Morphology of polyacrylonitrile

Abstract

rhe present investigation revealed that the features like : single crystals, twin crystals, hedrites and spherulites could be grown by changing the concentration or temperature of crystallization of polyacrylonitrile (PAN) from its solution in propylene carbonate and following the technique of film-formation method of crystallization. Different stages of growth have been also reported. The well defined single crystals of PAN could be grown in the temperature range of 105 to 150°C, even from the dilute solution. Single crystals of PAN could be also grown from comentrated solution (> 2.5 yo) a t higher temperature. Formation of spherulites from sheaf and hedrites has been achieved by increasing the concentration of the polymer solution. Lamellar thickness is found to increase with crystallization temper.ature.The potentiality of the film-formation technique is that it provides an extended ran,qe of concentration and temperature not only for the kinetic study but also for the growth of single crystals from polymer solutions. ZUSAMMENFASSUNG :Durch h d e r u n g von Konzentration oder Temperatur bei der Kristallisation von Polyacrylnitril aus Losung in Propylen-carbonat durch die Filmbildungsmethode konnenje nach den Bedingungenbevorzugt Einkristalle, Zwillingskristalle, Hedrithe und Sphiirolite erhalten werden. Einkristalle entstehen im Bereicb von 105 bis 150°C aus verdiinnter Losung und aus konzentrierter Losung (> 2,5 yo) bei hoherer Temperatur. Durch Zunahme der Polymerkonzentration wircl die Bildung von Garbensphiiroliten und Hedrithen erreicht. Die Lamellendicke wiichst mit der Kristallisationstemperatur an.Der Vorteil der Filmbildungstechnik liegt darin, da13 sie einen weiten Konzentratiions-und Temperaturbereich anbietet, der nicht nur fur kinetische Untersuchungen, sondern auch fur das Wachstum von Einkristallen aus der Polymerlosung geeignet ist.

Crystallization of polyacrylonitrile: Growth mechanisms for various growth features

“…The spherulites had negative and zero birefringence. Gohil et al (2) have reported non birefringence spherulites and other growth features (3,4) grown from propylene carbonate solution of PAN. Several growth stages of spherulites developing from sheaf and hedrites were reported (2,4).…”

Electron microscopic studies of SBS block copolymers I. A method to study the temperature dependence of phase separation

“…After removal of the glass slide from the solution, it is kept for a period of 0.5 to 2 h in the atmosphere of solvent vapor. Pertinent features of this method for studying the semicrystalline polymers have been previously discussed [11][12][13][14][15][16][17][18].…”

“…The "Film Formation Method of Crystal Growth", developed in our laboratory [11][12][13][14][15][16][17][18], provides a means of preparing thin films with uniform thicknesses. A schematic representation of the device used is shown in Figure 1.…”

Etching and the morphology of branched and cross-linked polyethylene

“…1-3) is brought about by the structural heterogeneity of polymer chains, which may be the consequence of enhanced nuclei density. This type of transition in the supermolecular structure is usually achieved by varying the polymer concentrations in solutions [1].…”

“…It is relatively easy to characterize the morphology in thin fdms with electron diffraction, surface replication, phase contrast and darkfield electron microscopic techniques [1][2][3][4]. Several other methods have been developed to increase the contrast of an amorphous phase in thin fdms of polymers [5,6].…”