Reconstruction Of Hydrogen Bonds Research Articles

Pressure-induced hydrogen bonds reconstruction of energetic material 3,6-dihydrazino-1,2,4,5-tetrazine: A DFT study

Pressure-induced changes in molecular structure can result in the reconstruction of hydrogen bonds. The structure and vibrational properties of hydrogen-bonded material 3,6-dihydrazino-1,2,4,5-tetrazine were calculated to 50 GPa. When compression, the compressibility displays anisotropy. At 37 GPa, the N-H length increases abruptly to 1.51 Å, suggesting that N-H has broken. The discontinuous changes indicate that 37 GPa is a critical point for structural changes. The hydrogen bond network becomes strengthened, resulting in a decrease in the vibrational activity of NH/NH2. At 37 GPa, the direction of NH correlated vibration modes change. In Hirshfeld analysis, the strengthening of N…H interactions was confirmed.

Enhanced self-healing driving force in polymer materials by regulating molecular structure

For self-healing polymers, obtaining excellent healing ability and mechanical properties usually need complex chemical structure, external healing conditions, and high manufacturing difficulty. Therefore, self-healing efficiency and rate, mechanical strength, and simple structure design as well as no additional healing conditions of the material are contradictory properties and are difficult to optimize simultaneously. Herein, self-healable thermoplastic poly (urethane urea) elastomers driven by surface energy were fabricated by the introduction of asymmetric alicyclic structures and the healing properties in polymers were optimized by regulating surface energy. The results showed that with the increasing of isophorone diamine contents, the surface energy driving force increased from 36 kPa to 149 kPa, the healing time decreased from 30d to 5d, and healing efficiency, and tensile strength reached 100.9% and 4.04 MPa at room temperature. At the same time, polymers also obtained a high healing efficiency under high-temperature healing conditions. The healing mechanism is that asymmetric alicyclic structures with steric hindrance and ring flip promote the dissociation of hydrogen bonds, provide sufficient chain mobility, decrease the junction density, and improve the surface energy as well as the dissociation and reconstruction of hydrogen bonds. Energetic polymer composites using thermoplastic poly (urethane urea) elastomers as matrix obtained excellent healing properties. This study will offer a novel healing approach for developing advanced self-healing polymer materials.

Ethanol‐Processable Polyfuran Derivative for Eco‐Friendly Fabrication of Organic Solar Cells Featuring Self‐Healing Function

Eco‐friendly fabrication of organic solar cells (OSCs) via alcohol or water is highly desired for their cost‐effective feature and benign profit for derived operators and ambient environment. Herein, a simple polyfuran derivative (PFO) that exhibits good solubility in ethanol/water solvent mixture is reported. Moreover, PFO displays broad optical absorption, high‐lying electronic energy level, and large hole mobility. The air‐ and ethanol‐processed PFO‐based OSCs deliver a fine efficiency of 2.25%. Even though only 45.24% of their initial efficiency is preserved for optimized devices after continuous illumination for 200 h in ambient atmosphere, the remained efficiency value of optimized devices can increase by 19.20% when undergoing intermittent illumination yet for the same light‐soaking time of 200 h. The self‐healing efficiency of devices suffering from discontinuous illumination is associated with the partial dissolution and reconstruction of hydrogen bonds in active layer. The results provide important guidelines for designing electroactive materials for safe and environmentally benign fabrication of OSCs with self‐sealing function.

Deep eutectic solvents boosting solubilization and Se-functionalization of heteropolysaccharide: Multiple hydrogen bonds modulation

In this study, the favorable feasibility of deep eutectic solvents (DESs) in solubilization and functionalization of natural heteropolysaccharide was validated by experiments and density functional theory calculations. This revealed that choline chloride-based DES/DMSO (dimethyl sulfoxide) binary mixed solvents possessed more and stronger hydrogen bonding sites, facilitating the balance between disruption and reconstruction of hydrogen bonds within branched heteropolysaccharide from Artemisia sphaerocephala (PAS) and achieving efficient solubilization. Further, due to the full exposure and activation of polysaccharide hydroxyls, the efficiency of DES/DMSO-mediated novel Se-functionalization was substantially enhanced compared to the conventional selenylation methods. The derivative exhibited conversion to lower molecular mass with rigid solution conformation based on co-solvent effect and predominant acidic environment influence. This study offered a framework for exploring the potential of individualized polysaccharide functionalization by modulating DES constituents to achieve multiple controllabilities in terms of conversion efficiency and derivative structure.

