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Optical Transparent Pmma Composite Reinforced By Coaxial Electrospun Pan Hollow Nanofibers

Description: Electrospinning has been recognized as an efficient technique for the fabrication of polymer fibers. These electrospun fibers have many applications across a broad range of industries. In this research, optical transparent composites were successfully fabricated by embedding polyacrylonitrile (PAN) hollow nanofibers into poly (methyl methacrylate) (PMMA) matrix. The hollow PAN nanofibers were prepared by coaxial electrospinning. The PAN was used as the shell solution, and the mineral oil was used as the core solution. The resulting fibers were then etched with octane to remove the mineral oil from the core. The hollow PAN fibers were then homogeneously distributed in PMMA resins to fabricate the composite. The morphology, transmittance and mechanical properties of the PAN/PMMA composite were then characterized with an ESEM, TEM, tensile testing machine, UV-vis spectrometer and KD2 Pro Decagon device. The results indicated that the hollow nanofibers have relatively uniform size with one-dimensional texture at the walls. The embedded PAN hollow nanofibers significantly enhanced the tensile stress and the Young's modulus of the composite (increased by 58.3% and 50.4%, respectively), while having little influence on the light transmittance of the composite. The KD2 Pro device indicated that the thermal conductivity of the PMMA was marginally greater than the PAN/PMMA composite by 2%. This novel transparent composite could be used for transparent armor protection, window panes in vehicles and buildings, and airplane windshield etc.
Date: May 2013
Creator: Antoine, Donley
Partner: UNT Libraries

GEM-type detectors using LIGA and etchable glass technologies

Description: Gas electron multipliers (GEMS) have been made by a deep X-ray lithography technique (LIGA process) using synchrotron radiation on polymethylmethacrylate (PMMA) and by UV processes using a UV etchable glass. Gain, stability and rate capability for these detectors are described.The LIGA detectors described consist of PMMA sheets of various thicknesses, 125mm to 350mm, and have 150mm x 150mm square holes spaced with a pitch of 300mm. Thin copper electrodes are plated on the top and bottom surfaces using a Damascene method, followed by electroless plating of the copper onto a palladium-tin base layer. For various thicknesses of PMMA measurements have been made of absolute gain vs. voltage, time stability of gain, and rate capability. The operating gas mixture was usually Ar/CO2 (70/30) gas, but some tests were also done using P10 gas. We also made GEM-like detectors using the UV etchable glass called Foturan, patterned by exposure to UV light and subsequent etching. A few measurements using these detectors will be reported, including avalanche gain and time stability.
Date: November 2, 2001
Creator: Ahn, S.K.; Kim, J.G.; Perez-Mendez, V.; Chang, S.; Jackson, K.H.; Kadyk, J.A. et al.
Partner: UNT Libraries Government Documents Department

Durability of Poly(Methyl Methacrylate) Lenses Used in Concentrating Photovoltaic Technology (Revised) (Presentation)

Description: Concentrating photovoltaic (CPV) technology recently gained interest based on its expected low levelized cost of electricity, high efficiency, and scalability. Many CPV systems employ Fresnel lenses composed of poly(methyl methacrylate) (PMMA) to obtain a high optical flux density on the cell. The optical and mechanical durability of these lenses, however, is not well established relative to the desired surface life of 30 years. Our research aims to quantify the expected lifetime of PMMA in key market locations (FL, AZ, and CO).
Date: January 1, 2012
Creator: Miller, D. C.; Carloni, J. D.; Pankow, J. W.; Gjersing, E. L.; To, B.; Packard, C. E. et al.
Partner: UNT Libraries Government Documents Department

Influence of temperature and strain rate on the compressive behavior of PMMA and polycarbonate polymers

Description: Compression stress-strain measurements have been made on commercial polymethylmethacrylate (PMMA) and polycarbonate (PC) polymers as a function of tcmperature (-197 C to 220 C) and strain rate. A split-Hopkinson-pressure bar (SJIPU) was used to achieve strain rates of about 2500 s-' and a servohydraulic tester was used for lower strain rate testing (0.001 to 5 s-'). The mechanical response of these transparent polymers is quite different. The strength of PC is weakly dependent on strain rate, only moderately dependent on temperature, and remains ductile to -197OC. In contrast, the strength of PMMA is linearly dependent on temperature and strongly dependent on strain rate. Significantly, PMMA develops cracking and fails in compression with little ductility ( 7 4 % total strain) at either low strain rates and very low temperatures (-197OC) or at high strain rates and temperatures very near ambient.
Date: January 1, 2001
Creator: Cady, C. M. (Carl McElhinney); Lopez, M. F. (Mike F.); Gray, G. T. (George T.), III; Idar, D. J. (Deanne J.) & Blumenthal, W. R. (William R.)
Partner: UNT Libraries Government Documents Department

