Quantization on curved surfaces

After a short review of the existing methods for quantization of curved manifolds, the free particle motions or the so‐called geodesic flows on axisymmetrical prolate and oblate ellipsoids are quantized using the isomorphism established by Neumann of these systems and the harmonic oscillator restricted to the unit sphere. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

From the plateau problem to periodic minimal surfaces in lipids,surfactants and diblock copolymers

A novel method is presented for generating periodic surfaces. Such periodic surfaces appear in all systems which are characterized by internal interfaces and which additionally exhibit ordering. One example are systems of AB diblock copolymers, where the internal interfaces are formed by the chemical bonds between the A and B blocks. In these systems at least two bicontinuous phases are formed: the ordered bicontinuous double diamond phase and the gyroid phase. In these phases the ordered domains of A monomers and B monomers are separated by a periodic interface of the same symmetry as the phases themselves. Here we present a novel method for the generation of such periodic surfaces based on the simple Landau-Ginzburg model of microemulsions. We test the method on four known minimal periodic surfaces, find two new surfaces of cubic symmetry, and show how to obtain periodic surfaces of high genus and n-tuply continuous phases (n > 2). So far only bicontinuous (n = 2) phases have been known. We point out that the Landau model used here should be generic for all systems characterized by internal interfaces, including the diblock copolymer systems.     

Methylsilylation of highly dispersed graphite surfaces

The chemisorption of hexamethyldisilazane on the surface of a highly dispersed graphite has been studied. It was shown that with increase in the reaction temperature, the amount of the grafted trimethysilyl groups increases. The characteristic features of the formation of the trimethylsilyl coating have been discussed on the basis of the data on the thermodesorption of water, carbon oxides and methane from graphite surfaces with mass-spectrometric monitoring.Deceased.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 184–186, March–April, 1992.     

Classification of hypothetical doubly and triply periodic porous graphitic structures by tilings of neck-like units

In this study, we extend the concept of constructing high-genus fullerenes with neck-like structures to the classification of a wide family of doubly periodic graphitic structures. The neck structures are obtained by peeling the outer (positively curved) part of a toroidal carbon nanotube off, meanwhile leaving the central hole unchanged. A doubly periodic structure is then characterized by the original tiling and the shape of the necks used. Through the consideration of the coloring problem of uniform tilings, a systematic method of constructing similar structures with periodicities along all three dimensions is developed. The P type Schwarzite, extensively studied in the literature, can be classified within the scheme if the shape of the necks is carefully chosen.     

Contact angles of drops on curved superhydrophobic surfaces

Superhydrophobic surfaces have contact angles that exceed 150 degrees and are known to reduce surface fouling, protect surfaces, and improve liquid-liquid separations. Electrospun sub-micron fiber mats can perform as superhydrophobic surfaces. Superhydrophobic behavior is typically measured on planar surfaces, whereas applications may require curved surfaces. This paper discuses the measurement of water contact angles of fiber mats formed on cylindrical surfaces to create superhydrophobic behavior on curved surfaces. Equations are derived that relate the radius of curvature of spherical and cylindrical surfaces and drop size to the observed contact angle on the curved surfaces. Calculations from the equations agree well with experimental observations on spherical surfaces reported in literature and on cylindrical surfaces created in our lab.     

Molecular electrostatic potential devices on graphite and silicon surfaces

We demonstrate that molecular gates using molecular electrostatic potentials (MEP) can be used on hydrogen-passivated silicon substrates without any disturbance of their behavior in vacuum; however, the use of graphite as a substrate strongly affects such behavior. As expected, the substrate may become one more design variable. The ability to have several substrate alternatives is very important for the practical implementation of this new scenario based on molecular potentials. In general, the effect of the substrate can be predetermined by calculating the MEP of the surface as this indicates how strongly its intrinsic potential is.     

Drop shape visualization and contact angle measurement on curved surfaces

The shape and contact angles of drops on curved surfaces is experimentally investigated. Image processing, spline fitting and numerical integration are used to extract the drop contour in a number of cross-sections. The three-dimensional surfaces which describe the surface-air and drop-air interfaces can be visualized and a simple procedure to determine the equilibrium contact angle starting from measurements on curved surfaces is proposed. Contact angles on flat surfaces serve as a reference term and a procedure to measure them is proposed. Such procedure is not as accurate as the axisymmetric drop shape analysis algorithms, but it has the advantage of requiring only a side view of the drop-surface couple and no further information. It can therefore be used also for fluids with unknown surface tension and there is no need to measure the drop volume. Examples of application of the proposed techniques for distilled water drops on gemstones confirm that they can be useful for drop shape analysis and contact angle measurement on three-dimensional sculptured surfaces.     

Modulated pattern formation of phospholipid monolayers on curved surfaces

Langmuir-Blodgett transfer of a dipalmitoylphosphatidylcholine monolayer onto macroscopically curved mica surfaces results in microscopic patterns of the transferred monolayer that differ from those of films transferred onto a flat mica substrate. On curved surfaces a modulated horizontal striped pattern evolves that has a zigzag boundary at the liquid condensed front of the stripe and a continuous straight boundary at the liquid condensed rear. We propose that the sensitivity of the pattern to the macroscopic curvature of the sample is due to a flow-controlled hydrodynamic instability caused by the subphase flow close to the three-phase contact line.     