Structure reorganization of cellulose hydrogel by green solvent exchange for potential plastic replacement

Petroleum-based plastics have raised great environmental concerns from the beginning of their production to the end-of-life cycle. It is urgently needed to develop sustainable and green materials with certain plastic properties. Herein, biobased cellulose films are fabricated from low quality cotton cellulose by manipulating its hydrogen bonding network with green solvents. The cellulose is dispersed in inorganic salts (ZnCl2/CaCl2) to form ionic hydrogels, and then transformed into tough and flexible films through ethanol exchange and air drying. Without extra hot-pressing treatment, the aggregate structure of cellulose is re-organized with the disruption and re-construction of hydrogen bonds. Benefiting from the densely packed structure and highly in-plane orientation, the cellulose film presents outstanding optical, thermal and mechanical properties. Such cellulose materials hold a potential for plastic replacement in the field of biodegradable packing.

A self-healing PDMS elastomer based on acylhydrazone groups and the role of hydrogen bonds

A PDMS elastomer based on acylhydrazone groups with both acid- and heat-assisted self-healing properties was successfully prepared from tetra-acylhydrazine-terminated PDMS and terephthalaldehyde through solution casting. The good healing performance was obtained with catalytic acetic acid for 24 h at 25 °C or by annealing at 120 °C for 2 h. The elastomer exhibited a reversible transition near 80 °C observed by rheological measurements and variable-temperature FTIR, which corresponded to the dissociation and reconstruction of hydrogen bonds between acylhydrazone groups. Since the non-equimolar sample presented similar behaviors with the equimolar sample, it verifies that the reversible dissociation/reformation of hydrogen bonds dominates the heat-assisted self-healing process. This finding will enable better understanding of the contribution of hydrogen bonding interactions in acylhydrazone self-healing systems, thus promoting the development of self-healing bulk materials based on acylhydrazone groups.

A robust, highly stretchable supramolecular polymer conductive hydrogel with self-healability and thermo-processability

Dual amide hydrogen bond crosslinked and strengthened high strength supramolecular polymer conductive hydrogels were fabricated by simply in situ doping poly (N-acryloyl glycinamide-co-2-acrylamide-2-methylpropanesulfonic) (PNAGA-PAMPS) hydrogels with PEDOT/PSS. The nonswellable conductive hydrogels in PBS demonstrated high mechanical performances—0.22–0.58 MPa tensile strength, 1.02–7.62 MPa compressive strength, and 817–1709% breaking strain. The doping of PEDOT/PSS could significantly improve the specific conductivities of the hydrogels. Cyclic heating and cooling could lead to reversible sol-gel transition and self-healability due to the dynamic breakup and reconstruction of hydrogen bonds. The mending hydrogels recovered not only the mechanical properties, but also conductivities very well. These supramolecular conductive hydrogels could be designed into arbitrary shapes with 3D printing technique, and further, printable electrode can be obtained by blending activated charcoal powder with PNAGA-PAMPS/PEDOT/PSS hydrogel under melting state. The fabricated supercapacitor via the conducting hydrogel electrodes possessed high capacitive performances. These cytocompatible conductive hydrogels have a great potential to be used as electro-active and electrical biomaterials.

A Mechanically Strong, Highly Stable, Thermoplastic, and Self-Healable Supramolecular Polymer Hydrogel.

Polymerization of glycinamide-conjugated monomer alone in concentrated aqueous solution enables facile formation of a mechanically strong and a highly stable supramolecular polymer (SP) hydrogel because of the cooperatively hydrogen-bonded crosslinking and strengthening effect from dual amide motifs. This SP hydrogel exhibits thermoplastic processability, injectability, and self-reparability because of the dynamic destruction and reconstruction of hydrogen bonds in response to temperature change.

中性子回折・散乱から見たプロトン伝導体Ｋ３Ｈ（ＳｅＯ４）２

Neutron powder diffraction, quasi elastic and inelastic scattering measurements were performed to examine the mechanism of phase transition and protonic conduction of K3H (SeO4) 2. SeO4 tetrahedra in the high-temperature phase (phase I) were rotationally displaced with the occupancy 1/3 and the crystal structure in the room temperature phase (phase II) remained locally. Proton distribution maps obtained from MEM describe that 13.4% of protons exist at inter-layer space. Proton diffusion constants were estimated as 1.9 (1) × 10-10 m2/s at 393 K and 2.1 (3) × 10-10 m2/s at 413 K respectively. A rotational mode of SeO4 tetrahedra causes change from R3m to C2/c. No soft mode was observed both of transversal acoustic and zone boundary optical modes, however, a diffusive spectrum was observed around 0 meV at the L-point (0.5 2 0) above Tc as an over-dumped phonon mode. The rotational mode of SeO4 tetrahedra drives the improper ferroelastic phase transition, and assists the disconnection and reconstruction of hydrogen bonds in the phase I.

