Film formation and thermal transitions of polymers studied by atomic force microscopy

Dissertation (PhD)--Stellenbosch University, 2002.ENGLISH ABSTRACT: The kinetics of drying and film formation of different polymeric latices were studied. Various theoretical models predict a strong dependency of the film formation characteristics on the particle size and morphology. This could be confirmed by experimental studies. The influence of particle size and morphology of differently structured latices on the film formation process was investigated by Atomic Force Microscopy (AFM) and Ultrasonic shear wave reflection. These two methods allow a comprehensive characterization of the drying and film formation process of emulsions. The studies confirmed the theoretical model, that the film formation behavior is influenced by the particle size and particle morphology. Furthermore the influence of different additives, such as coalescent solvents and rheology modifiers on the film formation behavior was investigated. As a second part of the studies, a novel technique was developed to measure thermal transitions of polymers with the AFM in the non-contact mode, using it as a Dynamic Mechanical Analyzer (DMA) on a local scale. The resonance frequency of the AFM cantilever was measured as a function of the temperature and thermal transitions of a polymer were clearly visible as changes in the resonance frequency / temperature response curve. Using the AFM in this mode allows the determination of the thermal properties of a material at a specific position on a sample, thereof on a macromolecular scale. A simple model was developed to explain the response of the cantilever caused by the transitions in the polymer and the related form of the frequency/temperature curves. This new technique adds a new dimension to standard thermal analysis techniques. It is now possible to resolve the individual thermal transitions of different polymer phases, for example in structured multiphase polymers.AFRIKAANSE OPSOMMING: Die kinetika van droging en filmvorming van verskeie polimeriese lateksverbindingse is ondersoek. Verskeie teoretiese modelle voorspel 'n sterk afhanklikheid tussen die filmvormingseienskappe, partikelgrootte en morfologie. Hierdie afhanklikhede is eksperimenteel bevestig. Die invloed van partikelgrootte en morfologie van verskillende lateksstrukture op die filmvormingsproses is deur atoominteraksiemikroskopie (Eng: Atomic Force Microscopy, AFM) sowel as ultrasoniese skuifweerstandgolfrefleksie ondersoek. Hierdie twee metodes bied 'n deurslaggewende karakterisering van die droging en filmvormingsproses van emulsies. Resultate bevestig die teoretiese model, nl. dat filmvorming deur partikelgrootte en morfologie beïnvloed word. Die invloed van verskillende bymiddels, insluitend reologie-modifiseerders op filmvorming, is ook ondersoek. Vervolgens is 'n nuwe tegniek ondersoek om die termiese oorgange van polimere met behulp van die AFM in nie-kontak modus (deur dit as 'n dinamiese meganiese analiseerder (DMA) te gebruik) te bestudeer. Die resonansie-frekwensie van die AFM-hefboom is bepaal as 'n funksie van temperatuur. Termiese oorgange van 'npolimeer is duidelik waarneembaar as veranderinge in die resonansfrekwensie/ temperatuur responskurwe. Deur gebruik te maak van die AFM in hierdie modus kan die termiese eienskappe van 'n materiaal by 'n spesifieke posisie op die monster op molekulêre skaal bepaal word. 'n Eenvoudige model is ontwikkel om die oorgange in die polimeer, en gevolglik die vorm van die frekwensie/temperatuur kurwes, dmv. die respons van die hefboom, te verduidelik Hierdie nuwe tegniek gee 'n nuwe dimensie tot die standaard tegnieke van termiese analise tegnieke. Dit is nou moontlik om individuele termiese oorgange van verskeie polimeerfases, byvoorbeeld in gestruktureerde multifase polimere, te ondersoek en op te lo

Physiological and growth responses to pollutant-induced biochemical changes in plants : a review

CITATION: Mulenga, C., Clarke, C. & Meincken, M. 2020. Physiological and growth responses to pollutant-induced biochemical changes in plants : a review. Pollution, 6(4):827-848, doi:10.22059/poll.2020.303151.821.The original publication is available at https://jpoll.ut.ac.irIndustrial activities compromise the ambient air quality at a local, regional and global level through gaseous and dust emissions. This study reviews uptake mechanisms and the associated phytotoxicity of pollutants in plants, focusing on heavy metals and SO2. It further describes detoxification mechanisms and the resultant biochemical and physiological changes in plants. Finally, the morpho-physiological and growth responses to stress-induced biochemical changes are discussed. Heavy metals and SO2 enter the plant tissue through the stomata, cuticular layers, lenticels and root hairs. In the plant cells, SO2 converts to SO32- or SO42- ions upon reacting with water molecules, which in excess are toxic to plants. However, the detoxification process of SO32- increases the production of reactive oxygen species (ROS). ROS are toxic to plants and damages biomolecules such as lipids, proteins, carbohydrates and DNA. On the other hand, heavy metals, such as Cu and Fe catalyse the Fenton/Haber-Weiss reactions, breaking down H2O2 into OH•. Additionally, Pb and Zn inhibit the activities of ROS-detoxifying enzymes, while other heavy metals bind to cellular layers making them rigid, thereby reducing cell division. Therefore, pollutant toxicity in plants affects biochemical parameters damaging organic molecules and limiting cambial activity. Damaged biomolecules inhibit the plant's capacity to carry out physiological functions, such as photosynthesis, stomatal functions, transpiration and respiration while impaired cambial activity reduces cell division and elongation resulting in reduced plant growth and productivity.https://jpoll.ut.ac.ir/article_78852.htmlPublisher's versio

