1,721,052 research outputs found
POLIMERI AD ALTE PRESTAZIONI PER L' OTTICA NON LINEARE DEL SECONDO ORDINE OTTENUTI PER "GRAFTING" DI COMPLESSI CROMOFORICI SU POLI-4-VINILPIRIDINA
No full textLight-induced spiral mass transport in azo-polymer films under vortex-beam illumination
No full textWhen an azobenzene-containing polymer film is exposed to non-uniform illumination, a light-induced mass migration process may be induced, leading to the formation of relief patterns on the polymer-free surface. Despite many years of research effort, several aspects of this phenomenon remain poorly understood. Here we report the appearance of spiral-shaped relief patterns on the polymer film under the illumination of focused Laguerre–Gauss beams with helical wavefronts and an optical vortex at their axis. The induced spiral reliefs are sensitive to the vortex topological charge and to the wavefront handedness. These findings are unexpected because the doughnut-shaped intensity profile of Laguerre–Gauss beams contains no information about the wavefront handedness. We propose a model that explains the main features of this phenomenon through the surface-mediated interference of the longitudinal and transverse components of the optical field. These results may find applica- tions in optical nanolithography and optical-field nanoimaging
VINYLPYRIDINE-STYRENE COPOLYMERS AS HOST POLYMER FOR CHROMOPHORIC COMPLEXES WITH HIGH SECOND ORDER NONLINEAR OPTICAL PROPERTIES
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Fluorescent polyurethanes based on a Schiff base Zn(II) complex containing benzothiazole
No full textCopper(II) chiral complexes as components of cholesteric liquid crystals for optical applications
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Frustration of H-Bonding and Frustrated Packings in a Hexamorphic Crystal System with Reversible Crystal–Crystal Transitions
No full textThe study of transitions between polymorphic phases is a less investigated chapter of the widely studied book of polymorphism. In this paper, we discuss the phase behavior of a new compound that has been rationally designed to show frustration of H-bonds for the strong amide N-H donor, which cannot be involved in H-bonding nor in van der Waals interactions. The compound (ImB) is a showcase of almost all possible cases of transitions between polymorphs [monotropic/enantiotropic, fast/slow, diffusive/displacive, and single-crystal-to-single-crystal (SCSC)] and of relation between polymorphs with different Z '. Six crystal phases (I, II, III, IV, V, and VI) were identified for it with five crystal-crystal transitions. Two transitions are reversible/SCSC/fast. Of the three monotropic transitions, all non-SCSC, one is slow, and the others are fast. Of the two enantiotropic SCSC transitions, one does not exhibit undercooling, while the other shows strong undercooling. Phase III, with Z ' = 6, is stable at room temperature between phase II (Z ' = 1), stable at high temperature, and phase IV (Z ' = 2), stable at low temperature. All six polymorphs are based on the same O-HO & boxH;C H-bonding synthon, which produces infinite chains in five polymorphs and ring tetramers in one. The sequence of reversible SCSC transitions IV reversible arrow III reversible arrow II involves a remarkable ping pong of the symmetry rules by which H-bonded chains are built. Based on all of this, a possible roadmap for prediction of SCSC transitions in crystals is shortly outlined
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