Superionic phase transitions and nuclear spin phonon relaxation by Raman processes inMe3H(SeO4)2 (Me = Na, K, and Rb)single crystals by 1H and Me NMR

Me3H(SeO4)2 (Me = Na, K, and Rb) single crystals were grown by the slow evaporation method, and the relaxation times ofthe 1H and Me nuclei in these crystals were investigated using FT NMR spectrometry. The1H T1 NMRresults for K3H(SeO4)2 and Rb3H(SeO4)2 single crystals were very different from those forNa3H(SeO4)2 crystals. Short1H relaxation timeswere found for K3H(SeO4)2 andRb3H(SeO4)2 at high temperatures,but not for Na3H(SeO4)2, which are attributed to the destruction and reconstruction of hydrogen bonds; thusK3H(SeO4)2 andRb3H(SeO4)2 have superionicphases, whereas Na3H(SeO4)2 does not. The temperature dependence of the relaxation rate for the23Na nucleusin Na3H(SeO4)2 crystals was in accord with a Raman process for nuclear spin–lattice relaxation. In contrast, the spin–lattice relaxation rates for the39K and87Rb nucleiin K3H(SeO4)2 and Rb3H(SeO4)2 single crystals exhibited a very strong temperature dependence, . The motions giving rise to this strong temperature dependence may be related to thehigh electrical conductivities of these crystals at high temperatures.

1H and 2H NMR relaxation study on the phase transitions of(NH4)3H(SO4)2 and (ND4)3D(SO4)2 single crystals

T1,T1ρ andT2 forthe 1H and 2H nuclei in (NH4)3H(SO4)2 and (ND4)3D(SO4)2 single crystals grown using the slow evaporation method were measured for phases I, II, III, IV and V.The 1H T1,T1ρ,and T2 values were found to exhibit different trends in phases II and III:T1,T1ρ and T2 for 1H do not change significantly near the phase transition at 265 K, whereasnear 413 K they change discontinuously. We conclude that theNH4+ and H(SO4)2− ions do not play an important role in the III–II phase transition, but do playimportant roles in the II–I phase transition. The liquid-like nature of the1H T1ρ andT2 above413 K is indicative of the destruction and reconstruction of hydrogen bonds. Moreover, the phase transitionsof the (NH4)3H(SO4)2 crystal are accompanied by changes in the molecular motion of the(NH4)+ ions. The variations with temperature of the2H T1 and T2 of (ND4)3D(SO4)2 crystals are not similar to those observed for the1H T1 andT2. Our comparison ofthe results for (NH4)3H(SO4)2 and(ND4)3D(SO4)2 crystals indicatesthe following: the 1H T1ρ andT2 of the(NH4)+ andH(SO4)2− ionsabove TC1 are characteristic of fast, liquid-like motion, which is not the case for(ND4)3D(SO4)2; andthe 2H T1 ofD(SO4)2− in(ND4)3D(SO4)2 is longerthan the 2H T1 of(ND4)+ in contrast tothe results for (NH4)3H(SO4)2 crystals.

Dynamics of superionic Rb 3H(SeO 4) 2 single crystals studied by 1H and 87Rb spin–lattice relaxation

The 1H and 87Rb spin–lattice relaxation and spin–spin relaxation times in superionic Rb 3H(SeO 4) 2 single crystals grown by the slow evaporation method were measured over the temperature range 160–450 K. The temperature dependencies of the 1H T 1, T 1 ρ , and T 2 are measured. In the ferroelastic phase, T 1 differs from T 1 ρ , which is in turn different from T 2, although these three relaxation times converge to similar values near 410 K. This transition seems to occur at temperature which is about 40 K lower than the superionic transition temperature. The observation of liquid-like values of the 1H T 1, T 1 ρ , and T 2 in the high temperature is compatible with the phase being superionic, indicating that the destruction and reconstruction of hydrogen bonds does indeed occur at high temperature. In addition, the 87Rb T 1 and T 2 values at high temperature were similar (on the order of milliseconds), a trend that was also observed for 1H T 1 and T 2. This behavior is expected for most hopping-type ionic conductors, and could be attributed to interactions between the mobile ions and the neighboring group ions within the crystal. The motion giving rise to this liquid-like behavior is related to the superionic motion.

