Janos H. Fendler

CHARACTERIZATION OF FERROELECTRIC LEAD ZIRCONATE TITANATE FILMS BY SCANNING FORCE MICROSCOPY

Scanning force microscopy (SFM) has been used for the determination of friction, phase transformation, piezoelectric behavior (in the contact mode), polarization state, and dielectric constant (in the noncontact mode) of nanometer regions of lead zirconate titanate (PZT) films. The use of the SFM tip in the contact mode, to polarize different nanoregions of the PZT film and to apply an oscillating field thereon, led to effective piezoelectric coefficients and piezoelectric loops. The measured effective piezoelectric coefficient was shown to depend appreciably on both the tip contact force and the quality of the tip-to-film electrical contact. In the noncontact mode, application of an ac signal (with a frequency ω) across the tip—PZT film—electrode system produced an oscillation of the tip at frequencies ω (fundamental or first harmonic) and 2ω (second harmonic). The signals at ω and 2ω were related to the state of polarization and the dielectric constant of the PZT film, respectively. Analysis of the comb...

Spreading of hydrophobic silica beads at water—air interfaces

Abstract Structured monoparticle layers, formed from 3 ± 1 μm diameter silica beads silylated to a greater (sample A) and a lesser (sample B) extent, have been investigated on water and on aqueous 1.0 M NaCl subphases in a Langmuir film balance. Hydrophobicities corresponding to the different extents of silylation were estimated by determining the wettabilities of identically treated 10 ± 1 μm silica beads. The advancing water contact angles of 98 ± 4° and 76 ± 4° have been calculated for samples A and B respectively. Visual observations of spreading and redispersity, and determinations of surface pressure—surface area isotherms, hysteresis and contact cross-sectional areas led to the assessment of the structural strengths of these two sets of silica beads. Appreciably stronger attractive interactions between neighboring silica beads have been found in structured monoparticle layers prepared from sample A than those formed from sample B. The less hydrophobic silica beads (sample B) were postulated to be separated from each other by a layer of water molecules in the structured monoparticle layer. This postulate has been supported by calculating the total interparticle interaction energies by applying the DLVO theory. Introduction of 1.0 M NaCl did not appreciably affect the behavior of structured monoparticle layers prepared from sample A. Significant creasing was observed, however, in the vicinity of the moving barrier upon the compression of structured monoparticle layers prepared from sample B.

Nanoparticles at air/water interfaces

Spreading of surfactant-coated metallic, semiconducting, magnetic and ferroelectric nanoparticles on water surfaces results in the formation of monoparticulate thick films which can be transferred, layer by layer, to solid substances. This technique of thin film formation, in turn, has led to advances in the formation of ultrathin films with potential applications in advanced electronic and electro-optical devices.

Cadmium sulfide particles in organomontmorillonite complexes

Abstract Cadmium sulfide (CdS) particles have been generated by the infusion of hydrogen sulfide into cadmium-salt-containing organomontmorillonite complexes dispersed in ethanol—water, ethanol—benzene and ethanol—cyclohexane mixtures. Montmorillonites ion exchanged to different extents by octadecylammonium and hexadecylpyridinium salts have been used as organomontmorillonite complexes. CdS formation has been examined as a function of the extent of surfactants present in the organomontmorillonite complexes, the composition of the solvents, and the concentration and type of cadmium salts used. Absorption and emission spectrophotometry, differential thermal analysis, dynamic laser light scattering and X-ray diffractometry have been utilized for monitoring CdS formation.

Biomineralization inspired preparation of nanoparticles and nanoparticulate films

Abstract Biomineralization inspired preparation of nanoparticles and nanoparticulate films is illustrated here by the in situ generation of nanoparticles under monolayers; the formation of nanoparticles in the aqueous pools of reversed micelles; and the self-assembly of ultrathin films composed of alternating layers of oppositely charged polyelectrolytes and nanoparticles.

