Smaller Surface Energy Research Articles

Interface behavior of Mn/PbTe(111) studied by scanning tunneling microscopy and X-ray photoemission spectroscopy

Mn overlayers growth on PbTe(111) have been investigated by using scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS). The strong chemical interactions were found during the formation of Mn/PbTe(111) interface. At the initial deposition of Mn, one part of Mn adatoms substitute Pb atoms on the PbTe(111) surface, forming a (√3 × √3)R30° MnTe phase, and the other part of Mn adatoms, together with the kicked-out Pb atoms, nucleate at the boundaries of the MnTe islands, forming loop islands around the MnTe islands as an intermediate state. Finally, they develop into regular 3D Pb capped Mn islands upon further Mn deposition. For Mn growth on the PbTe surface where Pb atoms are almost completely substituted by Mn, the deposited Mn atoms either cooperate into the 3D Pb capped Mn islands promoting the upright growth of the 3D Pb capped Mn islands, or nucleate and grow on the MnTe superstructure areas. Free Pb layer always floats on the top of surface, indicating that Pb layer has smaller surface energy, and Mn adatoms always exchange the positions with the underneath Pb atoms during the growth.

Liquid crystal alignment properties of polystyrene derivatives containing fluorinated side groups

The liquid crystal (LC) alignment properties of a series of polystyrene derivatives containing various fluorinated side chain terminal moieties, such as 4-fluorophenoxymethyl, 3,4,5-trifluorophenoxymethyl, pentafluorophenoxymethyl, and 4-trifluoromethoxyphenoxymethyl groups, were investigated. These polymers could induce homeotropic and/or homogeneous planar LC alignment on their surfaces by changing the LC molecules and rubbing conditions. For example, when a positive (MJ001929 from Merck) and negative dielectric anisotropic LC mixture (MLC-7026-000 from Merck) were used, homeotropic LC alignment was observed in the LC cells made from unrubbed films of pentafluorophenoxymethyl- and 4-trifluoromethoxyphenoxymethyl-substituted polystyrenes with a smaller surface energy, whereas random planar LC alignment was observed in those made from the other polymers with a larger surface energy. On the other hand, homeotropic LC alignment behavior was observed in all the LC cells made from unrubbed films of all the polystyrene derivatives when 5CB was used as the LC material.

Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

Ab initio restricted Hartree‐Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter) that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001)‐(1 × 1) surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.

Competitive protein adsorption on biomaterial surface studied with reflectometric interference spectroscopy

Reflectometry interference spectroscopy (RIfS) is known as a highly sensitive and robust technique for direct, label-free detection of the interaction of biomacromolecules in real time and in situ. The aim of the present study was to investigate the competitive protein adsorption on the surface of fluorocarbon end-capped poly(carbonate) urethane (PCUF) and polystyrene (PS) based on the RIfS method. The surface energy and microstructures of PCUF and PS were characterized by contact angle measurement and atomic force microscopy. Interfacial energies between these surfaces and the proteins were then calculated. The protein adsorption experiments were carried out with both single solution and ternary solutions composed of albumin, fibrinogen and immunoglobulin-G (IgG). The results of surface characterization showed that PCUF was more hydrophilic than PS with a smaller surface energy, and micro-phases separation of PCUF was observed. RIfS analysis results revealed that more albumins, less fibrinogen and IgG were detected on the PCUF surface compared with PS after simplex and competitive protein adsorption, which indicated that PCUF had a preferential adsorption for albumin. The special morphology, smaller surface energy and calculated interfacial energies between PCUF and proteins may be responsible for the better blood compatibility of PCUF compared to PS. The results suggest that RIfS could serve as a novel, effective method for studying the competitive protein adsorption on biomaterial surfaces.

