Architecting soft materials using fluidic gates: A practical analogy to Boolean logic

Soft materials often derive their functionality from the hierarchical arrangement of disparate phases. While hierarchy can develop spontaneously after certain systems are perturbed, self-assembled micron-scale structures are rather limited to particular architectures, such as the fractal aggregates found in colloidal gels and the tortuous pores found in bijels. To gain access to designer hierarchies, we engineered serpentine, millifluidic devices to assemble advecting materials into voxelated patterns. The `advective assembly' devices include three basic elements: (1) T-junctions which combine flows, (2) T-junctions which split flow, and (3) corners which rotate flow. These elements are combined in modular sequences as one would combine "AND", "OR", and "NOT" gates to form a Boolean circuit. The Boolean-inspired formalism is implemented in MATLAB Simulink and validated experimentally using viscoplastic suspensions. Within appropriate rheological constraints, the assembled architectures are determined by the contours of the device rather than the composition of the constituents. We highlight the utility of this geometrically-dictated process in two different applications: patterning hydrogel cross-linking density to program shape actuation [10.1021/acsami.2c02069], and intensifying emulsification of high-viscosity ratio systems [10.1002/aic.17192]. This work exemplifies advective assembly's broad potential to encode useful soft material structure using modular flows.