Composite Membranes Research Articles

Facile fabrication of robust and tight PIMs-based TFC hollow fiber membranes with a semi-interpenetrating polymer network via liquid phase cross-linking for organic solvent nanofiltration

Resource recovery and reuse are essential for sustainable development, particularly for high-value resources such as homogeneous (photo)catalysts, active pharmaceutical ingredients, and high-value natural compounds, which can offer economic benefits. Recently, organic solvent nanofiltration (OSN) for resource recovery has gained significant attention owing to its advantages including low energy consumption and seamless integration with other processes. Polymers of intrinsic microporosity (PIMs) have great potential as membrane materials for OSN, owing to their excellent pore properties and solution processability. However, swelling and dissolution of PIMs in organic solvents can impede the filtration performance of PIMs-based OSN membranes. In this study, we fabricated thin-film composite hollow fiber membranes for OSN based on PIMs with improved organic solvent stability using a semi-interpenetrating polymer network (semi-IPN) formed by cross-linking Matrimid with 1,6-Hexanediamine with the PIMs through the liquid phase cross-linking method. Semi-IPNs mitigate swelling and tighten the pores of PIMs-based membranes, enabling excellent filtration and molecular separation performance. Furthermore, the fabricated PIMs with a semi-IPN membrane exhibited excellent rejection performance (>96%) for homogeneous photocatalysts, allowing successful concentration and recovery via OSN. Therefore, PIMs-based membranes with a semi-IPN hold great promise as OSN membranes for the recovery of valuable resources.

Radiative cooling materials prepared by SiO2 aerogel microspheres@PVDF-HFP nanofilm for building cooling and thermal insulation

Radiative cooling is promising in meeting the current global demand for green sustainable development. However, the effective cooling of the existing radiant cooler will be limited due to the serious solar energy absorption and poor thermal insulation performance on the cold side. To addresss these issues, we propose herein a novel composite material of silicon dioxide (SiO2) aerogel microspheres combined with polyvinylidene fluoride-cohexafluoropropylene (PVDF-HFP) nanofiber membrane, in which SiO2 aerogel microspheres are firstly synthesized by sol-gel method and then incorporated into PVDF-HFP nanofiber membrane to give radiative cooling performance. As we expected, the molecular vibration characteristics of PVDF-HFP nanofiber membrane and the phonon polarization resonance of Si-O-Si bond in the transparent window can enhance the infrared emissivity of the membrane surface. In addition, the high porosity and the mesoporous structure formed by the interconnection of nano-network skeletons of SiO2 aerogel microspheres determine its excellent thermal insulation performance. The as-prepared material displays that the average solar reflectance of the composite membrane is 96.07 % and the average infrared emissivity of the atmospheric window is 94.95 %. Notably, when the average solar radiation intensity is 885.56 W•m−2, the passive radiative cooling temperature during the day can reach 11.2 °C. Furthermore, this material has excellent self-cleaning and thermal insulation performance, making it a potential radiant cooling candidate in many fields.

Enhanced solid-electrolyte interface efficiency for practically viable hydrogen-air fuel cell systems

Proton exchange membrane fuel cells (PEMFCs) provide an appealing sustainable energy system, with the solid-electrolyte membrane playing a crucial role in its overall performance. Currently, sulfonated poly(1,4-phenylene ether-ether sulfone) (SPEES), an aromatic hydrocarbon polymer, has garnered considerable attention as an alternative to Nafion polymers. However, the long-term durability and stability of SPEES present a significant challenge. In this context, we introduce a potential solution in the form of an additive, specifically a core–shell-based amine-functionalized iron titanate (A–Fe2TiO5), which holds promise for improving the lifetime, proton conductivity, and power density of SPEES in PEMFCs. The modified SPEES/A–Fe2TiO5 composite membranes exhibited notable characteristics, including high water uptake, enhanced thermomechanical stability, and oxidative stability. Notably, the SPEES membrane loaded with 1.2 wt% of A–Fe2TiO5 demonstrates a maximum proton conductivity of 155 mS cm−1, a twofold increase compared to the SPEES membrane, at 80 °C under 100% relative humidity (RH). Furthermore, the 1.2 wt% of A–Fe2TiO5/SPEES composite membranes exhibited a maximum power density of 397.37 mW cm−2 and a current density of 1148 mA cm−2 at 60 °C under 100% RH, with an open-circuit voltage decay of 0.05 mV/h during 103 h of continuous operation. This study offers significant insights into the development and understanding of innovative SPEES nanocomposite membranes for PEMFC applications.

