The effects of sequential cross-linking and scission polymer networks formed in two states strain are investigated using molecular dynamics simulations. Two-stage studied which a network the unstrained state (stage 1) undergoes additional uniaxially strained 2). equilibrium stress is measured before after removing some or all original cross-links. results interpreted terms generalized independent hypothesis. In where first-stage cross-links subsequently removed, fraction (quantified by...

Polymer networks undergoing cross-linking reactions are studied using molecular dynamics simulations to investigate how the stress is influenced by coupling between and deformation. For cross-linked in undeformed state, modulus increases linearly with cross-link density as expected from rubber elasticity theory. When cross-links added a network that was uniaxially deformed, remains constant accordance independent hypothesis of Tobolsky. deformed subsequently released, permanent set observed....

The permanent set of cross-linking networks is studied by molecular dynamics. uniaxial stress for a bead−spring polymer network investigated as function strain and cross-link density history, where cross-links are introduced in unstrained strained networks. found from the after it returns to state-of-ease zero. simulations compared with theory using independent hypothesis, together various theoretical rubber elasticity theories: affine, phantom, constrained junction, slip-tube, double-tube...

This paper describes the finite element implementation of a recently developed constitutive model for chemical aging rubber in deformed states. The was from molecular dynamics simulations that investigated two stage networks. includes effects multiple stages cross-linking and scission while sample is physical entanglements. Given deformation history sample, calculations using this are shown to make quantitative predictions permanent set experimental systems.

Finite element (FE) filtering facepiece respirators (FFRs) were developed and mated to the new headforms with a cervical spine model. The FFRs from three manufacturers included sizing systems: (i) single one-size-fits all, (ii) an FFR two sizes (S/M M/L), (iii) (S, L/M, XL). method (FEM) simulations of 16 headform respirator combinations (5 6 respirators) used examine maximum contact pressure changes for five cases: static head, flexion, extension, left rotation, right rotation. For each...

In a respirator fit test, subject is required to perform series of exercises that include moving the head up and down rotating left right. These movements could affect sealing properties during test consequently factors. model-based system, it desirable have similar capability predict newly designed respirators. our previous work, finite element modeling (FEM)-based contact simulation between headform filtering facepiece was carried out. However, assumed be static or fixed. This paper...

Personal protective equipment (PPE) stockpiles in the United States were established to facilitate rapid deployment of medical assets sites affected by public health emergencies. Large quantities PPE introduced into US because need protect healthcare and other professionals during these events. Because most stockpiled was acquired during, or immediately following, large-scale events, such as pandemic influenza planning (2005-2008), SARS (2003), H1N1 (2009-10), Ebola (2014-15), aging poses a...

Molecular dynamics (MD) simulations were carried out on a blend of 50 unit, pearl-necklace chains with the object examining effect intermolecular attractions structure and thermodynamics. Repulsive interactions imposed between sites so that effective hard core diameter B type was 1.2 times A chains. Simulations performed for series runs in which attractive systematically varied from zero to full Lennard-Jones value. Examination radial distribution functions revealed had very little up point...

Medical countermeasure stockpiles in the United States are designed to support healthcare workers and public during health emergencies; they include supplies of personal protective equipment (PPE). As part typical PPE manufacturing processes, appropriate test methods used ensure that devices provide adequate performance. At time manufacture, performance is often measured weighed against an objective standard quality, resulting a pass or fail attribute being assigned individual items thence...

Simple polymer blends were studied by simulations with the intent of probing response structurally asymmetric chains to progressively stronger attractive interactions strengths. It was found, for miscible blends, that intermolecular pair correlation functions, g(r)’s, varied less than 10% from those associated blend strictly repulsive interactions. When used purposes calculating changes in pressure due strength, g(r)’s either or systems could be interchangeably perturbation theory. On other...

The diffuse behavior of penetrants in simple polymer melts was investigated by molecular dynamics simulation. For the case where melt consisted pearl-necklace chains, diffusive loose pearl seen to be qualitatively different than would expected realistic models melts. In particular, there little or no “non-Fickian” region; variation diffusion coefficient with penetrant diameter what one expect for through small liquids; and, finally, long time tail velocity autocorrelation displayed a “−3/2”...

Background Device manufacturers who seek to market their pediatric facemasks in the United States (U.S.), as part of anthropometric data requirement, need demonstrate mask designs are expected fit intended user population. However, currently there no well accepted test methodologies for facemasks. In addition, unlike N95 respirators, maximum flow rate, and pressure drop at that rate have not been established. Method The objective this article is three-fold; use a literature survey determine...

Powered air-purifying respirators (PAPRs) are worn to protect workers from hazardous respiratory exposures in a wide range of workplaces, including healthcare. However, PAPRs may diminish the ability wearers correctly hear words spoken by others, potentially interfering with safe performance healthcare duties. Accordingly, impact during use on speech intelligibility (SI) and consequently user safety, usability, patient care is not well studied. The objectives this study were (1) determine...