Browsing by Author "Barrera, Enrique V."
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Item A Multiscale Model of the Enhanced Heat Transfer in a CNT-Nanofluid System(2011) Lee, Jonathan Winnie; Barrera, Enrique V.; Meade, Andrew J., Jr.Over the last decade, much research has been done to understand the role of nanoparticles in heat transfer fluids. While experimental results have shown "anomalous" thermal enhancements and non-linear behavior with respect to CNT loading percentage, little has been done to replicate this behavior from an analytical or computational standpoint. This study is aimed towards using molecular dynamics to augment our understanding of the physics at play in CNT-nanofluid systems. This research begins with a heat transfer study of individual CNTs in a vacuum environment. Temperature gradients are imposed or induced via various methods. Tersoff and AIREBO potentials are used for the carbon-carbon interactions in the CNTs. Various chirality CNTs are explored, along with several different lengths and temperatures. The simulations have shown clear dependencies upon CNT length, CNT chirality, and temperature. Subsequent studies simulate individual CNTs solvated in a simple fluidic box domain. A heat flux is applied to the domain, and various tools are employed to study the resulting heat transfer. The results from these simulations are contrasted against the earlier control simulations of the CNT-only domain. The degree by which the solvation dampens the effect of physical parameters is discussed. Effective thermal conductivity values are computed, however the piecewise nature of the temperature gradient makes Fourier's law insufficient in interpretting the heat transfer. Nevertheless, the computed effective thermal conductivities are applied to classical models and better agreement with experimental results is evident. Phonon spectra of solvated and unsolvated CNTs are compared. However, a unique method utilizing the Irving-Kirkwood relations reveals the spatially-localized heat flux mapping that fully illuminates the heat transfer pathways in the solid-fluid composite material. This method confirms why conventional models fail at predicting effective thermal conductivity. Specifically, it reveals the volume of influence that the CNT has on its surrounding fluid.Item A parametric study of sulfuric acid anodized 5657 aluminum alloy coatings for thermal control applications(1998) Klampfl, Bernhard F.; Barrera, Enrique V.The optical response of sulfuric acid anodized 5657 aluminum alloy coatings was determined to be greatly dependent upon trace and alloying element concentration. An improved method for WDS analysis of anodized coatings was developed to preclude processing errors and improve spatial resolution since it was shown that the possibility of contamination and/or coating modification must be considered in the development of sample preparation procedures and electron beam parameters. Measured element concentrations were compared with reflectance data to determine the affect of each on absorptance. Silicon and zinc concentrations were much higher than expected, the source of these elements being the substrate 5657 Al alloy. Both of these elements play a role in absorptance and the glass forming abilities of silicon may also affect the structural characteristics of SAA coatings produced on 5657 Al alloy.Item A scattered data approximation tool to map carbon nanotube dispersion to the processing parameters in polymer nanocomposites(2009) Lee, Jonathan W.; Barrera, Enrique V.The relationship of nanocomposite dispersion was studied with the variation of dispersion techniques and other processing parameters. Examining all permutations of the various factors in the laboratory is a challenging task. In this thesis, we propose to map a correlation between inputs and output via a self-adaptive scattered data approximation method. The proposed greedy algorithm, Sequential Function Approximation (SFA), reveals the multidimensional behavior of the system, provides the sensitivity of each input, and presents the combination of inputs that is most suitable for a specific output. In this research, we have collected data from various research institutions and applied it to SFA. The results show that CNT weight percent, sonication time, CNT modification, and high shear mixing time are key factors that affect the dispersion. This thesis discusses SFA, the data, and the results in detail. This work serves as a proof of concept and recommended future work is discussed.Item A structural analysis of Al(3)Ti and Al(3)Ti-Nb titanium trialuminides by XRD and EXAFS(1997) Chen, Jinmin; Barrera, Enrique V.In an effort to expand the composition range over