers in solution using pulsed-field-gradient NMR and small-angle neutron scattering (SANS), respectively. The diffusion coefficients exhibit a plateau below a characteristic polymer concentration, which we identify as the overlap threshold concentration c ⋆ . Above c ⋆ , in a crossover region between the dilute and semidilute regimes, the (long-time) self-diffusion coefficients are found, universally, to decrease exponentially with polymer concentration at all crowder packing fractions, consistent with a structural basis for the long-time dynamics. The radius of gyration obtained from SANS in the crossover regime changes linearly with an increase in polymer concentration, and must be extrapolated to c ⋆ in order to obtain the radius of gyration of an individual polymer chain. When the polymer radius of gyration and crowder size are comparable, the polymer size is very weakly affected by the presence of crowders, consistent with recent computer simulations. There is significant chain compression, however, when the crowder size is much smaller than the polymer radius gyration.
We apply pulsed-field-gradient NMR (PFG NMR) technique to measure the translational diffusion for both uncharged and charged polysaccharide (Ficoll70) in water. Analysis of the data indicates that the NMR signal attenuation above a certain packing fraction can be adequately fitted with a bi-exponential function. The self-diffusion measurements also show that the Ficoll70, an often-used compact, spherical polysucrose molecule, is itself nonideal, exhibiting signs of both softness and attractive interactions in the form of a stable suspension consisting of monomers and clusters. Further, we can quantify the fraction of monomers and clusters. This work strengthens the picture of the existence of a bound water layer within and around a porous Ficoll70 particle.
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