Nucleation of Polymer Droplets

Abstract

The nucleation of droplets of polyethylene, polyethylene oxide, polym''Ymethylene, nylon 6, poly (3,3bis-chloromethyloxacYclobutane), isotactic polypropylene, and isotactic polystyrene, suspended in silicone oil, has been investigated. Under conditions of slow cooling (0.1 °C/min), two different phenomena were observed; occasional droplet solidification at low degrees of subcooling, the number of droplets solidified and the temperature at which nucleation occurred being a function of the thermal melt history; and a sudden catastrophic, history-independent, nucleation phenomenon at large subcooling. The latter event may be identified as a critical phenomenon occurring at a subcooling D.Tc which is only slightly dependent upon the rate of cooling.For polyethylene and isotactic polypropylene, the t:..T.'s correspond closely with values obtained by other authors using different suspending media and have been identified with homogeneous nucleation. Homogeneous nucleation may also be explored by the method of kinetic-rate measurements, with the advantage that rate constants can be evaluated directly rather than by theoretical derivation. Interfacial energies calculated from nucleation theory using the first (slow-cooling) method, have been compared in this work with those obtained from the second (isothermal) method. Such comparison shows that the isothermal method gives values of the same order as, but somewhat lower than, the slow-cooling method.For the other polymers, most of which are glass-forming, it is not entirely clear that the catastrophic event corresponds with homogeneous nucleation. Whereas critical supercooling and solidification rates resemble those for homogeneous nucleation, there is evidence that the interfacial energies recovered are too low and the circumstances surrounding the catastrophic event suggest that the suspending medium may be catalyzing nucleation.

Preparation and Properties of PTFE-PMMA Core-Shell Nanoparticles and Nanocomposites

“…This peculiar crystallization behavior, recently described and thoroughly discussed [22] for a series of PTFE-PMMA core-shell nanoparticles, can be rationalized within the frame of the fractionated crystallization mechanism [23,24]. Due to the compartmentalization of PTFE within the core-shell nanoparticles, the number of the dispersed PTFE particles is much greater than the number of heterogeneities that usually nucleate the polymer in bulk.…”

Impact of Nanoscale Confinement on Crystal Orientation of Poly(ethylene oxide)

“…The recrystallization exotherm appeared at 40 8C (T c,PEO ), only 58 lower than that of the PEO control. Because the crystallization temperature of the nanolayers was close to that of the bulk and much higher than that of homogeneous nucleation, usually put between À10 and 0 8C, [19,20] it was concluded that crystallization of the PEO nanolayers nucleated on heterogeneous nuclei, such as catalyst residues, high molecular weight gel particles, or dust particles.…”

Effect of polystyrene on poly(ethylene terephthalate) crystallization

“…Crystallization ends at very low rate, due to depletion of crystallizable polymer and (for high crystallinity materials) to a decrease of the interfacial area caused by interference between competing growing crystals, among other reasons. Between initial and final stages, the crystallization rate reaches a maximum, at a temperature identified as crystallization temperature of the polymer 1,[28][29][30][31][32][33][34][35][36][37][38] . The cold crystallization temperature of PET samples tested increased from 110 °C when heated at 1 °C/min to 150 °C when heated at 50 °C/min.…”

“…It should be noted that, under the tests conditions PS is a completely amorphous polymer, immiscible in PET; the solubility limit of PS in PET is believed to be less than 1%, thus it is possible that once the solubility limit between PET and PS to be reached PS is segregated at amorphous zone then producing little effect on the crystalline phase of PET. In literature database several explanations are presented for the multiple crystallization phenomenon: two kinds of amorphous regions, inter-lamellar and inter-spherulite, different crystalline geometries, co-crystallization and fractional crystallization, secondary or recrystallization effects 6,9,11,12,14,28,[30][31]35,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] . PET crystallization in PET/PS blends proceeds at a higher temperature and lower crystallization rate than in the neat resin.…”