The importance of renewable energy sources is becoming clearer and clearer as unsustainable energy sources are running out and global warming is getting worse. Energy derived from sunlight is already commonly used, but more energy can be produced from sunlight when solar cells become cheaper. Organic solar cells use organic compounds as semiconductors which can be prepared from solutions, resulting in lower production costs. However, these semiconductors;Poly(3-hexylthiophene) and [6,6]-Phenyl-C61-butric acid methyl ester, are commonly dissolved inhalogenated and aromatic solvents. These solvents have toxic properties, which is why alternative solvents should be identified. Potential solvents were predicted by using the Hansen solubilityparameters and thin films were prepared by spin-coating the solutions. The thin films were evaluated with absorption spectroscopy, the fluorescence spectroscopy and atomic force microscopy. Since the alternative solvents had lower solubilites than the commonly used solvents, i.e., chlorobenzene, ortho-dichlorobenzene and chloroform, the absorption of the films with new solvents were lower as well. Using tetrahydrofuran resulted in the highest absorption of the used solvents, while xylene hada better film morphology. Increasing the absorption was attempted by spin-coating multiple thin films on top each other or by using a lower rotational speed. Spin-coating multiple films had nouniform effect on the absorption, while lowering the rotational speed increased the absorption, but not enough to equal the original absorption. Contrasting the results of the absorption spectra, the morphology improved when multiple layers were used while the film with the lower rotational speed’s morphology got worse. In conclusion, tetrahydrofuran and xylene are the best alternative solvents and using multiple layers as well as decreasing the rotational speed show improvements oneither the morphology or the absorption.

The solubility of cellobiose in 18 organic liquids and water was measured at 20°C. Hydrogen bond acceptors were the most effective solvents. Three models were analyzed to evaluate their accuracy and to understand factors that affect cellobiose solubility: Hansen solubility parameters (HSP), linear free energy relationship (LFER), and UNIQUAC functional-group activity coefficients (UNIFAC). The HSP of cellobiose were determined and the model was able to distinguish between most good and poor solvents, however, proved to be occasionally unreliable due to a false negative. The LFER model produced an empirical equation involving contributions from solvent molar refraction, polarizability, acidity, basicity, and molar volume, which predicted cellobiose solubilities to within ±2 log units. LFER indicated that good solvents were highly polarizable and had low molar volume, which was consistent with the good solvents found for cellobiose. A modified version of UNIFAC that includes an association term (A-UNIFAC) predicted the solubility of cellobiose in water and alcohols to within ±0.6 log units, indicating that A-UNIFAC can be used to predict the solubility of cellobiose and other carbohydrates provided additional data to extend the model to solvents other than water and alcohols.

Dispersing co-crystals in a polymeric carrier may improve their physicochemical properties such as dissolution rate and solubility. Additionally co-crystal stability may be enhanced. However, such dispersions have been little investigated to date. This study focuses on the feasibility of dispersing co-crystals in a polymeric carrier and theoretical calculations to predict their stability. Acetone/chloroform, ethanol/water, and acetonitrile were used to load and grow co-crystals in a HPMCAS film. Caffeine-malonic acid and ibuprofennicotinamide co-crystals were prepared using solvent evaporation method. The interactions between each of the co-crystals components and their mixtures with the polymer were studied. A solvent evaporation approach was used to incorporate each compound, a mixture, and co-crystals into HPMCAS films. Differential scanning calorimetry data revealed a higher affinity of the polymer to acidic compounds than their basic counterparts as noticed by the depression of the glass transition temperature (Tg). Moreover, the same drug loading produced films with different Tgs when different solvents were used. Solubility parameter values (SP) of the solvents were employed to predict that effect on the depression of polymer Tg with relative success. SP values were more successful in predicting the preferential affinity of two acidic compounds to interact with the polymer. This was confirmed using binary mixtures of naproxen, flurbiprofen, malonic acid, and ibuprofen. On the other hand, dispersing basic compounds such as caffeine or nicotinamide with malonic acid in HPMCAS film revealed the growth of co-crystals. A dissolution study showed that the average release of caffeine from films containing caffeine-malonic acid was not significantly different to that of films containing similar caffeine concentration. The stability of the caffeine-malonic acid co-crystals in HPMC-AS was prolonged to 8 weeks at 95% relative humidity and 45°C. The theory developed in this project, that an acidic drug with a SP value closer to the polymer will dominate the interaction process and prevent the majority of the other material from interacting with the polymer, may have utility in designing co-crystal systems in polymeric vehicles

No description available.

