Synthesis and characterization of periodic mesoporous organosilicas from bridged organosilanes in the presence of mixed salts

A simple but effective synthetic pathway to periodic mesoporous organosilicas (PMOs) has been put forward in this article. The novelty of the present preparative route lies in that, for specific examples, highly ordered ethane- and benzenesilica PMOs can be facilely prepared in the presence of an inorganic salt pair within a wide compositional range, where no addition of mineral acids was necessary. Most of interest is that crystal-like pore walls were observed for the large-pore benzenesilica PMO promoted by this novel system, which has rarely been reported for copolymer-assembled organosilicas, even though the degree of molecular order is not as perfect as those benzenesilicas prepared under basic conditions utilizing cationic surfactants as template. Characterization results based on a series of techniques indicated that both inorganic salts are important for the assembly of ordered mesostructures under the present system, and a plausible formation mechanism deduced from the “salt-assisted” concept as previously reported for mesoporous nonsiliceous materials was discussed.     

Vibrational frequencies of (H2O) n and (D2O) n clusters for n = 2 and 8: possible relevance to inelastic neutron scattering of ice

Hartree-Fock plus MP2 corrections are reported for the vibrational frequencies in (H₂O)₂ and (D₂O)₂ and in the cubic octamers (H₂O)₈ and (D₂O)₈. The motivation was the inelastic incoherent neutron scattering of ice as studied experimentally by Li et al. (J.-C. Li, D. Londono, D.K. Ross, J.L. Finney, S.M. Bennington and A.D. Taylor (1992). J. Phys. Cond. Matter, 4, 2109). Some contact is made between our results and these experiments, and also with earlier infrared and Raman studies of Bertie and coworkers.     

Adsorption behavior of nicotine on periodic mesoporous organosilicas

In this study, we focused on the adsorption of nicotine from aqueous solution such as water and simulated body fluids (SBFs), where SBF has ion concentrations approximately equal to those of human blood plasma. We prepared periodic mesoporous organosilica (PMO) materials as adsorbents from 4,4-bis(triethoxysilyl)biphenyl (BTES-biphenyl), 1,4-bis(triethoxysilyl)benzene (BTES-benzene) and bis[3-(trimethoxy silyl)propyl]amine (BTMS-amine) as precursors and investigated on their adsorption behavior of nicotine as a guest material under different solvent conditions. For this work, two different kinds of SBF, c-SBF and r-SBF, have been chosen, where c-SBF is a transitional SBF solution, and r-SBF is a modified SBF solution that is closer to human blood plasma. Adsorption of nicotine on PMOs has been characterized by a UV-Vis spectroscopy. The adsorption behavior was strongly dependent on the isoelectric point and hydrophobicity of the PMO as well as the hydrophobicity of nicotine.     

咪唑基介孔有机硅材料固载磷钼酸催化剂的制备及烯烃环氧化性能

以含有咪唑阳离子的周期性介孔有机硅（PMO-ILs）材料为载体,制备了一类固载化磷钼酸（PMA）多相催化材料（PMA@PMO-ILs）,并采用N₂吸附-脱附实验、X射线衍射、原子吸收光谱、差热-热重分析、红外光谱、紫外光谱及固体核磁共振技术研究了材料的结构及物理化学性质. 结果表明,磷钼酸通过静电相互作用被成功固载到PMO-ILs载体表面和孔道中,且在制备过程中磷钼酸及载体基本结构均未发生变化. 反应结果表明,PMA@PMO-ILs材料在以叔丁基过氧化氢为氧化剂的环辛烯环氧化反应中表现出一定的催化活性和很高的选择性. 中断实验结果表明,催化剂的主要活性中心在反应过程中未发生明显流失,且催化剂经多次循环使用后活性及选择性基本保持不变. PMO-ILs中大量的咪唑阳离子能有效稳定磷钼酸阴离子,使该催化材料表现出良好的稳定性.     