Electrospun a-Si using Liquid Silane/Polymer Inks

Description: Amorphous silicon nanowires (a-SiNWs) were prepared by electrospinning cyclohexasilane (Si{sub 6}H{sub 12}) admixed with polymethylmethacrylate (PMMA) in toluene. Raman spectroscopy characterization of these wires (d {approx} 50-2000 nm) shows 350 C treatment yields a-SiNWs. Porous a-SiNWs are obtained using a volatile polymer.
Date: December 9, 2010
Creator: Schulz, Doug
Partner: UNT Libraries Government Documents Department

Electrospun a-Si using Liquid Silane/Polymer Inks

Description: Amorphous silicon nanowires (a-SiNWs) were prepared by electrospinning cyclohexasilane (Si{sub 6}H{sub 12}) admixed with polymethylmethacrylate (PMMA) in toluene. Raman spectroscopy characterization of these wires (d {approx} 50-2000 nm) shows 350 C treatment yields a-SiNWs. Porous a-SiNWs are obtained using a volatile polymer.
Date: December 1, 2010
Creator: Schulz, D.L.; Hoey, J.M.; Smith, J.; Lovaasen, J.; Braun, C.; Dai, X. et al.
Partner: UNT Libraries Government Documents Department

Beamline and exposure station for deep x-ray lithography at the Advanced Photon Source

Description: APS is a third-generation synchrotron radiation source. With an x-ray energy of 19.5 keV and highly collimated beam (<0.1 mrad), APS is well suited for producing high-aspect-ratio microstructures in thick resist films (> 1 mm) using deep x-ray lithography (DXRL). The 2-BM beamline was constructed and will be used for DXRL at APS. Selection of appropriate x-ray energy range is done through a variable-angle mirror and various filters in the beamline. At the exposure station, the beam size will be 100(H) x 5(V) mm{sup 2}. Uniform exposure will be achieved by a high-speed (100 mm/sec) vertical scanner, which allows precise angular ({approximately}0.1 mrad) and positional (< 1 {mu}m) control of the sample, allowing full use of the highly collimated beam for lateral accuracy and control of sidewall slopes during exposure of thick resists, as well as generation of conicals and other profiles. For 1-mm-thick PMMA, a 100 x 25 mm{sup 2} area can be fully exposed in about 1/2 hr, while even 10-mm-thick PMMA will require only 2-3 hours.
Date: December 31, 1996
Creator: Lai, B.; Mancini, D.C.; Yun, W. & Gluskin, E.
Partner: UNT Libraries Government Documents Department

DYNAMICS OF POLYMERS AT INTERFACES

Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project addresses fundamental questions concerning the behavior of polymers at interfaces: (1) What processes control the formation of an adsorbed layer on a clean surface? (2) What processes control the displacement of preadsorbed polymers? (3) Can one accurately predict the structure of polymer layers? To answer these questions, using neutron reflectivity, we have studied adsorbed layers of the polymer poly(methyl methacrylate) (PMMA) onto a quartz substrate. The polymer density profiles were derived from the neutron reflectivity data. We have shown that dry films exhibit behavior predicted by mean-field theory in that the equilibrated layer thickness scales with the molecular weight of the polymer. Also, we find that the profiles of the polymers in solution qualitatively agree with those predicted by reflected random walk (RRW) theories, yet the profiles are not in quantitative agreement.
Date: November 1, 1999
Creator: SMITH, G.S.; MAJEWSKI, J. & AL, ET
Partner: UNT Libraries Government Documents Department

Deformations and stress in PMMA during hard x-ray exposure for deep lithography.

Description: The availability of high-energy, high-flux, collimated synchrotrons radiation has extended the application of deep X-ray lithography (DXRL) to thickness values of the PMMA resist of several millimeters. Some of the most severe limitations come from plastic deformation, stress, and cracks induced in PMMA during exposure and development. We have observed and characterized these phenomena quantitatively. Profilometry measurements revealed that the PMMA is subjected either to local shrinkage or to expansion, while compression and expansion evolve over time. Due to material loss and crosslinking, the material undergoes a shrinkage, while the radiation-induced decomposition generates gases expanding the polymer matrix. The overall dynamics of the material microrelief and stress during and after the exposure depend on the balance between compaction and outgassing. These depend in turn on the exposure conditions (spectrum; dose, dose rate, seaming, temperature), post-exposure storage conditions, PMMA material properties and thickness, and also on the size and geometry of the exposed patterns.
Date: August 17, 1999
Creator: Moldovan, N.
Partner: UNT Libraries Government Documents Department