which Al$\sb3$Ti is stable, various amounts of niobium were substituted for titanium and processed by melt-spinning. In order to characterize $\rm Al\sb3Ti\sb{x}Nb\sb{y},$ where x + y = 1 and y = 0.0, 0.1, 0.2, and 0.4 intermetallics, XRD and EXAFS were employed. Several samples were annealed both at 600$\sp\circ$C and 1000$\sp\circ$C. XRD showed that for all the samples the only structure present was the tetragonal DO$\sb{22}$ structure. The DO$\sb{22}$ structure was stable even after high temperatures heat treatments. Niobium atoms were observed to occupy titanium sites in DO$\sb{22}$ by EXAFS. Furthermore, in the unannealed samples, increasing wheel speed of the melt spinning process or the niobium concentration tended to distort the crystal structure. It was observed that Ti EXAFS had different results from the Nb EXAFS beyond their occupying similar sites. The samples were found to experience an order-disorder-order process with change of the annealing temperatures.Item Ab Initio Simulation of the Effect of Common Organic Solvents on Carbon Nanotubes and Customizable 2D van der Waals Heterostructures for Photocatalysis(2021-08-13) Quintanilla, Francisco Adan; Barrera, Enrique V.Part 1: Carbon nanotube (CNT) wires are a promising material for electric applications. This study focuses on the interaction between CNTs and organic solvents. A scheme for finding optimal adsorption sites without any assumptions is implemented based on Monte Carlo methods and molecular dynamics. Systems with several molecules can be produced to model different levels of coverage. Density functional theory is used to calculate the binding energy and charge transfer. 6 different organic solvents are studied: 3 non-polar (methane, benzene, cyclohexane) and 3 polar (dichloromethane, isopropanol, and pyridine), as well as iodine for reference. Iodine and dichloromethane act as electron donors, while the hydrocarbons and pyridine have small charge transfer. At higher concentrations iodine forms polyiodide chains that bind more strongly with CNTs and become electron acceptors. This understanding can help studies in which CNT wires are doped through solutions containing an organic solvent. Part 2: In the past years hundreds of new 2D materials have been discovered or predicted. The rise of materials databases detailing the electronic structure of thousands of predicted 2D materials, and high-throughput calculations and filtering can help select materials for specific applications. This work takes advantage of this to study 2D van der Waals heterostructures (VDWH) for water splitting. Results show which transition metal dichalcogenides (TMDs), MXenes and MXY Janus layers are the most promising candidates for photocatalytic water splitting. Solar power to electron conversion efficiencies of up to 29% are calculated for VDWH MXene/TMD and MXY Janus/TMD heterostructures. It is also discovered that the ideal heterostructure for light absorption consists of two 2D semiconductor materials with similar conduction band maxima but different valence band maxima.Item Advanced computational techniques for incompressible/compressible fluid-structure interactions(2005) Kumar, Vinod; Tapia, Richard A.; Barrera, Enrique V.Fluid-Structure Interaction (FSI) problems are of great importance to many fields of engineering and pose tremendous challenges to numerical analyst. This thesis addresses some of the hurdles faced for both 2D and 3D real life time-dependent FSI problems with particular emphasis on parachute systems. The techniques developed here would help improve the design of parachutes and are of direct relevance to several other FSI problems. The fluid system is solved using the Deforming-Spatial-Domain/Stabilized Space-Time (DSD/SST) finite element formulation for the Navier-Stokes equations of incompressible and compressible flows. The structural dynamics solver is based on a total Lagrangian finite element formulation. Newton-Raphson method is employed to linearize the otherwise nonlinear system resulting from the fluid and structure formulations. The fluid and structural systems are solved in decoupled fashion at each nonlinear iteration. While rigorous coupling methods are desirable for FSI simulations, the decoupled solution techniques provide sufficient convergence in the time-dependent problems considered here. In this thesis, common problems in the FSI simulations of parachutes are discussed and possible remedies for a few of them are presented. Further, the effects of the porosity model on the aerodynamic forces of round parachutes are analyzed. Techniques for solving compressible FSI problems are also discussed. Subsequently, a better stabilization technique is proposed to efficiently