Harry W. Rollins

Preparation of polymer-protected semiconductor nanoparticles through the rapid expansion of supercritical fluid solution

Abstract Poly( N -vinyl-2-pyrrolidone)-stabilized semiconductor cadmium sulfide nanoparticles with an average particle size of ∼33 A were prepared by using a new method based on the rapid expansion of supercritical solution. The nanoparticles were characterized by use of UV/Vis diffuse reflectance spectroscopy, powder X-ray diffraction, luminescence, and transmission electron microscopy methods.

Nanoscale metal sulfides in perfluorinatedionomer membranes

The preparation and characterization of nanoscale metal sulfide particles in perfluorinated ionomer membranes, including Nafion and those based on the sulfonimide ionomer and the bis(sulfonyl)methane ionomer, are reported. The results suggest that these membrane films all contain hydrophilic structural cavities and that the nanoscopic structures of the sulfonimide ionomer and bis(sulfonyl)methane ionomer membranes are quite similar to that of the commercial Nafion film. Properties of the nanoscale particles in the ionomer membranes are presented, and their implications for the understanding of membrane nanoscopic structural details are discussed.

Effects of photochemical reactions of pyrene in alcohol and aqueous solvent systems on spectroscopic analyses

Although pyrene is a popular fluorescent molecular probe in analytical and bioanalytical chemistry, its photostability is hardly understood. This paper reports a surprising finding that pyrene undergoes significant photochemical reactions in alcohol and aqueous solvents under the condition of exposing a sample solution to excitation irradiation in an emission spectrometer for a short period of time. The reactions yield at least two photoproducts, whose fluorescence spectra overlap severely with that of pyrene. Implications of pyrene photochemical reactions in alcohol and aqueous solvent systems to existing and future applications of pyrene as a fluorescent molecular probe are discussed.

Steady-state and time-resolved fluorescence spectroscopic probing of microstructures and properties of perfluorinated polyelectrolyte membranes

A systematic luminescence spectroscopic study of the microstructures and properties of Nafion®, the Dow Chemical films, and the newly synthesized sulfonimide ionomer membrane is reported. The strongly environment-sensitive luminescent probes 6-propionyl-2-(N,N-dimethylamino)naphthalene, 4-(N,N-dimethylamino)benzonitrile, pyrene, and ethidium bromide were used. The results suggest that the different perfluorinated ionomer membranes have generally similar properties with respect to the luminescent molecular probes and that the membrane structures consist of a substantial region that may be characterized as a heterogeneous mixture of water molecules and branches of the perfluorinated polymers. In addition, the effects of thermally stressing the ionomer membranes in an aqueous solution at temperatures up to 250°C on the properties of the membranes are evaluated and discussed.

Fluorescence spectroscopic probing of two distinctive microenvironments in perfluorinated ionomer membranes

Ethidium bromide was used as fluorescent molecular probe in the understanding of structural properties of Nafion, Dow Chemical, and sulfonimide ionomer membranes. The fluorescence lifetime results show that the probe is located in the interfacial region of the membrane structure, and that the interfacial region is inhomogeneous, consisting of two distinct subsections of different hydrophilicities. The ionomer membranes under consideration have similar structural properties with respect to the ethidium cation probing, despite the fact that their corresponding ionomers have different molecular structures. The fluorescence lifetime results also show that there are considerable mobilities throughout the interfacial region, which allow diffusional quenching processes. Finally, results of effects of hydrothermally stressing Nafion membrane at elevated temperatures on structural properties of the membrane are discussed.

Spectroscopic investigations of intramolecular and intermolecular excimers of 1,3-di(2-naphthyl) propane and methylnaphthalenes in supercritical carbon dioxide

Abstract Intramolecular excimer formation in 1,3-di(2-naphthyl)propane was studied spectroscopically in room-temperature solutions and in supercritical CO 2 . The results were compared with those of intermolecular excimer formation in l-methylnaphthalene and 2-methylnaphthalene under the same experimental conditions. The implication of the results to the concept of local concentration augmentation as a mechanism for the solute-solute clustering in supercritical fluids is discussed along with the known results of enhanced pyrene intermolecular excimer formation in supercritical CO 2 under near-critical conditions.

Similar Behavior Between Polyfullerenes and Charged Polymers. Extreme Polyelectrolyte Effects in Gel Permeation Chromatography Studies

Abstract Fullerene polymers with high fullerene contents were studied by use of gel permeation chromatography (GPC). Surprisingly, the polymer samples exhibit the chromatographic behavior that is characteristic of charged polymers. The extreme poly electrolyte effects observed for the fullerene polymers are rationalized in terms of localized charges in the polymer structures due to large polarizibilities of the polymeric fullerenes.

Ground state charge transfer complex of [84]fullerene and N,N-diethylaniline

The formation of the [84]fullerene–N,N-diethylaniline ground state charge transfer complex at different N,N-diethylaniline concentrations and temperatures has been studied by absorption spectroscopy and by use of a chemometric method principal component analysis to determine the absorption spectrum of the complex and the thermodynamic parameters of the C84 monomer–complex equilibrium.