The technical pre-feasibility to use briquettes made from wood and agricultural waste for gasification in a downdraft gasifier for electricity generation

Biomass can be converted to energy through various thermochemical and biological processes. Gasification is one of the thermochemical processes that has recently gained popularity, because it achieves higher conversion efficiencies than, for example, incinerators, boilers or furnaces. Fixed-bed downdraft gasifiers are preferred for electricity generation, because they produce very little tar, but on the other hand, they are limited with regard to biomass properties, such as particle size, bulk density and moisture content. Biomass material with a heterogeneous size is usually processed into pellets or briquettes, which have to be mechanically strong enough to be handled. Cohesive strength is provided by residual moisture and lignin present in most biomass. However, the briquetting process becomes more complicated if one wants to add agricultural waste products that do not necessarily contain lignin as binders. The aim of this work was to process wood chips, grape skins and chicken litter into briquettes that are mechanically stable and have a sufficiently high energy content, as well as adequate bulk density for gasification. The performance of these briquettes in a downdraft gasifier was simulated with a program developed for wood, which was modified to optimise the briquette yield. The results showed a gasification performance comparable to solid pine wood, implying that the blended briquettes could be used as fuel for a downdraft biomass gasifier. Unfortunately, the briquettes proved too instable to experimentally verify the performance in a gasifier. This paper describes the properties of the briquettes as well as the gasification simulation results

Estudio del trabajo para incrementar la productividad en el proceso de pintado de la Empresa Adan Car E.I.R.L., Smp, 2020

El presente proyecto de investigación titulado “Estudio del Trabajo para Incrementar la Productividad en el Proceso de Pintado de la Empresa Adan Car E.I.R.L., Smp, 2020”, tiene como objetivo general, determinar cómo la Aplicación del Estudio del Trabajo incrementa la Productividad en el Proceso de Pintado. La investigación es tipo aplicada con un diseño experimental – cuasiexperimental. La población será el proceso de pintado de vehículos livianos A1 y como criterio de inclusión un periodo de 25 días, que serán evaluadas antes y después de la ejecución del estudio del trabajo. La muestra es igual a la población, se utilizó la técnica de la observación y se usaron los siguientes instrumentos: fichas de registro de tomas de tiempo, formato para el estudio de tiempos, tablas de registro de diagramas de procesos, tablas para evaluar la eficiencia, eficacia y productividad y el cronómetro; además, se utilizó el programa de Microsoft Excel 2016 y SPSS versión 22 para lograr los resultados de significancia que fueron de 0,011 en productividad, eficiencia 0,034 y eficacia 0,005; aceptándose la hipótesis del trabajo por ser menor a 0.05. Se validaron los instrumentos de recolección de datos por tres jueces expertos en el tema

An assessment of the costs and benefits of using Acacia saligna (Port Jackson) and recycled thermoplastics for the production of wood polymer composites in the Western Cape province, South Africa

Acacia saligna (Port Jackson) is one of the most pervasive IAPs in South Africa. The government’s control efforts have by and large not been co-financed by the private sector due to a lack of incentives. Here we develop a system dynamics model to assess the costs and benefits of using the invasive Acacia saligna for the production of wood polymer composites (WPCs). The cumulative net present value for clearing Acacia saligna and making WPCs amounts to approximately ZAR122.1 million for the baseline scenario (no WPC production), and is estimated to be ZAR144.4 million for Scenario 2 (WPC production with 20% co-financing), ZAR172.7 million for Scenario 3 (50% co-financing) and ZAR211.2 million for Scenario 4 (100% co-financing). In addition to these direct financial benefits, the control of Acacia saligna also offers benefits with respect to employment, an increase in the state’s tax revenue base, and an increase in the contribution to GDP.The Department of Environmental Affairs (DEA) and the Working for Water programme.http://www.aaae-africa.org/afjaream2018Economic

Determination of the Glass Transition Temperature of Freestanding and Supported Azo-Polymer Thin Films by Thermal Assisted Atomic Force Microscopy

In this paper we introduce and apply the method for determination of the glass transition temperature of the sub-100 nm thick freestanding and supported polymer films based on thermally assisted atomic force microscopy (AFM). In proposed approach changes of the phase of an oscillating AFM cantilever are used to determine glass transition temperature. An anomalous decrease of the glass transition temperature for both free-standing and supported azobenzene-functionalized polymer thin films is shown

