We design and lithographically fabricate pre-assembled colloidal linkages of custom-shaped, discrete mobile microscale tiles, which are coupled together by lock-and-key sub-particle features, yielding hinge-like semi-flexible steric bonds. Using roughness-controlled depletion attractions, we confine released lithographic particles to a plane immediately above the wafer, yielding long-lived fluctuating Brownian mobile colloidal linkages, which we call polylithomers. These colloidal polylithomers are analogs of molecular polymers, yet their Brownian dynamics can be readily observed and measured using optical microscopy. We construct and study curvilinear, branched, bridged-spiral, dendritic, and mesh-like polylithomers having customized pre-assembled dimensions, topologies, configurations, intrinsic local curvatures, persistence lengths, and bond extensibilities that are otherwise difficult, if not impossible so far, to make by bottom-up self-assembly of colloidal or molecular methods. By developing a routine for tracking the positions and orientations down to the monomer scale and applying statistical mechanics, ensembles of measured conformations of entire polylithomers are used to infer spatially resolved average bond characteristics. We make extensible polylithomers having bonds that offer a longitudinal translational sliding degree of freedom that is atypical of bonds in molecular polymers. Thus, through top-down design, steric lock-and-key polylithomers provide access to unusual morphologies, conformations, and bonding potentials that are not present in molecular or other types of colloidal polymers. Besides revealing equilibrium fluctuations, we also demonstrate the potential for making and studying the evolution of far-from-equilibrium polymer systems.

Lithographic colloidal polymers of steric lock-and-key linkages

ACS Spring 2022

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