Quantitative Analysis of the Stability of Pd Dendrimer-Encapsulated Nanoparticles

The stability of Pd dendrimer-encapsulated nanoparticles (DENs) in air-, N(2)-, and H(2)-saturated aqueous solutions is reported. The DENs consisted of an average of 147 atoms per sixth-generation, poly(amidoamine) dendrimer. Elemental analysis and UV-vis spectroscopy indicate that there is substantial oxidation of the Pd DENs in the air-saturated solution, less oxidation in the N(2)-saturated solution, and no detectable oxidation when the DENs are in contact with H(2). Additionally, the stability improves when the DEN solutions are purified by dialysis to remove Pd(2+)-complexing ligands such as chloride. For the air- and N(2)-saturated solutions, most of the oxidized Pd recomplexes to the interiors of the dendrimers, and a lesser percentage escapes into the surrounding solution. The propensity of Pd DENs to oxidize so easily is a likely consequence of their small size and high surface energy.

Comb-Like Fluorinated Polystyrenes Having Different Side Chain Interconnecting Groups

Comb-like fluorinated polystyrenes with different side chain interconnecting groups between backbone and side chain, such as ether (PST−O), thioether (PST−S) and sulfone (PST−SO2), were synthesized in order to examine the effect of the interconnecting groups on the surface order and properties. Near edge X-ray absorption fine structure spectroscopy and grazing incidence wide-angle X-ray diffraction showed that PST−SO2 with very polar sulfone groups exhibited a lower tilt angle of the fluorinated helix to the surface normal as well as higher packing density of fluorinated alkyl side chains than PST−O and PST−S, which have less polar groups. As a result of the ordered structure at the polymer-air interface, PST−SO2 has a smaller surface energy and better stability in water than PST−O and PST−S. These results suggest that the introduction of polar groups to the side chains of comb-like fluorinated polymers can improve the surface properties including the hydrophobicity and stability of fluorinated surfaces.

Surface modification of Lexan treated by RF plasma

Lexan is normally characterized by low hardness, poor adhesion on SiO 2 and small surface energy. In this work, the effect of argon RF plasma (13.6 MHz) with various treatment times (1–10 min) on the wettability, hardness, crystallinity, thermal stability and the surface energy of Lexan is investigated using thermogravimetric analysis (TGA), X-ray diffraction analysis (XRD) and contact angle measurement.

Microstructure and dielectric properties of ferroelectric barium strontium titanate ceramics prepared by hydrothermal method

Ba x Sr1-x TiO3, nanoparticles with different Ba compositions were synthesized by a hydrothermal method. The mechanism of hydrothermal reactions was discussed based on DTA/TG, XRD and TEM characterizations. The result showed that perovskite structure was developed through the mutual diffusion between the intermediate phases and TiO2 phase. The grain size of the Ba0.77Sr0.23TiO3 (BST77) powders was about 20–40 nm. BST ceramics were made from the hydrothermal-derived BST powders and the dielectric properties of the BST ceramics were measured. Due to the small grain size and active surface energy of the BST powders prepared by hydrothermal method, the BST ceramics showed low sintering temperature. It was found that the BST77 ceramics sintered at 1280 °C showed dielectric constant peak dispersion which was believed to be caused by dimension domino effect.

Preparation and Characterization of Nano‐TATB Explosive

AbstractNano‐TATB was prepared by solvent/nonsolvent recrystallization with concentrated sulfuric acid as solvent and water as nonsolvent. Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) were used to characterize the appearance and the size of the particles. The results revealed that nano‐TATB particles have the shape of spheres or ellipsoids with a size of about 60 nm. Due to their small diameter and high surface energy, the particles tended to agglomerate. By using X‐ray powder diffraction (XRD), broadening of diffraction peaks and decreasing intensity were observed, when the particle sizes decreases to the nanometer size range. The corrected average particle size of nano‐TATB was estimated using the Scherrer equation and the size ranged from 27 nm to 41 nm. Furthermore, the specific surface area and pore diameter of nano‐TATB were determined by BET method. The values were 22 m2/g and 1.7 nm respectively. Thermogravimetric (TG) and Differential Scanning Calorimetric (DSC) curves revealed that thermal decomposition of nano‐TATB occurs in the range of 356.5 °C–376.5 °C and its weight loss takes place at about 230 °C. Furthermore, a slight increase in the weight loss was observed for nano‐TATB in comparison with micro‐TATB.

