The Role of Nanoparticle Layer Separation in the Finite Deformation Response of Layered Polyurethane-Clay Nanocomposites

Anisotropic Alignment of Bacterial Nanocellulose Ionogels for Unconventionally High Combination of Stiffness and Damping

Ionogels are emerging materials for advanced electrochemical devices; however, their mechanical instability to external stresses has raised concerns about their safety. This study reports aligned bacterial nanocellulose (BC) ionogel films swelled with the model ionic liquid (IL) of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄) for an unprecedented combination of high stiffness and high energy dissipation without significant loss of ionic conductivity. The aligned BC ionogel films are prepared through wet-state stretching methods, followed by drying and swelling by ILs. The aligned ionogel films exhibit significantly improved dynamic mechanical properties, overcoming the mechanical conventional limit of traditional materials by 2.0 times at 25 °C and by a maximum of 4.0 times at 0 °C. Additionally, the same samples exhibit relatively high ionic conductivities of 0.16 mS cm^-1 at 20 °C and 0.45 mS cm^-1 at 60 °C with storage moduli over 10 GPa. The synergistic effect of the mechanical reinforcements by alignment of the BC nanofibers and the plasticizing effects by ILs could be attributed to the significant enhancement of dynamic mechanical properties and the retention of ionic conductivities. These results will lead to a deeper understanding of the material design for mechanically superior ionogel systems with increasing demands for advanced electronic and electrochemical devices.

Interphase in Polymer Nanocomposites

The lightweight and high-strength functional nanocomposites are important in many practical applications. Natural biomaterials with excellent mechanical properties provide inspiration for improving the performance of composite materials. Previous studies have usually focused on the bionic design of the material's microstructure, sometimes overlooking the importance of the interphase in the nanocomposite system. In this Perspective, we will focus on the construction and control of the interphase in confined space and the connection between the interphase and the macroscopic properties of the materials. We shall survey the current understanding of the critical size of the interphase and discuss the general rules of interphase formation. We hope to raise awareness of the interphase concept and encourage more experimental and simulation studies on this subject, with the aim of an optimal design and controllable preparation of polymer nanocomposite materials.

An Investigative Study on the Progress of Nanoclay-Reinforced Polymers: Preparation, Properties, and Applications: A Review

Nanoclay-reinforced polymers have attracted considerable universal attention in academic and industrial research due to their outstanding properties and their ever-expanding utilization in diversified applications. In that regard, in the present review, the structure of layered silicate clay, as well as procedures for clay material modification, are outlined. We also discuss the general characterization techniques, synthesis methods, and various properties of polymer-clay nanocomposites (PCNs), and some examples likewise are depicted from the scientific literature. The study's primary goal is to provide an up-to-date survey of polymer-clay nanocomposites and their specific applications in industries such as automotive, flame-retardant, and biomedical applications, coating, and packaging.

Mechanically and thermo-driven self-healing polyurethane elastomeric composites using inorganic–organic hybrid material as crosslinker

Self-healable, recyclable, and robust polyurethane elastomeric composites by thermally driven Diels–Alder chemistry using inorganic–organic hybrid material as crosslinker.

The Future of Layer-by-Layer Assembly: A Tribute to ACS Nano Associate Editor Helmuth Möhwald

Layer-by-layer (LbL) assembly is a widely used tool for engineering materials and coatings. In this Perspective, dedicated to the memory of ACS Nano associate editor Prof. Dr. Helmuth Möhwald, we discuss the developments and applications that are to come in LbL assembly, focusing on coatings, bulk materials, membranes, nanocomposites, and delivery vehicles.

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.

