Thèse Gelification Interfaciale pour la Production de Mousses Solides Biosourcées H/F

Doctorat_Gouv

Établissement : Université Grenoble Alpes
École doctorale : I-MEP² - Ingénierie - Matériaux, Mécanique, Environnement, Energétique, Procédés, Production
Laboratoire de recherche : Laboratoire Rhéologie et Procédés
Direction de la thèse : Hugues BODIGUEL ORCID 0000000323486966
Début de la thèse : 2026-10-01
Date limite de candidature : 2026-05-15T23:59:59

Foam-like materials are essential and widely used in daily life and industrial applications due to their lightweight, porous architecture, excellent mechanical energy-absorption capacity and low thermal conductivity. However, most commercially available foams are derived from petroleum-based materials, raising significant environmental and health concerns. This project targets the bio-based foams (biofoams) made from natural, renewable polymers such as polysaccharides, and provide a pathway toward a more sustainable and circular materials economy. The project will benefit from the strong expertise in biopolymer gelation, rheology, and soft matter physics at the LRP, complemented by collaborations with the physicochemistry laboratory CERMAV.

Precisely engineering the architecture of biofoams remains challenging. The simplest and most cost-effective approach relies on creating a liquid foam precursor by dispersing gas into a biopolymer solution, where the bubble size is expected to determine the pore size of the biofoam. In practice, however, this strategy is hindered by a critical bottleneck: liquid foams are mechanically weak and prone to destabilization through bubble coalescence, coarsening, and liquid film drainage. These consequences ultimately lead to foam collapse and poor control over the final porous structure. To overcome this limitation, the central strategy of this project is to reinforce bubble interfaces and inter-bubble liquid films by tunable biopolymer gelation.

The core scientific question is how to control biopolymer gelation kinetics at gas-liquid interfaces and within thin liquid films, and how this control can be harnessed to tailor bubble dynamics in foam generation. Gelation in foams occurs in a complex and highly confined environment. Gas-liquid interfaces impose strong constraints on the mobility, conformation, and assembly of biopolymers, leading to gelation kinetics that might differ from those in the bulk phase. The first objective of the project is therefore to elucidate the mechanisms of gelation kinetics at interfaces and in thin liquid films within biofoams. Moreover, biopolymer gelation can occur over a wide range of timescales, from seconds to hours or even days. The second objective is to investigate how gelation kinetics compete with and influence foam dynamics such as bubble coalescence, coarsening, and drainage.

To address these objectives, the project adopts a bottom-up experimental approach. First, a dedicated microrheology setup will be developed to decouple interfacial rheology from the rheology of the thin liquid films. This enables independent characterization of gelation kinetics at interfaces and in the confined bulk. Second, a microfluidic platform will be designed to enable real-time visualization and quantification of bubble dynamics in the presence of tunable gelation learned from the first step. This approach will directly link gelation kinetics to pore size control in the biofoams.

Overall, this project leverages fundamental insights into biopolymer gelation kinetics to control the architecture and mechanical properties of biofoams, bridging the fields of materials science, soft matter physics, and engineering. The knowledge developed in this project are expected to pave the way toward scalable biofoam production for applications such as packaging, thermal insulation, and energy absorption.

Surfactants and/or nanoparticles are the classical stabilizers used to produce and stabilize liquid foams [1,2]. Their preferential staying at the gas-liquid interfaces reduces the interfacial energy, thereby decreasing the probability of bubble coalescence [3]. Yet, foams stabilized by such agents lack sufficient mechanical resistance to slow down coarsening and liquid drainage [4], resulting in limited lifetimes that are often insufficient for subsequent processing.

Gelifying liquid foams, through the transformation of the viscous liquid phase into a soft, solid-like gel, is anticipated to enable long-term foam stabilization. This transition is not only highly sensitive to pH [5], temperature [6], ionic strength [7], but also to the spatial confinement [8]. In liquid foams, biopolymers are confined to highly curved gas-liquid interfaces and in liquid films with thicknesses ranging from nanometers to micrometers. Under such conditions, biopolymer mobility, conformation, and intermolecular interactions differ markedly from those in the unconfined bulk phase. Consequently, gelation kinetics are governed not only by the intrinsic chemical or physical crosslinking mechanisms (e.g., alginate crosslinked with Ca2+ ions), but also by interfacial adsorption, confinement, and drainage-driven concentration gradients. The interfacial gelation kinetics therefore cannot be directly inferred from bulk rheological measurements.

Previously, interfacial gelation has been investigated in open gas-liquid systems using classical bicone [9] or double wall-ring [10] geometries mounted on rotational rheometers. While these techniques provide valuable insight into time-dependent interfacial rheology, they cannot be directly applied to gelation kinetic measurement in biofoams, where strong confinement and the small length scales of thin liquid films dominate. In parallel, studies on thin liquid films have shown that capillary drainage induces progressive film thinning and polymer concentration gradients, effects that are particularly pronounced for biopolymers undergoing gelation. Despite these advances, a quantitative understanding of how gelation kinetics at interfaces and in confined films couple to foam dynamics-such as coalescence, coarsening, and drainage-remains largely unexplored. Understanding the competition between gelation kinetics and foam destabilization is therefore critical for tailoring the architecture of the final biofoams.

Caractériser et comprendre les mécanismes de gelification aux interfaces et en volume
Caractériser et optimiser leurs cinétiques respectives

This project will primarily integrate microfluidics with advanced microscopy to achieve the objectives. Overall, a microrheology approach based on a microfluidic platform will be developed. The project is structured into three work packages (WPs).

WP1 - Rheology determination of biopolymer gelation in bulk. A systematic database of gelation kinetics for bulk biopolymer solutions (e.g., alginate, pectin, and cellulose nanofibers) will be established. A rotational shear rheometer will be used to characterize gelation timescales by varying key parameters such as pH, temperature, and ionic concentration. These bulk rheological measurements will provide reference timescales for gelation in unconfined conditions and insights into the resulting mechanical stiffness of the gels.

WP2 - Characterization of gelation at interfaces and within thin liquid films. Gelation at gas-liquid interfaces and in thin liquid films will be investigated using a microfluidics-adapted thin film balance setup [11]. Thin biopolymer liquid films will be formed under well-controlled pressure conditions using a high-precision pressure controller. Different tracer particles, selectively localized at the gas-liquid interface and within the film bulk, will be tracked independently using fast confocal microscopy. To investigate the influence of drainage on biopolymer transport and gelation, flow conditions within the film will be tuned by varying the applied pressure.

WP3 - Real-time visualization of bubble dynamics and their competition with gelation. A dedicated microfluidic platform combining a flow cell with a pressure controller will be developed to study bubble dynamics during gelation. The microfluidic devices will be fabricated using standard soft-lithography techniques. For simplicity, quasi-two-dimensional (2D) foams will be generated, with initial bubble sizes tuned by adjusting the gas-to-liquid flow-rate ratio. The entire setup will be integrated into a custom-built optical imaging system with a variable field of view. A high-speed camera will be used to monitor bubble dynamics [12] in real time under different gelation kinetics.