capture and accurately predict the shocks in supersonic flows. The numerical examples simulated here require high performance computing. Therefore, numerical tools using distributed memory supercomputers with message passing interface (MPI) libraries were developed.Item Ballistic limit equation for hypervelocity impact on composite-orthotropic materials(2004) Cruz Banuelos, Jose Santiago; Barrera, Enrique V.Two new ballistic limit equations for hypervelocity impact on homogeneous and composite-orthotropic materials have been developed for a velocity range above 6 km/s. The methodology used to develop the ballistic limit equations involves Kirchhoff's plate theory for a two plate fundamental structure comprising a shield and back plate. The Boundary Element Method is used to calculate the deformation and the moments when the load, is uniformly distributed over a circular area of the back plate, and is applied quickly so that the momentum transferred to the loaded area is equal to twice the momentum of the original projectile. The Von Mises yield criterion is used to account for elastic-plastic deformations into homogeneous materials and the Tsai-Hill yield criterion is used to account for elastic-plastic deformations into composite-orthotropic materials. The ballistic limit equations developed are compared with existing ballistic limit equations based on empirical and semi empirical formulations. It can be seen that our results are in good agreement with experimental measurements of spherical projectiles impacted on a two-plate shield at hypervelocity.Item Carbon Nano-Onions Reinforced Multilayered Thin Film System for Stimuli-Responsive Drug Release(MDPI, 2020) Mamidi, Narsimha; Velasco Delgadillo, Ramiro Manuel; Gonzáles Ortiz, Aldo; Barrera, Enrique V.Herein, poly (N-(4-aminophenyl) methacrylamide))-carbon nano-onions (PAPMA-CNOs = f-CNOs) and anilinated-poly (ether ether ketone) (AN-PEEK) have synthesized, and AN-PEEK/f-CNOs composite thin films were primed via layer-by-layer (LbL) self-assembly for stimuli-responsive drug release. The obtained thin films exhibited pH-responsive drug release in a controlled manner; pH 4.5 = 99.2% and pH 6.5 = 59.3% of doxorubicin (DOX) release was observed over 15 days. Supramolecular π-π stacking interactions between f-CNOs and DOX played a critical role in controlling drug release from thin films. Cell viability was studied with human osteoblast cells and augmented viability was perceived. Moreover, the thin films presented 891.4 ± 8.2 MPa of the tensile strength (σult), 43.2 ± 1.1 GPa of Young’s modulus (E), and 164.5 ± 1.7 Jg−1 of toughness (K). Quantitative scrutiny revealed that the well-ordered aligned nanofibers provide critical interphase, and this could be responsible for augmented tensile properties. Nonetheless, a pH-responsive and mechanically robust biocompatible thin-film system may show potential applications in the biomedical field.Item Carbon Nanotubes Filled Polymer Composites: A Comprehensive Study on Improving Dispersion, Network Formation and Electrical Conductivity(Rice University, 2010) Chakravarthi, Divya Kannan; Barrera, Enrique V.In this dissertation, we determine how the dispersion, network formation and alignment of carbon nanotubes in polymer nanocomposites affect the electrical properties of two different polymer composite systems: high temperature bismaleimide (BMI) and polyethylene. The knowledge gained from this study will facilitate optimization of the above mentioned parameters, which would further enhance the electrical properties of polymer nanocomposites. BMI carbon fiber composites filled with nickel-coated single walled carbon nanotubes (Ni-SWNTs) were processed using high temperature vacuum assisted resin transfer molding (VARTM) to study the effect of lightning strike mitigation. Coating the SWNTs with nickel resulted in enhanced dispersions confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS). An improved interface between the carbon fiber and Ni-SWNTs resulted in better surface coverage on the carbon plies. These hybrid composites were tested for Zone 2A lightning strike mitigation. The electrical resistivity of the composite system was reduced by ten orders of magnitude with the addition of 4 weight percent Ni-SWNTs (calculated with respect to the weight of a single carbon ply). The Ni-SWNTs - filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts indicated by the minimal carbon fiber pull out. Methods to reduce the electrical resistivity of 10 weight percent SWNTs -- medium density polyethylene (MDPE) composites were studied. The composites processed by hot coagulation method were subjected to low DC electric fields (10 V) at polymer melt temperatures to study