Neutron scattering study of pentanol solubilization in sodium octanoate micelles

We extend a previous small-angle neutron scattering study of sodium octanoate (NaC₈) micelles to the ternary system sodium octanoate/pentanol/water. The use of contrast variation through selective deuteration of individual components together with explicit computation of interference effects, permits us to deduce the location of pentanol (C₅OH) in the micelles. Our main conclusion is that, although the micelles grow as (C₅OH) is solubilised, there is no concomitant variation in the NaC₈ aggregation number. At low alcohol concentrations, the C₅OH is located near the NaC₈ polar heads, while at higher concentration the -OH groups are distributed throughout the micellar core.     

INS investigation of disaccharide/H2O mixtures

Inelastic neutron scattering (INS) on pure water and on aqueous solutions of homologous disaccharides, such as trehalose and sucrose, are presented. Neutron spectra were collected over a temperature range of 253 to 353 K by using the spectrometer MARI at the ISIS pulsed neutron source of the Rutheford Appleton Laboratory (Chilton, UK). The MARI spectrometer allowed us to get information on the hydrogen bond strength for the two homologous disaccharide/H₂O mixtures by analysing their low frequency vibrational properties.     

Vibrational dynamics of a glass forming liquid in nanoscopic confinement as probed by inelastic neutron scattering

In this article we present incoherent inelastic neutron scattering results, as a function of temperature, on the vibrational dynamics of a glass-forming liquid, namely propylene glycol, confined to the 26 Å pores of a controlled porous glass. The aim is to elucidate the effects induced by surface interactions (chemical traps) and geometrical restrictions (physical traps) on the fast microscopic dynamics of hydrogen-bonded liquids. The most prominent effect is the appearance of the ‘boson peak’ in the vibrational spectra. It is ascribed to an excess density of vibrational states due to quasilocalized collective atomic vibrations induced by confinement. A destructuring effect on the transient aggregates with the highest degree of connectivity, promoted by PG in the bulk phase, is hypothesized under confinement as a consequence of interactions, via hydrogen bond, between the hydroxyl groups (OH) of the PG molecule and the active silanol groups (Si–OH) on the surface of the porous glass.

Interfacial and/or finite-size effects are also found to give rise to a destructuring effect, under confinement, of the disordered Longitudinal Acoustic Mode, together with a broadening of the highest frequency torsional vibration and a stabilization, vs. T, of the internal CCO bending vibration.     

X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine (DMP) chloranilic acid (CLA) complex

The DMP · CLA and DMP · CLA-d₂ crystals below 100 K are monoclinic, space group P2₁/c with four molecules in the unit cells. Infinite chains of hydrogen bonded counterparts are formed with O?N distances equal to 2.767(2) and 2.639(2) for non-deuterated DMP · CLA. Deuteration leads to the Ubbelohlde effect particularly well manifested in the second short O–H?N bridge (elongation by ca. 0.02 Å). In the IR spectra a Had?i’s trio of the broad absorption is observed characteristic of strong hydrogen bonds. In the INS spectra the vibrational density of states and methyl rotational tunnel splittings were determined. The temperature dependence of tunneling bands enabled to make mode assignments and to determine the methyl rotational potentials. Comparison of the results to the pure electron donor DMP was made and the difference found can be almost completely assigned to the steric changes of the environment. A weak isotope effect with deuteration of the OH?N bridges of the DMP · CLA complex is assigned to a charge transfer of δe/e = 0.006.     

Inelastic neutron scattering studies on low frequency vibrations of pentachlorophenol

Inelastic neutron scattering (INS) and DFT theoretical studies on pentachlorophenol (PCP) and d-PCP were performed. IR and Raman spectra were also measured for comparison. A special attention was focused on low frequency modes in INS spectra, which provide information about modes into which the co-ordinates of the hydrogen and chlorine atoms are involved. The intensity of respective INS bands is discussed based on the cross-sections of nuclei and calculated relative amplitudes of vibrations. The appearance of overtones and summation frequencies in INS spectra was evidenced.     

