A method of obtaining polymer with markedly decreased entanglements concentration in melt, via high-pressure crystallization of high-density polyethylene (HDPE), is elaborated. It is shown, by calculations and experiments, that melting of chain-extended crystals obtained in this process provides a chain-disentangled melt for a period of 20-30 min. The disentanglement is tested by means of spherulite growth rate measurements in a regime II melt crystallization. Spherulites grow faster from partially disentangled melt than from melt with normal concentration of entanglements: the growth rate is increased by 25-45%, and the conversion rate is also markedly higher. The difference is augmenting with decreasing undercoolingsconsistently with conclusions made from nucleation theory including reptationsand decaying with increasing time of melt annealing at 160°C before crystallization, which is a result of entanglements reconstitution. The crystallization behavior in initially chain disentangled samples subjected to 25-30 min melt annealing is typical of entangled polyethylene, which indicates a complete entanglement restoration. The activation energy for reptation, determined from these data, is approximately 25 kJ/mol. Differences in overall isothermal crystallization kinetics of chain entangled and chain disentangled samples are considerable at moderate undercooling. The nucleation density during crystallization from disentangled melt is reduced in consequence of desorption of chains from heterogeneities surfaces during prior high-pressure crystallization of the samples. Melt annealing causes readsorption and restoration of normal nucleation density. The morphology of samples crystallized from a chain-disentangled melt is significantly different than those crystallized from a chain-entangled melt while the crystal thicknesses are similar.

No abstract

Superhydrophobic surfaces were obtained by superposition of microstructure—defined by replication of laser micromachined masters, with nanostructure—created by durable epoxy/γ-Al2O3nanoparticle composite, used for replication. Hierarchical surface topography thus obtained consisted of hexagonally spaced microcavities and nanoparticle agglomerates, exposed on the replica surface by radio frequency (RF) air plasma etching. Surface topography was further enhanced by rims around the microcavity edges, resulting from nanosecond laser micromachining defects in aluminum masters. Subsequent wet chemical hydrophobization with 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (PFTDTES) provided superhydrophobic behavior in replicas with a microcavity spacing of 30 μm, as indicated by a water contact angle of 160° and a sliding angle of 8°. The preparation method is relatively simple, inexpensive, and potentially scalable.