Thermo-elastic properties of heterogeneous materials with imperfect interfaces: Generalized Levin's formula and Hill's connections

We study the thermo-elastic properties of heterogeneous materials containing spherical particles or cylindrical fibres. The interface between the matrix and second-phase inhomogeneity is imperfect with either the displacement or the stress experiencing a jump across it. We relate the effective coefficient of thermal expansion (CTE) to the effective elastic moduli and thereby generalize Levin's formula, and reveal two connections among the effective elastic moduli, thereby generalizing Hill's connections. In contrast to the classical results, the effective CTE in the presence of an imperfect interface is strongly dependent on the size of the inhomogeneity, besides the interface elastic and thermo-elastic properties. This size dependence has been accurately captured by simple scaling laws.     

Growth and interface study of 2 in diameter CdZnTe by THM technique

Growth interface of large diameter CdZnTe ingots grown from Te solution by travelling heater method have been studied. Both macroscopic and microscopic investigations were carried out. The results indicated that the shape of the interface strongly governs the grain growth on the ingot, while the microscopic morphology of the growth interface is responsible for Te inclusions in the grown crystal.     

Large volume injection of water in gas chromatography–mass spectrometry using the Through Oven Transfer Adsorption Desorption interface: Application to multiresidue analysis of pesticides

In the present work, the potential of the Through Oven Transfer Adsorption Desorption (TOTAD) interface for the large volume injection (LVI) of aqueous samples in gas chromatography (GC) using a mass spectrometry (MS) detector is demonstrated. To this end, a new method for the determination of pesticides in water is presented, being the first developed method in which injection of large amounts of polar solvents using the TOTAD interface and an MS detector are combined, is applied to the determination of pesticides in water. Water samples, as large as 5 ml, were directly injected into a capillary GC. No sample pre-treatment step other than simple filtration was needed. The TOTAD interface allows the introduction of several millilitres of water, while maintaining good chromatographic characteristics. The water is almost entirely eliminated, so that LVI of aqueous samples and an MS detector can be used without problems. Organophosphorus, organochlorine, and triazine pesticides were determined in one run. Calibration curves were linear in the range tested and the sensitivity achieved injecting 5 ml of water sample was sufficient for most of the target pesticides but not for all of them. Sensitivity of the analysis can be improved by increasing the sample volume. No variability was observed in the retention times and relative standard deviations from absolute peak areas were good, considering that they corresponded to the overall analysis. The method was applied to the analysis of pesticide residues in real water samples.     

Green's functions for infinite bi-material planes of cubic quasicrystals with imperfect interface

The problem of an infinite plane which is composed of two half-planes with different cubic quasicrystal materials subjected to line phonon and phason forces is investigated. By virtue of the general solution of cubic quasicrystals, a series of displacement functions is adopted to obtain Green's functions in the closed form. For the bonding along the bi-material interface three different models account for different coupling conditions.     

Effects of oxygen vacancy on adhesion of incoherent metal/oxide interface by first-principles calculations

We investigate effects of oxygen vacancies on adhesion behavior of incoherent Ni/MgO(0 0 1) interface with large misfit, based on the density functional theory. We demonstrate that oxygen vacancies at any local atomic configuration of the incoherent geometry enhance the image-chargelike interaction between the ions in MgO and the ion-induced images in Ni, and stabilize adhesion of the Ni/MgO(0 0 1) interface. The adhesion energy of the defective interface is remarkably larger than that of the perfect interface. We also show that force constants of the adhesive interactions near the oxygen vacancies are comparable to the Ni-Mg bond at the perfect interface. The vacancy-induced enhancement of the image electron accumulation hardly contributes to the interfacial stiffness, while it is reduced by losing the covalent Ni-O interaction due to an ontop oxygen vacancy.     

A sharp-interface interpretation of a continuous density model for homogenization of gravity-driven flow in porous media

We examine homogenization methods applied to sharp-interface and diffuse-interface models for gravity-driven flow in heterogeneous porous media. Our work specifically examines a matrix of models that includes (1) a variable media, diffuse-interface model, (2) a variable media, sharp-interface model, (3) a homogenized media, diffuse-interface model and (4) a homogenized media, sharp-interface model. We connect all four of these models via homogenization theory and sharp-interface limits. We show that existing results based on homogenization methods applied to sharp-interface models can be recovered by a less direct but more rigorous approach involving well-established homogenization theory and sharp-interface limits.     

