Summer 2012 Research and Participants

Gas Barrier Properties of Three-Component Thin Films

REU Student: Chadley Box

Faculty Mentor: Dr. Jaime Grunlan

Thin films are applied on a surface to alter properties such as gas transmission rate, electrical conductivity, or hydrophobicity. A thin film gas barrier would inhibit oxygen transmission which in turn can reduce the amount of material needed in food packaging and inflatables. It would also be effective protection to sensitive organic components used in flexible electronics without adding rigidity. The Layer by Layer (LbL) assembly technique is used to construct multi-component, multi-layer films of less than a micrometer in thickness. LbL’s main construction mechanism comes from the electrostatic attraction of alternating positive and negatively charged components. This makes two-component (bilayer) and four-component (quadlayer) films predominant. Three-component (trilayer) systems, which must make use of other bonding mechanisms, have not been sufficiently studied. This project found growth in two trilayer systems: poly(vinyl amine)/natural sodium montmorillonite/poly(acrylic acid) (PVA/MMT/PAA) and PEI(branched polyethylenimine)/MMT/PAA. Thickness of 20 trilayers was found to be 405 and 100 nanometers respectively. Gas barrier testing of these two systems at 20 trilayers determined the oxygen transmission rate (OTR) to be under the detection limit of measurement, 0.005 cc/m2/day*atm. This study shows successful growth of two trilayer systems with comparable results to a previously studied quadlayer recipe, PEI/PAA/PEI/MMT, which also had an undeterminable OTR and a thickness of 50.9 nm at 4 quadlayers.

Characterization of Semicrystalline Polymers and Polymer Nanocomposites

REU Student: Maytee Chantharayukhonthorn, University of Texas at Austin

Faculty Mentor: Dr. Hung-Jue Sue

Nanofillers such as carbon nanotubes (CNTs) have become integral parts of modern materials research. Polyether ether ketone, or PEEK, is a polymer with mechanical and thermal properties favorable for high demand applications. Enhancing PEEK with nanofillers can lead to greater properties, opening up the usage of the material to even more demanding applications. This study characterizes PEEK with different nanofillers, analyzing shear loss and storage moduli, glass transition temperature, crystallization temperature and percent crystallization. We show that PEEK functionalized with 0.5 and 1 wt% CNTs show little difference in properties compared to virgin PEEK, even after annealing. However, we also show that PEEK, when copolymerized with polyetherimide (PEI) and combined with ZrP nanoplatelets and 0.5 wt% CNTs, has significant changes to its properties, especially with a large glass transition temperature shift after annealing. This work shows the potential property altering effects of copolymerization and the introduction of ZrP nanoplatelets to PEEK.

Parametric Analysis of MHD Couette Flow Using Magnetohydrodynamic Gas Kinetic Method

REU Student: Valerie Ferdin, Texas A&M University at Corpus Christi

Faculty Mentor: Dr. Jacques Richard

In this research project, we discuss the fluid mechanics behind the Magnetohydrodynamic Gas Kinetic Method (MGKM). Magnetohydrodynamics (MHD) studies the dynamics of electrically conducting fluids. The Gas Kinetic Method (GKM) is a finite volume solver, based on the solution to the Boltzmann-BGK equation for the particle distribution function. It computes fluxes to update cell-centered macroscopic properties such as density, momentum, and energy. MGKM further develops GKM by adding source terms which account for the effect of electromagnetic fields on conducting fluid to the conservation equations. This study is a computational analysis of plasma dynamics in different applications ranging from materials processing to bio-medical. Numerical simulations of 2D channel flows such as Couette flow and Hartmann flow were performed to test the effects of varying non-dimensional flow parameters such as Reynolds number, Hartmann number, Magnetic Reynolds number, and Mach number. The effects of compressibility at a high Mach number (M≅0.75) were of particular interest.

