Experimentally determined temperature-concentration phase diagrams of monodisperse alkanes with chains containing between 100 and 200 carbons

The temperature-concentration phase (T-c) diagrams of the uniform n-alkanes C102H206, C122H246, C162H326, and C198H398 in toluene have been determined for solution concentrations in the range 0.1 to 6% (w/w). The shorter alka nes display a "classical" behavior with the expected, strong dependence of dissolution temperature on solution concentration. The longest alkane displ ays a very different, "polymeric" type behavior with a concentration indepe ndent dissolution temperature (for both extended and folded chain crystals) . It is argued that no current theory of polymer dissolution is able to exp lain this behavior. It is suggested that a locally higher concentration occ urs when molecules are partially attached to a crystal either during crysta llization or dissolution, and that this increased local concentration accou nts for the independence of dissolution temperature on the global concentra tion. There are some small variations in the dissolution temperature of cry stals of the same thickness grown at the same concentration, but at differe nt temperatures. These are ascribed to differences in the stacking of the s eparate layers. (C) 1999 John Wiley & Sons, Inc.