Controlled nanostructure and high loading of single-walled carbon nanotubes reinforced polycarbonate composite

Abstract This paper presents an effective technique to fabricate thermoplastic nanocomposites with high loading of well-dispersed single-walled carbon nanotubes (SWNTs). SWNT membranes were made from a multi-step dispersion and filtration method, and then impregnated with polycarbonate solution to make thermoplastic nanocomposites. High loading of nanotubes was achieved by controlling the viscosity of polycarbonate solution. SEM and AFM characterization results revealed the controlled nanostructure in the resultant nanocomposites. Dynamic mechanical property tests indicated that the storage modulus of the resulting nanocomposites at 20 wt% nanotubes loading was improved by a factor of 3.4 compared with neat polycarbonate material. These results suggest the developed approach is an effective way to fabricate thermoplastic nanocomposites with good dispersion and high SWNT loading

An Assessment Of Forcite Approaches In Predictiing Young’s Modulus From Crystal Structure

University of Minnesota M.S. thesis. July 2019. Major: Pharmaceutics. Advisor: Changquan Sun. 1 computer file (PDF); vii, 52 pages.Improving the efficiency of tablet manufacturing in pharmaceutical industry has always attracted great concern. The mechanical properties of drugs are important for successful tablet production Thus, the knowledge of mechanical properties of pharmaceutical compound in pre-formulation stage facilitates tablet formulation development. A fast and accurate computational method for predicting crystal mechanical properties from crystal structure is extremely valuable since the availability of pharmaceutical active ingredients (APIs) is usually very limited. Methods based on the potential surface energy simulation are fast but their accuracy has not been systematically evaluated using a large set of crystals. The goal of the current study was to evaluate accuracy of predicted Young’s modulus (E) using the Forcite module in commercial software, Material Studio. The predicted E values of 50 organic crystals were compared to experimental values obtained by nanoindentation to assess their accuracy. A method to predict the E values on specific crystal faces was established to improve correlation by accounting for anisotropy of crystal mechanical properties. The correlation with experimental values remained poor. Detailed analyses of calculated E map of three crystals still failed to produce accurate E. Thus, the current Forcite module in Materials Studio for routine crystal form screening should be used with caution

Análisis de adsorción del colorante azoico naranja ácido 7 (sodio; 4 - [(2-hidroxinaftalen-1-il) diazenil] bencenosulfonato) de la industria textil ecuatoriana sobre grafeno mediante simulaciones computacionales para establecer condiciones óptimas de operación.

