Water molecules on the liquid superlubricity interfaces achieved by phosphoric acid solution

: We present the first experimental measurements of the orientation and hydrogen bonding character of interfacial water molecules in their gaseous state in coexistence with the bulk liquid water. These interfacial vapor state molecules are distinct from the surface free OH and the interfacial liquid state water molecules and show a preferred orientation with their hydrogen atoms directed towards the liquid surface. The goal to develop a molecular level picture of water orientation and bonding at this vapor-liquid boundary where liquid phase water molecules coexist with vapor phase molecules has fascinated scientists for decades. Whereas most theoretical and experimental studies in recent years are converging on a consistent description of interfacial water on the liquid side of the interface, there is considerable disparity in the theoretical description of water molecules on the vapor side. A primary factor in this lack of consensus is the paucity of available data that unequivocally measures the properties of these interfacial vapor state molecules. As with theoretical efforts in this area, the low density of these vapor state interfacial water molecules is experimentally problematic. In this paper we present the first vibrational spectroscopic measurements of interfacial water vapor species in coexistence with their liquid phase. These detected vapor state molecules have a preferred orientation relative to the surface plane and have minimal hydrogen bonding to adjacent water molecules as manifested in the energy and linewidth of the spectral OH stretching modes examined. These molecules are distinctly different than the water molecules with a dangling bond into the vapor phase, or water in the liquid portion of the interface where hydrogen bonding between water molecules is strong.

Interactions of the polyelectrolyte partially hydrolyzed polyacrylamide (HPAM) with water and cations at air/liquid interfaces were studied using phase-sensitive sum frequency generation (SFG) vibrational spectroscopy. In contrast to the conventional SFG vibrational spectroscopy which measures only the amplitude of the second-order susceptibility |χ(2)|, the heterodyne-detected SFG measures the complex χ(2) which contains information about the absolute orientation of surface molecules. While the OH groups of water near a neat air/water interface mostly pointed down to the bulk (downward), the presence of the polyelectrolyte caused flipping of water molecules with the hydrogen being oriented upward. With 10–7 M HPAM, water showed a highly ordered structure with a single peak near 3100 cm–1, but higher concentrations resulted in a less ordered water structure with multiple peaks. The addition of the monovalent cation Na+ to the polyelectrolyte solution did not affect the conformation of the polyelectrolyte, though the water molecules flipped back to a structure similar to that of a neat air/water interface with the hydrogen pointing down. On the other hand, the addition of divalent cation Ca2+ not only changed the conformation of the polyelectrolyte but also completely destroyed the ordered structure of interfacial water molecules. The observed phenomena support the polymer–ion complex model in which a divalent cation can interact with two intrachain or interchain charges and form a jointing point. The amorphous nature of the polymer–ion complex explained the disappearance of the ordered water structure in the presence of divalent cations.

Chemical activation of pine sawdust using aqueous solutions of phosphoric and boric acid was studied. Thermogravimetric analyses of the impregnated lignocellulosic precursor as well as their reactivities are presented. The role of the activating agents in the thermal decomposition of the precursor and their effects on the development of porosity in activated carbons is discussed. The use of boric acid as activating agent and a final heat treatment temperature (HTT) of 600 °C produced some porosity and activated carbons with a surface area of 600 m2 g−1. With a HTT of 450 °C, molecular sieve‐like materials were produced. In contrast, phosphoric acid activation produced activated carbons with high surface areas. The amount of phosphoric acid retained in the precursor was, as expected, a function of the initial concentration as well as the impregnation time and temperature. The fact that the activated carbon porosity increases with the phosphoric acid content per gram of precursor was confirmed. The use of 6 M phosphoric acid solution and HTT of 450 °C produced the activated carbon with the highest surface area, about 1600 m2 g−1. The high degree of microporosity which developed in phosphoric acid‐activated carbons is related to the low reactivity during the thermal treatment of chemical activation. The presence of up to 10% oxygen during HTT with phosphoric acid activation caused only small textural changes. Copyright © 2003 Society of Chemical Industry

Using the pH sensitivity of switchable surfactants to understand the role of the alkyl tail conformation and hydrogen bonding at a molecular level in elucidating emulsion stability