Aging-Resistant Functionalized LDH⁻SAS/Nitrile-Butadiene Rubber Composites: Preparation and Study of Aging Kinetics/Anti-Aging Mechanism

With the aim of improving the anti-aging properties of nitrile-butadiene rubber (NBR), a functional organic filler, namely LDH⁻SAS, prepared by intercalating 4-amino-benzenesulfonic acid monosodium salt (SAS) into layered double hydroxides (LDHs) through anion exchange, was added to nitrile-butadiene rubber (NBR), giving the NBR/LDH⁻SAS composites. Successful preparation of LDH⁻SAS was confirmed by XRD, TGA and FTIR. LDH⁻SAS was well dispersed in the NBR matrix, owing to its strong interaction with the nitrile group of NBR. The obtained NBR/LDH⁻SAS composites exhibited excellent thermo-oxidative aging resistance as shown by TGA-DSC. Further investigation by ATR-FTIR indicated that SAS can capture the radical groups, even during the aging process, which largely accounts for the improved aging resistance.

Thermochromic Artificial Nacre Based on Montmorillonite

Nacre-inspired nanocomposites have attracted a great deal of attention in recent years because of their special mechanical properties and universality of the underlying principles of materials engineering. The ability to respond to external stimuli will augment the high toughness and high strength of artificial nacre-like composites and open new technological horizons for these materials. Herein, we fabricated robust artificial nacre based on montmorillonite (MMT) that combines robustness with reversible thermochromism. Our artificial nacre shows great potential in various fields such as aerospace and sensors and opens an avenue to fabricate artificial nacre responsive to other external stimuli in the future.

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.

Aligned bioinspired cellulose nanocrystal-based nanocomposites with synergetic mechanical properties and improved hygromechanical performance

Natural high-performance materials inspire the pursuit of ordered hard/soft nanocomposite structures at high fractions of reinforcements and with balanced supramolecular interactions. Such biomimetic design principles remain difficult to realize for bulk nanocomposites. Herein, we establish an effective drawing procedure that induces a high orientation of crystalline cellulose nanocrystals (CNCs) in a matrix of carboxymethylcellulose (CMC) at high level of reinforcements (50 vol %). We show such alignment in rather thick bulk films and report synergetic improvement with a simultaneous increase of stiffness, strength, and work-to-fracture as a function of the degree of alignment. Scanning electron microscopy and two-dimensional X-ray diffraction quantify the alignment of the cylindrical nanoparticles and link it to the extent of drawing and improvements in mechanical properties. We further show that the decline in mechanical properties of such waterborne all biobased nanocomposites at high relative humidity can be balanced using supramolecular modulation of the ionic interactions by exchanging the monovalent Na(+) counterion, present in CMC and CNC with di- or trivalent Cu(2+) and Fe(3+). This contribution demonstrates the importance of aligning one-dimensional reinforcements to achieve synergetic improvement in mechanical properties in sustainable bioinspired nanocomposites and suggests pathways to prepare water-stable materials based on a waterborne processing route.

Preparation of UV-curable functionalized phosphazene-containing nanotube/polyurethane acrylate nanocomposite coatings with enhanced thermal and mechanical properties

Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotubes with active hydroxyl groups were fabricated via an in situ template method under mild conditions, and then modified by acryloyl chloride to obtain the acryloyl-group functionalized PZS (f-PZS) nanotubes.

Fabrication of Meso-Porous Sintered Metal Thin Films by Selective Etching of Silica Based Sacrificial Template

Meso-porous metal materials have enhanced surface energies offering unique surface properties with potential applications in chemical catalysis, molecular sensing and selective separation. In this paper, commercial 20 nm diameter metal nano-particles, including silver and copper were blended with 7 nm silica nano-particles by shear mixing. The resulted powders were cold-sintered to form dense, hybrid thin films. The sacrificial silica template was then removed by selective etching in 12 wt% hydrofluoric acid solutions for 15 min to reveal a purely metallic meso-porous thin film material. The impact of the initial silica nano-particle diameter (7–20 nm) as well as the sintering pressure (5–20 ton·m⁻²) and etching conditions on the morphology and properties of the final nano-porous thin films were investigated by porometry, pyknometery, gas and liquid permeation and electron microscopy. Furthermore, the morphology of the pores and particle aggregation during shear mixing were assessed through cross-sectioning by focus ion beam milling. It is demonstrated that meso-pores ranging between 50 and 320 nm in average diameter and porosities up to 47% can be successfully formed for the range of materials tested.