No description available.

This thesis reports an investigation of hydroxypropylmethylcellulose (HPMC) as a new solid-surface room-temperature phosphorescence (SSRTP) sample matrix. The high background phosphorescence originating from filter paper substrates can interfere with the detection and quantitation of trace-level analytes. High-purity grades of HPMC were investigated as SSRTP substrates in an attempt to overcome this limitation. When compared directly to filter paper, HPMC allows the spectroscopist to achieve greater sensitivity, lower limits of detection (LOD), and lower limits of quantitation (LOQ) for certain phosphor/heavy-atom combinations since SSRTP signal intensities are stronger. For example, the determination of the analytical figures of merit for a naphthalene/sodium iodide/HPMC system resulted in a calibration sensitivity of 2.79, LOD of 4 ppm (3 ng), and LOQ of 14 ppm (11 ng). Corresponding investigations of a naphthalene/sodium iodide/filter paper system produced a calibration sensitivity of 0.326, LOD of 33 ppm (26 ng), and LOQ of 109 ppm (86 ng). Extended purging with dry-nitrogen gas yields improved sensitivities, lower LOD's, and lower LOQ's in HPMC matrices when LOD and LOQ are calculated according to the IUPAC guidelines.To test the universality of HPMC, qualitative SSRTP spectra were obtained for a wide variety of probe phosphors offering different molecular sizes, shapes, and chemical functionalities. Suitable spectra were obtained for the following model polycyclic aromatic hydrocarbons (PAHs): naphthalene, p-aminobenzoic acid, acenaphthene, phenanthrene, 2-naphthoic acid, 2-naphthol, salicylic acid, and triphenylene.Filter paper and HPMC substrates are inherently anisotropic, non-heterogeneous media. Since this deficiency cannot be addressed experimentally, a robust statistical method is examined for the detection of questionable SSRTP data points and the deletion of outlying observations. If discordant observations are discarded, relative standard deviations are typically reduced to less than 10% for most SSRTP data sets. Robust techniques for outlier identification are superior to traditional methods since they operate at a high level of efficiency and are immune to masking effects.The process of selecting a suitable sample support material often involves considerable trial-and-error on the part of the analyst. A mathematical model based on Hansen's cohesion parameter theory is developed to predict favorable phosphor-substrate attraction and interactions. The results of investigations using naphthalene as a probe phosphor and sodium iodide as an external heavy-atom enhancer support the cohesion parameter model.This document includes a thorough description of the fundamental principles of phosphorimetry and provides a detailed analysis of the theoretical and practical concerns associated with performing SSRTP. In order to better understand the properties of both filter paper and HPMC, a chapter is devoted to the discussion of the cellulose biopolymer. Experimental results and interpretations are presented and suggestions for future investigations are provided. Together, these results provide a framework that will support additional advancements in the field of solid-surface room-temperature phosphorescence spectroscopy. / Ph. D.

Yes / The extraction of bioactive compounds, produced by plant cell cultures, directly from their culture medium, which contains other by-products, is a great challenge. Resveratrol extraction from its grapevine cell cultures is considered here as an example to improve the extraction processes from plant cell cultures using solubility parameters. Successive liquid-liquid extraction (LLE) processes were exploited to extract resveratrol from the culture medium with an extraction ratio approaching 100%, high selectivity and minimum amounts of solvents. The calculations of partition coefficients as a function of solubility parameters demonstrated that benzyl benzoate is the most suitable intermediate solvent to extract resveratrol from its aqueous medium. The calculations also illustrated the high ability of methanol and ethanol to extract resveratrol from benzyl benzoate. The physicochemical properties of benzyl benzoate and processing conditions were exploited to separate it from aqueous media and organic solvents. The agitation method, component ratios and extraction time were studied to maximize the extraction yield. Under the best studied conditions, the recovery of resveratrol from different culture media approached ∼100% with a selectivity of ∼92%. Ultimately, the improved extraction processes of resveratrol are markedly efficient, selective, rapid and economical. / Mohammad Amin Mohammad gratefully acknowledges CARA (The Council for At-Risk Academics, Stephen Wordsworth and Ryan Mundy) for providing the financial support for an academic fellowship.

