Hirofumi Okabayashi

Late stage dynamics of phase separation processes of binary mixtures containing surfactants

Late stage dynamics of phase separation processes of immiscible binary mixtures containing surfactants (amphiphilic molecules) is investigated by computer simulations on the hybrid model proposed by the present authors [T. Kawakatsu and K. Kawasaki, Physica A 167, 690 (1990)]. With use of this hybrid model, one can investigate large scale phenomena while retaining the intramolecular structures of surfactant molecules. Simulations are performed both for irregular bicontinuous and micellar domain formation processes taking the thermal fluctuation effects into account. In the very late stage, the coarsening of the domain structures is considerably slowed down both for bicontinuous and micellar domain formation processes due to the low interfacial tension of the surfactant–adsorbed interfaces. Scaled scattering structure functions are also calculated, which possess the characteristic features of the experimentally observed scattering functions of microemulsions and polymer blends containing amphiphilic block ...

Diffuse reflectance infrared Fourier transform spectral study of the thermal and adsorbed-water effects of a 3-aminopropyltriethoxysilane layer modified onto the surface of silica gel

Abstract Infrared absorption spectra of some polyaminopropylsiloxane (poly-APS) samples with different degrees of polymerization have been examined. The results show that this difference results in a marked variation in the environment of the NH 2 groups. The thermal and adsorbed-water effects on the silane-coated layer of silica gel samples, modified with 3-aminopropyltriethoxysilane (APTS), have also been investigated using a diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic method. The results are summarized as follows. For the silica gel samples, the DRIFT spectral features in the CH stretch and NH 2 bend modes are almost independent of temperature within the range 303–373 K, indicating stable environments for the aminopropylsilyl segments of the silane-coated layer. For a sample which was treated with a higher APTS concentration, the spectral features were little affected by adsorption of water, while the effect of adsorbed water on a sample treated with a small APTS concentration led to observation of pronounced spectral features. These results have been ascribed to the difference in the degree of polymerization of the silane-coated layer between the samples.

A proton nuclear magnetic resonance study on the release of bound water by inhalation anesthetic in water-in-oil emulsion

Water-in-oil emulsion was prepared from glycerol-alpha-monooleate, n-decane and water, and was used to analyze the behavior of bound water molecules in response to the addition of an inhalation anesthetic, enflurane. The motion of water molecules is monitored by proton nuclear magnetic resonance spectroscopy. To the first approximation, the half-height width of the proton signal of dispersed water is related to the spin-spin relaxation time and represents the motion of the water molecule. It appears that one of the two OH moieties of glycerol-alpha-monooleate forms a hydrogen bond with the water molecule in average. The half-height width of the dispersed water proton showed a maximal value when the glycerol alpha-monooleate/n-decane mole ratio was 4 X 10(-2). The cause of this maximum is not immediately clear, but it is suggested that the assembly mode of glycerol-alpha-monooleate may be different between the lower and higher concentration range. Enflurane decreased the half-height width of the dispersed water, indicating an increase in the motion of water molecules. This results demonstrates that the anesthetic weakened the hydrogen bond between water and glycerol-alpha-monooleate molecules, and released bound interfacial water. It is postulated that dehydration of the interface, as shown by the release of bound water, would interfere with the transport of current-carrying hydrated ions through membranes and may constitute a molecular mechanism of anesthesia.

Kinetics of interaction of 3-aminopropyltriethoxysilane on asilica gel surface using elemental analysis and diffuse reflectanceinfrared Fourier transform spectra

In order to study the kinetics of interaction of 3-aminopropyltriethoxysilane (APTS) on silica gel, silica gel samples reacted with APTS were prepared by sampling the reaction mixture from the reactor at various time intervals, and the concentrations of 3-aminopropylsilyl (APS) groups modified on the silica gel surface were determined by elemental analysis. From the reaction time dependence of the APS concentration, it has been found that, after an initial fast reaction of APTS and silica gel, a slower second reaction and a much slower third reaction subsequently occur. For the three processes, the reaction rate constants (k obs /s -1 ) have been estimated and found to be k obs i =1.00×10 -1 s -1 for the initial reaction, k obs s =6.91×10 -3 s -1 for the second reaction and k obs t =4.20×10 -4 s -1 for the third reaction. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were measured for the same samples. Bands at 3734–3739 cm -1 were observed in the OH stretch mode region, and were found to decrease in intensity with reaction time, reflecting the rate of reaction of APTS on the silica gel. Analysis of an OH stretching band has also furnished reaction rate constants that are very similar to those obtained from the time dependence of the APS concentration. A mechanism for the three reaction processes is postulated.

The proton magnetic resonance spectra and molecular conformations of sodium n-acyl sarcosinates in aqueous solution

Proton magnetic resonance spectra of sodium N-acyl sarcosinates were measured in deuterium oxide solution, and the change of molecular conformations of these surfactants due to formation of micelles was investigated. The population of the trans configuration of surfactant molecules relative to that of the cis configuration was found to increase with increasing concentration. The increase of the trans configuration at the critical micelle concentration was marked. This observation indicates that the trans configuration of sodium N-acyl sarcosinates is more stable in the micelle state than in the mono-molecular dispersion state.

