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No description available.

No description available.

No description available.

The aim of the work carried out was to develop an analytical method for characterising sorbitan ester surfactants, which could be used to monitor their manufacture and establish structure activity relationships. HPLC was the first analytical technique used, however despite evaluating various stationary and mobile phases a repeatable method could not be found. High temperature GC with splitless injection was then tried. A range of single polyol esters of varying fatty acid chain lengths were prepared and analysed to establish the ester species that would elute from the column. Using optimised conditions for the injector, detector and final oven temperature of 380 degC and a DB1-ht column, it was found that all possible ester species elute for the short chain fatty acid esters studied. However as the chain length increases the number of ester species eluting decreases, for the longer fatty acid chain length esters based on oleic and stearic acid the sorbitan and sorbitol tri esters are the largest esters to elute. HT-GC analysis of a range of manufactured sorbitan mono esters based on palmitic, stearic and oleic acid was successful with all the mono ester species separated and identified and these separated from the di and tri esters. Validation of the method with sorbitan mono oleate showed that the method was precise and therefore a suitable method for characterising sorbitan mono esters. HT-GC with on-column injection was also investigated and it was found that for the longer chain fatty acid esters more ester species eluted than when using splitless injection. Validation would be required to establish the precision of the method, however it may also be a suitable method for characterising sorbitan esters.

Foam is important for many processes such as enhanced oil recovery and firefighting. Although a large volume of foam is desirable for these particular applications, for other applications it needs to be suppressed, for example, in washing machines. In order to suppress foam formation, an anti-foam agent is added to the foaming solution. An anti-foam agent may take the form of oil, solid particles (generally of the micron (Jlm) size range), or a combination of both. This thesis is concerned with understanding the foaming and anti-foaming of nonionic surfactants of the polyoxyethylene glycol ether type of general structure H-(CH₂)n(O-CH₂-CH₂)mOH (abbreviated to CnEm). In the first results chapter, the foaming of the homologous series of CnEm surfactants is investigated in the absence of any additives (Le. anti-foam agents). The foamability of the surfactant is determined by measuring the volume of foam generated by bubbling nitrogen gas, through the surfactant solution as a function of surfactant concentration. It is found that the surfactant concentration corresponding to the transition from non-foaming to foaming behaviour, C(1I2), is less than the critical micelle concentration cmc for short tailed surfactants (low n) and greater than the cmc for long tailed surfactants (higher n). This is explained in terms of two requirements which must both be fulfilled before a surfactant can stabilise foam. Firstly, the rate of adsorption of the surfactant must be sufficiently fast to stabilise a foam bubble as it is being formed and secondly, the level of surfactant adsorption must be sufficiently high relative to the adsorption isotherm such that there is sufficient surfactant surrounding the bubble for it to be stable. Chapter 4 examines a new mechanism for the way in which oil may affect the stability of aqueous foam. It is known that alkane vapours can co-adsorb with surfactant at the air-water surface to form mixed alkane/surfactant monolayers. The effects of alkane vapours on the foamability and foam stability for foams stabilised by CnEm surfactants of different head and tail chain lengths has been systematically investigated. The addition of alkane vapours within the gas stream during foam formation increases C(1I2) to concentrations in excess of the cmc, i.e. oil vapours inhibit foamability. In addition to the effects on foamability, oil vapours also accelerate the decay rates of foams (i.e. reduce the foam stability). Chapter 5 looks at the effects that nanometre (run)-silica particles of different hydrophobicities have on aqueous foams stabilised by C₁₂E₅. In the past, most studies have focussed on solid particles in the Jlm size range. It is found that the nonionic surfactant can adsorb onto the surface of the silica particles, lowering the equilibrium surfactant concentration. This adsorption is the highest for the most hydrophobic silica particles. Reducing the equilibrium surfactant concentration lowers the foamability of the system. Whilst the foamability is decreased, the foam stability is increased however. This is explained in terms of the silica particles blocking the drainage channels in the foam by networking together in solution and thus slowing liquid drainage from the foam. Finally in chapter 6, the effects that oil and run-sized silica particles have when used in combination on foam stabilised by C₁₂E₅ are investigated. Here it is found that a synergistic anti-foam action is observed for some systems i.e. the oil and particles are more effective when used together than individually. When silica particles of an intermediate hydrophobicity are used, there is a sharp increase in the foamability and foam stability for many of the systems. These differences in foaming behaviour are explained in terms of the hydrophobicity of the overall entity which is formed when surfactant, oil and run-sized silica particles of different initial hydrophobicities are shaken together to produce foam.

