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X-ray scattering and magnetic birefringence studies of aqueous solutions of chromonic molecular aggregates.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	X-ray scattering and magnetic birefringence studies of aqueous solutions of chromonic molecular aggregates./
作者:	Luoma, Robert J.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 1995,
面頁冊數:	119 p.
附註:	Source: Dissertations Abstracts International, Volume: 56-11, Section: B.
Contained By:	Dissertations Abstracts International56-11B.
標題:	Molecules. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9518298
ISBN:	9798208736005

X-ray scattering and magnetic birefringence studies of aqueous solutions of chromonic molecular aggregates.
Luoma, Robert J.

X-ray scattering and magnetic birefringence studies of aqueous solutions of chromonic molecular aggregates. - Ann Arbor : ProQuest Dissertations & Theses, 1995 - 119 p.

Source: Dissertations Abstracts International, Volume: 56-11, Section: B.

Thesis (Ph.D.)--Brandeis University, 1995.

This item must not be sold to any third party vendors.

In aqueous chromonic mesogens, flat molecules of ring systems with highly water-soluble side groups stack to form long rods. At sufficiently high concentrations, these rods interfere with each other to form liquid crystals. To study the growth of the stacks, I used magnetically induced birefringence and X-ray diffraction on aqueous chromonic solutions of disodium cromoglycate and Sunset Yellow FCF. I compared the data against the results of computer models. In the isotropic phase, the solutions of Sunset Yellow FCF showed a change in the magnetically induced birefringence with volume fraction that could be explained by a combination of the effects of a divergence due to the phase transition and an average stack size that grew as the square root of the concentration. In the nematic phase, the x-ray patterns of Sunset Yellow FCF solutions showed two equatorial nematic peaks, two meridian peaks and several diffuse features. Except near the phase transition, the meridian peak thickness along the director showed no significant variation; the meridian peak thickness near the phase transition was consistent with the average stack size found in the isotropic phase. At high concentrations, the nematic peaks had angular widths narrower than the angular disorder found from the meridian peaks. The magnetically induced birefringence studies of disodium cromoglycate showed a discontinuous behavior in the isotropic phase. A simple aggregation model indicated that, below a critical concentration, the solution contained mostly monomers, but, once a certain threshold was exceeded, large stacks quickly grew. The phase transition seemed to depend strongly on the onset of large stack formation. In both systems, for the observed mean lengths, the isotropic-nematic phase transition occured at a volume fraction that was about an order of magnitude lower than the monodisperse hard-rod predictions of the Onsager theory but similar to predictions of some theoretical models of polydisperse systems.

ISBN: 9798208736005Subjects--Topical Terms:

592642
Molecules.

X-ray scattering and magnetic birefringence studies of aqueous solutions of chromonic molecular aggregates.
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500 $a Source: Dissertations Abstracts International, Volume: 56-11, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
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506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a In aqueous chromonic mesogens, flat molecules of ring systems with highly water-soluble side groups stack to form long rods. At sufficiently high concentrations, these rods interfere with each other to form liquid crystals. To study the growth of the stacks, I used magnetically induced birefringence and X-ray diffraction on aqueous chromonic solutions of disodium cromoglycate and Sunset Yellow FCF. I compared the data against the results of computer models. In the isotropic phase, the solutions of Sunset Yellow FCF showed a change in the magnetically induced birefringence with volume fraction that could be explained by a combination of the effects of a divergence due to the phase transition and an average stack size that grew as the square root of the concentration. In the nematic phase, the x-ray patterns of Sunset Yellow FCF solutions showed two equatorial nematic peaks, two meridian peaks and several diffuse features. Except near the phase transition, the meridian peak thickness along the director showed no significant variation; the meridian peak thickness near the phase transition was consistent with the average stack size found in the isotropic phase. At high concentrations, the nematic peaks had angular widths narrower than the angular disorder found from the meridian peaks. The magnetically induced birefringence studies of disodium cromoglycate showed a discontinuous behavior in the isotropic phase. A simple aggregation model indicated that, below a critical concentration, the solution contained mostly monomers, but, once a certain threshold was exceeded, large stacks quickly grew. The phase transition seemed to depend strongly on the onset of large stack formation. In both systems, for the observed mean lengths, the isotropic-nematic phase transition occured at a volume fraction that was about an order of magnitude lower than the monodisperse hard-rod predictions of the Onsager theory but similar to predictions of some theoretical models of polydisperse systems.
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