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Kim B.-G.,Macromolecular Science and Engineering | Park H.J.,Macromolecular Science and Engineering | Guo L.J.,Macromolecular Science and Engineering | Kim J.,Macromolecular Science and Engineering | Kim J.,University of Michigan
ACS Applied Materials and Interfaces | Year: 2011

To investigate the structure-dependent aggregation behavior of conjugated polymers and the effect of aggregation on the device performance of conjugated polymer photovoltaic cells, new conjugated polymers (PVTT and CN-PVTT) having the same regioregularity but different intermolecular packing were prepared and characterized by means of UV-vis spectroscopy and atomic force microscopy (AFM). Photovoltaic devices were prepared with these polymers under different polymer-aggregate conditions. Polymer aggregation induced by thermal annealing increases the short circuit current but provides no advantage in the overall power conversion efficiency because of a decrease in the open circuit voltage. The device fabricated from a pre-aggregated polymer suspension, acquired from ultrasonic agitation of a conjugated polymer gel, showed enhanced performance because of better phase separation and reduced recombination between polymer/PCBM. © 2011 American Chemical Society.

Lee J.,Macromolecular Science and Engineering | Kim J.,Macromolecular Science and Engineering | Kim J.,University of Michigan
Chemistry of Materials | Year: 2012

A novel fabrication method of monophasic, biphasic, and triphasic alginate microparticles having sensory polydiacetylene (PDA) liposomes has been developed to achieve selective and more sensitive multitargeting detection in solution. In this alginate microparticle based detection system, the sensory PDA liposomes are concentrated in the particles rather than being diluted in a solution, which is the case of a conventional solution based detection system, providing superior sensitivity and stability. The biphasic nature of the alginate microparticles was realized by coinjecting two different PDA liposome/alginate mixture solutions into a CaCl 2 solution using a simple combined needle injection system. The size and the constituent of the Janus particles and the extended triphasic particles could be independently manipulated by controlling a centrifugal force and formulating the composition of the PDA liposome solutions, respectively. The multitargeting capability of such mutiphasic alginate particles was demonstrated by fluorescence microscopy. The presented particle-based detection system has a great potential to be combined with a microfluidic device for the development of advanced biosensors having a high throughput screening capability. © 2012 American Chemical Society.

Abidian M.R.,University of Michigan | Corey J.M.,University of Michigan | Kipke D.R.,University of Michigan | Martin D.C.,Macromolecular Science and Engineering | Martin D.C.,University of Delaware
Small | Year: 2010

An in vitro comparison of conducting-polymer nanotubes of poly (3,4-ethylenedioxythiophene) (PEDOT) and poly (pyrrole) (PPy) and to their film counterparts is reported. Impedance, charge-capacity density (CCD), tendency towards delamination and neunte outgrowth are compared. For the same deposition charge density, PPy films and nanotubes grow relatively faster vertically, while PEDOT films and nanotubes grow more laterally. For the same deposition charge density (1.44C cm-2), PPy nanotubes and PEDOT nanotubes have lower impedance (19.5±2.1 kΩ for PPy nanotubes and 2.5 ± 1.4 kΩ for PEDOT nanotubes at 1 kHz) and higher CCD (184 ± 5.3 mCcm-2 for PPy nanotubes and 392 ± 6.2 mC cm-2 for PEDOT nanotubes) compared to their film counterparts. However, PEDOT nanotubes decrease the impedance of neural-electrode sites by about two orders of magnitude (bare iridium 468.8 ± 13.3 kΩ at 1 kHz) and increase capacity of charge density by about three orders of magnitude (bare iridium 0.1 ± 0.5 mC cm-2). During cyclic voltammetry measurements, both PPy and PEDOT nanotubes remain adherent on the surface of the silicon dioxide while PPy and PEDOT films delaminate. In experiments of primary neurons with conducting-polymer nanotubes, cultured dorsal root ganglion expiants remain more intact and exhibit longer neuntes (1400 ± 95 μm for PPy nanotubes and 2100 ± 150 μm for PEDOT nanotubes) than their film counterparts. These findings suggest that conducting-polymer nanotubes may improve the long-term function of neural microelectrodes. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

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