Yes / The mechanical property enhancement of polymer reinforced with nano-thin clay platelets (of high aspect ratio) is associated with a high polymer-filler interfacial area per unit volume. The ideal case of fully separated (exfoliated) platelets is generally difficult to achieve in practice: a typical nanocomposite also contains multilayer stacks of intercalated platelets. Here we use numerical modelling to investigate how the platelet properties affect the overall mechanical properties. The configuration of platelets is modelled using a statistical interpretation of the Representative Volume Element (RVE) approach, in which an ensemble of "sample" heterogeneous material is generated (with periodic boundary conditions). A simple Monte Carlo algorithm is used to place non-intersecting platelets in the RVE according to a specified set of statistical distributions. The effective stiffness of the platelet-matrix system is determined by measuring the stress (using standard Finite Element analysis) produced as a result of applying a small deformation to the boundaries, and averaging over the entire statistical ensemble. In this work we determine the way in which the platelet properties (curvature, filling fraction, stiffness, aspect ratio) and the number of layers in the stack affect the overall stiffness enhancement of the nanocomposite. Thus, we bridge the gap between behaviour on the macroscopic scale with that on the scale of the nano-reinforcement, forming part of a multi-scale modelling framework.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Polymer Science) at University of Stellenbosch. / ENGLISH ABSTRACT: The preparation of poly(acrylonitrile/methyl acrylate) [poly(AN-co-MA)] copolymers and poly(AN-co-MA)/clay nanocomposites, via emulsion polymerization, their characterisation, and the relationships between their molecular structures and physical properties are described. The copolymer composition was varied, and the properties of the products were analysed and correlated to copolymer composition. The free volume properties of the copolymer were dependent on the glass transition temperature (Tg), which is dependant on the copolymer composition. The copolymer crystallinity decreased with increasing MA content. The decrease in crystallinity and increase in both o-Ps lifetime and o-Ps intensity with decreasing Tg was caused by the enhanced chain mobility brought about by the incorporation of methyl acrylate. The poly(acrylonitrile-co-methyl acrylate)/clay nanocomposites with 60% AN:40% MA (mol:mol) ratio were prepared using montmorillonite clay modified via adsorption, using 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS), via in-situ intercalation polymerization. The poly(AN-co-MA)/clay nanocomposites with different clay loadings showed no difference in morphology. They exhibited improved thermomechanical properties and higher thermal stability than the neat copolymers. The melt rheology results of these nanocomposites showed an improved storage modulus as well as increased shear thinning behaviour with increasing clay content. However, the nanocomposites exhibited long-time relaxation behaviour and their chemical structures evolved during analysis. This was attributed to cyclisation reactions taking place at the temperature used during the oscillatory tests. The sorption isotherms of water vapour in these nanocomposites followed a dualmode sorption behaviour (BET type II mode). Hysteresis was observed in sorption/desorption isotherms of these nanocomposites. The equilibrium water uptake was higher in the nanocomposites compared to the neat copolymers, and it increased with increasing clay content, especially at high water activities (0.8). Although diffusion and permeability decreased with increasing clay content the solubility increased due to the hydrophilic nature of the clay. Despite the decrease in diffusion and permeability parameters the free volume hole radius of the nanocomposites remained constant, but a slight decrease in free volume hole number was observed. / AFRIKAANSE OPSOMMING: Die bereiding van poli(akrilonitriel/metielakrilaat) [poli(AN-ko-MA)] kopolimere en poli(AN-ko-MA)/klei nanosamestellings deur middel van emulsiepolimerisasie, hul karakterisering asook die ooreenkoms tussen hul molekulêre strukture en fisiese eienskappe is beskryf. Die kopolimeersamestelling is gevarieer, en eienskappe is geanaliseer en dan gekorreleer met die kopolimeersamestelling. Die vrye-volume eienskappe van die kopolimeer was afhanklik van die glasoorgangstemperatuur (Tg) wat weer afhanklik is van die kopolimeersamestealling. Die kristalliniteit van die kopolimeer het verminder met die hoeveelheid MA teenwoordig. Die afname in kristalliniteit en toename in