In a further example synthesis process provided by the invention, a monomer stream is flowed at a selected flow rate, through a fluidic channel and illumination is projected to the monomer stream to polymerize at least one microstructure in the monomer stream by the illumination. At least one polymerization termination species is provided, at internal walls of the fluidic channel, which terminates at the channel walls active polymerization sites at which polymerization could occur during polymerization of the microstructure. This quenches polymerization at those sites and preserves a non-polymerized volume of the monomer stream adjacent to the channel walls.
This high-throughput technique enables superior control over microstructure geometry, shape, composition, and anisotropy. Non-spheroidal polymeric microstructures each having a plurality of distinct material regions can be synthesized by the technique, as can planar polymeric microstructures each having a plurality of distinct material regions.
The MIT method of immiscible microstructure synthesis is of sufficient generality to enable synthesis of a wide range of non-spherical particles with such chemical anisotropy; e.g., amphiphilic particles with a rod-like hydrophobic tail and a disk-shaped hydrophilic head can be synthesized. Such a library of particles can be useful when studying the effect of geometry and chemical anisotropy on meso-scale self assembly and rheology. In addition, structures with more complicated motifs like w-o-w can also be formed quite easily.
The invention provides lithographic-based microfluidic methodology that can be employed to continuously or near-continuously synthesize polymeric microstructures of varied complex shapes, chemistries, and functionalities with an elegant dual lithography-polymerization step.
FIG. 10D schematically shows a polymeric microstructure 330 synthesized across two monomer streams and employing a mask shape that provides a distinct feature geometry for the microstructure region corresponding to each of the monomer streams. FIG. 10E schematically shows a polymeric microstructure 334 synthesized across five monomer streams and employing an S-shaped mask 336. The differentiation in polymer species is preserved across the structure.
In accordance with the invention, the co-flowing monomer streams employed to synthesize polymeric microstructures can be miscible, chemically similar streams. In this case, the interface between different regions in a resulting microstructure is not sharp, due to molecular diffusion. Diffusion-limited mixing that is characteristic of laminar flow can be exploited to ensure that the streams flow distinctly through a microfluidic device, but molecular diffusion between adjacent polymerized regions can here occur. If co-flowing monomer streams instead are immiscible, then a sharp interface between synthesized polymeric regions can be enforced, producing microstructures having regions with sharply-segregated chemistries and differing surface energies.
FIG. 10F is an example of a polymeric microstructure 340 synthesized across two monomer streams one of which provides a hydrophilic polymer region 342 and one of which provides a hydrophobic polymer region 344. The interface 346 between the two regions in the microstructure is characteristically curved due to the disparate surface energies of the two regions. The amphiphilic nature of such a microstructure can be exploited to enable self-assembly of populations of such microstructures.
FIGS. 10G-10H are schematic views of polymeric microstructures 352, 358, synthesized by lithography and polymerization through multiple co-flowing monomer streams rather than across co-flowing monomer streams. As shown in FIG. 10G, employing a circular mask 350, a three-material microstructure is produced in which the composition of the circular cross section of the structure is changed through the thickness of the structure. Similarly, as shown in FIG. 10H, a star-shaped polymeric microstructure is synthesized across four differing monomer streams to produce a microstructure 358 having a differing composition through the thickness of the star-structure, with the composition constant in a given star-shaped plane of the structure.
In addition to these limitations in polymeric microstructure composition and geometry, conventional polymeric microstructure synthesis generally requires isotropic structural arrangements of materials. Further, the through-put of such processes is typically limited by a requirement for making one structure at a time or a limited photo-mask-defined field of structures at a time. These limitations in polymeric microstructure synthesis through-put, microstructure geometry, morphology, and functionality have restricted the ability to address the growing number of critical applications for which polymeric microstructures could be well suited.