El objetivo fue analizar la adsorción del colorante azoico naranja acido 7 (sodio; 4 - [(2- hidroxinaftalen-1-il) diazenil] bencenosulfonato) de la industria textil ecuatoriana sobre grafeno mediante simulaciones computacionales para establecer condiciones óptimas de operación. Se realizó un estudio bibliográfico para determinar el punto de partida de la investigación. Verificando que no existía estudios previos de dinámica molecular para la adsorción de colorantes azoicos, se encontró los coeficientes necesarios para realizar la simulación mediante cálculos DFT ab-initio. Las simulaciones permitieron encontrar los valores de los descriptores químicos globales y locales del sistema molécula colorante-grafeno como el potencial químico de -3.773 eV, una dureza química de 1.776 eV, potencial de ionización igual a 5.549 eV y también la afinidad electrónica de 1.997 eV. También se presenta una energía de adsorción del sistema de -17.039 kJ/mol, valor que expresa que no existe una adsorción química entre el grafeno y la molécula colorante; lo que se demuestra también a través de las simulaciones de los resultados, los cuales se trabajaron a diferentes temperaturas, desde 280 K hasta 310 K con intervalos de 10 grados; diferentes radios de la membrana para cambiar el caudal de la simulación y con diferentes presiones. Las simulaciones permiten observar el movimiento de las moléculas a medida que transcurre el tiempo y verificar a nivel atómico que sucede entre las membranas de grafeno, el agua y el colorante azoico naranja ácido 7. Con los resultados obtenidos también se propone un sistema en el cual, a pesar de no tener una adsorción, se pueda tener una disminución de la concentración del colorante azoico al pasar por una estructura de grafeno, demostrando una reducción del colorante hasta 175 picosegundos, con lo cual se podría armar un sistema experimental con esas características. Finalmente, todos los datos obtenidos fueron verificados mediante varias fuentes bibliográficas asegurando la confiabilidad de las simulaciones realizadas.El objetivo fue analizar la adsorción del colorante azoico naranja acido 7 (sodio; 4 - [(2- hidroxinaftalen-1-il) diazenil] bencenosulfonato) de la industria textil ecuatoriana sobre grafeno mediante simulaciones computacionales para establecer condiciones óptimas de operación. Se realizó un estudio bibliográfico para determinar el punto de partida de la investigación. Verificando que no existía estudios previos de dinámica molecular para la adsorción de colorantes azoicos, se encontró los coeficientes necesarios para realizar la simulación mediante cálculos DFT ab-initio. Las simulaciones permitieron encontrar los valores de los descriptores químicos globales y locales del sistema molécula colorante-grafeno como el potencial químico de -3.773 eV, una dureza química de 1.776 eV, potencial de ionización igual a 5.549 eV y también la afinidad electrónica de 1.997 eV. También se presenta una energía de adsorción del sistema de -17.039 kJ/mol, valor que expresa que no existe una adsorción química entre el grafeno y la molécula colorante; lo que se demuestra también a través de las simulaciones de los resultados, los cuales se trabajaron a diferentes temperaturas, desde 280 K hasta 310 K con intervalos de 10 grados; diferentes radios de la membrana para cambiar el caudal de la simulación y con diferentes presiones. Las simulaciones permiten observar el movimiento de las moléculas a medida que transcurre el tiempo y verificar a nivel atómico que sucede entre las membranas de grafeno, el agua y el colorante azoico naranja ácido 7. Con los resultados obtenidos también se propone un sistema en el cual, a pesar de no tener una adsorción, se pueda tener una disminución de la concentración del colorante azoico al pasar por una estructura de grafeno, demostrando una reducción del colorante hasta 175 picosegundos, con lo cual se podría armar un sistema experimental con esas características. Finalmente, todos los datos obtenidos fueron verificados mediante varias fuentes bibliográficas asegurando la confiabilidad de las simulaciones realizadas

Modelizado molecular de nanocomposites de matriz polimérica reforzados con nanotubos de carbono

135 p.El objetivo de la Tesis es estudiar el comportamiento interfacial de nanotubos de carbono embebidos en una matriz polimérica mediante el uso de herramientas de modelizado molecular. Para ello se modelizan en primer lugar los nanotubos funcionalizados y se estudian sus propiedades elásticas. Posteriormente, se plantea el estudio de la influencia de las propiedades geométricas de los nanotubos en el cálculo de la resistencia interfacial de cizalladura. Los resultados obtenidos para distintas longitudes se usan por primera vez en el caso de simulaciones moleculares como datos de entrada para un modelo de shear-lag, siguiendo la metodología de los ensayos experimentales de pull-out. Esta aproximación, no ha sido abordada con anterioridad en la literatura mediante simulaciones moleculares y permite por una parte entender las diferencias de los valores en literatura y por otra calcular propiedades que estaban fuera del alcance de las aproximaciones previas, tales como la resistencia máxima de cizalladura de la interfase, el valor del módulo de cizalladura de la matriz en las proximidades del nanotubo, y el parámetro ¿ que sirve como medida de la eficiencia en la transferencia de carga. Finalmente, se utilizan nanotubos funcionalizados y los módulos de Young calculados 2, para aplicar la metodología combinada de simulación molecular/teoría de shear-lag en nanotubos funcionalizados con distintos grupos funcionales y en distintos porcentajes de funcionalización, con el objetivo de analizar los mejores candidatos de entre los estudiados, para actuar como refuerzo de la matriz polimérica

