Model Of Smectic Research Articles

Thermal Fluctuations of Oriented Lipid Membranes by Nonspecular Neutron Reflectometry

We present a novel method to measure and to analyze lipid bilayer fluctuations based on time-of-flight nonspecular neutron reflectivity (TOF-NSNR). To validate this approach, we compare the results obtained on the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) to NSNR data collected in the conventional monochromatic mode. For the DMPC model system in its fluid Lα phase, we determine the fluctuation spectrum of an averaged bilayer in an oriented multilamellar stack and compare the result to the predictions of the linearized smectic free energy functional. In particular, we show how the smectic penetration depth Λ can be determined from the measurements. Furthermore, significant changes in the fluctuation spectrum of DMPC are observed upon the interaction with the antimicrobial peptide magainin 2 and cannot be explained by the smectic model.

Self-organization in nanoscopic poly(alkylthiophene) films on water

Ultra-thin layers (10 - 50nm) of poly(alkyl)thiophenes (PATs) spread on water from diluted chloroform solutions were studied by means of synchrotron radiation. The molecular orientation in the films was obtained using grazing incidence diffraction (GID) and reflectometry, for both doped and pristine samples. Despite alkanes being hydrophobic, the side chains tend to orient perpendicularly to the water subphase. The study reveals the presence of crystalline order with a high degree of preferred orientation. A smectic model for the polymeric layers is in good agreement with the experimental data.

Smectic model for liquid films on solid surfaces. Part 1.—Application to monolayer boundary lubrication

A qualitative theory of films of hydrocarbon solutions of fatty acids described in a previous publication correlates many experimental data. According to this theory the fatty acid molecules and solvent molecules are arranged in layered structures similar to those in smectic mesophases. A simplified method for calculating the attractive energy between two such layers is described. The fatty acid molecules are assumed to behave as hard rods of constant electric polarizability and diamagnetic susceptibility. A potential describing the interaction between two rods is derived and used in a lattice sum calculation to compute the total energy of interaction of two layers as a function of average separation of molecules within a layer, relative position of the two layers and the distance between layers. Calculation of frictional force and coefficient of friction by means of this model show good agreement with a similar calculation of Cameron if the proper assumption about the relative magnitude of energy as a function of relative position is made.