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

Meincken, Martina (2002-03)

Dissertation (PhD)--Stellenbosch University, 2002.

Thesis

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 los

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