Plasticity of brittle epoxy resins during debonding failures

A remarkably high degree of plasticity in brittle epoxies during debonding failures is reported. The plasticity is exhibited by the presence of ridges on the debonded surfaces having a width and height above the general level of these surfaces of the order of 100 nm. The surfaces of the more rigid substrates from which the debonding has occurred, by contrast, are smooth after debonding. The ridges have been found in several forms: in more or less straight rows parallel to the debonding fracture direction; as irregularly-shapes rings or craters, probably formed from secondary crack growth; as paraboloids, which also seem to be related to secondary crack growth; and as serpentine rows more or less perpendicular to the debonding fracture direction. This behaviour has been exhibited by various epoxy formulations. The 100 nm widths and heights for the ridges suggest that during debonding, plastic deformation has occurred rather uniformly in the epoxy to a depth below the interface of this order. This behaviour is in contrast to the simple notion of brittle fracture, in which atoms or molecules separate across planes in an elastically strained body. It differs also from the bulk fracturing process with these resins, in which a smaller amplitude, more random ridge and groove texture, referred to as the “basic longitudinal” or “fingering” texture, is seen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44693/1/10853_2005_Article_BF01168982.pd

Doping Polypyrrole Films with 4-N-Pentylphenylboronic Acid to Enhance Affinity towards Bacteria and Dopamine.

Here we demonstrate the use of a functional dopant as a fast and simple way to tune the chemical affinity and selectivity of polypyrrole films. More specifically, a boronic-functionalised dopant, 4-N-Pentylphenylboronic Acid (PBA), was used to provide to polypyrrole films with enhanced affinity towards diols. In order to prove the proposed concept, two model systems were explored: (i) the capture and the electrochemical detection of dopamine and (ii) the adhesion of bacteria onto surfaces. The chemisensor, based on overoxidised polypyrrole boronic doped film, was shown to have the ability to capture and retain dopamine, thus improving its detection; furthermore the chemisensor showed better sensitivity in comparison with overoxidised perchlorate doped films. The adhesion of bacteria, Deinococcus proteolyticus, Escherichia coli, Streptococcus pneumoniae and Klebsiella pneumoniae, onto the boric doped polypyrrole film was also tested. The presence of the boronic group in the polypyrrole film was shown to favour the adhesion of sugar-rich bacterial cells when compared with a control film (Dodecyl benzenesulfonate (DBS) doped film) with similar morphological and physical properties. The presented single step synthesis approach is simple and fast, does not require the development and synthesis of functional monomers, and can be easily expanded to the electrochemical, and possibly chemical, fabrication of novel functional surfaces and interfaces with inherent pre-defined sensing and chemical properties