Effect of Particle Size on Gas Permeability of Filled Superglassy Polymers

Filler Influence on H2 Permeation Properties in Sulfur-CrossLinked Ethylene Propylene Diene Monomer Polymers Blended with Different Concentrations of Carbon Black and Silica Fillers

Filler effects on H₂ permeation properties in sulfur-crosslinked ethylene propylene diene monomer (EPDM) polymers blended with two kinds of carbon black (CB) and silica fillers at different contents of 20 phr–60 phr are investigated by employing volumetric analysis in the pressure exposure range of 1.2 MPa~9.0 MPa. A linear relationship is observed between the sorbed amount and pressure for H₂ gas, which is indicative of Henry’s law behavior. The hydrogen solubility of EPDM composites increases linearly with increasing filler content. The magnitude of hydrogen solubility for the filled EPDM composites is dependent on the filler type. The hydrogen solubility is divided into two contributions: hydrogen absorption in the EPDM polymer and hydrogen adsorption at the filler surface. Neat EPDM reveals pressure-dependent bulk diffusion behavior. However, with increasing filler content, the diffusivity for the filled EPDM composites is found to be independent of pressure. The magnitude of filler effects on the hydrogen permeation parameter is measured in the order of high abrasion furnace CB~semireinforcing furnace CB ˃ silica, whose effect is related to the specific surface area of CB particles and interfacial structure. The correlation between the permeation parameters and filler content (or crosslink density) is discussed.

Nanoparticle Shape Influence over Poly(lactic acid) Barrier Properties by Molecular Dynamics Simulations

Climate change is leading us to search for new materials that allow a more sustainable environmental situation in the long term. Poly(lactic acid) (PLA) has been proposed as a substitute for traditional plastics due to its high biodegradability. Various components have been added to improve their mechanical, thermal, and barrier properties. The modification of the PLA barrier properties by introducing nanoparticles with different shapes is an important aspect to control the molecular diffusion of oxygen and other gas compounds. In this work, we have described changes in oxygen diffusion by introducing nanoparticles of different shapes through molecular dynamics simulations. Our model illustrates that the existence of curved surfaces and the deposition of PLA around them by short chains generate small holes where oxygen accumulates, forming clusters and reducing their mobility. From the several considered shapes, the sphere is the most suitable structure to improve the barrier properties of the PLA.

Explaining the Sensitivity of Polymer Segmental Relaxation to Additive Size Based on the Localization Model

We use molecular simulations to examine how the dynamics of a coarse-grained polymer melt are altered by additives of variable size and interaction strength with the polymer matrix. The effect of diluent size σ on polymer dynamics changes significantly when its size is comparable to the polymer segment size. For each σ, we show that the localization model (LM) quantitatively describes the dependence of the segmental relaxation time τ on temperature T in terms of dynamic free volume, quantified by the Debye-Waller factor ⟨u^{2}⟩. Within this model, we show that the additive size alone controls the functional form of the T dependence. The LM parameters reach asymptotic values when the diluent size exceeds the monomer size, converging to a limit applicable to macroscopic interfaces.

The effect of nanoparticles on gas permeability with polyimide membranes and network hybrid membranes: a review

Polyimide membranes and network hybrid membranes exhibit high permeability despite good thermal and chemical stability, and high selectivity in gas mixture separation. In this study, the effect of nanoparticle distribution on the network polymer network, and changes in permeability, selectivity, and structure of the composite lattice membrane are investigated. According to the obtained permeability results, this increase in permeability was due to the increase of polymer network free volume and the formation of cavities in the nanoparticle-polymer interface. The significant results were that the permeability growth of gases with larger molecular size such as methane and nitrogen was higher than other gases. A comparison of the permeability growth of gases with the increasing volume fraction of nanoparticles confirms the dominance of the molecular sieve mechanism and the type of membrane transport mechanism change over polyimide and network Hybrid.

Modeling Permeation through Mixed-Matrix Membranes: A Review

Over the past three decades, mixed-matrix membranes (MMMs), comprising an inorganic filler phase embedded in a polymer matrix, have emerged as a promising alternative to overcome limitations of conventional polymer and inorganic membranes. However, while much effort has been devoted to MMMs in practice, their modeling is largely based on early theories for transport in composites. These theories consider uniform transport properties and driving force, and thus models for the permeability in MMMs often perform unsatisfactorily when compared to experimental permeation data. In this work, we review existing theories for permeation in MMMs and discuss their fundamental assumptions and limitations with the aim of providing future directions permitting new models to consider realistic MMM operating conditions. Furthermore, we compare predictions of popular permeation models against available experimental and simulation-based permeation data, and discuss the suitability of these models for predicting MMM permeability under typical operating conditions.

Interfacial regions in spherical nanoparticle-doped glassy polymers: interfaces or interphases?

By computational simulation, we provide new evidence supporting a high-free-volume interphase in spherical nanoparticle-doped glassy polymers and offer a generic framework for understanding how this interphase is shaped.