44 research outputs found
Structural characterization of water and ice in mesoporous SBA-15 silicas: II. The 'almost-filled' case for 86 angstrom pore diameter
No full textNeutron diffraction measurements for D2O in SBA-15 silica of pore diameter 86 angstrom have been made in a temperature range from 300 to 100 K. The pore-filling factor for the liquid phase is 0.95, resulting in an `almost-filled' sample. The nucleation and transformation of the ice phase were determined for cooling and warming cycles at two different rates. The primary nucleation event at 258 K leads to a defective form of ice-I with predominantly cubic ice features. For temperatures below the main nucleation event, the data indicate the formation of an interfacial layer of disordered water/ice that varies with temperature and is reversible. The main diffraction peak for the water phase shows similar features to those observed in earlier studies, indicating enhanced hydrogen bonding and network correlations for the confined phase as the temperature is decreased. A detailed profile analysis of the triplet peak is presented in the accompanying paper (Seyed-Yazdi et al 2008 J. Phys.: Condens. Matter 20 205108)
REVERSE HEMIMICELLE FORMATION OF 1-DECANOL FROM HEPTANE AT THE SOLUTION GRAPHITE INTERFACE
No full textBased on a two-step adsorption mode (i.e., in the first step the amphiphiles are adsorbed through van der Waals attraction between the amphiphiles and the solid, e.g., carbon black; then, in the second step, the so called reverse hemimicelles form through hydrogen bonding and/or other polar interactions between the adsorbed amphiphiles) and the mass-action law, an isotherm equation is derived for adsorption of amphiphiles on solids from nonpolar solvents. The result has been quantitatively supported by the adsorption data of 1-decanol from heptane at the solution/graphite interface reported by G.H. Findenegg et al. The average aggregation number of the reverse hemimicelles, evaluated from the general adsorption isotherm equation, is in the range of 3-6, in the temperature range of 15-35??C, and decreases with increasing temperature.Chemistry, PhysicalSCI(E)EI0ARTICLE2-4339-3454
Brewster angle microscopy and capillary wave spectroscopy as a means of studying polymer films at liquid/liquid interfaces
No full textDe-mixing dynamics of a binary liquid system in a controlled-pore glass
No full textHellweg T, Schemmel S, Rother G, Brulet A, Eckerlebe H, Findenegg GH. De-mixing dynamics of a binary liquid system in a controlled-pore glass. The European Physical Journal E. 2003;12:1-4.The temperature-induced microphase separation of the binary liquid system iso-butyric acid+heavy water (iBA + D2O) in a mesoporous silica glass (CPG-10-75) of nominal pore width 7.5 nm was investigated by neutron spin-echo spectroscopy (NSE) and neutron small-angle scattering (SANS). Two mixtures of different composition were studied at different scattering angles at temperatures above and below the bulk phase transition temperature. The phase separation in the pore space is found to occur at a lower temperature than the bulk transition and extends over a significant temperature range. The effective diffusion coefficient derived from NSE at low scattering angles is found to decrease by one order of magnitude from 70 C-circle to 20 C-circle. This observation is attributed to the growing size of concentration fluctuations having a cut-off at ca. 8 nm, which corresponds to the mean pore size. The dynamics of the concentration fluctuations appears to be strongly influenced by the confinement in the pores, as it differs strongly from the bulk behaviour. These results are consistent with the preliminary results of the SANS study
Neutron diffraction and NMR relaxation studies of structural variation and phase transformations for water/ice in SBA-15 silica: I. The over-filled case
No full textNeutron diffraction and NMR relaxation measurements have been made of water/ice in SBA-15, a mesoporous silica constituting an ordered array of cylindrical mesopores of pore diameter similar to 86 angstrom, over the temperature range 180-300 K in a cooling and heating cycle. The over-filled sample shows the initial formation of hexagonal ice on the outside of the silica grains, followed by the nucleation of cubic ice inside the pores at a lower temperature. Neutron scattering profiles for the cubic ice peaks are significantly broadened and indicate a defective structure, as observed in previous experiments on ice formation in sol-gel and MCM-type silicas. Below the pore freezing temperature the intensity of the cubic ice peaks exhibit a significant increase, down to the lowest experimental temperature, indicating a reversible conversion of defective ice to ordered ice crystals. The peak profile analysis for the two ice patterns indicates a systematic variation in the position as a function of temperature, giving values of the expansion coefficients that are slightly lower than other measurements for the bulk phase. NMR results on proton relaxation as a function of temperature indicate the presence of a mobile phase for temperatures below pore freezing that supports the view that there is interconversion between brittle and plastic phases of ice
Thickness of adsorbed nitrogen films in SBA 15 silica from small angle neutron diffraction
No full textAdsorption of non-ionic surfactants from aqueous solutions on graphite: adsorption isotherms and calorimetric enthalpies of displacement for C8E4 and related compounds
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