A study of the nature of coordination in metal monothiocarbamates based on infrared spectroscopy and the HSAB concept

The nature of coordination in metal monothiocarbamates is shown to depend on the hardness or softness of the metal ton. Thus, the monothiocarbamate ion acts as a monodentate ligand with metal-sulphur bending when the metal ion is a soft acid while it acts as a bidentate ligand when the metal ion is a hard acid; it can exhibit either behaviour when the metal ion is a borderline acid. In dialkyltin and dialkylmonocholorotin complexes, the monothiocarbamate ion acts as a bidentate ligand with strong Sn-S bonding while in trialkyl-or triaryl-tin complexes it acts essentially as a monodentate ligand. Thus, R₃Sn(I) seems to be a soft or borderline acid while R₂Sn(II) is a hard acid.     

Symmetry assignments of excited states of [Pt2H8P8O20]4− by polarization ratio spectroscopy

Linear polarization ratios were measured on the title compound. The symmetry of the lowest excited singlet state was confirmed as ¹A_2u. Emission from the triplet term was negatively polarized when excitation occurred in the strong singlet but positively polarized upon excitation directly to the triplet, confirming the E_U symmetry assignment of the emitting triplet component.     

The thermal fragmentation of 1,3,4-diathiazol-2-ones

Thermal expulsion of carbon oxusulphide from 1,3,4-dithiazol-2-ones in the presence of DMAD affords nitrile sulphide-derived dimethyl isothiazole-4,5-dicarboxylates.     

Stimuli‐responsive buckling mechanics of polymer films

Thin polymer films may undergo a wide variety of elastic instabilities that include global buckling modes, wrinkling and creasing of surfaces, and snapping transitions. Traditionally, these deformations have usually been avoided as they often represent a means of mechanical failure. However, a new trend has emerged in recent years in which buckling mechanics can be harnessed to endow materials with beneficial functions. For many such applications, it is desirable that such deformations happen reversibly and in response to well‐defined signals or changes in their environment. While significant progress has been made on understanding and exploiting each type of deformation in its own right, here we focus on recent advances in the control and application of stimuli‐responsive mechanical instabilities. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1441–1461     

Effect of stress biaxiality on the high-strain fatigue behavior of an aluminum-copper alloy

Although there is now a considerable volume of high-strain (<10⁵ cycles) fatigue data for uniaxial tension-compression and simple-bending conditions, relatively little information is available regarding the effects of stress and strain biaxiality. A method which has been used to study the effects of biaxiality on longlife fatigue strength is to subject thin-walled tubes to repeated internal pressure and an end load which is in phase with, and a linear function of, the pressure. The object of the present research was to use this method to study the influence of stress biaxiality on the high-strain fatigue behavior of a high strength, aluminum-4% copper alloy at room temperature. From a continuum-mechanics point of view, this material is completely elastic after the first few load cycles. Cylinder results for hoop to axial stress ratios of 2:1, 1:1, 1:2 and 2: ?1 suggest that fatigue failure of this material in the life range 10³ to 10⁵ cycles is primarily dependent on the maximum range of tensile stress. This conclusion and a study of fracture surfaces led to the use of linear-elastic fracture mechanics to interpret the fatigue and brittle fracture behavior of these cylinders.     

Establishment and enforcement of food standards in the U.K. and the EEC

Food legislation is enacted throughout the world, both to protect the health of the consumer and to prevent fraud. The food analyst plays a major part in the enforcement of such legislation, particularly as modern analytical techniques now enable trace constituents at ng/g levels to be detected.     

Effect of contact angle hysteresis on the measurement of capillary forces

We conduct experimental investigations of macroscopic capillary forces between two flat rigid substrates characterized by their advancing and receding contact angles with water. Our results exhibit excellent agreement with theoretical predictions obtained by the numerical solution of the capillary equation. On the basis of this comparison, we use the measurements of the capillary force to investigate the phenomenon of contact angle hysteresis. We present examples of force measurements for surfaces that display low, moderate, and high contact angle hysteresis and compare results for a larger variety of substrates. Finally, we show that for the case of water, the role of viscosity is insignificant within the range of force and velocity measured in the present work.     

Capillary forces between chemically different substrates

Motivated by experimental results, we present numerical and analytical calculations of the capillary force exerted by a capillary bridge spanning the gap between two parallel flat plates of asymmetric wettability. Depending on whether the sum of the two contact angles is smaller or larger than 180 degrees, the capillary force is either attractive or repulsive at small separations D between the plates. In either cases the magnitude of the force diverges as D approaches zero. The leading order of this divergence is captured by an analytical expression deduced from the geometry of the meniscus of a flat capillary bridge. The results for substrates with different wettability reveal an interesting behavior: with the sum of the contact angles fixed, the magnitude of the capillary force and the rupture separation decreases as the asymmetry in contact angles is increased. In addition, we present the rupture separation, i.e., the maximal extension of a capillary bridge, as a function of the contact angles. Our results provide an extensive picture of surface wettability effects on capillary adhesion.