High Temperature Phase Transition in Cs3D(SO4)2

The M3XðYO4Þ2 type crystals have so-called zerodimensional hydrogen bonds consisting of isolated YO4{X{YO4 dimers, where M 1⁄4 NH4, K, Rb, Cs; X 1⁄4 H, D; Y 1⁄4 Se, S. It is well known that some of the member crystals undergo successive structural phase transitions, and show marked isotope effects on the antiferroelectric (ferroelectric) phase transitions below room temperature. On the other hand, above room temperature, most of the members exhibit the ferroelastic-superionic phase transitions, and show a high electric conductivity above the transition points. The high temperature phase transitions are due to the destruction and the reconstruction of hydrogen bonds. However, for most cases, the phase transition points do not exhibit the normal type of isotope effect on deuteration. These show the negative isotope effect in which lowering of the transition temperature is seen by the deuteration, for example, Cs3H(SeO4)2 ! Cs3D(SeO4)2. Tricesium hydrogen disulfate, Cs3H(SO4)2, (abbreviated as TCHS) also belongs to M3XðYO4Þ2 type crystals. So far no phase transition point has been reported in TCHS above and below room temperature. Then the deuterated compound TCDS may exhibit the ferroelastic-superionic phase transition at a some point above room temperature, if this compound follows the negative isotope effect on ferroelastic-superionic transition temperature (Ti). In order to confirm the effect on Ti in TCDS, the measurements of the dielectric constant, the electric conductivity and the differential scanning calorimetry (DSC) are performed. Single crystals of TCDS were prepared by successive recrystallizations from D2O solution containing Cs2SO4 and H2SO4 with molar ratio 3 : 1. Both (001) and (00 1) planes of the sample crystal were coated with Ag paste electrodes. The electric capacity and the complex impedance were measured in the direction perpendicular to the (001) plane, in the temperature region from 350K to 450K, with an automatic LCR-meter, HIOKI-3531, using 100KHz electromagnetic wave. The dielectric constant and the electric conductivity of TCDS were calculated from the data of electric capacity and the complex impedance, respectively. The temperature fluctuation of the sample is suppressed within 0:1K by a precise temperature controller. The measurement by DSC was performed in the temperature region from 350K to 470K in the heating rate of 3 C/min. It was also comfirmed by DSC signals that no protonated compounds TCHS exhibited the phase transition in the temperature region from 350K to 490K. In Fig. 1, the temperature dependence of the dielectric constant of TCDS is shown; the dielectric constant increases with increasing temperature and jumps discontinuously at about 422K. On further heating, it decreases rapidly. when temperature is increased further, the dielectric constant increases exponentially. The temperature dependence of the dielectric constant around 422K seen in Fig. 1 is similar to those found in the cases of the ferroelastic-superionic phase transitions of Cs3D(SeO4)2 and K3H(SeO4)2. 5,6) The temperature dependence of the electric conductivity of TCDS is plotted in Arrhenius coordinates as shown in Fig. 2. The conductivity has a value of about 5:0 10 8 cm 1 at 350.1K (1000=T 2:86) and increases sharply with increasing temperature up to about 422K (1000=T 2:37). The electric conductivity jumps suddenly from 7:3 10 7 cm 1 to 9:7 10 4 cm 1 at 422K, and drops just above this temperature as seen also in the case of the dielectric constant in Fig. 1. On further heating, it increases exponentially. The temperature dependence of the electric conductivity shown in Fig. 2 is very similar to that of AgI which undergoes the superionic phase transition. High values of dielectric constant above 422K in Fig. 1 may be considered as due to high electric conductivities in this temperature region. However, the reason for the dropping of just above 422K is unknown. According to Fig. 1. Temperature dependence of the real part of dielectric constant 0 of Cs3D(SO4)2 along the direction perpendicular to the (001) plane at 100KHz.

Raman Scattering Study of Rb3H(SeO4)2Single Crystal in High Temperature Phases

Raman scattering from a single crystal of Rb 3 H(SeO 4 ) 2 has been observed in the frequency range between 20 cm -1 and 1000 cm -1 at phases I (482.6 K, 466.8 K, 443.3 K) and II (391.2 K, 301.2 K, 78.6 K). The measured spectra in phase II were assigned to the normal modes of SeO 4 tetrahedra vibration. In phase I, this compound shows high electric conductivity due to the hopping of protons. A new Raman line has been found at 826 cm -1 in this high temperature phase. It is suggested that this line is caused by the stretching mode of a single Se–O bond in SeO 4 tetrahedra, accompanied by destruction and reconstruction of hydrogen bonds.