beide die o-Ps leeftyd en o-Ps intensiteit met afname in Tg is veroorsaak deur die beter kettingbeweegbaarheid wat veroorsaak is deur die byvoeging van metielakrilaat. Die poli(akrilonitriel-ko-metielakrilaat)/klei nanosamestellings met 60% AN:40% MA (mol:mol) verhouding is berei deur die gebruik van montmorillonietklei, gemodifiseer deur die adsorpsie van 2-akrielamido-2-metiel-1-propaansulfoonsuur (AMPS) deur middel van 'n in-situ interkaleringspolimerisasie. Die poli(AN-ko-MA)/klei nanosamestellings het, ten spyte van die verskillende hoeveelhede klei wat gebruik is, geen verandering in morfologie getoon nie. Hulle het wel beter termodinamiese eienskappe en hoër termiese stabiliteit as die oorspronklike kopolimere getoon. Die smeltreologie resultate van hierdie nanosamestellings het ‘n beter stoormodulus getoon, sowel as toenemende skuifverdunningsgedrag met 'n verhoogde klei inhoud. Tog het die nanosamestellings lang tyd-ontspanningsgedrag getoon en die chemiese struktuur het verander tydens analise. Dit word toegeskryf aan die sikliese reaksies wat plaasvind by die temperatuur wat gebruik is tydens die ossillatoriese toetse. Die sorpsie isoterme van waterdamp in hierdie nanosamestellings het ‘n dubbel-styl sorpsiegedrag gevolg (BET tipe II styl). Histerese is waargeneem in sorpsie/desorpsie isoterme van hierdie nanosamestellings. Die ewewig in wateropname van die nanosamestellings was hoër as vir dié van die oorspronklike kopolimere en dit het toegeneem met 'n toenemende klei inhoud, veral by hoë humiditeit (0.8). Al het die diffusie en deurlaatbaarheid afgeneem met 'n toename in die klei inhoud, het die oplosbaarheid toegeneem as gevolg van die hidrofiliese karakter van die klei. Ten spyte van die afname in diffusie en deurlaatbaarheidsparameters, het die radius van die vryevolume openinge van die nanosamestellings konstant gebly, maar ‘n klein afname in die aantal vrye-volume openinge is gevind.

In the past two decades polymer/clay nanocomposites (PCNs) have emerged as promising materials that exhibit remarkably improved properties when compared to conventional composites and pristine polymers. Such improvements strongly depend on the dispersion of clay nanoparticles in the polymer matrix. In spite of great efforts expended in characterizing clay dispersion, effective, simple and quantitative techniques are still needed. This work addresses this challenge by presenting new aspects of 1H solid-state NMR for quantifying clay dispersion in PCNs filled with clay containing paramagnetic ions. Employing these 1H solid-state NMR methods, some structure-processing-deformation relationships of PCNs were derived, and basic insights into nuclear relaxation and spin diffusion in PCNs were gained as well. Detailed models and analyses were described for 1H spin-lattice relaxation in the presence of paramagnetic clays in PCNs. Relaxation recovery was analytically correlated to clay dispersion in two ways: one is the initial relaxation recovery which is related to clay surface area, and the other is the spin-lattice relaxation time which is related to interparticle spacing. These two NMR observables were employed to quantitatively observe the evolution of clay morphology in poly(propylene)/clay (PP/MMT) nanocomposites upon equibiaxial stretching, as well as upon in situ uniaxial deformation. The initial relaxation recovery was independently utilized to determine the polymer-clay interfacial surface area and the degree of clay exfoliation. We demonstrated the capabilities of our models in quantitatively characterizing several materials, including poly(vinyl alcohol), nylon 6, poly(å-caprolactone) (PCL), poly(lactic acid) (PLA) and PP nanocomposites. These results were used to examine the dependence of clay morphology upon processing (strain ratio, strain rate, temperature), deformation (extension), component characteristics (polymer molecular weight, clay surface modification) and clay content. Effects of paramagnetic Fe3+ concentration and external magnetic field strength on 1H spin-lattice relaxation in PCNs were also investigated and discussed. In particular, low field separates the initial relaxation recovery into two stages: one related to clay content and the other related to the polymer-clay interfacial surface area. The low field was observed to enhance the paramagnetic contribution to the spin-lattice relaxation rate, increasing its sensitivity to clay morphology. In addition, measurements of long-distance spin diffusion coefficients for a variety of polymers and paramagnetic characteristics of organically modified clay were explored. Overall, the utility of NMR relaxometry in characterizing PCNs has been significantly expanded and successfully demonstrated in this dissertation.

