No description available.

<p>The aim of this thesis work was to investigate theadsorption of surfactants to different nonpolar interfaces.Particularly, the effects of the polar group and the nature ofthe hydrophobic interface were elucidated. The interfacialbehavior of the liquid-vapor interface was investigated bymeans of surface tension measurements. Here the effect of thepolar group and the hydrocarbon chain length was investigatedin a systematic manner. It was found that the shorter of thetwo chains examined, decyl, generated a larger surface pressurecontribution than the longer, dodecyl. Furthermore, the sugarbased surfactants behaved differently as compared to theethylene oxide based ones. The former could be modelled byassuming a hard disc behavior of the head group while thelatter displayed polymeric behavior. The influence of saltconcentration on the surface tension behavior of an ionicsurfactant, sodium dodecyl sulphate, was investigated. Theresult could be rationalized by employing the Gouy- Chapmanmodel to the polar region. Furthermore, mixtures of two sugarbased surfactants were investigated by surface tensionmeasurements and the adsorbed amount of the two components atthe interface atdifferent concentrations and fractions in thebulk were obtained by applying the Gibbs surface tensionequation. It was found that the molecule with the smaller headgroup adsorbed preferentially, and more so as the totalsurfactant concentration was increased. These findings could beexplained by considering the interactions generated by thedifferent head groups. The adsorption of sugar surfactants toan isolated hydrophobic surface was studied by means of wettingmeasurements and the behavior was similar to that at theliquid-vapor interface. Wetting isotherms were measured on twodifferent hydrophobic surfaces where the covalently attachedhydrophobic layers were in a crystalline and fluid state,respectively. The wetting results revealed that the sugarsurfactants anchored in the fluid hydrophobic layer. This had asignificant influence on the force profile. For example, at thecrystalline surface the surfactant monolayers were easilyremoved as the surface came into contact at relatively lowapplied loads. This was not the case when the hydrophobic layerwas in a fluid state. Here a significant fraction of thesurfactants remained between the surfaces. Disjoining pressureisotherms were measured using a sugar based surfactant thatwere thoroughly purified and compared to the as receivedsample. Even the purified sample showed a double-layer forcealthough lower as compared to the as received, one. Asignificant difference in foam stability was also observed.</p>

Includes vita. / Title from PDF of title page. / Document formatted into pages; contains 224 pages. / Thesis (Ph.D.)--University of South Florida, 2004. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Particle Nucleation is the forcing function in the Emulsion Polymerization processes and it plays an important role in dictating the final properties of the latex produced. Identification of the main nucleation sites and characterizing them in terms of their size and composition is important for elucidating the mechanism of particle nucleation. This research focuses on identifying the most likely nucleation locus in emulsion polymerization processes by characterizing the initial conditions of the reaction mixture. In order to achieve this objective, a methodology was devised, which used a non-reacting model emulsion system instead of the original emulsion. The model emulsion system selected has the same dispersion properties as that of the monomer emulsion system, but different optical properties. The model emulsion system enabled the study of the distribution of the emulsifier using Uv vis spectroscopy. / ABSTRACT: This approach also eliminated the time constraint associated with sampling during a polymerization reaction. A quantitative deconvolution using the turbidity equation, was done on the transmission Uv vis spectra of the emulsions. This enabled the characterization of the emulsions in terms of their particle size distribution, particle number and the composition of the droplet populations comprising them. The studies conducted provide the experimental evidence for a previously unidentified nano-droplet population of size range 30 to 100nm in diameter. To further support this experimental evidence, calculations were performed to obtain the emulsifier distribution over the nano-droplet population. The calculations suggest the probability of existence of the nano-droplet population to be much higher than the probability of the existence of the swollen micelles. / ABSTRACT: The results, depending upon the emulsification conditions, indicate the presence of about 15 % to 80% of the dispersed phase in the nano-droplet population. The large interfacial area offered by the nano-droplet population due to their high particle numbers and high percentage of the dispersed oil phase in them, make them the most probable particle nucleation loci in emulsion polymerization processes. Designed experiments were performed to experimentally observe the changes in the nano-droplet populations. The effects of the process variables, namely pH, surfactant concentration and temperature, on the size and compositional characteristics of the nano-droplet population were investigated. The results suggested that the surfactant to oil ratio was the dominating factor governing the size and the weight percent of the dispersed phase in the nano-droplet population. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Reproduction de : Thèse de doctorat : Chimie théorique, physique, analytique : Lille 2 : 2008. / Résumé en français et en anglais. Titre provenant de l'écran-titre. RMN = Résonance Magnétique Nucléaire. Bibliogr. p. 221-242.

