Micromechanical analysis of the behavior of stiff clay

Cementations formed in geological timescale are observed in various stiff clays.A micromechanical stress strain model is developed for modeling the effect of cementation on the deformation behavior of stiff clay.The proposed approach considers explicitly cementations at intercluster contacts,which is different from conventional model.The concept of inter-cluster bonding is introduced to account for an additional cohesion in shear sliding and a higher yield stress in normal compression.A damage law for inter-cluster bonding is proposed at cluster contacts for the debonding process during mechanical loading.The model is used to simulate numerous stress-path tests on Vallericca stiff clay.The applicability of the present model is evaluated through comparisons between the predicted and the measured results.In order to explain the stress-induced anisotropy arising from externally applied load,the evolution of local stresses and local strains at inter-cluster planes are discussed.     

Antioxidant Effects and Phytochemical Properties of Seven Taiwanese Cirsium Species Extracts

In the present investigation, we compared the radical-scavenging activities and phenolic contents of seven Taiwanese Cirsium species with a spectrophotometric method. We further analyzed their phytochemical profiles with high-performance liquid chromatography–photodiode array detection (HPLC–DAD). We found that the flower part of Cirsium japonicum var. australe (CJF) showed the best radical-scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and the hypochlorite ion, for which the equivalents were 6.44 ± 0.17 mg catechin/g, 54.85 ± 0.66 mmol Trolox/g and 418.69 ± 10.52 mmol Trolox/g respectively. CJF also had the highest contents of total phenolics (5.23 ± 0.20 mg catechin/g) and phenylpropanoids (29.73 ± 0.72 mg verbascoside/g). According to the Pearson’s correlation coefficient, there was a positive correlation between the total phenylpropanoid content and ABTS radical-scavenging activities (r = 0.979). The radical-scavenging activities of the phenylpropanoids are closely related to their reducing power (r = 0.986). HPLC chromatograms obtained in validated HPLC conditions confirm that they have different phytochemical profiles by which they can be distinguished. Only CJF contained silicristin (0.66 ± 0.03 mg/g) and silydianin (9.13 ± 0.30 mg/g). CJF contained the highest contents of apigenin (5.56 ± 0.09 mg/g) and diosmetin (2.82 ± 0.10 mg/g). Among the major constituents, silicristin had the best radical-scavenging activities against DPPH (71.68 ± 0.66 mg catechin/g) and ABTS (3.01 ± 0.01 mmol Trolox/g). However, diosmetin had the best reducing power and radical-scavenging activity against the hypochlorite anion (41.57 ± 1.14 mg mmol Trolox/g). Finally, we found that flavonolignans (especial silicristin and silydianin) and diosmetin acted synergistically in scavenging radicals.     

CdxHg(1−x)Te Alloy Colloidal Quantum Dots: Tuning Optical Properties from the Visible to Near‐Infrared by Ion Exchange

The energy gap between valence and conduction levels in colloidal semiconductor quantum dots can be tuned via the nanoparticle diameter when this is comparable to or less than the Bohr radius. In materials such as cadmium mercury telluride, which readily forms a single phase ternary alloy, this quantum confinement tuning can also be augmented by compositional tuning, which brings a further degree of freedom in the bandgap engineering. Here it is shown that compositional control of 2.3 nm diameter Cd_xHg_(1?x)Te nanocrystals by exchange of Hg²⁺ in place of Cd²⁺ ions can be used to tune their optical properties across a technologically useful range, from 500 nm to almost 1200 nm. Data on composition‐dependent changes in the optical properties are provided, including bandgap, extinction coefficient, emission energy and spectral shape, Stokes shift, quantum efficiency, and radiative lifetimes as the exchange process occurs, which are highly relevant for those seeking to use these technologically important QD materials.     

A New Ent‐Trachylobane Diterpenoid from the Roots of Sapium Sebiferum

A new ent‐trachylobane diterpenoid, saposebifeic acid, together with thirteen known compounds, were isolated from the roots of Sapium sebiferum. Compounds, 5,7,8‐trimethoxycoumarin, baccatin, n‐alkyl trans‐ferulate and 2,6‐dimethoxyquinone, were reported for the first time from this plant. The structures of the new and known compounds were established on the basis of extensive 1D and 2D NMR spectral data.     

