2,223 research outputs found
Bernard Williams
No full textAn edited multi-author volume assessing the moral philosophy of the late British philosopher Bernard Williams. Contributors: Adrian Moore, John Skorupski, Alan Thomas, Robert B Louden, Michael Stocker, A. A. Long, Edward Crai
Bernard Brodie and the bomb: at the birth of the bipolar world
No full textBernard Brodie (1910-1978) was a leading 20th century theorist and philosopher of war. A key architect of American nuclear strategy, Brodie was one of the first civilian defense intellectuals to cross over into the military world. This thesis explores Brodie’s evolution as a theorist and his response to the technological innovations that transformed warfare from World War II to the Vietnam War. It situates his theoretical development within the classical theories of Carl von Clausewitz (1780-1831), as Brodie came to be known as “America’s Clausewitz.” While his first influential works focused on naval strategy, his most lasting impact came within the field of nuclear strategic thinking. Brodie helped conceptualize America’s strategy of deterrence, later taking into account America’s loss of nuclear monopoly, the advent of thermonuclear weapons, and proliferation of intercontinental ballistic missiles. Brodie’s strategic and philosophical response to the nuclear age led to his life-long effort to reconcile Clausewitz’s theories of war, which were a direct response to the strategic innovations of the Napoleonic era, to the new challenges of the nuclear age. While today’s world is much changed from the bipolar international order of the Cold War period, contemporary efforts to apply Clausewitzian concepts to today’s conflicts suggests that much can be learned from a similar endeavor by the previous generation as its strategic thinkers struggled to imagine new ways to maintain order in their era of unprecedented nuclear danger.acceptedVersionei tietoa saavutettavuudest
Influence of surfactant structure on the double inversion of emulsions in the presence of nanoparticles
No full textThe double inversion of emulsions from oil-in-water (o/w) to water-in-oil (w/o) and back to o/w is a novel approach developed using oppositely charged mixtures of solid particles and surfactant molecules [B.P. Binks, J.A. Rodrigues, Angew. Chem. Int. Ed. 46 (2007) 5389] . This work extends these preliminary results reported for the cationic surfactant di-decyldimethylammonium bromide (di-C 10 DMAB), by studying the influence of surfactant chain length for symmetrical cationic surfactants. Two double-chain surfactants with hydrocarbon chain lengths of 8 or 12 are used here to stabilise emulsions with dodecane in the presence of silica nanoparticles (Ludox HS-30). Double inversion of emulsions is also possible with these surfactants. However, multiple emulsions of both types are observed when the most hydrophobic surfactant di-C 12 DMAB is used, occurring near the boundaries of the first and second inversion, respectively. A phase diagram is introduced, in which the double inversion of emulsions occurs at various particle-to-surfactant ratios, in particular at low concentrations of silica particles between 0.1 and 4 wt.%. © 2009 Elsevier B.V. All rights reserved
Edible surfactants at fluid-fluid interfaces
Get PDFThis thesis probes into the adsorption properties of several edible surfactants/fats at a range of fluid-fluid interfaces, e.g. air-oil, air-water and water-oil. Based on this, various colloidal materials are fabricated including aqueous and oil foams, simple and multiple emulsions, foamed and aerated emulsions. Among these materials, oil foams are the focus. Different techniques are applied to characterise the resulting materials and reveal the underlying stabilisation mechanisms, such as differential scanning calorimetry, rheology, X- ray diffraction, infrared spectrometry, surface/interfacial tension, contact angle, dynamic light scattering, optical and cryo-scanning electron microscopy.Ultra-stable edible oil foams can be prepared from neat vegetable oils containing mainly long-chain, unsaturated fatty acids in their triglyceride molecules in the absence of an added foaming agent. Upon cooling/warming these oils, crystals of high melting fractions form in a low melting liquid oil yielding an oil gel. Such oil gels can be whipped to fabricate oil foams stabilized by pre-formed fat crystals. Foaming behavior depends on the oil composition and the degree of supercooling. Optimum foaming yields an over-run of ~ 40% for peanut oil and ~ 110% for olive oil. Oil foams devoid of drainage, coarsening or coalescence are achievable. We demonstrate that high melting triglyceride crystals possess a higher fraction of saturated fatty acids than the original oil. In addition, ultra-stable oil foams can be destabilized by heating due to the dissolution of the crystals in the continuous phase and at the air-oil surface.Very stable oil foams can also be fabricated from mixtures of hydrophobic sugar ester surfactants and vegetable oils. Nevertheless, a novel foaming strategy is adopted during which aeration is first performed in the one-phase region followed by rapid cooling and then storing at low temperature. For sucrose ester surfactants, we first study the effect of aeration temperature and surfactant concentration on foamability and foam stability cooled from an one- phase oil solution. Unlike previous reports, both foamability and foam stability decrease upon decreasing the aeration temperature into the two-phase region containing