Thèse de doctorat : Chimie : Nancy 1 : 2000. / 2000NAN10008. Titre provenant de l'écran-titre.

The ability to select low-cost, high-performance surfactants for a wide range of crude oils under a wide range of reservoir conditions has improved dramatically in recent years. Surfactant formulations (surfactant, co-surfactant, co-solvent, alkali, polymer, and electrolyte) were developed by using a refined phase behavior approach. Such formulations nearly always result in more than 90% oil recovery in core flood when good surfactants with good mobility control are used. The advances that have improved performance, reduced cost, increased robustness, and extended the range of reservoir conditions for these formulations are described in this work. There are thousands of possible combinations of the chemicals that could be tested for each oil and each chemical combination requires many observations over a long time period at reservoir temperature for proper evaluation. It would take too long, cost too much and in many cases not even be feasible to test all combinations. In practice the scientific understanding is used to match up the surfactant/co-surfactant/co-solvent characteristics with the oil characteristics, temperature, salinity, hardness and so forth. Synthesized and new surfactants with much larger hydrophobes and more branching than previously available were tested. New classes of co-solvents and co-surfactants with superior performance were test to improve aqueous solubility. These new developments resulted in improved ASP formulations for both oils that react with alkali to make soap and oils that do not. Many of these developments are synergistic and taken together represent a breakthrough in reducing the cost of chemical flooding and thus its commercial potential. / text

Carbon nanotubes (CNTs) exhibit unique and fascinating intrinsic electrical, optical, thermal or mechanical properties that lead to a plethora of potential applications in composite materials, electronics, energy storage, medicine, among others. However, the manipulation of nanotubes is not trivial and there are significant difficulties to overcome before achieving their full potential in applications. Because of their high aspect ratio and strong tube-to-tube van der Waals interactions, nanotubes form bundles and ropes that are difficult to disperse in liquids. In this thesis, the topic of dispersing carbon nanotubes in water was addressed by several experimental methods such as nuclear magnetic resonance (NMR) diffusometry and light/electron microcopy. The main goal was to obtain molecular information on how the dispersants interact with carbon nanotubes. In dispersions of single-walled carbon nanotubes (SWNTs) in water, only a small fraction of the polymeric dispersant (Pluronic F127) was shown to be adsorbed at the CNT surface. Regarding dynamic features, the residence time of F127 on the SWNT surface was measured to be in the order of hundred milliseconds, and the lateral diffusion coefficient of the polymer along the nanotube surface proved to be an order of magnitude slower than that in the solution. The surface coverage of SWNTs by F127 was also investigated and the competitive adsorption of F127 and the protein bovine serum albumin, BSA, was assessed. F127 was found to bind stronger to the CNT surface than BSA does. Low molecular weight dispersants, viz. surfactants, were also investigated. Using carefully controlled conditions for the sonication and centrifugation steps, reproducible sigmoidal dispersibility curves were obtained, that exhibited an interesting variation with molecular properties of the surfactants. Various metrics that quantify the ability of different surfactants to disperse CNTs were obtained. In particular, the concentration of surfactant required to attain maximal dispersibility depends linearly on alkyl chain length, which indicates that the CNT-surfactant association, although hydrophobic in nature, is different from a micellization process. No correlation between dispersibility and the critical micellization concentration, cmc, of the surfactants was found. For gemini surfactants of the n-s-n type with spacer length s and hydrophobic tail length n, the dispersibility of multiwalled carbon nanotubes (MWNTs) also followed sigmoidal curves that were compared to those obtained with single-tailed homologues. The increase in spacer length caused an increase in the dispersion efficiency. The observations indicate a loose type of monolayer adsorption rather than the formation of micelle-like aggregates on the nanotube surface. With the future goal of embedding nanotubes in liquid crystal (LC) phases and thereby creating nanocomposites, the effect of the spacer length on the thermotropic behavior of the gemini 12-s-12 surfactant was investigated. Different mesophases were observed and a non-monotonic effect of the spacer length was found and rationalized within a model of the surfactant packing in the solid state. The relative binding strength of simple surfactants to CNTs was assessed by the amount of F127 they displace from the CNT surface upon addition. Anionic surfactants were found to replace more F127, which was interpreted as a sign of stronger binding to CNT. The data collected for all surfactants showed a good correlation with their critical dispersibility concentration that suggests the existence of a surface coverage threshold for dispersing nanotubes. On the macroscopic scale, the formation of weakly bound CNT aggregates in homogeneous dispersions was found to be induced by vortex-shaking. These aggregates could quickly and easily be re-dispersed by mild sonication. This counterintuitive behavior was related to the type of dispersant used and of the duration of mechanical agitation and was explained as a result of loose coverage by the dispersant. / <p>This Ph.D thesis was completed under the Thesis Co-supervision Agreement between KTH Royal Institute of Technology and the University of Port. QC 20151105</p>

