The influence of external stress on the hydrothermal and chemical contraction of native collagen was investigated. The coincidence of isometric and isotonic data was observed. This permits the consideration of the isometric curve from the beginning of contraction to the critical point as a phase diagram of the system in coordinates of stress temperature. The existence of a certain critical tension and a corresponding critical temperature or of a critical tension and critical KCNS concentration is suggested. This result is in accordance with the predictions of the theory of order-disorder transitions in these unidimensional systems. Using the formulas of this theory we calculated the enthalpy of the hydrothermal contraction of collagen, the enrichment of salt for its chemical contraction and the cooperativity parameters for both processes.
SynopsisIt is shown in the c a s e of poly-2,2'-0ctamethylene-5,5'-dibenzimidazole that polyalkylene dibenzimidazoles can be crystallized. The studies of fibers and films, prepared from formic acid solution, involved different experimental techniques, such as x-ray diffraction, infrared spectroscopy, differential thermal analysis (DTA), and thermogravimetry (TGM). The x-ray patterns reveal that the highly ordered crystallites must be present in the fibers a s well a s in the films, The x-ray data suggest a possible model of chain conformation within crystallites. The heating of films and fibers to temperatures of 120 to 14OOC. (far below the previously reported softening point) brings about amorphization. In the same temperature range is observed a discontinuity in the TGM curve, an endothermic peak in the DTA, and most intense changes in the infrared absorption spectra. The crystalline structure is not restored on cooling and can be obtained again only after treatment with formic acid. The weight losses of fibers and f i l m s on heating accompanied by amorphization are about 15%; nevertheless, thermal degradation seems not to take place, the weight losses of the initial polymer, up to 4OO0C., being less than 2%. All the data presented lead the tentative conclusion that we observed a formation and thermal degeneration of solvated polymer-solvent crystals, a phenomenon up to now not, apparently, observed in ordinary synthetic polymers. The hypothesis explains fully all the pecularities of the poly-2,2'-octamethylene-5,5'-dibenzirnidazole crystallization habit,
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