Nanoconfinement Effect Research Articles

Nanoconfinement Controls Mechanical Properties of Elastomeric Thin Films.

Mastering mechanical properties of polymers at nanometer scale is highly demanded yet remains challenging. Pioneering advances determined Young's modulus in ultrathin polymer films and attained unprecedented results including rubbery stiffening. However, many viscoelastic properties such as dynamic mechanical behavior of freestanding nanoconfined polymer films are still unknown. Here we demonstrate striking changes of stiffness and the ratio between elastic and viscous responses in thin PDMS films, using a microvibrational system which enables direct measurements of dynamic stress-strain relation of freestanding films. The results show that elastic modulus is enhanced by a factor of 135 in 50 nm films than the bulk, while the viscous response substantially increases at strains >0.05 in 125 nm films. These observations exhibit significant alterations of viscoelasticity under nanoconfinement. With insights on the underlying mechanism of these results, this study is expected to provide new evidence toward gaining a comprehensive understanding of nanoconfinement effect of soft matter.

Studies on nanoconfinement effect of NiO-SiO2 spin glass within mesoporous Al2O3 template

Nanoconfinement studies in the glass system xNiO-(1-x)SiO2 having x values as 0.2 and 0.4 were carried out by preparing nanocomposites using mesoporous alumina template. These samples were studied using wide and small angle xrd data. BET analysis was conducted to find the surface area and pore size distribution of the virgin and nanocomposite samples. The microstructure and distribution of transition metal ions in the system were delineated using STEM-EDAX mapping. XPS data provide the quantitative analysis of Ni2+/Ni3+ species present in the system. Theoretical modeling using DFT simulations were implemented to understand the nanoconfinement effect which was in corroboration with the experimental findings. The theoretical model was validated using UV-Vis absorption spectrum. The magnetodielectric results were explained considering Catalan’s model having positive magnetoresistance. Nyquist plot studies were employed to visualize the realistic circuit model with contributions from different layers present in the nanocomposites. The temperature dependent resistivity data were explained using small polaron hopping model and the inter-site separation between Ni2+/Ni3+ ions was found to be larger in nano confined system than the corresponding bulk glass. Existence of more conducting species manifest a significant enhancement in percentile change of MD, MR & conductivity values for NC-2 compared to NC-1. Study of ZFC-FC magnetization curves effectively substantiate spin glass characteristics which exhibit freezing temperature at 4.1 K. The existence of spin glass behavior are well interpreted in terms of memory effect and relaxation dynamics study.

In-situ synthesis of N, S co-doped hollow carbon microspheres for efficient catalytic oxidation of organic contaminants

Metal-free heteroatom doped nanocarbons are promising alternatives to the metal-based materials in catalytic ozonation for destruction of aqueous organic contaminants. In this study, N, S co-doped hollow carbon microspheres (NSCs) were synthesized from the polymerization products during persulfate wet air oxidation of benzothiazole. The contents of doped N and S as well as the structural stability were maneuvered by adjusting the subsequent N2-annealing temperature. Compared with the prevailing single-walled carbon nanotubes, the N2-annealed NSCs demonstrated a higher catalytic ozonation activity for benzimidazole degradation. According to the quantitative structure-activity relationship (QSAR) analysis, the synergistic effect between the graphitic N and the thiophene-S which redistributed the charge distribution of the carbon basal plane contributed to the activity enhancement of the N2-annealed NSCs. Additionally, the hollow structure within the microspheres served as the microreactor to boost the mass transfer and reaction kinetics via the nanoconfinement effects. Quenching and electron paramagnetic resonance (EPR) tests revealed that benzimidazole degradation was dominated by the produced singlet oxygen (1O2) species, while hydroxyl radicals (•OH) were also generated and participated. This study puts forward a novel strategy for synthesis of heteroatom-doped nanocarbons and sheds a light on the relationship between the active sites on the doped nanocarbons and the catalytic performance.

