Dynamic Behavior Of Water Research Articles

Light-scattering study of phase transitions in aqueous solutions of nonionic amphiphiles.

The dynamical behavior of water in aqueous solutions of the nonionic polyoxyethylene surfactant ${\mathrm{C}}_{10}$${\mathrm{H}}_{21}$(${\mathrm{OCH}}_{2}$${\mathrm{CH}}_{2}$${)}_{5}$OH has been studied using Raman and depolarized Rayleigh-wing scattering, with particular attention to changes due to the structural phase transitions apparent at relatively large amphiphile concentrations. The frequencies and intensities of the two principal components evident in Raman spectra of the water O-H stretching band change at the hexagonal to isotropic phase transition. The width and intensity of the single resolvable line in the depolarized Rayleigh spectra similarly change at this transition: the relaxation time of the rotational water mode increases in the hexagonal phase. The changes are all consistent with an increase in the hexagonal phase of the proportion of water bound to the oxyethylene head groups: the environment of water in the system differs significantly from that in bulk water. At the lamellar to isotropic phase transition very much smaller changes were apparent, but only in the Raman scattering data. This lesser sensitivity suggests that in the lamellar phase almost all of the water is bound to the amphiphile head groups, as in the isotropic phase at such volume fractions. The changes in water dynamics reflect the structural changes in the solutions at the phase transitions, in particular the differing packing constraints in the various phases.

Dynamics of Water in the Aluminophosphate Molecular Sieve VPI-5: A 2H NMR Study

The dynamic behavior of water in the channels of VPI-5 has been reexamined in order to arrive at a motional model which applies throughout the temperature range from 225 to 348 K. An earlier model is unsuccessful in part of this range. We show that there are at least two sites for the intracrystalline water; one is bound to framework aluminum and undergoes rotational motion about the Al-OH 2 bond; the other site is a free site within the VPI-5 channels. The motion in this site is approximately isotropic. The results show an interesting dynamic behavior in the temperature range 261-297 K and are discussed with reference to a six-site motional model, which includes a consideration of internal rotations of the water molecules

Dynamic behavior of water in hydro-swollen crosslinked polymer gel as studied by PGSE 1H NMR and pulse 1H NMR

1H NMR measurements on spin-lattice relaxation time (T1) and spin-spin relaxation time (T2) were carried out on hydro-swollen crosslinked poly(methacrylic acid) (PMAA) gel to elucidate molecular motion of water molecules contained in the gel as a function of the degree of crosslinking. From these experimental results, it was found that 1H T1 and T2 decrease with an increase of the degree of crosslinking. This shows that molecular motion of water molecules is strongly restrained owing to crosslinking. Further, pulsed-field-gradient spin-echo 1H NMR measurements were carried out to determine the self-diffusion coefficient of water molecules (DH2O contained in the PMAA gel at 300 K as a function of the degree of crosslinking. From these experimental results, it was found that the DH2O value decreases with an increase of the degree of crosslinking. This shows that translational molecular motion of water molecules is restrained by crosslinking.

1H pulsed NMR study of bombyx mori silk fibroin: Dynamics of fibroin and of absorbed water

AbstractThe dynamical behavior of the Bombyx mori silk fibroin chain and of absorbed water in silk fiber, film, and powder has been studied by 1H pulsed nuclear magnetic resonance (NMR). Segmental motions do not occur and only the rapid rotation of the methyl groups of alanine residues is observed from −120 to 130°C. This is independent of the conformation or form of the silk fibroin samples. Magnetization of dry silk fibroin by the solid‐echo method shows a single Gaussian decay, while two components are observed in the solid‐echo signals of films containing 6–10 w/w% water. An immobile component with a T2 value of 11 μs is attributed to silk fibroin, and the mobile component to bound water. The T2 of the latter varies from 50 to 200 μs, depending on the sample. The dynamical behavior of water trapped in the film is discussed on the basis of these T2 values.

Structure and dynamics of liquid water between plates

Using the recently developed SPC-FP water model (simple point charge model with flexible bonds and polarization) and the molecular dynamics method, we investigate the structure and properties of liquid water between two rigid plates. In one case the plates are neutral and in the other the plates are electrically charged. In both cases substantial differences from bulk state water are found, structurally and dynamically. We observe some anomalies compared with normal liquids and attribute these to the breakage of hydrogen bonds under the influence of the solid–liquid interface. Adding an external torque enhances such breakage through the attempted alignment of the water molecules. A combination of these two contributions determines the resultant dynamical behavior of water between charged plates. The information obtained from this work should be helpful in the understanding of ‘‘hydrophobic effects’’ in aqueous solutions. The behavior of water near large polar or nonpolar molecular solutes is also revealed by these studies.

