I focus my research on understanding how colloidal systems structure themselves along non-equilibrium pathways. I investigate three main processes: emulsification, drying and precipitation, using a large diversity of systems at the crossroads of engineering, chemistry and biology.
Drying of complex colloidal systems. These studies rests on the design of a millifluidic drying cell ensuring unidirectional advection/diffusion and set boundary conditions. A large panel of techniques are instrumented around this cell such as SAXS and Raman microscopy, which give respectively structure and composition gradients. This theme has received the support of ANR under the young researcher grant COATING.
- (a) Humidity-insensitive water evaporation. A counterintuitive mechanism has been uncovered upon drying non-ideal aqueous solutions. For instance, evaporating surfactant solutions will lead to the build-up of mesophases at the air/liquid interface, which display a low permeability to water. When the air gets dryer, evaporation should be quicker but it is actually compensated by the decrease of water permeability to the thickening of the interfacial layer. Such a behavior is expected when large water activity changes are observed in the concentrated solute region and low permeabilities or mutual diffusion coefficients. This is expected to be the general case for molecular mixtures or dispersions behaving like molecular mixtures in the dry regime. (published)
- (b) Lung surfactant (with J. Andersson, in collaboration with E. Sparr (Lund university) and J. Perez-Gil (Madrid university). We reconstitute lung surfactant films from extracts and study the interplay between molecular composition and mesostructures in physiologically relevant conditions. (published and on-going)
- (c) Colloidal dispersions (with J. Crassous, Aachen university). We investigate how a complex colloidal dispersion dries, in connection with the work on molecular mixtures. (to be published)
- (d) Peptide self-assembly (with S. Kuczera and U. Olsson, Lund university). We use the drying setup to align peptide nanotubes and thus perform their 3D chacterization using projection methods such as SAXS. (to be published)
Silica precipitation in semi-batch methods (with C. Manfoumbi, M. Meireles, B. Biscans). This project has been attacked from two different angles: one fundamental and one industrial, which have converged. From a fundamental standpoint, we wanted to know how the multi-scale structure of precipitated silica could be tuned by continuous addition of silicates. From an industrial standpoint, silica precipitation in unfavorable in a hydrometallurgical step since it poses filtrability issues. By precisely tuning the mesostructure of the precipitating silica, filtrability issues were lifted. (to be published)
Emulsions stabilized by gum Arabic (with M. Atgié and O. Masbernat). We investigate the stabilization of emulsions by a natural hydrocolloid, gum Arabic, used since ancient times and still in use nowadays for instance in flavored beverages. Gum Arabic is a highly complex system and we study systematically interfacial coverage and structuration to unravel the exceptional stabilization mechanism it can provide to emulsions. This leads to a more rational design of industrial formulations. This research is conducted with the support of ANR LabCom SoPhy. (Three publications under evaluation)
Emulsions stabilized by lipids (with O. Masbernat, J. Andersson and L. Garcia). We investigate the stabilization of emulsions by phospholipids, which is an important industrial issue but remains a dark corner or emulsion science. (on going)
Nanoemulsification (with B. Cabane, U. Olsson, R. Botet)
- (a) Nanoemulsification through hydration changes: how to obtain nanoemulsions through simple water addition or temperature changes by tricking a self-assembly system out of equilibrium.
- (b) Nanoemulsification and nanoprecipitation through solvent-shifting: understanding what leads to uniform dispersions/emulsions in a glass of Ouzo or to produce beta-carotene for salmon feeding.
- (c) The negative charge at oil/water interfaces: showing that carboxylate impurities quantitatively explain the negative charge of purified oil/water interfaces, which has been observed for more than a century.
- (d) Emulsion coarsening by molecular exchange when droplets contact: unraveling a new mechanism by which emulsions can coarsen even when there is no coalescence nor Ostwald ripening, which is controlled by the surfactant film.
Enzymatic synthesis of alkylglucosides using supramolecular agents (with T. Börner and P. Adlercreutz, Lund university, Biotechnology division).
Cyclodextrins are used as both substrate and complexing agents and this dual role leads to a complicated coupling that is unveiled in order to design optimum process performance.
Application & Teaching
– 1 PhD students: Nouha El Amri
– 1 post-docs: Jenny Andersson
– PhD student: Marina Atgié, Christian Manfoumbi, Brice Courtois, Airama Albisa Novo
– 1 post-doc : Léo Garcia
Teaching activities : Colloids & Surfaces course in M1 Membrane Engineering
Collaborators: Emma Sparr and Ulf Olsson (Lund university), Vincent Mansard (LAAS), Simon Tricard (LCPNO), Jesus Perez-Gil (Madrid university), Martine Meireles and Béatrice Biscans (LGC)
2018 The impact of non-equilibrium conditions in lung surfactant: structure and composition gradients in multilamellar, ACS Central Science, J. Andersson, K. Roger*, M. Larsson, E. Sparr .
2018 Evaporation, diffusion and self-assembly at drying interfaces, Physical Chemistry Chemical Physics, 20, 10430-10438 , K. Roger*, E. Sparr, H. Wennerström.
2016 Nanoemulsification in the vicinity of phase inversion: Disruption of bicontinuous structures in oil/surfactant/water systems, Current Opinion in Colloid & Interface Science, 15 120-128, K. Roger*.
2016 Controlling Water Evaporation through Self-Assembly, PNAS, 113 (37) 10275-10280 , K. Roger*, M. Liebi, J. Heimdal, D. Pham and E. Sparr.
2016 How do interactions control droplet size during nanoprecipitation, Current Opinion in Colloid & Interface Science, 22 108-112, R. Botet*, K. Roger**.
2015 Emulsion Ripening through Molecular Exchange at Droplet Contacts, Angewandte Chemie, 54, 1452-1454, K. Roger*, U. Olsson, R. Schweins and B. Cabane.
2014 Hydrophobic Complexation Promotes Enzymatic Surfactant Synthesis from Alkyl Gluco- side/Cyclodextrin Mixtures, ACS Catalysis, 4 (8), pp 2623–2634, T. Börner, K. Roger, P. Adlercreutz.
2013 Surface Charge of Polymer Particles in Water: The Role of Ionic End-Groups, Langmuir, 29 (36), pp 11244-11250, K. Roger*, M. Eissa, A. Elaissari and B. Cabane.
2013 Coalescence of repelling colloidal droplets : a route to monodisperse populations, Langmuir, 29 (19), pp 5689-5700, K. Roger*, R. Botet and B. Cabane.
2012 Uncontaminated interfaces are uncharged : a reply, Angewandte Chemie, 51 (52), pp 12943-12945, K. Roger*, B. Cabane.
2012 Why are hydrophobic/water interfaces negatively charged?, Angewandte Chemie, 51 (23), pp 5625-5628, K. Roger*, B. Cabane.
2011 Superswollen microemulsions stabilized by shear and trapped by a temperature quench, Langmuir, 27 (17), pp 10447-10454, K. Roger*, U. Olsson, M. Zackrisson-Oskolkova, P. Lindner and B. Cabane.
2011 Emulsification through surfactant hydration : The PIC process revisited, Langmuir, 27(2), pp 604-611, K. Roger*, B. Cabane and U. Olsson.
2010 Formation of 10-100 nm size-controlled emulsions through sub-PIT cycles,
Langmuir, 26 (6), pp 3860-3867, K. Roger*, B. Cabane and U. Olsson .