Advanced electro-assisted filtration of crude oil/water using a conductive mullite whiskers membrane

This study presents the development and characterization of a conductive composite membrane aimed at efficient oil-water separation via electrofiltration. The membrane comprises interconnected OH-functionalized multi-walled carbon nanotubes (OH-MWCNTs) and polyvinyl alcohol (PVA). Optimization parameters, including surface electrical resistance, water contact angle, and pure water permeance, were conducted, yielding an optimized membrane with a surface resistance of 256 Ω/sq, a contact angle of 39±2°, and a pure water permeance of 508.15 LMH/bar. The critical electric field intensity (Ecrit) was identified at 8–10 V, beyond which voltage increments had minimal flux impact. Electrofiltration experiments, incorporating filtration and backwashing, demonstrated enhanced permeate flux and oil particle removal rates under an applied electric field. Despite salt presence inducing flux reduction and fouling increase, membrane performance was still enhanced by the electric field. Energy consumption analysis revealed a 32 % reduction when combining electrical field with conventional filtration and backwashing, even at 1 mM concentration, compared to conventional filtration alone. This conductive composite membrane presents a promising, sustainable solution for effective crude oil/water separation across industries, offering improved performance, reduced fouling, and lower energy consumption.

Sulfonated polybenzimidazole membrane with graphene oxide additive for 2,3-butanediol/water separation: A molecular simulation

Membrane separation for 2,3-butanediol (2,3-BDO) recovery from fermentation broth is highly valued for sustainable and renewable processes, but it requires efficient membrane materials. This work evaluates the sulfonated polybenzimidazole (sPBI) and its graphene oxide (GO) doped composite membrane for separating 2,3-BDO and water via atomistic simulations. Density functional theory calculations are applied to identify various forms of sPBI structures and quantify their binding interactions with 2,3-BDO and water. Classical molecular dynamic simulations are used to evaluate the structural changes, diffusivity, and selectivity of 2,3-BDO and water in different sPBI models, GO surfaces, and GO-doped sPBI composite models. Our results suggest that sPBI slightly increases the crystallinity of the membrane structures, enhances the adsorption strength for both 2,3-BDO and water, and improves the water/2,3-BDO selectivity by 2–3 times. The GO surfaces display a maximum selectivity at a surface coverage of 0.1–0.15 for both hydroxyl and epoxy surface groups. The addition of GO flakes to sPBI creates new interaction sites for 2,3-BDO and water at the interface of sPBI and GO, and the water/2,3-BDO selectivity of GO-doped sPBI models is further increased up to 3 times. This work illustrates how the integrated addition of sPBI and GO flakes offers a promising approach to selective separation of 2,3-BDO and water, providing theoretical guidance for polybenzimidazole-based membranes in the potential application of 2,3-BDO recovery.

Rare earth europium recovery using selective metal-organic framework incorporated mixed-matrix membrane

Rare-earth elements (REEs) play a crucial role in state-of-the-art technologies and sustainable energy generation. However, conventional production methods of REE often instigate detrimental impacts on environment. Hence, the development of efficient and sustainable hydrometallurgical methods for REE recovery from complex solution has become a crucial research focus. This study investigates a mixed-matrix membrane composed of a highly europium selective metal-organic framework-based adsorbent, Cr-MIL-PMIDA, embedded in sulfonated poly(ether ketone) (SPEK) polymer membrane matrix to preferentially concentrate europium (Eu3+) ions in the presence of other competing cations. The activated membrane notably reduced ionic conductivity for Eu3+ compared to other multivalent ions. Membrane extraction experiments further confirmed the selective behavior, demonstrating slower diffusion for Eu3+ compared to Mg2+ and Zn2+ cations. Especially, at pH 5, Mg2⁺ and Zn2⁺ recovery was greater than 30%, whereas Eu³⁺ recovery remained lower than 4%. We propose that the strong chemical affinity between the phosphate group and Eu3+ help partition of the Eu3+ ions in the membrane phase and inhibit the diffusion and further partitioning of the Eu3+ ion from bulk solution. Furthermore, we demonstrate the stability of the composite membrane and the embedded MOF particles in aqueous solution for up to 12 days without degradation, attributing it to the robust chemical stability of the MOF structure.