the effect of viscosity, nanotube welding, dispersion and, resultant changes in electrical resistivity. The electrical resistivity of the composites was reduced by two orders of magnitude compared to 10 wt% CNT-MDPE baseline. For effective alignment of SWNTs, a new process called Electric field Vacuum Spray was devised to overcome viscosity within the dispersed nanotube polymer system, and produce conductive MDPE-SWNT thin films. Polarized Raman spectroscopy and scanning electron microscopy (SEM) analysis on the samples showed an improvement in SWNT -- SWNT contacts and alignment in the polymer matrix. The resistivity of the samples processed by this new method was two order magnitudes lower than the samples processed by hot coagulation method subjected to electric field.Item Carbon nanotubes filled polymer composites: A comprehensive study on improving dispersion, network formation and electrical conductivity(2010) Chakravarthi, Divya Kannan; Barrera, Enrique V.In this dissertation, we determine how the dispersion, network formation and alignment of carbon nanotubes in polymer nanocomposites affect the electrical properties of two different polymer composite systems: high temperature bismaleimide (BMI) and polyethylene. The knowledge gained from this study will facilitate optimization of the above mentioned parameters, which would further enhance the electrical properties of polymer nanocomposites. BMI carbon fiber composites filled with nickel-coated single walled carbon nanotubes (Ni-SWNTs) were processed using high temperature vacuum assisted resin transfer molding (VARTM) to study the effect of lightning strike mitigation. Coating the SWNTs with nickel resulted in enhanced dispersions confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS). An improved interface between the carbon fiber and Ni-SWNTs resulted in better surface coverage on the carbon plies. These hybrid composites were tested for Zone 2A lightning strike mitigation. The electrical resistivity of the composite system was reduced by ten orders of magnitude with the addition of 4 weight percent Ni-SWNTs (calculated with respect to the weight of a single carbon ply). The Ni-SWNTs - filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts indicated by the minimal carbon fiber pull out. Methods to reduce the electrical resistivity of 10 weight percent SWNTs --- medium density polyethylene (MDPE) composites were studied. The composites processed by hot coagulation method were subjected to low DC electric fields (10 V) at polymer melt temperatures to study the effect of viscosity, nanotube welding, dispersion and, resultant changes in electrical resistivity. The electrical resistivity of the composites was reduced by two orders of magnitude compared to 10 wt% CNT-MDPE baseline. For effective alignment of SWNTs, a new process called Electric field Vacuum Spray was devised to overcome viscosity within the dispersed nanotube polymer system, and produce conductive MDPE-SWNT thin films. Polarized Raman spectroscopy and scanning electron microscopy (SEM) analysis on the samples showed an improvement in SWNT --- SWNT contacts and alignment in the polymer matrix. The resistivity of the samples processed by this new method was two order magnitudes lower than the samples processed by hot coagulation method subjected to electric field.Item Cisplatin@US-tube Carbon Nanocapsules for Enhanced(2014-02-28) Guven, Adem; Wilson, Lon J.; Colvin, Vicki L.; Barrera, Enrique V.; Lewis, Michael T.The use of chemotherapeutic drugs in cancer therapy is often limited by problems with administration such as insolubility, inefficient biodistribution, lack of selectivelty, and inability of the drug to cross cellular barriers. To overcome these limitations, various types of drug delivery systems have been explored, and recently, carbon nanotube (CNT) materials have garnered special attention in the area. This thesis details the preparation, characterization, and in vitro and in vivo testing of a new, ultra-short single-walled carbon nanotube (US-tube)-based drug delivery system for the treatment of cancer. In particular, the encapsulation of cisplatin (CDDP), a widely-used anticancer drug, within US-tubes has been achieved by a loading procedure that is reproducible, and the resulting CDDP@US-tube material characterized by high-resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and inductively-coupled optical emission spectroscopy (ICP-OES). Dialysis studies performed in phosphate-buffered saline (PBS) at 37 °C have demonstrated that CDDP release from CDDP@US-tubes can be controlled (retarded) by wrapping the CDDP@US-tubes with Pluronic®-F108 surfactant. The anticancer activity of Pluronic-wrapped CDDP@US-tubes (W-CDDP@US-tubes) has been evaluated against two different breast cancer cell lines, MCF-7 and MDA-MB-231, and found to exhibit enhanced cytotoxicity over free CDDP. Moreover, it has been shown that CDDP release from W-CDDP@US-tubes nanocapsules can be stimulated remotely by a radiofrequency (RF) field which disrupts the Pluronic coating to release CDDP. RF-induced release-dependent cytotoxicity of W-CDDP@US-tubes has been evaluated in vitro against two different liver cancer cell lines, Hep3B and HepG2, and found to exhibit superior cytotoxicity compared to W-CDDP@US-tubes not exposed to RF. Finally, in vivo biodistribution and therapeutic efficacy of the CDDP@US-tube material has been evaluated against three different breast cancer xenograft mouse (SCID/Bg) models, and found to exhibit greater efficacy in suppressing tumor growth than free CDDP for both a MCF-7 cell line xenograft model and a BCM-4272 patient-derived xenograft (PDX) model. The CDDP@US-tubes also demonstrated prolonged circulation time compared to free CDDP which enhances permeability and retention (EPR) effects resulting in significantly more CDDP accumulation in tumors, as determined by Platinum (Pt) analysis via inductively-coupled plasma mass-spectrometry (ICP-MS).Item Computational techniques for aerodynamic simulations of multiple objects emphasizing paratrooper-aircraft separation(2005) Udoewa, Victor; Barrera, Enrique V.; Tapia, Richard A.Our target is to develop computational techniques for studying aerodynamic interactions between multiple objects with emphasis on studying the fluid mechanics and dynamics of an object exiting and separating from an aircraft. The object could be a paratrooper jumping out of a transport aircraft or a package of emergency aid dropped from a cargo plane. These are applications with major practical significance, and what I learn and what I develop can make a major impact on this technology area. In all these cases, the computational challenge is to predict the dynamic behavior and path of the object, so that the separation process is safe and effective. This is a very complex problem because it has an unsteady, three-dimensional nature and requires the solution of complex equations that govern the fluid dynamics of the object and the aircraft together, with their relative positions changing in time. The gravitational and aerodynamic forces acting on the object determine its dynamics and path. Sometimes those aerodynamic forces are not properly computed due to excessively thick numerical boundary layers (numerical meaning unphysical and unreal). Methods for reducing this thickness are presented here. The aerodynamic forces heavily depend on the unsteady flow field around the aircraft. The computational tools I am developing are based on the simultaneous solution of the time-dependent Navier-Stokes equations governing the airflow around the aircraft and the separating object, as well as the equations governing the motion of that object. These computational methods include suitable mesh update techniques that are essential for simulations with my core computational technique---the Deforming-Spatial-Domain/Stabilized Space-Time (DSD/SST) formulation. In the research I present here, I focus on developing mesh update methods that help me perform my computations with more numerical accuracy and better computational efficiency. These methods range from remeshing tactics with reduced distortion, to methods reducing the error introduced through projection and, finally, even to a mesh moving alternative---Fluid Object Interaction Subcomputation Technique (FOIST). In FOIST, moving object problems are computed with an approximation technique, without the costs of mesh moving, remeshing, or projection.Item Containerless mixing of metals and polymers with fullerenes and nanofibers to produce reinforced advanced materials(2008-01-29) Barrera, Enrique V.; Bayazitoglu, Yildiz; Rice University; United States Patent and Trademark OfficeThe present invention relates to fullerene, nanotube, or nanofiber filled metals and polymers. This invention stems from a cross-disciplinary combination of electromagnetic and acoustic processing and property enhancement of materials through fullerene or nanofiber additives. Containerless processing (CP) in the form of electromagnetic field enduced and/or acoustic mixing leads to controlled dispersion of fullerenes, nanotubes, or nanofibers in various matrices. The invention provides methods of mixing that highly disperse and align the fullerenes, nanotubes, or nanofibers within the matrices of metals and polymers. The invention provides new compositions of matter and multifunctional materials based on processing, composition, and degree of