Cellulose nanorods in liquid crystalline elastomers for improved actuators

Nanotechnology plays a central role in ‘tailoring’ materials’ properties and thus improving its performances for a wide range of applications. Coupling nature nano-objects with nanotechnology results in materials with enhanced functionalities. The main objective of this master thesis was the synthesis of nanocrystalline cellulose (NCCs) and its further incorporation in a cellulosic matrix, in order to produce a stimuli-responsive material to moisture. The induced behaviour (bending/unbending) of the samples was deeply investigated, in order to determine relationships between structure/properties. Using microcrystalline cellulose as a starting material, acid hydrolysis was performed and the NCC was obtained. Anisotropic aqueous solutions of HPC and NCC were prepared and films with thicknesses ranging from 22μm to 61μm were achieved, by using a shear casting technique. Microscopic and spectroscopic techniques as well as mechanical and rheological essays were used to characterize the transparent and flexible films produced. Upon the application of a stimulus (moisture), the bending/unbending response times were measured. The use of NCC allowed obtaining films with response times in the order of 6 seconds for the bending and 5 seconds for the unbending, improving the results previously reported. These promising results open new horizons for building up improved soft steam engines.

Development of new membranes based on ionic liquid materials for gas separation

In the field of energy, natural gas is an essential bridge to a clean, low carbon, renewable energy era. However, natural gas processing and transportation regulation require the removal of contaminant compounds such as carbon dioxide (CO2). Regarding clean air, the increasing atmospheric concentrations of greenhouse gases, specifically CO2, is of particular concern. Therefore, new costeffective, high performance technologies for carbon capture have been researched and the design of materials with the ability to efficiently separate CO2 from other gases is of vital importance.(...)

40 K Liquid Neon Energy Storage Unit

A thermal Energy Storage Unit (ESU) could be used to attenuate inherent temperature fluctuations of a cold finger, either from a cryocooler working or due to sudden income heat bursts. An ESU directly coupled to the cold source acts as a thermal buffer temporarily increasing its cooling capacity and providing a better thermal stability of the cold finger (“Power Booster mode”). The energy storage units presented here use an enthalpy reservoir based on the high latent heat of the liquid-vapour transition of neon in the temperature range 38 - 44 K to store up to 900 J, and that uses a 6 liters expansion volume at RT in order to work as a closed system. Experimental results in the power booster mode will be described: in this case, the liquid neon cell was directly coupled to the cold finger of the working cryocooler, its volume (12 cm3) allowing it to store 450 J at around 40 K. 10 W heat bursts were applied, leading to liquid evaporation, with quite reduced temperature changes. The liquid neon reservoir can also work as a temporary cold source to be used after stopping the cryocooler, allowing for a vibration-free environment. In this case the enthalpy reservoir implemented (24 cm3) was linked to the cryocooler cold finger through a gas gap heat switch for thermal coupling/decoupling of the cold finger. We will show that, by controlling the enthalpy reservoir’s pressure, 900 J can be stored at a constant temperature of 40 K as in a triple-point ESU.

40 K Neon liquid energy storage unit

Cryocoolers have been progressively replacing the use of the stored cryogens in cryogenic chains used for detector cooling, thanks to their higher and higher reliability. However, the mechanical vibrations, the electromagnetic interferences and the temperature fluctuations inherent to their functioning could reduce the sensor’s sensitivity. In order to minimize this problem, compact thermal energy storage units (ESU) are studied, devices able to store thermal energy without significant temperature increase. These devices can be used as a temporary cold source making it possible to turn the cryocooler OFF providing a proper environment for the sensor. A heat switch is responsible for the thermal decoupling of the ESU from the cryocooler’s temperature that increases when turned OFF. In this work, several prototypes working around 40 K were designed, built and characterized. They consist in a low temperature cell that contains the liquid neon connected to an expansion volume at room temperature for gas storage during the liquid evaporation phase. To turn this system insensitive to the gravity direction, the liquid is retained in the low temperature cell by capillary effect in a porous material. Thanks to pressure regulation of the liquid neon bath, 900 J were stored at 40K. The higher latent heat of the liquid and the inexistence of triple point transitions at 40 K turn the pressure control during the evaporation a versatile and compact alternative to an ESU working at the triple point transitions. A quite compact second prototype ESU directly connected to the cryocooler cold finger was tested as a temperature stabilizer. This device was able to stabilize the cryocooler temperature ((≈ 40K ±1 K) despite sudden heat bursts corresponding to twice the cooling power of the cryocooler. This thesis describes the construction of these devices as well as the tests performed. It is also shown that the thermal model developed to predict the thermal behaviour of these devices, implemented as a software,describes quite well the experimental results. Solutions to improve these devices are also proposed.