We report the structure and dynamics of layered water structure near a bilayer heterosurface using classical molecular dynamics simulations and network graph theory. The heterosurfaces of our choice are technologically essential and well-studied hexagonal boron nitride (h-BN) and graphitic carbon nitride (g-C3N4). Starting with the water density distribution profile, we have studied different hydrogen bondings (HBs) associated with distance and angle distributions and correlated them with the HB count, followed by the investigations of dynamic properties. We realize the oddity while corresponding to the tetrahedral order parameter (TOP), HB donor/acceptor count, and HB lifetime. A quantitative gap is observed between the TOP and HB counts, and we perceive another structural factor playing a significant role. We observe a 2D sheetlike arrangement of hydrogen-bonded water molecules, namely, 2D-HB, in the interfacial layer instead of 3D tetrahedral arrangements. 2D-HB qualitatively acts as a key descriptor of the hydrophobicity of the interface. The probability of higher TOP among the interfacial layer water molecules is less for h-BN compared to g-C3N4. However, the per-water HBs for both the heterosurfaces remain indistinguishable, implying the existence of another significant physical factor related to HB. Hence, 2D-HB serves as a deciding factor. In the case of h-BN, water molecules in the first layer form extended 2D sheets compared to the second and bulk, which is not a scenario for g-C3N4. Following the network graph theory, we calculated the temporal evolution of the maximum number of water molecules connected in a single network. The layer 1 water molecules have slower orientational dynamics, higher HB lifetime, and consequently slower translational diffusion than layer 2 and bulk water molecules. The experimental studies suggested that the contact angle of water on h-BN can vary from 61.4 to 85.8°, higher than that of g-C3N4, depending on the surface stacking, support material, and exposure to air, which effectively makes h-BN more hydrophobic compared to g-C3N4. The interfacial water molecules have a smaller HB lifetime and a faster diffusion coefficient than g-C3N4. The HB lifetime of water molecules in bulk is less than that in the interface, irrespective of the surface. A slower reorientation lifetime, that is, 2.69 ps, for g-C3N4 interfacial water molecules is observed versus 2.20 ps for h-BN. Our results agree with the experimental observations and can help to understand the hydrophobicity of other relevant materials.

Phosphoric acid is the core material for the fertilizer industry; however, it is incredibly corrosive to manufacturing plants’ structures, mainly steel. Corrosion is one of the most severe problems encountered during phosphate fertilizer manufacturing. Recently, plant extracts have been commonly used as corrosion inhibitors because they are cheap and environmentally friendly. Steel corrosion in a 20% aqueous phosphoric acid solution in the absence and presence of fenugreek seed (Fen) or cape gooseberry leaf (CgL) extracts was investigated using the electrochemical impedance spectroscopy technique, potentiodynamic polarization measurement, scanning electron microscope, and quantum chemical calculations. Fourier Transform Infrared, FTIR, was used to identify the functional groups in Fen and CgL extracts. The inhibition efficiency for steel in 20% aqueous phosphoric acid was roughly equal to 80% for 0.4 g/L CgL and 1.2 g/L Fen extracts. A scanning electron microscope showed that the chemical constituents of extracts block the surface roughness of steel, decreasing the corrosion rate. The activation parameters indicated the effectiveness of the extracts at a higher temperature. Measurements of the potential of zero charges showed that the steel surface is positively charged in the phosphoric acid solution. Quantum chemical computations were also employed to examine the corrosion inhibition mechanisms of the natural extracts.

