In this project, nanocomposite films and coatings, based on renewable resources, were prepared. A hemicellulose biopolymer, based on xylan, was used as the matrix, and cellulose nanowhiskers (CNWs), as the functional additive. The xylan based matrix is an oxygen, grease and aroma barrier, making it a suitable raw material for packaging applications. Cellulose nanowhiskers were used to improve the mechanical properties and thermal stability of the hemicellulose while improving the barrier properties at high relative humidity. The focus of this thesis was processing and characterization of xylan based nanocomposites’ films and coatings. Two grades of xylans, A and B, and food contact approved plasticizer were used to prepare homogeneous films and coatings of nanocomposites, containing 2.5, 5 and 10 wt% of CNWs. The microscopy study showed no aggregations of CNWs in micro scale. Crosslinking was efficiently performed on A films and coatings, and a crosslinking density of about 70% was obtained. X-ray diffraction studies revealed a semicrystalline structure for A matrices and an amorphous one for B. The addition of CNWs resulted in an increase of crystallinity in both A and B samples. Dynamic mechanical thermal analysis showed that addition of whiskers tended to increase the storage modulus at high temperature (90°C) region. Furthermore, crosslinking as well as small amounts of whiskers (2.5 to 5 wt%) resulted in a shift of tan δ peak of nanocomposites to higher temperatures. Mechanical testing revealed a trend of improved mechanical stability in nanocomposites with small amounts of whiskers, whereas the Young’s modulus, maximum strain and maximum stress increased. However, the mechanical properties decreased at 10 wt% CNW content, probably due to aggregation of whiskers. Moreover, barrier tests, like crisp bag, grease permeability and especially oxygen permeability, indicated improved barrier properties of the materials at moist conditions. In general, improvements in barrier and mechanical performance of the material were observed, resulting from combination of CNW addition and crosslinking. / <p>Validerat; 20111121 (anonymous)</p>

Clays are ubiquitous near the Earth’s surface. Medicinal properties of these nontoxic minerals have been intuitively recognized since ancient times. Up till now, clays have been used in pharmaceutical formulations as active agents and excipients. Currently, there is an urgent need to seek advanced, functional materials with low environmental impact. Answering to that trend, clay-biopolymer nanocomposites were synthesized in this thesis and applied in a drug delivery system. In the first part of the thesis, Portuguese clay from a bentonite deposit in Benavila (Portugal) was collected from six sampling sites and characterized. The highest content of clay fraction, approximately 30%, was found in two of the sampling sites. After purification, the smectite-rich samples were analyzed with respect to clay content, mineralogical and chemical composition, physicochemical and mechanical properties. SEM-EDS revealed that the smectite present in the ore is montmorillonite with varying Fe content. This was also indicated by the means of XRD, XRF and FTIR. The Benavila sample, which was richest in smectite, as well as the sodium Wyoming montmorillonite from the Source Clay Repository (SWy-2) were successfully used to synthesize clay-biopolymer nanocomposites. The chosen biopolymers were the plant-extracted polysaccharides – neutral guar gum and its cationic form. The obtained materials were thoroughly characterized by XRD, TGA and NMR, and the intercalated structure was reported. The prepared nanocomposites were loaded with an anti-inflammatory drug ibuprofen and tested in an in-vitro release system. The drug-loaded materials were characterized with XRD, TGA and NMR. A membrane diffusion method was chosen as a dissolution testing strategy and the drug was quantified by UV-Vis spectroscopy. The materials exhibited improved properties as a noticeable reduction of release rate was achieved.