A total of twenty-eight Bacillus spp. isolated from value-added surimi nuggets and their raw ingredients, were tested against each other and selected reference strains of Bacillus and Clostridium for their production of inhibitory substances using the deferred antagonism assay plating method. The isolated Bacillus strains showed inhibitory activity against all Bacillus strains, with the exception of the producer strain, as well as being effective against various strains of C. botulinum (type A, B and E). Subsequent studies showed that the inhibitory activity was detected in the culture supernatant in the late stationary phase of growth prior to sporulation. The inhibitory activity of two Bacillus strains (FN2A and FN33) were selected for further study. The inhibitory substances produced by these two strains were proteinaceous in nature, heat stable (100°C for 15min) and unaffected by organic solvents. A comprehensive study was conducted on the structural characterization of the inhibitor produced by B. subtilis FN2A using FPLC, FTIR, MS and MS/MS. Structural analysis of the inhibitor produced by B. subtilis FN2A showed that it was similar in structure to Surfactin. / Preliminary studies have shown that the Surfactin-like-compound from B. subtilis FN2A was produced in significant amounts during growth in bread with maximum production occurring in the late stationary phase (72h), at 30--35°C and at pH 6.5--7.0. Optimization studies on the production of the Surfactin-like-compound by B. subtilis FN2A in bread using a response surface methodology approach showed that temperature (33--36°C); autoclaving time (30 min); inoculum level (4%), alkali pre-treatment (0.16%), water activity (0.995) and pH 6.66 enhanced the production of the Surfactin-like-compound in bread. The compound produced under these optimal conditions also maintained its activity when subjected to various processing treatments (autoclaving, freezing and freeze drying). / Initial studies showed that low levels (1% w/w) of the Surfactin-like-compound inhibited the growth of B. cereus and proteolytic and non-proteolytic strains of C. botulinum in a model agar system. However, it had no effect on non-proteolytic strains of C. botulinum when bread, or methanol extracts of bread (1--20%), were added to formulated value-added sterile trout nuggets, with all nuggets being toxic after 28 days at 12°C. Furthermore, inoculation of B. subtilis FN2A directly into nuggets also failed to inhibit growth of non-proteolytic strains of C. botulinum. Omitting certain ingredients in the formulation failed to enhance the anti-botulinal effect of the bread or methanol extracts of the Surfactin-like-compound in the value-added nuggets. However, reducing the pH of the nuggets to ~5.5 enhanced the anti-botulinal effect of the Surfactin-like-compound. Further research is required to improve the dispersibility of the Surfactin-like-compound to inhibit the growth of C. botulinum in food systems.