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The search for more productive seeds and with better transport and storage conditions has developed the interest of companies and researchers. In this section, nanotechnology, in particular, polymer / clay nanocomposites has proved to be an excellent alternative. By means of these nanomaterials it is possible to transport assets that allow the plant to better growth, productivity and germination rates, through the transport of fertilizers, agrochemicals or even essential micronutrients. The aim of this work was to synthesize and study nanocomposites polymer / clay; poly (hydroxyethyl methacrylate), pure laponite (pHEMA / Lap) and enriched with manganese micronutrients (pHEMA / LapMn). These materials aim to provide water and concomitantly provide nutrients to the seeds. The best formulation for the samples, amounts of polymer and clay was studied, and from this the micronutrient was incorporated into the formulation. The materials were characterized by absorption spectroscopy in the infrared region (FTIR), X-ray diffractometry (XRD) and thermogravimetry (TG). In addition, the water uptake capacity of the samples was evaluated. TG results showed an increase in thermal stability due to the interaction of the polymer chain with the clay. The XRD study showed that pure Lap and Lap Mn presented similar basal spacing to that found in the literature and that the nanocomposite had an exfoliated structure of the materials. The observation of the degree of swelling of the samples showed that the nanocomposites showed a capacity of water absorption 10% higher than the pure hydrogel. The seed coating affected the germination rate of the seeds, showing an optimization of this process. / A busca por sementes mais produtivas e com melhores condições de transporte e armazenamento tem desenvolvido o interesse de empresas e pesquisadores. Nesta vertente, a nanotecnologia, em especial, os nanocompósitos polímero/argila tem se mostrado uma excelente alternativa. Por meio destes nanomateriais é possível transportar ativos que possibilitem a planta melhor crescimento, produtividade e taxas de germinação, por meio do transporte de fertilizantes, agroquímicos ou até micronutrientes essenciais. Neste trabalho buscou-se sintetizar e estudar nanocompósitos polímero/argila; poli(metacrilato de hidroxietila) (pHEMA), laponita pura (pHEMA/Lap) e enriquecida com micronutrientes manganês (pHEMA/LapMn). Estes materiais tem por objetivo fornecer água e concomitantemente fornecer nutrientes para as sementes. Estudou-se qual a melhor formulação para as amostras, quantidades de polímero e de argila e a partir desta incorporou-se o micronutriente a formulação. Os materiais foram caracterizados por espectroscopia de absorção na região do infravermelho (FTIR), difratometria de raios X (DRX) e termogravimetria (TG). Além disso, a capacidade de absorção de água das amostras foi avaliada. Houve aumento da estabilidade térmica decorrente da interação da cadeia polimérica com a argila. O estudo por DRX mostrou que a Lap pura e a Lap Mn apresentaram espaçamento basal similar ao encontrado na literatura e que o nanocompósito apresentou estrutura esfoliada dos materiais. A observação do grau de intumescimento das amostras mostrou que os nanocompósitos apresentaram uma capacidade de absorção de água 10% superior à do hidrogel puro. O revestimento das sementes prejudicou a taxa de germinação das mesmas mostrando-se necessário uma otimização deste processo. / São Cristóvão, SE