Nanoparticle dispersion in polymer nanocomposites by spin-diffusion-averaged paramagnetic enhanced NMR relaxometry

We developed an analytical relationship between nuclear magnetic relaxation and interparticle spacings in polymer nanocomposites filled with paramagnetic-impurity-containing clay nanoparticles. Using (1)H NMR relaxometry, clay nanoparticle dispersion was quantified and agrees with interparticle spacing distributions determined from statistical analysis of TEM images. Some information on the overall quality of clay dispersion is revealed. This work offers a new approach and new insights into nanoparticle dispersion in polymer nanocomposites.

Nanoparticle dispersion in polymer nanocomposites by spin-diffusion-averaged paramagnetic enhanced NMR relaxometry: scaling relations and applications

Scaling relations were identified between NMR relaxometric observables and nanoparticle contents/spacings that enable predictions of clay dispersion in polymer nanocomposites.

Deoxyguanosine phosphate mediated sacrificial bonds promote synergistic mechanical properties in nacre-mimetic nanocomposites

We show that functionalizing polymer-coated colloidal nanoplatelets with guanosine groups allows synergistic increase of mechanical properties in nacre-mimetic lamellar self-assemblies. Anionic montmorillonite (MTM) was first coated using cationic poly(diallyldimethylammonium chloride) (PDADMAC) to prepare core-shell colloidal platelets, and subsequently the remaining chloride counterions allowed exchange to functional anionic 2'-deoxyguanosine 5'-monophosphate (dGMP) counterions, containing hydrogen bonding donors and acceptors. The compositions were studied using elemental analysis, scanning and transmission electron microscopy, wide-angle X-ray scattering, and tensile testing. The lamellar spacing between the clays increases from 1.85 to 2.14 nm upon addition of the dGMP. Adding dGMP increases the elastic modulus, tensile strength, and strain 33.0%, 40.9%, and 5.6%, respectively, to 13.5 GPa, 67 MPa, and 1.24%, at 50% relative humidity. This leads to an improved toughness seen as a ca. 50% increase of the work-to-failure. This is noteworthy, as previously it has been observed that connecting the core-shell nanoclay platelets covalently or ionically leads to increase of the stiffness but to reduced strain. We suggest that the dynamic supramolecular bonds allow slippage and sacrificial bonds between the self-assembling nanoplatelets, thus promoting toughness, still providing dynamic interactions between the platelets.

Reinforcement of polyether polyurethane with dopamine-modified clay: the role of interfacial hydrogen bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures.

Layer-by-layer assembled PVA/Laponite multilayer free-standing films and their mechanical and thermal properties

Structural arrangements of nanoplatelets in a polymer matrix play an important role in determining their properties. In the present study, multilayered composite films of poly(vinyl alcohol) (PVA) with Laponite clay are assembled by layer-by-layer (LBL) deposition. The LBL films are found to be hydrated, flexible and transparent. A facile and solvent-free method-by depositing self-assembled monolayers (SMA) of a functional silane on substrates-is demonstrated for preparing free-standing LBL films. Evolution of nanostructures in LBL films is correlated with thermal and mechanical properties. A well-dispersed solvent-cast PVA/Laponite composite film is also studied for comparison. We found that structurally ordered LBL films with an intercalated nanoclay system exhibits tensile strength, modulus and toughness, which are significantly higher than that of the conventional nanocomposites with well-dispersed clay particles and that of pure PVA. This indicates that clay platelets are oriented in the applied stress direction, leading to efficient interfacial stress transfer. In addition, various grades of composite LBL films are prepared by chemical crosslinking and their mechanical properties are assessed. On account of these excellent properties, the LBL films may find potential use as optical and structural elements, and as humidity sensors.