A thesis submitted to the Faculty of Science, University of the Witwatersrand in partial fulfilment of the requirement for the degree Doctor of Philosophy (PhD) in Chemistry. Johannesburg, June 2017. / Due to a high global demand for energy, research groups have been focusing a lot of energy into finding alternative and cleaner energy sources. Solar power has all the attributes to be the energy of the future. Solar power is abundantly available and is a cleaner form of energy as compared to the market-leading fossil fuels. In this thesis, we consider new materials that can be used in hybrid solar cells. These new materials combine the properties of inorganic nanomaterials and polymers. The nanomaterials possess unique properties that can be exploited and the polymers allow for the thin films to potentially be light weight and flexible. Copper selenide was synthesized and characterized to produce particles with different sizes as a function of time. These size variations are shown to emit a spectrum of different colours. In addition the particles synthesized at various temperatures are reported. Temperature had an effect on the size of the particles with bigger sizes obtained as the temperature was increased. Also shown in the results is that Cu2Se nanocrystals were quite resistant to changes with the sizes marginally increasing with increasing time and temperature. A hybrid material using a conductive polymer polyvinylcarbazole (PVK) and copper selenide was synthesized and used as the active layer via a spin coating technique to fabricate a solar cell. Varying amounts (10% - 50%) of Cu2Se nanocrystals were used in the polymer nanocomposites. The 10% weight loading resulted in the highest efficiency of 0.74% whilst successive addition of the nanocrystals affected the polymeric structure of PVK thus resulting in solar cells with even lower efficiencies. Niobium selenide was synthesized via the colloidal method using TOP/HDA combination for the first time. The effect of time on the particles synthesized using a 1:1 mole ratio of Nb:Se was negligible with particles showing similar properties. The XRD of the samples revealed that they were amorphous thus making it difficult to conclusively say that niobium selenide was synthesized successfully. The samples were then annealed however only small improvements were observed. The concentration of the selenium was then increased in order to form the more common NbSe2 and NbSe3. The XRD showed the formation of NbSe2 and NbSe3 for 1:2 and 1:3 Nb:Se ratios respectively. In addition, the particles resembled 2D nanostructures readily observed in layered materials such as NbSe2 and NbSe3. However, some impurities in the form of oxides were still observed. Hybrid solar cells prepared from the amorphous 1:1, 1:2 and 1:3 Nb:Se samples were fabricated. The NbSe3 composite had the best performing solar cell with the power conversion efficiency of 3.234% with the amorphous particles generating no current. / LG2017

Passive radiative cooling favors the transfer of energy to the deep space (2.7K) by emitting in the transparent atmosphere region (8-13m) and reflecting incoming solar irradiation. To achieve desired daytime or night time cooling performance, scientists have explored various fine-tuned photonic material combinations and layering techniques. However, the high cost, UV absorption or telecommunication interferences due to the metallic material used. Scalable and low-cost nonmetal materials have been studied, but the absorption in the UV range still remains a limitation. Single crystal CaCO_3was found to be highly reflective in the UV range, but it has not been explored for radiative cooling applications yet. In this work we first studied the reflectance in the solar range of seashells of multi-millimeters thick, and found over 70% reflectance. Inspired by this promising result, we fabricated a bio-inspired material — CaCO_3 acrylic nanocomposite, and optimized the nanoparticle size to most strongly reflect the sunlight. We analyzed its performance using Mie Theory and Monte Carlo Simulation for multiple size distribution with dependent scattering correction. The results are in excellent agreement with the experimental data. With 60% volume concentration, the simulation results showed that the total solar reflectance of CaCO_3 can achieve up to 97% . Insights obtained from this work will aid researchers in selecting economical, scalable, and manufacturable materials for radiative cooling applications. <br>

