Nanoconfinement Effect Research Articles

Cyclodextrin Nano‐Assemblies Enabled Robust, Highly Stretchable, and Healable Elastomers with Dynamic Physical Network

AbstractArtificial materials with biomimic self‐healing ability are fascinating, however, the balance between mechanical properties and self‐healing performance is always a challenge. Here, a robust, highly stretchable self‐healing elastomer with dynamic reversible multi‐networks based on polyurethane matrix and cyclodextrin‐assembled nanosheets is proposed. The introduction of cyclodextrin nano‐assemblies with abundant surface hydroxyl groups not only forms multiple interfacial hydrogen bonding but also enables a strain‐induced reversible crystalline physical network owing to the special nanoconfined effect. The formation and dissociation of a dynamic crystalline physical network under stretching–releasing cycles skillfully balance the contradiction between mechanical robustness and self‐healing ability. The resulting nanocomposites exhibit ultra‐robust tensile strength (40.5 MPa), super toughness (274.7 MJ m−3), high stretchability (1696%), and desired healing efficiency (95.5%), which can lift a weight ≈ 100 000 times their own weight. This study provides a new approach to the development of mechanically robust self‐healing materials for engineering applications such as artificial muscles and healable robots.

Acidic layer-enhanced nanoconfinement of anions in cylindrical pore of single-walled carbon nanotube

The adsorption of the nitrate ion by the cylindrical pore of single-walled carbon nanotubes (SWCNT) was found to be aided by an acidic adsorbed layer. Adsorbed water in the vicinity of the pore wall can supply protons through ionization, forming the acidic layer, according to Raman spectra and results of solution pH fluctuations caused by ion species adsorption. Such an acidic adsorbed layer leads to surplus adsorption of anionic species where the adsorbed amount of nitrate ions is much larger than that of cations. Also, we could observe the Raman bands being assignable to the symmetrical stretching mode at an extremely high-frequency region for nano-restricted nitrate ions compared to any other bulk phases. The abnormal band shift of adsorbed nitrate ions indicates that the nitrate ions are confined in the pore under the effects of nanoconfinement by the pore and the strong interaction with the acidic layer in the pore. Our results warn that we have to construct the adsorption model of aqueous electrolytes confined in carbon pores by deliberating the acid layer formed by the adsorbed water.

Revealing the Combined Nanoconfinement Effect by Soft and Stiff Inclusions in PMMA/Silica CO2 Blown Foams

AbstractThis study shows the importance of nanoparticle (NP) spatial arrangement on the nucleation, morphology, and properties of nanocomposite foams. It probes CO2 blown PMMA with three types of nanosilica structures with exactly the same chemical composition: aggregates, chain bound clusters, and individually dispersed NPs. A systematic but nontrivial scaling of morphology, glass transition temperature, static and impact mechanical properties, and thermal conductivity is discussed with special regard to the combined nanoconfinement by soft and stiff inclusions. The presented results suggest a limited potential of simultaneous toughening by nanoreinforcement and shear banding, which can draw significant implications for both the fundamental science and industrial practice dealing with nanoreinforced cellular materials.

Atomic insights into melting behaviours of phase change material confined in nanospace

In this study, a molecular dynamics simulation was performed to provide atomic insights into the melting behaviours of phase change materials confined in nanospace. NaCl was used as the phase change material while SiC act as the porous matrix. Both static and dynamic behaviours of atoms were analysed. The morphology evolution was illustrated and the local structure was depicted. At the low temperature, nanoconfined NaCl remains the cubic crystal structure although some atoms slightly deviate from the lattice point. After melting, the system becomes disordered and the regular crystal structure disappears. The morphology evolution is consistent with the change in the micro-structure. After melting, the main distance between cations and anions becomes shorter and the coordination number in the short range is larger than that before melting. Atomic motion is characterised using the Lindemann index. At the solid and liquid states, the increase in the Lindemann index is slow while near the phase transition point, the increase is dramatic. Compared to the bulk NaCl, the balance position more approaches the central ion. Finally, the nanoconfinement effect on melting point and latent heat, two critical thermodynamic properties for phase change materials, is discussed. The depressed melting point and latent heat are attributed to the coulombic interaction and the micro-structure difference respectively. This study aims to provide atomic insights into the melting behaviours of nanoconfined phase change materials.