Structural Optimization with Matlab's Optimization Toolbox

REU Student: Terry Huang, Texas A&M University

Faculty Mentor: Dr. John Whitcomb

The focus of this research is to utilize the Matlab’s optimization toolbox for structural and material optimization. Optimization is the process of iterating through many possible solutions in order to find the best outcome (minimizing or maximizing the output) while also satisfying a set of constraints or boundary conditions. Structural optimization is of great importance because it can help lower the weight or cost of a certain structure or material. Optimization incorporates many techniques ranging from solving differential equations to using algorithms found in software packages such as Matlab’s optimization toolbox. Optimization problems can be solved analytically or graphically through these techniques.

The Mechanics of Nanorope

REU Student: Collin Marshall, Texas A&M University

Faculty Mentor: Dr. Jim Boyd

This study investigated the effects of van der Waals interactions and the elastic strain energy of assembly on the equilibrium configuration of nanowire clusters into nanorope. Unlike macroscopic rope, which retains its arrangement due to the permanent helical shape of constituent wires, nanowires are bent and twisted into helices, and remain adhered through their attractive van der Waals interactions. An expression for the strain energy in terms of the rope parameters, wire radii, separation distance, and helix angle, was determined using linear elasticity theory. The van der Waals energy was found using Hamaker’s method of summation. Since an analytical solution is almost impossible to find, Mathematica software was used to numerically calculate the magnitude of this energy as it varies with the rope parameters. A plot of these points was made and a curve fit was applied to give a general solution that is dependent on the above parameters. By adding these terms together and minimizing the total potential energy, the equilibrium configuration of the rope could then be analyzed and discussed. The three cases of van der Waals interactions studied in this paper were: intrawire, intralayer, and interlayer.

Finite element analysis of a multi-functional composite house

REU Student: William D. Scholten, Texas A&M University

Faculty Mentor: Darren Hartl

The purpose of this investigation was to develop a technique using finite element analysis in Abaqus to analyze a geometrically complex architectural design of a multi-functional composite house that implements fiber elements to stiffen the structure. In order to analyze the design, realistic boundary conditions and loads were applied, quasi-isotropy was assumed for the material properties due to the orientation of the lamina, and Tsai-Hill failure criteria was implemented on an Abaqus model of a previous version of the design. Throughout this investigation, many parametric studies were performed on the model without fiber elements in order to observe how variations in loads, material properties, and thickness affect the model. As a result of this investigation, a Python code was developed that would create and then tie fiber elements onto the surface of the house. In order to test the accuracy of the model, test specimens made out of a similar composite as the one used for the Abaqus model were fabricated, and then tension and bending tests were performed on the specimens.

Enhanced Understanding of Engineering Concepts via Interactive Documentation

REU Student: Jessica Williams, Brigham Young University

Faculty Mentor: Dr. John Whitcomb

Wolfram Research’s Computable Document Format (CDF) and Microsoft’s Visual Basic for Applications (VBA) were used to develop instructional material to expedite the understanding of structural mechanics concepts. Primarily, research involved exploring the capabilities of the respective programming tools through an examination of compilations found in books and online along with new proof of concept work. Achieving the requisite understanding of each program’s capabilities preceded the construction of simple coding samples with basic structural mechanics concepts. After analyzing the programs, the advantages and disadvantages of each were summarized. These programming innovations broaden teaching methods by increasing student interaction and conceptualization.

Mechanical Properties of Graphene and Graphene Nano-Ribbons

REU Student: Gregory Wilson

Faculty Mentor: Dr. Tahir Cagin

Using an equation of state suited for 2D structures that describes how the hydrostatic change in surface area is related to the total free energy in the molecular structure and yields the measure of the material’s resilience to isotropic stretching (the layer modulus γ) as one of the parameters. We give results for graphene and we also include results for BN, GeC, and SiC in the isostructural honeycomb structure for comparison. Our results show that, of the honeycomb structures, graphene is the most resilient to stretching with a value of about γ0 = 207 Nm−1, which is significantly higher that other similar isostructural honeycomb structures. We also calculate the Young’s and shear moduli from the four non-zero 2D elastic constants, that we obtain from experiments