Prediction of contact angle on a microline patterned surface

The Cassie and Baxter’s equation has been modified to predict wetting phenomena on a microline patterned surface with the concept of effective solid-liquid interfacial energy. This interfacial energy was deduced from the total energy barrier at a metastable equilibrium and Helmholtz free energy. The contact angle predicted by the modified equation is reasonably close to the experimental data for the microline patterned surface.     

A Note on the Thermomechanics of Curvature Flows in IR3 and on Surfaces in IR3

Equations for the evolution of curves in IR³ and on surfaces in IR³ are derived from a configurational force balance, a mechanical version of the second law, and suitable constitutive assumptions. Both the isotropic and anisotropic cases are considered.Sommario.In questo lavoro si derivano le equazioni di evoluzione per curve in IR³ e su superfici di IR³, utilizzando un bilancio di forze configurazionali, una versione meccanica del secondo principio e opportune ipotesi costitutive. Sono trattati sia il caso isotropo che anisotropo.     

Glass transition and relaxation behavior of epoxy nanocomposites

With advances in nanoscience and nanotechnology, there is increasing interest in polymer nanocomposites, both in scientific research and for engineering applications. Because of the small size of nanoparticles, the polymer–filler interface property becomes a dominant factor in determining the macroscopic material properties of the nanocomposites. The glass‐transition behaviors of several epoxy nanocomposites have been investigated with modulated differential scanning calorimetry. The effect of the filler size, filler loading, and dispersion conditions of the nanofillers on the glass‐transition temperature (T_g) have been studied. In comparison with their counterparts with micrometer‐sized fillers, the nanocomposites show a T_g depression. For the determination of the reason for the T_g depression, the thermomechanical and dielectric relaxation processes of the silica nanocomposites have been investigated with dynamic mechanical analysis and dielectric analysis. The T_g depression is related to the enhanced polymer dynamics due to the extra free volume at the resin–filler interface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3849–3858, 2004     

Surface contribution versus bulk contribution in surface nonlinear optical spectroscopy

Received: 20 September 1998     

Measuring the Au(1 1 1) surface state at the solid–liquid interface

We present the first direct observation of an occupied noble metal surface state at the metal/liquid interface. The Au(1 1 1) Shockley-like surface state was measured by scanning tunneling spectroscopy (STS) at the Au(1 1 1)/n-tetradecane interface. These results show that the surface state of gold survives in a liquid environment, and can be probed by STS. More generally it indicates that STS can be used to study electronic properties of surfaces at the solid/liquid interface, and that spectra can be directly compared to measurements and calculations of a surface’s electronic structure in ultra-high vacuum.     

Interfacial adhesion mechanisms in incompatible semicrystalline polymer systems

The mechanism of adhesion at semicrystalline polymer interfaces between isotactic polypropylene (iPP) and linear low‐density polyethylene (PE) was studied with transmission electron microscopy (TEM) and an asymmetric‐double‐cantilever‐beam test. From the TEM images, both the interfacial width and the lamellar thickness of the polymers were extracted. During annealing, the interfacial width increased with the annealing temperature, and this indicated the accumulation of amorphous polymers at the interface. The interfacial strength, determined from the critical fracture energy (G_c), also increased with the annealing temperature and reached a maximum above the melting temperatures of iPP and PE, whereas the smallest G_c value was obtained below the melting temperatures of the two materials. A mechanism of interfacial strengthening was proposed accounting for the competition between the interdiffusion of PE and crystallization of iPP. As the annealing temperature increased, the rates of PE diffusion and iPP crystallization increased. Although the crystallization of iPP hindered the interdiffusion of PE, both the interfacial width and the fracture energy increased with the temperature, and this indicated that PE interdiffusion dominated iPP crystallization. Below the critical temperature, the fracture surfaces of both iPP and PE were smooth, and chain pullout dominated the fracture mechanism. Above the critical temperature, iPP crystallization still hindered the interdiffusion, and crazes could be seen on the iPP side. Above the melting temperatures of the two materials, ruptured surfaces could also be seen on the PE side, and crazing was the fracture mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2667–2679, 2004     

The epitaxial growth of Pd electrodeposition on Au(1 0 0) studied by LEED and RHEED

The epitaxial growth of Pd adlayers electrochemically deposited onto Au(1 0 0) has been studied by LEED, RHEED and AES. For the first 6 ML, the Pd deposits grow pseudomorphically on Au(1 0 0) with a lateral expansion of 4.5% with respect to bulk Pd. The strain in the expanded commensurate (1 × 1) Pd layers on Au(1 0 0) begins to be relieved at the Pd coverage between 6 and 9 ML range by formation of a compressed Pd film with respect to Au(1 0 0) surface and the compression increases continuously with thickness. At ca. 20 ML Pd the lattice constant of the film approaches to the bulk Pd and three-dimensional Pd islands develop since around 30 ML coverage. No superstructure due to the Pd-Au surface alloy can be found for coverages from monolayer up to 30 ML Pd on Au(1 0 0). A c(2 × 2) phase has been observed on the Pd-deposited Au(1 0 0) electrodes, which is ascribed to an ordered Cl adlayers adsorbed on Pd adlayers rather than a Pd-Au surface alloy.     

Mn-doped GaN/AlN heterojunction for spintronic devices

We present first principles calculations of Mn-doped GaN/AlN(0001) heterostructures obtained within the framework of density functional theory by using plane wave pseudopotential techniques. We found that for diluted Mn concentration this system present an integer magnetization that is a fingerprint of half-metallic property; this suggests the possibility to use this junction as a spin injector.     

Determination of the heterogeneous association constants of metal ions to omega-mercaptoalkanoic acids by using double-layer capacity measurements.

The binding of metal ions to ligands in homogeneous solutions and that to the same ligands anchored to metallic surfaces through self-assembled monolayers (SAMs) are expected to differ primarily due to the difference in the degree of freedom of the ligands and the surface potential. We studied the heterogeneous binding of CdII ions to omega-mercaptoalkanoic-acid SAMs on Au. This was accomplished by adding metal ions at a constant pH and following the changes in the double-layer capacity. A mathematical treatment, which is based on calculating the electrochemical-potential differences at the double layer-solution interface, has been developed. Our approach follows that proposed by White et al. and Kakiuchi, who used the acid-base equilibrium at the monolayer-electrolyte interface as a means of calculating the pK of ionizable SAMs. Experimentally, SAMs of omega-mercaptoalkanoic acids, HS(CH2)nCO2H, with different chain lengths (i.e., n=2, 5, and 10) in 0.1 M sodium perchlorate were assembled on Au surfaces and studied. The capacity was measured first in the absence of CdII at different pH values, and then at a constant pH while increasing the concentration of CdII in the solution. We found that the interfacial capacity decreased as the concentration (of either protons or CdII) increased. The results matched the model fairly well, which allowed the extraction of the thermodynamic equilibrium constant that is established at the monolayer-electrolyte interface. The suggested mathematical treatment of this model system is simple and yet very useful for estimating the heterogeneous association constants of metal ions by SAMs.