Spelling suggestions: "subject:"2transition emperature"" "subject:"2transition atemperature""
91 |
Towards stimuli-responsive functional nanocomposites: smart tunable plasmonic nanostructures Au-VO2Kana, Jean Bosco Kana January 2010 (has links)
Philosophiae Doctor - PhD / The fascinating optical properties of metallic nanostructures, dominated by collective oscillations of free electrons known as plasmons, open new opportunities for the development of devices fabrication based on noble metal nanoparticle composite materials. This thesis demonstrates a low-cost and versatile technique to produce stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical properties. Albeit challenging, further control using thermal external stimuli to tune the local environment of gold nanoparticles embedded in VO2 host matrix would be ideal for the design of responsive functional nanocomposites. We prepared Au-VO2 nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering (ICMS) known as hollow cathode magnetron sputtering for the first time and report the reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting the external temperature stimuli. The structural, morphological, interfacial analysis and optical properties of the optimized nanostructures have been studied. ICMS has been attracting much attention for its enclosed geometry and its ability to deposit on large area, uniform coating of smart nanocomposites at high deposition rate. Before achieving the aforementioned goals, a systematic study and optimization process of VO2 host matrix has been done by studying the influence of deposition parameters on the structural, morphological and optical switching properties of VO2 thin films. A reversible thermal tunability of the optical/dielectric constants of VO2 thin films by spectroscopic ellipsometry has been intensively also studied in order to bring more insights about the shift of the plasmon of gold nanoparticles imbedded in VO2 host matrix. / South Africa
|
92 |
Structural and Dynamical Properties of Organic and Polymeric Systems using Molecular Dynamics SimulationsLorena Alzate-Vargas (8088409) 06 December 2019 (has links)
<p>The use of atomistic level simulations like molecular dynamics are becoming a key part in the process of materials discovery, optimization and development since they can provide complete description of a material and contribute to understand the response of materials under certain conditions or to elucidate the mechanisms involved in the materials behavior.</p>
<p>We will discuss to cases in which molecular dynamics simulations are used to characterize and understand the behavior of materials: i) prediction of properties of small organic crystals in order to be implemented in a multiscale modeling framework which objective is to predict mechanically induced amorphization without experimental input other than</p>
<p>the molecular structure and ii) characterization of temperature dependent spatio-temporal domains of high mobility torsions in several bulk polymers, thin slab and isolated chains; strikingly we observe universality in the percolation of these domains across the glass transition.</p>
<p>However, as in any model, validation of the predicted results against appropriate experiments is a critical stage, especially if the predicted results are to be used in decision making. Various sources of uncertainties alter both modeling and experimental results and therefore the validation process. We will present molecular dynamics simulations to assess uncertainties associated with the prediction of several important properties of thermoplastic polymers; in which we independently quantify how the predictions are affected by several sources. Interestingly, we nd that all sources of uncertainties studied influence predictions, but their relative importance depends on the specific quantity of interest.</p>
|
93 |
Towards stimuli-responsive functional nanocomposites: Smart tunable plasmonic nanostructures au-v02Kama Kama, Jean Bosco January 2010 (has links)
Magister Philosophiae - MPhil / The fascinating optical properties of metallic nanostructures, dominated by collective
oscillations of free electrons known as plasmons, open new opportunities for the
development of devices fabrication based on noble metal nanoparticle composite
materials. This thesis demonstrates a low-cost and versatile technique to produce
stimuli-responsive ultrafast plasmonic nanostructures with reversible tunable optical
properties. Albeit challenging, further control using thermal external stimuli to tune the
local environment of gold nanoparticles embedded in V02 host matrix would be ideal
for the design of responsive functional nanocomposites. We prepared Au-V02
nanocomposite thin films by the inverted cylindrical reactive magnetron sputtering
(ICMS) known as hollow cathode magnetron sputtering for the first time and report the
reversible tuning of surface plasmon resonance of Au nanoparticles by only adjusting
the external temperature stimuli. The structural, morphological, interfacial analysis and
optical properties of the optimized nanostructures have been studied. ICMS has been
attracting much attention for its enclosed geometry and its ability to deposit on large
area, uniform coating of smart nanocomposites at high deposition rate. Before
achieving the aforementioned goals, a systematic study and optimization process of
V02 host matrix has been done by studying the influence of deposition parameters on
the structural, morphological and optical switching properties of V02 thin films. A
reversible thermal tunability of the optical/dielectric constants of V02 thin films by
spectroscopic ellipsometry has been intensively also studied in order to bring more
insights about the shift of the plasmon of gold nanoparticles imbedded in V02 host
matrix.
|
94 |
Vibration Characteristics of Axially Graded Viscoelastic BeamsHeras Segura, Mariona 06 May 2019 (has links)
No description available.
|
95 |
Transesterification, Phase Transition, Rheology, and Mechanical Properties of Blends of Thermoplastic Polyester and Thermotropic PolyesterWu, Chonggang 17 May 2006 (has links)
No description available.