Neutron scattering and electrophoresis of dodecyldimethylamine oxide micelles

Small-angle neutron scattering (SANS) measurements were carried out at 25 °C on dodecyldimethylamine oxide solutions under different conditions. In media with no added salt, the micelle aggregation number remained nearly constant (70–78) over the range of the degree of ionization, α_M, between 0 and 0.73 in contrast with the sharp critical micelle concentration increase in a narrow range of α_M from 0.35 to 0.40. This characteristic α_M dependence that deviates markedly from the prediction of the regular solution approach is thus shown to take place without a considerable change with respect to micelle size and shape. The surface electric potential employed to calculate the intermicellar repulsion under the Debye–Hückel approximation was found to be much lower than the actual surface potential determined from hydrogen ion titration. This inconsistency was solved by introducing a rescaled particle size for the hard-sphere interaction part. The surface potential from SANS was rather similar to the zeta potential determined by electrophoretic light scattering. In the range of NaCl concentrations higher than about 0.2 M, micelle growth was observed for both the hemihydrochloride (1:1 complex) and the cationic species and the growth into a cylindrical shape was confirmed. Received: 3 March 1999 Accepted in revised form: 22 April 1999     

Neutron scattering studies on micelles of dodecylhexaoxyethylene glycol monoether

Small angle neutron scattering studies have been made on solutions of dodecylhexaoxyethylene glycol in D₂O above the critical micelle concentration and as a function of temperature. It was possible to fit the experimental data at low values of scattering vector using a cylindrical model for the micelle shape.     

Molecular simulation study on adsorption of methanol/water mixtures in mesoporous silicas modified pore surface silylation

Two types of molecular simulation techniques have been utilized to investigate adsorption of methanol/water mixtures in a mesoporous silica with a hydrophobic pore surface: the NVT-ensemble Molecular Dynamics method with the melt-quench algorithm for modeling a fully-silylated mesoporous silica and the μVT-ensemble Orientaional-Biased Monte Carlo method for calculating adsorption isotherms. Adsorption isotherms of methanol and water at 333 K are calculated for an equi-relative-pressure mixture (each component has the same relative pressure which is defined as the ratio of the partial pressure to the saturation pressure of the pure gas) together with pure gases. In the case of the pure gas, water hardly adsorb even at elevated pressures, while the adsorption isotherm for methanol shows the condensable adsorption. On the other hand, in the case of the mixture, water molecules are substantially adsorbed along with methanol molecules, showing an isotherm representing the condensation mechanism. In addition, it is found that the separation factor of methanol to water is the highest in the case of monolayer adsorption from a liquid mixture.     

Mutual interactions in a ternary protein/bioprotectant/water system

The dynamics of hydration water play a key role in many biological processes. The activity and function of proteins are strongly affected by the presence of water, which interacts primarily by means of hydrogen bonding. These interactions are examined in this work by a comparison of neutron vibrational spectra (Inelastic Neutron Scattering, INS) of dry lysozyme and hydrated lysozyme at h = 0.7 (g of H₂O/g of protein) with those of a lysozyme/water mixture at the same hydration value in the presence of the glass-forming bioprotectant trehalose. A difference spectrum, obtained by subtracting the dry lysozyme spectrum from that of the lysozyme/water mixture, yields the hydration water spectrum which is compared to the INS spectra of different kinds of ice in order to determine the changes induced by lysozyme on the hydrogen-bonded network of water. An additional comparison is performed by using a double-difference spectrum obtained by subtracting both the dry lysozyme and the trehalose spectra from the lysozyme/trehalose/water ternary spectrum. The effects of the mutual interactions among the three components, i.e. protein, disaccharide and water, are determined by comparison of the spectra of the dry systems (lysozyme, trehalose) with the difference spectra obtained from subtraction of the dry systems from the binary systems. It is concluded that the interfacial water more strongly affects the intermolecular mode region at low frequencies, whereas the vibrational spectra at high frequencies are more influenced by lysozyme and trehalose.     

