Birefringence magnetic

When a magnetic field H is applied in the isotropic phase, the free energy per mole is written as 

As the magnetic birefringence is given by Anj =Cla(T-T ), where C is directly proportional to the ratio is 

A magnetic field can orient the polymer and thus cause birefringence. According to eqn (8.83), the anisotropic part of the refiractive index is written as 

Let (and Xi) the magnetic susceptibility of the polymer parallel (and perpendicular) to the magnetic field. In the presence of the magnetic field H, such a polymer feels the potential (see eqn (8.81)) 

For a weak magnetic field, eqn (10.68) gives, to the lowest order of H, 

Thus not only the relaxation time r but also the steady-state value Szz(°°) diverge as v approaches v. The magnetic birefringence in rodlike 

The pretransitional effect can be also observed by viscoelasticity. Firstly we derive the constitutive equation from the kinetic equation. Again, eqn (10.39) in the presence of the velocity gradient k is rewritten to give a kinetic equation for (see eqn (8.149))  

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The rotational diffusion coefficient Dr of a rodlike polymer in isotropic solutions can be measured by electric, flow, and magnetic birefringence, dynamic light scattering, and dielectric dispersion. However, if the polymer has some flexibility, its internal motion makes it difficult to extract Dr for the end-over-end rotation of the chain from data of these measurements. In other words, Dr can be measured only for nearly rodlike polymers. 

Single-bilayer dihexadecyl phosphate (DHP) vesicles Magnetite particles prepared in situ in vesicles, from Fe2+/Fe3+ and OH Particles were characterized by magnetic birefringence 790... 

Magnetic birefringance (Cotton-Mounton effect) and electric birefringance (Kerr effect) of nitrobenzene, p-dinitrobenzene and 1,3.5-trinitrobcnzene was... 

Lewis BA et al (1985) Magnetic birefringence studies of dilute purple membrane suspensions. Biophys 147(2) 143-150... 

This effect is related to the Cotton-Mouton effect of magnetic birefringence. 

Fig. 2.5.1. Magnetic birefringence in the isotropic phase of PAA the horizontal dashed line gives the value for nitrobenzene at 22.5 °C. (After Zadoc-Kahn. " )...

Fig. 2.5.3. The electric birefringence (Tsvetkov and Ryumtsev," open circles) and the reciprocal of the magnetic birefringence (Zadoc-Kahn," full circles) in the isotropic phase of PAA versus temperature. The lines represent the theoretical...

If) = 0, A e given by (2.5.14) varies essentially as T— In such materials, the electric and magnetic birefringence may be expected to exhibit the same type of behaviour over a wide temperature range. Measurements" on pure samples of hexylcyanobiphenyl, a nematogen... 

We find an increase in the transition temperature linear in Ve, and a continuous second order transition above a certain critical external field. The external field can cause ordering in the isotropic phase (fig. 5), As an application, the magnetic birefringence in a isotropic liquid crystalline polymer melt has been calculated and good agreement with measurements of Haret is found. 

Secondly, due to the large molecular anisotropy, rodlike polymers are much more easily oriented by an external field and show large birefringence. This enables us to use electric or magnetic birefringence as a practical tool to study the rotational motion of these polymers. ... 

DNA is the most studied example of semiflexible polyelectro-lytes. The effect of salt concentration on conformational properties of DNA was studied by light scattering, force-extension experiments, transient electric birefringence, magnetic birefringence, ... 

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