“Study of Electro-thermal Effects on PLA Materials Fed with AC Currents”

Given the rise in the emergence of new composite materials, their multifunctional properties, and possible applications in simple and complex structural components, there has been a need to unravel the characterization of these materials. The possibility of printing these conductive composite materials has opened a new area in the design of structural components which can conduct, transmit, and modulate electric signals with no limitation from complex geometry. Although several works have researched the behaviour of polymeric composites due to the immediate growth, however, the electrothermal behaviour of the material when subjected to varying AC applied voltage (Joule’s effect) has not been thoroughly researched. This study presents the characterization of the electrothermal behaviour of conductive composites of a polylactic acid matrix reinforced with conductive carbon black particles (CB-PLA). An understanding of this behaviour would contribute to the improved work in additive manufacturing of functional electro-mechanical conductive materials with potential application in energy systems, bioelectronics, etc. In this study, the electrothermal interplay is monitored under applied AC voltage, varying lengths, and filament printing orientations (longitudinal, oblique, and transverse). Each sample was printed using the fused deposition modeling technique such that each specimen has three different lengths (1L, 2L, 2.75L). To this end, deductions were made on properties that affect composite’s efficiency and life expectancy. The result of this study shows a great influence of printing orientation on material properties of 3D printed conductive composites of CB-PLA. The result also identifies the contribution of AC applied voltage to composites' stabilization time. This knowledge is important to provide experimental background for components' electrothermal interplay, estimate possible degradation and operating limits of composite structures when used in applications.

Modeling Ultrafast Spectroscopy of the NADH Dimer: From UV-VIS to X-rays

Ultrafast pump-probe spectroscopy is a conceptually simple and versatile tool for resolving photoinduced dynamics in molecular systems. Due to the fast development of new experimental setups, such as synchrotron light sources and X-ray free electron lasers (XFEL), new spectral windows are becoming accessible. On the one hand, these sources have enabled scientist to access faster and faster time scales and to reach unprecedent insights into dynamical properties of matter. On the other hand, the complementarity of well-developed and novel techniques allows to study the same physical process from different points of views, integrating the advantages and overcoming the limitations of each approach. In this context, it is highly desirable to reach a clear understanding of which type of spectroscopy is more suited to capture a certain facade of a given photo-induced process, that is, to establish a correlation between the process to be unraveled and the technique to be used. In this thesis, I will show how computational spectroscopy can be a tool to establish such a correlation. I will study a specific process, which is the ultrafast energy transfer in the nicotinamide adenine dinucleotide dimer (NADH). This process will be observed in different spectral windows (from UV-VIS to X-rays), accessing the ability of different spectroscopic techniques to unravel the system evolution by means of state-of-the-art theoretical models and methodologies. The comparison of different spectroscopic simulations will demonstrate their complementarity, eventually allowing to identify the type of spectroscopy that is best suited to resolve the ultrafast energy transfer.