Thesis (Ph. D. (Chemistry)) -- University of Limpopo, 2019 / This work presents the synthesis, characterisation and application of poly(vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) membrane prepared using a phaseinversion method. PVDF-HFP was blended with either functionalised multi-walled carbon nanotubes (MWCNTs), poly-amidoamine (PAMAM) dendrimeric MWCNTs or silver (Ag) nanoparticles and their combinations. Nanocomposite blends such as MWCNTs/PVDF-HFP, PAMAM-MWCNTs/PVDF-HFP, Ag-MWCNTs/PVDF-HFP and Ag-PAMAM-MWCNTs/PVDF-HFP were synthesised successfully. A variety of PVDF-HFP composite membranes prepared were characterised by X-ray powder diffraction (XRD), fourier transform infrared (FTIR), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and contact angle. The fMWCNTs, Ag-MWCNTs, PAMAM-MWCNTs and Ag-PAMAMMWCNTs nanocomposites were further characterised by Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). FTIR spectra of PAMAMMWCNTs confirmed the formation of functional groups such as COOH, NCO, NH2 and PAMAM dendrimer. XRD analysis demonstrated that the crystallite sizes of the silver nanoparticles were larger (8.4 nm) than those of Ag-MWCNTs (7.8 nm) and Ag-PAMAM/MWCNTs (6.4 nm) nanocomposites. These findings were further confirmed by TEM analysis which showed Ag nanoparticles, Ag-MWCNTs and Ag-PAMAM/MWCNTs having diameters of silver particles between 9 to 20 nm, 5 to 10 nm and 4 to 8 nm respectively. The reduced Ag particle sizes was due to the complexation of MWCNTs and PAMAMMWCNTs with Ag metal ions, which correlates with an enhanced surface area in the nanocomposite membranes, leading to good filtration and antibacterial properties. TGA studies demonstrated that the thermal stability of PVDF-HFP composite membrane was greatly enhanced by the addition of PAMAM-MWCNTs. However, the composite membranes consisting of both Ag nanoparticles and MWCNTs on PVDFHFP did not improve the structural stability of PVDF-HFP. All composite membranes have shown stability up to 400 oC. The contact angle, porosity, swellability and water content measurements of the composite membranes were improved showing enhanced hydrophilicity due to addition of MWCNTs, PAMAM-MWCNTs and/or Ag nanoparticles. The scanning electron microscopy (SEM) images have depicted the formation of microporous structure, with few MWCNTs on the surface strongly interacting with PVDF-HFP as demonstrated by TGA, XRD and FTIR data. SEM cross-sections of PVDF-HFP composite membranes showed a mixture of fingure-like microvoids with a membrane diameter of approximately 180 μm. The BET data showed an improved surface area, pore volume and pore sizes of PVDF-HFP composite membranes when blended with fMWCNTs and PAMAM. These membranes also showed high fouling resistance, good desalination and high Cd(II) ions rejections during permeability studies. E. coli filtration studies indicated that 2.5 wt.% Ag-MWCNTs/PVDF-HFP and 1.8 wt.% Ag-PAMAM-MWCNTs/PVDF-HFP composite membranes displayed good microbial load reduction (100%) and excellent antibacterial properties as evidenced by the bacterial growth on the edges of the membranes. The microbial, physicochemical and chemical analysis of surface water samples from Sekhukhune area showed that the water was contaminated with Enterobacteriaeceae, E. coli, total coliform with high turbidity and total suspended solids above the South African national standard (SANS 241) water guidelines. After filtration with 1.8 wt.% Ag-MWCNTs/PVDF-HFP composite membrane, turbidity was reduced to 4 Nephelometric turbidity units (NTU), total suspended solids to 1 mg/L while Enterobacteriaeceae, E. coli and total coliform were undetectable and complied with SANS 241 limits. Chromium concentration levels were reduced from 0.194 to 0.0138 mg/L, after filtration with 1.8 wt.% Ag-PAMAM-MWCNTs/PVDF-HFP composite membrane also within acceptable SANS 241 limits. Adsorption studies of all composite membranes demonstrated that the adsorption processes of Cd(II) ions was well conformed to Freundlich model (R2 = 0.999), which suggests that the sorption process met heterogeneous adsorption. However, for Cr(VI) ions studies, the adsorption process was conformed to both Langmuir (R2 = 0.999) and Freundlich (R2 = 0.998) model which suggest that that the adsorption process meet both monolayer and heterogeneous adsorption. The maximum adsorption capacity fitted by Langmuir isotherm was 166.7 and 9.72 mg/g for Cd(II) ions (at optimum pH 6.5) and Cr(VI) ions (at optimum pH 2.5) respectively, using 1 wt.% PAMAM-MWCNTs/PVDF-HFP composite membrane. The adsorption capacities of Cd(II) ions were higher than those of Cr(VI) ions, which is thought to be due to the properties of the composite membrane material. According to the thermodynamic parameters, the Cd(II) and Cr(VI) ions adsorption process was spontaneous and endothermic. Reusability studies showed that PVDF-HFP composite membranes can be reused at least 4 times with an adsorption loss of only 5% for 1 wt.% PAMAMMWCNTs/PVDF-HFP composite membrane, confirmed by TGA and ICP-OES analysis. The 1 wt.% PAMAM-MWCNTs-PVDF-HFP composite membrane exhibited a higher selectivity towards Cd(II) over Cu(II), Zn(II) and Ni(II) in binary and quaternary metal adsorption studies.

