  Self-assembly of simple molecules into complex phases can be driven by
physical constraints, for instance, due to selective molecular uptake by
nanoporous surfaces. Despite the significance of surface-mediated assembly in
evolution of life, physical routes to molecular enrichment and assembly have
remained overlooked. Here, using a lyotropic chromonic liquid crystal as model
biological material, confined within nanoporous microfluidic environments, we
study molecular assembly driven by nanoporous substrates. We demonstrate that
nanoporous polydimethylsiloxane (PDMS) surfaces, due to selective permeation of
water molecules, drive transition of disordered isotropic phase to ordered
nematic, and higher order columnar phases under isothermal conditions.
Synergistically, by tailoring the wettability, the surface-to-volume ratio, and
surface topography of the confinements, we program the lyotropic phase
transitions with a high degree of spatial and temporal control. Using a
combination of timelapse polarized imaging, quantitative image processing, and
a simple mathematical model, we analyze the phase transitions, and construct a
master diagram capturing the role of surface wettability and channel geometry
on programmable lyotropic phase transitions. Intrinsic PDMS nanoporosity and
confinement cross-section, together with the imposed wettability regulate the
rate of the N-M phase transition; whereas the microfluidic geometry and
embedded topography enable phase transition at targeted locations. We harness
the emergent long-range order during N-M transition to actuate elasto-advective
transport of embedded micro-cargo, demonstrating particle manipulation concepts
governed by tunable phase transitions. Our results present a programmable
physical route to material assembly, and offer a new paradigm for assembling
genetic components, biological cargo, and minimal synthetic cells.