Nature of dynamic gradients, glass formation, and collective effects in ultrathin freestanding films

Molecular, polymeric, colloidal, and other classes of liquids can exhibit very large, spatially heterogeneous alterations of their dynamics and glass transition temperature when confined to nanoscale domains. Considerable progress has been made in understanding the related problem of near-interface relaxation and diffusion in thick films. However, the origin of "nanoconfinement effects" on the glassy dynamics of thin films, where gradients from different interfaces interact and genuine collective finite size effects may emerge, remains a longstanding open question. Here, we combine molecular dynamics simulations, probing 5 decades of relaxation, and the Elastically Cooperative Nonlinear Langevin Equation (ECNLE) theory, addressing 14 decades in timescale, to establish a microscopic and mechanistic understanding of the key features of altered dynamics in freestanding films spanning the full range from ultrathin to thick films. Simulations and theory are in qualitative and near-quantitative agreement without use of any adjustable parameters. For films of intermediate thickness, the dynamical behavior is well predicted to leading order using a simple linear superposition of thick-film exponential barrier gradients, including a remarkable suppression and flattening of various dynamical gradients in thin films. However, in sufficiently thin films the superposition approximation breaks down due to the emergence of genuine finite size confinement effects. ECNLE theory extended to treat thin films captures the phenomenology found in simulation, without invocation of any critical-like phenomena, on the basis of interface-nucleated gradients of local caging constraints, combined with interfacial and finite size-induced alterations of the collective elastic component of the structural relaxation process.

Effect of the molecular weight on the depth profiling of PMMA thin films using low‐energy Cs+ sputtering

In this work, we investigate the influence of the molecular weight of poly(methyl methacrylate) (PMMA) thin films coated on silicon wafer on the time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) sputtering mechanisms and kinetics during depth profiling using low‐energy monoatomic caesium ions. The sputtering yield volumes are determined as function of molecular weight, film thickness and beam energy. The results show that the sputtering yield volume decreases with increasing molecular weight Mw down to a threshold value below which it becomes nearly constant, as previously observed with argon cluster ions. The relevance of physical parameters such as the glass transition temperature Tg—determined here from ellipsometry measurements—and the entanglement of the polymer chains to account for this behaviour is discussed. The variation of the sputtering yield was also found to vary logarithmically with the primary beam energy. In addition, preliminary experiments carried out using a low molecular weight PMMA (4 kg/mol) evidenced a nanoconfinement effect similar to that observed with argon cluster sputtering but of lower magnitude.

Nanoconfinement Effect for Signal Amplification in Electrochemical Analysis and Sensing.

Owing to the urgent need for electrochemical analysis and sensing of trace target molecules in various fields such as medical diagnosis, agriculture and food safety, and environmental monitoring, signal amplification is key to promoting analysis and sensing performance. The nanoconfinement effect, derived from nanoconfined spaces and interfaces with sizes approaching those of target molecules, has witnessed rapid development for ultra-sensitive analyzing and sensing. In this review, the two main types of nanoconfinement systems - confined nanochannels and planes - are assessed and recent progress is highlighted. The merits of each nanoconfinement system, the nanoconfinement effect mechanisms, and applications for electrochemical analysis and sensing are summarized and discussed. This review aims to help deepen the understanding of nanoconfinement devices and their effects in order to develop new analysis and sensing applications for researchers in various fields.

Cu-Zn oxides nanoparticles supported on SBA-15 zeolite as a novel adsorbent for simultaneous removal of H2S and Hg0 in natural gas

Inspired by the fact that H2S can easily decompose on some metal oxides to form sulfur species and the resulting products are usually used as Hg0 removal active sites, a novel Cu-Zn mixed oxide supported SBA-15 zeolite was controllably synthesized for simultaneous removal of Hg0 and H2S. The Cu-Zn nanoparticles with a particle size range of 4.4–5.0 nm were successfully confined and uniformly dispersed in the two-dimensional mesopores of SBA-15. The obtained 1Cu1Zn/SBA-15 adsorbent presented an outstanding H2S and Hg0 removal efficiencies at 30 °C and 30,000 h−1, and the H2S and Hg0 capture capacities reached to 296.78 mg·g−1 and 12.75 mg·g−1 at a 10% breakthrough. In addition, the spent adsorbent could be regenerated in a 5% O2 and 95% N2 atmosphere at 600 °C without obvious degradation of adsorption capacities over five cycles. We considered that the doping effects of Cu-Zn oxides were beneficial for its excellent H2S and Hg0 removal performance at low temperatures, and the nano-confinement effect of SBA-15 was conducive to prevent the oxides nanoparticles from agglomeration in the regeneration process, thus achieving the outstanding regeneration performance. Furthermore, the polysulfide polymer formed by chemisorption of H2S on the Cu-Zn oxides surface was confirmed to be the Hg0 active sites, which could react with gaseous mercury to form HgS. This work provided an effective way for simultaneous removal of H2S and Hg0 in natural gas by confining nano-sized active metal oxides into the mesopores of zeolites.