Catalytic Conversion of Benzothiophene Over a H-ZSM5 Catalyst, Reactivity and a Kinetic Model

Nowadays and due to environmental legislations, a world-wide attention has been given towards clean transportation fuels with emphasis on sulfur contents reduction. These efforts on the other hand are challenged by the poor qualities of crude oils. The existing desulfurization technologies such as hydrodesulfurization are not capable to cope with new firm standards. Hence, it is extremely desirable to develop a catalytic desulfurization process to meet both sulfur limits and refining economics. As one aspect of this objective, it is of great importance to study and comprehend the behaviour and chemistry of individual sulfur species present in transportation fuels cuts. Zeolites namely, H-ZSM5 has shown a potential catalyst for a desulfurization process for gasoline fuel range. Acidity and shape selectivity of these zeolites make it viable for such a process eliminating the use of hydrogen. With aiming to light diesel fraction desulfurization, this dissertation provides insights and understanding of benzothiophene sulfur species conversion over a H-ZSM5 zeolite catalyst. The H-ZSM5 particles were dispersed in an inert silica-alumina matrix to diminish possible cracking of diesel model compound (n-dodecane). This catalyst was characterized using standard techniques including: a) NH3-TPD, b) N2 adsorption, c) Particle size distribution, d) X-ray diffraction, e) SEM-EDX, and f) Pyridine FTIR. Catalytic and thermal runs were performed in the CREC Riser Simulator that mimics the industrial FCC unit. This reaction system was operated at close to atmospheric pressure, 350°C – 450°C temperatures, and 3, 5, 7 seconds reaction times. Thermal cracking was found to be negligible under the studied reaction conditions. Experimental results from catalytic runs showed a higher benzothiophene conversion over n-dodecane conversion. This was true despite the difference in benzothiophene and n-dodecane molecular sizes. The experimental results of this PhD dissertation are also supported with a molecular dynamics (MD) simulation study that studies self diffusivity of benzothiophene and n-dodecane in ZSM-5 zeolite. In addition and using the obtained experimental data, a heterogeneous kinetic model is proposed for benzothiophene conversion over H-ZSM5 catalyst. Numerical non-linear regression leads to model parameters estimations with low confidence intervals suggesting the adequacy of this kinetic model