Objective: To establish a method for the determination of 2, 3-Butanedione (BUT) in the air of workplace, which including the process of collection by absorption in phosphoric acid aqueous solution and the process of analysis and detection by high performance liquid chromatography with derivatization. Methods: In October 2022, a porous glass plate absorption tube containing 10 ml of 0.01% phosphoric acid solution was used to collect BUT in the air of the workplace at a flow rate of 0.2 L/min. The absorption solution was derived by 2, 4-dinitrophenylhydrazine for 75 min and separated on a SB-C18 column (250 mm×4.6 mm, 5 μm) . At the column temperature of 30 ℃, the mixture of acetonitrile-water (V∶V, 1∶1) was eluted at the flow rate of 1.0 ml/min. It was detected by UV detector (λ=365 nm) , qualitatived by retention time and quantitatived by external standard. Results: It showed that BUT in phosphoric acid aqueous solution could be stored for at least 7 d at 4 ℃. There was a linear relationship within the determination range of 0.05-6.00 μg/ml, the linear regression equation was y=89.610x+0.133, r=0.9999. The sampling absorption efficiencies were 98.33%-100.00%, the detection limit of the method was 0.005 μg/ml, the minimum detection concentration was 0.016 mg/m(3) (based on V(0)=3.0 L) . The recovery rates were 95.96%-102.44%, the intra batch precision were 4.36%-7.78%, and the inter batch precision were 4.96%-6.06%. Conclusion: The method has the advantages of simple operation, high sensitivity and good accuracy. It can prevent the loss and degradation of BUT. It can be used for the determination of BUT in the air of workplace.

24 GUIDANCE FOR ETHICAL DEVELOPMENT OF DIGITAL PHENOTYPING TOOLS FOR MENTAL HEALTH APPLICATIONS

Reactive molecular dynamics (ReaxFF) simulations are used to explore the atomic-level tribochemical mechanism of amorphous silica (a-SiO2) in a nanoscale, single-asperity contact in an aqueous environment. These sliding simulations are performed in both a phosphoric acid solution and in pure water under different normal pressures. The results show that tribochemical processes have profound consequences on tribological performance. Water molecules could help avoid direct adhesive interaction between a-SiO2 surfaces in pure water under low normal load. However, formation and rupture of interfacial siloxane bonds are obviously observed under higher normal load. In phosphoric acid solution, polymerization of phosphoric acid molecules occurs, yielding oligomers under lower load, and tribochemical reactions between the molecules and the sliding surfaces could enhance wear under higher load. The bridging oxygen atoms in silica play an important role in the formation of interfacial covalent bonds, and hydrogen is found to have a weakening effect on these bonds, resulting in the rupture during shear-related loading. This work sheds light on tribochemical reactions as a mechanism for lubrication and wear in water-based or other tribological systems.

Poly(2,5-benzimidazole) membranes (ABPBI) doped with phosphoric acid (PA) are known to serve as promising electrolytes in fuel cells. The addition of triflic acid, which exist in its dissociated form (TFA), is known to enhance the efficiency of PA-doped ABPBI membranes. In the present work, we employ classical molecular dynamic simulations to characterize the structure and dynamics of ABPBI + PA, ABPBI + TFA and ABPBI + PA + TFA blends with varying levels of hydration. The structural properties seen from the radial distribution functions (RDFs) show that the distance between two adjacent imidazole units on the polymer chain remain unaffected by hydration and the type of blend. The end-to-end polymer chain distance and radius of gyration are also unaffected by hydration and the type of blend, illustrating that the stability of polymer membranes under various hydrated acidic environments remains unaffected. The number of PA, TFA and water molecules in the cluster around the polymer membrane (skewed and extended form) is found to depend significantly on the extent of hydration. The lowest water mobility was obtained from the ABPBI + PA + TFA blend, which suggests that this blend could be the most effective in reducing acid leaching from the membrane matrix.

Adsorption isotherm and kinetics of diffusion of water accumulated between polypropylene thin film and Si substrate: Neutron reflectivity investigation