A new theoretical approach to the thermodynamic calculation of high-temperature oxidation of Ni-Cr alloys

In calculations, not only the Gibbs formation energy of nickel and chromium oxides and thermodynamic activities of the alloy components, but also the Gibbs surface energy of a Ni-Cr alloy is taken into account. The method is based on the adsorption model of the alloy oxidation, according to which the adsorption of an alloy component with the smaller surface energy, namely, nickel, at the alloy-oxide film interface boundary shifts the dynamic equilibrium between the alloy and oxide-film components toward the formation of NiO. For the oxidation of Ni-Cr alloys, which are solid solutions with an fcc lattice, at 1123 to 1473 K, concentration boundaries of the chromium content in the alloy are calculated for the case of the prevailing formation of Cr2O3 oxide, which determines the high heat resistance of Ni-Cr alloys.

Ab initio comparative study of C54 and C49 TiSi2 surfaces

A theoretical comparison of C54 and C49 TiSi2 surfaces is presented, using ab initio plane-wave ultrasoft pseudopotential method based on generalized gradient approximation (GGA). The different surface energies of TiSi2 have not only been calculated out, but the preferential formation of C49 phase in solid-state reaction could be explained by smaller surface energies and Poisson's ratio of C49 TiSi2 as well. As for polar C54 TiSi2(1 0 0) and C49 TiSi2(0 1 0) surfaces, the Si termination surfaces are more stable.

Monte Carlo Simulation of Cube-Texture Evolution during Grain Growth of High-Purity Nickel

A Monte Carlo Potts model has been used to investigate cube-texture strengthening during grain growth in rolled high-purity Ni-tapes. The initial conditions for the simulations have been taken from electron back-scatter pattern (EBSP) orientation maps of already fully recrystallized samples. Experimentally, grain growth leads to an increase in the cube volume fraction to >95% , accompanied by an approximately ten-fold increase in the grain size. High cube volume fractions can be predicted under a number of conditions, though a small surface energy advantage of just 2% for cube-oriented grains is required to match the texture strengthening to the grain size change. An additional issue of interest is the influence on the grain growth of the large area-fraction of twin boundaries in the fully recrystallized condition. The presence of boundaries with low energy has a strong influence on the simulated microstructural evolution.

Effect of High-Energy-Electron Irradiation on Nonisothermal Crystallization Kinetics in P(VDF-TrFE) 65/35 mol% Copolymers

ABSTRACTThe effect of the high-energy-electron irradiation on the crystallization process in poly(vinylidene fluoride-trifluoroethyelene) [(P(VDF-TrFE)] 65/35 mol% copolymers was studied by nonisothermal crystallization using the differential scanning calorimetry (DSC) technique. The experimental data are analyzed using modified Avrami, Ozawa, and combined Avrami-Ozawa methods. It is found that the crystals grow in three dimensions in the irradiated samples. It is found that the irradiation results in a lower crystallization temperature and a lower crystallization activation energy. It is also found that the irradiated samples have a lower crystallization temperature than the unirradiated samples. All these results indicate that the crystals grown in the irradiated samples have a smaller surface energy, which corresponds to a thicker interfacial layer.

A new approach to spherically symmetric junction surfaces and the matching of FLRW regions

We investigate timelike junctions (with surface layer) between spherically symmetric solutions of the Einstein-field equation. In contrast to previous investigations, this is done in a coordinate system in which the junction surface motion is absorbed in the metric, while all coordinates are continuous at the junction surface. The evolution equations for all relevant quantities are derived. We discuss the no-surface layer case (boundary surface) and study the behaviour for small surface energies. It is shown that one should expect cases in which the speed of light is reached within a finite proper time. We carefully discuss necessary and sufficient conditions for a possible matching of spherically symmetric sections. For timelike junctions between spherically symmetric spacetime sections we show explicitly that the time component of the Lanczos equation always reduces to an identity (independent of the surface equation of state). The results are applied to the matching of Friedmann–Lemaître–Robertson–Walker (FLRW) models. We discuss ‘vacuum bubbles’ and closed–open junctions in detail. As illustrations several numerical integration results are presented, some of them indicate that (observers comoving with) the junction surface can reach the speed of light within a finite time.

