Acta Crystallographica Section E: Crystallographic Communications
The cis- form of diaminodibenzocyclooctane (DADBCO, C16H18N2) is of interest as a negative coefficient of thermal expansion (CTE) material. The crystal structure was determined through single-crystal X-ray diffraction at 100 K and is presented herein.
Abstract not provided.
ACS Macro Letters
Fine control over the thermal expansion and contraction behavior of polymer materials is challenging. Most polymers have large coefficients of thermal expansion (CTEs), which preclude long performance lifetimes of composite materials. Herein, we report the design and synthesis of epoxy thermosets with low CTE values below their Tg and large contraction behavior above Tg by incorporating thermally contractile dibenzocyclooctane (DBCO) motifs within the thermoset network. This atypical thermomechanical behavior was rationalized in terms of a twist-boat to chair conformational equilibrium of the DBCO linkages. We anticipate these findings to be generally useful in the preparation of materials with designed CTE values.
This report describes an adhesively bonded, Asymmetric Double Cantilever Beam (ADCB) fracture specimen that has been expressly developed to measure the toughness of an alumina (Al203)/epoxy interface. The measured interfacial fracture toughness quantifies resistance to crack growth along an interface with the stipulation that crack-tip yielding is limited and localized to the crack-tip. An ADCB specimen is a variant of the well-known double cantilever beam specimen, but in the ADCB specimen the two beams have different bending stiffnesses. This report begins with a brief overview of how crack-tip mode mixity (i.e., a measure of shear-to- normal stress at the crack-tip) is a distinguishing feature of interfacial fracture. Which is then followed by a detailed description of relevant design, fabrication, testing, and associated data analysis techniques. The report then concludes by presenting illustrative results that compare the measured interfacial toughness of an alumina/epoxy interface when the alumina is silane-coated and when the alumina is not silane coated. This page left blank