Bonding of atomic phosphorus to polycyclic hydrocarbons and curved graphitic surfaces

We present a theoretical study of the bonding of atomic phosphorus to planar hydrocarbons and to curved graphite-like surfaces. We find that bonding of phosphorus to planar polycyclic hydrocarbons induces curvature away from the phosphorus atom, as defined by the pyramidalization angle. Similarly, bonding of atomic phosphorus to the [5,5] fulvalene-circulene semifullerene and buckminsterfullerene is only possible on the convex side of the carbon surface. On the other hand, we find the interaction of atomic phosphorus with the concave side of fullerene-like surfaces to be nonbonding for both quartet and doublet spin states. We find the prerequisite for stable epoxy-type bonds within these systems is the ability of the carbon atoms to maintain or induce curvature away from the P.C=C bond.     

Modeling liquid crystal bilayer structures with minimal surfaces

This paper describes a new convenient and accurate method of calculating x-ray diffraction integrated intensities from detailed cubic bilayer structures. The method is employed to investigate the structure of a particular surfactant system (didodecyldimethylammonium bromide in a solution of oil and heavy water), for which single-crystal experimental data have recently been collected. The diffracted peak intensities correlate well with theoretical structures based on mathematical minimal surfaces. Optimized electron density profiles of the bilayer are presented, providing new insight into key features of the bilayer structure.     

The synthesis of curved and linear structures from a minimal set of monomers

[reaction: see text] Spiro-ladder oligomers of designed shape were assembled from a set of two enantiomeric bis-amino acid monomers. Two tetramers of differing monomer sequence were synthesized to study the effect of monomer stereochemistry upon macromolecular shape. Two-dimensional NMR experiments were used to determine the conformational preference of the monomers within the context of the oligomers. The results of this structural study were used to design two pentamers: one resembling a rod and another with a curved shape. The pentamers were end-labeled with naphthyl and dansyl groups. The design hypothesis was confirmed by measuring the efficiency of fluorescence resonance energy transfer between the naphthyl and dansyl fluorophore pair.     

Recent advances in the use of curved single crystal surfaces

In surface science, research traditionally employs macroscopically flat surfaces of single crystals. Curved surfaces have been applied more sporadically, but their history stretches back for many decades. Realization of the potential benefits and practical applications in surface physics and surface chemistry research progressed slowly in the 20th century. In more recent decades, research employing partial cylinders and dome-shaped crystals have found renewed interest. Modern surface sensitive techniques are being employed allowing the inherent large range of surface structures to reveal new insights. We briefly review the history, describe several types of surfaces and the range of structures they contain, suggest a notation for common types of curved surfaces, and discuss recent studies in more detail. We mainly focus on metal samples. We close with a short outlook.     

Ionization of water clusters by collisions with graphite surfaces

We present experimental results on the scattering of neutral water clusters from graphite surfaces. We use cluster beams with an average cluster size up to 3700 molecules and an incident velocity of 1300 m/s, and study the emission of negatively and positively charged cluster fragments from the surface. The ionization probability is found to depend on cluster size and surface temperature, and for a given mean cluster size the emission rate of positive and negative cluster ions follows the Arrhenius equation. In the surface temperature range 950–1450 K, activation energies of 0.52±0.02 and 3.1±0.3 eV are determined for the emission of positive and negative ions, respectively. The emission of negative cluster fragments is attributed to electron transfer from the surface, and we estimate an electron affinity of 1.4±0.3 eV for large water clusters. Positive cluster fragments are proposed to be formed by dissocative ionization inside the cluster, followed by removal of the negative ion during surface contact.     

Adhesion between graphite and modified polyester surfaces: a theoretical study

This study examines the adhesion of graphite to functionalized polyester surfaces using a range of qualitative and quantitative measures of theoretical adhesion. Modifications to the polyester surfaces include the addition of hydroxyl, carboxyl, or fluorine substituents with coverages of 0.4 and 0.9 groups per nm(2). In each case, the introduction of substituents to the surface of the polyester was calculated to lead to reduced adhesion to graphite. Effects of surface relaxation on adhesion are studied by employing different simulation protocols. The theoretical results suggest one mechanism to reduce adhesion to carbonaceous solids is to increase atomic roughness using strongly hydrophilic or alternatively strongly hydrophobic substituents.     

The activity of dispersed oxides on natural and exfoliated graphite surfaces

Experimental data obtained indicate that ion exchange on the graphite surface can be attributed to impurity oxides. During exfoliated graphite oxidation reactions, inorganic oxides act as catalysts (Fe₂O₃, Cr₂O₃), inhibitors (B₂O₃, Al₂O₃) or are inert.     

Scaling aspects of block co-polymer adsorption on curved surfaces from nonselective solvents

In this paper, we have developed a geometric-based scaling model that describes the adsorption of diblock copolymer chains from good solvents and theta-solvents onto reactive surfaces of varying curvatures. To evaluate the impact of particle size on the adsorption process, we probed the adsorption of poly(styrene-b-methymethacrylate) (PS-PMMA) diblock copolymers from solvents with different degrees of selectivity on aluminum oxide (Al(2)O(3)) surfaces belonging to particles of different sizes. When the adsorbed PMMA layer is dense enough (in the case of a theta-solvent for the PMMA block), our results show good correlation between the theory and experimental results, pointing to the formation of a PMMA adsorption layer and a brushlike PS layer. Conversely, when adsorption occurs from a nonpreferential solvent, particularly on particles with high curvature, the PMMA adsorption layer at the surface becomes less dense and the grafted PS moiety exhibits a transitional morphology consisting of several layers of increasingly sparsely spaced blobs.     

Synthesis and structure of triply bridged purinophanes

The title compounds were synthesized as a model for studying the relationship between the hypochromism and the stacking mode of two purine rings. By comparing 1 with other purinophanes it was concluded that the fully overlapped orientation of two purine rings gives the largest hypochromicity.