Fingering patterns on an expanding miscible drop in a rotating Hele‐Shaw cell

We perform a detailed numerical study for the evolution of an expanding miscible drop in a rotating Hele‐Shaw cell. Two mathematical formulations applied to model the coating layer expansion during practical spin‐coating process, such as thinning of the layer by cell pressing and drop spreading outward due to injection, are investigated. Including miscible interfacial stresses, we focus on the investigation of dynamical and morphological influences of two different stabilizing parameters: the gap width parameter for the pressing cell and the injecting strength. In the case of a pressing cell, the fingering features of the expanding miscible drop, such as the critical radius, are distinct from those ones in the experiments of spin coating due to the different distributions of the inherent radial velocity. On the other hand, the global interfacial evolutions of an expanding drop with an additional injection bear remarkable resemblances to their immiscible counterparts. The better agreement for an injecting model suggests its appropriateness when we simulate the emerging fingering instabilities in the spin‐coating process. Moreover, we investigate the effects of Coriolis force at higher miscible Bond numbers. Coriolis force affects significantly the onset of fingering instability and the tilting angles of fingers. These stable effects are in line with the results from the previous studies for miscible and immiscible flow fields. Copyright © 2007 John Wiley & Sons, Ltd.     

A reliable synthesis of 2- and 6-amino-β-cyclodextrin and permethylated-β-cyclodextrin

A new, reliable method for the introduction of an amine group at positions 2 or 6 of β-cyclodextrin and permethyl-β-cyclodextrin is described. It involves selective tosylation followed by azide substitution and almost quantitative reduction with triphenylphosphine followed by hydrolysis of the phosphinimine intermediate.     

Poly(p‐phenylenevinylene) presenting pendent pentaphenylene dendron groups for light‐emitting diodes

We have synthesized, using the Gilch method, a novel poly(p‐phenylenevinylene) derivative (PPV‐PP) containing two pendent pentaphenylene dendritic wedges, and have characterized its structure and properties. The incorporated side chain pentaphenylene dendrons serve as solubilizing groups, prevent π‐stacking interactions from occurring between the polymer main chains, and suppress the formation of excimers in the solid state. Photoluminescence studies indicate that efficient intramolecular energy transfer occurred from the photoexcited pentaphenylene groups to the poly(p‐phenylenevinylene) backbone. The polymer film exhibits a maximum emission at 510 nm and had a photoluminescence efficiency of 46%, which is similar to that measured in dilute solution. The photoluminescence spectra remained almost unchanged after thermal annealing at 150 °C for 20 h, and displayed inhibited excimer formation. Polymer light‐emitting diodes that we fabricated in the configuration ITO/PEDOT/PPV‐PP/Mg:Ag/Ag exhibited a maximum emission peak at 513 nm, corresponding to the green region [x = 0.30 and y = 0.62 in the Commission Internationale de L'Eclairage (CIE) chromaticity coordinates]. The maximum brightness and maximum luminance efficiency were 1562 cd/m² and 1.93 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5147–5155, 2005     

High performance thermosets from a curable Diels–Alder polymer possessing benzoxazine groups in the main chain

A high‐molecular‐weight polymer (PBz) possessing reactive benzoxazine groups in the main chain was prepared through the Diels–Alder reaction using bis(3‐furfuryl‐3,4‐dihydro‐2H‐1,3‐benzoxazinyl)isopropane (BPA‐FBz) and bismaleimide (BMI) as monomers. The chemical structure of PBz is characterized with FTIR and ¹H NMR. The polymer PBz was further thermally reacted with a high performance polymer (PBz‐R) through the ring‐opening addition reaction of benzoxazine groups and the addition reaction of maleimide groups. PBz‐R exhibit a high glass transition temperature of 242 °C, good thermal stability, high flame retardancy, high mechanical strength, and great flexibility. Another crosslinked polymer (PBz‐BR) curing from the mixture of BPA‐FBz and BMI was also prepared. The properties of PBz‐BR are also attractive but, however, not as good as what observed with PBz‐R. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6509–6517, 2008