Bicontinuous interfacially jammed emulsion gels or bijels are a new class of soft materials containing both surfactants and particles. They are, however, distinguished from conventional surfactant‐stabilized and particle‐stabilized systems. Due to the partitioning of percolating sheets of particles in a bicontinuous morphology, the interpenetrating phases are stabilized by kinetically arresting the phase separation process. This leads to the generation of rheological features in bijels with a range of viscoelastic properties based on types, size, anisotropy, and volume fractions of particles. Research on bijels has been around for only about 15 years, and the need for substantial research is recognized in the fabrication of bijels. Herein, the focus is on fabricating on fabricating bijels using solvent transfer‐induced phase separation (STRIPS) and from polar oils, cationic/anionic surfactants, and various nanoparticles to investigate their microstructure–properties relation. Using the newly emerged liquid‐in‐liquid 3D printing approach, the fabrication of these bijels via STRIPS into arbitrary complex designs which are not reported before is shown. The rheological properties of the printed bijels and the baths used for printing are characterized. This work paves the way for the production of bijels using a broader range of materials and hence their application in various fields.

Associative surfactants systems involving polar oils have recently been shown to stabilize immiscible liquids by forming nanostructures at the liquid interface and have been used to print soft materials. Although these associating surfactant systems show great promise for creating nanostructured soft materials, a fundamental understanding of the self-assembly process is still unknown. In this study, a ternary phase diagram for a system of cationic surfactant cetylpyridinium chloride monohydrate (CPCl), a polar oil (oleic acid), and water is established using experiment and simulation, to study the equilibrium phase behavior. A combination of visual inspection, small-angle X-ray scattering (SAXS), and rheological measurements was employed to establish the phase behavior and properties of the self-assembled materials. Dissipative particle dynamics (DPD) is used to simulate the formation of the morphologies in this system and support the experimental results. The ternary phase diagram obtained from the simulations agrees with the experimental results, indicating the robustness of the computational simulation as a supplement to the mesoscale experimental systems. We observe that morphological transitions (e.g., micelle-to-bilayer and vesicle-to-lamellar) are in agreement between experiments and simulations across the ternary diagram. DPD simulations correctly predict that associative surfactant systems form new nanoscale phases due to the co-assembly of the components. The established ternary phase diagram and the DPD model pave the way towards predicting and controlling the formation of different mesostructures like lamellar or vesicles, opening new avenues to tailor and synthesize desired morphologies for applications related to liquid-in-liquid 3D printing.