Photocatalytic oxidation degradation of tetracycline over La/Co@TiO2 nanospheres under visible light

The oxygen-vacancy-rich La/Co@TiO2 nanospheres for the photo catalytic degradation of tetracycline were prepared by a simple two-step method. 3 wt%La/Co@TiO2 nanospheres had better photocatalytic performance of the degradation of tetracycline than that of the other catalysts under visible light may be due to the synergistic effect between La/Co and TiO2 and nano-confined effect. The catalytic experimental results showed the degradation ratio of tetracycline (40 mg/L) were 100% for 90 min. XPS, Raman, and photoelectrochemical results showed appropriate number of oxygen vacancies existed on the surface of TiO2, which could improve the activation efficiency of dissolved oxygen in tetracycline solution because they accelerated the electron transfer rate in the system and inhibited the photoelectron-hole pair recombination under visible light. The EPR and radical scavenger tests showed h+, O2−, and ·OH were the main active species for the degradation of tetracycline. Also, the possible mechanism and intermediates of the tetracycline degradation process were speculated under the visible light. La/Co@TiO2 nanospheres would be a promising photocatalyst for wastewater treatment.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis.

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.

Catalytic ozonation of antibiotics by using Mg(OH)2 nanosheet with dot-sheet hierarchical structure as novel nanoconfined catalyst.

Antibiotic pollution has caused important concern for international and national sustainability. Catalytic ozonation is a quick and efficient technique to remove contaminants in aquatic environment. This study firstly developed a nanosheet-growth technique for synthesizing Li-doped Mg(OH)2 with dot-sheet hierarchical structure as catalyst to ozonize antibiotics. Metronidazole could be totally removed through ozonation catalyzed by Li-doped Mg(OH)2 in 10min. Approximately 97% of metronidazole was eliminated in 10min even the catalyst was used for 4 times. Reaction rate constant of Li-doped Mg(OH)2 treatment was about 3.45 times that of nano-Mg(OH)2 treatment, illustrating that the dot-sheet hierarchical structure of Li-doped Mg(OH)2 exhibited nano-confinement effect on the catalytic ozonation. Approximately 70.4% of metronidazole was mineralized by catalytic ozonation using Li-doped Mg(OH)2. Temperature of 25°C was more suitable for catalytic ozonation of metronidazole by Li-doped Mg(OH)2. Ions generally inhibited the catalytic ozonation of metronidazole while only 0.005molL-1 of Cl- slightly enhanced the ozonation rate, illustrating complicated mechanisms existed for ozonation of metronidazole catalyzed by Li-doped Mg(OH)2. The possible mechanisms of the ozonation of metronidazole using Li-doped Mg(OH)2 included direct ozonation and ozonation catalyzed by radical ·O2-, reactive oxygen species 1O2 and intermediate (H2O2). The synthesized Mg(OH)2 nanosheet with dot-sheet hierarchical structure is a novel nanoconfined material with excellent reusability and catalytic performance.