Aqueous solutions of phosphoric acid (H3PO4) of varying concentrations have ionic conductivities as high as 0.25 Scm−1 at ambient temperatures which cannot be accounted for on the basis of regular hydrodynamic movement of mobile ions. We report careful measurements of self-diffusion coefficients (D) of mobile species for the 85 wt% (14.6 M) phosphoric acid solution over a range of temperature from 293 to 353 K, using H1 (I=1/2) and P31 (I=1/2) pulsed gradient Hahn spin-echo (PGSE) techniques. The experimental D values are interpreted together with previously published viscosity (η) and conductivity (σ) data. The data show that protons diffuse faster than the phosphorus carrying species. The diffusion data for both nuclear species are found to be linear on an Arrhenius plot with activation energies of 25 and 36 kJ mol−1 for H1 and P31 species, respectively. Analysis on the basis of the Nernst–Einstein relation yields a proton transference number of t≈0.99 and a proton charge carrier number density of n≈1.6×1028 m−3. A plot of the product Dη as a function of temperature suggests that the proton and phosphorus species undergo significantly different mass transport mechanisms. In particular the P31 data show a nonlinear increase in Dη with temperature, while the H1 data exhibit a decrease in Dη with increasing temperature which is not expected for hydrodynamically simple fluids. The latter behavior is attributed to the water mediated transfer of protons between the phosphate groups. Room temperature P31 diffusion coefficients of condensed phosphates are also reported, and as expected the diffusion coefficient is dependent on the size of the moving species.

The N-cyan-N’-hydroxymethyl guanidine(CHMG) was synthesized and the effect of various facts during reaction to the yield was studied. The structure of the product was determined by IR spectrometry. An aqueous solution of CHMG, melamine(MA) and phosphoric acid (PA) was compounded according to a certain molar ratio. After the wood samples were impregnated with the aqueous solution in certain condition, they were dried step by step, and were cured, then the amino resin flame retardants were obtained. We emphasized studying on the effects of the molar ratio of the three components to the flame retardancy. The oxygen index(OI) of the wood test samples and the leach resistance value(LRV) of the flame retardants were determined. While the molar ratio of CHMG: MA: PA was 5: 1: 6.5, and the loading agents ratio(RFR) was 1.92%, the OI of dahurian larch came up to 45, and the average of LRV was 49.59%. The results show that if the optimum molar ratio of CHMG: MA: PA is chosen and the wood is treated in special conditions, amino resin flame retardant with leach resistance to wood can be obtained.

*These authors contributed equally to this work.The molecular-level insight of protein adsorption and its kinetics at interfaces is crucial because of its multifold role in diverse fundamental biological processes and applications. In the present study, the sum frequency generation (SFG) vibrational spectroscopy has been employed to demonstrate the adsorption process of bovine hemoglobin (BHb) protein molecules at the air-water interface at interfacial isoelectric point of the protein. It has been observed that surface coverage of BHb molecules significantly influences the arrangement of the protein molecules at the interface. The time-dependent SFG studies at two different frequencies in the fingerprint region elucidate the kinetics of protein denaturation process and its influence on the hydrogen-bonding network of interfacial water molecules at the air-water interface. The initial growth kinetics suggests the synchronized behavior of protein adsorption process with the structural changes in the interfacial water molecules. Interestingly, both the events carry similar characteristic time constants. However, the conformational changes in the protein structure due to the denaturation process stay for a long time, whereas the changes in water structure reconcile quickly. It is revealed that the protein denaturation process is followed by the advent of strongly hydrogen-bonded water molecules at the interface. In addition, we have also carried out the surface tension kinetics measurements to complement the findings of our SFG spectroscopic results.

Molecular simulations were performed to investigate the origin of the strong repulsive force acting on a protein as the protein approaches an oligo (ethylene glycol) self-assembled monolayer (OEG-SAM) surface. Since the repulsive force is mainly generated from water molecules, the force from the water molecules near the surface was calculated layer by layer to further identify the molecular origin of the repulsive force. Results show that the strong repulsive force acting on the protein near the OEG-SAM surface is dominantly generated by the interfacial water molecules located between the OEG-SAM surface and lysozyme. A hydroxyl-terminated SAM (OH-SAM) surface was used for comparison. No significant repulsive force was observed from the water molecules between the protein and OH-SAM surface. Further studies show that the dipole distribution of the interfacial water molecules is significantly affected by the OEG-SAM surface, as opposed to the negligible impact from the OH-SAM surface. The interfacial water molecules above the OEG-SAM surface stay longer and reorient more slowly than those above the OH-SAM surface. These results from this work support the hypothesis that the OEG-SAM surface interacts strongly with interfacial water molecules and creates a stable hydration layer that prevents proteins from adsorbing to the surface.