Thermal Expansion and Hydration Behavior of PMMA Moulding Materials for LIGA Applications

Description: The thermal expansion coefficient, swelling characteristics and solute uptake kinetics of three PMMA molding materials (Perspex-CQ, Acrylite OP-1 and Solacryl 2750) are reported. Over the temperature range of 22 C to 50 C, all three materials exhibited similar CTE values of approximately 7.5 x 10{sup -5} C{sup -1}. Swelling characteristics, measured as the change in length of coupons were examined in three environments: deionized water, Ni Sulfamate plating solution and Ni Watts plating solution. Total swelling after {approx}150 hours of exposure was similar for all materials in each environment but were different for each environment examined: {approx}0.42% for de-ionized water, {approx} 0.30% for the Ni Sulfamate and {approx} 0.36% for the Ni-Watts plating solutions. Solute uptake kinetics were measured between 4 C and 50 C and the pre-exponential term (D{sub o}) and the activation energy (QD) are reported for each material in the three environments. Do values ranged between 0.07 and 0.45 cm{sup 2}/sec depending on the environment. Q{sub D} showed little variation, ranging between 4.1 and 4.4 x 10{sup 5} J/mole.
Date: February 1, 2003
Creator: Goods, Steven H.
Partner: UNT Libraries Government Documents Department

Dimensional errors in LIGA-produced metal structures due to thermal expansion and swelling of PMMA.

Description: Numerical methods are used to examine dimensional errors in metal structures microfabricated by the LIGA process. These errors result from elastic displacements of the PMMA mold during electrodeposition and arise from thermal expansion of the PMMA when electroforming is performed at elevated temperatures and from PMMA swelling due to absorption of water from aqueous electrolytes. Both numerical solutions and simple analytical approximations describing PMMA displacements for idealized linear and axisymmetric geometries are presented and discussed. We find that such displacements result in tapered metal structures having sidewall slopes up to 14 {micro}m per millimeter of height for linear structures bounded by large areas of PMMA. Tapers for curved structures are of similar magnitude, but these structures are additionally skewed from the vertical. Potential remedies for reducing dimensional errors are also discussed. Here we find that auxiliary moat-like features patterned into the PMMA surrounding mold cavities can reduce taper by an order of magnitude or more. Such moats dramatically reduce tapers for all structures, but increase skew for curved structures when the radius of curvature is comparable to the structure height.
Date: April 1, 2004
Creator: Kistler, Bruce L.; Dryden, Andrew S.; Crowell, Jeffrey A.W. & Griffiths, Stewart K.
Partner: UNT Libraries Government Documents Department

Demonstration of a monolithic micro-spectrometer system

Description: The starting design of our spectrometer was based on a modified Czerny-Turner configuration containing five precision surfaces encapsulated in a monolithic structure. We were interested in exploring novel system designs, fabrication technologies, and examining numerous material systems, in the development of the micro- spectrometer. Our purpose at the early stages was to demonstrate the feasibility of the technology and not an attempt to address a specific sensing problem. Thus we had great liberty to select the first prototype material, which was optical quality polymethyl methacrylate (PMMA). However for most aerospace applications, more robust materials would be required such as BK7, sapphire, quarts, etc. In addition, these materials, as well as many III-V and II-VI, would allow tremendous wavelength flexibility to support most applications. Although many of these materials can be diamond-turned, some brittle substrates require ductile-grinding with some post-polishing to achieve the desired performance.
Date: December 31, 1995
Creator: Rajic, S. & Egert, C.M
Partner: UNT Libraries Government Documents Department

Simultaneous PVDF/VISAR measurement technique for isentropic loading with graded density impactors

Description: A simultaneous PVDF/VISAR measurement technique was used for isentropic-loading experiments with a polymethyl methacrylate (PMMA) specimen. The experiments used a graded density impactor accelerated onto a tantalum driver backed with PMMA and then lithium fluoride windows for each experiment. Simultaneous measurements made at each window interface provided precise transit time and particle velocity measurements which can be used to determine the stress-vs-strain loading path using Lagrangian analysis techniques. The experimental technique provides access to 40 GPa stress levels in PMMA under isentropic-loading conditions.
Date: October 1, 1997
Creator: Anderson, M.U.; Chhabildas, L.C. & Reinhart, W.D.
Partner: UNT Libraries Government Documents Department

Off-specular x-ray scattering studies of the morphology of thin films

Description: We discuss the scattering of x-rays from thin films at a surface or interface decorated with a morphology of islands and how these effects manifest themselves in the specular reflectivity and the diffuse (off-specular) scattering. We show how this technique has been used to study block copolymer films decorated with islands on the surface and the development of electrochemically induced pitting on a Cu electrode in an electrolyte solution.
Date: September 1, 1996
Creator: Sinha, S.K.; Feng, Y.P. & Melendres, C.A.
Partner: UNT Libraries Government Documents Department

Enhanced adhesion buffer layer for deep x-ray lithography using hard x-rays.

