Nanoporous calcium carbonate-based substrates for controlled delivery of functional materials (October 2011 - present)
Modified calcium carbonates (MCCs) are highly porous, highly absorptive (mainly for charged species), have a high surface area and have a wide range of sizes and morphologies and currently have great application as fillers and pigments in paper-coating, paints and plastics. The overall aim of my doctoral research project is to find new applications for MCCs through the study and development of these MCCs as active substrates for the slow delivery of functional materials, and is in collaboration with Omya AG (headquarters based in Oftringen, Switzerland).
MCCs are made from particles of calcium carbonate that have been acid etched to make them dual porous. Dual porosity includes inter-particle pores (i.e. the pores between particles) and intra-particle pores (i.e. the pores within particles), which can be characterised using mercury intrusion porosimetry (MIP). Measurements will also be made with a zero length cell (ZLC) to quantify the effects of the characteristics of the MCCs on their diffusion rates of functional materials, such as drugs and flavours, in order to introduce new applications in the food and pharmaceutical industries.
A ‘zero-length’ cell (ZLC) is a device invented by Ruthven et al. (1988), and further developed within the Environmental and Fluid Modelling Group (EFMG) at Plymouth using organic solvents. It is comprised of two sinters between which a mono-layer of porous material is sandwiched. The whole device is connected to a High Performance Liquid Chromatography (HPLC) unit, and allows the precise study of the diffusion characteristics from the material.
In order to obtain more varied measurements, the ZLC will be extended to hold more than a monolayer of sample. In the future, the solvent used will progress to saline, and then synthesised stomach and/or oesophagus fluids and saliva in order to test the systems’ ability to withstand the human body's digestive fluids.
Investigations during the first year of the project have involved studying the diffusion and sorption of anethole in ethanol with MCCs, and various methodologies have been developed to study sorption kinetics in vitro and in the ZLC. Anethole, characterised by its aniseed scent and flavour, is the primary component of Pastis and other liqueurs. Anethole is poorly soluble in water and highly soluble in ethanol, thereby creating a cloudy solution known as the ‘Ouzo effect’ when certain ratios of these three components are mixed. In the distant future, the possibilities and complexities of using this ‘Ouzo effect’ as a three-phase delivery system will be investigated.
An overview of my current research work (Nov. 2012): the pink squares represent work that is not mine, the purple squares represent my current work and stubs into potential fruitful lines of investigation, and the blue boxes represent future work that I hope to complete.
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(submitted as partial fulfilment for the degree of B. Sc. (Hons) Applied Chemistry)
Investigation of Modified Calcium Carbonates as slow-release agents for bioactive materials (September 2010 - March 2011)
This work was undertaken at the University of Plymouth under Professor G.P. Matthews, and was the foundation for my doctoral work. Below is the abstract of my completed and submitted dissertation, for which I obtained a score of 85%. If you would like a copy of my dissertation, please so not hesistate to contact me.
The desorption and diffusion characteristics of various grades of modified calcium carbonate (MCC) were investigated. A novel ‘zero-length’ (ZLC) designed for liquid systems was used, where an effective monolayer of sample was sandwiched between two fine stainless steel sinters. The ZLC was then connected to a high performance liquid chromatography (HPLC) system under high pressure to allow sufficient flow rate of the mobile phase (benzene in cyclohexane) through the sinter. The ZLC was then used to measure the diffusion from, and desorption within, the intra-particle structure of the benzene in cyclohexane system. The desorption and diffusion coefficient of a sample was calculated, and the sample with the slowest diffusion rate, and therefore the smallest coefficient, pertained to a more complex internal structure. When comparing the properties of the samples with their diffusion and desorption coefficients it is apparent that a combination of a high surface area and a smaller particle size makes for a slower diffusion rate.
The high surface area modified calcium carbonate (HSA MCC) was then analysed using mercury intrusion porosimetry (MIP), where the maximum pore size distribution of the sample was calculated from its unimodal distribution as 797.15nm. The unimodal distribution shows that the sample has distinct inter-particle and intra-particle pores.
The HSA MCC was subjected to nitrogen adsorption where its surface area was calculated using the Langmuir and BET equations as 145.42 and 93.50 m2 g-1, respectively. The BET isotherm gave a better fit, however both equations established that the HSA MCC had the largest surface area of all samples analysed during the investigation, which confirms its slow diffusion properties.
MIP data of the simply modified calcium carbonate (S MCC) and the averagely modified calcium carbonate (A MCC) were used to model the structures in Pore-Cor Research Suite after being intruded with mercury, and confirmed that the A MCC is more porous than the S MCC. The software generated a 3-dimensional void structure using an annealed simplex that fitted an Euler-Beta function. The software then modelled diffusion within the porous network, assuming Fickian diffusion, with diffusion coefficients based on Einstein-Stokes coefficients that were corrected for steric hindrance. These samples were chosen because they had significantly differing properties from one another. The diffusion simulation obtained the same results as the ZLC; that the A MCC diffuses much slower than the S MCC, therefore demonstrating that diffusion is certainly due to structural differences within the samples.
MCCs already have application in the paper, cosmetic and drug industry. The ZLC experiments and Pore-Cor diffusion simulation established that the diffusion characteristics are governed by the structure of the sample. Therefore, further research into characterising and investigating the structure that gives the slowest diffusion would be a promising investment into developing slow-release materials for various uses, as the MCCs could then be tailored to suit its use.
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The analysis of the waters of la Estación Hidrobiológica y la Laguna de Chascomús: effects on the Argentinean Silverside (July - September 2010)
During my undergraduate studies, I was lucky enough to obtain a 2 month analytical chemistry placement in Argentina via the International Association for the Exchange of Students for Technical Experience (IAESTE) run by the British Council. So, during the summer after my second year of study I flew to Buenos Aires to work in the Centro de Estudios Transdisciplinarios del Agua within the Veterinary Faculty at the University of Buenos Aires. I was overseen by doctoral students (at the time) Nahuel Schenone and Juan José Troncoso. For more information please see this external link.
When I returned from Buenos Aires, I entered an essay-based competition run by IAESTE, and was able to win the title of IAESTE Trainee of the Year 2010!
Below is an excerpt from the introduction of the report that I wrote, which includes all data collected. For a copy of the report, please so not hesistate to contact me.
The hydro-biological of Station Chascomús (la Estación Hidrobiológica de Chascomús) opened on November 7th 1943 and currently is the home to silverside from many different origins in order to help repopulate the area of pejerrey, as there are decreased numbers due to sport fishing and tourism. The hydro-biological station also carries out basic research.
The silverside (Odontesthes bonariensis), also known as the “pejerrey” in Spanish, is a highly valued food and sport fish both in Argentina and abroad, and has been introduced to Chile, Japan, and Italy.
Their typical habitats are ‘lagunas,’ the most common lenitic water bodies of the wet Pampa, an extensive loess plain under an East-West climate gradient of decreasing rain. Lagunas range usually between 30 and 6,078 ha, with depths below 4 m and often rather less. Some of them maintain high-salinity levels because of marine origin or the increased East–West aridity gradient. They lack thermal stratification and have a wide range of physical and chemical traits. Bottom sediment is mud like, with scarce clay, fine siliceous sand thicker than loess and abundant organic matter. Lower depths and the richness of loess in phosphorous usually result in a common eutrophic state.
This study was carried out in order to investigate the levels of trace metals and other analytes in order to determine the effects of these components on the Argentinean Silverside and the impact on the environment. The samples were taken from seven sites in “la Estación Hidrobiológica de Chascomús,” and a sample was also taken from “la Laguna de Chascomús.”
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