PhD position (M/F) — "Nucleation and liquid-liquid phase separation in polymer solutions: experimental access to the early stages of nucleation"

Job Description

Thesis Subject

Classical Nucleation Theory (CNT) fails to predict nucleation rates, with discrepancies of several orders of magnitude. This is largely because critical nuclei form at the nanometer scale, below optical resolution. In polymer solutions (chain length N), the free energy of mixing delta F follows Flory-Huggins behavior: the entropic contribution, scaling as 1/N, is weak, which pushes the critical radius R* up to the mesoscopic scale (100 nm to 10 micrometers) and makes nucleation optically resolvable. These systems also serve as models for cellular biocondensates, whose arrested growth remains unexplained.
This thesis aims to directly confront experimentally measured nucleation parameters with CNT predictions: independently measuring the interfacial tension gamma and the driving force delta F to predict R* = 2 gamma / delta F. Gamma will be measured by micropipette aspiration and by the spinning drop method, and delta F by microDSC and dynamic light scattering, alongside the construction of the corresponding phase diagrams.
We will then aim to observe individual nucleation events to extract R*, nucleus density, and induction time, and to probe the pre-nucleation regime (R smaller than R*) in search of possible non-classical pathways. These nucleation events will be observed directly in thermostated microfluidic compartments, which limit heterogeneous nucleation on the channel walls, using fast confocal microscopy; the pre-critical regime will be probed by fluorescence correlation spectroscopy (FCS). Complementary structural characterization by SAXS, carried out through an external collaboration, will provide a mean-field measurement of nucleation and condensation dynamics, which we will compare with the single-event observations.

Your Work Environment

This project, funded by the ANR JCJC grant MORNING coordinated by Ambre Bouillant), is carried out jointly at the MSC laboratory (Université Paris Cité) and the Gulliver laboratory (ESPCI Paris, PSL), giving access to the full range of instruments required: micropipette, μDSC and DLS, fast confocal microscope, as well as cleanroom microfabrication facilities. A collaboration is planned with Clémence Le Cœur (ICMPE / Laboratoire Léon Brillouin, CEA Saclay) for SAXS characterization, including an already-funded synchrotron measurement campaign, and with Domenico Truzzolillo (University of Montpellier) for interfacial tension measurements by spinning drop. The student will therefore work across two sites; the division of their time between the two will be determined jointly.

Profile and skills sought
Interest in experimental soft matter physics, equally comfortable with theoretical aspects
Interest in or experience with microfluidics, thermodynamics, and interfacial transport
Skills in image analysis and programming (Python, Fiji) will be highly valued
Autonomy, rigor, and scientific curiosity

Constraints and risks

-

Compensation and benefits

Compensation

2300 € gross monthly

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.

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