No description available.

No description available.

The reactions of dichlorine and dibromine on compound semiconductors follow a pattern of halogenation of the substrate surface, followed by solvation of the halogenated products and removal of the secondary products in the etchant solutions. The reactions of hypochlorite and hydrogen peroxide follow a similar pattern, beginning with oxidation of the substrate surface, followed by subsequent hydration in the etchant solution and final product removal. The solubility of the products and the action of the polishing pad and abrasive are all critical to the passivation of the surface and the production of a polished substrate. The pH dependence of sodium hypochlorite is explained in terms of its composition. At low pH (<8) the main component of the etchant solution is dichlorine. At high pH (>8) the main component of the etchant solution is hypochlorite anion. Thus hypochlorite solution may be considered as a parallel to dibromine at low pH, but is more consistent with the behaviour of hydrogen peroxide at high pH. Thus, aqueous sodium hypochlorite solution may be formulated as part of the series O-O, O-X, X-X, where X represents a halogen. The General Model for Chemomechanical Polishing is formulated on the basis of the three stages of reaction observed for all the reagents examined: Oxidation of the substrate; solvation/hydration of the oxidation products; removal of the products from the substrate surface. Novel bromine-based organic reagents have been designed, synthesised and used to etch and polish gallium arsenide and cadmium telluride substrates. These compounds have shown that properties such as stock removal rate, pH dependence and selectivity may be predicted and even designed into etchants to produce the optimum conditions for polishing a given substrate.