The solution-diffusion model: “Rumors of my death have been exaggerated”

The solution-diffusion (SD) model has been instrumental in the advancement of membrane science, due to its simplicity, transparency, and utility in process engineering. However, some doubts have recently been raised, concerning the fundamental validity of SD. These have largely been based on apparent discrepancies between molecular dynamics simulations and several features, deemed inherent to SD, that appeared in early reports — namely, the exact nature of the pressure and concentration distributions within the membrane. Herein, we re-visit the underlying physics of SD in the context of composite membranes, making no a-priori assumptions and, particularly, highlighting the role of polymer thermodynamics and the mechanics of a loaded, swollen film, supported by a porous substrate. The analysis provides a coherent view, linking the solvent concentration profile within the film and the resultant flux-pressure relations with the polymer rigidity and, importantly, the way in which the film is supported. It is shown that, although the flux may generally vary non-linearly with the feed pressure and depend on the film-support geometry, for rigid films – most common in real operations – SD predicts a linear behavior, virtually independent of specific geometry and pressure distribution. Moving forward, we stress the importance and need for further refinements of the SD model, driven by insight from molecular dynamics, thermodynamics and mechanics, while maintaining its applicability to process design.

Surface functionalization of cellulose derived from hemp by tetraethyl orthosilicate (TEOS) and poly vinylidene fluoride (PVDF)-based composite separator membrane for lithium-ion batteries (LIBs)

Separators play a crucial role in enhancing the electrochemical performance of lithium-ion batteries (LIBs). However, achieving separators with exceptional electrochemical performance and high stability remains a significant challenge. In this study, we meticulously designed composite membranes based on polyvinylidene fluoride (PVDF) with varying contents of microcrystalline cellulose/tetraethyl orthosilicate (MCC/TEOS). The increase in hydrophilicity of PVDF by adding MCC-TEOS weight contents endowed the 3 wt% MCC/TEOS-based PVDF separator membrane with superior electrolyte absorption and reduced resistance, resulting in an impressive ionic conductivity of 0.514 mS/cm higher than the pristine PVDF membrane (0.253 mS/cm). Furthermore, the LIB cell utilizing the 3 wt % MCC/TEOS-based PVDF separator membrane consistently demonstrated stable charge/discharge profiles at a rate of 0.2C, achieving a specific capacity of 98 mAh/g, compared to only 43 mAh/g for the pristine PVDF membrane. These findings underscore the significant potential of MCC/TEOS as a biofiller for bio-membranes, making it an optimal choice for applications in LIBs.

Reconstructing Electrically Conductive Nanofiltration Membranes with an Aniline-Functionalized Carbon Nanotubes Interlayer for Highly Effective Toxic Organic Treatment.

Conductive nanofiltration (CNF) membranes hold great promise for removing small organic pollutants from water through enhanced Donnan exclusion and electrocatalytic degradation. However, current CNF membranes face limitations in conductivity, structural stability, and nanochannel control strategies. This work addresses these challenges by introducing aniline-functionalized carbon nanotubes (NH2-CNTs) as an interlayer. NH2-CNTs enhance the dispersibility and adhesion of pristine carbon nanotubes, leading to a more conductive and stable composite nanofiltration membrane. The redesigned NH2-CNTs interlayered conductive nanofiltration (NICNF) membrane exhibits a 10-fold increase in conductivity and a high response degree (80%) with excellent cyclic stability, surpassing existing CNF membranes. The synergistic effects of enhanced Donnan exclusion, voltage switching, and electrocatalysis enable the NICNF membrane to achieve selective recovery of mixed dyes, 98.97% removal of residual wastewater toxicity, and a 5.2-fold increase in permeance compared to the commercial NF270 membrane. This research paves the way for next-generation multifunctional membranes capable of the efficient recovery and degradation of toxic organic pollutants in wastewater.

