Alexis Darras

This PhD project, based at the University of Bristol's School of Physics, focuses on the transition dynamics and stabilization of streamers in the gravitational collapse of colloidal gels. Colloidal gels are soft, disordered materials formed by networks of micron-scale particles in fluid, widely used in foods, pharmaceuticals, and inks due to their long-term stability. However, under gravity, these gels can collapse by reorganizing and forming fluid channels (streamers) that destabilize the structure, followed by a slower compaction. The project aims to investigate the poorly understood transition between these regimes, with the goal of informing the design of more stable suspensions and improving the understanding of biomedical tests such as erythrocyte sedimentation. The research will compare collapse dynamics in two systems: colloidal gels and full blood. Advanced techniques such as confocal microscopy, rheometry, and particle tracking will be used to image microstructural changes and tracer trajectories during collapse. Colloidal gels allow for high-resolution imaging with fluorescent particles, while full blood presents optical challenges due to hemoglobin absorption but offers direct relevance to bioclinical applications. By comparing these systems, the project seeks to develop analogies between simpler colloids and complex biological fluids, building on recent findings that highlight the complexity of collapse but leave transition mechanisms unexplained. The project is co-supervised by Dr Alexis Darras (School of Physics) and Prof Paul Bartlett (School of Chemistry), combining expertise in soft matter physics and colloidal chemistry. Additional support is available from the Quantum and Soft Matter group, including Dr Francesco Turci and Prof Wuge Briscoe, as well as clinical guidance from Dr Sarah Westbury and Dr Sanne Lugthart. The research will benefit from access to advanced imaging facilities at the University of Bristol. Successful candidates will join the vibrant Physics Graduate School, which offers comprehensive induction, targeted skills training, and a supportive research community. The School of Physics is committed to diversity and equality, holding a Bronze Athena Swan award and a Physics Juno Champion award. Funding for home students covers living expenses at the UKRI rate, full tuition fees, and training/support expenses. A small number of fully-funded places are available for outstanding international candidates, and students with external or partial funding are also welcome to apply. Applicants should have a first degree in physics or a related subject (at least UK upper second-class honours or equivalent), or a relevant postgraduate master's qualification. International applicants should consult the university's guidance for country-specific requirements. English language proficiency at Profile F is required for non-native speakers. The application deadline is 19 January 2026. To apply, submit a CV, personal statement, and transcripts via the University of Bristol application system, specifying 'Bristol Physics Research Scholarships' as your funding source. For further information, contact the Bristol Physics Graduate School at [email protected].