Abstract: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, … Show more
“…Comparing the results of Eq. (12) with the existing experimental data [26], we find that the present results are in good agreement with the experimental results (Fig. 2).…”
Section: Model Of Undulation Forcesupporting
confidence: 92%
“…He asserted that the undulation force essentially varies with c −3 , where c is the separation between neighboring membranes [20]. Although some assumptions and simplifications were introduced in Helfrich's investigations [20,21], his results were still supported by succeeding studies, including theoretical [1,[22][23][24][25] and experimental work [11,26], as well as computational simulations [27,28]. Recently, Freund [29] reexamined the entropic force under conditions in which some of Helfrich's assumptions [20] were abandoned.…”
Undulation force, an entropic force, stems from thermally excited fluctuations, and plays a key role in the essential interactions between neighboring surfaces of objects. Although the characteristics of the undulation force have been widely studied theoretically and experimentally, the distance dependence of the force, which constitutes its most fundamental characteristic, remains poorly understood. In this paper, first, we obtain a novel expression for the undulation force by employing elasticity and statistical mechanics and prove it to be in good agreement with existing experimental results. Second, we clearly demonstrate that the two representative forms of the undulation force proposed by Helfrich and Freund were respectively the upper and lower bounds of the present expression when the separation between membranes is sufficiently small, which was intrinsically different from the existing results where Helfrich's and Freund's forms of the undulation force were only suitable for the intermediate and small separations. The investigations show that only in a sufficiently small separation does Helfrich's result stand for the undulation force with a large wave number and Freund's result express the force with a small wave number. Finally, a critical acting distance of the undulation force, beyond which the entropic force will rapidly decay approaching zero, is presented.
“…Comparing the results of Eq. (12) with the existing experimental data [26], we find that the present results are in good agreement with the experimental results (Fig. 2).…”
Section: Model Of Undulation Forcesupporting
confidence: 92%
“…He asserted that the undulation force essentially varies with c −3 , where c is the separation between neighboring membranes [20]. Although some assumptions and simplifications were introduced in Helfrich's investigations [20,21], his results were still supported by succeeding studies, including theoretical [1,[22][23][24][25] and experimental work [11,26], as well as computational simulations [27,28]. Recently, Freund [29] reexamined the entropic force under conditions in which some of Helfrich's assumptions [20] were abandoned.…”
Undulation force, an entropic force, stems from thermally excited fluctuations, and plays a key role in the essential interactions between neighboring surfaces of objects. Although the characteristics of the undulation force have been widely studied theoretically and experimentally, the distance dependence of the force, which constitutes its most fundamental characteristic, remains poorly understood. In this paper, first, we obtain a novel expression for the undulation force by employing elasticity and statistical mechanics and prove it to be in good agreement with existing experimental results. Second, we clearly demonstrate that the two representative forms of the undulation force proposed by Helfrich and Freund were respectively the upper and lower bounds of the present expression when the separation between membranes is sufficiently small, which was intrinsically different from the existing results where Helfrich's and Freund's forms of the undulation force were only suitable for the intermediate and small separations. The investigations show that only in a sufficiently small separation does Helfrich's result stand for the undulation force with a large wave number and Freund's result express the force with a small wave number. Finally, a critical acting distance of the undulation force, beyond which the entropic force will rapidly decay approaching zero, is presented.
“…e . 16 , and with ( iii ) a low enough value of the membrane lateral tension.Figure 2Typical evolution of a C 10 E 3 solution that has experienced shearing during sample preparation. Images are taken from Supplementary Movie M2, during quenching at 30 °C.…”
Section: Resultsmentioning
confidence: 99%
“…In the W + L α two phase region, the lamellar phase can often be fragmented into unilamellar vesicles 15 . The bending rigidity of the C 10 E 3 bilayer was determined to be 5 k B T at room temperature 16 . Vesicles, lamellar phase and sponge phase represent different topologies of the bilayer.…”
The lamellar-to-sponge phase transition of fluorescently labelled large unilamellar vesicles (LUVs) of the non-ionic surfactant triethylene glycol mono n-decyl ether (C10E3) was investigated in situ by confocal laser scanning microscopy (CLSM). Stable dispersions of micrometer-sized C10E3 LUVs were prepared at 20 °C and quickly heated at different temperatures close to the lamellar-to-sponge phase transition temperature. Phase transition of the strongly fluctuating individual vesicles into micrometre-sized sponge phase droplets was observed to occur via manyfold multilamellar morphologies with increasing membrane confinement through inter- and intra- lamellar fusion. The very low bending rigidity and lateral tension of the C10E3 bilayer were supported by quantitative image analysis of a stable fluctuating membrane using both flicker noise spectroscopy and spatial autocorrelation function.
“…24,27,49,50 Despite the fact that these NMR and MRI methods have been extensively used for investigating macroscopic domain alignment in liquid crystals, 8,9,14,15,18,19,21,23,24,26,27,40,44,[49][50][51][52][53][54][55] there are so far no reported studies where the full order tensor has been mapped with spatial resolution. In principle, such tensor maps could be obtained by acquiring spatially resolved 2 H spectra 24,27,[55][56][57] for multiple orientations of the main magnetic field. 58 Unfortunately, such an experimental approach would require combinations of NMR hardware that are exceedingly rare.…”
The macroscopic physical properties of a liquid crystalline material depend on both the properties of the individual crystallites and the details of their spatial arrangement. We propose a diffusion MRI method to estimate the director orientations of a lyotropic liquid crystal as a spatially resolved field of Saupe order tensors. The method relies on varying the shape of the diffusion-encoding tensor to disentangle the effects of voxel-scale director orientational order and the local diffusion anisotropy of the solvent. Proof-of-concept experiments are performed on water in lamellar and reverse hexagonal liquid crystalline systems with intricate patterns of director orientations.
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