✍ Scribed by Ingo Lieberwirth; Joachim Loos; Jürgen Petermann; Andrew Keller
No coin nor oath required. For personal study only.
Thin films of isotactic polystyrene (iPS) were deformed on a carbon supported TEM grid at temperatures between 210 °C and 240 °C. The elongation of the supercooled polymer melt films is localized in a deformation zone due to the formation of cracks within the brittle carbon support film, whereas the adjoining areas stay in a relaxed state. Since the nucleation of fibrous ("shish") crystals needs an orientation mechanism to align the molecular chains, their origin is located in the deformation zone. It is shown that the subsequent growth of the shish crystal can propagate into the relaxed melt although it has to surmount the adhesion to the carbon substrate. From these results the conclusion is drawn that the shish crystal growth 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.
📜 SIMILAR VOLUMES
## Abstract For Abstract see ChemInform Abstract in Full Text.
## On the Mechanism of Crystal Growth from Undercooled Melts The mechanism of crystal growth from undercooled melts is studied experimentally by means of a simple capillary technique. Thymol and Na&&O,. 5 H,O are used as model substanc,es. Dislocation-free crystal faces of these compounds are obta
Techniques of containlerless processing are applied to undercool and solidify metals and alloys. These techniques allow direct measurements of crystal growth velocity as a function of undercooling. Experimental results are presented for pure Ni, dilute Ni-B alloys, and intermetallic compounds of FeS