Trapped Water Molecules Research Articles

Low-energy ball milling effect on the dielectric response and electrical transport mechanisms of natural clinoptilolite zeolites in a wide temperature range

Zeolites are spectacular natural minerals that can replace other expensive or hazardous materials in wide-range applications by virtue of their unique physico-chemical properties. In this study, a comprehensive investigation of the possible effects of low-energy mechanical ball milling on the dielectric response and electrical conduction mechanisms of natural clinoptilolite zeolites was carried out in 300–800 K temperature range through current-voltage (I-V) and capacitance-conductance (C-G) experimental measurements. Two samples were prepared; one with 1-hour hand grinding and another with 8-hours ball milling. Both samples exhibited a typical semiconductor behavior beyond 400 K and the conductivity obeyed Jonscher power law where transport mechanisms were governed by non-overlapping small polaron tunneling and correlated barrier hopping models at separate temperature ranges. It was mainly deduced that the presence of trapped water molecules within naturally grown zeolites contributes to the increase of both dielectric constant and conductivity. In addition, milling effect on the structural, morphological, mechanical and thermal properties was investigated respectively through X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size analysis (PSA) as well as a combination of thermogravimetric analysis (TGA) and differential thermal analysis (DTA). XRD confirmed the clinoptilolite phase and monoclinic crystal structure of the prepared samples and suggested a decrease in crystallite size with milling. SEM images manifested a corn flake-like structure of clinoptilolite grains and suggested a decrease in porosity, roughness and particle size under stirring effect. The decrease in overall particle size as a result of the milling process was also confirmed by PSA. Through TGA and DTA, the overall mass and water losses were estimated as a function of temperature, and this along with the morphological observation were correlated with the observed electrical and dielectric properties of the prepared samples. All in all, it was deduced that such naturally grown electroceramics have the potential to be used as natural dielectric capacitors as well as semi-insulator (SI) substrates in integrated circuits of electronic devices.

Metal-insulator phase transition in the δ−(BEDT−TTF)4 [2,6-anthracene- bis(sulfonate)] ·4H2O studied by infrared spectroscopy

Temperature dependence of polarized infrared (IR) reflectance spectra of two-dimensional weakly dimerized organic conductor $\ensuremath{\delta}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{4}$[2,6-anthracene-bis(sulfonate)]$\ifmmode\cdot\else\textperiodcentered\fi{}4{\mathrm{H}}_{2}\mathrm{O}$ with $\frac{1}{4}$-filled band has been measured to investigate the metal-insulator phase transition at ${T}_{\mathrm{MI}}=85\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ linked to charge ordering (CO). Vibrational bands related to $\mathrm{C}=\mathrm{C}$ stretching vibrations of the BEDT-TTF donor molecule give evidence of the CO and charge fluctuations both in the metallic and insulating phases above and below 85 K, respectively. Considerable modifications of the vibrational features due to electron-molecular vibration coupling are also observed. The phase transition is associated with the reorganization of hydrogen $\mathrm{OH}\ensuremath{\cdots}\mathrm{O}$ bonds in anion layers between the sulfonate moieties of the anion and the trapped water molecules, which is transmitted to conducting BEDT-TTF layers through weaker C-$\mathrm{H}\ensuremath{\cdots}\mathrm{O}$ bonds. The analysis of electronic bands confirms the presence of strong electronic correlations in the material. Two electronic absorptions are observed in the mid-IR region, attributed to transitions between Hubbard bands and transitions inside BEDT-TTF dimers. A low-energy electronic absorption in the far-IR region is attributed to collective excitations of the short-range charge order. Below 85 K, the opening of a charge gap of \ensuremath{\sim}24 meV is observed both parallel and perpendicular to the BEDT-TTF stacking direction. The spectroscopic data indicate that the CO phase transition is a consequence of both Coulomb interactions between charge carriers and donor-acceptor interactions.

An improved water-harvesting cycle.

Tuning metal-organic frameworks at the atomic level helps release trapped water molecules.

Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Isolation and Identification of Pseudo Seven-Coordinate Ru(III) Intermediate Completing the Catalytic Cycle of Ru-bda Type of Water Oxidation Catalysts

Hydrogel-assisted paper-based lateral flow sensor for the detection of trypsin in human serum

The detection of trypsin and its inhibitor is significantly important for both clinical diagnosis and disease treatment. Herein, we demonstrate a hydrogel-assisted paper-based lateral flow sensor for the detection of trypsin and its inhibitor for the first time. The gelatin hydrogel is hydrolyzed based on the gel-to-sol transition in the presence of trypsin, which results in the release of the trapped water molecules in the gelatin hydrogel. By placing one end of a pH indicator strip onto the hydrolyzed gelatin hydrogel, water is flowing along the pH indicator strip. However, in the absence of trypsin, water cannot flow along the pH indicator strip as the water molecules are trapped in the gelatin hydrogel. The detection limit of the system reaches as low as 1.0 × 10−6 mg/mL, and it is also applied to the quantitative detection of trypsin in human serum. In addition, the detection of a clinical drug aprotinin that is an inhibitor of trypsin is also successfully achieved. Noteworthy, only the gelatin hydrogel, pH indicator strip, and PS substrate are needed to fulfill the detection of trypsin without the need of other chemicals or reagents. Overall, we develop a particularly simple, elegant, robust, competitive, high-throughput, and low-cost approach for the rapid and label-free detection of trypsin and its inhibitor, which is very promising in the development of commercial products for sensing, diagnostic, and pharmaceutical applications. Besides, the hydrogel-assisted paper-based lateral flow sensor can also be employed to detect other analytes of interest by use of different stimuli-responsive hydrogel systems.

Intrinsic Contributions of 2'-Hydroxyl to the Hydration of Nucleosides at the Monomeric Level.

Although many reports have revealed structural differences between DNA and RNA at the polymeric level, there are no comparative studies with 2'-deoxyribonucleoside and ribonucleoside to explore the role of the 2'-OH group at the monomeric level under the same conditions. Inspired by this, herein, the intrinsic contributions of the 2'-OH group in the nucleoside have been systematically investigated by directly solving the single-crystal structures of 2'-deoxy-2-aminoadenosine (1), 2-aminoadenosine (2), and 2-aminoarabinofuranosyladenine (3) in water. The 2'-OH group not only influenced the conformation and base-pair pattern of the single-nucleoside molecule, but also played a fundamental role in the entire supramolecular structure. Interestingly, compound 1, which did not contain the 2'-OH group, displayed strong hydration, whereas 2 and 3 (with the 2'-OH group in the opposite direction) exhibited no hydration, which was completely different from that observed in nucleic acids. Meanwhile, compound 1 trapped water molecules to form unique trihydrol moieties, which further served as the backbone to construct the simplest double-chain DNA-like structures. To this end, to investigate the effect of the biological environment on these unique structures, the solvent was changed from water to phosphate-buffered saline (PBS). Surprisingly, such a subtle adjustment led to entirely different superstructures, consisting of 2D lamellar structures in water and 3D porous structures in PBS. These large morphological differences could be attributed to delicate ion hydration, which was also confirmed through variable-temperature X-ray analysis, SEM, and intermolecular interaction energy calculations. In summary, this study comprehensively investigated the intrinsic contributions of 2'-hydroxyl to the hydration of nucleosides at the monomeric level; this is helpful to further understand the differences in DNA/RNA and the impact of their surrounding environment.

Molecular Dynamics Study of Water Diffusivity in Graphene Nanochannels

Transport properties of nano-confined fluids such as diffusivity can exhibit utterly distinctive characteristics compared to the transport properties in the bulk due to the interactions between atoms in the solid walls and fluid atoms as well as the confinements. In this paper, the diffusivity of water confined in the graphene nanochannels is calculated by molecular dynamics simulations through the Einstein equation, and the results show that the diffusivity of nano-confined water is obviously anisotropic, i.e., the perpendicular (vertical to the graphene walls) diffusivity is obviously lower than the diffusivity in the parallel plane. By studying the Lagrangian dynamics of molecules in the confined region, we realize that the anisotropy can be attributed to the trapping of water molecules in the potential wells near the graphene walls, resulting in the inhibition of the molecular mobility in the perpendicular direction. Meanwhile, the proportion of confined water molecules decreases with increasing channel height and the contributions of the trapped water molecules on the inhibited mobility in the perpendicular direction are weakened. As a result, the diffusivity in all directions approaches the bulk values at high channel heights. The obtained results are helpful in revealing the mechanisms of water diffusion in nanospaces from the molecular level.

Thermal conductivity of confined-water in graphene nanochannels

Transport properties of nano-confined fluids present distinctive characteristics comparing to the bulk fluids owing to the confinements and the additional fluid-solid interactions. Here, the thermal conductivity of water confined in the graphene nanochannels is calculated by equilibrium molecular dynamics simulations with the Green-Kubo formula. The results show that the thermal conductivity of nano-confined water is obvious anisotropic, i.e. the perpendicular thermal conductivity is obviously lower than the longitudinal thermal conductivity. This anisotropic thermal conductivity is caused by the inhibited molecular collisions in the perpendicular direction but the enhanced collisions in the longitudinal direction because of the trap of water molecules in the potential wells near the graphene walls. With increasing the channel height, the contributions of the trapped water molecules on the inhibited thermal conductivity in the perpendicular direction and the enhanced thermal conductivity in the longitudinal direction are both weakened, such that the thermal conductivity in the three directions all approach to their bulk values. In summary, the anisotropy and size-dependence of the thermal conductivity of confined water in graphene nanochannels are identified and the underlying mechanisms are revealed from the insights of thermodynamic physics.

