A Polymer-Based Microfluidic Device with Electrolyte-Enabled Distributed Transducers (EEDT) for Distributed Load Detection

The capability of detecting distributed static and dynamic loads is indispensable in a wide variety of applications, such as examining anatomical structures of biological tissues in tissue health analysis and minimally invasive surgery (MIS) and determining the texture of an object in robotics. This dissertation presents a comprehensive study of a polymer-based microfluidic device with electrolyte-enabled distributed transducers and demonstrates a new concept on using a single microfluidic device for distributed-load detection, which takes advantage of the low-cost microfluidic fabrication technology and the low modulus and biocompatibility of polymer. The core of the device is a single deformable polymer microstructure integrated with electrolyte-enabled transducers. While distributed loads are converted to different levels of deflections by the polymer microstructure, the deflections of the microstructure are translated to resistance changes by the five pairs of distributed transducers underneath the microstructure. Firstly, the design and working principle of the device is described. Then, due to its simple but efficient configuration, a standard fabrication process well developed for polydimethylsiloxane(PDMS)-based microfluidic devices is detailed and employed to fabricate this device. After that, the experimental setups for characterizing the device performance in static, step and sinusoidal inputs are illustrated. The experimental data then are collected and processed by using custom-built electronic circuits and custom LabVIEW/Matlab program to characterize the device performance. Lastly, the performance analysis of the device is conducted to obtain the performance parameters such as device sensitivity and load resolution. In summary, this polymer-based microfluidic device not only demonstrates the new concept and the capability of detecting distributed static and dynamic loads with a single device, with a thorough experimental study on the performance and characterization of this PDMS-based microfluidic device to correlate the device performance to its design parameters, but also the potential application of directly adopting this experimental method to measure the elasticity/viscoelasticity of a soft tissue

Studies of charge transport and phase transition equilibria in blends of ionic liquids for dye-sensitised solar cells

In this work a comprehensive characterisation of four ionic liquid (IL) based electrolyte systems for dye-sensitised solar cells (DSSCs) was performed by determination of triiodide diffusion coefficients, conductivities and liquid ranges. The electrolytes, consisting of iodine, 1-methyl-3-propylimidazolium iodide (MPII), and a low viscosity solvent IL, were examined at varying IL molar ratios and fixed iodine concentration, as well as at fixed IL molar ratio and varying iodine concentrations. Diffusion and conductivity measurements were conducted over a broad temperature range to analyse the electrolyte properties in regards to thermal stress of the DSSC for later practical application. The triiodide diffusion coefficient and the electrolyte conductivity typically increase with decreasing MPII concentration or increasing temperature, caused by decreasing electrolyte viscosity. Generally, strong non-Stokesian diffusion behaviour was found for all electrolytes, decreasing at higher temperatures. In contrast to MPII concentration and temperature, the triiodide concentration had no distinct effect on the triiodide diffusion. Determination of the electrolyte�s liquid ranges by thermal analysis with simultaneous recording of conductivity yielded unexpected narrow liquid ranges for the electrolytes based on 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and 1-ethyl-3-methylimidazolium tetrafluoroborate. For the electrolyte systems based on 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, in principle, wider liquid ranges were obtained. However, for most of their blends no phase transitions were obtained. Investigation of conductivity and phase transition points of eleven pure ILs yielded in several cases conductivity data and melting points that were not previously reported. Consideration of fragility, based on the temperature dependence of conductivity, yielded that all examined ILs are fragile glass formers and show strong non-Arrhenius behaviour

Concurrent Spatial Mapping of the Viscoelastic Behavior of Heterogeneous Soft Materials Via a Polymer-Based Microfluidic Device