Thesis (MScEng)--Stellenbosch University. / ENGLISH ABSTRACT: Carbon dioxide (CO2) is classified as the main greenhouse gas (GHG) contributing to global warming. Estimates by the Intergovernmental Panel on Climate Change (IPCC) suggest that CO2 emissions must be reduced by between 50 to 85% by 2050 to avoid irreversible impacts. Carbon capture and storage (CCS) strategies can be applied to de-carbonize the emissions from fossil-fueled power plants. Compared to other CCS techniques, post-combustion capture (PCC) is most likely to be implemented effectively as a retrofit option to existing power plants. At present however CCS is not yet commercially viable. The main challenge with CCS is to reduce the inherent energy penalty of the CO2 separation stage on the host plant. Seventy-five to eighty percent of the total cost of CCS is associated with the separation stage. There are several technologies available for separating CO2 from power plant flue gas streams. Reactive absorption with aqueous amine solutions has the ability to treat low concentration, low pressure and large flux flue gas streams in industrial-scale applications. It is most likely to be the first technology employed commercially in the implementation of CCS. The energy required for solvent regeneration however, is high for the standard solvent used in reactive absorption processes, i.e. MEA. This leads to a reduction in thermal efficiency of the host plant of up to 15%. Alternative solvent formulations are being evaluated in an attempt to reduce the energy intensity of the regeneration process. The main objective of this study was to establish a novel, simplified thermodynamic method for solvent screening. Partial solubility parameters (PSPs) were identified as the potential basis for such a method. The major limitation of this approach is that the model doesn’t account for effects from chemical reaction(s) between materials, e.g. CO2 reacting with aqueous alkanolamine solutions; considering only the effects from dissolution. The EquiSolv software system was developed based on PSP theory. The Hansen 3-set PSP approach was used to describe the equilibrium behaviour of CO2 absorbing in task specific solvents. The Hansen theory was expanded to a 4-set approach to account for contributions from electrostatic interactions between materials. The EquiSolv program was used successfully to screen large sets of solvent data (up to 400 million formulations) in the search for suitable alternative solvent formulations for CO2 absorption. The secondary objective of this study was to evaluate the ability of the proposed PSP model to accurately predict suitable alternative solvents for CO2 absorption through preliminary experimental work. A series of CO2 absorption experiments were conducted to evaluate the absorption performance of predicted alternative solvent formulations. The predicted alternative solvent formulations exhibited a significant improvement in absorption performance (up to a 97% increase in the measured absorption capacity) compared to conventional solvent formulations. Statistical analysis of the experimental results has shown that there is a statistically significant concordant relationship between the predicted and measured rankings for the absorption performance of the predicted solvent formulations. Based on this it was concluded that PSP theory can be used to accurately predict the equilibrium behaviour of CO2 absorbing in task specific solvents. Recently ionic liquids (ILs) have been identified as potential alternatives to alkanolamine solutions conventionally used for CO2 absorption. Absorption experiments were conducted as a preliminary assessment of the absorption performance of ILs. Results have shown ILs to have significantly improved performance compared to conventional alkanolamine solvents; up to a 96% increase in the measured absorption capacity compared to conventional solvents. Future work should focus on developing task specific ionic liquids (TSILs) in an attempt to reduce the energy intensity of solvent regeneration in CO2 absorption processes. / AFRIKAANSE OPSOMMING: Koolsuurgas (CO2) word geklassifiseer as die vernaamste kweekhuis gas (GHG) wat bydra to globale verwarming. Beramings deur die Interregeringspaneel oor Klimaatsverandering (IPKV) toon aan dat CO2 emissies teen 2050 verminder moet word met tussen 50 en 85% om onomkeerbare invloede te vermy. Verskeie koolstof opvangs en bergings (KOB) strategieë kan toegepas word ten einde die koolstof dioksied konsentrasie in die emissies van kragstasies wat fossielbrandstowwe gebruik, te verminder. Naverbranding opvangs (NVO) is die mees aangewese KOB tegniek wat effektief toegepas kan word op bestaande kragstasies. Tans is KOB egter nog nie kommersieël lewensvatbaarvatbaar nie. Die hoof uitdaging wat KOB in die gesig staar is om die energie boete inherent aan die CO2 skeidingstap te verminder. Tussen vyf-en-sewentig en tagtig persent van die totale koste van KOB is gekoppel aan die skeidingstap. Daar is verskeie metodes beskikbaar vir die skeiding van CO2 uit die uitlaatgasse van kragstasies. Reaktiewe absorpsie met waterige oplossings van amiene kan gebruik word om lae konsentrasie, lae druk en hoë vloei uitlaatgasstrome in industriële toepassings te behandel. Dit is hoogs waarskynlik die eerste tegnologie wat kommersieël aangewend sal word in die toepassing van KOB. Die oplosmiddel wat normalweg vir reaktiewe absorpsie gebruik word (d.w.s. MEA) benodig egter ‘n groot hoeveelheid energie vir regenerasie. Dit lei tot ‘n afname in die termiese doeltreffendheid van die voeder aanleg van tot 15%. Alternatiewe oplosmiddelstelsels word tans ondersoek in ‘n poging om the energie intensiteit van die regenerasieproses te verminder. Die hoof doelwit van hierdie studie was om ‘n nuwe, ongekompliseerde termodinamiese metode te vestig vir die keuring van alternatiewe oplosmiddels. Parsiële oplosbaarheidsparameters (POPs) is geïdentifiseer as ‘n moontlike grondslag vir so ‘n metode. Die model beskryf egter slegs die ontbindings gedrag van materiale. Die effekte van chemise reaksie(s) tussen materiale, bv. die tussen CO2 en waterige oplossings van alkanolamiene, word nie in ag geneem nie. Die POP teorie het gedien as grondslag vir die ontwerp van die EquiSolv sagteware stelsel. Die Hansen stel van drie POPs is gebruik om die ewewigsgedrag te beskryf van CO2 wat absorbeer in doelgerig-ontwerpte oplosmiddels. Die Hansen teorie is verder uitgebrei na ‘n stel van vier POPs om die bydrae van elektrostatiese wisselwerking tussen materiale in ag te neem. Die EquiSolv program is verskeie kere met groot sukses gebruik vir die sifting van groot stelle data (soveel as 400 miljoen formulasies) in die soektog na alternatiewe oplosmiddels vir CO2 absorpsie. Die sekondêre doelwit van die studie was om die vermoë van die voorgestelde POP model om geskikte alternatiewe oplosmiddels vir CO2 absorpsie akkuraat te voorspel, te ondersoek deur voorlopige eksperimentele werk. ‘n Reeks CO2 absorpsie eksperimente is gedoen ten einde die absorpsie werkverrigting van die voorspelde alternatiewe oplosmidels te ondersoek. ‘n Verbetering in absorpsie werkverrigting van tot 97% is gevind vir die voorspelde oplosmiddels vergeleke met die van oplosmiddels wat tipies in die industrie gebruik word. Statistiese ontleding van die eksperimentele resultate het getoon dat daar ‘n beduidende ooreenstemming tussen die voorspelde en gemete rangskikking van die voorspelde oplosmiddels se werkverrigting bestaan. Dus kan POP teorie gebruik word om die absorpsie van CO2 in doelgerig-ontwerpte oplosmiddels akkuraat te beskryf. Ioniese vloeistowwe (IVs) is onlangs geïdentifiseer as moontlike alternatiewe oplosmidels vir die alkanolamien oplossings wat normaalweg gebruik word vir CO2 absorpsie. Absorpsie eksperimente is gedoen ten einde ‘n voorlopige raming van die absorpsie werkverrigting van IVs te bekom. Daar is bevind dat IVs ‘n beduidende verbetering in werkverrigting toon in vergelyking met die alkanolamien oplosmiddels wat normaalweg gebruik word. ‘n Verbetering in absorpsie werkverrigting van tot 96% is gevind vir die voorspelde IV-bevattende oplosmiddels vergeleke met die van oplosmiddels wat tipies in die industrie gebruik word. Die fokus van toekomstige navorsing moet val op die ontwikkeling van doelgemaakte ioniese vloeistowwe (DGIVs) in ‘n poging om die energie intensiteit van oplosmiddel regenerasie in CO2 absorpsie prosesse te verminder.

