Oscillatory shear response of moisture barrier coatings containing clay of different shape factor

Oscillatory shear rheology of barrier coatings based on dispersed styrene-butadiene latex and clay of various shape factors or aspect ratio has been explored. Barrier performance of these coatings when applied to paperboard has been assessed in terms of water vapour transmission rates and the results related to shape factor, dewatering and critical strain. It has been shown that a system based on clay with high shape factor gives a lower critical strain, dewatering and water vapour transmission rate compared with clays of lower shape factor. The dissipated energy, as calculated from an amplitude sweep, indicated no attractive interaction between clay and latex implying a critical strain that appears to be solely dependent on the shape factor at a constant volume fraction. Particle size distribution was shown to have no effect on the critical strain while coatings of high elasticity exhibited high yield strains as expected. The loss modulus demonstrated strain hardening before the elastic to viscous transition. The loss modulus peak was identified by a maximum strain which was significantly lower for a coating based on clay with a high shape factor. The characteristic elastic time was found to vary between 0.6 and 1.3s. The zero shear viscosity of barrier dispersion coatings were estimated from the characteristic elastic time and the characteristic modulus to be of the order of 25-100 Pa s.     

Complications in metathesis reactions involving Grignard reagents: Effect of solvent on products obtained from the interaction of PhMgBr with GaCl3 or InBr3

The important role of supporting solvent in transmetallation reactions involving Grignard reagents is highlighted in the formation and crystallisation of the Group 13 ‘ate’ species, [Mg₃Br₃Cl₂(Et₂O)₆][GaPh₂Br₂] (1), [Mg₃Br₅(Et₂O)₆][InPh₂Br₂] (2), [MgBr(THF)₅][GaPh₃Br] (3), [MgBr(THF)₅][InPh₃Br] (4), [Mg(THF)₆][GaPh₂Br₂]₂ (5) obtained by reaction of PhMgBr with gallium and indium halides. The compounds have been characterised by ¹H NMR, elemental analyses, and single-crystal X-ray diffraction.     

Conformational Polymorphism in N‐(4′‐methoxyphenyl)‐ 3‐bromothiobenzamide

Three conformational polymorphs of N‐(4′‐methoxyphenyl)‐3‐bromothiobenzamide, yellow α, orange β, and yellow γ, have been identified by single‐crystal X‐ray diffraction. The properties and structure of the polymorphs were examined with FT Raman, FTIR (ATR), and UV/Vis spectroscopy, as well as differential scanning calorimetry. Computational data on rotational barriers in the isolated gas‐phase molecule indicate that the molecular conformation found in the α form is energetically preferred, but only by around 2 kJ mol^?1 over the γ conformation. The planar molecular structure found in the β form is destabilized by 10–14 kJ mol^?1, depending on the calculation method. However, experimental evidence suggests that the β polymorph is the most stable crystalline phase at room temperature. This is attributed to the relative planarity of this structure, which allows more and stronger intermolecular interactions, that is, more energetically effective packing. Calculated electronic‐absorption maxima were in agreement with experimental spectra.