Baigiamojo darbo tikslas – nustatyti paviršinio aktyvumo medžiagų micelių susidarymo koncentracijas ir įvertinti tirpalų rūgštinių-bazinių savybių pokyčius paviršinio aktyvumo medžiagų ir rūgštinių dažiklių vandeniniuose tirpaluose. Kritinė micelių susidarymo koncentracija nustatyta atlikus tirpalų elektrinio laidumo ir šviesos absorbcijos matavimus, naudojantis konduktometriniu bei spektrofotometriniu tyrimo metodais. Dažiklių rūgštinių-bazinių savybių kitimas vandeniniuose tirpaluose įvertintas nustačius dažiklio disociacijos konstantų neigiamo logaritmo vertes ir termodinaminius parametrus. Paviršinio aktyvumo medžiagų, tokių kaip natrio dodecilsulfato, dodeciltrimetilamonio chlorido ir joninio tirpalo 1-dodecil-3-metilimidazolio chlorido kritinės micelių susidarymo koncentracijos buvo nustatytos Žaliojo B dažiklio vandeniniuose bei buferiniuose tirpaluose. Nustatyta, kad paviršinio aktyvumo savybe pasižyminčių medžiagų kritinės micelių susidarymo koncentracijų vertės priklauso nuo tirpalo pH, o didinant tirpalo joninę jėgą jos mažėja. Rūgštinio Oranžinio 7 ir Rūgštinio Mėlynojo 80 dažiklių disociacijos konstantų neigiamo logaritmo pKr vertės kito priklausomai nuo vandeninio tirpalo temperatūros, pH vertės ir naudotų skirtingos prigimties paviršinio aktyvumo medžiagų. Nustatyta, kad Rūgštinio Oranžinio 7 dažiklio rūgštinės savybės stipriausiai išreikštos, kai tirpale buvo amfoterinės paviršinio aktyvumo medžiagos – kokoamidopropilbetaino, o Rūgštinio Mėlynojo 80 -... [toliau žr. visą tekstą] / The aim of this work was to determinate the critical micelle concentration of surfactants and to evaluate the variation of acidic-basic properties of acidic dyes and surfactants solutions. The critical micelle concentration was determinated by the measurements of electrical conductivity and absorption, using electrical conductivity and UV-vis absorption spectrometry methods. The variation of acidic-basic properties of dyes in aqueous solutions was evaluated by estimation the values of the negative logarithm of dissociation constant of the dye and thermodynamic parameters of dyes-surfactants solution. The critical micelle concentration of sodium dodecyl sulfate, dodecyltrimethylammonium chloride and 1-dodecyl-3-methylimidazolium chloride was determinated in aqueous and phosphate buffered solutions of the Janus Green B dye. The value of critical micelle concentration of anionic, cationic surfactants and ionic compound depends on the pH value of the solutions, it can be observed that increasing the ionic strength of solution the value of critical micelle concentration decreases. The values of the negative logarithm of dissociation constant of Acid Orange 7 and Acid Blue 80 dyes varied depending on the temperature of aqueous solution, the pH value and the nature of used surfactants. It was estimated, that the lowest value of pKa of Acid Orange 7 dye was then the amphoteric surfactant - cocamidopropyl betaine was used in the dye solution and for Acid Blue 80 dye – nonionic... [to full text]

<p>The aim of this study was to compare the water quality of raw wastewater and treated sewage effluents from three different sewage treatment plants in the Western Cape, South Africa. The treatment plants investigated are on the same river system. Sewage treatment plant 1 and 2 use older technologies, while sewage treatment plant 3 has been upgraded and new technologies (membrane bioreactor) were incorporated in the treatment processes. The first objective was to determine the occurrence of total coliforms, Escherichia coli (E. coli) and fluoroquinolone and sulfamethoxazole antibiotic residues in raw wastewater and treated sewage effluents. Bacteria in treated sewage effluents can result in diseases such as dysentery, gastroenteritis, and typhoid upon exposure. A chromogenic test was used to screen for coliforms and E. coli. Enzyme linked Immunosorbent Assays (ELISA) were used to quantitate antibiotic residues (fluoroquinolones and sulfamethoxazole) in raw wastewater and treated sewage effluents. This study showed that bacteria are present in raw wastewater and residual bacteria are released with treated sewage effluents from sewage treatment plants.</p>