Hot-melt extruded solid dispersion technique is increasingly employed to improve the solubility of poorly water-soluble drugs. The technique relies on the enhanced solubility of the amorphous form of the drug compared to its crystalline counterpart. These systems however are thermodynamically unstable. This means that the drug crystallises with time. Therefore, efforts to measure the stability of these systems over the life span of the product are crucial. This study focused on investigating the use of Hansen Solubility Parameters to quantify polymer-drug interaction and to predict the stability of solid dispersions. This was achieved through a systematic review of hot-melt extruded solid dispersion literature. The study also investigated the use of a combined mechanical and rheological model to characterise the physicochemical and release behaviour of three solid dispersion immediately after preparation and after storage for one month at 40oC or three months at room temperature. Results revealed that the total solubility parameter |ΔбT| was able to predict the stability of the systems for more than 4 months using a cut-off point of 3 MPa-1 with a negative predictive value of 0.9. This was followed by ΔбD with a cut-off point of 1.5 MPa- 1. Moreover, Dynamic Mechanical Analyser and shear rheometry data were shown to be more sensitive than Differential Scanning Calorimetry, Powder X-Ray Diffraction, Scanning Electron Microscope and Fourier Transform Infrared in detecting crystallisation and the interaction between the drug and the polymer. The Dynamic Mechanical Analyser data were consistent with the dissolution behaviour of the samples when comparing the freshly prepared samples with those after storage. The results highlight the need for a unified characterisation approach and the necessity of verifying the homogeneity of mixing during the extrusion process.

