89 Nash Grove Lane

Wokingham, United Kingdom

89 Nash Grove Lane

Wokingham, United Kingdom
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Aben S.,BASF | Aben S.,University of Fribourg | Holtze C.,BASF | Tadros T.,89 Nash Grove Lane | Schurtenberger P.,Lund University
Langmuir | Year: 2012

Preventing creaming or sedimentation by the addition of thickeners is an important industrial challenge. We study the effect of the addition of a "free" nonadsorbing polymer (xanthan gum) on the stability against creaming of sterically stabilized O/W emulsions. Therefore, we analyze our samples using microscopy and rheological measurements. At low xanthan concentrations, the emulsions cream. However, above a certain concentration a three-dimensional network of droplets is formed, which can prevent creaming. We attribute the formation of this structure to depletion attraction. The rheological behavior of an emulsion that is macroscopically stable should be elastic, while it should be viscous for a creaming emulsion. In order to distinguish between stable and unstable samples, we measure their relaxation time by mechanical rheology and find a good correlation to the visual observation. However, the measured relaxation times are much shorter than the time-scales, on which we observe creaming. We hypothesize that the measured relaxation time is related to the droplet-droplet interaction. This determines the frequency at which microscopic rearrangements occur, which weaken the network structure prior to creaming. Based on this interpretation, the relaxation time gives direct access to the microstructural processes involved in creaming. We therefore suggest using it as a predictive parameter of creaming stability. © 2012 American Chemical Society.


Deng D.,BASF | Boyko V.,BASF | Pancera S.M.,BASF | Tadros T.,89 Nash Grove Lane
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2011

The influence of addition of sodium polyacrylate (with 3 different molecular weights PA20=2500g/mol, PA30=8000g/mol and PA40=15,000g/mol) on the stability of TiO2 dispersions was investigated using particle size (determined by static light scattering), zeta potential and rheological measurements. Diluted dispersions as well as those containing 20% TiO2 were dispersed by sonication for 5min. The results show that without sonication and in the absence of NaPAA large aggregates with mean volume diameter of 3.89μm are produced. On sonication for 5min, the aggregates are broken down giving a mean volume diameter of 0.239μm. Addition of NaPAA at low concentration (0.2 and 0.4%) resulted in a large increase in mean volume diameter indicating aggregation of the initially formed small aggregates on sonication. When the concentration of NaPAA was ≥1%, the aggregates became dispersed giving mean volume diameter of about 0.2μm. These particle size measurements were confirmed by using SEM and TEM measurements. The zeta potential of diluted TiO2 dispersion in the absence of NaPAA gave an isoelectric point of pH∼6. The effect of addition of sodium polyacrylate PA20, PA30 and PA40 on the zeta potential of TiO2 dispersions at pH=3 showed neutralization of the positive charge on TiO2 particles reaching a zero charge at PAA concentration of 0.3-0.4% above which the particles acquired a negative charge that increase with further increase of PAA concentration reaching a plateau value of -45mV when the PAA concentration was ≥1%. Steady state measurement showed that addition of PA20 to the TiO2 dispersion causes a dramatic reduction in yield value when PA concentration is ≥1%. Oscillatory measurements were obtained for 30% TiO2 suspension without any sonication. The frequency was kept constant at 1Hz, and the stress was gradually increased till a critical value was reached above which the modulus showed a rapid decrease with further increase of the stress. In this way both elastic modulus G' and critical stress were measured as a function of PAA concentration. The results showed an initial increase in the elastic modulus reaching a maximum at critical PAA concentration above which there was a rapid reduction in both rheological parameters. These results indicated flocculation of TiO2 dispersion at low PAA concentration which was accounted for/by charge neutralization and/or bridging. When the PAA concentration was ≥1% all dispersions showed low G' and critical stress indicating a highly deflocculated system. An attempt was made to correlate the rheological results with zeta potential measurements. © 2011 Elsevier B.V.


