1,721,506 research outputs found
The Gaussian curvature of the oil-water interface in an isometric bicontinuous microemulsion
No full textSmall-angle neutron scattering (SANS) measurements are made on a three-component isometric (equal volume fractions of water and oil) microemulsion system, composed of AOT/water (0.4% NaCl)/D-octane, in the one-phase channel near the three-phase region at and around the hydrophile-lipophile balance temperature. A previous SANS contrast variation experiment indicated that the microstructure of this type of isometric microemulsion is bicontinuous in water and oil with the surfactant film at the interface having a zero mean curvature. We analyze SANS data taken with an oil-water contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters a, b and c, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function appropriate for the microemulsion system. The model analysis results in good agreement with the intensity data in an absolute scale. We then use the three parameters. so obtained to calculate the average Gaussian curvature of the interface. We discuss the variation of the average Gaussian curvature as a function of the surfactant volume fraction and its implication on the degree of local order of the bicontinuous structure. We also show a 3-D reconstructed morphology of the most disordered microemulsion
Measurements of the curvatures of random surfaces by scattering experiments: the case of bicontinuous microemulsions
No full textA small-angle neutron scattering (SANS) study is made on a three-component isometric (equal volume fractions of water and oil) ionic microemulsion system, composed of AOT/brine/decane. SANS measurements are made as a function of volume fraction of surfactant within the one-phase channel next to the three-phase region at the hydrophile-lipophile balance (HLB) salinity and at a constant temperature. A previous SANS contrast variation experiment indicated that the microstructure of this type of isometric microemulsion at and around the HLB temperature is bicontinuous in water and oil, with a mono-layer of surfactant film situated at the oil-water interface, having zero mean curvature. We analyze SANS data taken with an oil-water contrast in terms of a modified Berk random wave model. We choose a spectral function which is an inverse 8-th order polynomial in wave number k, containing three length scales 1/a, 1/b, and 1/c. The spectral function has finite second and fourth moments. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function for the micro-phase-separated microemulsions. The model shows good agreement with the intensity data;in an absolute scale. We then use the three parameters so obtained to calculate the average square mean curvature and the average Gaussian curvature of the interface. We determine the variation of these curvatures and the underlying spectral functions as a function of the surfactant volume fraction and discuss their implication on the degree of local order of the bicontinuous structure. We also show 3-d morphologies of two of the microemulsions generated by this model
Water confined in MCM-41: a mode coupling theory analysis
No full text""In this paper we analyze molecular dynamics simulation results on supercooled water in a. MCM-41 pore in order to test the mode coupling theory. A layer analysis must be performed for. water in the pore in order to exclude the contribution of water bound to the strongly hydrophilic. surface. Upon supercooling a range of temperatures is reached where the liquid follows the. mode coupling theory. From the power law behavior of the relaxation times extracted from the. Kohlrausch–William–Watts fit to the self-intermediate scattering function, we obtain the. crossover temperature TC and the γ exponent of the theory. The time–temperature superposition. principle is also satisfied. A fit to the von Schweidler law yields a coefficient b from which all. the other parameters of the theory have been calculated. In particular, we obtained the same. value of γ as extracted from the power law fit to the relaxation times, in agreement with the. requirements of the theory. For very low temperatures, the mode coupling theory no longer. holds as hopping processes intervene and water turns its behavior to that of a strong liquid."
