Observation of shish crystal growth into nondeformed melts

Thin films of isotactic polystyrene (iPS) were deformed on a carbon support ed TEM grid at temperatures between 210 degrees C and 240 degrees C. The el ongation of the supercooled polymer melt films is localized in a deformatio n zone due to the formation of cracks within the brittle carbon support fil m, whereas the adjoining areas stay in a relaxed state. Since the nucleatio n of fibrous ("shish") crystals needs an orientation mechanism to align the molecular chains, their origin is located in the deformation zone. It is s hown that the subsequent growth of the shish crystal can propagate into the relaxed melt although it has to surmount the adhesion to the carbon substr ate. From these results the conclusion is drawn that the shish crystal grow th can be an autocatalytic process, which induces a self-orientation of the molecules in the growth front of the crystal tip and does not necessarily need an external flow field. (C) 2000 John Wiley & Sons, Inc.