|
96 |
Molecular modeling of graphite/vinyl ester nanocomposite properties and damage evolution within a cured thermoset vinyl ester resinNacif El Alaoui, Reda 25 November 2020 (has links)
The non-reactive Dreiding and the reactive ReaxFF atomic potentials were applied within a family of atom molecular dynamics (MD) simulations to investigate and understand interfacial adhesion in graphene/vinyl ester composites. First, a liquid vinyl ester (VE) resin was equilibrated in the presence of graphene surfaces and then cured, resulting in a gradient in the monomer distribution as a function of distance from the surfaces. Then the chemically realistic relative reactivity volume (RRV) curing algorithm was applied that mimics the known radical addition regiochemistry and monomer reactivity ratios of the VE monomers during three-dimensional chain-growth polymerization. Surface adhesion between the cured VE resin and the graphene reinforcement surfaces was obtained at a series of VE resin “crosslink densities.” Both pristine and oxidized graphite sheets were employed separately in these simulations using a Dreiding potential. The pristine sheets serve as a surrogate for pure carbon fibers while oxidizing the outer graphene sheets serve as a model for oxidized carbon fibers. Hence, the effects of local monomer distribution and temperature on the interphase region formation and surface adhesion can be investigated. Surface adhesion was studied at various curing conversions and as a function of temperature. Uniaxial loading simulations were performed at different curing conversions for both models to predict the composites’ modulus of elasticity, Poisson’s ratio, and yield strength. The same analysis was performed for the neat cured matrix. The glass transition temperature (Tg) for the homogenized composite and neat VE matrix was determined at different degrees of curing. Subsequent MD simulations were performed to predict structural damage evolution and fracture in the neat VE matrix. The ReaxFF potential was used to quantify irreversible damage due to bond breakage in the neat VE matrix for different degrees of cure, stress states, temperatures, and strain rates. The predicted damage mechanisms in the bulk VE thermosetting polymer were directly compared to those for an amorphous polyethylene (PE) thermoplastic polymer.
|
97 |
HIGH PERFORMANCE BLENDS AND COMPOSITES: PART (I) CLAY AEROGEL/POLYMER COMPOSITES PART (II) MECHANISTIC INVESTIGATION OF COLOR GENERATION IN PET/MXD6 BARRIER BLENDSBandi, Suneel A. 12 July 2006 (has links)
No description available.
|
98 |
Thermodynamic and glass transition behavior in CO<sub>2</sub>-Polymer systems emphasizing the surface regionLiu, Dehua 21 September 2006 (has links)
No description available.
|
99 |
A MOLECULAR DYNAMICS BASED STUDY OF BULK AND FINITE POLYSTYRENE-CARBON DIOXIDE BINARY SYSTEMSSrivastava, Anand 02 November 2010 (has links)
No description available.
|
100 |
Manufacture of and Environmental Effects on Carbon Fiber-Reinforced PhenylEthynyl-Terminated Poly(EtherImide)Bullions, Todd Aaron 18 September 2000 (has links)
The initial objective of this research project was to determine the feasibility of manufacturing carbon fiber-reinforced (CFR) composites with a matrix consisting of a phenylethynyl-terminated version of a thermoplastic poly(etherimide) termed PETU. Successful composite manufacture with 3,000 g/mol (3k) PETU led to a survey of CFR 3kPETU mechanical properties for comparison with other high-performance composites. Encouraging results led to a study of moisture sorption effects on CFR 3kPETU properties. The success of these initial studies spawned the large scale production of 2,500 g/mol (2.5k) PETU.
Thermal characterization of neat and CFR 2.5kPETU via differential scanning calorimetry, dynamic mechanical thermal analysis, and parallel plate rheometry resulted in an understanding of the influence of cure time and temperature on reaction progress via both reaction kinetics and monitoring of the glass transition temperature. From the rheological characterization, a two-stage, dual-Arrhenius model was developed to successfully model isothermal complex viscosity over the range of processing temperatures.
Neat 2.5kPETU and CFR 2.5kPETU specimens were exposed separately to elevated temperature environments of different moisture and different oxygen concentrations to evaluate the effects of moisture absorption, moisture desorption, and thermal oxidation on material properties. Moisture absorption took place in a 90 °C / 85% relative humidity environment followed by moisture desorption in a 90 °C / 10% relative humidity environment. Thermal-oxidative aging for up to 5000 hours took place at 204 204 °C in environments of four different oxygen partial pressures: 0.0 kPa, 2.84 kPa, 20.2 kPa, and 40.4 kPa. Following exposure to the different aging environments, the specimens were tested for retention of mechanical properties. In addition, moisture sorption properties were measured.
Results from the moisture sorption studies on CFR 3kPETU and CFR 2.5kPETU suggest that fully cured composites will withstand moisture absorption and desorption with negligible effects on mechanical properties, whereas, lack of full cure allows moisture sorption to permanently damage the composites. Despite a lack of mass loss or visual evidence of degradation following thermal-oxidative aging, a decline in mechanical properties was observed with the reduction becoming greater with longer aging times and higher oxygen partial pressures. / Ph. D.
|
Page generated in 0.3591 seconds