ISSN:
0021-9304
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Medicine
,
Technology
Notes:
1. With the help of ionotropic gels it is possible to duplicate native structures consisting of two materials, one of them the matrix. 2. Counter-ions combined with the ionic groups on the ordered polyelectrolytes can be exchanged. With certain counter-ions an insoluble, crystalline precipitate is formed immediately after the ion-exchange process as an ordered reaction product, i.e., nucleation. 3. Ionotropic gels were crosslinked through the secondary hydroxyl groups (uronic acid residuals) in such a way that the rate of ion exchange was only slightly lower, that no great shrinkage resulted, and that the pores remained free of extraneous polymers. 4. The microscopic structure of ionotropic gels can be divided into (a) a part with secondary structure with micellar particles and hollow pores and (b) a part with tertiary structure with lamellae and isopores. 5. On crystallization in shrunken gels the crystals enter into the tertiary structure - both intracapillary as well as interlamellar - due to spatial reasons. 6. Through control of the shrinkage of the gels, one can regulate the way in which the ordered crystals enter into the two structures. 7. One can change the size of the crystallites by variation of the degree of crosslinking. The higher the degree of crosslinking, the smaller the crystallite. 8. By treatment with waves of ions one can increase the solid content of the gel to values from 50 to 70%. One obtains gels with a mechanical strength like that of bones, teeth, shells, or pearls. The phenomenon of intramicellar crystallization is reversible. Monovalent counter-ions, as well as H-ions, dissolve and extract the included secondary substance. One then obtains the original crosslinked gel. 10. The gel has always to be formed first. Without the ordered base structure (matrix) one obtains unordered crystallites such as occur in the chalklike fields of the pearl shells.
Additional Material:
14 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jbm.820010204
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