Biofilms are a common mode of yeast growth in which cells adhere to each other and adhere to abiotic surfaces to form complex multicellular structures. Living together in biofilms provides cells with several beneficial features compared to planktonic cells. Undoubtedly, protection and resistance are advantages of life inside colony biofilms. Biofilms are found in many environments and play many important roles in commercial industries. However, biofilms can also be extremely dangerous in clinical settings. There is thus great interest in studying biofilms and how to eliminate them. In this study, we used wild yeast Saccharomyces cerevisiae colony biofilm as an ideal system to investigate potential functions of the yeast Cyc8-Tup1 transcriptional corepressor complex in the regulation of yeast adhesion, and biofilm formation on agar and at solid-liquid interfaces. Unexpectedly, we have found that Cyc8p and Tup1p antagonistically control the formation of structured biofilm colonies on agar and FLO11 expression. Cyc8p itself acts as a key repressor of FLO11, whereas Tup1p promotes the formation of biofilm colonies and induces FLO11 expression by inhibiting the repressive function of Cyc8p and preventing Flo11p degradation possibly by inhibiting an extracellular protease. In addition, other features...

The mechanical properties of the polymer-modified mortar are markedly improved over conventional cement mortar. We utilized recycled ABS in powder form and a polymer latex emulsion, polymer percentage ranges from 0 to 25 percent by polymer/cement ratio were investigated. The mechanical properties investigated were compression strength and adhesion strength. Compression strength effects did not have an impact on adhesion strength. Adhesion strength was calculated with pullout testing apparatus designed by the author. Results indicate that recycled ABS had a lower adhesive strength than the acrylic latex emulsion and the base mortar, but did increase in adhesive strength when mixed with maleic-anhydride. The adhesive strength was investigated for a Fiber Reinforced Polymer (FRP) made of an "E" glass fiber that is a continuous strand roving oriented and pre-tensioned longitudinally in an isopthalic polyester matrix material. The FRP rebar was compared to standard steel rebars, and found that the standard steel corrugated rebar had a higher adhesive strength, due to mechanical interlocking. This was clarified by measurements using a smooth steel rebar. Characterization of the polymer-modified mortar was conducted by pore analysis and scanning electron microscopy. Scanning Electron Microscopy was implemented to view the polymer particles, the cement fibrils formed by the hydration, and to prove Ohama's theory of network structure.

Salmonella enterica is a facultative intracellular pathogen, able to invade various hosts and successfully replicate within them. Invasion of polarized cells by S. enterica serovar Typhimurium (STM) occurs in dependence of the type 1 secretion system (T1SS), encoded on Salmonella Pathogenicity Island 4 (SPI4). The 595 kDa non-fimbrial adhesin SiiE is the substrate of the SPI4-T1SS and mediates the first close contact to the host cells apical side. This allows for the type 3 secretion system (T3SS) of the SPI1 to translocate its effector proteins into the host cells cytosol, leading to actin remodeling, membrane ruffle formation and finally uptake of the pathogen. The SPI4-T1SS belongs to the family of ATP-binding cassette (ABC) transporters and is characteristically composed of the ATPase SiiF in the inner membrane (IM), the periplasmic adaptor protein (PAP) SiiD and the secretin SiiC. Further there are two non-canonical proteins encoded, namely SiiA and SiiB, which are known to form a proton channel in the IM. Every single subunit was found to be essential for invasion of polarized cells. The substrate SiiE is transiently retained on the cell surface during secretion process and protrudes the lipopolysaccharide (LPS) layer, a step essential for adhesion. Following translocation of the SPI1-T3SS effector proteins, SiiE is released into the extracellular space. Utilizing a variety of techniques, I was able to show that the transient retention of SiiE only occurs in the outer membrane (OM) protein SiiC and not in the whole two membrane-spanning T1SS. My analyses showed that the proton channel SiiAB is involved in initial steps of secretion and not necessary for release of SiiE, further narrowing down possible modes of action. I found a potential proteolytic cleavage site in the N-terminal part of SiiE, essential for release of the adhesin and discovered a potential retention domain in its N-terminus, too bulky to pass through the secretin. Additionally, I gained first hints that the large cytosolic domain of SiiB is not only involved in SiiE retention mechanism, but also in flagellar-dependent movement under swarming conditions. Using dual-color 3D direct stochastic optical reconstruction microscopy (dSTORM), I was able to localize SiiAB in the IM and SiiB not only at the SPI4-T1SS, but during SiiE retention maximum primarily at the flagellum. Intriguingly, the synthetic expression of siiAB as well as synthetic expression of the flagellar stator unit motAB both showed an increase of velocity. Furthermore, I successfully established murine and human intestinal organoid cell culture for microscopic and quantitative analyses of STM and S. Paratyphi A (SPA) invasion processes. Thus, with this work I was able to reveal new insights of the SPI4-T1SS, its substrate SiiE and the non-canonical subunits SiiAB that pave the way for further SPI4-T1SS investigations and also other secretion systems and their associated subunits.

