Highly oriented gold/nanoclay-polymer nanocomposites for flexible gas barrier films

A versatile “3M” methodology to obtain superhydrophobic PDMS-based materials for antifouling applications

Fouling, including inorganic, organic, bio-, and composite fouling seriously affects our daily life. To reduce these effects, antifouling strategies including fouling resistance, release, and degrading, have been proposed. Superhydrophobicity, the most widely used characteristic for antifouling that relies on surface wettability, can provide surfaces with antifouling abilities owing to its fouling resistance and/or release effects. PDMS shows valuable and wide applications in many fields, and due to the inherent hydrophobicity, superhydrophobicity can be achieved simply by roughening the surface of pure PDMS or its composites. In this review, we propose a versatile “3M” methodology (materials, methods, and morphologies) to guide the fabrication of superhydrophobic PDMS-based materials for antifouling applications. Regarding materials, pure PDMS, PDMS with nanoparticles, and PDMS with other materials were introduced. The available methods are discussed based on the different materials. Materials based on PDMS with nanoparticles (zero-, one-, two-, and three-dimensional nanoparticles) are discussed systematically as typical examples with different morphologies. Carefully selected materials, methods, and morphologies were reviewed in this paper, which is expected to be a helpful reference for future research on superhydrophobic PDMS-based materials for antifouling applications.

Mechanically Strong, Thermally Stable Gas Barrier Polyimide Membranes Derived from Carbon Nanotube-Based Nanofluids

Gas barrier membranes with impressive moisture permeability are highly demanded in air or nature gas dehumidification. We report a novel approach using polyetheramine oligomers covalently grafted on the carbon nanotubes (CNTs) to engineer liquid-like CNT nanofluids (CNT NFs), which are incorporated into a polyimide matrix to enhance the gas barrier and moisture permeation properties. Benefiting from the featured liquid-like characteristic of CNT NFs, a strong interfacial compatibility between CNTs and the polyimide matrix is achieved, and thus, the resulting membranes exhibit high heat resistance and desirable mechanical strength as well as remarkable fracture toughness, beneficially to withstanding creep, impact, and stress fatigue in separation applications. Positron annihilation lifetime spectroscopy measurements indicate a significant decrease in fractional free volume within the resulting membranes, leading to greatly enhanced gas barrier properties while almost showing full retention of moisture permeability compared to that of the pristine membrane. For membranes with 10 wt % CNT NFs, the gas transmission rates, respectively, decrease 99.9% for CH₄, 94.4% for CO₂, 99.2% for N₂, and 97.9% for O₂ compared with that of the pristine membrane. Most importantly, with the increasing amount of CNT NFs, the hybrid membranes demonstrate a simultaneous increase of barrier performance and permselectivity for H₂O/CH₄, H₂O/N₂, H₂O/CO₂, and H₂O/O₂. All these results make these membranes potential candidates for high-pressure natural gas or hyperthermal air dehydration.

hBN Flake Embedded Al2O3 Thin Film for Flexible Moisture Barrier

Due to the vulnerability of organic optoelectronic devices to moisture and oxygen, thin-film moisture barriers have played a critical role in improving the lifetime of the devices. Here, we propose a hexagonal boron nitride (hBN) embedded Al2O3 thin film as a flexible moisture barrier. After layer-by-layer (LBL) staking of polymer and hBN flake composite layer, Al2O3 was deposited on the nano-laminate template by spatial plasma atomic layer deposition (PEALD). Because the hBN flakes in Al2O3 thin film increase the diffusion path of moisture, the composite layer has a low water vapor transmission ratio (WVTR) value of 1.8 × 10-4 g/m2 day. Furthermore, as embedded hBN flakes restrict crack propagation, the composite film exhibits high mechanical stability in repeated 3 mm bending radius fatigue tests.

Layer-by-layer assembled multilayers of charged polyurethane and graphene oxide platelets for flexible and stretchable gas barrier films

With the advent of the era of consumer-oriented displays and mobile devices, the importance of barrier film coatings for securing devices from oxygen or moisture penetration has become more salient. Recently developed approaches to generate gas barrier films in a combination of polyelectrolyte multilayer matrices and incorporated inorganic nanosheets have shown great potential in outperforming conventional gas barrier films. However, these films have the intrinsic drawback of vulnerability to brittleness and inability to stretch for flexible device applications. To overcome this issue, we present a method in which we prepare multilayered films of complementarily charged polyurethane and graphene oxide platelets using spin-assisted, layer-by-layer self-assembly to obtain well-stacked film structures. As a result, the multilayered, thin films deposited on a poly(ethylene terephthalate) (PET) substrate can exhibit significantly reduced oxygen penetration properties (∼30 cc m-2 day-1 for the oxygen transmission rate) while still demonstrating large bending or stretching deformations. Therefore, the proposed approach in this study is anticipated to be extensively utilized for surface coating and protection of flexible and stretchable devices under various operating conditions.