Time-resolved small-angle neutron scattering study of polyethylene crystallization from solution

With time-resolved small-angle neutron scattering (TR-SANS), the crystallization kinetics of polyethylene from deuterated o-xylene solutions upon a temperature jump have been investigated. On the basis of a morphological model of coexisting lamellar stacks and coil chains in solution, experimental data have been quantitatively analyzed to provide structural information, such as the lamellar long period, the lamellar crystal thickness, the thickness of the amorphous layers between lamellae, the degree of crystallinity, and the crystal growth rate at various degrees of undercooling. The viability of TR-SANS for studying polymer crystallization is demonstrated through the consistency of these measurements and well-established knowledge of polyethylene crystallization from xylene solutions. One unique feature of this experimentation is that both the growth of lamellar crystals and the condensation of coil chains from solution are monitored simultaneously. The ratio of the crystal growth to the chain consumption rate decreases rapidly with a decreasing degree of undercooling. The Avrami analysis suggests that the growth mechanism approaches two-dimensional behavior at higher temperatures, and this is consistent with the observation of an increasing ratio of the sharp-surface area to the bulk crystal growth rate with temperature. The limitations, possible remedies, and potentials of TR-SANS for studying polymer crystallization are discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3133–3147, 2004     

Ultra-small-angle X-ray and neutron scattering study of colloidal dispersions

The ultra-small-angle X-ray and neutron scattering techniques are useful techniques for the investigation of colloidal systems. The very high small-angle resolution of these scattering techniques has provided important and novel information to elucidate the formation mechanism of colloidal crystals. The Bonse–Hart optical system is expected to become a standard tool for investigating mesoscopic structures.     

Location and Vibrations of Hydrogen in La2C3H1.5

We report on the incorporation of hydrogen into La₂C₃ and on the characterisation of its position. Temperature‐dependent X‐ray investigations show that the hydrogenation process is reversible and the product La₂C₃H_1.5 is amorphous. In principle, IR and Raman spectroscopies can provide some structural information, but in the present study, they are of only limited value. Inelastic neutron scattering (INS) has advantages for measuring the H‐vibrations in La₂C₃H_1.5 and these are compared with the results of molecular dynamics simulations. A structural model based on published pair‐potentials predicts that hydrogen (or deuterium) occupies the “tetrahedral” holes in the lanthanum sublattice. This model also accounts for the observed vibrational spectra.     

Small-angle neutron scattering study on microstructure of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) in water

By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D₂O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 °C in a temperature range of transparent sol below 30 °C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration W_p > 3.5% (w/v), corresponding to opaque gel above 30 °C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 °C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior.     

Proton tunnelling in the intramolecular hydrogen bond of 9-Hydroxyphenalenone

Inelastic neutron scattering spectra of the 9-hydroxyphenalenone and ring deuterated analogue reveal an intense band at 91 cm⁻¹ with all characteristics anticipated for a tunnelling the transition of a (quasi)symmetric double minimum potential for proton transfer along the intramolecular hydrogen bond. This frequency is compared to those previously reported for similar systems.     

Neutron Scattering Studies of Structure and Self-Assembly of Star-Shaped Polymers with Fullerene Centres in Solutions

Protonated star-shaped polystyrenes with single and double fullerene C₆₀ core and the hybrid stars with pairs of polar and non-polar arms (tertbuthylmetacrylate, polystyrene) have been studied in deuterated toluene (20 °C) by small-angle neutron scattering at low and moderate polymer concentrations (c₁ ∼ 1 g/dl, c₂ ∼ 3–6 g/dl) to evaluate the peculiarities of fullerene centre action on polymers self-assembly in solutions. As we found, the cores composed of two fullerenes, linked via Si(CH₃)₂-bridge, induce stars' anisotropic interactions and association into chain-like structures (correlation radius ∼400–600 nm). Meanwhile, the single-core stars of polystyrene and hybrids organize globular clusters (size ∼ 10³ nm) those geometry do not change significantly by polymer content variation.     

Theoretical and experimental study of the inelastic neutron scattering spectra of β-5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one

The inelastic neutron scattering (INS) spectra of β-5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (β-NTO) are presented to 1400 cm⁻¹. The β-NTO vibrational frequencies observed differ considerably from the -NTO vibrational frequencies and normal mode frequency calculations for the isolated molecule. The INS spectrum contains detail unobserved in the previous IR studies, including combinations and overtones of the phonon and internal modes of β-NTO. The INS spectra are compared with periodic DFT calculations to show that the periodic DFT results correctly predict the solid-state molecular vibrational frequencies.