Postdoctoral researcher (M/F) , Photo-switchable permeability of stabilized aqueous emulsions

Job Description

Missions

Context
Water-in-water emulsions, such as PEG/dextran mixtures, spontaneously sequester hydrophilic solutes. They are produced without oil or organic solvents and are used in biotechnology, food, and cosmetics. Yet, their use is limited by challenges in long-term stabilization and control of molecular transport across their interfaces. In the ANR project SHEILA, we investigate an original stabilization strategy based on lyotropic lamellar phases that self-assemble into structured and impermeable interfacial coatings. The challenge now is to make the membrane permeability switchable.
The postdoctoral project, supported by the ANR SHEILA, aims to develop stimuli-responsive strategies to control interfacial permeability and molecular exchange. We recently started exploring this question with temperature-responsive lamellar phases, in which structural defects generate pores. The project will investigate how pore structure and size affect the transport of molecular probes. In parallel, we aim to make that control local, fast, and reversible by using light as the stimulus. Light-responsive surfactants and photoacids will be explored to locally modify interfacial properties and trigger localized permeability. A major component of the project will be built around a microscopy platform recently developed in the lab that makes it possible to create multiwavelength spatially patterned illumination of the sample and precise temperature control. This will involve programming of illumination strategies and image-analysis routines. Patterned illumination will let us address individual droplets, or even selected regions of a single droplet, and open and close pores where and when we choose.

Scientific and applied perspectives
Light-addressable permeability of a self-assembled membrane opens several directions:
• Spatiotemporally controlled microreactors: gating the access of reagents to a droplet makes it possible to start, pause, or sequence reactions in individual compartments, using only a projected light pattern.
• Communication between droplets: light-controlled exchange between neighboring droplets would let us build and test chemical communication networks.
• Fundamental soft-matter questions: light provides a precise and reversible way to nucleate and anneal defects in a lamellar phase, enabling quantitative studies of pore dynamics and of the link between local molecular state and the permeability of multilamellar films.

Mission
The postdoctoral researcher will design, characterize, and exploit lamellar membranes at the interface of aqueous droplets whose permeability can be switched by a local optical stimulus. Possible strategies include:
• photoswitchable amphiphiles (e.g. azobenzene-based surfactants or co-surfactants) that change bilayer curvature, packing, or defect density under light.
• photoacids or photobases that locally modify the pH, and thus the ionization state and cohesion of pH-sensitive bilayers.
• photothermal approaches that use a light-absorbing species to locally heat the bilayer and trigger temperature-induced defect formation.

Activity

- Formulation and characterization of water-in-water emulsions stabilized by thermoresponsive and light-responsive lamellar phases.
- Quantification of molecular exchange and of the stimulus-responsive, reversible permeability of the lamellar phase using fluorescent probes.
- Calibration and further development of an existing microscopy setup combining patterned illumination and temperature control.
- Programming illumination protocols and image analysis to monitor emulsion dynamics and quantify their response to localized stimuli.
- Analysis and dissemination of results, and coordination with project partners.

Your Profil

Skills

- Education: PhD in physical chemistry, soft matter physics, colloid science, materials science or a related field.
- Technical skills: Experience in formulation, optical microscopy, instrumentation, programming or image analysis (Python, ImageJ/Fiji). A taste for instrumentation would be an asset.
- Transferable skills: Autonomy, scientific curiosity, a hands-on approach and the ability to troubleshoot experimental problems in a multidisciplinary environment. Good scientific writing and communication skills (reports, scientific presentations), as well as proficiency in scientific English.

Your Work Environment

The postdoctoral researcher will work at the Centre de Recherche Paul Pascal (CRPP), located in Pessac, France, in close interaction with a PhD student on the stabilization and characterization of the droplets. The project brings together three CRPP teams (Bio2.0, Colloids Interfaces and Assemblies, and Soft Matter: Structure and Dynamics) with complementary expertise in lamellar phases, ATPS formulation, fluorescence and confocal microscopy, light patterning and theory. The CRPP offers a highly interdisciplinary environment at the interface of physical chemistry, physics and soft matter science. Researchers have access to a broad range of experimental facilities and expertise, spanning sample formulation, optical microscopy and quantitative characterization of soft materials (including SAXS, DLS, SEM, TEM).
The project will benefit from an existing microscopy setup that the postdoctoral researcher will help further develop, providing opportunities to combine optical instrumentation, programming and experimental soft matter research.

The position falls within a restricted area subject to French regulations on the protection of scientific and technical potential (Protection du potentiel scientifique et technique, PPST). Appointment is therefore subject to authorization by the competent authority of the French Ministry of Higher Education and Research (MESR).

Constraints and risks

Risks associated with handling standard chemicals, solvents and surfactants, as well as using laser diodes.

Compensation and benefits

Compensation

€3041–€4216 gross per month depending on experience

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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