form birefringence

form birefringence

[¦fȯrm ‚bī·ri′frin·jəns]
(optics)
Birefringence of a liquid caused by the orientation of rod-shaped particles in the liquid whose thickness and separation are much smaller than a wavelength of light.
References in periodicals archive ?
1975 Microtubular origin of mitotic spindle form birefringence. Demonstration of the applicability of Wiener's equation.
For form birefringence, the [[DELTA]n.sub.f] of polypropylene [26] was used as this value is not reported for PVA [27].
The total birefringence is due to the crystalline and amorphous phases in addition to a form birefringence (which is generally negligible).
In the case of semicrystalline polymers, the overall residual birefringence ([DELTA]n) is the sum of amorphous ([DELTA][n.sub.a]) and crystalline ([DELTA][n.sub.c]) contributions and form birefringence ([DELTA][n.sub.f]) as [40]
In this research, for simplicity, it is assumed that the contribution of form birefringence ([DELTA][n.sub.f]) and thermal birefringence in the amorphous region ([DELTA][n.sub.a.sup.th]) to the total residual birefringence is neglected.
Otherwise, the SOR was violated due to the contribution of form birefringence in the case of immiscible blends.
where [DELTA][n.sub.i.sup.0] is the intrinsic birefringence of the i-polymer, [[phi].sub.i] is the volume fraction, [f.sub.i] is the orientation function, and [DELTA][n.sub.F] is the form birefringence. The orientation function f can be defined by:
where X is the function crystallinity, [DELTA][n.sub.am] and [DELTA][n.sub.c] are the amorphous and crystalline birefringences, and we neglect form birefringence (24).
The measured birefringence of an oriented semicrystalline polymer can arise from three contributions- molecular orientation plus form birefringence and distortion birefringence (14).
where [Delta]n is the birefringence measured, X crystalline fraction, [f.sub.c] crystalline orientation factor, [[[Delta].sub.c].sup.0] intrinsic birefringence for crystalline phase, [[[Delta].sub.am].sup.0] for amorphous phase and the form birefringence [Delta][[n.sub.form].sup.0].
Ohkoshi and Nagura (28) have suggested that the difference may come from the contribution of form birefringence and trans conformations in the amorphous phase.