Papers by Author: Ronald F. Ziolo

Abstract: The properties of polymer/semiconducting nanoparticle (NP) composites-materials used in hybrid, bulk-heterojunction photovoltaic materials-are dependent on the interaction of the NPs and polymer. Composite films of water soluble polymers and CdS NPs have been produced both by synthesizing the NPs within the polymer matrix and by adding the CdS NPs, containing a capping agent, to the polymer. The composites have been characterized by microscopy as well as 1H, 13C and 113Cd solid-state NMR. When synthesizing the NPs within the polymer, the polymer matrix plays a role in the cadmium sulfide NP nucleation, growth and structure. In the blended system, the dominant interaction between the glycerol capping agent and sulfonated polymer is observed to be hydrogen bonding.

Abstract: Piezoelectric fibrous membranes of barium titanate (BTO) – polyvinylidene fluoride (PVDF) nanocomposites were studied. BTO nanoparticles of about 40 nm were synthesized by the sol-gel method and mixed in PVDF–dimethyl formamide solutions at 0, 0.1, 1 and 3 wt.% relative to the polymer weight. The suspensions were electrospun using a horizontal set-up with an applied voltage of 15 kV. The samples were heat treated for 24 hours at 100°C in air to increase the crystallinity of the polymer. The heat treatment induced a phase transformation from α to β phase in the pure polymer sample, while the nanocomposite membranes did not undergo such phase transformation. It was found that the addition of nanoparticles affected not only the morphology and diameter of the fibers, but also the content of beta phase of the polymer. In order to pursue the crystallization of β phase, additional samples were prepared by surface modification of the BTO nanoparticles and the addition of tetraisopentyl ammonium chloride. The best results were obtained with the last additive, which lead to the crystallization of only β phase and a homogeneous fibrous morphology. All these aspects were strongly correlated and consequently, governed the ferroelectric behavior of the samples.

Abstract: New magnetic polyurethane nanocomposite foams have been synthesized by the one-shot method. The opened-cell soft foams contain a dispersion of uniformly sized nanocrystalline iron oxide prepared ex situ by the high temperature thermal decomposition of iron acetylacetonate in phenyl ether in the presence of oleic acid. The magnetic particles were dispersed in polyol by sonication prior to the reaction of the latter with isocyanate to produce the magnetic foams. A 7 wt% loading of iron oxide yielded a soft, flexible foam with a room temperature magnetization of 3.5 emu/g at one Tesla. Higher loadings of iron oxide are possible without destruction of the soft open-cell polyurethane structure. Physicochemical characterization of the foams will be presented along with magnetic and mechanical properties. Potential applications include smart materials such as magnetic shape memory foams, adhesive-free metal to foam seals, inductively coupled thermal foams and applications for conformable foams having a magnetic component such as healthcare products.

Abstract: Bromobenzenethiol passivated gold nanoparticles were mixed with a poly(phenylene ethynylene) bearing thioester flexible sequences in order to obtain a fluorescent composite for optical biosensors. The particles and the composite were characterized by 1H, 13C NMR, UV-Vis and fluorescence spectroscopy, TEM and STEM. The particles are homogeneously dispersed in the polymer matrix as observed by electron microscopy. The NMR spectra suggest that the gold particles and the poly(phenylene ethynylene) are probably interacting through the sulfur atoms of the –C(O)S- and –CH2-S-CH2- moieties of the flexible sequences of the polymer as well as through  interactions between the aromatic ring of 4-bromobenzenthiol and the conjugated backbone of pPET3OC12-sqS. The quantum yield of the composite both in solution and in solid state films is slightly lower than that of pPET3OC12-sqS because of the quenching effect of gold. Nonetheless, a change of the fluorescence intensity of the composite films can be detected as a consequence of the contact with microorganisms. Preliminary microbiological assays indicate an antimicrobial effect of the composite film with the E. coli bacteria.