Michael L. Myrick

Nanomechanical Characterization of Single-Walled Carbon Nanotube Reinforced Epoxy Composites

Nanomechanical properties of single-walled carbon nanotube (SWNT) reinforced epoxy composites with varying weight percentage (0, 1, 3, and 5 wt%) of nanotubes were measured by nanoindentation and nanoscratch techniques. Hardness and elastic modulus were measured using a nanoindenter. Scratch resistance and scratch damage were studied using the AFM tip sliding against the SWNT reinforced sample surfaces. Nanoindentation/nanoscratch deformation and fracture behaviour was studied by in situ imaging of the indentation impressions/scratch tracks. Viscoelastic properties of the nanocomposites were measured using nanoindentation dynamic mechanical analysis tests. The reinforcing mechanisms are discussed with reference to the nanotube dispersion, interfacial bonding, and load transfer in the SWNT reinforced polymer composites.

Elimination of Background in Fiber-Optic Raman Measurements

A Novel fiber-optic configuration with forward-scattering light collection is used to measure Raman spectra using long optical fibers with little background interference. This probe design allows control over the sample volume, and measurements can be made at considerable distances from the face of the optrode. The properties of this optical configuration are discussed, as well as its advantages and disadvantages. Normal Raman spectra were measured with this technique, with fibers as long as 100 m. The performance of the probe is not affected by highly scattering solutions. A similar technique was used to measure surface-enhanced Raman spectra on Ag electrodes with 250-m fibers.

Multivariate optical computation for predictive spectroscopy.

A novel optical approach to predicting chemical and physical properties based on principal component analysis (PCA) is proposed and evaluated using a data set from earlier work. In our approach, a regression vector produced by PCA is designed into the structure of a set of paired optical filters. Light passing through the paired filters produces an analog detector signal that is directly proportional to the chemical/physical property for which the regression vector was designed. This simple optical computational method for predictive spectroscopy is evaluated in several ways, using the example data for numeric simulation. First, we evaluate the sensitivity of the method to various types of spectroscopic errors commonly encountered and find the method to have the same susceptibilities toward error as standard methods. Second, we use propagation of errors to determine the effects of detector noise on the predictive power of the method, finding the optical computation approach to have a large multiplex advantage over conventional methods. Third, we use two different design approaches to the construction of the paired filter set for the example measurement to evaluate manufacturability, finding that adequate methods exist to design appropriate optical devices. Fourth, we numerically simulate the predictive errors introduced by design errors in the paired filters, finding that predictive errors are not increased over conventional methods. Fifth, we consider how the performance of the method is affected by light intensities that are not linearly related to chemical composition (as in transmission spectroscopy) and find that the method is only marginally affected. In summary, we conclude that many types of predictive measurements based on use of regression (or other) vectors and linear mathematics can be performed more rapidly, more effectly, and at considerably lower cost by the proposed optical computation method than by traditional dispersive or interferometric instrumentation. Although our simulations have used Raman experimental data, the method is equally applicable to Near-IR, UV-vis, IR, fluorescence, and other spectroscopies.

Raman and Near-Infrared Studies of an Epoxy Resin

A quantitative comparison of Raman and Fourier transform near-infrared (FT-NIR) spectroscopic techniques for the analysis of epoxy curing is performed. It is shown that the Raman technique yields a linear calibration curve much like FT-NIR. Band assignments in the Raman spectrum of diglycidyl ether of bisphenol-A (DGEBA) were performed by studying Raman spectra of smaller model compounds.

Comparison of some fiber optic configurations for measurement of luminescence and Raman scattering

Measurements are made for a number of dual fiber optic configurations to determine their relative sensitivity using bare fibers and graded-refractive-index lenses. An analysis of the background fiber emission for a typical silica-on-silica fiber (Diaguide, 200-microm core) is presented, and the origin (core or cladding) for several prominent Raman peaks is determined. Also, a forward-scattering fiber geometry is introduced, and the dependence of sensitivity on the type of optical termination and fiber separation is determined.