Description: The first step in the fabrication of microstructure using deep x-ray lithography (DXRL) is the irradiation of a x-ray sensitive resist like polymethylmethacrylate (PMMA) by hard x-rays. At the Advanced Photon Source, a dedicated beamline allows the proper exposure of very thick (several mm) resists. To fabricate electroformed metal microstructure with heights of several mm, a PMMA sheet is glued onto a metallic plating base. An important requirement is that the PMMA layer must adhere well to the plating base. The adhesion is greatly reduced by the penetration of even a small fraction of hard x-rays through the mask absorber into the substrate. In this work we will show a novel technique to improve the adhesion of PMMA onto high-Z substrates for DXRL. Results of the improved adhesion are shown for different exposure/substrate conditions.
Date: August 28, 1998
Creator: De Carlo, F.
Partner: UNT Libraries Government Documents Department

Frequency doubling in poled polymers using anomalous dispersion phase-matching

Description: The authors report on a second harmonic generation in a poled polymer waveguide using anomalous dispersion phase-matching. Blue light ({lambda} = 407 nm) was produced by phase-matching the lowest order fundamental and harmonic modes over a distance of 32 {micro}m. The experimental conversion efficiency was {eta} = 1.2 {times} 10{sup {minus}4}, in agreement with theory. Additionally, they discuss a method of enhancing the conversion efficiency for second harmonic generation using anomalous dispersion phase-matching to optimize Cerenkov second harmonic generation. The modeling shows that a combination of phase-matching techniques creates larger conversion efficiencies and reduces critical fabrication requirements of the individual phase-matching techniques.
Date: October 1, 1995
Creator: Kowalczyk, T.C.; Singer, K.D. & Cahill, P.A.
Partner: UNT Libraries Government Documents Department

Noise measurements in shunted, shorted, and fully electroded quartz gauges in the Saturn plasma radiation source x-ray simulator

Description: This paper describes recent work to improve the measurement of the stress response of materials to intense, short pulses of radiation. When Saturn fires, large prompt electrical noise pulses are induced in stress measurement circuits. The conventional wisdom has been that the shorted guard ring quartz gauge was the only configuration with acceptable prompt signal-to-noise characteristics for stress measurements in this pulsed radiation environment. However, because of abnormal signal distortion, the shorted guard ring gauge is restricted to a maximum stress of about 8 kbars. Below this level, the normal, quantified signal distortion is correctable with analytical deconvolution techniques. The shunted guard ring gauge is acceptable for Egli fidelity measurements to about 25 kbars with negligible signal distortion. Experiments were conducted on the Saturn soft x-ray source which show that higher fidelity shunted guard ring gauges can successfully measure stress with acceptable induced noise. We also found that a 50-ohm impedance matching resistor at the gauge reduced the prompt noise amplitude and improved the baseline quality of the measurement prior to shock wave arrival.
Date: August 1, 1995
Creator: Barrett, W.H.; Greenwoll, J.I.; Smith, C.W.; Johnson, D.E. & De La Cruz, C.F.
Partner: UNT Libraries Government Documents Department

X-ray lenses fabricated by deep x-ray lithography.

Description: Refractive x-ray lenses have been fabricated using deep x-ray lithography. Lenses were produced directly in 1- to 6-mm-thick sheets of polymethylmethacrylate (PMMA) with as many as 100 cylindrical lenses along the optical axis. The fabrication process consists of exposing the PMMA sheets to high-energy synchrotron radiation through a mask of 50-micron-thick gold on silicon and subsequent development in ketone. The lenses are suitable for use in synchrotron radiation from a bending magnet at the Advanced Photon Source in the energy range of 8-16 keV. Results of measurements of focus quality, flux density gain, and scatter are presented and discussed with regard to the quality of lens material and fabrication method. Means for improving the performance of the lenses is discussed.
Date: September 26, 2002
Creator: Mancini, D. C.; Moldovan, N.; Divan, R.; DeCarlo, F. & Yaeger, J.
Partner: UNT Libraries Government Documents Department

Segmental interpenetration at polymer interfaces. [Progress report]