All-Solid-State PVC-Membrane Cu(II)-Selective Potentiometric Microsensor Based on a Novel Calix[4]arene Derivative

In this study, 25,27-dihydroxy-26,28-bis(ethoxycarbonylbutyoxy)-5,11,17,23-p-tert-butylcalix[4]arene was used as an ionophore for the preparation of a novel all-solid-state type microsensor to make a selective potentiometric response towards Cu(II) ions. The optimum membrane composition of the microsensor was determined as 2% (w/w) ionophore, 67% (w/w) bis (2-ethylhexyl) sebacate (DOS), 30% (w/w) polyvinylchloride (PVC), and 1%(w/w) potassium tetrakis 4-chlorophenyl borate (KTpClPB). The Cu(II)-selective microsensor exhibited a highly selective Nernstian response of 31.3±2.1 mV slope (R2: 0.997) with a short response time (15 s) over the concentration range of 10−5 to 10−1 mol L−1 of Cu(II) ions for 8 weeks with no significant difference in potentials. The microsensor was effectively performed in the pH range of 5.0–8.0, with low detection limit as 7.63×10−7 mol L−1, and a temperature range of 15−40 °C. The prepared microsensor was successfully used both as an indicator electrode in the potentiometric titration of Cu(II) ions with EDTA and also in the determination of the Cu(II) content of environmental water samples. When the potentiometric results were compared with ICP-OES, they were found to be in good agreement with ICP-OES results at a 95% confidence level.

Combined water electrolysis and 2D hydron sepaator for enhanced hydrogen isotope separation

This research presents the fabrication and analysis of a graphene/Nafion composite membrane designed to enhance the hydrogen separation performance of a water electrolyzer by leveraging the isotope effect in hydron transport through monolayer graphene, serving as a 2D hydron separator. The composite membrane exhibits lower proton conductivity than a Nafion membrane, leading to a 12 % decrease in water electrolysis cell efficiency at 75 °C. However, the incorporation of monolayer graphene substantially enhances the hardness of the membrane by a factor of 1.38, as measured by nanoindentation. The addition of monolayer graphene also increases the activation energy required for through-plane conduction of H+ and D+, with the graphene itself showing a twofold higher conductivity for H+ over D+. In electrolysis cells containing the composite membrane, the H/D and H/T separation factors improved by approximately 1.4 and 2 times, respectively, compared with those of a Nafion membrane, with a maximum H/T separation factor of ∼ 15 at 15 °C. Although increases in temperature reduce the separation factor, the operation time and the concentration of heavier isotopes in the feed water were found to minimally affect the separation efficiency.

Precise control of transmembrane current via regulating bionic lipid membrane composition.

The transport of ions through biological ion channels is regulated not only by their structural characteristics but also by the composition of the phospholipid membrane, which serves as a carrier for nanochannels. Inspired by the modulation of ion currents by lipid membrane composition, exemplified by the activation of the K+ channel of Streptomyces A by anionic lipids, we present a biomimetic nanochannel system based on combining DNA nanotechnology with two-dimensional graphene oxide (GO) nanosheets. By designing multibranched DNA nanowires, we assemble programmable DNA scaffold networks (DSNs) on the GO surface to precisely control membrane composition. Modulating the DSN layers from one to five enhances DNA composition, yielding a maximum 12-fold enhancement in ion current, primarily due to charge effects. Incorporating DNAzymes facilitates reversible modulation of membrane composition, enabling cyclic conversion of ion current. This approach offers a pathway for creating devices with highly efficient, tunable ion transport, applicable in diverse fields like mass transport, environmental protection, biomimetic channels, and biosensors.

Preparation and regulation of high-strength and high-permeability porous ceramic/PDMS composite membranes for gas-liquid separation

Methane detection is crucial in identifying combustible ice within the energy sector. The gas–liquid separation membrane, a key component of methane sensors, plays a critical role in effectively separating methane and water. It significantly enhances the efficiency and stability of detecting methane concentration in situ. However, the related permeability and mechanical property present conflicting requirements in order to achieve optimal membrane performance. This work proposes an investigation into the mass transfer performance of a high-strength composite membrane, utilizing PDMS as the functional layer and porous ceramics as the supporting layer. By adjusting the pore distribution of the porous ceramics, particularly through the use of spherical graphite as a porogen, the study examines the impact of spherical graphite (SG) on the support layer’s morphology and its ability to regulate pore structure. Results indicate that incorporating spherical graphite with a porogen content of 10 wt% and a particle size of 25 μm enhances connections between ceramic grains, resulting in a flexural strength of 56.36 MPa and a permeability coefficient of 1861.57 barrer. This configuration demonstrates good waterproof and breathable performance. Overall, this research presents a novel approach for fabricating methane-water separation membranes, offering valuable insights for underwater methane detection efforts.