Swelling Curve in Terms of Effective Stress for Expansive Clays

Expansive soils can present an unsaturated state where the soil exhibits volume changes due to both moisture variations that change the state of stresses and moisture variations that interact with its mineralogical characteristics. These special kinds of soils are normally clay type soils that had suffered isomorphous substitution creating a charge imbalance of the clay mineral crystals. This imbalance promotes the trapping of water molecules by the clay particles. It is commonly assumed that a high plasticity index can be an indication of a clay´s high swell potential. However, in arid regions, it is possible to have clays with very high swell potential and low plasticity indexes due primarily to a decrease in the state of effective stress, which will produce expansion of the material. It is common practice to study the swelling characteristics of these soils by performing free-swell tests that can be used for designing removal and replacement backfills or drilled shafts. However, the expansion percentage obtained from this type of test is actually in terms of total stresses and not in terms of effective stress, as it is commonly assumed. Moreover, it is highly dependent on the magnitude of the preload used. This paper presents some efforts made to obtain the swelling part of the curve in terms of effective stresses from the traditional free-swell test. It was hypothesized that the shape of this curve could either have the shape of the rebound curve from a saturated consolidation test or a shape similar to the soil-water characteristic curve.

Imaging and Dynamics of Water Hexamer Confined in Nanopores

Epitaxial two-dimensional (2D) nanostructures with regular patterns show great promise as templates for adsorbate confinement. Prospectively, employing 2D semiconductors with reduced density of states leads to a long excited-state lifetime that allows us to directly image the dynamics of the adsorbate. We show that epitaxial blue phosphorene (blueP) on Au(111) provides such a platform to trap water molecules in the periodic nanopores without formation of strong bonds. The trapped water aggregate is tentatively assigned to a hexamer based on our scanning tunneling microscopy studies and first-principles calculations. Real-space observation of conformational switching of the hexamer induced by inelastic electrons is achieved by using low-temperature scanning tunneling microscopy with molecular resolution. We found a localized interfacial charge rearrangement between the water hexamer and P atoms underneath that is responsible for the reversible desorption and adsorption of water molecules by changing the sample bias polarity from positive to negative, offering a promising strategy for engineering the electronic properties of blueP.

Structure of Dense Adsorption Layers of Escin at the Air-Water Interface Studied by Molecular Dynamics Simulations.

Saponins are natural surfactants with high surface activity and unique surface properties. Escin is a triterpenoid saponin which has unusually high surface viscoelasticity [Golemanov et al. Soft Matter 2013, 9, 5738] and low permittivity to molecular gas diffusion of its adsorption layers. In our previous study [Tsibranska et al. Langmuir 2017, 33, 8330], we investigated the molecular origin of this unconventional behavior and found that escin molecules rapidly assemble in a compact and stable surface cluster. This behavior was explained with long-range attraction between the hydrophobic aglycones combined with intermediate dipole-dipole attraction and strong short-range hydrogen bonds between the sugar residues in the adsorbed escin molecules. In this study, we performed atomistic molecular simulations of escin molecules in dense adsorption layers with two different areas per molecule. The results show that the surfactant molecules in these systems are much less submerged in water and adopt a more upright position compared to the dilute layers studied previously. A significant number of trapped water molecules are located around the hydrophilic groups placed above the water equimolecular surface to solvate them in the dense layer. To maintain the preferred orientation of the escin molecules with respect to the interface, the most compact adsorption layer acquires a significant spontaneous curvature. The substantial elasticity of the neutral escin layers, as in our previous study, is explained with the presence of a specific interaction, which is intermediate between hydrogen bonding and dipole-dipole attraction (populated lengths in the range 0.16 to >0.35 nm), supplemented by substantial flexibility of the surfactant heads, optimal curvature of the interface, and significant normal displacement of the molecules to allow their tight surface packing. The simulations reveal long-range order within the layers, which signifies the role of the collective behavior of the saponin molecules in such dense adsorption layers.

Atomistic Molecular Dynamics Simulations of the Lower Critical Solution Temperature Transition of Poly( N-vinylcaprolactam) in Aqueous Solutions.