Description: During the first year of this proposal significant strides have been made in understanding the nature of the interface in symmetric, diblock copolymers and the nature of the interface formed between immiscible homopolymers. Emphasis has been placed on the symmetric, diblock copolymers of polystyrene (PS) and polymethylmethacrylate (PMMA) since these diblock copolymers and the corresponding homopolymers are available over a wide range of molecular weight with narrow molecular weight distributions. In addition, the homopolymers and copolymers can be obtained with different levels of deuteration. Thus, these materials form a model system by which systematic studies on the interfacial behavior of homopolymers and block copolymers can be performed.
Date: December 31, 1989
Creator: Russell, T. P. & Fleming, W. W.
Partner: UNT Libraries Government Documents Department

Final LDRD report : advanced plastic scintillators for neutron detection.

Description: This report summarizes the results of a one-year, feasibility-scale LDRD project that was conducted with the goal of developing new plastic scintillators capable of pulse shape discrimination (PSD) for neutron detection. Copolymers composed of matrix materials such as poly(methyl methacrylate) (PMMA) and blocks containing trans-stilbene (tSB) as the scintillator component were prepared and tested for gamma/neutron response. Block copolymer synthesis utilizing tSBMA proved unsuccessful so random copolymers containing up to 30% tSB were prepared. These copolymers were found to function as scintillators upon exposure to gamma radiation; however, they did not exhibit PSD when exposed to a neutron source. This project, while falling short of its ultimate goal, demonstrated the possible utility of single-component, undoped plastics as scintillators for applications that do not require PSD.
Date: September 1, 2010
Creator: Vance, Andrew L.; Mascarenhas, Nicholas; O'Bryan, Greg & Mrowka, Stanley
Partner: UNT Libraries Government Documents Department

Report on 1992/1993 activities

Description: Over the past several years, at least four different techniques have been developed for probing the behavior of homopolymers and block copolymers at surfaces and interfaces. These include neutron reflectivity, grazing incidence x-ray scattering, dynamic secondan, ion mass spectrometry and electron microscopy. In the upcoming year It is proposed to make key uses of these developments to gain a quantitative understanding of the Interfacial behavior of homopolymers and block copolymers. In addition, the newly discovered lower disorder to order phase transition will be investigated further, is the role a surface or an interface plays in influencing the structure and segmental distribution of polymers in the vicinity of an interface. These areas are outlined below.
Date: July 1, 1996
Creator: Russell, T.P.
Partner: UNT Libraries Government Documents Department

Dimensional variation and roughness of LIGA fabricated microstructures

Description: We have measured the dimensional variation and sidewall roughness of features on PMMA micro- components fabricated by deep x-ray lithography in order to assess the effect of dimensional variation on subsequent assembly operations. Dimensional measurements were made using a stylus profilometer with a repeatability in step height of better than 0.01 {mu}m. Roughness measurements were made with the same profilometer scanning in a direction perpendicular to the length of the parts. 22 {mu}m and 54 {mu}m features exhibited dimensional variations described by a Gaussian distribution with standard deviations of 0.202 {mu}m and 0.381 {mu}m, respectively. This corresponds to a maximum relative variation of between 0.6% and 0.9%. Sidewall roughnesses were found to be in the range of 0.02 {mu}m to 0. 03 {mu}m, an insignificant contribution to the total variation when compared to overall dimensional variation. Several potential sources of this variation are discussed, but no single cause was identified as the source of the significant dimensional variation observed here.
Date: October 1, 1996
Creator: Egert, C.M.; Wood, R. & Malek, C.K.
Partner: UNT Libraries Government Documents Department

A near-field optical microscopy nanoarray

Description: Multiplexing near-field scanning optical microscopy (NSOM) by the use of a nanoarray with parallel imaging is studied. The fabrication, characterization, and utilization of nanoarrays with {approximately} 100 nm diameter apertures spaced 500 nm center-to- center is presented. Extremely uniform nanoarrays with {approximately} 10{sup 8} apertures were fabricated by electron beam lithography and reactive ion etching. The nanoarrays were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). In this paper we utilize these nanoarrays in a laser-illuminated microscope with parallel detection on a charge- coupled device (CCD). Detection of B-phycoerythrin (B-PE) molecules using near-field illumination is presented. In principle, our system can be used to obtain high lateral resolution NSOM images over a wide-field of view (e.g. 50-100 {mu}m) within seconds.
Date: December 31, 1996
Creator: Semin, D.J.; Ambrose, W.P.; Goodwin, P.M.; Kwller, A. & Wendt, J.R.
Partner: UNT Libraries Government Documents Department