High-Throughput Fabrication Method for Producing a Silver-Nanoparticles-Doped Nanoclay Polymer Composite with Novel Synergistic Antibacterial Effects at the Material Interface

In this study, we report a high-throughput fabrication method at industrial pilot scale to produce a silver-nanoparticles-doped nanoclay-polylactic acid composite with a novel synergistic antibacterial effect. The obtained nanocomposite has a significantly lower affinity for bacterial adhesion, allowing the loading amount of silver nanoparticles to be tremendously reduced while maintaining satisfactory antibacterial efficacy at the material interface. This is a great advantage for many antibacterial applications in which cost is a consideration. Furthermore, unlike previously reported methods that require additional chemical reduction processes to produce the silver-nanoparticles-doped nanoclay, an in situ preparation method was developed in which silver nanoparticles were created simultaneously during the composite fabrication process by thermal reduction. This is the first report to show that altered material surface submicron structures created with the loading of nanoclay enables the creation of a nanocomposite with significantly lower affinity for bacterial adhesion. This study provides a promising scalable approach to produce antibacterial polymeric products with minimal changes to industry standard equipment, fabrication processes, or raw material input cost.

Hydrolyzed hexagonal boron nitride/polymer nanocomposites for transparent gas barrier film

A flexible thin gas barrier film formed by layer-by-layer (LBL) assembly has been studied. We propose for the first time that hexagonal boron nitride (h-BN) can be used in LBL assembly. When dispersed in water through sonication-assisted hydrolysis, h-BN develops hydroxyl groups that electrostatically couple with the cationic polymer polydiallyldimethylammonium chloride (PDDA). This process produces hydroxyl-functional h-BN/PDDA nanocomposites. The nanocomposites exhibit well exfoliated and highly ordered h-BN nanosheets, which results in an extremely high visual clarity, with an average transmittance of 99% in the visible spectrum. Moreover, well aligned nanocomposites extend gas diffusion path that reduce water vapor transmission rate to 1.3 × 10^-2 g m^-2 d^-1. The simple and fast LBL process demonstrated here can be applied in many gas barrier applications.

Interdigitated crystalline MMT–MCA in polyamide 6

A novel interdigitated crystalline MMT–MCA shows outstanding fire retardancy owing to homogeneous dispersion of MMT and MCA in PA6.

Edge Charge Neutralization of Clay for Improved Oxygen Gas Barrier in Multilayer Nanobrick Wall Thin Films

Layer-by-layer (LbL) assembled polymer-clay multilayer thin films are known to provide transparent and flexible gas barrier. In an effort to further lower the oxygen transmission rate (OTR) of these nanobrick wall thin films, sodium chloride was introduced into montmorillonite (MMT) suspension as an "indifferent electrolyte". At pH 6.5 the amphoteric edge sites of MMT have a neutral net charge, and a moderate concentration of NaCl effectively shields the charge from neighboring platelets, allowing van der Waals forces to attract the edges to one another. This edge-to-edge bonding creates a much more tortuous path for diffusing oxygen molecules. An eight-bilayer (BL) polyethylenimine (PEI)/MMT multilayer coating (∼50 nm thick), assembled with 5 mM NaCl in the aqueous clay suspension, exhibited an order of magnitude reduction in oxygen permeability (∼4 × 10^-20 cm³·cm/(cm²·Pa·s)) relative to its salt-free counterpart. This result represents the best barrier among polymer-clay bilayer systems, which is also lower than SiO_x or Al_xO_y thin films. At higher NaCl concentration, the strong charge screening causes edge-to-face bonding among MMT nanoplatelets, which leads to misalignment in assembled films and increased OTR. This "salty-clay" strategy provides an efficient way to produce better multilayer oxygen barrier thin films by altering ionic strength of the MMT suspension. This simple modification reduces the number of layers necessary for high gas barrier, potentially making these multilayer films interesting for commercial packaging applications.

Million-Fold Decrease in Polymer Moisture Permeability by a Graphene Monolayer

Flexible, transparent, and moisture-impermeable materials are critical for packaging applications in electronic, food, and pharmaceutical industries. Here, we report that a single graphene layer embedded in a flexible polymer reduces its water vapor transmission rate (WVTR) by up to a million-fold. Large-area, transparent, graphene-embedded polymers (GEPs) with a WVTR as low as 10(-6) g m(-2) day(-1) are demonstrated. Monolayered graphene, synthesized by chemical vapor deposition, has been transferred onto the polymer substrate directly by a very simple and scalable melt casting process to fabricate the GEPs. The performances of the encapsulated organic photovoltaic (OPV) devices do not vary even after subjecting the GEPs to cyclic bending for 1000 cycles. Accelerated aging studies of working OPV devices encapsulated in the GEPs show a 50% lifetime of equivalent to 1 000 000 min, which satisfies the requirements of organic electronics.

Facile polymerization of β-cyclodextrin functionalized graphene or graphene oxide nanosheets using citric acid crosslinker by in situ melt polycondensation for enhanced electrochemical performance

In this study, we report a facile, environmental friendly route to synthesize water-insoluble β-cyclodextrin (β-CD)/graphene oxide (GO) or reduced graphene oxide (rGO) nanocomposite hydrogels.

Reactive interlayer based ultra-low moisture permeable membranes for organic photovoltaic encapsulation

Reactive water vapor barrier materials with zero valent iron and copper nanoparticles for organic device encapsulation.

Fabrication of poly(β-cyclodextrin-co-citric acid)/bentonite clay nanocomposite hydrogel: thermal and absorption properties

A β-cyclodextrin (β-CD)/bentonite clay (BNC) nanocomposite hydrogel was prepared through combining in situ intercalative polymerization and melt intercalation methods.