Deng D.,BASF | Boyko V.,BASF | Pancera S.M.,BASF | Nestle N.,BASF | Tadros T.,89 Nash Grove Lane
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2010

The stability of concentrated CaCO3 suspensions (40wt%) on addition of sodium polyacrylate (NaPAA, PA20, with molar mass of 2100) has been investigated using rheological measurements. On addition of NaPAA to the suspension, there is a selective adsorption of PA fraction with molar mass of 2000-5000. This selective adsorption is due to entropic effects and heterogeneous charge distribution. The smaller sized polyelectrolyte chains can more easily find local patches at the interface, devoted of previously adsorbed molecules, which are characterized by more favourable interaction profile. Steady-state shear stress-shear rate curves were obtained as a function of PA20 concentration (0-0.7wt%). All suspensions showed pseudoplastic flow curves (shear thinning behavior) with some thixotropy. In the absence of PA20, and in the presence of 0.1% PA20 the flow curves show significant hysteresis indicating weak flocculation. This was confirmed by measuring the particle size of the suspension on dilution of system. On further addition of PA20 (0.2-0.7wt%), the suspensions showed much less thixotropy and the weak flocs produced were broken down on dilution giving a mean diameter of about 1μm. The flow curves could be fitted to the Herschel Bulkley model and values of the yield value σβ, consistency index k and shear thinning index n were obtained as a function of PA20 concentration. Initial addition of PA20 (0.1wt%) caused an increase in σβ and k indicating more flocculation at this PA20 concentration. The data showed a reduction in σβ from 7.6Pa at 0.1wt% PA20 to 1.7Pa at 0.7% PA20. The rheological results also showed a continuous reduction in k and increase in the value n (less shear thinning behavior). However, all suspensions showed weak flocculation at such high CaCO3 concentrations (40wt%). Further insights into the flocculation behavior of CaCO3 suspensions with added NaPAA were gained in proton TD-NMR studies of the water phase of the suspension and sediment phases. This weak flocculation could be significantly reduced on dilution of the suspension from 40 to 20wt%. A plot of σβ versus ζ2 showed non-linear behavior and this clearly indicated that the stability of CaCO3 suspensions in the presence of NaPAA could not be accounted for in terms of the DLVO theory. The presence of adsorbed loops and tails of NaPAA molecules on CaCO3 suspensions could play a major role in the stability of the suspensions. © 2010 Elsevier B.V.


Amine C.,BASF | Dreher J.,BASF | Helgason T.,BASF | Tadros T.,89 Nash Grove Lane
Food Hydrocolloids | Year: 2014

The emulsifying properties and emulsion stability of medium chain triglyceride (MCT) oil in water emulsions stabilized by plant proteins (potato, soy, and pea) as well as those extracted from milk (sodium caseinate and whey) have been investigated at two different pH values (7 and 10). The effect of protein type, concentration, pH and temperature has been studied using droplet size distribution, interfacial tension, and interfacial elasticity measurements. The interfacial tension is measured as a function of concentration ranging from 0.01% to 2.5% using the pendant drop method. The interfacial elasticity is also measured using the oscillating drop technique. The stability of the resulted emulsions is assessed using a stress test whereby the emulsions are placed at 60 or 40°C for 24h by measuring the droplet size distribution before and after the stress test. The interfacial tension decreases with increase of the pH and increase of the protein concentration pH value. A higher elasticity at the oil/water interface is obtained at pH=10 when compared to that at pH=7 for both Na-caseinate and pea proteins. Fine and stable emulsions are obtained at pH=10, showing good correlation between interfacial tension and emulsion formation as well as between interfacial elasticity and emulsion stability for milk and plant proteins. © 2014 Elsevier Ltd.