Coordination-driven in-situ controlled synthesis of cellulose-based fluorescent composite with tunable color for decoration, anti-counterfeiting, and accurate color recognition

Fluorescent composites have widespread applications in many aspects. Wood-derived cellulose is a renewable, easily processed and biodegradable, and cellulose-based fluorescent composites are highly favored for in different fields. However, the existing cellulose-based fluorescent composites still have many urgent problems to be solved, such as unstable luminescence properties and easy shedding of luminescent substances, and the development of their practical applications is still a formidable challenge. Herein, a green and mild strategy for the in-situ controllable synthesis of cellulose-based fluorescent composites membrane (CFM) was developed. Firstly, delignified wood (DW) was modified with citric acid, and then lanthanide ions were introduced on modified DW through coordinated covalent bonds. Additionally, the luminescence mechanism of CFM is proposed. CFMs show adjustable color for decorative and light conversion and can be accurately identified for data protection, which increases the high value-added of cellulose-based composites. The stable luminescent properties were maintained after sonication for 30 min or solvent immersion for three months. Therefore, this work presents a new approach for the synthesis of CFM, which provides an environment-friendly strategy for manufacturing cellulose-based fluorescent materials, which is significant for the subsequent development of environment-friendly composites for anti-counterfeiting and decorative applications.

Identification of clinical prognosis features and significant DNA methylation regulation in pineoblastoma.

Pineoblastoma (PB) represents a great challenge for clinical management due to lack of a specific therapeutic regimen. This study aims to identify relevant prognostic factors and potential treatment targets by mining public databases. The clinical characteristics and survival data of PB patients were obtained from the SEER database between 2000 and 2019 for Cox regression analysis and nomogram construction. The PB's DNA methylation data was acquired from two GEO datasets, GSE133801 and GSE215240, for bioinformatics analysis. Of 383PB patients, Cox univariate analysis unveiled that male gender (p = 0.017), age younger than 3years at diagnosis (p < 0.001) and absence of radiotherapy (p < 0.001) correlated with poorer overall survival (OS), the subsequent multivariate analysis confirmed sex (p = 0.036), age (p < 0.001) and radiotherapy (p = 0.005) as independent prognostic factors for OS. A nomogram showed robust predictive accuracy as evidenced by AUC values (1-year OS: 0.774, 3-year OS: 0.692, 5-year OS: 0.643). DNA methylation analysis observed tumor hypomethylation, notably in promoter regions. Later, the GO enrichment analysis of aberrantly methylated genes indicated associations with embryonic organ development, cellular membrane composition and DNA-binding transcription, while KEGG analysis revealed enrichment in tumor-associated MAPK, calcium and RAS signaling pathways. The prognosis of PB is closely associated with sex, age and receipt of radiotherapy, potentially linked to aberrations in the RAS and MAPK signaling pathways. The individual case suggests that dasatinib and trametinib are potential targeted therapies for improving PB prognosis.

Environmental Influence on Bacterial Lipid Composition: Insights from Pathogenic and Probiotic Strains.

The lipid composition of bacterial membranes is pivotal in regulating bacterial physiology, pathogenicity, and interactions with hosts. This study presents a comprehensive analysis of bacterial membrane lipid profiles across diverse Gram-positive and Gram-negative species. Utilizing matrix-assisted laser desorption/ionization (MALDI) in conjunction with advanced chemometric tools, we investigate the influence of environmental factors, isolation sources, and host metabolism on bacterial lipid profiles. Our findings unveil significant variations in lipid composition attributed to factors such as carbon/energy availability and exposure to chemicals, including antibiotics. Moreover, we identify distinct lipidomic signatures associated with pathogenic and probiotic bacterial strains, shedding light on their functional properties and metabolic pathways. Notably, bacterial strains isolated from clinical samples exhibit unique lipid profiles influenced by host metabolic dysregulation, particularly evident in conditions such as diabetic foot infections. These results deepen our understanding of the intricate mechanisms governing bacterial membrane lipid biology and hold promise for informing the development of innovative therapeutic and biotechnological strategies.