In dieser Arbeit wird das neue Prinzip der „Selbstinkompatiblen Lösungsmittel“ vorgestellt. Es wird theoretisch abgeleitet, dass eine Mischung aus zwei Substanzen mit ungünstigen Wechselwirkungen bereitwillig eine weitere Substanz aufnehmen sollte, die diese ungünstigen Wechselwirkungen durch Verdünnen vermindert. Dies sollte umso stärker ausgeprägt sein, je ungünstiger die Wechselwirkungen zwischen den beiden ersten Substanzen sind. Da sich jedoch Substanzen mit sehr ungünstigen Wechselwirkungen physikalisch nicht mischen, entstand die Idee, diese Substanzen durch eine kovalente Bindung aneinander zu binden. Ein solches Molekül, das aus zwei inkompatiblen Hälften besteht, wird im Folgendem Selbstinkompatibles Lösungsmittel genannt. Die in dieser Arbeit gewählten Substanzen zeigen mäßige Inkompatibilität, deshalb ist ein Vergleich zwischen einfachen physikalischen Mischungen und kovalent verknüpften Molekülhälften noch möglich. Dieses Prinzip wird für binäre und ternäre Mischungen quantitativ berechnet und experimentell in drei Serien von Experimenten bestätigt: i) unter Verwendung von Lösungskalorimetrie und Bestimmung der Wechselwirkungsparameter zwischen Komponente 3 und einer bereits hergestellt physikalischen binären Mischung aus Komponente 1 und 2, ii) unter Verwendung von Lösungskalorimetrie und Bestimmung der Wechselwirkungsparameter zwischen Komponente 3 und den selbstinkompatiblen Losungsmitteln, die den in (i) gewählten Mischungen entsprechen und iii) aus der Sättigungslöslichkeit der Komponente 3 in den entsprechenden selbstinkompatiblen Lösungsmitteln. In diesen drei verschiedenen Messserien wird stets der gleichen Trend beobachtet: Die Selbstinkompatibilität eines Lösungsmittels begünstigt den Lösevorgang. / In this thesis a new principle of Self Incompatible Solvent is introduced. It is shown theoretically that a preexisting mixture of two substances (compound 1 and 2) with unfavorable interactions will readily dissolve a third compound because it diminishes the unfavorable interaction between the compound 1 and 2 by dilution. This behavior should be the stronger the more unfavorable the interactions between compound 1 and 2 are. However, substances with strong unfavorable interactions will not mix. Therefore the idea pursued here is to enforce the desired preexisting mixture for example by linking compound 1 covalently to compound 2. Such a molecule that is composed of two incompatible parts is called Self Incompatible Solvent in this work. In this thesis examples of incompatible compounds that show moderate incompatibility are chosen, therefore it was possible to do a comparison between simple physical mixtures and covalently linked incompatible molecules. The theoretical prediction of the theory is compared with experiments. This principle is calculated quantitatively for binary and ternary mixtures and compared with the experimental results in three distinct series of experiments: i) by using solution calorimetry and calculation of the interaction parameters between compounds 3 and the preexisting binary mixture of compound 1 and 2, ii) by using solution calorimetry and calculation of the interaction parameters between compound 3 and the Self Incompatible Solvent that correspond to the mixtures used in (i) and iii) from the saturation solubility of compound 3 in the Self Incompatible Solvent. The results obtained from the theoretical prediction and these obtained from the three different series of experiments show the same trend: the self incompatibility of the solvent improves the dissolution process.