We developed a new sensing motif for the detection and quantification of creatinine, which is an important small molecule marker of renal dysfunction. This novel sensor motif is based on our intelligent polymerized crystalline colloidal array (IPCCA) materials, in which a three-dimensional crystalline colloidal array (CCA) of monodisperse, highly charged polystyrene latex particles are polymerized within lightly cross-linked polyacrylamide hydrogels. These composite hydrogels are photonic crystals in which the embedded CCA diffracts visible light and appears intensely colored. Volume phase transitions of the hydrogel cause changes in the CCA lattice spacings which change the diffracted wavelength of light. We functionalized the hydrogel with two coupled recognition modules, a creatinine deiminase (CD) enzyme and a 2-nitrophenol (2NPh) titrating group. Creatinine within the gel is rapidly hydrolyzed by the CD enzyme in a reaction which releases OH(-). This elevates the steady-state pH within the hydrogel as compared to the exterior solution. In response, the 2NPh is deprotonated. The increased solubility of the phenolate species as compared to that of the neutral phenols causes a hydrogel swelling which red-shifts the IPCCA diffraction. This photonic crystal IPCCA senses physiologically relevant creatinine levels, with a detection limit of 6 microM, at physiological pH and salinity. This sensor also determines physiological levels of creatinine in human blood serum samples. This sensing technology platform is quite general. It may be used to fabricate photonic crystal sensors for any species for which there exists an enzyme which catalyzes it to release H(+) or OH(-).

A series of polybenzimidazoles (PBIs) incorporating main chain pyridine groups were synthesized from the pyridine dicarboxylic acids (2,4‐, 2,5‐, 2,6‐ and 3,5‐) and 3,3′,4,4′‐tetraaminobiphenyl, using polyphosphoric acid (PPA) as both solvent and polycondensation reagent. A novel process, termed the PPA process, has been developed to prepare phosphoric acid (PA) doped PBI membranes by direct‐casting of the PPA polymerization solution without isolation or re‐dissolution of the polymers. The subsequent hydrolysis of PPA to PA by moisture absorbed from the atmosphere usually induced a transition from the solution state to a gel‐like state and produced PA‐doped PBI membranes with a desirable suite of physiochemical properties. The polymer structure characterization included inherent viscosity (I.V.) determination as a measurement of polymer molecular weight and thermal stability assessment via thermogravimetric analysis. Physiochemical properties of the doped membrane were studied by measurements of the PA doping level, ionic conductivity and mechanical properties. The resulting pyridine‐based polybenzimidazole membranes displayed high PA doping levels, ranging from 15 to 25 mol of PA per PBI repeat unit, which contributed to their unprecedented high proton conductivities of 0.1 to 0.2 S cm–1 at 160 °C. The mechanical property measurements showed that the pyridine‐based PBI membranes were thermally stable and maintained mechanical integrity even at high PA doping levels. Preliminary fuel cell tests demonstrated the feasibility of the novel pyridine‐based PBI (PPBI) membranes from the PPA process for operating fuel cells at temperatures in excess of 120 °C without any external humidification.

Regioregular poly(3-hexylthiophene) (P3HT) produces thermoreversible gel in xylene. The gel is brownish-red in color. SEM and TEM studies indicate the presence of fibrillar network. WAXS and electron diffraction pattern indicate the presence of P3HT crystallites in the gel. The gels exhibit a first-order phase transition when heated in DSC. A time-dependent UV−vis study indicates that gelation in this system is probably accompanied by two different processes, e.g., (1) coil-to-rod transformation and (2) aggregation of rods to form the crystallites producing the gel. The gelation rate (t gel -1) measured from the test tube tilting method is analyzed using the equation t gel -1 = f(C) f(T), where f(c) = φ n , φ being the reduced overlapping concentration and n is an exponent. The average “n” value determined is 0.52, which indicates that three-dimensional percolation is a suitable model for this gelation. The gelation rate is analyzed according to the Flory−Weaver theory of coil-to-helix transition, and the free energy of activation (ΔF) for the coil-to-rod transformation is found to be 23.7 kcal/mol. It is also analyzed using the theory of fibrillar crystallization in solution, and the free energy of formation of critical size crystalline nucleus (ΔG*dil) is found to be 37.5 kcal/mol. The conductivity of the dried P3HT gel becomes enhanced by ∼10 times that of the cast film in the undoped state, but in the doped state there is an ∼50-fold increase.

Polyaniline (PANI) forms thermoreversible gels in four different sulfonic acids, e.g., dinonylnaphthalene sulfonic acid (DNNSA), dinonylnapthalene disulfonic acid (DNNDSA), (camphor-10-sulfonic acid (CSA), and dodecyl sulfonic acid (DSA), when made from the formic acid medium. The gelation behavior of 15% PANI-sulfonic acid (weight to weight) gels are reported here. The morphology, studied from the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), indicates the presence of fibrillar network structure in all of the systems. The thermal study of the gels indicates reversible first-order phase transition during both cooling and heating processes in a differential scanning calorimeter (DSC-7). The WAXS patterns of the gels are different from that of the PANI (EB) from and from each other. Sulfonic acid-subtracted FT-IR spectra of the gels indicate presence of new peaks due to gelation. From the WAXS, electron diffraction, and thermal investigations of the gels, it has been inferred that crystallization is the cause of gelation. The conductance of the gels have an order of 10 -2 to 10 -1 S/cm at 27 °C. A lamellar model for the gel structure, consisting of PANI layer and sulfonic acid layers, is used to explain the gel, and the thermoreversibility is believed to be due to the crystallization of the extended tails of the sulfonic acids under the doped condition.