id summary reporter owner description type status priority milestone component resolution keywords cc workpackage
1066 Add Maier-Saupe type orientational distribution smk78 "On testing 4.2 beta User Matt Helgeson expressed dismay that the functional forms for orientational distributions were still the same as those for polydispersity. The issue being that the current distributions (Gaussian, log-normal, etc) are all unphysical for orientaional purposes because they are not periodic. And the array function is ''mostly useless...since fitting routines cannot change entries in the input array''.
@butler asked what distributions would be appropriate.
Matt replied ''In our experience, the anisotropy/orientation distribution from almost every elongated object we've measured (WLMs, polymers, rodlike particles) follows a Maier-Saupe type distribution. The general functional form involves exponentials of Legendre polynomials. I've attached a couple papers that go into various levels of sophistication in this regard. Eqn. 1 of Picken et al. (Macromolecules 1990) shows the basic functional form that tends to work for elongated systems which show two-fold symmetry. This can be generalized to n-fold symmetry, as in Bhattacharjee et al. (Molecular Physics 1981) eqn. 2.''
''There are also much more rheologically consistent models that one can achieve by solving the Smoluchowski equation in various situations. For example, for shear flow, some of this was actually worked out by Norm Wagner and Lynn Walker during Lynn's Ph.D. (Macromolecules 1994). However, for a simple functional form for fitting, the Maier-Saupe type equations seem to work pretty well.''
" defect new major SasView 4.3.0 SasView SasView GUI Enhancements