40 K neon liquid energy storage unit

Cryocoolers have been progressively replacing the use of the stored cryogens in cryogenic chains used for detector cooling, thanks to their higher and higher reliability. However, the mechanical vibrations, the electromagnetic interferences and the temperature fluctuations inherent to their functioning could reduce the sensor’s sensitivity. In order to minimize this problem, compact thermal energy storage units (ESU) are studied, devices able to store thermal energy without significant temperature increase. These devices can be used as a temporary cold source making it possible to turn the cryocooler OFF providing a proper environment for the sensor. A heat switch is responsible for the thermal decoupling of the ESU from the cryocooler’s temperature that increases when turned OFF. In this work, several prototypes working around 40 K were designed, built and characterized. They consist in a low temperature cell that contains the liquid neon connected to an expansion volume at room temperature for gas storage during the liquid evaporation phase. To turn this system insensitive to the gravity direction, the liquid is retained in the low temperature cell by capillary effect in a porous material. Thanks to pressure regulation of the liquid neon bath, 900 J were stored at 40K. The higher latent heat of the liquid and the inexistence of triple point transitions at 40 K turn the pressure control during the evaporation a versatile and compact alternative to an ESU working at the triple point transitions. A quite compact second prototype ESU directly connected to the cryocooler cold finger was tested as a temperature stabilizer. This device was able to stabilize the cryocooler temperature ((≈ 40K ±1 K) despite sudden heat bursts corresponding to twice the cooling power of the cryocooler. This thesis describes the construction of these devices as well as the tests performed. It is also shown that the thermal model developed to predict the thermal behaviour of these devices,implemented as a software, describes quite well the experimental results. Solutions to improve these devices are also proposed.

How do current term structure model behave beyond the last liquid point?: A comparison of the DNS and Smith-Wilson methods

A Work Project, presented as part of the requirements for the Award of a Master’s Double Degree in Finance from Maastricht University and NOVA – School of Business and Economics

Characterization of an OPCPA laser amplifier based on the nonlinear crystal YCOB

The work described in this thesis was performed at the Laboratory for Intense Lasers (L2I) of Instituto Superior Técnico, University of Lisbon (IST-UL). Its main contribution consists in the feasibility study of the broadband dispersive stages for an optical parametric chirped pulse amplifier based on the nonlinear crystal yttrium calcium oxi-borate (YCOB). In particular, the main goal of this work consisted in the characterization and implementation of the several optical devices involved in pulse expansion and compression of the amplified pulses to durations of the order of a few optical cycles (20 fs). This type of laser systems find application in fields such as medicine, telecommunications and machining, which require high energy, ultrashort (sub-100 fs) pulses. The main challenges consisted in the preliminary study of the performance of the broadband amplifier, which is essential for successfully handling pulses with bandwidths exceeding 100 nm when amplified from the μJ to 20 mJ per pulse. In general, the control, manipulation and characterization of optical phenomena on the scale of a few tens of fs and powers that can reach the PW level are extremely difficult and challenging due to the complexity of the phenomena of radiation-matter interaction and their nonlinearities, observed at this time scale and power level. For this purpose the main dispersive components were characterized in detail, specifically addressing the demonstration of pulse expansion and compression. The tested bandwidths are narrower than the final ones, in order to confirm the parameters of these elements and predict the performance for the broadband pulses. The work performed led to additional tasks such as a detailed characterization of laser oscillator seeding the laser chain and the detection and cancelling of additional sources of dispersion.

Design and characterization of novel biopolymeric structure using biocompatible ionic liquids

The main objective of this thesis was the development of polymeric structures from the dissolution of FucoPol, a bacterial exopolysaccharide (EPS), in a biocompatible ionic liquid, choline acetate. The FucoPol was produced by the bacteria Enterobacter A47 using glycerol as carbon source at controlled temperature and pH (30ºC and 7, respectively). At the end of 3 days it was produced 7 g/L of FucoPol. The net yield of Fucopol in glycerol (YP/S) was 0.22 g/g and the maximum productivity 2.37 g/L.d This polymer was characterized about its composition in sugars and acyl groups (by High-Performance Liquid Chromatography - HPLC), containing fucose (35 % mol), galactose (21 % mol), glucose (29 % mol), rhamnose (3% mol) and glucuronic acid (12% mol) as well as acetate (14.28 % mol), pyruvate (2.15 % mol) and succinate (1.80 % mol). Its content of water and ash was 15% p/p and 2% p/p, respectively, and the chemical bonds (determined by Infrared Spectroscopy - FT-IR) are consistent to the literature reports. However, due to limitations in Differential Scanning Calorimetry (DSC) equipment it was not possible to determine the glass transition temperature. In turn, the ionic liquid showed the typical behavior of a Newtonian fluid, glass transition temperature (determined by DSC) -98.03ºC and density 1.1031 g/cm3. The study of chemical bonds by FT-IR showed that amount of water (8.80%) influenced the visualization of the bands predicted to in view of their chemical structure. After the dissolution of the FucoPol in the ionic liquid at different temperatures (50, 60, 80 and 100 ° C) it was promoted the removal of this by the phase inversion method using deionized water as a solvent, followed by drying in an oven at 70 ° C. The mixtures before and after the phase inversion method were characterized through the studies mentioned above. In order to explore possible application field’s biocompatibility assays and collage on balsa wood tests were performed. It was found that the process of washing with water by the phase inversion method was not totally effective in removing the biocompatible ionic liquid, since all FucoPol – IL mixtures still contained ionic liquid in their composition as can be seen by the DSC results and FT-IR. In addition, washing the mixtures with water significantly altered the composition of FucoPol. However, these mixtures, that developed a viscous behavior typical of a non-Newtonian fluid (shear-thinning), have the potential to be applied in the biomedical field as well as biological glues.