Organic molecules on metalic surfaces : a thoretical investigation

Orientador: Douglas Soares GalvãoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica "Gleb Wataghin"Resumo: Recentemente, a primeira nanoroda molecular foi caracterizada a partir de experimentos com o microscópio de tunelamento eletrônico (STM). Foi demonstrado que a molécula de hidrocarboneto (C44H24) especificamente desenhada poderia rolar sobre a superfície de cobre ao longo da direção [110] da superfície. A molécula consiste em duas rodas baseadas no grupo triptycene as quais são conectadas por um eixo. Nós reportamos um estudo teórico da simulação desse processo. Usamos métodos ab initio (DMol 3) e de dinâmica molecular clássica (UFF). Consideramos diferentes orientações cristalográficas ([111], [110], e [100]) para a superfície de cobre, a fim de determinar como estas diferentes orientações afetam o processo de rolamento molecular. Nossos resultados estão em boa acordância com os dados experimentais disponíveis. As simulações mostraram que o mecanismo de rolamento só é possível para a direção [110]. Para as outras direções ([111] e [100]) a superfície é muito suave e não pode prover o torque necessário para o processo de rolamento. Para estes casos a molécula somente desliza (movimento de translação), sem rolar quando interage com a ponta do microscópio. Para a direção [110] a separação espacial entre as colunas de cobre é suficiente para travar a molécula e criar um torque. Além da superfície correta, a posição relativa da molécula sobre a superfície é muito importante. A molécula deve estar com seu eixo principal paralelo à direção [110]. Este efeito de comensurabilidade, entre a molécula e a superfície, é similar a difusão seletiva na superfície recentemente observada para outras classes de moléculas orgânicas. Os perfis experimentais observados para o empuramento, puxamento e rolamento também podem ser explicados em termos destas características geométricas entre a molécula e as diferentes direções cristalográficas do cobreAbstract: Recently, the first molecular nanowheel was characterized with scanning tunneling micro-scope experiments. It was demonstrated that a specifically designed hydrocarbon molecule (C44H24) could roll over a copper substrate along the [110] direction of a surface. The molecule consists in two wheels based on two triptycene groups which are connected by an axle. We report a theoretical study of the simulations of this process. We used ab initio (DMol 3) and classical molecular dynamics methods (UFF). We have considered different crystallographic orientations ([111], [110], and [100]) for the copper surface, in order to determine how these different orientations affect the molecular rolling processes. Our results are in good agreement with the available experimentally data. The simulations showed that the rolling mechanism is only possible for the [110] direction. For the others directions ([111] and [100]) the surfaces are too smooth and cannot provide the necessary torque to the rolling process. For these cases the molecule just slides (translational movement), without rolling when interact with the STM tip. For the [110] direction the spatial separation among rows of copper atoms is enough to trap the molecule and to create a torque. Besides the correct surface the relative position of the molecule on the surface is very important. The molecule should be with its main axis in the parallel direction to [110]. This commensurability effect, between the molecule and the surface, is similar to the surface selective diffusion recently observed for other classes of organic molecules. The experimental observed pushing, pulling, and rolling profiles can also be explained in terms of these geometrical features between the molecule and the different Cu crystallographic directionsMestradoMestre em Físic

Mechanistic Understanding of Co-crystal solubility and dissolution by using a combination of Experimental and Molecular Modelling Techniques

The purpose of this study is to improve the solubility, dissolution rate and permeability of poorly water-soluble drugs by understanding the mechanism of dissolution at molecular level of Flufenamic acid and Carbamazepine co-crystals in the presence of polymers. This study has been separated into four sections: (1) Formation of pharmaceutical co-crystals: Three pharmaceutical co-crystals of poorly water soluble active pharmaceutical ingredient (API) of Flufenamic acid (FFA) and Carbamazepine (CBZ) were synthesized, including 1:1 Flufenamic acid-theophylline co-crystal (FFATP CO), 1:1 Flufenamic acid-nicotinamide co-crystal (FFA-NIC CO) and 1:1 Carbamazepine-nicotinamide co-crystal (CBZ-NIC CO). The results of Fourier Transform Infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and X-ray Powder Diffraction (XRPD) confirmed the formation of co-crystals. (2) The effect of polymers on the surface dissolution of co-crystals: The influence of three polymers (polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and a copolymer of N-vinly-2- pyrrolidone (60%) and vinyl acetate (40%) (PVP-VA)) on the surfaces of FFA-TP CO, FFA-NIC CO and CBZ-NIC CO was studied using Atomic force Microscopy (AFM), Scanning electron microscopy (SEM) and Raman spectroscopy. It was found that the co-crystals have different dissolution mechanisms, and that addition of polymers can alter the dissolution properties of co-crystals by interacting with the crystal faces. (3) The molecular interactions between the drugs, co-formers and polymers were investigated using Nuclear Magnetic Resonance (NMR) and Diffusion Ordered Spectroscopy (DOSY). It was found that the type of a polymer, its concentration, and the interaction of the polymer with a co-former in solution will significantly affect the FFA and CBZ co-crystals (4). Molecular modelling of free drug molecules with coformers and polymers in the presence of water molecules: Results indicate bulk precipitation could be occurring for FFA molecules in solution and that PVP-VA was an effective precipitation inhibitor for all three co-crystals studied in solution. Overall, PVP was an effective polymer for surface precipitation inhibitor and PVP-VA was the most effective inhibitor for precipitation in solution