This dissertation presents a novel experimental technique, namely concurrent spatial mapping (CSM), for measuring the viscoelastic behavior of heterogeneous soft materials via a polymer-based microfluidic device. Comprised of a compliant polymer microstructure and an array of electrolyte-enabled distributed resistive transducers, the microfluidic device detects both static and dynamic distributed loads. Distributed loads deform the polymer microstructure and are recorded as resistance changes at the locations of the transducers. The CSM technique identifies the elastic modulus of soft materials by applying a precisely controlled indentation depth using a rigid probe to a sample placed on the device. The spatially-varying elastic modulus of the sample translates to a non-uniform load, causing a non-uniform deformation of the microstructure and variations in the recorded resistance changes. The CSM technique measures the loss modulus of soft materials through a dynamic measurement by applying varying sinusoidal loads to a sample placed on the device. The spatially-varying loss modulus of the sample causes the microstructure to respond with corresponding time delay. Consequently, the phase shift between the sinusoidal load and deflection of the sample along its length are captured by the distributed transducers. As the first step of the experimental protocol, control experiments are implemented on the device to determine its static performance and system-level dynamic parameters. Next, the CSM technique is applied to both homogeneous and heterogeneous synthetic soft materials to measure their elastic moduli by applying a precisely controlled indentation depth through a probe, and the recorded load and device deflection are the output. The data are processed to obtain the overall load and the deflection of the sample at each transducer location and are further used to extract the elastic modulus distribution of the sample. The CSM technique is then applied to measure the loss modulus of soft materials. The measurable sinusoidal loads are the input, and the sinusoidal deflections of the device are the output. By applying the Fast Fourier Transform (FFT) algorithm and the nonlinear regression method, the data are processed to obtain the phase shift between the applied load and the device response along its microchannel length as well as the system-level parameters, namely stiffness (K), damping coefficient (D), and mass (M). In conjunction with the system-level parameters of the system with the device, obtained from the control experiment, the stiffness and the damping coefficient of a sample are calculated, and the sample’s loss modulus distribution is estimated accordingly. This CSM technique successfully measures the spatially-varying elastic modulus and loss modulus of soft materials. As compared with the nanoindentation-based technique, the CSM technique demonstrates its efficiency in spatially mapping the viscoelastic behavior of a sample without excluding interactions among neighboring compositions in a sample

Ionic Liquid Enhancement of Polymer Electrolyte Conductivity and their Effects on the Performance of Electrochemical Devices

Ionic liquids (ILs) are molten salts at ambient temperature and consist of poorly coordinating cations and anions. They have good electrical conductivity with a wide voltage window and high thermal stability, but negligible vapor pressure. ILs can enhance ionic conductivity when added to polymer electrolytes. Conductivity enhancement is due to the additional ions supplied by the IL, the plasticizing nature of the IL and the low viscosity that facilitates ion mobility. The plasticizing nature of ILs softens the polymer chain giving rise to easier polymer segmental motion. Increase in polymer segmental motion implies that IL can increase amorphousness of a polymer electrolyte (PE). This article discusses the involvement of ionic liquid as electrolytes in selected devices, namely dye sensitized photovoltaics, batteries, fuel cells and supercapacitors

Understanding the Mechanical Behavior of Costal Cartilage at Their Curved Exterior Surface Via a Tactile Sensor with a Built-In Probe for Distributed-Deflection Detection