Template Electropolymerization of Polypyrrole Nanostructures on Highly Ordered Pyrolytic Graphite Step and Pit Defects

Polypyrrole nanostructures with diameters {le}10 nm have been electropolymerized using step and pit defects on highly ordered pyrolytic graphite (HOPG) as templates for electropolymerization. Step defects were naturally occurring, and pits were formed via oxidation of freshly cleaved surfaces of an HOPG water by heating at {approximately}640 C. Underpotential deposition of {approximately}80 mV caused polypyrrole to form only on the step and pit edges of HOPG at and not on the basal plane. The size of these nanostructures could be controlled by limiting the pyrrole polymerization time at anodic potentials. Recent modeling results allow the morphology of the deposition to be inferred, and the authors find the electrochemical data consistent with wire-shaped growth for up to 30 s at constant potential, after which the growth changes morphology. Scanning tunneling microscopy data confirm this result. Preliminary studies show that these polypyrrole nanostructures can be removed by sonication.

Structural and mechanical characterization of nanoclay-reinforced agarose nanocomposites.

Nanoclay-reinforced agarose nanocomposite films with varying weight concentration ranging from 0 to 80% of nanoclay were prepared, and structurally and mechanically characterized. Structural characterization was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). It was found that pre-exfoliated clay platelets were re-aggregated into particles (stacked platelets) during the composite preparation process. Each particle consists of approximately 11 clay platelets stacked together. The nanoclay particles were homogeneously dispersed within an agarose matrix. The clay particles were oriented with a slight preference of the stacked platelets being parallel to the composite films surface within the low loading composite films. Mechanical properties of the nanocomposite films were measured by tensile, three-point bending and nanoindentation tests. Mechanical testing results show that nanoclays provide a significant enhancement to the tensile modulus and strength. For the 60% clay nanocomposite, its elastic modulus increases up to 21.4 GPa, which is five times higher than that of the agarose matrix. Based upon the structural characterization, a theoretical model has been developed to simulate the mechanical behaviour of the nanoclay-reinforced polymer composites.

Fluorescence Fingerprint of Waters: Excitation-Emission Matrix Spectroscopy as a Tracking Tool

In this report, an optical method for tracking sources of water entering rivers and oceans is applied to the Congaree River in Columbia, South Carolina. The Congaree River forms at the confluence of two rivers, the Saluda and the Broad. Excitation-emission matrix (EEM) spectra of water samples from the rivers were constructed by scanning emission spectra from 300 to 600 nm as a function of excitation wavelength from 200 to 290 nm. The two sources of water in the Congaree River were easily distinguishable on the basis of the EEM spectra of the water samples. In addition, the average composition of water in the Congaree River and hence the relative flow rates of inflowing Saluda and Broad Rivers could be determined. In this report, the characteristic fluorescence of the river water samples and the stability of the EEM spectra of the river samples over several months are presented.

Growth and Characterization of a Porous Aluminum Oxide Film Formed on an Electrically Insulating Support

Thin films of porous anodic aluminum oxide have been prepared on an electrically insulating support by the anodization of aluminum films sputtered onto glass slides. The resulting transparent aluminum oxide films were characterized by scanning electron microscopy and variable angle ellipsometry. Subsequently, the film was modeled from the ellipsometric data taken. An underlying conductive medium is not necessarily needed to bring about nearly complete anodization of the aluminum layer.

Precision in multivariate optical computing

Multivariate optical computing (MOC) is an instrumentation design concept for optically demultiplexing the spectroscopic signals in radiometric measurements. The advantages of optically demultiplexing are improved precision, optical throughput, improved reliability, and reduced cost of instrumentation. Conceptually, the instrument implements a multivariate regression vector whose dot product with the spectrum yields a single value related to a spectroscopically active physical property of interest. Instrumentation designs for implementing MOC are diverse, and there has been no systematic comparison of the performance of these designs. This report develops a general expression for comparing the precision of the different instrumentation designs of MOC. Additionally, an expression is given for the transition from low- to high-signal-limited performance of MOC instrumentation. These two general expressions are applied to the traditional multivariate analysis and five examples of MOC.