Numerical Justification of Branched Laminated Microstructure with Surface Energy

A mathematical model is given to study the branched laminated microstructure in austenite-martensite phase transition. A numerical method based on a mesh transformation method is applied to a two dimensional elastic crystal model, and the numerical results show that, for sufficiently small surface energy density and sufficiently long laminates, the branched laminates are energetically favorable; the numerical results also show that there is certain finite order asymptotically self-similar structure in the branched laminates.

Model calculations for copper clusters on Au(111) surfaces

Using the semi-empirical embedded-atom method, the structure of small copper clusters on Au(111) surfaces has been investigated both by static and dynamic calculations. By varying the size of roughly circular clusters, the edge energy per atom is obtained; it agrees quite well with estimates based on experimental results. Small three-dimensional clusters tend to have the shape of a pyramid, whose sides are oriented in the directions of small surface energy. The presence of a cluster is found to distort the underlying lattice of adsorbed copper atoms.

Increased Osteoblast and Decreased Smooth Muscle Cell Adhesion on Biologically-inspired Carbon Nanofibers

ABSTRACTOsteoblast (the bone-forming cells) and smooth muscle cell adhesion was investigated on carbon nanofiber formulations of various diameters (specifically, from 60 to 200 nm) and surface energies (from 25 to 140 mJ/m2) in the present in vitro study. Results provided the first evidence that osteoblast adhesion increased with decreased carbon nanofiber diameter after 1 hour. In contrast, smooth muscle cell adhesion was not dependent on carbon nanofiber diameter. Moreover, the present study demonstrated that smooth muscle cell adhesion decreased with increased carbon nanofiber surface energy after 1 hour. Alternatively, osteoblast adhesion was not affected by carbon nanofiber surface energy. Since adhesion is a crucial prerequisite for subsequent functions of cells (such as the deposition of bone by osteoblasts), the present results of controlled adhesion of both osteoblasts and a competitive cell line (i.e., smooth muscle cells) demonstrate that carbon nanofibers with small diameters and high surface energies may become the next-generation of orthopedic implant materials to enhance new bone synthesis. These criteria may prove critical in the clinical success of bone prostheses.

Phase behavior and material properties of hollow nanoparticles

Effective pair potentials for hollow nanoparticles such as those made from carbon (fullerenes) or metal dichalcogenides (inorganic fullerenes) consist of a hard core repulsion and a deep, but short-ranged, van der Waals attraction. We investigate them for single-walled and multiwalled nanoparticles and show that in both cases, in the limit of large radii the interaction range scales inversely with the radius R, while the well depth scales linearly with R. We predict the values of the radius R and the wall thickness h at which the gas-liquid coexistence disappears from the phase diagram. We also discuss unusual material properties of the solid, which include a large heat of sublimation and a small surface energy.

