Fernando Leal-Calderon

Rupturing of bitumen-in-water emulsions: experimental evidence for viscous sintering phenomena

Abstract In this paper, we present experimental evidence for viscous sintering phenomena in a gel formed by bitumen emulsion droplets. When a destabilizing agent is added to the initially stable emulsion, a gel forms, which, further contracts by preserving the geometry of the container. The observed contraction phenomenon is reminiscent of the classical sintering process in ceramics, aerogels, etc. We study the shape relaxation of two coalesced droplets using a micropipette technique as well as the contraction kinetics of the macroscopic gel. The linear dependence of the contraction rate on the viscosity of the bitumen is in agreement with the classical viscous sintering theory.

Free fatty acids and their esters modulate isothermal crystallization of anhydrous milk fat.

The effect of free fatty acids with different chain lengths or unsaturation degree on anhydrous milk fat (AMF) crystallization was evaluated. The impact of esterification was also studied using three triglycerides. Melted blends containing the additives at concentrations lower than 12wt.% were quenched at 25°C and isothermal crystallization was monitored by pulsed low-resolution nuclear magnetic resonance. In parallel, polarized light microscopy was used to observe the microstructure. Compounds based on long chain saturated fatty acids, i.e. palmitic, stearic, eicosanoic acids, tripalmitin and tristearin accelerated crystallization. Conversely, propanoic, hexanoic and oleic acids slowed down the process, while triacetin had no impact. Interestingly, above a critical concentration, the addition of palmitic, stearic or eicosanoic acids caused a transition from a one-step to two-step process. Gompertz model was used to fit the experimental data and to assess the influence of the molecular properties of the additives on the kinetic parameters.

Influence of formulation on the oxidative stability of water-in-oil emulsions

The oxidation of water-in-oil (W/O) emulsions was investigated, emphasizing the impact of compositional parameters. The emulsions had approximately the same average droplet size and did not show any physical destabilization throughout the study. In the absence of pro-oxidant ions in the aqueous phase, lipid oxidation of the W/O emulsions was moderate at 60°C and was in the same range as that measured for the neat oils. Oxidation was significantly promoted by iron encapsulation in the aqueous phase, even at 25°C. However, iron chelation reduced the oxidation rate. Emulsions based on triglycerides rich in polyunsaturated fatty acids were more prone to oxidation, whether the aqueous phase encapsulated iron or not. The emulsions were stabilized by high- and low-molecular weight surfactants. Increased relative fractions of high molecular weight components reduced the oxidation rate when iron was present.

Direct technique for monitoring lipid oxidation in water-in-oil emulsions based on micro-calorimetry

An experimental device based on the measurement of the heat flux dissipated during chemical reactions, previously validated for monitoring lipid oxidation in plant oils, was extended to follow lipid oxidation in water-in-oil emulsions. Firstly, validation of the approach was performed by correlating conjugated diene concentrations measured by spectrophotometry and the heat flux dissipated by oxidation reactions and measured directly in water-in-oil emulsions, in isothermal conditions at 60°C. Secondly, several emulsions based on plant oils differing in their n-3 fatty acid content were compared. The oxidability parameter derived from the enthalpy curves reflected the α-linolenic acid proportion in the oils. On the whole, the micro-calorimetry technique provides a sensitive method to assess lipid oxidation in water-in-oil emulsions without requiring any phase extraction.

Characterization of lipid oxidation in plant oils by micro-calorimetry

A new experimental device was developed, based on the measurement of the heat flux dissipated during chemical reactions. The technique was exploited for real time monitoring of lipid oxidation in plant oils. The thermopiles were used in adiabatic configuration in order to measure the entire heat flux and improve sensitivity. Measurements were operated with a resolution of few μW as required to follow low exothermic reactions like oxidation. The validation of the device was performed by correlating conjugated diene concentrations measured by spectrophotometry and the heat flux dissipated by oxidation reactions. Our experimental approach involved several plant oils analyzed in isothermal conditions. This novel technique provides a versatile, sensitive, solvent-free and yet low-cost method to assess lipid oxidation stability, particularly suitable for the fast screening of plant oils.

Monodisperse Oil-in-Water Emulsions Stabilized by Proteins: How To Master the Average Droplet Size and Stability, While Minimizing the Amount of Proteins

Hexadecane-in-water emulsions were fabricated by means of a microfluidizer using two types of protein stabilizers, sodium caseinate (NaCAS) and β-lactoglobulin (BLG). A study of the dependence of the mean droplet diameter and protein coverage on protein concentration was performed. At low protein concentrations, the emulsions were monodispersed and their mean droplet size was governed by the so-called limited-coalescence process. In this regime, the interfacial coverage was constant and was deduced from the linear evolution of the total interfacial area as a function of the amount of adsorbed proteins. In emulsions based on NaCAS, almost all of the initial protein contents were adsorbed at the interfaces. Emulsions formulated at very low protein content underwent unlimited coalescence after prolonged storage or when submitted to centrifugation. Additional NaCAS was incorporated in the continuous phase, right after the emulsification process, as a means of ensuring kinetic stability. The interfacial coverage increased after protein addition. Other strategies including acidification and salt addition were also probed to gain stability. Instead, in emulsions based on BLG, only partial adsorption of the initial protein content was observed. The corresponding emulsions remained kinetically stable against coalescence, and no further addition of protein was required after emulsification. Our approach allows to obtain monodisperse, kinetically stable emulsions and to master their average droplet size, while minimizing the amount of proteins.

Influence of Implants Composition on Melatonin Release from Ethylcellulose Matrix

BACKGROUNDnMelatonin release from Ethylcellulose matrix has never been studied on the whole range of compositions.nnnOBJECTIVEnTo perform a comprehensive study about the influence of the melatonin loading on its release from solid ethylcellulose implants, from both a kinetic and structural point of view.nnnMETHODnCylindrical implants differing in their Melatonin:Ethylcellulose ratio were fabricated to cover a large range of compositions. Drug release was assayed by in vitro dissolution tests in CTAB micellar solutions. The 2D imaging of implant chemical composition during Melatonin release was performed by confocal Raman spectroscopy. FT-IR spectroscopy and Karl-Fisher technique were employed to study implants hydration.nnnRESULTSnA drug radial leakage, whatever the implant composition, is imaged. The apparent diffusion coefficient, D of melatonin was evaluated considering Fickian radial diffusion: its value ranges from 2 to 6 10-12 cm2/s depending on the EC content. The variation of the characteristic drug delivery time with composition was non-monotonous and two different regimes were identified.nnnCONCLUSIONnA micellar transport of Melatonin was found. The two regimes in drug release were interpreted considering the polymer barrier effect, the initial porosity and M domains connectivity.