6,825 research outputs found
Morphology Development in Model Polyethylene via Two-Dimensional Correlation Analysis
Two-dimensional (2D) correlation analysis is applied to synchrotron X-ray scattering data to characterize
morphological regimes during nonisothermal crystallization of a model ethylene copolymer (hydrogenated polybutadiene,
HPBD). The 2D correlation patterns highlight relationships
among multiple characteristics of structure evolution, particularly the extent to which separate features change simultaneously versus sequentially. By visualizing these relationships during cooling, evidence is obtained for two separate physical processes occurring in what is known as “irreversible crystallization” in random ethylene copolymers. Initial growth of primarily lamellae into unconstrained melt (“primary-irreversible crystallization”) is distinguished from subsequent secondary lamellae formation in the constrained, noncrystalline regions
between the primary lamellae (“secondary-irreversible crystallization”). At successively lower temperatures (“reversible crystallization”), growth of the crystalline reflections is found to occur simultaneously with the change in shape of the amorphous halo, which is inconsistent with the formation of an additional phase. Rather, the synchronous character supports the view that growth of frustrated crystals distorts the adjacent noncrystalline material. Furthermore, heterocorrelation analysis of small-angle and wideangle X-ray scattering data from the reversible crystallization regime reveals that the size of new crystals is consistent with fringedmicellar structures (~9 nm). Thus, 2D correlation analysis provides new insights into morphology development in polymeric systems
Multipolar third-harmonic generation driven by optically-induced magnetic resonances
We analyze third-harmonic generation from high-index dielectric nanoparticles
and discuss the basic features and multipolar nature of the parametrically
generated electromagnetic fields near the Mie-type optical resonances. By
combining both analytical and numerical methods, we study the nonlinear
scattering from simple nanoparticle geometries such as spheres and disks in the
vicinity of the magnetic dipole resonance. We reveal the approaches for
manipulating and directing the resonantly enhanced nonlinear emission with
subwavelength all-dielectric structures that can be of a particular interest
for novel designs of nonlinear optical antennas and engineering the magnetic
optical nonlinear response at nanoscale.Comment: 24 pages, 6 figure
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