Synthetic Laponite-clay particles with a platelet-like shape display strong gelation when dispersed in aqueous solutions because of their positively charged rims and negatively charged flat surfaces. In this thesis, my aim was to modify the surfaces of these clay particles such that we can both access their liquid crystalline (LC) discotic phase and further build transparent and mechanically resilient coatings with a 3D "brick-and-mortar" structure that is similar to that observed in natural mother of pearl (nacre). I first introduce a simple strategy that successfully suppresses Laponite's ageing phenomenon and enables the system's isotropic-to-LC phase transition. By grafting Laponite particle surfaces with comb-like polymers, poly (L-lysine)-g-poly (ethylene glycol) (PLL-PEG), I was able to screen negative surface charges and ensure steric stabilisation. Besides using long-chain polymers, I also coated the positively charged Laponite rims with small, barrel-shaped molecules cucurbit[7]uril (CB[7]). By carefully tuning the ratio between CB[7] and Laponite, the system experienced a macroscopic phase separation into a Laponite-poor suspension and a birefringent LC gel. Inspired by the hierarchical structure of nacre, here I also demonstrate a simple approach to fabricate polymer-clay hybrid films via a water-evaporation process. In this third method, Laponite platelets were bridged by natural abundant polymers (carboxymethyl cellulose) through hydrogen bonding. This hybrid material possesses high transparency, flexibility and an outstanding fire-retardant property. After Ca2+ ion-coordination of these cellulose-Laponite composite films, the interface between the polymers and clays was further strengthened, leading to enhanced mechanical properties along with improved thermal- and water-resistance. I also present that using Dextran as a depletant, sterically stabilised Laponite can access its liquid crystal phase under low clay concentration. Finally, I show that Laponite can be coated with various polymers (PEO, chitosan, sodium alginate) for the purpose of obtaining LC gels and hybrid films. I believe that our findings on surface-modification of clay particles can open new routes to large-scale and inexpensive production of bio-inspired functional materials.

Polymers are intrinsically poor thermal conductors, which are ideal for thermoelectrics, but low electrical conductivity and thermopower have excluded them as feasible candidates as thermoelectric materials in the past. However, recent progress in polymer technology, particularly nanomaterial-polymer composites, can bring them into degenerate semiconductor or metallic regimes by incorporating a small amount of conductive filler. I demonstrate that such polymer nanocomposites can be viable for light-weight and economical thermoelectrics by using a segregated network approach for the nanocomposite synthesis. The thermoelectric properties were further improved by a change of stabilizer and drying conditions. The thermoelectric properties of the segregated network nanocomposites were measured for carbon nanotubes and the thermoelectric figure of merit, ZT, was calculated at room temperature. The influence on thermoelectric properties from filler concentration, stabilizer materials and drying condition are also discussed.

In this study, PEEK/SiO2 nanocomposites were fabricated by means of simple compression molding technique. The performances and properties of the resulting PEEK nanocomposites were examined in terms of tensile loading, hardness, dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicated that the modified nanosilica was seen to disperse more uniformly than the unmodified counterparty. The XRD patterns of the modified-silica filled PEEK composites reveal a systematic shift toward higher angles, suggesting the smaller d-spacing of the PEEK crystallites. As for the thermal properties of the resulting PEEK nanocomposites, there is no significant difference for the melting and crystallization temperatures, as well as the degree of crystallization between the modified and unmodified silica filled PEEK nanocomposites. The TMA results show that the coefficient of thermal expansion (CTE) becomes lowered when the content of the nanosilica increases. Furthermore, the CTE of the modified-silica filled PEEK nanocomposites shows the higher CTE values, as compared with those of the unmodified counterparts. In addition, the inclusion of the nanosilica could improve the microhardness and the stiffness of the resulting PEEK nanocomposites with the sacrifice of the elongation, as evident from the tension and DMA testing.

Self-assembled polymer nanocomposites are a promising class of advanced materials with unique structures and tunable properties. Control over the spatial arrangement and ordering of the constituent material is essential to developing composites with defined morphologies and properties. Here I report the synthesis of poly(n-butyl acrylate-b-styrene) from the surface of functionalized montmorillonite clay (MMT) via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The application of ARGET ATRP to MMT surface-initiated polymerizations results in a robust and reproducible method for synthesizing well-defined tethered block copolymers. The chosen block copolymer architecture of the composite materials resembles that of a thermoplastic elastomer, with glassy PS domains sandwiching the rubbery PnBA domain, which is divided by the clay platelets. The structure was characterized by several techniques that examine the self-assembly and degree of clay exfoliation. Preliminary analysis of the material properties indicates elastomeric behavior. / text