Nakach M.,Sanofi S.A. | Authelin J.-R.,Sanofi S.A. | Tadros T.,89 Nash Grove Lane | Galet L.,Ecole des Mines d'Ales | Chamayou A.,Ecole des Mines d'Ales
International Journal of Pharmaceutics | Year: 2014

This paper describes a systematic approach to select optimum stabilizer for the preparation of nano-crystalline suspensions of an active pharmaceutical ingredient (API). The stabilizer can be either a dispersant or a combination of dispersant and wetting agent. The proposed screening method is a quick and efficient way to investigate a large number of stabilizers based on the principles of physical-chemistry and employs a stepwise approach. The methodology has been divided in two main parts; the first part being focused on the qualitative screening with the objective of selecting the best candidate(s) for further investigation, the second part has been focused on quantitative screening with the objective to optimize the ratio and amount of wetting and dispersing agents, based on wettability, surface charges measurement, adsorption evaluation, process-ability evaluation and storage stability. The results showed clearly that SDS/PVP 40/60% (w/w) (sodium dodecyl sulfate/poly(vinyl pyrrolidone)) at a total concentration of 1.2% was the optimum stabilizer composition, at which the resulting nanosuspensions were stable for more than 50 days at room temperature. © 2014 Elsevier B.V. All rights reserved.


Tadros T.,89 Nash Grove Lane
Advances in Colloid and Interface Science | Year: 2011

The interaction forces between adsorbed polymer layers were investigated. Two types of graft copolymers that were adsorbed on hydrophobic surfaces have been investigated: (i) a graft copolymer consisting of polymethylmethacrylate/ polymethacrylic acid back bone (the B chain) on which several poly(ethylene oxide) chains are grafted (to be referred to as PMMA/PEO n); and (ii) a graft copolymer consisting of inulin (linear polyfructose with degree of polymerization > 23) (the A chain) on which several C 12 chains are grafted (INUTEC SP1). In the first case adsorbed layers of the graft copolymer were obtained on mica sheets and the interaction forces were measured using the surface force apparatus. In the second case the interaction forces were measured using Atomic Force Microscopy (AFM). For this purpose a hydrophobically modified glass sphere was attached to the tip of the cantilever of the AFM and the glass plate was also made hydrophobic. Both the sphere and the glass plate contained an adsorbed layer of INUTEC SP1. In the surface forces apparatus one essentially measures the energy E(D)-distance D curves for the graft copolymer of PMMA/PEO n between mica surfaces bearing the graft copolymer and this could be converted to interaction energy between flat surfaces. Using the de Gennes scaling theory, it is possible to calculate the interaction energy between the polymer layers. The same graft copolymer was used in latex dispersions and the high frequency modulus G′ ∞ was measured as a function of the volume fraction φ of the dispersion. This high frequency modulus could be related to the potential of mean force. In this way one could compare the results obtained from rheology and those obtained from direct measurement of interaction forces. In the AFM method, the interaction forces are measured in the contact area between two surfaces, i.e. a spherical glass particle and a glass plate. Both glass spheres and plates were hydrophobized using dichlorodimethylsilane. Results were obtained for adsorbed layers of INUTEC SP1 in water and in the presence of various concentrations of Na 2SO 4 (0.3, 0.8, 1.0 and 1.5 mol dm -3). All results showed a rapid increase of force with a decrease of separation distance and the forces were still repulsive up to the highest Na 2SO 4 concentration. This explains the high stability of dispersions when using INUTEC SP1 as stabilizer. © 2011 Elsevier B.V. All rights reserved.


