This paper describes a very simple and robust microfluidic device for digitizing samples into an array of discrete volumes. The device is based on an inherent fluidic phenomenon, where an incoming aqueous sample divides itself into an array of chambers that have been primed with an immiscible phase. Self-digitization of sample volumes results from the interplay between fluidic forces, interfacial tension, channel geometry, and the final stability of the digitized samples in the chambers. Here we describe experiments and simulations that were used to characterize these parameters and the conditions under which the self-digitization process occurred. Unlike existing methods used to partition samples into array, our method is able to digitize 100% of a sample into a localized array without any loss of sample volume. The final volume of the discretized sample at each location is defined by the geometry and size of each chamber. Thus, we can form an array of samples with varying but predefined volumes. We exploited this feature to separate the crystal growth of otherwise concomitant polymorphs from a single solution. Additionally, we demonstrated the removal of the digitized samples from the chambers for downstream analysis, as well as the addition of reagents to the digitized samples. We believe this simple method will be useful in a broad range of applications where a large array of discretized samples is required, including digital PCR, single-cell analysis, and cell-based drug screening.

We have synthesized a new class of highly efficient nonlinear optical (NLO) chromophores based on the novel tricyanopyrroline (TCP) electron acceptor. Molecular linear and nonlinear optical properties of the prototypical chromophores were measured and calculated to understand structure-property relationships. One such chromophore showed molecular first hyperpolarizability (β) of (8700 ( 702) × 10 -30 esu at excitation wavelengths of 1.9 µm, and another showed macroscopic electro-optic (EO) coefficients (r 33 ) of 51 pm/V at 1.55 µm with 20 wt % chromophore loading when poled with 65 V/µm in amorphous polycarbonate film. Synthetic strategies for extending the utility of the acceptor and chromophores are discussed.

The concept of syncrystallization was reinvestigated by focusing on phthalic acid (PA) grown with methyl red (MR). Crystals are alternately red and yellow in adjacent growth sectors. X-ray structures of MR and its cocrystals, revealing MR in the neutral, zwitterionic, and protonated states, as well as measurements of linear birefringence and linear dichroism of mixed crystals, were used to investigate mechanisms of PA coloring. These experiments were complemented by force field calculations of the lowest energy stable surfaces of expressed facets and energies of MR on and in crystals, as well as molecular orbital calculations of MR. Two MR species were detected in PA having distinct energies, polarizations, and face selectivities. Assignments of structures to these MRs, previously thought to be neutral and protonated, required a nuanced analysis of hydrogen bonds. The essential difference between yellow and red species is whether the MR carboxylic acid proton is inter- or intramolecularly hydrogen bound. Inferences about mixed crystal structure drawn from an examination of cocrystals of PA and MR are inconsistent with polarization spectroscopy signaling caution when using stoichiometric compounds as models of dilute solid solutions. Upon heating mixed crystals, linear dichroism diminishes and oriented, elongated pools of MR separate and pass through the bulk in directions perpendicular to the direction of elongation. These bâtonnets subsequently crystallize leaving macroscopic oriented crystals of a MR-rich phase within PA. No evidence was found for the simultaneous crystallization of MR and PA; however, the MR reorientation on heating as well as the separation and recrystallization of a MR-rich phase are distinct processes that could be embraced by the literal meaning of syncrystallization.