surfactant crystals. At high temperature in the one-phase region, substantial foaming is achieved within minutes of whipping, but foams ultimately collapse within a week. We show that surfactant molecules are surface-active at high temperature and that hydrogen bonds form between surfactant and oil molecules. Cooling these foams substantially increases foam stability due to both interfacial and bulk surfactant crystallisation in situ. The generic nature of our findings is demonstrated for a range of vegetable oil foams with a maximum over-run of 330% and the absence of drainage, coalescence and disproportionation being obtained. In analogy with sucrose esters, long-term oil foams with a maximum over-run of ⁓ 275% are yielded based on mixtures of sorbitan esters and vegetable oil.Reasonably stable aqueous foams can be prepared from mixtures of a series of sucrose ester surfactants and water, during which the effect of surfactant HLB and pH is investigated. The foaming functionality of sucrose esters is closely linked to the physicochemical properties of bulk liquid before aeration, including aggregate morphology and size, zeta potential, viscosity, and surface tension. At the natural condition, in comparison to the micelle-forming aqueous solutions of sodium dodecyl sulfate (SDS), the foaming capacity of sucrose ester dispersions containing vesicles is lower due to slower adsorption kinetics of surfactant molecules towards the air-water surface. By contrast, the resulting foams are much more stable than SDS foams. This is attributed to the steric hindrance of giant vesicles and that electrostatic repulsion existing between adjacent vesicles within the liquid films and Plateau borders of the foam. Amidst the investigated sucrose esters, lower HLB tends to yield improved foam stability. The effect of lowering pH on the dispersion and foaming characteristics of two relatively hydrophobic sucrose esters in water is then discussed. Upon lowering pH, the morphology of surfactant aggregates in bulk liquid and the interfacial properties are altered. Meanwhile, their foamability is improved markedly due to more rapid adsorption dynamics of surfactant monomers towards the air-water surface.As seen above, sucrose ester is versatile adsorbing readily at various fluid-fluid interfaces. Is it feasible to stabilise multiple interfaces simultaneously in the same system using sucrose ester alone? Herein we report for the first time on the preparation of a multitude of colloidal materials using one and the same sucrose ester sample through facile protocols, i.e. air-in-oil (a/o) and air-in-water (a/w) foams, oil-in-water (o/w), water-in-oil (w/o), and oil-in- water-in-oil (o/w/o) emulsions, air and water-in-oil (a & w/o) foamulsions and air-in-oil-in- water (a/o/w) emulsions.Overall, the research in this thesis gives insight into the adsorption modes of several types of edible surfactants/fats at a range of fluid-fluid interfaces. Besides, various colloidal materials are fabricated via facile protocols. Despite this, the stabilisation mechanism of the air-oil surface with surfactants/fats of varying architecture is not fully understood yet. For the sake of application, further investigations on novel colloidal materials using oil foams as templates are needed as well
Use of Mg(OH)2 particles as stabilisers in Pickering emulsions
Get PDFTwenty-six different samples of magnesium hydroxide particles were formed from various reactants and under varied reaction conditions. The morphologies of the different magnesium hydroxide samples were assessed via SEM and TEM and their zeta potentials were also measured. The particles were also characterised by XRD and FT-IR. The majority of the samples were of around 150-250 nm in diameter and had either a rod-like morphology or were platelets. However, some rod-like samples grew much larger, being around 2 μm in length. Zeta potential of the samples did not greatly vary and for each of the twenty-six samples; zeta potential was in the range of 15 mV ±6 mV.Isooctane–in–water and methyl methacrylate–in–water emulsions were produced from the samples of magnesium hydroxide. Isooctane–in–water emulsions had much better long-term stability than MMA-in-water emulsions, which underwent complete phase separation very quickly; the most stable MMA-in-water emulsion destabilised within a week. The long-term stability of MMA-in-water emulsions improved upon the addition of an electrolyte, but the emulsions destabilised within a month. Factors such as particle concentration, presence of electrolyte and temperature were varied for isooctane–in–water emulsions. Emulsions containing isooctane and MMA as the oil phase were also prepared, with varied fractions of each oil. The greater the fraction of isooctane when in mixtures with MMA, the more stable the subsequent emulsion. Contact angle measurements were conducted on brucite, raw magnesium hydroxide, proving magnesium hydroxide is hydrophilic
Use of Mg(OH)2 particles as stabilisers in Pickering emulsions