in situ processing.Item Covalently Functionalized Carbon Nano-Onions Integrated Gelatin Methacryloyl Nanocomposite Hydrogel Containing γ-Cyclodextrin as Drug Carrier for High-Performance pH-Triggered Drug Release(MDPI, 2021) Mamidi, Narsimha; Velasco Delgadillo, Ramiro Manuel; Barrera, Enrique V.Herein, poly (n-(4-aminophenyl) methacrylamide)) carbon nano-onions (PAPMA-CNOs = f-CNOs) and γ-cyclodextrin/DOX-complex (CD) reinforced gelatin methacryloyl (GelMA)/f-CNOs/CD supramolecular hydrogel interfaces were fabricated using the photo-crosslinking technique. The physicochemical properties, morphology, biodegradation, and swelling properties of hydrogels were investigated. The composite hydrogels demonstrated enriched drug release under the acidic conditions (pH 4.5 = 99%, and pH 6.0 = 82%) over 18 days. Owing to the f-CNOs inclusion, GelMA/f-CNOs/CD supramolecular hydrogels presented augmented tensile strength (σult = 356.1 ± 3.4 MPa), toughness (K = 51.5 ± 0.24 Jg−1), and Young’s modulus (E = 41.8 ± 1.4 GPa). The strengthening of GelMA/f-CNOs/CD hydrogel systems indicates its good dispersion and the degree of polymer enveloping of f-CNOs within GelMA matrixes. Furthermore, the obtained hydrogels showed improved cell viability with human fibroblast cells. Nevertheless, the primed supramolecular hydrogels would pave the way for the controlled delivery systems for future drug delivery.Item Development and characterization of a nanofiber-reinforced thermoplastic composite(1999) Lozano, Karen; Barrera, Enrique V.Polypropylene composites with vapor-grown carbon nanofibers (VGCF's) as reinforcement were prepared. The fibers used have an rage diameter of 200 nm with interesting thermal, electrical and mechanical properties which make them very promising for engineering applications. Fiber purification and activation of functional groups were conducted, where amorphous carbon particles were successfully removed, achieving, high purity fibers. Sample preparation was performed using conventional plastic processing technologies. Interactions between the fibers and the matrix were analyzed by physical, mechanical and electrical properties of the composite. Thermal physical analysis on the samples showed that the presence of the fibers influenced the morphology and crystallinity of the matrix. The decomposition temperature, as well as the crystallization rate increased with increasing fiber content. The electrical resistivity of the prepared composites decreased 12 orders of magnitude providing a potential composite for ESD applications. The addition of VGCF's showed an increase in stiffness of 350. Melt viscosity values were also increased by the VGCF reinforcement. Dispersion, porosity, and bonding aspects were also analyzed.Item Development of Functionalized Carbon Nano-Onions Reinforced Zein Protein Hydrogel Interfaces for Controlled Drug Release(MDPI, 2019) Mamidi, Narsimha; González-Ortiz, Aldo; Lopez Romo, Irasema; Barrera, Enrique V.In the current study, poly 4-mercaptophenyl methacrylate-carbon nano-onions (PMPMA-CNOs = f-CNOs) reinforced natural protein (zein) composites (zein/f-CNOs) are fabricated using the acoustic cavitation technique. The influence of f-CNOs inclusion on the microstructural properties, morphology, mechanical, cytocompatibility, in-vitro degradation, and swelling behavior of the hydrogels are studied. The tensile results showed that zein/f-CNOs hydrogels fabricated by the acoustic cavitation system exhibited good tensile strength (90.18 MPa), compared with the hydrogels fabricated by the traditional method and only microwave radiation method. It reveals the magnitude of physisorption and degree of colloidal stability of f-CNOs within the zein matrix under acoustic cavitation conditions. The swelling behaviors of hydrogels were also tested and improved results were noticed. The cytotoxicity of hydrogels was tested with osteoblast cells. The results showed good cell viability and cell growth. To explore the efficacy of hydrogels as drug transporters, 5-fluorouracil (5-FU) release was measured under gastric and intestinal pH environment. The results showed pH-responsive sustained drug release over 15 days of study, and pH 7.4 showed a more rapid drug release than pH 2.0 and 4.5. Nonetheless, all the results suggest that zein/f-CNOs hydrogel could be a potential pH-responsive drug transporter for a colon-selective delivery system.Item Dispersion of carbon nanotubes in vinyl ester polymer composites(2010) Pena-Paras, Laura; Barrera, Enrique V.This work focused on a parametric study of dispersions of different types of carbon nanotubes in a polymer resin. Single-walled (SWNTs), double-walled (DWNTs), multi-walled (MWNTs) and XD-grade carbon