Capsules are employed in a range of industries as essential vehicles for the storage and delivery of drugs, biologically active species, surfactants, and personal care formulations. Key performance aspects are dictated by the capsule's overall shape and dimensions, porosity and internal microstructure. Various approaches are employed in the fabrication of capsules with precise size and shape control. This work focuses on the formation of capsules by the selective removal of solvent from monodisperse solution droplets - produced using microfluidics - upon immersion in an external solvent. The microfluidic generation of microporous polymer capsules using an ex-situ phase inversion process is presented and the effect of various process parameters on capsule structure and internal microstructure examined. These include polymer concentration, droplet size and non-solvent quality. Further, the effect of ternary solution thermodynamics on the microstructure of the capsules is explored, and precise control over pore size and distribution is demonstrated. Building on these findings and polymer-colloid phase behaviour, the fabrication of nanocomposite capsules, generated from polymer-nanoparticle mixtures, is reported and a well-defined external and internal morphology diagram established. These include nucleated and bicontinuous microstructures, as well as isotropic and non-isotropic external shapes. Upon dissolution, rapid and modulated, pulsed, release of the nanoparticle clusters over timescales ranging seconds to hours is demonstrated. The release profile is found to be dependent on capsule morphology, and a systematic study of the role of extraction solvent and kinetics on capsule gradient structure is presented; this provides an effective strategy to decouple demixing and coarsening timescales from the capsule solidification time, and is exploited to controllably design capsules with varied internal microstructures: hollow, core-shell, bicontinuous and compact domains. Overall, the work presents a robust and facile microfluidic approach for the design and fabrication of microcapsules, exhibiting a wide range of internal and external morphologies, by exploiting solution/mixture thermodynamics, solvent exchange kinetics, and phase inversion.

Micro-tubular solid oxide fuel cells (MT-SOFCs) have received increasing research interest in the past decade. However, current development is restricted in R&D phase due to several technical challenges, such as expensive manufacturing route, which limits mass-scale production, and the difficulties in efficient current collection, especially from the small lumen of micro-tubes. In terms of fabrication, conventional routes usually consist of repetitions of coating and sintering, which is both time and cost-consuming. To tackle this problem, a phase inversion-assisted co-extrusion process has been established in this study, which dramatically simplifies the fabrication process, with improved adhesion. The phase inversion process could lead to the formation of an asymmetric structure, comprising micro-channels and a sponge-like structure. The former morphology could facilitate fuel transport, while the latter provides reactive sites for electrochemical reactions. The feasibility of the new manufacturing route has been established by fabricating anode/anode functional layer (AFL)/electrolyte triple-layer hollow fibers and the results suggest that inserting an AFL could effectively improve power density by 30% due to enlarged triple-phase boundary. As for the current collection from the lumen side, a new nickel-based current collector has been developed via co-extrusion. By controlling the fabrication parameters, a deliberate mesh-structure has been obtained with uniformly distributed entrances. Inserting this nickel-based inner layer considerably increases the electrical conductivity of anode and reduces gas diffusion resistance. After a complete cell was constructed, systematic electrochemical performance tests were undertaken. It has been illustrated that more uniform current collection has been achieved and contact loss, which is the major contributor towards ohmic loss in conventional current collectors, has been significantly reduced to less than 10% of total ohmic loss. This result indeed highlights the features of process economy and high efficiency of the new current collection design and suggests this design to be suitable for large-scale stack construction.

No description available.