L'étape de pré-désinfection, traitement préalable à la stérilisation des dispositifs médicaux (DM) en établissement de santé, requiert l'utilisation de produits combinant à la fois des propriétés de nettoyage et de désinfection. L'actif antimicrobien utilisé majoritairement dans les nettoyants pré-désinfectants est le chlorure de didécyldiméthylammonium ([DiC10][Cl]), ammonium quaternaire bicaténaire. Il est reconnu particulièrement efficace vis-à-vis des microorganismes et notamment des levures, telle que Candida albicans. Un postulat en chimie de formulation établit qu'un mélange archétype composé du [DiC10][Cl] et d'un tensioactif non ionique de type alcool gras polyéthoxylé (CiEj), suffit à atteindre la double revendication de nettoyage et désinfection. Cependant, nous avons récemment identifié une perte significative de l'activité levuricide (Candida albicans) du [DiC10][Cl] en présence de certains types de CiEj, en particulier les C12E8. Cette perte d'activité est rédhibitoire au traitement des DM. Puisque le mécanisme biocide n'est pas clairement établi pour les sels d'ammonium quaternaires bicaténaires, en particulier vis-à-vis des levures, nous nous sommes référés dans un premier temps à une étude détaillée des relations structure-activité. Nous avons ainsi étudié l'influence de la longueur de la chaîne alkyle des ammonium quaternaires bicaténaires et de la nature du contre-ion. L'utilisation de modèles mathématiques nous a permis d'établir une relation parabolique entre l'activité biocide du [DiC10][Cl] et son logP. Dans un second temps, nous nous sommes concentrés sur les systèmes fondés sur les mélanges [DiC10][Cl] et alkyl-éther de polyoxyéthylène, CiEj (i = 10, 12, j = 4, 6, 8), pour divers rapports [DiC10][Cl]/CiEj. Nous avons étudié les propriétés d'auto-agrégation et l'activité biocide sur Candida albicans des mélanges. La combinaison de différentes techniques expérimentales (tensiométrie, conductimétrie et électrode spécifique à ammonium quaternaires) et des calculs théoriques nous ont conduits à rationaliser les processus de comicellisation. Nous avons montré, pour la première fois, comment une meilleure connaissance du comportement des mélanges permet de comprendre, voire, de prédire son activité biocide. Nous avons démontré que la forme active du [DiC10][Cl] était la forme unimère ([DiC10][Cl]libre ) et que la quantité de [DiC10][Cl]libre pouvait être optimisée par un ajustement de la structure chimique du CiEj (C10E8 versus C12E8).Convaincus de l'intérêt en éco-conception des tensioactifs d'origine végétale, avec notamment les alkypolyglucosides (APG), nous avons enfin cherché à remplacer tout ou partie des alcools gras polyéthoxylés. Soucieux du maintien de l'activité biocide du [DiC10][Cl], nous avons caractérisé sur les plans physicochimique et microbiologique les mélanges binaires [DiC10][Cl]/APG puis ternaires [DiC10][Cl]/APG/CiEj. Ce dernier cas nous a permis d’envisager de conjuguer efficacité biocide, détergence accrue et bénéfice pour l’environnement. / The pre-disinfection treatment prior to the sterilization of medical devices (MD) in health care institutions, requires the use of combining both the properties of cleaning and disinfection. The active antimicrobial used mostly in pre-disinfectant cleaners is didecyldimethyl ammonium chloride ([DiC10] [Cl]), quaternary ammonium double-stranded. He is known particularly effective vis-à-vis micro-organisms, including yeasts such as Candida albicans. An assumption in chemistry formulation sets a mixture composed of the archetypal [DiC10] [Cl] and a nonionic polyethoxylated fatty alcohol type (CiEj), is sufficient to meet the dual demands of cleaning and disinfection. However, we have recently identified a significant loss of activity yeasticidal (Candida albicans) of [DiC10] [Cl] in the presence of certain types of CiEj, especially C12E8. This loss of activity is unacceptable to the treatment of DM. Since the mechanism is unclear biocide for double-stranded quaternary ammonium salts, particularly with respect to the yeast, we initially referred to a detailed study of structure-activity relationships. We have studied the influence of the length of the alkyl chain of quaternary ammonium and double-stranded nature of the ion-cons. The use of mathematical models has enabled us to establish a parabolic relationship between the biocidal activity of [DiC10] [Cl] and logP. In a second step, we focused on systems based on mixtures [DiC10] [Cl] and alkyl polyoxyethylene ether, CiEj (i = 10, 12, j = 4, 6, 8), various reports [ DiC10] [Cl] / CiEj. We studied the properties of self-aggregation and biocidal activity of Candida albicans mixtures. The combination of different experimental techniques (tensiometry, conductivity and specific quaternary ammonium electrode) and theoretical calculations led us to streamline the comicellisation. We have shown for the first time, how a better understanding of the behavior of mixtures to understand, or even to predict its biocidal activity. We have shown that the active form of [DiC10] [Cl] was the form unimère ([DiC10] [Cl] free) and the amount of [DiC10] [Cl] free could be optimized by adjusting the chemical structure of CiEj (C10E8 C12E8 versus). Convinced of the interest in eco-design of surfactants of vegetable origin, including the alkypolyglucosides (APG), we finally sought to replace all or part of polyethoxylated fatty alcohols. Anxious to maintain the biocidal activity of [DiC10] [Cl], we characterized the physicochemical and microbiological plans binary mixtures [DiC10] [Cl] / APG and ternary [DiC10] [Cl] / APG / CiEj. The latter case allowed us to consider combining biocidal efficacy, detergents and increased environmental benefit.