NEGATIVE-PRESSURE EFFECTS DURING THE ISOTHERMAL CRYSTALLIZATION OF ISOTACTIC POLY(PROPYLENE) STUDIED BY LIGHT AND ATOMIC-FORCE MICROSCOPY

The formation of holes during the late stage of the isothermal crystal lization in thin films of isotactic poly(propylene) between two cover glasses was observed by light microscopy and atomic force microscopy. This behavior can be described consistently by the well-known negative pressure effect. Light microscopy reveals the simultaneous and sudden occurrence of a large number of small holes at the liquid-solid inter face after the liquid in front of the spherulites is completely confin ed by other spherulites for a certain time interval. In exceptional ca ses only a few holes appear and finally large cavities are formed. Ato mic force microscopy measurements carried out in the height mode are a ble to prove the hole formation in front of the spherulites. Furthermo re, a substantial thinning of the two-dimensional spherulites in thin films can be observed prior to the hole formation.