Concentration effects in solid-state CD spectra of chiral atropisomeric compounds

Atropisomerism is one of the basic concepts in stereochemistry. Chiral crystals of stereochemically labile atropisomers that originated from Mirror Symmetry Breaking (MSB) can only be characterized by solid-state chiroptical techniques. Herein, solid-state circular dichroism and UV-Vis spectra of six atropisomeric compounds (most of them were obtained from MSB) have been studied. A concentration effect including a wavelength shift and inverse concentration-dependence has been found and preliminarily explained by the absorption flattening effect, scattering effect and the torsion in the molecular structures.National Natural Science Foundation of China[20973136, 20974028, 20732004]; Natural Science Foundation of Fujian Province[2010J01048

Tear strength of filled rubbers

The strength of black-filled rubbers has been investigated under a variety of test conditions using various compounding formulations, of both strain-crystallizing and non-strain-crystallizing elastomers. The enhancement in the tear strength is substantial when knotty tearing occurs. In knotty tearing, the crack tip grows perpendicularly to the general direction of propagation. This effectively increases the tip diameter and thus the tear strength. A strong correlation between tearing energy and knot diameter (measured in the unstrained state) has been found in the present investigation. Factors which affect the development of knotty tearing were investigated. It was found that knotty tearing is affected by the degree of strain-crystallization, molecular mobility, nature and concentration of crosslinks, the type and concentration of carbon black, temperature and tear rate. The onset of knotty tearing appears to be related to the development of strength anisotropy at the tip of the tear. The effect of this anisotropy on the energy to propagate tearing in the direction of pre-straining was investigated using split tear test-pieces. The tearing energy for crack propagation in the direction of molecular orientation gives a quantitative measure of strength anisotropy developed in the vulcanizate as a consequence of pre-straining. It was found that, in a stretched vulcanizate, the tearing energy to propagate tearing in this direction was a factor of about 20 lower than the tearing energy of the unstretched vulcanizate. In a certain type of black-filled vulcanizate, the anisotropy introduced during pre-stressing to large extension still persisted even after the pre-stretch was removed. The present investigation shows that the anisotropy introduced by pre-stressing is associated with the set. The tearing energy of a pre-stressed vulcanizate was found to correlate strongly with the set

Interfacial layering in a three-component polymer system

We study theoretically the temporal evolution and the spatial structure of the interface between two polymer melts involving three different species (A, A* and B). The first melt is composed of two different polymer species A and A* which are fairly indifferent to one another (Flory parameter chi_AA* ~ 0). The second melt is made of a pure polymer B which is strongly attracted to species A (chi_AB 0). We then show that, due to these contradictory tendencies, interesting properties arise during the evolution of the interface after the melts are put into contact: as diffusion proceeds, the interface structures into several adjacent "compartments", or layers, of differing chemical compositions, and in addition, the central mixing layer grows in a very asymmetric fashion. Such unusual behaviour might lead to interesting mechanical properties, and demonstrates on a specific case the potential richness of multi-component polymer interfaces (as compared to conventional two-component interfaces) for various applications.Comment: Revised version, to appear in Macromolecule

Photolithographic patterning of conducting polyaniline films via flash welding

In this work, two significant advances in photolithographic patterning of polyaniline (PANI) films are reported. Firstly, flash welding was enhanced through the use of polymeric substrates, enabling complete penetration of the welding of PANI films with thicknesses ranging from 5 to over 14 mu m, significantly thicker than reported previously. Masking of parts of the PANI films during flash welding enabled the formation of adjacent conducting and insulating regions as the welding changes the electrical properties of the film. Raman spectroscopy was used to determine the sharpness of these edges, and indicated that the interface between the flash welded and masked regions of the PANI films was typically less than 15 mu m wide. Secondly, using longpass filters, light with a wavelength less than 570 nm was found not to contribute to the welding process. This was confirmed by the use of a 635 nm laser diode for welding the PANI films. This novel approach enabled patterning of PANI films using a direct writing technique with a narrow wavelength light source