Tadros T.,89 Nash Grove Lane
Chemistry Letters | Year: 2012

The interaction forces between adsorbed layers of two graft copolymers were directly measured using surface force apparatus and atomic force microscopy. Two types of graft copolymers that were adsorbed on hydrophobic surfaces were used: (i) a graft copolymer consisting of poly(methyl methacrylate)/ poly(methacrylic acid) backbone (the B chain) on which several poly(ethylene oxide) chains are grafted (to be referred to as PMMA/PEQ) and (ii) a graft copolymer consisting of inulin (linear polyfructose with degree of polymerization greater than 23) (the A chain) on which several C12 chains are grafted (INUTEC SP1). In the first case, adsorbed layers of the graft copolymer were obtained on mica sheets and the interaction forces were measured using the surface force apparatus. In the second case, the interaction forces were measured using atomic force microscopy (AFM). For this purpose, a hydrophobically modified glass sphere was attached to the tip of the cantilever of the AFM and the glass plate was also made hydrophobic. Both the sphere and the glass plate contained an adsorbed layer of INUTEC SP1. The curves of energy E(D) versus distance D for the graft copolymer of PMMA/PEO, between mica surfaces bearing the graft copolymer could be used to estimate the interaction energy between flat surfaces, by using Derjaguin approximation for cross cylinders. The results were compared with the theoretical calculations using de Gennes scaling theory. The agreement between experimental results and theoretical calculations was satisfactory. The same graft copolymer was used in latex dispersions, and the high frequency modulus G' was measured as a function of the volume fraction of the dispersion. This high-frequency modulus could be related to the potential of mean force. In this way. one could compare the results obtained from rheology and those obtained from direct measurement of interaction forces. In the AFM method, the interaction forces are measured in the contact area between two surfaces, i.e., the surfaces of a spherical glass particle and a glass plate. The glass spheres and plates were hydrophobized using dichlorodimethylsilane. Results were obtained for adsorbed layers of INUTEC SP1 in water and in the presence of various concentrations of Na2SO4 (0.3, 0.8, 1.0, and 1.5 mol dm 3). All results showed a rapid increase in force with a decrease in the separation distance, and the forces were repulsive up to the highest Na 2SO 4 concentration. This explains the high stability of dispersions when using INUTEC SP1 as the stabilizer. © 2012 The Chemical Society of Japan.


Tadros T.,89 Nash Grove Lane
Advances in Colloid and Interface Science | Year: 2011

The interparticle interactions in concentrated suspensions are described. Four main types of interactions can be distinguished: (i) "Hard- sphere" interactions whereby repulsive and attractive forces are screened. (ii) "Soft" or electrostatic interactions determined by double layer repulsion. (iii) Steric repulsion produced by interaction between adsorbed or grafted surfactant and polymer layers. (iv)and van der Waals attraction mainly due to London dispersion forces. Combination of these interaction energies results in three main energy-distance curves: (i) A DLVO type energy-distance curves produced by combination of double layer repulsion and van der Waals attraction. For a stable suspension the energy-distance curve shows a "barrier" (energy maximum) whose height must exceed 25 kT (where k is the Boltzmann constant and T is the absolute temperature). (ii) An energy-distance curve characterized by a shallow attractive minimum at twice the adsorbed layer thickness 2δ and when the interparticle-distance h becomes smaller than 2δ the energy shows a sharp increase with further decrease of h and this is the origin of steric stabilization. (iii) an energy-distance curve characterized by a shallow attractive minimum, an energy maximum of the DLVO type and a sharp increase in energy with further decrease of h due to steric repulsion. This is referred to as electrosteric repulsion. The flocculation of electrostatically and sterically stabilized suspensions is briefly described. A section is devoted to charge neutralization by polyelectrolytes and bridging flocculation by polymers. A distinction could be made between "dilute", "concentrated" and "solid suspensions" in terms of the balance between the Brownian motion and interparticle interaction. The states of suspension on standing are described in terms of interaction forces and the effect of gravity. The bulk properties (rheology) of concentrated suspensions are described starting with the case of very dilute suspensions (the Einstein limit with volume fraction φ ≤ 0.01), moderately concentrated suspensions (0.2 > φ ≥ 0.1) taking into account the hydrodynamic interaction and concentrated suspensions (φ > 0.2) where semi-empirical theories are available. The rheological behavior of the above four main types of interactions is described starting with "hard-sphere" systems where the relative viscosity-volume fraction relationship could be described. The rheology of electrostatically stabilized suspensions was described with particular reference to the effect of electrolyte that controls the double layer extension. The rheology of sterically stabilized systems is described using model polystyrene suspensions with grafter poly(ethylene oxide) layers. Finally the rheology of flocculated suspensions was described and a distinction could be made between weakly and strongly flocculated systems. © 2011 Elsevier B.V. All rights reserved.