Controlling the optical properties and analyzing mechanical, dielectric characteristics of MgO doped (PVA–PVP) blend by altering the doping content for multifunctional microelectronic devices

The solution-cast method was used to synthesize magnesia (MgO) nanoparticles filled poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) blend matrix (80/20 wt %) based polymeric nanocomposite (PNC) films (i.e., [PVA–PVP]–x wt % MgO; x = 0, 0.06, 0.3, 0.6, 3.1, and 6.25). Most of these PNC materials structures are amorphous, according to an X-ray diffraction investigation. The blend surface was smooth and homogeneous under SEM, confirming PVA and PVP compatibility. MgO loading, on the other hand, enhanced the surface roughness. According to optical investigations, the film's transmittance, and energy bandgap decreased as the Mg+2 -ions increased. Tensile strength has also improved from 5.92 MPa to 10.65 MPa, while Young's modulus has enhanced from 51.16 to 166.4 MPa. From 100 Hz to 1 MHz, the dielectric and electrical spectra of these films were measured. Due to the nanoconfinement effect, it has been determined that the dispersion of MgO nanoparticles in the PVA–PVP blend matrix dramatically increases the dielectric permittivity. With increasing frequency, the dielectric permittivity of these PNC films decreases while the ac electrical conductivity increases. When the temperature of a PNC film is raised, a nonlinear rise in dielectric permittivity is seen, and the dc electrical conductivity of the film follows the Arrhenius law. The nonlinear I–V curves improve with increased Mg+2 ion concentration. These findings suggest that PVA/PVP blend matrix loaded with MgO NPs provides appropriate structural, optical, and electrical characteristics, expanding its potential industrial uses, particularly in optical components and devices.

Improving crystallinity and ordering of PBTTT by inhibiting nematic to smectic phase transition via rapid cooling

The liquid crystalline (LC) phase can promote the long-range ordering of conjugated polymer films. Therefore, the effects of different single LC phases and the coexistence of multiple LC phases on film morphology deserve further study. In this work, we found that distinct film morphologies can be obtained by undergoing different LC transition processes. It was demonstrated that Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) undergoes a high-temperature nematic LC I phase and a low-temperature smectic LC Ⅱ phase by optical images, in-situ UV–vis spectroscopy and Fourier transform infrared spectroscopy (FTIR). When the PBTTT is rapidly cooled from the melt to solid thin film at 130 °C/min, the films crystallize from LC I directly and keep the nematic-like texture. When the melt is slowly cooled at 1 °C/min, the films crystallize after transforming from LC I to LC II and retain the smectic-like texture. The former films exhibit 24.5 times higher crystallinity than the latter. Meantime, the lamellar packing d100 distance increases from 21.06 Å to 23.85 Å, and the intercrystallite distance increases from 9 nm to 25 nm, respectively. The restraint chain mobility in the highly ordered smectic phase and the nanoconfinement effect induced by phase separation between LC I and LC II are responsible for the reduced crystalline order in the films experienced by LC I and LC II. This work emphasizes the importance of LC phases and rational annealing programs on morphology design.

Engineering hierarchical MXenes-based nanoarchitecture as superior nanoenhancer for fire-safe BMI resin

It is well-recognized that, the inferior fire safety has been the stumbling block for the extensive usages of bismaleimide resin (BMI). Hence, a ternary hierarchical MXenes-based nanoarchitecture (CMAMX) is rationally engineered, towards suppressing the heat and toxicants emissions of BMI. By incorporating 2.0 wt% CMAMX, the marked reductions of 36.5%, 32.9%, 33.5%, 29.2% on peak heat release rate, total heat release, peak smoke production rate, total smoke production are observed. Moreover, the peak CO production rate and peak CO2 production rate are decreased by 40.0% and 54.0%. Additionally, TG-IR test offers evidences for the impeded releases of NO and HCN gases. These results strongly corroborate the strength of CMAMX in impairing the heat and toxicants generations of BMI. Interestingly, the improved mechanical properties are acquired after using CMAMX, deriving from the multiple hydrogen bond interactions and induced nanoconfinement effect. For instance, the tensile toughness is promoted by 50.7%. Briefly, this contribution may be encouraging for the engineering of MXenes-based nanostructure, towards constructing high-performance polymer composites.