Nanocomposite polymer beads for cell detection

Circulating tumor cells (CTCs) may induce metastases when detached from the primary tumor. The numbers of these cells in blood offers a valuable prognostic indication. Magnetoresistive sensing is an attractive option for CTC counting. In this technique, cells are labeled with nancomposite polymer beads that provide the magnetic signal. Bead properties such as size and magnetic content must be optimized in order to be used as a detection tool in a magnetoresistive platform. Another important component of the platform is the magnet required for proper sensing. Both components are addressed in this work. Nanocomposite polymer beads were produced by nano-emulsion and membrane emulsification. Formulations of the oil phase comprising a mixture of aromatic monomers and iron oxide were employed. The effect of emulsifier (surfactant) concentration on bead size was studied. Formulations of polydimethilsiloxane (PDMS) with different viscosities were also prepared with nano-emulsion method resulting in colloidal beads. Polycaprolactone (PCL) beads were also synthetized by the membrane emulsification method. The beads were characterized by different techiques such as dynamic light scattering (DLS), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Additionally, the magnet dimensions of the platform designed to detect CTCs were optimized through a COMSOL multiphysics simulation.

Development and modulation of magnetic responsive supported ionic liquid membranes

The work presented in this thesis aims at developing a new separation process based on the application of supported magnetic ionic liquid membranes, SMILMs, using magnetic ionic liquids, MILs. MILs have attracted growing interest due to their ability to change their physicochemical characteristics when exposed to variable magnetic field conditions. The magnetic responsive behavior of MILs is thus expected to contribute for the development of more efficient separation processes, such as supported liquid membranes, where MILs may be used as a selective carrier. Driven by the MILs behavior, these membranes are expected to switch reversibly their permeability and selectivity by in situ and non-invasive adjustment of the conditions (e.g. intensity, direction vector and uniformity) of an external applied magnetic field. The development of these magnetic responsive membrane processes were anticipated by studies, performed along the first stage of this PhD work, aiming at getting a deep knowledge on the influence of magnetic field on MILs properties. The influence of the magnetic field on the molecular dynamics and structural rearrangement of MILs ionic network was assessed through a 1H-NMR technique. Through the 1H-NMR relaxometry analysis it was possible to estimate the self-diffusion profiles of two different model MILs, [Aliquat][FeCl4] and [P66614][FeCl4]. A comparative analysis was established between the behavior of magnetic and non-magnetic ionic liquids, MILs and ILs, to facilitate the perception of the magnetic field impact on MILs properties. In contrast to ILs, MILs show a specific relaxation mechanism, characterized by the magnetic dependence of their self-diffusion coefficients. MILs self-diffusion coefficients increased in the presence of magnetic field whereas ILs self-diffusion was not affected. In order to understand the reasons underlying the magnetic dependence of MILs self-diffusion, studies were performed to investigate the influence of the magnetic field on MILs’ viscosity. It was observed that the MIL´s viscosity decreases with the increase of the magnetic field, explaining the increase of MILs self-diffusion according to the modified Stokes- Einstein equation. Different gas and liquid transport studies were therefore performed aiming to determine the influence of the magnetic behavior of MILs on solute transport through SMILMs. Gas permeation studies were performed using pure CO2 andN2 gas streams and air, using a series of phosphonium cation based MILs, containing different paramagnetic anions. Transport studies were conducted in the presence and absence of magnetic field at a maximum intensity of 1.5T. The results revealed that gas permeability increased in the presence of the magnetic field, however, without affecting the membrane selectivity. The increase of gas permeability through SMILMs was related to the decrease of the MILs viscosity under magnetic field conditions.(...)