CdSe 1D/2D Mixed-Dimensional Heterostructures: Curvature-Complementary Self-Assembly for Enhanced Visible-Light Photocatalysis.

Mixed-dimensional heterostructures (MDHs), which combine nanomaterials of different dimensionalities deliver on the promise to bypass intrinsic limitations of a given low-dimensional material. Here, a strategy to engineer MDHs between two low-dimensional materials by curvature-complementary self-assembly is described. CdSe nanotubes rolled from 2D nanosheets and 1D CdSe nanorods, with negative and positive curvatures, respectively, are selected to illustrate complementary curvature self-assembly. The assembly process, optical, and photoelectrical properties of the CdSe MDHs are thoroughly investigated. Several remarkable features of CdSe MDHs, including increased light absorption, efficient charge separation, and appropriate bandgap structure are confirmed. The MDHs significantly alleviate the sluggish kinetics of electron transfer in the quantum sized CdSe subunits (onset potential of 0.21V vs RHE for MDHs; 0.4V lower than their low-dimensional building blocks), while the spatial nano-confinement effect in the CdSe MDHs also assists the interfacial reaction kinetics to render them ideal photocatalysts for benzylamine oxidation (conversion >99% in 4h with a two times higher rate than simple mixtures). The results highlight opportunities for building MDHs from low-dimensional building blocks with curvature-complementary features and expand the application spectrum of low dimensional materials in artificial photosynthesis.

Crystallization of C18 in mesoporous silica: Effect of surface functionalization and nanoconfinement

Fully releasing the thermal storage capacity of Phase change materials (PCMs) requires the integration of surface functionalization and nanoconfinement effect and therefore ingenious design of the pore size and surface property of supports. Herein, this work thoroughly explores the influence of synergistic coupling between nanoconfinement effect and interfacial hydrogen bonding strength from the carriers and the core materials on the crystallization behavior of C18 PCMs molecules. Rejoicingly, the fusion enthalpy of octadecanol/NH2-LP-SBA-15-CH3 composite can be as high as 186.08 J/g, which is much higher than those of other composite PCMs. The interfacial interaction plays a dominant role in the crystallization of C18 PCMs in large nanopores (e.g., 6.79 ~ 12.55 nm), hence the more suitable hydrogen bond strength between the supports and C18 may be advantageous to trigger the nucleation of more molecular chains. However, the decisive factor for the crystallization of C18 PCMs will be converted to nanoconfinement effect in small nanopores (e.g., 2.53 ~ 3.78 nm). Density functional theory (DFT) calculations are employed to propose atomic-level surface interactions. The obtained shape-stable composite PCMs exhibit excellent chemical compatibility, ultrahigh thermal stability, elevated thermal conductivity and outstanding cyclability, which are important prerequisites for the fascinating energy storage system.

A nanoconfined-LiBH4 system using a unique multifunctional porous scaffold of carbon wrapped ultrafine Fe3O4 skeleton for reversible hydrogen storage with high capacity

LiBH4 with a capacity of 18.5 wt% H2, is a promising high-capacity hydrogen storage material; however, it suffers from high operation temperature and poor reversibility. Herein, a novel structural LiBH4 system prepared via a nanoconfinement technique, coupling with in-situ introduced catalysts, is developed. By using a unique passionfruit-like porous hybrid composed of carbon wrapped ultrafine Fe3O4 skeleton (p-Fe3O4@C) as scaffold, synergetic effects of nanoconfinement, catalysis and surface destablization are achieved, which significantly improve the overall hydrogen storage properties of LiBH4. With an optimized LiBH4 loading of 60 wt%, the confined system initiates dehydrogenation at a low temperature of 175 °C and rapidly desorbs 7.8 wt% H2 at 350 °C within 30 min. Moreover, the dehydrogenated system shows a high reversibility under relatively moderate hydrogenation conditions. A dehydrogenation capacity of 6.2 wt% remains after 20 cycles. The system can be flexibly compacted, showing a volumetric hydrogen density as high as 79.4 g L−1, where there is almost no dehydrogenation property deterioration compared with its powder counterpart. The present work provides new insights in developing advanced complex hydride-based hydrogen storage systems through functional and structural designs.