A relative permeability model considering nanoconfinement and dynamic contact angle effects for tight reservoirs

With a sharp reduction in conventional oil and gas resources, tight oil and gas resources have attracted great interest in the petroleum industry. Relative permeability plays an important role in modeling fluid flow in tight reservoirs. Here, considering the nanoconfinement effects (abnormal viscosity effect (AVE) and slip effect) and dynamic contact angle (DCA) effect, a relative permeability model for tight reservoirs is proposed. The results show that the proposed model can accurately describe the relative permeability in tight reservoirs. As the AVE of water or oil increases, the relative permeability of water decreases, while the relative permeability of oil hardly changes for rocks with an average pore radius of 298 nm and decreases for the ones with an average pore radius of 49 nm. As the slip length of oil increases, the relative permeabilities of both water and oil decrease. As the DCA effect increases, the relative permeability of water increases, while the relative permeability of oil is unchanged. With a decrease in the pore size, the nanoconfinement effects on relative permeability become more notable, while the DCA effect on relative permeability becomes smaller. This work is of great significance to the development of tight reservoirs.

Melting Temperature Depression and Phase Transitions of Nitrate-Based Molten Salts in Nanoconfinement.

Hybrids of nitrate-based molten salts (KNO3, NaNO3, and Solar Salt) and anodic aluminum oxide (AAO) with various pore sizes (between 25 and 380 nm) were designed for concentrated solar power (CSP) plants to achieve low melting point (<200 °C) and high thermal conductivity (>1 W m–1 K–1). AAO pore surfaces were passivated with octadecyl phosphonic acid (ODPA), and the results were compared with as-anodized AAO. The change in phase transition temperatures and melting temperatures of salts was investigated as a function of pore diameter. Melting temperatures decreased for all salts inside AAO with different pore sizes while the highest melting temperature decrease (ΔT = 173 ± 2 °C) was observed for KNO3 filled in AAO with a pore diameter of 380 nm. Another nanoconfinement effect was observed in the crystal phases of the salts. The ferroelectric phase of KNO3 (γ-phase) formed at room temperature for KNO3/AAO hybrids with pore size larger than 35 nm. Thermal conductivity values of molten salt (MS)/AAO hybrids were obtained by thermal property analysis (TPS) at room temperature and above melting temperatures of the salts. The highest increase in thermal conductivity was observed as 73% for KNO3/AAO-35 nm. For NaNO3/AAO-380 nm hybrids, the thermal conductivity coefficient was 1.224 ± 0.019 at room temperature. To determine the capacity and efficiency of MS/AAO hybrids during the heat transfer process, the energy storage density per unit volume (J m–3) was calculated. The highest energy storage capacity was calculated as 2390 MJ m–3 for KNO3/AAO with a pore diameter of 400 nm. This value is approximately five times higher than that of bulk salt.

Facile preparation of α-MnO2 nanowires for assembling free-standing membrane with efficient Fenton-like catalytic activity

Assembling MnO2 nanowires into macroscopic membrane is a promising engineered technology for catalyst separation and enhancement of Fenton-like reaction activity, yet its development is limited by the deficiencies in preparation and property modulation of the MnO2 nanowires. In this work, we developed a facile method using C2H5OH and CH3COOK as reductive and vital control reagents to react with KMnO4 by hydrothermal reaction at 140 °C for 12 h, to prepare the ultralong α-MnO2 nanowires up to tens of micrometers with high purity and aspect ratio. Such strategy not only had the advantages of being mild, easily controlled and environmental pollution-free, but also endowed α-MnO2 nanowires with excellent ability as a Fenton catalyst when assembled into free-standing membrane for degrading phenolic compounds (kobs = 0.0738 ∼ 0.1695 min−1) in a continuous flow reaction. The reactive oxygen species (i.e., •OH) from Fenton-like reaction were enriched within this α-MnO2 nanowire membrane via nanoconfinement effect, which further enhanced the mass transportation of •OH available for phenolic contaminants. MnO2 nanowire membrane using our method possessed the high practical potential for water purify due to its easy-preparation and enhanced catalytic performances.

