PubMed · 9345637
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1997. Biophysical methods.. https://doi.org/10.1016/s0959-440x(97)80090-5
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Chain-chain interactions in a corona of polymers tethered to a spherical core under good solvent conditions are studied using Monte Carlo simulations. The total scattering function of the corona as well as different partial contributions are sampled. By combining the different contributions in a self-consistent approach, it is demonstrated that the corona can be regarded as a quasi-two-dimensional polymer solution, with a concentration dependence analogous to that of an ordinary polymer solution. Scattering due to the corona profile and density fluctuation correlations are separated in this approach. The osmotic compressibility is extracted from the latter, and it is shown to be a universal function of surface coverage, with some deviations at high coverage due to surface curvature effects.
The physics of soft materials can be investigated using nuclear spin-lattice relaxation, which depends on the spectral densities of motion in the MHz range. For the first time, NMR relaxation has been used to study influences of the acyl length, polar head groups, a cosurfactant, and cholesterol on the viscoelastic properties of membrane lipids. The results imply the concept of elastic deformation is relevant on lengths approximately equal to the bilayer thickness and less, involving a broad spectrum of collective modes which contribute to the forces between lipid bilayers.
We describe the dynamics of three-dimensional fluid vesicles in steady shear flow in the vicinity of a wall. This is analyzed numerically at low Reynolds numbers using a boundary element method. The area-incompressible vesicle exhibits bending elasticity. Forces due to adhesion or gravity oppose the hydrodynamic lift force driving the vesicle away from a wall. We investigate three cases. First, a neutrally buoyant vesicle is placed in the vicinity of a wall that acts only as a geometrical constraint. We find that the lift velocity is linearly proportional to shear rate and decreases with increasing distance between the vesicle and the wall. Second, with a vesicle filled with a denser fluid, we find a stationary hovering state. We present an estimate of the viscous lift force that seems to agree with recent experiments of Lorz et al. [Europhys. Lett. 51, 468 (2000)]. Third, if the wall exerts an additional adhesive force, we investigate the dynamical unbinding transition that occurs at an adhesion strength linearly proportional to the shear rate.