In situ monitoring of sorption and drying of polymer films and coatings: self-referencing, nearly temperature-independent fluorescence sensors

Ionomers From Kraft Lignin for Renewable Energy Applications

Converting industrial/agricultural lignin-rich wastes to efficient, cost-effective materials for electrochemical devices (e.g., fuel cells) can aid in both bio- and energy economy. A major limitation of fuel cells is the weak ion conductivity within the ~2-30-nm thick, ion-conducting polymer (ionomer)-based catalyst-binder layer over electrodes. Here, we strategically sulfonated kraft lignin (a by-product of pulp and paper industries) to design ionomers with varied ion exchange capacities (IECs) (LS x; x = IEC) that can potentially overcome this interfacial ion conduction limitation. We measured the ion conductivity, water uptake, ionic domain characteristics, density, and predicted the water mobility/stiffness of Nafion, LS 1.6, and LS 3.1 in submicron-thick hydrated films. LS 1.6 showed ion conductivity an order of magnitude higher than Nafion and LS 3.1 in films with similar thickness. The ion conductivity of these films was not correlated to their water uptake and IECs. Within the three-dimensional, less dense, branched architecture of LS 1.6 macromolecules, the -SO3H and -OH groups are in close proximity, which likely facilitated the formation of larger ionic domains having highly mobile water molecules. As compared to LS 1.6, LS 3.1 showed a higher glass transition temperature and film stiffness at dry state, which sustained during humidification. On the contrary, Nafion stiffened significantly upon humidification. The smaller ionic cluster within stiff LS 3.1 and Nafion films thus led to ion conductivity lower than LS 1.6. Since LS x ionomers (unlike commercial lignosulfonate) are not water soluble, they are suitable for low-temperature, water-mediated ion conduction in submicron-thick films.

Effect of a silica nanofiller on the structure, dynamics and thermostability of LDPE in LDPE/silica nanocomposites

Study of molecular interactions and dynamics in LDPE–silica nanocomposites using FTIR spectroscopy.

Detection of amines with extended distyrylbenzenes by strip assays

We herein describe the synthesis and property evaluation of three novel aldehyde-substituted pentameric phenylenevinylenes carrying branched oligo(ethylene glycol) (swallowtail, Sw) substituents. The targets were synthesized by a combination of Heck coupling and Wittig or Horner reactions of suitable precursor modules. If the pentameric phenylenevinylene carries only two of these Sw substituents, it is no longer water-soluble. When six of the Sw substituents are attached, regardless of their position, the pentameric phenylenevinylenes are well water-soluble. The dialdehydes were investigated with respect to their amine-sensing capabilities both in water as well as in the solid state, sprayed onto thin layer chromatography (TLC) plates (alox, silica gel, reversed phase silica gel). The recognition of amine vapors using the sprayed-on phenylenevinylene dialdehydes is superb and allows the identification of different amines on regular silica TLC plates via color changes, analyzed by a statistical tool, the multivariate analysis of variance (MANOVA) protocol.

Humidity effects on the wetting characteristics of poly(N-isopropylacrylamide) during a lower critical solution transition

Poly(N-isopropylacrylamide) (PNIPAM) is expected to find utility in tissue engineering and drug delivery, among other biomedical applications. These applications capitalize on the intrinsic lower critical solution temperature (LCST) of the polymer: below the LCST, enthalpic gain from intermolecular hydrogen bonding between PNIPAM and water molecules dominates the solvation; above the LCST, entropic effects resulting from the intramolecular hydrogen bonding between the carboxyl and amide groups of PNIPAM lead to water expulsion. The dependence of the LCST upon the molecular weight, solvent, and solution activity (i.e., solute concentration) has been studied extensively. However, what has not been previously explored is the effect of humidity on the characteristic properties of the polymer. Herein, we show that the relative humidity affects the water adsorption dynamics of PNIPAM as well as the magnitude of the transition that occurs at the LCST of the polymer. In short, the magnitude of the LCST transition decreases with an increasing relative humidity, and the time period over which adsorption occurs decreases with the temperature.

Antiplasticization and Water Uptake of Nafion Thin Films

Fluorescence of 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) was measured to probe the local motion within 70-600 nm thick Nafion films at controlled levels of hydration. Thinner films showed increased confinement under dry conditions as evidenced by their high fluorescence intensity values per unit thickness. Antiplasticization, or a stiffening of the film, was observed as an increase in fluorescence intensity when the sample was exposed to low water activity (≤30% RH) and the extent of antiplasticization changed with film thickness. At higher relative humidities, the films became plasticized with water and the fluorescence of CCVJ declined. Quartz crystal microbalance (QCM) experiments revealed higher hydration numbers (λ = nH₂O/nSO₃H) in thinner films on SiO₂ surfaces. The higher water uptake in thin films was explained by considering the polymer order at the Nafion-SiO₂ interface and the influence of this interfacial layer on the swelling properties of thin films.