Nanoconfinement effect of nanoporous carbon electrodes for ionic liquid-based aluminum metal anode

Rechargeable aluminum batteries (RABs), which use earth-abundant and high-volumetric-capacity metal anodes (8040 mAh cm−3), have great potential as next-generation power sources because they use cheaper resources to deliver higher energies, compared to current lithium ion batteries. However, the mechanism of charge delivery in the newly developed, ionic liquid-based electrolytic system for RABs differs from that in conventional organic electrolytes. Thus, targeted research efforts are required to address the large overpotentials and cycling decay encountered in the ionic liquid-based electrolytic system. In this study, a nanoporous carbon (NPC) electrode with well-developed nanopores is used to develop a high-performance aluminum anode. The negatively charged nanopores can provide quenched dynamics of electrolyte molecules in the aluminum deposition process, resulting in an increased collision rate. The fast chemical equilibrium of anionic species induced by the facilitated anionic collisions leads to more favorable reduction reactions that form aluminum metals. The nanoconfinement effect causes separated nucleation and growth of aluminum nanoparticles in the multiple confined nanopores, leading to higher coulombic efficiencies and more stable cycling performance compared with macroporous carbon black and 2D stainless steel electrodes.

Nanocavity-enriched Porous Cu2O Catalyst for Selective CO2 Reduction to Multicarbon Products through the Nanoconfinement Effect

Nanocavity-enriched Porous Cu2O Catalyst for Selective CO2 Reduction to Multicarbon Products through the Nanoconfinement Effect

Decoupling of Glassy Dynamics from Viscosity in Thin Supported Poly(n-butyl methacrylate) Films.

We utilized fast scanning calorimetry to characterize the glass transition temperature (Tg) and intrinsic molecular mobility of low-molecular-weight poly(n-butyl methacrylate) thin films of varying thicknesses. We found that the Tg and intrinsic molecular mobility were coupled, showing no film thickness-dependent variation. We further employed a unique noncontact capillary nanoshearing technique to directly probe layer-resolved gradients in the rheological response of these films. We found that layer-resolved shear mobility was enhanced with a reduction in film thickness, whereas the effective viscosity decreased. Our results highlight the importance of polymer–substrate attractive interactions and free surface-promoted enhanced mobility, establishing a competitive nanoconfinement effect in poly(n-butyl methacrylate) thin films. Moreover, the findings indicate a decoupling in the thickness-dependent variation of Tg and intrinsic molecular mobility with the mechanical responses (shear mobility and effective viscosity).

Recent Development in Nanoconfined Hydrides for Energy Storage.

Hydrogen is the ultimate vector for a carbon-free, sustainable green-energy. While being the most promising candidate to serve this purpose, hydrogen inherits a series of characteristics making it particularly difficult to handle, store, transport and use in a safe manner. The researchers’ attention has thus shifted to storing hydrogen in its more manageable forms: the light metal hydrides and related derivatives (ammonia-borane, tetrahydridoborates/borohydrides, tetrahydridoaluminates/alanates or reactive hydride composites). Even then, the thermodynamic and kinetic behavior faces either too high energy barriers or sluggish kinetics (or both), and an efficient tool to overcome these issues is through nanoconfinement. Nanoconfined energy storage materials are the current state-of-the-art approach regarding hydrogen storage field, and the current review aims to summarize the most recent progress in this intriguing field. The latest reviews concerning H2 production and storage are discussed, and the shift from bulk to nanomaterials is described in the context of physical and chemical aspects of nanoconfinement effects in the obtained nanocomposites. The types of hosts used for hydrogen materials are divided in classes of substances, the mean of hydride inclusion in said hosts and the classes of hydrogen storage materials are presented with their most recent trends and future prospects.