Phase equilibrium modeling for interfacial tension of confined fluids in nanopores using an association equation of state

Two novel interfacial tension (IFT) models are presented, and four thermodynamic models—CPA-G, PCPA-G, CPA-P, and PCPA-P—based on the cubic-plus-association (CPA) equation of state and four IFT models are presented to predict the IFTs of fluids in bulk and nanopores. Among three association schemes of H2S that were studied, the 0d-1a association scheme is suitable for predicting mutual solubility of H2S-H2O system. The CPA-G and PCPA-G models can accurately describe the IFTs of H2S-H2O, CO2-H2O, CO2-n-C10H22, and CH4-n-C10H22 systems, whereas the CPA-P and PCPA-P models are inappropriate for IFTs of systems containing H2O. The IFTs of confined fluids in nanopores are lower than those in bulk. Under the same condition, IFTs of confined fluids decrease with an increase in pressure, but increase with the pore radius. Further, the effects of nanoconfinement for IFTs of confined fluids mainly occur at a pore radius below 100 nm.

Electrochemical Discrimination of Salbutamol from Its Excipients in VentolinTM at Nanoporous Gold Microdisc Arrays.

The emergence of specific drug–device combination products in the inhalable pharmaceutical industry demands more sophistication of device functionality in the form of an embedded sensing platform to increase patient safety and extend patent coverage. Controlling the nebuliser function at a miniaturised, integrated electrochemical sensing platform with rapid response time and supporting novel algorithms could deliver such a technology offering. Development of a nanoporous gold (NPG) electrochemical sensor capable of creating a unique fingerprint signal generated by inhalable pharmaceuticals provided the impetus for our study of the electrooxidation of salbutamol, which is the active bronchodilatory ingredient in VentolinTM formulations. It was demonstrated that, at NPG-modified microdisc electrode arrays, salbutamol is distinguishable from the chloride excipient present at 0.0154 M using linear sweep voltammetry and can be detected amperometrically. In contrast, bare gold microdisc electrode arrays cannot afford such discrimination, as the potential for salbutamol oxidation and chloride adsorption reactions overlap. The discriminative power of NPG originates from the nanoconfinement effect for chloride in the internal pores of NPG, which selectively enhances the electron transfer kinetics of this more sluggish reaction relative to that of the faster, diffusion-controlled salbutamol oxidation. Sensing was performed at a fully integrated three-electrode cell-on-chip using Pt as a quasi-reference electrode.

Stimulus-Responsive Graphene with Periodical Wrinkles on Grooved Microfiber Arrays: Simulation, Programmable Shape-Shifting, and Catalytic Applications.

This work demonstrates a facile fabrication of stimulus-responsive, periodically wrinkled graphene sheets on grooved microfiber arrays with fast and reversible shape change, multiresponsiveness, and programmable deformation, with the aid of finite element analysis (FEA). The cellulose acetate (CA) microfibers, endowing responsiveness to humidity and solvents, are designed to grooved shape and assembled into a well-aligned fibrous mat by electrospinning. Under the guidance of FEA simulation, the stiff reduced graphene oxide (RGO) sheets, serving as a photoresponsive component, could ably bind on grooved CA microfibers with favorable interlocked interfacial-structure. Through simple direct-writing and hot-pressing, the grooved CA arrays interlocked the conformal RGO sheets by water-induced self-clamping, and enabled the generation of periodic wrinkles within RGO sheets to maximize interfacial areas. By simply adjusting the orientation of written RGO patterns relative to uniaxial CA microfibers, programmed and omnidirectional shape-shifting were obtained to minimize strain energy, consisting with the dynamic deformation process simulated by FEA. Upon remote light or contactless humidity stimuli, the RGO/CA mat shows a rapid response (≤1 s), large amplitude (angle change ≥150°, 1.62 cm-1), sophisticated 3D motions, and lifts objects that weigh 12.7-times its own weight up to over 1/3 of own height within 1 s. After loading catalytical nanoparticles, the RGO/CA mat could rapidly move to the targeted position by continuous crawling even on a slippery surface, and served as a microchannel reactor to trigger a reaction in built-in microchannels with suppressing catalyst leaching while accelerating reaction kinetics by both nanoconfinement and photothermal effect.

Reversing the Irreversible: Thermodynamic Stabilization of LiAlH4 Nanoconfined Within a Nitrogen-Doped Carbon Host.