Beginning of earthquakes modeled with the Griffith's fracture criterion

AbstractWe present a source model for the beginning of earthquakes based on the Griffith's fracture criterion. The initial state is a critical state of pre-existing circular fault, which is on the verge of instability. After the onset of instability, the fault grows with a progressively increasing rupture speed, satisfying the condition of fracture energy balance at the crack tip. We investigate the difference in rupture growth patterns in two classes of models that are considered to represent end-member cases. In the first model (Spontaneous model), we assume that the surface energy varies smoothly as a function of position in the crust. In this model, faults with small initial dimensions grow in regions with small surface energy, and those with large initial dimensions, in large surface energy. The rupture velocity increases progressively until it reaches its limiting value. The synthetic velocity seismogram at far field shows a weak initial phase during the transitional stage to limiting velocity. The time taken to reach the limiting velocity is proportional to the initial length of pre-existing fault. Therefore, the duration of the weak initial phase scales with the initial length of fault. In the second model (Trigger model), we envisage that there are many pre-existing faults in the crust with various lengths. These faults are stable because they encounter some obstacle at their ends (e.g., fault segmentation, strong asperity, etc.). This situation is modeled with a local increase of surface energy near the ends of fault. An earthquake is triggered when the obstacle is suddenly removed (i.e., sudden weakening) or the stress is suddenly increased locally to overcome the obstacle. Once an earthquake is triggered, the fault growth is governed by the ambient surface energy. In this model, the rupture speed attains its limiting velocity almost instantly. The synthetic velocity seismogram at far field shows an abrupt, linear increase in amplitude without the weak initial phase that appears in the Spontaneous model. Both models can be unified using a trigger factor defined as a fractional perturbation of the surface energy at the ends of fault relative to the ambient surface energy. The Spontaneous model is characterized by a small trigger factor, and the Trigger model, by a large trigger factor. Thus, the seismic initiation phase with and without the slow initial phase can both occur depending on the trigger factor. The variability in the observed seismic initiation phase may represent a variation surface energy (strength) distribution surrounding the pre-existing cracks. A theoretical consideration of rupture arrest by barriers using the Griffith's fracture criterion does not support the scaling relation between the nucleation moment and the eventual size of earthquake.

Dendritic crystal growth for weak undercooling. II. Surface energy effects on nonlinear evolution

We extend the previous work of Kunka, Foster, and Tanveer [Phys. Rev. E 56, 3068 (1997)] by incorporating small but nonzero surface energy effects in the nonlinear dynamics of a conformal mapping function $z(\ensuremath{\zeta},t)$ that maps the upper-half \ensuremath{\zeta} plane into the exterior of a dendrite. In this paper, we specifically examine surface energy effects on the singularities of $z(\ensuremath{\zeta},t)$ in the lower-half \ensuremath{\zeta} plane, as they move toward the real axis from below. Until the time when any of the singularities of the corresponding zero-surface-energy solution or a surface-energy-generated daughter singularity cluster comes very close to the real axis, the leading-order outer solution is the zero-surface-energy solution in a strip of the lower-half complex that includes the real axis (i.e., the interface). There is an inner region around each singularity of the zero-surface-energy solution where surface energy plays a dominant role. However, the scalings in such an inner region, and hence the equation itself, must be modified when such singularities are very close to the real axis. The relative ordering of anisotropy, surface energy, and singularity strength strongly influences the form of the inner equations and hence their solutions. A singularity with initial strength weaker than some critical value is dissipated over a fast time scale by surface energy effects, leaving no trace of the initial singularity. This cutoff in singularity strength limits the size and growth rate of the interfacial disturbances that singularities generate. Also, the variation of time scale over which surface energy acts, due to differing singularity strengths in an ensemble, is shown to account for a $|y{|}^{1/2}$ coarsening rate for some intermediate range of distances, |y|, from the dendrite tip. As in the case of the isotropic Hele-Shaw problem [S. Tanveer, Philos. Trans. R. Soc. London, Ser. A 343, 155 (1993)], we find here too that each initial zero of ${z}_{\ensuremath{\zeta}}$ gives birth to a ``daughter'' singularity cluster that moves away from the zero and necessarily approaches the real axis, before dispersing. One effect of this ``daughter'' singularity cluster, if it approaches the real axis before any other singularity, is to singularly perturb a smoothly evolving zero-surface-energy solution. In addition, numerical and analytical results for a certain general class of initial conditions indicate that daughter-singularity effects necessarily prevent an interface from ever approaching the cusp implied by the corresponding zero-surface-energy solution. Finally, we find that for a set of localized distortions, the local rescaling of dependent and independent variables (i.e., on an ``inner scale'') leads to the original equations, with an effectively larger surface-energy parameter.