Counterion dependence of water of hydration in DNA gel

The cooling process of DNA gel (20 wt./wt.%–40 wt./wt.%) with various counterions has been investigated by low frequency Raman spectroscopy and differential scanning calorimetry (DSC). We have found that the dynamics of water of hydration is different among counterion species below 0 °C. For K-, Rb-, Sr-, and Ba-DNA gels, a part of nonfreezing water slowly changes its dynamical structure, when the gel is kept at ∼−30 °C after cooling below −50 °C. This relaxation process can be monitored both by the frequency increment of the lowest Raman band from ∼17 to ∼20 cm−1 and by the intensity increment of an extra endothermic peak in DSC heating curves. We propose that this relaxation process corresponds to the crystallization of a part of nonfreezing water and is caused by the rearrangement of the secondary hydrated water including counterions when the temperature is held at ∼−30 °C. This relaxation process cannot be observed for NH4- and Li-DNA gels. For Na-, Mg-, and Ca-DNA gels, this phenomenon is more complicated. The dynamical behavior of water of hydration in DNA gels is thus concluded to be different among counterion species.

Behavior of water molecules associated with the phase transitions in the binary system of dioctadecyldimethylammonium chloride and water studied by proton and deuterium magnetic resonances

Solid state proton magnetic resonance spectra were measured for the binary system of dioctadecyldimethylammonium chloride and water in different phases and at different compositions. From the lineshape and relaxation measurements it was shown that water in each phase consisted of multicomponents. In particular, the existence of intermediate water detected by thermal analyses was proved. NMR data also provided information on the dynamic behavior of water. The motion of the intermediate water in the gel phase was remarkable. By analysis of the split 1H NMR pattern due to dipole coupling and quadrupole splitting in the deuterium magnetic resonance spectra, an image of the motion of the intermediate water could be obtained.

Solvent dynamics in aqueous PEO–salt solutions studied by nuclear magnetic relaxation

The dynamical behaviour of water in aqueous PEO solutions has been studied by 2H and 17O nuclear magnetic relaxation measurements. A two-phase model is introduced to analyse the water mobility in the PEO hydration phase. The water mobility in the hydrated phase is retarded by a factor of 2 to 5. The anisotropic reorientation of water molecules in the proximity of PEO and the dP-dependence on the 2H and 17O relaxation rates are interpreted qualitatively by local PEO dynamics, preferential orientations of water molecules and deuteron exchange among water molecules and hydroxy end-groups.

Dynamic Behavior of Water in Lyotropic Ternary Mixtures

Abstract The diffusion of water molecules in lyotropic mixtures of potassium palmitate/potassium laurate/water was investigated using pulsed-field gradient nuclear magnetic resonance (PFG-NMR). The self-diffusion constant of water as a function of temperature was measured in two samples having different compositions and found to be sensitive to the structures of the different mesophases. Deuterium nuclear magnetic resonance (D-NMR) experiments were also performed on a mixture containing D2O, in a temperature rang where a rectangular mesophase (RBa ) coexists with a lamellar (La ) mesophase. The diffusion data, combined with the D-NMR spectral profiles allowed for the study of the size of the mixed mesophase domains.

Study on Dynamic Behavior of Water in Drain Traps

Air pressure pulses occurred in drainage pipes induce oscillating motions of water in drain traps accompanied with the outflow of a part of the water. This paper deals with the behavior of the water as the transient response of oscillation system. In this system, mass of the water decreases momentarily. A mathematical model for the system is introduced. With making impulse response model experiments and the simulations, the system parameters of the mathematical model are indentified. This method is one of the system identification methods in modern automatic control theory.

Influence of hydrophobic solutes on the dynamic behavior of water

Influence of hydrophobic solutes on the dynamic behavior of water

Dynamical behavior of water- and gas-saturated porous bodies

Dynamical behavior of water- and gas-saturated porous bodies

Molecular motions in compressed liquid water

Proton and deuteron NMR spin–lattice relaxation times in liquid water and heavy water were measured as a function of pressure and temperature in the range 10–90°C and 1 bar–9 kbar. D2O was also studied at 150 and 200°C. Availability of density and viscosity data under these experimental conditions enabled us to separate the effects of temperature and density on the spin–lattice relaxation times, T1, and viscosities. Under the assumption that the intermolecular dipolar contribution to the proton T1 follows the changes in shear viscosity with temperature and density, we separated the intramolecular and intermolecular dipolar contributions to the proton T1. We found that at a temperature of 10°C the initial increase in density leads to faster reorientation of the water molecules. The effect was much smaller at 30°C. Analysis of the experimental data on H2O and D2O leads to the conclusion that compression diminishes the coupling between the rotational and translational motions of water molecules. The change in the nature of the rotation–translation coupling with increasing density is mainly responsible for the failure of the Debye equation to describe the density effects on the reorientation of water molecules. In the case of D2O we find a relatively small variation in the deuteron quadrupole coupling constant with increasing density. Its average value is approximately 230 kHz over the range of our experimental conditions. Another experimental finding of this study is the decrease in the activation energies for relaxation and shear viscosity with increasing density. All the experimental evidence indicates that compression of water leads to significant distortion and/or disruption of the hydrogen bond network with the important consequence that the dynamic behavior of water under high compression resembles more that of a ’’normal’’ molecular liquid of comparable molecular size. At high densities the hard core repulsive interactions begin to dominate over the directional interactions which are mainly responsible for the open structure of liquid water at low temperatures and pressures.