No full textTwenty-six different samples of magnesium hydroxide particles were formed from various reactants and under varied reaction conditions. The morphologies of the different magnesium hydroxide samples were assessed via SEM and TEM and their zeta potentials were also measured. The particles were also characterised by XRD and FT-IR. The majority of the samples were of around 150-250 nm in diameter and had either a rod-like morphology or were platelets. However, some rod-like samples grew much larger, being around 2 μm in length. Zeta potential of the samples did not greatly vary and for each of the twenty-six samples; zeta potential was in the range of 15 mV ±6 mV.Isooctane–in–water and methyl methacrylate–in–water emulsions were produced from the samples of magnesium hydroxide. Isooctane–in–water emulsions had much better long-term stability than MMA-in-water emulsions, which underwent complete phase separation very quickly; the most stable MMA-in-water emulsion destabilised within a week. The long-term stability of MMA-in-water emulsions improved upon the addition of an electrolyte, but the emulsions destabilised within a month. Factors such as particle concentration, presence of electrolyte and temperature were varied for isooctane–in–water emulsions. Emulsions containing isooctane and MMA as the oil phase were also prepared, with varied fractions of each oil. The greater the fraction of isooctane when in mixtures with MMA, the more stable the subsequent emulsion. Contact angle measurements were conducted on brucite, raw magnesium hydroxide, proving magnesium hydroxide is hydrophilic
Novel stabilisation of emulsions with polyelectrolyte complexes
Get PDFThe concept of a novel stabiliser of oil-water emulsions has been put forward, being the polyelectrolyte complex (PEC) formed between oppositely charged water-soluble polymers in cases where either polymer alone is incapable of stabilising an emulsion. Four oppositely charged synthetic polyelectrolytes (strong and weak) are selected, which allowed four polymer mixtures to be studied. The behaviour of their mixtures in water is correlated with that of emulsions after addition of oil.Aqueous polymer mixtures are investigated via dynamic light scattering to determine the size of the aggregates. Moreover, various optical techniques are used to identify the type of associative phase separation (precipitation or complex coacervation) and their shape. The effects of polyelectrolyte (PEL) mixing ratio, pH, [PEL] and salt content are studied in detail. In general, PEC particles are obtained as a result of a strong electrostatic interaction while complex coacervates arise from weak interactions. Around equal mole fractions of the two polymers, the zeta potential of the aggregates reverses in sign. Spherical complexes of diameters of few hundreds nanometres are obtained at low polyelectrolyte concentration. However, by increasing the initial [PEL], primary particles aggregate. Aggregated PEC particles have an irregular shape while coacervate droplets, which contain high amounts of water, are spherical and have no special internal structure, as observed from TEM images. Under specific conditions, coacervate droplets completely coalesce giving rise to the formation of the so-called coacervate phase. The effect of increasing the salt concentration is comparable in both PEC precipitates and coacervates and causes an initial destabilisation of the aqueous dispersion due to complex aggregation, followed by dissolution of the electrostatic complex at high salt concentrations.For the emulsion study, the same parameters as for aqueous PEC dispersions are evaluated, as well as the oil volume fraction (ϕo). The complete study is carried out with dodecane despite oils of different chemistry and polarity have also been considered throughout this thesis. The most stable emulsions to both creaming and coalescence are prepared with aqueous PEC dispersions containing complexes of almost neutral charge. By increasing the polyelectrolyte concentration, emulsions become more stable. However, at high [PEL], aggregation levels are relatively high and emulsion stability is slightly worse as big particles can easily be dislodged from the oil-water interface compared to smaller ones. From cryo-SEM images, close-packed particle layers are detected at drop interfaces as well as particle aggregation in the continuous phase. By increasing the oil volume fraction in the emulsion, the droplet diameter increases constantly up until a point where oil droplets appear to be deformed and the viscosity of the emulsion increases substantially. This suggests the formation of high internal phase emulsions (HIPEs), which is rare in particle-stabilised systems, where catastrophic phase inversion is the usual outcome. Taking advantage of the intrinsic fluorescence of the used PEL, confocal microscopy turns out to be a useful technique to visualise where PEC particles are placed upon homogenisation. At high oil volume fractions, particles are only detected around oil droplets, whereas at low oil volume fractions, excess particles remain at the continuous aqueous phase providing extra stability against coalescence. As for aqueous PEC dispersions, the concentration of salt has a remarkable effect on emulsion stability. For emulsions stabilised with PEC particles, by increasing the aggregation level, emulsions become completely unstable. However, at a relatively high salt content, emulsions re-stabilise due to adsorption of uncharged individual polymer molecules. Emulsions with coacervate droplets can be prepared by the addition of oil stepwise and multiple homogenisation steps. However, unlike PEC particles, the system is sensible to the oil type. The feasibility of the coacervate phase to spread at the oil-water interface is discussed in terms of the relevant spreading coefficients and predictions are compared with experiments for a range of oils. We encounter oils whose drops become engulfed by the coacervate phase as well as oils where no engulfing occurs.Therefore, from the findings obtained from four different polyelectrolyte combinations, we can claim that emulsion stability is given by the presence of PEC at the oil-water interface as individual PEL are not surface-active on their own. Despite this work being a complete starting point for the basic understanding of emulsions stabilised by mixtures of oppositely charged polymers, we are not yet in a position to predict definite rules of behaviour in both aqueous PEC dispersions and emulsions containing them. Further investigation of other polyelectrolyte combinations is required to develop a better understanding of this area