Relative permeability estimation of oil−water two-phase flow in shale reservoir

Oil−water two-phase flow is ubiquitous in shale strata due to the existence of connate water and the injection of fracturing fluid. In this work, we propose a relative permeability model based on a modified Hagen−Poiseuille (HP) equation and shale reconstruction algorithm. The proposed model can consider the nanoconfined effects (slip length and spatially varying viscosity), oil−water distribution, pore size distribution (PSD), total organic matter content (TOC), and micro-fracture. The results show that the increasing contact angles of organic matters (OM) and inorganic minerals (iOM) increase the relative permeability of both oil and water. As the viscosity ratio increases, the relative permeability of oil phase increases while that of water phase decreases, due to the different water−oil distribution. The effective permeability of both oil and water decreases with the increasing TOC. However, the relative permeability of water phase increases while that of oil phase decreases. The increasing number and decreasing deviation angle of micro-fracture increase the effective permeability of oil and water. However, micro-fracture has a minor effect on relative permeability. Our model can help understand oil−water two-phase flow in shale reservoirs and provide parameter characterization for reservoir numerical simulation.

Atomistic Assessment of Melting Point Depression and Enhanced Interfacial Diffusion of Cu in Confinement with AlN.

The continuing trend in heterogeneous integration (i.e., miniaturization and diversification of devices and components) requires a fundamental understanding of the phase stability and diffusivity of nanoconfined metals in functional nanoarchitectures, such as nanomultilayers (NMLs). Nanoconfinement effects, such as interfacial melting and anomalous fast interfacial diffusion, offer promising engineering tools to enhance the reaction kinetics at low temperatures for targeted applications in the fields of joining, solid-state batteries, and low-temperature sintering technologies. In the present study, the phase stability and atomic mobility of confined metals in Cu/AlN NMLs were investigated by molecular dynamics, with the interatomic potential compared to the ab initio calculations of the Cu/AlN interface adhesion energy. Simulations of the structural evolution of Cu/AlN nanomultilayers upon heating in dependence on the Cu nanolayer thickness demonstrate the occurrence of interfacial premelting, a melting point depression, as well as extraordinary fast solid-state diffusion of confined Cu atoms along the defective heterogeneous interfaces. The model predictions rationalize recent experimental observations of premelting and anomalous fast interface diffusion of nanoconfined metals in nanostructured Cu/AlN brazing fillers at strikingly low temperatures.

Nanoconfined Gas Flow Behavior in Organic Shale: Wettability Effect

A clear understanding of nanoconfined gas flow behavior in shale gas reservoirs is beneficial for its efficient development. Nanopores in the shale gas reservoirs are characterized by complex surface chemistry and composition, as well as affinity, while their impact on methane flow has not been investigated comprehensively before. In light of current research status, this article proposes a simple yet robust theoretical model, incorporating bulk-gas flow flux and surface diffusion of adsorption gas. In particular, wettability effect, indicating the influences of the shifted critical properties and adsorption thickness, is captured as well. In this article, gas physical attributes, such as gas compressibility factor and gas viscosity, are modified under the nanoconfinement effect and wettability effect, and also the variation of effective pore size, induced by surface wettability, is considered. Notably, wettability effect in this article is described by using a macroscopic form, surface contact angle, facilitating the model applicability. In addition, both the bulk-gas flow model and surface-diffusion model, developed in this research, are able to achieve excellent agreements compared with the existed documents, clarifying the reliability of the proposed model. Meanwhile, key role of wettability effect on nanoconfined gas flow behavior, especially for surface diffusion of adsorption gas, is demonstrated. Results show that (a) the gas flux in small nanopores may exceed that in large nanopores, due to the predominant role of surface diffusion, while pore size is less than 10 nm; (b) the absence of real gas effect will lead to inaccurate characterization of nanoconfined gas flow capacity, and the magnitude can reach 7% for pore size of 5 nm and will enlarge with further pore size shrinkage; (c) wettability effect governs the total gas flux when pore size is less than 10 nm, while its impact will be greatly mitigated when pore size is greater than 50 nm. This article provides a comprehensive investigation to shed light on surface wettability on gas flow behavior through nanopores.