We derive the complete set of macroscopic dynamic equations for ferrogels under an external magnetic field, including the magnetization as an independent dynamic degree of freedom. The magnetoelasticity comes in the form of magnetostriction and through the magnetic part of the Maxwell stress. Various dynamic couplings of the elastic degree of freedom with the magnetization and the magnetic field are found. We discuss static elongation, shear deformations, and the modified sound spectrum in the presence of an external magnetic field.
Transient 1-2 plane small-angle x-ray scattering measurements of micellar orientation in aligning and tumbling nematic surfactant solutions Steady and transient rheological behavior of mesophase pitches J. Rheol. 42, 781 (1998); 10.1122/1.550912 X-ray scattering investigation of highly concentrated poly(benzyl glutamate) solutions under shear flow
We derive hydrodynamic equations for nematic ferrofluids (ferronematics) in the limit that the magnetic degree of freedom has relaxed to its equilibrium value. We concentrate on novel dynamic effects linear in the magnetic field. We show that flow alignment, heat conduction, diffusion, thermodiffusion, viscosity and director reorientation are all modified by the presence of an external field. In particular, the new effects describe reversible (irreversible) couplings, where the conventional effects are irreversible (reversible). We discuss, how these effects can be measured. In principle, this description is applicable to conventional nematics, too, although huge magnetic fields are expected to be necessary for detecting the new effects in this case. PACS. 61.30.-v Liquid crystals -75.50.Mm Magnetic liquids -05.70.Ln Nonequilibrium irreversible thermodynamics
A mean-field theory of globules of random amphiphilic copolymers in selective solvents is developed for the case of an annealed copolymer sequence: each unit can be in one of two states, H (insoluble) or P (soluble or less insoluble). The study is focussed on the regime when H and P units tend to form long blocks, and when P units dominate in the dilute phase, but are rare in the globule core. A first-order coil-to-globule transition is predicted at some T = T(cg). The globule core density at the transition point increases as the affinity of P units to the solvent, epsilon, is increased. Two collapse transitions, coil --> "loose" globule and "loose" globule --> "dense" globule, are predicted if epsilon is high enough and P units are marginally soluble or weakly insoluble. H and P concentration profiles near the globule surface are obtained and analyzed in detail. It is shown that the surface excess of P units rises as epsilon is increased. The surface tension decreases in parallel. Considering the interaction between close enough surfaces of two globules, we show that they always attract each other at a complete equilibrium. It is pointed out, however, that such equilibrium may be difficult to reach, so that partially equilibrium structures (defined by the condition that a chain forming one globule does not penetrate into the core of the other globule) are relevant. It is shown that at such partial equilibrium the interaction is repulsive, so the globules may be stabilized from aggregation. The strongest repulsion is predicted at the coil-to-globule transition point T(cg): the repulsion force decreases with the distance between the surfaces according to a power law. In the general case (apart from T(cg)) the force vs. distance decay becomes exponential; the decay length xi diverges as T --> T(cg). The developed theory explains certain anomalous properties observed for globules of amphiphilic homopolymers.
We present a theory for the reverse analysis on the sequence information of a single H/P two-letter random hetero-polymer (RHP) from its force-extension (f − z) curves during quasi static stretching. Upon stretching of a self-assembled RHP, it undergoes several structural transitions. The typical elastic response of a heteropolymeric globule is a set of overlapping saw-tooth patterns. With consideration of the height and the position of the overlapping saw-tooth shape, we analyze the possibility of extracting the binding energies of the internal domains and the corresponding block sizes of the contributing conformations.
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