Slow dynamics of interfacial water
No full textThe highlights of our recent high-resolution quasi-elastic incoherent neutron: scattering studies of the translational dynamics of water molecules contained in the micropores of Vycor glass and on the surface of a deuterated protein are summarized. The incoherent quasi-elastic spectra from the confined H2O are first analyzed by a confined diffusion model to obtain the elastic incoherent structure factor (EISF), the short-time self-diffusion constant (D), and the probability per unit time for a jump (1/(tau 0)) as functions of the surface coverage and temperature. The effect of the confinement on the slowing down of the translational motion is discussed. An alternative interpretation of the slow dynamics based on a molecular mechanism of a cage effect and an approach to the kinetic glass transition is put forth
A general expression for the maximum force in peeling a tape from a rigid substrate with an initial crack
No full textAssuming a Dugdale cohesive zone, recently a simple Euler beam model has been proposed to understand the transient peeling on an elastic film from a rigid substrate at 90 degrees from the substrate. The model also shows with sufficiently high bending stiffness, a peak force emerges larger than the Rivlin-Kendall steady-state value, scaling with the fourth root of bending stiffness. From the maximum force during peeling, and its steady-state value which is given by the Rivlin-Kendall well-known model, a simultaneous characterisation of the most important cohesive properties (cohesive strength and toughness of the interface) is obtained from a single test. This maximum force eventually saturates at a value which depends on cohesive strength alone. The presence of possibly inevitable initial cracks at the edge of the interface obviously reduces the peak force, and here, we give a simple closed-form approximate solution for this case too
Measurement of interfacial curvatures in micro-phase-separated bicontinuous structures using small-angle neutron scattering
No full textA method for SANS data analysis is proposed which enables one to directly compute the average mean, Gaussian and square mean curvatures of the interface in systems with a micro-phase-separated bicontinuous structure. This method also leads to a Sd reconstruction of the connected internal interface which allows one to visualize the mesoscopic scale morphology of the material, The method has been successfully applied to various bicontinuous structures such as: microemulsions made of surfactant, water and oil, porous silica glasses and phase-separated homopolymer blends. In this lecture, we show examples of analyses of SANS data taken from one-phase bicontinuous microemulsions at the hydrophile-lipophile-balance temperature and a light scattering intensity taken from a symmetric micro-phase-separated polymer blend at the late stage of spinodal decomposition
Measurement and Interpretation of Curvatures of the Oil–Water Interface in Isometric Bicontinuous Microemulsions
No full textA small-angle neutron scattering (SANS) study was carried out on a three-component isometric (equal volume fractions of water and oil) ionic microemulsion system, composed of AOT/brine/decane [AOT= surfactant sodium bis(ethylhexylsufo)succinate]. SANS measurements were made as a function of volume fraction of surfactant within the one-phase channel at the hydrophile–lipophile balance (HLB) salinity and at a constant temperature. We analyzed SANS data taken with oil–water contrast in terms of a modified Berk random wave model. The good agreement of the model with SANS intensity requires a proper form of spectral function. We chose a spectral function which is an inverse eighth-order polynomial in wave number k, containing three length scales 1/a, 1/b and 1/c. The spectral function has finite second and fourth moments. The model shows good agreement with the intensity data in an absolute scale. The three parameters so obtained were then used to calculate the average square mean curvature and the average Gaussian curvature of the interface. The variation of these curvatures and the underlying spectral functions as a function of the surfactant volume fraction were determined and their implications for the degree of local order of the bicontinuous structure are discussed.</jats:p
Mesoscopic scale structures in self-organized surfactant solutions determined by small-angle neutron scattering
No full textA novel procedure for SANS data analysis is described which enables one to use the fitted parameters to compute the average mean. Gaussian and square mean curvatures of the interface in systems which show a micro-phase-separated bicontinuous structure. This procedure also leads to a 3-D reconstruction of the connected internal interface which allows one to visualize the mesoscopic scale morphology of the material. The method has been successfully applied to Various bicontinuous structures such as microemulsions made of surfactant, water and oil, porous silica glasses and phase-separated homopolymer blends. In this lecture, we show examples of analyses of SANS;lata taken from one-phase bicontinuous microemulsions at the hydrophile-lipophile-balance temperature and a light scattering intensity taken from a symmetric micro-phase-separated polymer blend at the late stage of spinodal decomposition. (C) 1998 Elsevier Science Limited. All rights reserved
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