Amyloid fibrils are a type of protein nanofibres that form when a normally soluble protein aggregates in a regular fashion via self-association. Their organised and repetitive β-sheet structure is thought to be a generic property of all proteins, depending on the environmental conditions. The nanometre size and high stability of these protein nanofibres are attractive features to exploit in bionanomaterials. This thesis aimed to manipulate insulin amyloid fibrils, as a model protein nanofibre system, through investigating the effect of chemical modification on insulin fibril formation in heterogeneous mixtures. Using acetylation, reduction carboxymethylation, reduction pyridylethylation, trypsin digestion and chymotrypsin digestion, it was shown that nanofibres can form in heterogeneous mixtures of modified insulin at variable rates to produce fibrils of distinct morphologies. Distinctively well defined, long, unbranched nanofibres were observed in the crude reduced carboxymethylated insulin mixture after incubation at 60°C (pH 7.4), which formed at a faster rate than native insulin. The crude reduced pyridylethylated insulin revealed the formation of “wavy” fibrils when exposed to 60°C and pH 1.6, compared to the straight native insulin amyloid fibrils. Although, the trypsin digestion inhibited nanofibre formation at 60°C and pH 1.6, chymotrypsin digestion of insulin produced a mixture of long and short nanofibres under the same conditons. Thus chemical modification provides a simple means of manipulating protein nanofibre assembly for use in bionanotechnology. Protein nanofibres were incorporated into a model polymer polyvinylalcohol (PVOH) film in order to assess the impact on material properties. A systematic study involving both insulin and a crude source of crystallin proteins derived from bovine eye lens was undertaken. A protein nanofibre-PVOH nanocomposite was successfully fabricated by a procedure of solution mixing and casting. Dynamic mechanical analysis showed that the addition of insulin fibrils did not change the stiffness of the PVOH. However, an increase in the stiffness of the PVOH-crude bovine eye lens composites was found. Both insulin and bovine eye lens nanofibres reduced the damping properties of the polymer, which suggested a reduction in molecular mobility/slipping. The results revealed that protein nanofibre formation can be controlled through the modification of the protein and that nanofibres may alter polymer properties in a protein specific manner. Employing these findings in the development of novel bionanomaterials that use the protein nanofibres as a form of natural scaffolding offers a fruitful avenue of future research.

The preparation and characterisation of novel nano-scale biodegradable biocomposite materials, consisting of bacterial cellulose (BC) in a poly(lactic acid) (PLA) matrix, are investigated. BC exhibits high purity, high mechanical strength and an ultra-fine fibrous 3D network structure, while PLA is low cost, biodegradable matrix material derived from natural resources. In this work, composites of BC reinforced PLA were prepared using a solution exchange process and compression molding. The microstructure of the raw materials and composites was characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The thermal properties and crystallinity of PLA and composites were measured using differential scanning calorimetry (DSC). The mechanical properties of pure PLA and composite materials were evaluated using static and dynamic mechanical analysis (DMA). In order to improve the interfacial adhesion between the BC and PLA matrix, BC was acetylated (ABC) or treated with 3-aminopropyltriethoxysilane (APS) coupling agent (SBC). The PLA was plasticized with glycerol (PLAG) in order to increase its ductility. As compared to the Young's modulus of neat PLA (1.9 GPa), ABC generated the highest increase in Young's modulus (4.8 GPa) of the resulting composites followed by BC (4.6 GPa) and SBC (4.5 GPa). The tensile strength of PLA (31 MPa) also was enhanced to 75 MPa with BC, 72 MPa with SBC or 38 MPa with ABC. The ductility of PLAG was degraded with the addition of glycerol. A large amount voids led to a reduction in the mechanical properties of PLAG and PLAG based composites. Every reinforcement led to an improvement in the storage modulus (E') of the neat PLA and PLAG, especially at temperatures above the glass transition temperature (Tg). The DMA results showed that the presence of BC based reinforcements significantly reduced the damping properties of PLA. The reinforcements also influenced the crystalline procedure of PLA. With the addition of BC or ABC to the PLA matrix, the melting points of the composites were increased ~ 4-7 ℃ with a slight change on crystallinity; the crystallinity of SBC-PLA composite decreased from 31.9 % to 26.9 % with only a change of ~ 1 ℃ in the melting point.