by Maleki et al., Chemical Engineering Science, 2021, 237(29): 116567
A way forward for high throughput fabrication of microcapsules with uniform size and mechanical properties was reported irrespective of the kinetic process of shell assembly. Microcapsules were produced using lab-scale emulsification equipment with a micro-engineered membrane in the size range 10–100 µm. The shell of the microcapsules was assembled at the water-oil interface by complexation of polyelectrolytes or cross-linking of proteins providing two different kinetic processes. Elasticity of microcapsules was characterized with an automated extensional flow chamber.
Process parameters were optimized to obtain suspensions with size variations of 15%. Some strategies were developed to obtain uniform elastic properties according to the kinetics of shell assembly. If kinetics is limited by diffusion, membrane emulsification and shell assembly have to be split into two steps. If kinetics is limited by the quantity of reactants encapsulated in the droplet, variations of elastic properties result only from size variations.Learn more
An automated rheometer for the characterisation of microcapsule mechanical properties
Various everyday products (eg. perfumes) are fabricated through a micro-encapsulation of an active substance that is further released upon a desired conditions. The design and fabrication of the microcapsules is often a tedious process by lack of appropriate characterization tools.
RheoSurf allows, through small deformations of capsules, the quantitative, precise and fully automated characterisation of their mechanical properties in terms of real physical properties.Learn more
22-23 Ocotober 2020, Paris, France
Organized by Claude Loverdo and Clément de LoubensLearn more
by Vilotte et al., Food Hydrocolloids, 2020, 106137
Whey protein isolates (WPI) can be aggregated upon heating to create new functional properties (e.g. texture), which depend on ag- gregate size and structural properties. In industrial conditions, aggregates are obtained in continuous processes at high temperature (≥ 75°C) in few minutes. When studying the kinetics of WPI aggregation at high temperature and under flow, one major issue is to develop a process in which heat transfer does not limit aggregation. To this end, we used a down-scaling approach in which a WPI solution flows in a heated capillary tube. We show that this process makes it possible to study both the kinetics of aggregation after few seconds and its dependence with the mean shear rate in isothermal conditions. The size and mass of aggregates and protein conformation were characterized by small-angle X-ray scattering and resonant mass measurement for a single physico-chemical condition (pH 7.0, 10 mM NaCl, 92°C, 4 % w/w WPI) which led to sub-micrometric aggregates. Firstly, we report that the size of aggregates were three times larger than when produced in a test tube. Secondly, the size and mass of aggregates reached a steady-state value in a few seconds, whereas the kinetics of aggregation and denaturation had a characteristic time of few minutes. Thirdly, the shear rate had no significant effect on the size of the aggregates, or on the aggregation kinetics. We concluded that WPI aggregation at 92°C is limited by a step of nucleation, and that the fact that aggregates produced in test tube were smaller is due to a slower thermalization.Learn more
by de Loubens et al., Techniques in Coloproctology, 2020, 1-7
Rectal evacuation involves multiple mechanisms that are not completely understood. The aim of this study was to quantify the rheologic property, i.e. yield stress, that governs the ease of deformation of a range of faeces of differing consistency and understand its influence on the pathophysiology of defaecation. Yield stresses of faeces of differing consistencies and Bristol scores were determined by the Vane test. We then explored the effects of this property on ease of defecation using a simple static model of the recto-anal junction based on the laws of flow for yield stress pastes and checked the conclusions by X-ray defaecography experience. The yield stress of faeces increased exponentially with their solid content, from 20 to 8000 Pa. The static model of the recto-anal junction showed that evacuation of faeces of normal consistency and yield stress is possible with moderate dilatation of the anal canal, whilst the evacuation of faeces with higher yield stress requires greater dilatation of the anal canal. X-ray defaecography showed that such increases occurred in vivo. The diameter of the recto-anal junction is increased to enable the passage of feces with high yield stress. The finite limits to such dilation likely contribute to fecal impaction. Hence difficulties in defaecation may result either from unduly high yield stress or pathologies of reflex recto-anal dilatation or a combination of the two.Learn more
Habilitation à Diriger des Recherches, Université Grenoble-Alpes
Microcapsules in flow : Dynamics, Stability and Interfacial Rheology
Thanks to my jury : Cécile Monteux (ESPCI), Manouk Abkarian (CBS), Davide Beneventi (LGP2), Laurent Davoust (SIMAP), Anne-Laure Biance (ILM), Chaouqi Misbah (LPhy), Frédéric Risso (IMFT)
Instabilities of micro-capsules in flow – break-up and wrinkle
Congratulations Kaili for your story on microcapsules!Learn more
by Naillon et al., Physical Review Fluids, 2019, 4, 053301
Particles migrate in the transverse direction of the flow due to the existence of normal stress anisotropy in weakly viscoelastic liquids. We test the ability of theoretical predictions to predict the transverse velocity migration of particles in a confined Poiseuille flow according to the viscoelastic constitutive parameters of dilute polymer solutions. First, we carefully characterize the viscoelastic properties of two families of dilute polymer solutions at various concentrations using shear rheometry and capillary breakup experiments. Second, we develop a specific three-dimensional particle tracking velocimetry method to measure with a high accuracy the dynamics of particles focusing in flow for Weissenberg numbers Wi ranging from 10-2 and 10-1, and particle confinement β of 0.1 and 0.2. The results show unambiguously that the migration velocity scales as Wiβ2, as expected theoretically for weakly elastic flows of an Oldroyd-B liquid. We conclude that classic constitutive viscoelastic laws are relevant to predict particle migration in dilute polymer solutions whereas detailed analysis of our results reveals that theoretical models overestimate by a few tenths the efficiency of particle focusing.Learn more
Thursday 4th of April 2019 from 2 pm to 3pm, salle de conférences (RDC) du bâtiment NANOBIO DCM, 570 rue de la chimie, 38610 GIERES
Verifiable modelling of physical processing in the various compartments of the gut
Summary - I discuss the rheological and physiological difficulties in predicting mixing and propulsion of digesta within the intestinal lumen. I also describe the use of spatiotemporal mapping to quantify movements in ex vivo segments of the intestinal wall in real time, the use of this data in computational fluid dynamic models to predict flow and mixing, and the concurrent use of dye marker excretion profiles to validate the models. Further I give an example of how discrepancies between the two can highlight previously unknown sources of mixing. Finally I discuss recent work of the stomach.