We developed microfluidic devices in order to test small volumes (<100 μL) of conjugated polymer solution containing harsh organic solvents at high strain rates and pressure while maintaining device rigidity and optical transparency. Microfluidic devices with narrow microchannels were fabricated in order to reach high shear and extensional strain rates up to about 10 6 s -1 and 10 5 s -1 , respectively. For shear experiments, we use narrow microchannels that are 28 μm wide and 25 μm tall. To minimize pressure drop, this narrow region is only 250 μm long and connects to large microchannels 500 μm wide on both sides. To minimize extensional flow resulting from the 500 to 28 μm contraction, the channel walls follow a hyperbolic shape which maintains a lower maximal extensional strain rate compared to an abrupt or linear contraction. For extensional flow experiments, we use a cross-slot design with microchannels 42 μm wide and 25 μm tall. Linear contractions were used to allow for wider channels (500 μm wide) before and after the cross slot to reduce the device's pressure drop. The device was fabricated using 1 mm thick glass slides (for retardance experiments) or thin glass coverslips (for micro-particle tracking velocimetry) for the top and bottom surfaces. Inlet and outlet holes were drilled into the top glass surface and then both glass surfaces were functionalized with a 3-(trimethoxysilyl)-propyl methacrylate silane (98%; Sigma-Aldrich Inc.). A perfluoropolyether (PFPE) with urethane methacrylate end groups (Fluorolink MD700) was used to define the microchannel. Two different fabrication processes were used depending on whether the top and bottom surfaces were thick 1 mm glass slides or thin cover slips (Figure and). The thick 1 mm glass slides and chemical bonding of the solvent resistant PFPE to methacrylatefunctionalized glass was necessary to allow for a microfluidic device that could withstand both the high pressure and organic solvent swelling while maintaining optical transparency and preventing stress-induced birefringence of the glass windows. To make fluidic connections, 30 ga polytetrafluoroethylene tubing (0.012" ID x 0.030") was flanged and clamped against the drilled inlet/outlet ports using a Viton o-ring (Dash no. 001, Square profile). For more information on the microfluidic device fabrication see supplementary section S1.