Polymerization process of the silane coupling agent 3-aminopropyltriethoxy silane – 1H NMR spectra and kinetics of ethanol release

Abstract In the 3-aminopropyltriethoxy silane–deuterated ethanol–H 2 O system, the rate of release of ethanol from the ethoxy groups, a reaction which occurs during the condensation process, has been followed by use of 1 H NMR spectroscopy at different temperatures. Two separate reaction processes have been identified, and values of the reaction rate constants and thermodynamic parameters ( E a , Δ H ‡ and Δ S ‡ ) have been calculated.

Fourier Transform Near-Infrared Attenuated Total Reflectance Spectroscopy of Silane Coupling Agents on Glass IRE

Attenuated total reflectance (ATR) has been shown to be highly sensitive for surface analysis. The major advantage of ATR is that the region of the specimen is restricted to a thin layer adjacent to the internal reflectance element (IRE). In an investigation of the surface reactions and interfacial effect of silane coupling agents on the surface of glass, a glass IRE was used in the near-infrared region (7000–4000 cm−1). This technique is useful for analyzing the near-surface of the glass IRE. By a comparison between each measured ATR spectrum and the transmission spectrum of the same glass IRE, it is possible to determine the mechanism of reaction of the silane coupling agent on the glass substrate. The process of dehydration was also investigated by calibration, with the use of the intensity of the band due to Si-OH groups. A condensation reaction occurs between molecules of the silane coupling agent in the bulk film. However, a small fraction of the agent reacts with the Si-OH groups of the glass at a lower rate. In this study, we show the transmission and ATR spectra of silane coupling agent reacted on a glass plate used for the IRE in the ATR method. With the use of the ATR method, the state of the dehydration condensation reaction, which involves hydrolyzing Si-OH at the surface, can be observed. Furthermore, the process of dehydration condensation reaction on the substrate of glass can also be compared with the bulk reactions measured by transmission.

Raman scattering study of the interaction of 3-aminopropyltriethoxy silane on silica gel. Time-dependent conformational change of aminopropylsilyl segments

Abstract Silica gel samples, modified with 3-aminopropyltriethoxy silane (APTS), have been prepared by sequentially sampling the substrate from the reaction vessel at various time intervals, and the Raman spectra of these samples have been measured. The CH stretch Raman bands at 2938 and 2981 cm −1 became more intense as the reaction proceeded. Kinetic analyses were then carried out, after making the assumption that the time dependence of relative Raman peak heights ( I 2938 / I 800 and I 2981 / I 800 ) is a pseudo-first order. The rate constants obtained are k =8.05×10 −4 s −1 for the 2938 cm −1 band and k =9.45×10 −4 s −1 for the 2981 cm −1 band. We may assume that the dependence of the change in intensity of the CH stretch Raman bands on time is a reflection of the change in conformation of the APS moieties.

FT-IR spectra of glycine oligomers

Abstract Fourier transform infrared spectra were revisited for glycine oligomers (trimer through hexamer) and polyglycine. Oligomers precipitated from aqueous solutions with acetone existed in the planar zigzag conformation similar to polyglycine I. Infrared spectra for the helical conformation similar to polyglycine II were also obtained for glycine pentamer and hexamer.

Saturable and unsaturable binding of a volatile anesthetic enflurane with model lipid vesicle membranes

Presence of specific receptors for volatile anesthetics has recently been proposed (Evers, A.S. et al. (1987) Nature 328, 157-160) by a finding that halothane uptake by the rat brain was characterized, in part, by saturable binding. We report here that volatile anesthetics bind model lipid membranes also with saturable and unsaturable kinetics. Binding of enflurane to dipalmitoylphosphatidylcholine vesicle membranes was measured by gas chromatography. At low anesthetic concentrations, comparable to the clinical level, the interaction was saturable. After reaching a temporary saturation, a sudden increase in the anesthetic binding to the membrane occurred, when the anesthetic concentration in the aqueous phase exceeded 2.7 mM, or 6.3 x 10(-2) atm partial pressure in the gas phase in equilibrium with the aqueous phase. The secondary binding was linear to the aqueous anesthetic concentrations and was unsaturable to the limit of this study. We also found that enflurane self-aggregated in water above 4 mM. When the aqueous concentration exceeded 6 mM, the aggregation number was about 8. We conclude that the saturable binding indicates adsorption onto the vesicle surface, and the unsaturable binding indicates multilayer stacking of the enflurane molecules, where the initially adsorbed molecules provide the binding sites to the succeeding molecules according to the multilayer condensation kinetics. The tendency of enflurane to self-aggregate in water promotes the multilayer stacking at the surface of the membrane.