With the increasing maturity of conventional oil resources and limited volumes of new conventional resources to replace production, attention has been focused on viscosity reduction to enhance oil production from brown-field reservoirs by the injection of light gases such as CO2. Also, viscosity plays a significant role in managing and controlling injection of CO2 into depleted oil reservoirs or saline aquifers for the purpose of carbon sequestration. In this study, experimental measurements on viscosity of crude oils and mixtures of crude oils injected with CO2 were performed using accurate technique including a vibrating-wire viscometer and a vibrating tube densimeter. However, for viscosity measurements involving crude oil using vibrating-wire viscometer, asphaltenes precipitation and deposition can be a problem making sensor to provide inaccurate and misleading results. To avoid this problem, the crude oil samples were carefully prepared using ASTM recommended procedure (ASTM2007-80) for separating asphaltenes. The performance and accuracy of a vibrating tube densimeter is critically dependent on the adopted calibration method. Two calibration methods were investigated: using vacuum and water; and using vacuum, water and toluene as standard fluids. The findings from subsequent validation procedures revealed that the method of calibration using vacuum, water and toluene lead to better performance of the density sensor. The percent average deviations remained within ± 0.2 % for density leading to percent average deviations within ± 5% for viscosity. In contrast, the percent average deviations of using vacuum and water method were above ± 0.2% for density and above ± 5% for viscosity. Consequently, the vacuum-water-toluene calibration of the densimeter was used. A vibrating-wire viscometer and a vibrating tube densimeter were used to measure the viscosity and density of crude oils Pi and NS. The temperatures studied were between (298.2 and 448.2) K and that of pressures were between (0.1 and 135) MPa. The experimental setup was further modified to measure the viscosity and density of mixtures of: Pi and CO2, and NS and CO2 for a range of compositions (0 ≤ wCO2 ≤ 0.11) at pressures between (0.1 and 70) MPa and temperatures between (298.2 and 448.2) K. The data were correlated with simple mathematical functions which express the viscosity and density in terms of pressure and temperature. The percent average deviations of the experimental data from the correlation equations were within ± 5 % for the viscosity and ± 0.2 % for density. The predictive capabilities of some physically-based viscosity models were tested using the experimental data. The models used were versions of the effective hard-sphere model for fluid mixture viscosity: (1) original model of Dymond and Assael, (2) an extended version by Caudwell et al, (3) and 1st and 2nd extended versions by Ciotta et al. The results obtained showed that the 2nd version of Ciotta et al model is capable of reproducing the viscosity prediction of crude oil within the limits of the percent average deviations of the experimental data, ± 5 %. For the mixtures of crude oil and CO2, the Caudwell et al model was able to predict the viscosity of both sets of mixtures (Pi and CO2 & NS and CO2) to within percent average deviations of ± 5 % from the experimental data. The injection of CO2 into the crude oils, markedly, reduced the viscosity of both crude oils.

There have been extensive studies of the kinetics of pristine carbonate minerals in acidified media including (CO2 + H2O) systems at elevated temperature and pressure conditions pertinent to carbon storage. However, most of those studies have not considered the several complexities that occur in real reservoirs. The goal of this study was to investigate some of these complexities and their impacts on reaction rates under reservoir conditions. The variables investigated in this study include: aqueous chemistry and ionic strength, saturation state, surface contaminants and chemical heterogeneity in reservoir minerals. The majority of the reaction rates reported in this study are from batch reactor experiments implementing a form of the rotating disk technique, which is chosen to eliminate mass transport effects. Calcite (CaCO3) dissolution kinetics were investigated in (CO2 + H2O + NaCl), (CO2 + H2O + NaHCO3), (CO2 + H2O + Na2SO4) and (CO2 + H2O + Mixed Salts) systems. These studies were carried out at temperatures ranging from (323 to 373) K and pressures ranging from (6 to 10) MPa. A minor increase in the dissolution rates as a function of ionic strength was observed in every system except for (CO2 + H2O + NaHCO3), where a marked reduction in dissolution rates was measured. These observations are consistent with the predicted changes in the pH of the aqueous system. The influence of saturation states in the dissolution kinetics of calcite was investigated in the (CO2 + H2O) system at a temperature T of 373 K and a pressure p of 6 MPa. Consistent with previous studies, the measured dissolution rates deviate from the classical transition state theory (TST) model which was developed for elementary reactions in homogeneous media. A modified TST expression was subsequently proposed. Next, the dissolution kinetics of three chemically heterogeneous carbonate reservoir rocks were investigated in (CO2 + H2O) system at T = 323 K and p = 10 MPa. For a single carbonate mineral in the heterogeneous matrix, the measured dissolution rates were found to be comparable to those of a chemically homogeneous system under similar experimental conditions. Finally, the impact of surface alterations (including adsorbed biofilms and crude-oil films) on calcite dissolution kinetics was investigated in (CO2 + H2O) systems at temperatures ranging from (325 to 333) K and pressures up to 10 MPa. Some of these films made a minor difference in reaction rates and the effects were found to be dependent on temperature, pressure, exposure time and reactor configurations. In this study, extensive characterizations were performed on both fluid and solid phases, and geochemical simulations were implemented in the PHREEQC software. Further, preliminary insights from Lattice Boltzmann modelling and reactive core flooding studies are presented.

No description available.

No description available.

No description available.

No description available.

No description available.