Poly( N-vinylcaprolactam) (PVCL) is a thermo-responsive polymer, which exhibits a lower critical solution temperature (LCST) in an aqueous solution. The LCST of this hydrophilic-to-hydrophobic transition is found to be strongly dependent on the salt-type and salt-concentration as well as on the molecular weight and concentration of the polymer. Here, atomistic molecular dynamics simulations have been successfully conducted for the first time to investigate the LCST transition of a 100 degree of polymerization PVCL chain in water, 1 M NaCl, 3.5 M NaCl, and 0.5 M CaCl2 solutions. Our results show that steric hindrance resulting from the bulky 7-member ring on the PVCL chain plays a critical role in the conformational transition. Moreover, the degrees of hydration and dehydration below or above the transition temperature are highly dependent on the specific solution condition and temperature. Water molecules are found to be trapped inside the collapsed polymer chains leading to the varying degrees of hydration and dehydration of the polymer chain in different solutions. Calculated water diffusion coefficients for both trapped and free water molecules agree very well with experimental measurements.

Reduction of water-molecule-induced current-voltage hysteresis in graphene field effect transistor with semi-dry transfer using flexible supporter

The polymethyl methacrylate-assisted wet transfer method of chemical vapor deposition (CVD) graphene has been widely used, thanks to its good coverage and simplicity. However, in the wet-transfer method, water molecules are inevitably trapped between the graphene and the substrate because the graphene is transferred to the substrate while floating in water. The trapped water molecules can cause the unwanted doping of graphene and hysteretic behavior in the current-voltage (I-V) curve. We here propose a new semidry transfer method using the Kapton tape as an additional flexible supporting layer. The N2 blowing and heating processes are added to vaporize the water molecules adsorbed on graphene layer right before the transfer step. By comparing the I-V characteristics of wet- and semidry-transferred graphene field effect transistor (GFET), the field effect mobility is found to be larger for the semidry-transferred GFET in comparison with the wet-transferred one, possibly due to the more uniform Coulomb potential landscape. Most importantly, the hysteretic behavior is found to be reduced in accordance with the decrease of the trapped water molecules. The averaged electron mobilities obtained from the GFET measurements are 1118cm2/Vs and 415cm2/Vs for semidry- and wet-transferred graphene, respectively. Our semidry transfer method can provide a simple and reliable way to transfer the CVD graphene onto an arbitrary substrate with the minimized number of trapped water molecules, which is readily applicable for large-scale substrates with potential of commercialization.

Partially dehydrated zinc hydroxide sulfate nanoplates reinforced coating for corrosion protection

In this work, partially dehydrated zinc hydroxide sulfate nanoplates are synthesized by facile chemical bath deposition together with subsequent heat dehydration. The nanoplates exhibit well-defined hexagonal plate structure with smooth surface and no visible defects can be observed. Then, the corrosion protection performance of the nanoplates-embedded fluorocarbon coatings was investigated in 3.5 wt% NaCl aqueous solution. It turns out that the well dispersed nanoplates greatly enhance the protection ability of composite coatings. Once electrolyte permeates into the coating matrix and reaches the surfaces of nanoplates, the nanoplates can actively trap water molecules and ions (Cl− and Na+) therein through phase transition behavior, thus inhibiting the diffusion of electrolyte to the interface between coating and substrate. Meanwhile, the concomitant swelling of nanoplates blocks the diffusion of corrosive media, thus further enhancing the protection performance. The multi-functions of this material impart superior passive barrier and active barrier abilities to polymer coating.

Supercooling Behavior and Dipole-Glass-like Relaxation in a Three-Dimensional Water Framework.

The dynamic behaviors of a new type of three-dimensional (3D) water framework symbiotic with 1D stacking organic guests, including an order-disorder transition of hydrogen atoms, a supercooling phenomenon during phase transition, and a dipole-glass-like relaxation behavior due to locally trapped water molecules, are presented. This extremely scarce 3D water framework, together with the rich dynamic behaviors it exhibits, provides new clues to design new ice-like models for promoting the fundamental understanding of the dynamic behavior of water in diverse solid-states.

Facile construction of terpridine-based metallo-polymers in hydrogels, crystals and solutions directed by metal ions

Driven by tunable metal-ligand interactions, a polydentate ligand TC containing terpyridine and carboxylic acid units was developed to construct metallo-polymers that showed multiple aggregation modes with controlled macroscopic properties. In the presence of different kind of Zn2+ ions or NaOH, TC could form metallo-polymers via π-π stacking and metal-ligand interaction that further trapped water molecules, resulting in hydrogels and crystals. Moreover, these TC/Zn2+ hydrogels could transform to soluble and fluorescent aggregates in the presence of NaOH due to the formation of binuclear metallo-polymers with enhanced ICT emission. The metal-ligand interactions tuned by different metal salts in gels, crystals, and sols were also studied and illustrated in detail, it was also proved that water was an essential linker for constructing Na+-based metallo-polymers from the TC/NaOH crystal data. This work demonstrated the engineered coordination pathways in generating controllable hydrogels and metallo-polymers for the first time, which led to novel approach for facilely constructing a number of hydrogels with tailorable macroscopic properties.