Boosting the H2/CO2 and H2/N2 selectivities of a graphene oxide membrane by shrinking the membrane interlayer spacing via thermal treatment

Graphene oxide (GO) membranes have been widely studied and used for gas separation processes, but some structural changes are necessary to guarantee high membrane selectivities. The thermal reduction process stands out for reducing the interlayer channel size of the GO nanosheets to improve the molecular sieving mechanism. Herein, thermally annealed GO layers were deposited on the outer surface of porous alumina hollow fiber substrates and the produced composite membranes were tested for selective hydrogen (H2) separations. The influence of the thermal annealing process at different mild temperatures (80 and 160 °C) on the characteristics of the GO structure was investigated towards the improvement of the membrane efficiency for H2 separation. ATR-FTIR results confirmed the elimination of oxygenated groups, and XRD analyses showed the GO interlayer space decreased from 8.71 to 7.38 Å after the thermal annealing process at 160 °C. The GO thermally annealed membrane presented an H2 permeance of 2032.47 ± 101.69 GPU and an H2/N2 selectivity of 12.16 ± 0.30, which is 315% greater than the selectivity of the pristine GO membrane. Hence, the application of the thermal reduction method to produce GO membranes with greater selectivities is a viable alternative to deal with gas separation processes.

Polymer Composite Electrolytes Membrane Consisted of Polyacrylonitrile Nanofibers Containing Lithium Salts: Improved Ion Conductive Characteristics and All‐Solid‐State Battery Performance

AbstractPolymer electrolyte membranes with superior lithium‐ion (Li+) conductivity and sufficient electrochemical stability are desired for all‐solid‐state lithium‐ion batteries (ASS‐LIBs). This paper reports novel polymer composite membranes consisting of polyacrylonitrile (PAN) nanofibers (Nfs) containing lithium salts. It is first revealed that the lithium salt addition increases polar surface groups on the PAN nanofibers. Subsequently, the lithium salts‐containing PAN nanofiber (PAN/Li Nf) composite membrane affects the matrix poly(ethylene oxide) (PEO)/lithium bis(trifluoromethyl sulfonylimide) (LiTFSI) electrolyte to increase the numbers of Li+ with high mobility. Consequently, the PAN/Li Nf composite membrane shows relatively good ion conductivity (σ = 9.0 × 10−5 S cm−1) and a considerably large Li+ transference number (tLi+ = 0.41) at 60 °C, compared to the PEO/LiTFSI membrane without nanofibers. The 6Li solid‐state NMR study supports that the PAN/Li Nf bearing abundant polar nitrile groups at their surface enhances Li+ diffusion in the PEO‐based electrolyte membranes. The galvanostatic constant current cycling tests reveal that the PAN/Li Nf composite membrane possesses good electrochemical and mechanical stabilities. The ASS‐LIB consisting of the PAN/Li Nf composite membrane shows significantly improved charge and discharge cycling performances, promising future all‐solid‐state batteries.

Trifunctional sphingomyelin derivatives enable nanoscale resolution of sphingomyelin turnover in physiological and infection processes via expansion microscopy

Sphingomyelin is a key molecule of sphingolipid metabolism, and its enzymatic breakdown is associated with various infectious diseases. Here, we introduce trifunctional sphingomyelin derivatives that enable the visualization of sphingomyelin distribution and sphingomyelinase activity in infection processes. We demonstrate this by determining the activity of a bacterial sphingomyelinase on the plasma membrane of host cells using a combination of Förster resonance energy transfer and expansion microscopy. We further use our trifunctional sphingomyelin probes to visualize their metabolic state during infections with Chlamydia trachomatis and thereby show that chlamydial inclusions primarily contain the cleaved forms of the molecules. Using expansion microscopy, we observe that the proportion of metabolized molecules increases during maturation from reticulate to elementary bodies, indicating different membrane compositions between the two chlamydial developmental forms. Expansion microscopy of trifunctional sphingomyelins thus provides a powerful microscopy tool to analyze sphingomyelin metabolism in cells at nanoscale resolution.

Recycled Cellulose Acetate/Cerium Vanadate Nanoparticles Composite Membranes with Tuned Ultraviolet and Blue Light Shielding Capabilities

Recycled Cellulose Acetate/Cerium Vanadate Nanoparticles Composite Membranes with Tuned Ultraviolet and Blue Light Shielding Capabilities