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH4 as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH4@NCMK-3 material releases H2 at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li3AlH6 intermediate observed in bulk. Moreover, >80% of LiAlH4 can be regenerated under 100 MPa H2, a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al-H bond dissociation energy and supports the observed change in the reaction pathway. The calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

Molecular insights into the interaction mechanism between C18 phase change materials and methyl-modified carbon nanotubes

Compared with pristine phase change materials (PCMs), nanopore-based composite PCMs generally have significant differences in thermophysical properties due to the nanoconfinement effect. However, experimental data are difficult to accurately reveal the microscopic molecular interaction mechanism between PCMs and nanoporous supporting materials. To overcome this difficulty, we systematically explored the molecular interactions between C18-PCM molecules with different functional groups (stearic acid, octadecanol, octadecylamine and octadecane) and methyl-modified carbon nanotubes (CNTs), and analyzed the spatial distribution and thermal characteristics of C18-PCM molecules in the pores of CNTs using molecular dynamics simulations. Molecular insights into the microscopic interaction mechanism between C18-PCM molecules and nanoporous CNTs were comprehensively proposed at the molecular scale. These constructive understandings provide meaningful theoretical references for the targeted construction of high-performance CNT-based composite PCMs for thermal storage applications.

Accelerating CO2 transport through nanoconfined magnetic ionic liquid in laminated BN membrane

The development of highly effective and durable CO2 separation membrane is still a challenge for the carbon capture and storage. Herein, a novel BN nanosheets supported magnetic ionic liquid membrane (BN-SMILM) is constructed by nanoconfining magnetic ionic liquid (MIL) [P6,6,6,14][FeCl4] to the two-dimentional (2D) nanochannels of laminated BN membrane. The 2D nanochannels provide a well support and restricted space for the MIL. The nanoconfinement effect makes the magnetic [FeCl4]- anions align along the center of 2D BN nanochannels, leading to selectively accelerate the CO2 transport. The nanoconfinement effect and CO2 separation mechanism are further explicated by the molecular dynamic simulations. As a result, compared with the polymer supported MIL membrane, the as-prepared BN-SMILM exhibits better CO2 separation performance, with CO2 permeability of about 227 Barrer and CO2/N2 selectivity of 90 that is above the 2008 Robeson upper-bound. The BN-SMILM also presents excellent long-term stability after 7 days operation, revealing the promising applications in CO2 separation. This work provides a new strategy to prepare high-performance supported liquid membrane materials towards practical environmental and energy application.

Fabrication of high-performance mixed-matrix membranes via constructing an in-situ crosslinked polymer matrix for gas separations

• A binaphthyl-ether tetramine was designed using to form an in-situ crosslinked polymer matrix. • Desirable interfacial morphology and uniform dispersion of TiO 2 were obtained in MMMs. • Overall gas separation properties of MMMs containing 5–23 wt% of TiO 2 were maintained. In this work, a b i n aphthyl-ether t etr a mine (BNTA) monomer was designed, synthesized, and reacted with 6FDA to form an in-situ crosslinked polyimide (6FDA-BNTA). Then, novel mixed-matrix membranes (MMMs) were prepared by incorporating the titanium dioxide (TiO 2 ) nanoparticles into the 6FDA-BNTA polymer matrix to fabricate TiO 2 /6FDA-BNTA MMMs for gas separations. The desirable interfacial morphology and uniform dispersion of TiO 2 were obtained due to the nano-confinement effect and stronger hydrogen bond interactions between TiO 2 and 6FDA-BNTA when compared with these of their linear analogues as polymer matrixes. The pristine 6FDA-BNTA membrane and MMMs containing 5–23 wt% of TiO 2 had good mechanical properties, which possessed tensile strengths in the range of 65.2–116.6 MPa and elongation at break of 4.8–7.8%. Gas transport results further revealed that the overall performances of TiO 2 /6FDA-BNTA MMMs were maintained with the increasing of the TiO 2 loading content. Specifically, 6FDA-BNTA MMMs with TiO 2 loading of 23 wt% exhibited the highest gas permeability (e.g. PCO 2 = 376.2 Barrer, PO 2 = 76.3 Barrer) and moderate selectivity (e.g. αCO 2 /N 2 = 24.3, αO 2 /N 2 = 4.9), locating near the Robeson 2008 upper bounds very closely for O 2 /N 2 , H 2 /N 2 , and CO 2 /CH 4 gas pairs. This facile approach, aiming at improving the incompatibility between two phases via constructing an in-situ crosslinked polymer matrix, provides a new insight for rational design of high-performance MMMs.