Liquid and vapour-phase antifungal activities of selected essential oils against candida albicans: microscopic observations and chemical characterization of cymbopogon citratus

<p>Abstract</p> <p>Background</p> <p>Use of essential oils for controlling <it>Candida albicans </it>growth has gained significance due to the resistance acquired by pathogens towards a number of widely-used drugs. The aim of this study was to test the antifungal activity of selected essential oils against <it>Candida albicans </it>in liquid and vapour phase and to determine the chemical composition and mechanism of action of most potent essential oil.</p> <p>Methods</p> <p>Minimum Inhibitory concentration (MIC) of different essential oils in liquid phase, assayed through agar plate dilution, broth dilution & 96-well micro plate dilution method and vapour phase activity evaluated through disc volatilization method. Reduction of <it>C. albicans </it>cells with vapour exposure was estimated by kill time assay. Morphological alteration in treated/untreated <it>C. albicans </it>cells was observed by the Scanning electron microscopy (SEM)/Atomic force microscopy (AFM) and chemical analysis of the strongest antifungal agent/essential oil has been done by GC, GC-MS.</p> <p>Results</p> <p>Lemon grass (<it>Cymbopogon citratus</it>) essential oil exhibited the strongest antifungal effect followed by mentha (<it>Mentha piperita</it>) and eucalyptus (<it>Eucalyptus globulus</it>) essential oil. The MIC of lemon grass essential oil in liquid phase (288 mg/l) was significantly higher than that in the vapour phase (32.7 mg/l) and a 4 h exposure was sufficient to cause 100% loss in viability of <it>C. albicans </it>cells. SEM/AFM of <it>C. albicans </it>cells treated with lemon grass essential oil at MIC level in liquid and vapour phase showed prominent shrinkage and partial degradation, respectively, confirming higher efficacy of vapour phase. GC-MS analysis revealed that lemon grass essential oil was dominated by oxygenated monoterpenes (78.2%); α-citral or geranial (36.2%) and β-citral or neral (26.5%), monoterpene hydrocarbons (7.9%) and sesquiterpene hydrocarbons (3.8%).</p> <p>Conclusion</p> <p>Lemon grass essential oil is highly effective in vapour phase against <it>C. albicans</it>, leading to deleterious morphological changes in cellular structures and cell surface alterations.</p

Visible Light Responsive Photocatalyst Induces Progressive and Apical-Terminus Preferential Damages on Escherichia coli Surfaces

BACKGROUND: Recent research shows that visible-light responsive photocatalysts have potential usage in antimicrobial applications. However, the dynamic changes in the damage to photocatalyzed bacteria remain unclear. METHODOLOGY/PRINCIPAL FINDINGS: Facilitated by atomic force microscopy, this study analyzes the visible-light driven photocatalyst-mediated damage of Escherichia coli. Results show that antibacterial properties are associated with the appearance of hole-like structures on the bacteria surfaces. Unexpectedly, these hole-like structures were preferentially induced at the apical terminus of rod shaped E. coli cells. Differentiating the damages into various levels and analyzing the percentage of damage to the cells showed that photocatalysis was likely to elicit sequential damages in E. coli cells. The process began with changing the surface properties on bacterial cells, as indicated in surface roughness measurements using atomic force microscopy, and holes then formed at the apical terminus of the cells. The holes were then subsequently enlarged until the cells were totally transformed into a flattened shape. Parallel experiments indicated that photocatalysis-induced bacterial protein leakage is associated with the progression of hole-like damages, further suggesting pore formation. Control experiments using ultraviolet light responsive titanium-dioxide substrates also obtained similar observations, suggesting that this is a general phenomenon of E. coli in response to photocatalysis. CONCLUSION/SIGNIFICANCE: The photocatalysis-mediated localization-preferential damage to E. coli cells reveals the weak points of the bacteria. This might facilitate the investigation of antibacterial mechanism of the photocatalysis

Bacterial Surface Appendages Strongly Impact Nanomechanical and Electrokinetic Properties of Escherichia coli Cells Subjected to Osmotic Stress

The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO3, cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700–900 kPa and ∼100–300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions

Powering Africa

CITATION: Meincken, M. 2012. Powering Africa. South African Journal of Science, 108(1/2), Art.#1062, doi:10.4102/sajs.v108i1/2.1062.The original publication is available at http://sajs.co.zaENGLISH ABSTRACT: Africa, as a developing continent, is in a position to learn from the mistakes of the developed world. In terms of energy production, instead of trying to meet its requirements with fossil fuels alone, it should aim to implement renewable energy strategies wherever possible in the course of extending supply to its people. In terms of connectivity, the situation differs from the developed world in that a large proportion of the population (typically outside urban centres) is not connected to the electricity grid. This proportion varies from about 10% connectivity in Uganda to nearly 100% in Mauritius. In South Africa, about 35% of the population are not connected to the main grid, and these are mostly people living in remote rural areas.http://sajs.co.za/powering-africa/meincken-martinaPublisher's versio