Tadros T.,89 Nash Grove Lane
Advances in Colloid and Interface Science | Year: 2015

Abstract The interaction forces between emulsion droplets containing adsorbed polymeric surfactants and the theory of steric stabilisation are briefly described. The results for the viscoelastic properties of O/W emulsions that are stabilised with partially hydrolysed poly(vinyl acetate) that is commonly referred to as poly(vinyl alcohol) (PVA) with 4% vinyl acetate are given. The effect of the oil volume fraction, addition of electrolytes and increasing temperature is described. This allows one to obtain various parameters such as the adsorbed layer thickness, the critical flocculation concentration of electrolyte (CFC) and critical flocculation temperature (CFT) at constant electrolyte concentration. The viscoelastic properties of O/W emulsions stabilised with an A-B-A block copolymer of polyethylene oxide (A) and polypropylene oxide (B) are described. These emulsions behave as viscoelastic liquids showing a cross-over-point between G′ (the elastic component of the complex modulus) and G″ (the viscous component of the complex modulus) at a characteristic frequency. Plots of G′ and G″ versus oil volume fraction ℙ show the transition from predominantly viscous to predominantly elastic response at a critical volume fraction ℙc. The latter can be used to estimate the adsorbed layer thickness of the polymeric surfactants. Results are also shown for W/O emulsions stabilised with an A-B-A block copolymer of polyhydroxystearic acid (PHS, A) and polyethylene oxide (PEO, B). The viscosity volume fraction curves could be fitted to the Dougherty-Krieger equation for hard-spheres. The results could be applied to give an estimate of the adsorbed layer thickness Δ which shows a decrease with increase of the water volume fraction. This is due to the interpenetration and/or compression of the PHS layers on close approach of the water droplets on increasing the water volume fraction. The last section of the review gives an example of O/W emulsion stability using an ABn graft copolymer of polyfructose (A) to which several C12 alkyl chains are grafted. The emulsions are stable both at high temperature and in the presence of high electrolyte concentrations (2 mol dm- 3 NaCl). This high stability is due to the strong adsorption ("anchoring") of the graft copolymer with several C12 alkyl chains and the strong hydration of the polyfructose chains both in water and in the presence of high electrolyte concentrations and temperature. Evidence for this high stability is obtained using disjoining pressure measurements which show a highly stable film between the emulsion droplets and absence of its rupture up to high pressures. © 2015 Elsevier B.V.


Miras J.,CSIC - Institute of Advanced Chemistry of Catalonia | Vilchez S.,CSIC - Institute of Advanced Chemistry of Catalonia | Solans C.,CSIC - Institute of Advanced Chemistry of Catalonia | Tadros T.,89 Nash Grove Lane | Esquena J.,CSIC - Institute of Advanced Chemistry of Catalonia
Soft Matter | Year: 2013

High internal phase emulsions (HIPEs) have been used as templates for the preparation of low-density highly porous chitosan foams. The formation of hydrogels and porous foams, by crosslinking in the external phase of O/W HIPEs, has been studied. The stability of the emulsions, prepared using a nonionic surfactant (C13/C15 alkyl chains with 7 moles ethylene oxide), was investigated using droplet size vs. time measurements, in the presence and absence of chitosan. The stability was also assessed using dynamic (oscillating) measurements, where the storage modulus (G′LVR) and cohesive energy density (Ec) were measured as a function of time. The effect of agitation was investigated by preparing the HIPEs at 700, 900 and 1200 rpm. The HIPEs prepared using nonionic surfactants in the absence of chitosan gave large droplet sizes but they were quite stable against coalescence. Addition of chitosan caused a significant reduction in droplet size and polydispersity, but the emulsions were less stable against coalescence. For emulsions prepared at low speeds of agitation (700 and 900 rpm), both G′LVR and Ec showed an initial increase of the modulus due to flocculation, but at times longer than 24 h, the flocculated emulsion showed coalescence. In the presence of chitosan, all HIPEs showed an exponential decrease in G′LVR and Ec with time, indicating coalescence of the emulsion. The crosslinking of chitosan with genipin was investigated using oscillatory and creep measurements. Both methods showed an increase in G′LVR, Ec and compliance J with time, reaching a plateau value when t ≥ 24 h. This clearly shows completion of the crosslinking process after 24 h. Finally, crosslinked chitosan porous foams were obtained and characterized by SEM, which showed uniform porous textures. © 2013 The Royal Society of Chemistry.

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