Solid State Phenomena Vols. 121-123

Abstract: Ultrahigh-Quality microcavity with whispering-gallery-mode (WGM) is a new kind of resonator with high quality. The evanescent wave of WGM plays an important role in surface enhanced Raman scattering (SERS). In this paper we study the relationship between coupling coefficient and evanescent wave of the WGM and the coupling character difference between the microsphere and the microstadium. Based on the finite-difference time-domain (FDTD), we calculate the coupling coefficient of different substances (water, C2H5OH, CHCL3, olive oil, C6H6 and CS2) with different dielectric constant and the mode volume ratio of the evanescent wave in microsphere and microstadium of the above substances in near field. The results show that (1) the mode volume ratio of evanescent wave will decrease with the increasing of the coupling coefficient; (2) the microstadium has a higher coupling coefficient than the sphere one.

Abstract: A systematic nanoelectrode-gated electron-tunneling molecular-detection concept with potential for rapid DNA sequencing has recently been invented at Oak Ridge National Laboratory (ORNL). A DNA molecule is a polymer that typically contains four different types of nucleotide bases: adenine (A), thymine (T), guanine (G), and cytosine (C) on its phosphate-deoxyribose chain. According to the nanoelectrode-gated molecular-detection concept, it should be possible to obtain genetic sequence information by probing through a DNA molecule base by base at a nanometer scale, as if looking at a strip of movie film. The nanoscale reading of DNA sequences is envisioned to take place at a nanogap (gate) defined by a pair of nanoelectrode tips as a DNA molecule moves through the gate base by base. The rationale is that sample molecules, such as the four different nucleotide bases, each with a distinct chemical composition and structure, should produce a specific perturbation effect on the tunneling electron beam across the two nanoelectrode tips. A sample molecule could thus be detected when it enters the gate. This nanoscience-based approach could lead to a new DNA sequencing technology that could be thousands of times faster than the current technology (Sanger’s “dideoxy” protocol-based capillary electrophoresis systems). Both computational and experimental studies are underway at ORNL towards demonstrating this nanotechnology concept.

Abstract: We calculate electron-transport properties within equilibrium, linear transport theory through the DNA nucleotide bases spanning two gold nanowires. Our quantum mechanical calculations show that single configurations of DNA bases A, C, T, and G have significantly different charge conductance characteristics. This result is consistent with the notion that it is possible to read the nucleotide base sequence on an individual DNA heteropolymer which is moving through a gap between electrically biased nanoelectrodes by measuring the changes in the electron-transport conductance.

Abstract: There is enormous scientific and economic interest in the development and evaluation of polymer nanocomposites due to the fact that the properties of a material become increasingly insensitive to flaws at the nanoscale, enabling the exploitation of the unique physical and mechanical properties of very small objects in large-scale components. However, the successful industrial implementation of such novel materials poses unique challenges which are not only related to the small size of the reinforcements. Decades of intensive research have shown that polymer nanocomposites differ from their counterparts based on traditional reinforcements in many ways and a fundamental understanding of the structure-propertyrelationships of such novel materials is only slowly emerging. Although issues such as the intrinsic properties of the nanoscale constituent as well as the degree of dispersion and orientation of individual filler particles clearly appear to be important factors, molecular interactions between the filler and the matrix during processing can lead to pronounced variations in the matrix microstructure. These variations in themselves lead to pronounced changes in the micro- and macromechanical deformation behaviour of the nanocomposites. A detailed investigation of fatigue crack growth behaviour of such novel materials for example is essential in order to understand the fracture mechanical performance and the transition from a ductile to a brittle behaviour which is often observed experimentally, especially in the case of amorphous matrices. However, as the size of the filler particles approaches the molecular level, the novel interactions at the interface or even in the interphase can lead to significant changes in the micromechanical deformation behaviour. Significant work has been carried out regarding the fracture mechanical investigation of polymer blends with both micro- and nanoscale morphologies and much can be learned by comparing the results of polymer nanocomposites to these more established polymer blends.

Abstract: Vapor growth carbon nanofibers (CNFs) were used as dopants for the epoxy resin (EP) matrix of unidirectional carbon fiber reinforced plastics (CFRPs). The doped laminates were compared to the reference one (with neat EP as matrix) with regard to their fracture toughness, and mechanical quasi-static and fatigue behaviour. Electrical resistance monitoring of the samples was used as a tool for sensing the damage propagation during the various loading configurations. Correlation between these results and acoustic emission (AE) data was also attempted.

Abstract: Fracture toughness and other mechanical properties of epoxies modified with nano-slica particles were measured to elaborate effects of nano-additives on fracture behaviour of the modified epoxies. Interlaminar fracture behaviours of the nano-silica modified CF/EP composites were subsequently investigated by conducting Mode-I and Mode-II interlaminar fracture toughness tests as well as transverse tension tests. It was found that the fracture toughness of the nano-silica modified epoxies and the interlaminar fracture toughness of nano-silica modified CF/EP composites have been increased significantly (>50%), while the strength and modulus of the materials remain unchanged or slightly higher. In particular, the nano-silica modified epoxies showed only very little reduction in the glass transition temperature (Tg).

Abstract: The carbon nanotube (CNT) surface is successfully modified using the UV/Ozone treatment and a triethylenetetramine (TETA) solution for use as the reinforcement for polymer matrix nanocomposites. These treatments along with ultrasonication are aimed to disperse the CNTs uniformly in the resin matrix, as well as to provide the CNT surface with chemical functionalities for adhesion with resin. Fourier transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are performed to evaluate the changes in chemical structure and surface functional groups arising from the chemical treatment. The practical implications of the surface functional groups for improving the interfacial adhesion are discussed.