Crystal nucleation in polyethylene: The droplet experiment

Abstract

The droplet technique was utilized to obtain estimates of the isothermal rate of homogeneous crystal nucleation in highly supercooled melts of unfractionated linear polyethylene. In a typical experiment a cell containing a suspension of several hundred micron‐size spherical droplets of the polymer was placed on a microscope hot stage and quenched from a temperature well above the melting point of polyethylene to the desired crystallization temperature. When viewed between crossed polarizers, the droplets were initially invisible but, upon freezing, they appeared as visible birefringent spheres. The time dependence of the process was followed by time‐lapse photography. Half times (T1/2) for the freezing of those droplets remaining unfrozen by the time the crystallization temperature was attained were thus obtained at a series of undercoolings and related to the desired nucleation rate constant I (nuclei cm.−1 sec.−1) by the equation I = In 2/T1/2/v, where v is the droplet volume. The temperature dependence of I, as obtained by the above procedure, was analyzed in accord with current theories of homogeneous nucleation of chain‐folded polymer crystals. From this analysis, an estimate, 14,960 ergs3 cm.−6 was made of the quantity (%sG2%sGe), where %sG and %sGe are, respectively, the lateral and end‐surface free energies of the crystal.

Crystal nucleation and the crystalmelt interfacial tension in linear hydrocarbons

“…At very large n, e.g., lo4, as in linear polyethylene, El is much larger [7,8], corresponding to a AT: -0.1 5, than the asymptotic value E l = 0.15 approached by the lower n-alkanes. Cormia et al [7] attributed this increase in El to the large energy oe, which might be associated with the formation of the end, presumably chain-folded, surface of the polymer crystals.…”

The Influence of Blend Morphology (Co‐Continuous or Sub‐Micrometer Droplets Dispersions) on the Nucleation and Crystallization Kinetics of Double Crystalline Polyethylene/Polyamide Blends Prepared by Reactive Extrusion

“…The production of fine dispersions of droplets has been a widely employed experimental strategy to study nucleation and crystallization in metals, organic compounds, and polymers. [6][7][8][9][10][11][12][13] In many works dealing with polymer blends the phenomenon of fractionated crystallization is observed as a consequence of the dispersion of a crystallizable polymer in an immiscible polymeric matrix. The term fractionated crystallization was introduced by Frensch et al [14] after studying several systems: PE/polymethylene oxide (POM), poly(vinylidene fluoride/polyamide-6 (PVDF/ PA-6), and poly(vinylidene fluoride)/poly(butylene terephthalate) (PVDF/PBTP).…”

Confined crystallization of polymers within anodic aluminum oxide templates

“…However, the study of the crystallization phenomena within confined microphases was studied for the first time in 1880 when Van Riemsdyk investigated the crystallization of gold droplets dispersions and found a large depression of the crystallization temperature (or higher supercooling) as compared with bulk gold. In the following years, many researchers performed similar studies in dispersed droplet systems like water, metals, alkenes, and polymers . In all these systems, a similar result was found: the crystallization within droplets occurs at much larger supercoolings than in bulk samples.…”