Objective (a): Control over Bijel Structure
We have made significant progress in understanding and controlling bijel (bicontinuous interfacially jammed emulsion gel) structure. Our efforts advanced the synthesis of bijels with continuous channel networks at submicrometer scales. We elucidated the underlying mechanisms of bijel formation using silica and alumina nanoparticles, demonstrating how self-assembly occurs during the phase separation of oil and water. The role of surfactants in facilitating bijel formation was systematically investigated, alongside the development of surfactant-free bijels stabilized solely by nanoparticles. These findings are broadly applicable to various bijel systems.
To support this, we developed innovative sample preparation techniques, including rapid screening methods and controlled printing processes for device fabrication. We also studied the fluid dynamics involved in bijel formation to optimize fabrication parameters.
Detailed insights into bijel formation dynamics were obtained using small-angle X-ray scattering (SAXS) at the European Synchrotron Radiation Facility (ESRF). This allowed us to identify key mechanisms of phase separation and nanoparticle assembly, and to demonstrate how these kinetics can be tuned through component concentration and additive introduction.
Objective (b): Reinforcement and Surface Functionalization of Bijels
We developed two reinforcement strategies for bijels. The first creates composite structures by integrating bijels with varied mechanical properties, enhancing overall strength and flexibility. The second approach chemically binds nanoparticles using tetraalkoxysilanes, acting as a "mortar" within the structure. This method has been generalized across different silane chemistries, and the reinforced structures were characterized via SAXS at ESRF.
We also focused on tuning the surface charge of bijels, a critical requirement for fluid transport (Objective c). Surface charge control was achieved through: (1) fabrication using highly charged nanoparticles, and (2) post-synthesis ionization of nanoparticle surfaces in reinforced bijels.
Objective (c): Liquid Transport and Functional Operation of Bijels
We discovered a method to induce liquid flow through bijels using an applied electrical voltage, which enables electrokinetic transport through the microscopic channels. We quantified flow rates as a function of voltage and bijel composition. Confocal laser scanning microscopy (CLSM) combined with fluorescence techniques was employed to visualize chemical transport through the bijel. In parallel, computational simulations were developed to predict transport rates and were validated against experimental data.
Additionally, we identified key factors affecting the long-term stability of the bijel’s fluid network. Specifically, we addressed the challenge of preventing unwanted rearrangement of the oil and water phases, which could disrupt continuous fluid transport. This stability enabled us to achieve, for the first time, continuous liquid-liquid extraction within a bijel. We studied solute transport from a flowing oil phase into a water phase moved electrokinetically through the bijel. Extraction rates were experimentally evaluated and simulated under varying flow conditions.
Exploitation and Dissemination
The results of this project have laid the foundation for advanced applications in membrane technology, soft robotics, and microfluidic devices. We are currently disseminating our findings through high-impact journal publications, international conferences, and workshops. Potential exploitation paths are being explored in collaboration with industrial partners, particularly in the areas of separations, sensing, and responsive materials.