Aeration of oils in the presence of both edible and non-edible surfactants
Get PDFUnlike aqueous foams, very little literature exists in the area of non-aqueous foams despite this being an important field industrially, e.g. in confectionary manufacture and in the oil industry. Since the air-oil surface tension is normally at least half that of the air-water surface tension, the driving force for the adsorption of surfactant at the air-oil surface is significantly lower. The foamability and foam stability of mixtures of surfactants in oil have been investigated in an effort to understand how to control the amount and stability of such foams. The surfactants studied include phospholipids, monoglycerides, diglycerides, fatty acids and alcohols in numerous oils. Incorporation of gases of different types (including air, carbon dioxide and nitrous oxide) has been achieved using different methods. These include aeration by a thermostatted foaming column and the dissolving of gas into a system via a soda siphon. Temperature effects have also been investigated with aerations conducted at 25, 45 and 60 °C amongst other temperatures. The effect of the saturation of diglycerides has also been studied.The solubility differences of the gases in oil no doubt influenced the process of disproportionation of bubbles, although drainage of oil and coalescence of bubbles occurs also. The foam half-life varied from minutes to months depending on the system composition. The effect of temperature was also found to influence the stability of the foam produced; in the case of compressed air as temperature increases foam stabilitydecreases.A whipped oil has also been produced with numerous two-component systems which has a stability of over 18 months. The formation of a gel was clearly important for the whipped oil production. Therefore the viscosity, solid content and solid surfactant size of the gel has been studied. It was clear through numerous investigations that temperature was crucial for foam formation and subsequent foam stability. Factors investigated were the effect of fatty acids and fatty alcohol chain length which highlighted the importance of the viscosity and solid content of a mixture prior to aeration for foam production. The basic behaviour of foams and previous relevant work in the area, along with results obtained are discussed in this thesis
Stabilisation and destabilisation of Pickering emulsions
Get PDFIn this thesis, the stabilisation and destabilisation of Pickering emulsions have been investigated. Organic electrolytes are added to hydrophilic silica and partially hydrophobic polystyrene latex particle dispersions to enable them to stabilise emulsions. A series of tetraalkylammonium salts (R4NX, X is an anion) is added to aqueous dispersions of hydrophilic silica particles, with the alkyl chain (R) systematically increasing from 1 (methyl) to 4 (butyl). The adsorption of R4N+ ions onto particle surface reduces the surface charge which increases the particle hydrophobicity. Consequently, the stability of oil-in-water (o/w) emulsions increases with salt concentration and the R chain length. In addition, we compare the arrangement of micron-sized silica particles at both curved droplet interfaces and at a planar oil-water interface in the presence of the butyl analogue.Tetrapentylammonium bromide (TPeAB) and sodium thiocyanate (NaSCN) induce charge reversal of negatively charged sulfate (SO4-) and positively charged amidine (C(NH)NH3+) latex particles, respectively. However, charge reversal of particles hardly influences the type or stability of emulsions. Water-in-oil (w/o) emulsions are preferentially stabilised by both types of particles with dodecane. In systems with carboxyl latex particles, no charge reversal is induced by TPeAB at studied concentrations. However, emulsions invert from w/o to o/w upon increasing TPeAB concentration when PDMS (silicone oil) of viscosity 1 cS and 50 cS is used as the oil phase. It is intriguing that the surface charge of particles plays a minor role in the stabilization of emulsions whereas the hydrophobic polystyrene part dominates the emulsion type.In addition, the destabilisation of both w/o and o/w Pickering emulsions using solid particles is explored. Destabilizers adsorb onto oil-water interfaces with the help of gentle stirring. If the particles are more wetted by the inner phase of droplets, the adsorbed particles traverse the interface entering the inner phase, which breaks the interface resulting in emulsion coalescence. Hence, monodispersed particles more wetted by the inner phase of droplets are preferred as the destabilizers. Overall, this research helps gain the understanding of particles at oil-water interface and expands the application of solid particles in the stabilization and destabilisation of emulsions
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