Effects of variation in modulator temperature during cryogenic modulation in comprehensive two‐dimensional gas chromatography

Many modulation systems in comprehensive 2D GC (GC×GC) are based on cryogenic methods. High trapping temperatures in these systems can result in ineffective trapping of the more volatile compounds, whilst temperatures that are too low can prevent efficient remobilisation of some compounds. To better understand the trapping and release of compounds over a wide range of volatilities, we have investigated a number of different constant temperature modulator settings, and have also examined a constant temperature differential between the cryo‐trap and the chromatographic oven. These investigations have led us to modify the temperature regulation capabilities of the longitudinally modulated cryogenic system (LMCS). In contrast to the current system, where the user sets a constant temperature for the cooling chamber, the user now sets the temperature difference between the cryo‐trap and the chromatographic oven. In this configuration, the cooling chamber temperature increases during the chromatographic run, tracking the oven temperature ramp. This produces more efficient, volatility‐dependent modulation, and increases the range of volatile compounds that can be analysed under optimal trap‐and‐release conditions within a single analytical run. This system also reduces cryogenic fluid consumption.     

Site-selective formation of optically active inclusion complexes of alkoxo-subphthalocyanines with beta-cyclodextrin at the toluene/water interface

Several subphthalocyanine derivatives that contain an alkoxo substituent as an axial ligand (RO-Subpc, R = 9-anthracenemethyl, benzyl, phenyl, 3,5-dimethylbenzyl, 3,5-dimethylphenyl, 4-methylbenzyl, and 4-methylphenyl) were synthesized. The formation of inclusion complexes of RO-Subpc with beta-CD in DMSO and at the toluene/water interface was investigated by UV/Vis absorption spectroscopy, induced circular dichroism (ICD), and nuclear magnetic resonance (NMR) measurements. Interfacial tension measurements suggested that beta-CD adsorbed as a monolayer at the toluene/water interface and probably orientated towards the toluene phase with its primary face. The 1:1 composition of beta-CD.RO-Subpc inclusion complexes was confirmed in DMSO and at the toluene/water interface for BzO-Subpc, PhO-Subpc, MeBzO-Subpc, and MePhO-Subpc. A 2:1 inclusion complex of AnO-Subpc formed in DMSO. The observed ICD spectra of beta-CDRO-Subpc inclusion complexes are discussed with respect to molecular modeling and the simulation based on Tinoco-Kirkwood theory. Interestingly, the ICD spectra of beta-CD.BzO-Subpc and beta-CD.MeBzO-Subpc inclusion complexes exhibited a negative sign in DMSO and a positive sign at the toluene/water interface. This reversal of the ICD sign strongly suggests a difference in the structure of the inclusion complexes: beta-CD at the interface formed the inclusion complex with its primary face, whereas the secondary face of beta-CD bound favorably to RO-Subpc in DMSO.     

Adsorption of hexyl-alpha,omega-bis(dodecyldimethylammonium bromide) gemini surfactant on silica and its effect on wettability

The adsorption of hexyl-alpha,omega-bis(dodecyldimethylammonium bromide) (C(12)C(6)C(12)Br(2)) gemini surfactant on silica and its effect on wettability have been studied. The structure of the adsorbed aggregates experiences an evolving course with the increase of C(12)C(6)C(12)Br(2) concentration. It is from no aggregates to circular islands, then to semicontinuous islands, and at last to the two-bilayer structure. No matter what kind of aggregates are in existence, their thickness values are to be the same 3.3+/-0.3 nm. The fraction of silica surface covered by the surfactant aggregates also varies from nearly zero at 0.05 mM to approximately 0.92 at 5.0 mM. The variation of contact angle against C(12)C(6)C(12)Br(2) concentration shows two distinct regions. The upward shift indicates that the surfactant molecules are adsorbed with their hydrophobic tails facing air upon increasing concentration, while the downward shift reveals that the surfactant aggregates are in existence with the hydrophilic headgroups facing air. IR spectra suggest that two different courses are involved with the increase of the surfactant concentration. One possible course is that the surfactant tails pack more closely and orderly, and the other may be that the spacer changes from stretched profile to bended conformation upon increasing the surfactant concentration.     

Possible transition from space-charge-limited to injection-limited conduction in poly(3-hexylthiophene) thin films

Two-terminal thin films of poly(3-hexylthiophene) (P3HT) with a wide electrode separation (150 m) has been studied using current-voltage characteristics at different temperatures. Space-charge-limited conduction (SCLC) with high injection barriers (1.3 eV) has been observed at all temperatures in the low electric field regime. A possible transition from SCLC to injection-limited conduction (ILC) is reported. The experimental results have been compared with the disorder-controlled injection model proposed by Arkhipov et al. [V.I. Arkhipov, H. von Seggern, E.V. Emilianova, Appl. Phys. Lett. 83 (2003) 5074; V.I. Arkhipov, E.V. Emilianova, Y.-H. Tak, H. Bässler, J. Appl. Phys. 84 (1998) 848; V.I. Arkhipov, U. Wolf, H. Bässler, Phys. Rev. B 59 (1999) 7514].