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The size of the anisotropic domains in a lyotropic liquid crystal is estimated using a new protocol for diffusion NMR. Echo attenuation decays are recorded for different durations of the displacement-encoding gradient pulses, while keeping the effective diffusion time and the range of the wave vectors constant. Deviations between the sets of data appear if there are non-Gaussian diffusion processes occurring on the time-scale defined by the gradient pulse duration and the length-scale defined by the wave vector. The homogeneous length-scale is defined as the minimum length-scale for which the diffusion appears to be Gaussian. Simulations are performed to show that spatial variation of the director orientation in an otherwise homogeneous system is sufficient to induce non-Gaussian diffusion. The method is demonstrated by numerical solutions of the Bloch-Torrey equation and experiments on a range of lamellar liquid crystals with different domain sizes.

We present a novel method for measuring interbilayer forces in lamellar liquid crystals of amphiphilewater systems. In a centrifuge the gravitational effect is easily strong enough to produce clearly observable concentration gradients. During the experiment the concentration profile in the test-tube is monitored using NMR imaging of the deuterium quadrupole splitting in the lamellar phase, by temporarily transferring the sample into a NMR spectrometer. We also present a theoretical analysis of the experiment, where interactions dominate over entropy of mixing effects. For a system at sedimentation equilibrium one obtains a direct measurement of the interbilayer force, or equivalently chemical potential of the components over a substantial concentration range. It requires long times to obtain equilibrium in the centrifuge but very useful information about equilibrium and dynamic parameters is also obtained through an analysis of the sedimentation process. Experiments were performed on samples of a dilute lamellar phase of the non-ionic surfactant C 10 E 3 . After a few days of centrifugation a consistent concentration pattern was observed. At the bottom of the sample there appears a pure water-phase. The concentration profiles stabilize after a long centrifugation time. If they are related to the phase boundary the different profiles superimpose. This observation is consistent with the theory and the observation allows for a determination of how the chemical potentials vary with composition. The observed profiles are consistent with a dominating undulation force with a bilayer bending rigidity of 4.8-5.1 kT.

An improved method to validate the relative humidity generation in sorption balancesWadsö, Lars; Anderberg, Anders; Åslund, Ingrid; Söderman, Olle General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractSorption balances are instruments in which samples are weighed as they are exposed to a programmed relative humidity (RH). Such instruments are used to measure sorption isotherms and to study solid-vapour interaction. There are different methods to validate the performance of the RH generation in such instruments by charging them with saturated salt solutions and ramping/stepping the RH past the deliquescence RH of the salts. In this paper an improved approach to perform validation is presented where the RH is kept stepwise constant at a quasirandomly chosen set of RH-values above and below the deliquescence RH. From the rates of Wadsö and Anderberg "An improved method to validate the relative humidity..." 2/29 change of mass as a function of RH it is possible to calculate the RH at which deliquescence takes place. This alternative method gives similar results as the slow ramp method, but is less sensitive to disturbances and less time consuming.