Nano-Confinement Effects on Structural Development and Organic Solvent-Induced Swelling of Ultrathin Carbon Molecular Sieve Films.

Successful implementation of carbon molecular sieve (CMS) membranes in large scale chemical processes inevitably relies on fabrication of high performance integrally skinned asymmetric or thin-film composite membranes. In principle, to maximize separation efficiency the selective CMS layer should be as thin as possible which requires its lateral confinement to a supporting structure. In this work, we studied pyrolysis-induced structural development as well as ethanol vapor-induced swelling of ultrathin CMS films made from a highly aromatic polyimide of an intrinsic microporosity (PIM–PI) precursor. Utilization of a light polarization-sensitive technique, spectroscopic ellipsometry, allowed for the identification of an internal orientation within the turbostratic amorphous CMS structure driven by the laterally constraining support. Our results indicated a significant thickness dependence both in the extent of pyrolytic collapse and response to organic vapor penetrant. Thinner, substrate-confined films (∼30 nm) collapsed more extensively leading to a reduction of microporosity in comparison to their thicker (∼300 nm) as well as self-supported (∼70 μm) counterparts. The reduced microporosity in the thinner films induced changes in the balance between penetrant-induced dilation (swelling) and filling of micropores. In comparison to thicker films, the initial lower microporosity of the thinner films was accompanied by slightly enhanced organic vapor-induced swelling. The presented results are anticipated to generate the fundamental knowledge necessary to design optimized ultrathin CMS membranes. In particular, our results reinforce previous findings that excessive reduction of the selective layer thickness in amorphous microporous materials (such as PIMs or CMS) beyond several hundred nanometers may not be optimal for maximizing their fluid transport performance.

Confinement effects on the solvation structure of solvated alkali [correction] metal cations in a single-digit 1T-MoS2 nanochannel: A first-principles study.

Confinement plays an important role in determining ion transport in porous materials, which, in turn, may influence the performance of many energy storage and desalination devices. In this work, we combined density functional theory (DFT) with an implicit solvation model and ab initio molecular dynamics (AIMD) to investigate the effects of nanoconfinement on several solvated alkaline metal cations in a single-digit 1T-MoS2 nanochannel. Our DFT calculations with a solvation model indicated that cations with stronger hydration energy introduce a higher number of co-intercalated water molecules into the channel, consistent with early experimental observation obtained for MXene (2D transition metal carbide) channels. The predicted optimal water numbers for the cations were then used for AIMD simulations that explicitly include the effects of the solvent. When compared with the cations in bulk solution, our simulations showed that the hydration structure and coordination number (CN) of the solvated cations confined in the MoS2 channel can be significantly altered. We found that larger cations with weaker hydration energy (K+, Rb+, and Cs+) exhibited a distinctive CN decrease under confinement, while smaller cations (Li+ and Na+) retained a similar hydration shell as in the bulk solution. More specifically, the hydration shell of large cations (K+, Rb+, and Cs+) in MoS2 showed similar features of the coordination angle to the bulk, which suggests the partially broken hydration shell with no geometry change under confinement. Our simulations provided insights into the change of the hydration structure of alkaline metal cations under confinement, which may have important implications on their transport in the 1T-MoS2 channel.

Nanoconfined gelation in systems based on stearic and 12-hydroxystearic acids: A calorimetric study

This study applies differential scanning calorimetry (DSC) to probe the effect of nanoconfinement on gelation of mineral oil (MO), soybean oil (SO), ethylene glycol (EG), polyethylene glycol (PEG), and polypropylene glycol (PPG) by low molecular weight gelators, stearic and 12-hydroxystearic acids. Nanoconfinement is accomplished by embedding the gels into silica nanopores. In agreement with our previous work on high molecular weight polymeric gelators, nanoconfinement invariably causes a decrease in the heat of gelation. The effect is linked to restricted molecular mobility, which hampers integration of the gelator molecules into the network as well as spatially limits its growth. A new effect discovered in this work is a decrease in the gelation temperature of the nanoconfined MO and SO systems. By combining an advanced isoconversional method with the Turnbull-Fisher nucleation model it has been possible to link this effect to deceleration of gelation that originates from an increase in the nucleation energy barrier. It has been proposed that whether nanoconfinement causes a decrease or an increase in the gelation temperature can depend on polarity of liquid. The proposal is upheld by measurements on the systems involving polar liquids (EG, PEG, PPG) that have demonstrated an increase in the gelation temperature under nanoconfinement.