This dissertation is aimed to determine the mechanical properties at the exterior surface of costal cartilages (CC) and examine how they vary with the cartilage length and the anatomical sites of CC in the ribcage via conformal indentation testing which is built upon a tactile sensor for distributed-deflection detection. The sensor entails a rectangular Polydimethylsiloxane (PDMS) microstructure sensing-plate integrated with a 5 ×1 transducer array with 0.75mm spatial resolution underneath and a built-in probe of 0.5mm×5mm×3mm above. By pressing the sensor against the exterior surface of a CC tissue with a pre-defined indentation pattern, the sensor conforms to the curved tissue surface via the built-in probe first, and then the mechanical properties of the tissue translate to the spatially distributed deflection in the sensor and register as resistance changes by the transducer array. As a load-bearing and non-stop deforming tissue from respiration, the mechanical properties of CC are critical for maintaining their structural health and delivering their function. CC have been used as a viable source of graft tissue for many autologous therapies and as a cell source for engineered articular cartilage (AC) due to its abundance and surgical accessibility. However, the mechanical properties of CC are not well understood yet. Chest wall deformities, such as Pectus Carinatum (PC), are known to arise from the disorder of CC, but their pathogenesis remains unknown and their surgical outcomes are unpredictable. The mechanical properties of the CC exterior surface influence diffusion of oxygen and nutrients and thus are intrinsic to maintaining their structural characteristics. However, very limited knowledge exists on the mechanical properties of peripheral CC due to their highly irregular geometries. In this dissertation, a novel testing method, conformal indentation, was used to measure the mechanical properties at the CC curved exterior surface, where the structural integrity of CC is retained. Conformal indentation was conducted at the anterior/posterior surfaces of whole porcine 5th -12th CC segments and the anterior/posterior surfaces and the superior/inferior borders of five human PC CC segments from the 7th ~10th ribs along the cartilage length to record their time-dependent response to a multi-step indentation-relaxation testing protocol. The instant indentation modulus and normalized relaxation of the CC segments were derived from the recorded data to quantify their elasticity and viscosity, respectively. The instant indentation modulus at the porcine CC and PC CC exterior surface are in the range of 130kPa ~500kPa and 98kPa~1173kPa, respectively, which are well below their counterpart at the CC transverse cross-sections. The normalized relaxation at the CC exterior surface is relatively high with low applied stress but becomes constant with high applied stress. The constant normalized relaxation at the porcine and PC CC exterior surfaces are in the range of 25%~40% and 5%~25%, respectively. The human CC have higher elasticity and lower viscosity than the porcine CC. Overall, the measured mechanical properties of CC vary with their anatomical sites and thus indicate the adaptation of CC to their local biomechanical environment in the ribcage

Sondas fluorescentes acuosolubles para metales tóxicos

En la presente memoria se describe la síntesis de puntos cuánticos (PCs) CdTe acuosolubles utilizando como ligandos estabilizantes el ácido tioglicólico (TGA), el ácido 2,3-dimercaptosuccínico (DMSA) y el ácido 2,3-dimercapto-1-propanosulfónico (DMPS) y su posterior recubrimiento con corazas ZnS o CdS. En primer lugar se obtuvieron PCs DMPS-CdTe (PC1). Posteriormente, el empleo conjunto de DMPS y TGA permitió preparar PCs mixtos TGA·DMPS-CdTe (PC2) con mejores propiedades ópticas que PC1. Tratando de reducir la toxicidad y mejorar las propiedades de los PCs preparados se abordó su recubrimiento mediante una coraza ZnS. Todos los intentos por preparar PCs núcleo/coraza CdTe/ZnS a partir de PC1 y PC2 empleando DMPS y ZnCl2 como precursores, resultaron infructuosos. Por esta razón, se emplearon núcleos TGA-CdTe, a partir de los cuales fue posible preparar PCs TGA-CdTe/DMPS-ZnS (PC3) y PCs TGA-CdTe/DMSA-ZnS (PC4). De forma análoga, partiendo de PC2 se obtuvieron PCs TGA·DMPS-CdTe/DMSA-ZnS (PC5) con un rendimiento cuántico que duplicó el de los núcleos de partida. También a partir de PC2, utilizando como precursores DMPS-CdCl2 y Na2S, se prepararon PCs TGA·DMPS-CdTe/DMPS-CdS (PC6), que al igual que PC5, mejoraron notablemente las propiedades ópticas de los núcleos de partida. Una vez sintetizados y caracterizados los PCs, se llevó a cabo un estudio de su eficacia como posibles sensores de iones metálicos en disolución. La fluorescencia de los PCs preparados se ve afectada, en mayor o menor medida, por la presencia de los iones Ni(II), Cu(II), Ag(I), Hg(II) y Pb(II). En general, los cationes metálicos que mayor reducción de la emisión provocan son Hg(II), con límites de detección que van de 4 nM para PC2 a 91 nM para PC4, y Cu(II), con LODs que oscilan entre 18 nM para PC4 y 0,25 μM para PC1