Translational diffiision

Takahara S, Sumiyama N, Kittaka S, Yamaguchi T, Belfissent-Fimel M-C. (2005) Neutron scattering study on dynamics of water molecules in MCM-41. 2. Determination of translational diffiision coefficient./P/tyr ChemB 109 11231-11239. 

Laser Photolysis. In most donor-acceptor compounds, the rate of the photoinduced forward ET is faster than the translational diffiision of a dilute electrolyte. Therefore, it can be assumed that in the absence of pre-association with the ground state of the probe, the free charge-separated species is formed... 

In liquids, one of the most celebrated equations that connects the microscopic dynamics of molecules with thermodynamics is the Adam-Gibbs relation. This relates the translational diffiisivity of the system to configurational entropy as follows ... 

Here is the translational diffiisivity. Sc is the configurational entropy, and A and C are temperature-independent constants. This beautiful relation between dynamics and thermodynamics has been used extensively to understand the... 

The translational diffiision coefficient in Eq. 11 can in principle be measured from boimdary spreading as manifested for example in the width of the g (s) profiles although for monodisperse proteins this works well, for polysaccharides interpretation is seriously comphcated by broadening through polydispersity. Instead special cells can be used which allow for the formation of an artificial boimdary whose diffusion can be recorded with time at low speed ( 3000 rev/min). This procedure has been successfully employed for example in a recent study on heparin fractions [5]. Dynamic fight scattering has been used as a popular alternative, and a good demonstra-... 

The diffusive translation of molecules has been extensively investigated in a number of molecular crystals. When the diffusing molecules are identical to the molecules of the crystal, one terms this motion self diffiision. Microscopically, it consists of a hopping motion of a molecule from its original lattice site to a neighbouring vacancy (see Chap. 4). For diffusion and self diffusion to take place at all, there must therefore be vacancies present in the lattice. They can either be attached to dislocations or small-angle grain boundaries, or they can be thermally activated. 

The presence of solutions (cpi < cpcr ) in the area of flat maximum on the curve of dependence Dv on cpi is determined by the competition of two factors on the one hand, it is the increase of amenability of matrix during dissolution of oligomer in it (as the consequence of plasticization). It results in decrease of resistibility of diffusion environment and in the growth of the diffusion rate correspondingly. On the other hand, thermodynamic non-ideality of solutions, caused by aggregation of diffiisant molecules, becomes stronger at spontaneous mixture of components. This evidently reduces the speed of translational diffusion. Therefore, the character of concentration dependence Dv for every... 

---