Exploring interfacial water trapping in protein-ligand complexes with multithermal titration calorimetry

In this work, we examine the hypothesis about how trapped water molecules at the interface between triosephosphate isomerase (TIM) and either of two phosphorylated inhibitors, 2-phosphoglycolate (2PG) or phosphoglycolohydroxamate (PGH), can explain the anomalous highly negative binding heat capacities (ΔCp,b) of both complexes, TIM–2PG and TIM–PGH. We performed fluorimetric titrations of the enzyme with PGH inhibitor under osmotic stress conditions, using various concentrations of either osmolyte: sucrose, ethylene glycol or glycine betaine. We also analyze the binding processes under various stressor concentrations using a novel calorimetric methodology that allows ΔCp,b determinations in single experiments: Multithermal Titration Calorimetry. The binding constant of the TIM–PGH complex decreased gradually with the concentration of all osmolytes, but at diverse extents depending on the osmolyte nature. According to the osmotic stress theory, this decrease indicates that the number of water molecules associated with the enzyme increases with inhibitor binding, i.e. some solvent molecules became trapped. Additionally, the binding heat capacities became less negative at higher osmolyte concentrations, their final values depending on the osmolyte. These effects were also observed in the TIM–2PG complex using sucrose as stressor. Our results strongly suggest that some water molecules became immobilized when the TIM-inhibitor complexes were formed. A computational analysis of the hydration state of the binding site of TIM in both its free state and its complexed form with 2PG or PGH, based on molecular dynamics (MD) simulations in explicit solvent, showed that the binding site effectively immobilized additional water molecules after binding these inhibitors.

Surface microstructure engenders unusual hydrophobicity in phyllosilicates.

We present a mechanism of intriguing polar hydrophobicity of a series of naturally formed minerals: their surface cavities can effectively trap water molecules, and the water trapping remarkably disrupts the hydrogen bond interaction among interfacial water and leads to considerable hydrophobicity. Diminishing water trapping by decreasing surface roughness can considerably enhance wettability, which illustrates that a Wenzel model is no longer valid for polar materials with atomic-scale roughness.

Temperature effects on spreading of water nano‐droplet on poly(methyl methacrylate): A molecular dynamics simulation study

ABSTRACTIn this article, the effect of temperature on the spreading behavior of a water nano‐droplet on poly(methyl methacrylate) substrate is investigated. The contact angle analysis illustrates that the spreading process occurs in a stage‐like manner and the increase in temperature causes a regime change from partial to total wetting. The interaction energy distributions show that there exist sites on the surface which could trap water molecules and provide a better path for other molecules to overcome the asperities. Estimations of the coefficients of self‐diffusivity suggest that temperature has a major effect in the reorientation stage, which results in the formation of the interfacial layer. In the second stage of spreading, temperature affects the process by providing sufficient energy for water molecules to overcome the interactions with the substrate. Therefore, this stage is controlled by the movement of water molecules on the surface and is highly influenced by their interaction with the surface asperities, strong interaction sites, and the carbonyl groups. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1532–1541

Structures and thermodynamics of water encapsulated by graphene

Understanding phase behaviors of nanoconfined water has driven notable research interests recently. In this work, we examine water encapsulated under a graphene cover that offers an ideal testbed to explore its molecular structures and thermodynamics. We find layered water structures for up to ~1000 trapped water molecules, which is stabilized by the spatial confinement and pressure induced by interfacial adhesion. For monolayer encapsulations, we identify representative two-dimensional crystalline lattices as well as defects therein. Free energy analysis shows that the structural orders with low entropy are compensated by high formation energies due to the pressurized confinement. There exists an order-to-disorder transition for this condensed phase at ~480–490 K, with a sharp reduction in the number of hydrogen bonds and increase in the entropy. Fast diffusion of the encapsulated water demonstrates anomalous temperature dependence, indicating the solid-to-fluid nature of this structural transition. These findings offer fundamental understandings of the encapsulated water that can be used as a pressurized cell with trapped molecular species, and provide guidance for practical applications with its presence, for example, in the design of nanodevices and nanoconfined reactive cells.