Preparation, characterization, and photocatalytic properties of layered-silicate-supported TiO2 and ZnO nanoparticles

TiO2 nanoparticles were prepared in 2-propanol and in water from titanium alkoxide, and ZnO nanoparticles were formed from aqueous ZnCl2 either in situ in sodium montmorillonite and in synthetic hectorite or, alternatively, were incorporated into the silicate lamellas. Transmission electron microscopy (TEM), X-ray diffraction, and Brunauer—Emmett—Teller measurements were used to establish the incorporation of semiconductor nanoparticles into the interlamellar space of the clays. The average particle diameter of the nanoparticles, determined by TEM, ranged between 4 and 14 nm. The photocatalytic activity of TiO2, intercalated into montmorillonite, for salicylic acid photooxidation was determined to be better than that elicited by TiO2 alone.

Anisotropic aggregates as the origin of magnetically induced dichroism in ferrofluids

Static and dynamic polarized and depolarized light scattering, static, and time‐resolved dichroic anisotropy, as well as conventional magnetization versus applied magnetic field determinations have been carried out on aqueous commercial ferrofluids and on surfactant aggregate stabilized Fe3O4 in aqueous solution. Over a dilution range of more than three orders of magnitude there is no evidence for field‐induced cooperative effects. The shape of the dichroic anisotropy versus applied field curve superimposes virtually exactly onto the magnetization curve. Rotational and translational diffusion coefficients indicate ellipsoidal magnetic aggregates with average minor to major axial ratios around 0.33 and major axis of 285 nm, which are insensitive to dilution, and far above the expected value of around 10 nm. Electron micrographs have revealed polydisperse clusters of around 150 nm composed of particles with sizes on the order of 10 nm. The scattered intensity autocorrelation curve shows no appreciable chang...

Potential of membrane-mimetic polymers in membrane technology

Abstract Development of new generations of membranes with high degrees of permeabilities and controllable mass transport properties requires a fundamental understanding of the relationship between molecular structures and permeabilities. Initiation of interdisciplinary research in biology, biophysics, polymer and colloid chemistry is proposed to provide the insight to membrane transport processes at the molecular level. Mother natures most talented transporter — the biological membrane — should inspire this endeavor. Following a survey of the properties of, and recognized transport mechanisms in, biomembranes, membrane-mimetic chemistry is introduced to serve as a bridge between biological and polymeric membranes. Surfactant aggregates — micelles, monolayers, organized multilayers (Langmuir—Blodgett films), bilayer lipid membranes (BLMs), vesicles and polymerized vesicles — are shown to be the media in membrane-mimetic chemistry. Properties of these organized surfactant assemblies are summarized. Emphasis is placed on the control of molecular transport in membrane-mimetic systems. Perspectives and prospectives of biomimetic membranology are discussed.

Distribution of functional groups grafted onto an ethylene-propylene copolymer

A theoretical model, based on the binomial (Bernoullian) distribution function, was employed for the prediction of functional group distribution in an ethylene-propylene copolymer randomly grafted by maleic anhydride. Using the experimentally determined graft level and molecular weight distribution function, the fraction of polymer molecules with given number of functional groups was calculated. The result was checked experimentally by a fluorescence method based on the excimer formation of pyrene fluorophores attached to the anhydride pendants. The time-resolved fluorescence from the pyrene-labeled copolymer yielded the fraction of polymer molecules with a single functional group. The fraction of singly labeled molecules was compared to the calculated functional group distribution and a reasonable agreement was found between the two. The distribution of grafted maleic anhydride was found to be apparently random among polymer molecules. The distribution of distances was calculated between randomly attached consecutive functional groups along the polymer backbone also. The result indicated that the distance distribution function (similar to a decaying exponential) is dominated by short distances.

In situ imaging of CdS and ZnS semiconductor particles in surfactant vesicles

Abstract The study of synthetic vesicles and micelles as organized media for photoelectron conversion, molecular electronics, and catalysis is an area of intensive research. In this regard, the study of semiconductor systems is particularly prominent. However, to date there has been no direct evidence for the location of these particles within the organized organic phase. Using a combination of dark field imaging, electron diffraction, and energy dispersive X-ray analysis, we have been successful in determining the structures and morphologies of in situ precipitated, coprecipitated, and sequentially precipitated colloidal CdS and ZnS on the surfaces of dihexadecyl phosphate vesicles. The precipitated particles have diameters in the range of 2–8.5 nm and cubic Zn-blende structures. Nucleation of the particles takes place at the phospholipid headgroups and particle aggregation is inhibited at the organic surface. The results provide information, for the first time, on the crystal chemical nature of these nanometer-size semiconductor particles studied in situ in the presence of an organic phase.