nanotubes (XD-CNTs) were dispersed in vinyl ester (VE) using an ultra-sonic probe at a fixed frequency. The power, amplitude, and mixing time parameters of sonication were correlated to the electrical and mechanical properties of the composite materials in order to optimize dispersion. The quality of dispersion was quantified by Raman spectroscopy and verified through optical and scanning electron microscopy. By Raman, the CNT distribution, unroping, and damage was monitored and correlated with the composite properties for dispersion optimization. Increasing the ultrasonication energy was found to improve the distribution of all CNT materials and to decrease the size of nanotube ropes, enhancing the electrical conductivity and storage modulus. However, excessive amounts of energy were found to damage CNTs, which negatively affected the properties of the composite. Based on these results the optimum dispersion energy inputs were determined for the different composite materials. The electrical resistivity was lowered by as much as 14, 13, 13, and 11 orders of magnitude for SWNT/VE, DWNT/VE, MWNT/VE, and XD-CNT/VE respectively, compared to the neat resin. The storage modulus was also increased compared to the neat resin by 77%, 82%, 45%, 40% and 85% in SWNT, SAP-f-SWNT, DWNT, MWNT and XD-CNT/VE composites, respectively. This study provides a detailed understanding of how the properties of, nanocomposites are determined by the composite mixing parameters and the distribution, concentration, shape and size of the CNTs. Importantly, it indicates the importance of the need for dispersion metrics to correlate and understand these properties.Item Evaluation of superelastic nitinol as a shielding material for hypervelocity impact(1999) Espinoza Magana, Nancy; Barrera, Enrique V.Superelastic Nitinol Shape Memory Alloy (SMA) as a shielding material for hypervelocity impact is investigated. Impact peak pressures from Rankine-Hugoniot equations and empirical figures of merit, which give a general evaluation of this material as a nickel titanium alloy, have been derived. Superelastic Nitinol was impacted at oblique and normal incidence using a two-stage light-gas gun and was evaluated as an intermediate layer in the Stuffed Whipple configuration and as bumper in the Whipple configuration. Its performance during oblique impacts is better than that of Kevlar and Al2024-T3. Superelastic SMA can dissipate impact energy through a martensitic phase transformation and through plastic yielding. Differential scanning calorimeter studies demonstrated that stress induced Martensite (SIM) is present in the hypervelocity impacted samples. Optical metallography and electron microscopy studies confirm the presence of SIM.Item Fabrication of carbon nanotube reinforced epoxy polymer composites using functionalized carbon nanotubes(2009-10-13) Khabashesku, Valery N.; Zhu, Jiang; Peng, Haiqing; Barrera, Enrique V.; Margrave, John L.; Margrave, Mary Lou; Rice University; United States Patent and Trademark OfficeThe present invention is directed to methods of integrating carbon nanotubes into epoxy polymer composites via chemical functionalization of carbon nanotubes, and to the carbon nanotube-epoxy polymer composites produced by such methods. Integration is enhanced through improved dispersion and/or covalent bonding with the epoxy matrix during the curing process. In general, such methods involve the attachment of chemical moieties (i.e., functional groups) to the sidewall and/or end-cap of carbon nanotubes such that the chemical moieties react with either the epoxy precursor(s) or the curing agent(s) (or both) during the curing process. Additionally, in some embodiments, these or additional chemical moieties can function to facilitate dispersion of the carbon nanotubes by decreasing the van der Waals attractive forces between the nanotubes.Item Fabrication of reinforced composite material comprising carbon nanotubes- fullerenes- and vapor-grown carbon fibers for thermal barrier materials- structural ceramics- and multifunctional nanocomposite ceramics(2007-12-11) Barrera, Enrique V.; Yowell, Leonard Lee, Jr.; Mayeaux, Brian Mitchell; Corral, Erica L.; Cesarano, Joseph, III; Rice University; United States Patent and Trademark OfficeThe present invention is directed towards a ceramic nanocomposite comprising a nanostructured carbon component inside a ceramic host. The ceramic nanocomposite may further comprise vapor grown carbon fibers. Such nanostructured carbon materials impart both structural and thermal barrier enhancements to the ceramic host. The present invention is also directed towards a method of making these ceramic nanocomposites and for methods of using them in various applications.