Adhesion lithography has been used to pattern nanogaps between two electrodes of the same or different metals onto a substrate. Patterning Al and Ti/Pt bilayer electrodes have been shown to form nanogaps leaving behind relatively consistent nanogaps of less than 12 nm between the electrodes. These nanogaps are formed without the need for adhesion lithography due to the bilayer spontaneously delaminating from the aluminum electrodes, In this study, the stresses in the Ti/Pt bilayer are investigated to determine the amount of stress required for delamination and the properties causing it. The goal is to recreate this stress mechanism in other patterned metals such as Au and Al. Heat cycling is used to induce high stress in other metal electrode combinations in an attempt to induce spontaneous delamination in Al and Au but fails up to 310°C annealing temperature. Theoretical methods are used to determine the stress: searching for an appropriate mathematical model and using finite element analysis in ABAQUS software to create a simulation of the delaminating Ti/Pt bilayer. The stress is found to be caused by the residual stresses in platinum and the high energy e-beam deposition method. An experimental value for the stress and the ability to recreate it in other metals remains elusive.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第19550号 / 医博第4057号 / 新制||医||1012(附属図書館) / 32586 / 京都大学大学院医学研究科医学専攻 / (主査)教授 坂井 義治, 教授 三嶋 理晃, 教授 開 祐司 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20587号 / 農博第2239号 / 新制||農||1052(附属図書館) / 学位論文||H29||N5076(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 植田 和光, 教授 矢﨑 一史, 教授 宮川 恒 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

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<p> The ability of a never-dried paper web on a paper machine to resist breakage is commonly referred to as paper wet-web strength. Low wet-web strength can lead to frequent breaks which interrupt production and lower paper machine efficiency. Currently, no commercial products provide the function of enhancing wet-web strength. Boronic acid derivatized polyvinylamine (PVAm-PBA) showed high instantaneous wet adhesion to regenerated cellulose membranes. The objective of the research summarized in this thesis was to determine the factors and mechanisms dictating PVAm-PBA adhesion to wet cellulose. In addition, narrowly distributed PVAm microgel was prepared and the wet adhesion of boronate-microgels to cellulose is reported.</p> <p> The phase behavior and surface tension of PVAm-PBA were measured as functions of pH and the degree of PBA substitution. The pH ranges over which phase separation occurred increased with PBA substitution. 150 kDa PVAm-PBA with 4% derivatization phased separated at pH 8.5 to 9.5.The copolymer based on 51 % substitution was insoluble over most of the pH range. The hydrophobicity of copolymers was reflected in the significant lowering of surface tension particularly at high pH. Additionally, fructose, which binds to borate, influenced the titration curves but did not influence surface tension.</p> <p> Pairs of wet, regenerated cellulose films were laminated with PVAm-PBA and the forces required to delaminate the never-dried laminates, were measured as functions of adhesive structure and application conditions. The greatest wet adhesion was obtained with 150 kDa PVAm with 16% of the amines bearing phenylboronic moieties. The pH at which the PVAm-PBA was adsorbed onto the cellulose was the dominant process parameter. The specific role of the phenyl boronic groups was illustrated in two ways: a) replacing the B(OH)2 with OH (i.e. phenol) gave much lower adhesion; and, b) wet adhesion was greatly reduced by the presence of sorbitol which effectively competes with cellulose for boronate binding sites.</p> <p> The interaction of boronate and cellulose was studied. Owing to poor solubility of cellulose, two model polymers: dextran and hydroxyethyl cellulose (HEC) and two saccharides: glucose and cellobiose were measured by boron NMR measurement, tensile extension, fluorescence spectra, viscometer and peeling test methods. In conclusion, carbon-1, 2 diols at one end of cellulose chain can react with boronic acid. By contrast, carbon-2, 3 diols, which are abundant on cellulose chains, cannot react with boronic acid and the other diols, such as carbon-3, 4 diols and carbon-4, 6 diols cannot react with boronic acid. The high adhesion of boronate containing polymers to cellulose membranes was attributed to boronate ester formation with the cellulose end groups on the membrane surfaces. </p> <p> Finally, a simple and effective methodology was demonstrated for the preparation of polyvinylamine microgel with a narrow distribution. Boronate derivatives of PVAm microgels displayed very high wet adhesion to cellulose over a broad pH range.</p> / Thesis / Doctor of Philosophy (PhD)

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