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Temperature affects significantly the rheological behavior of neat water Wyoming Na-bentonite dispersions. The results of a very systematic study are presented regarding rheological measurements of 7% mass concentration at different temperatures, ranging between 25 and 80°C at atmospheric pressure. Higher temperature increased the shear stresses at low shear rates while the effect was much smaller at higher shear rates. The Herschel-Bulkley rheological model fitted extremely well all data. The yield stress increased linearly with temperature by almost threefold , the flow consistency index decreased exponentially with temperature by almost five-fold and the flow behavior index increased by about 20%, tending towards the Newtonian value. At low shear rates (b 100 rpm corresponding to b170 1/s Newtonian shear rates), which represent very well the shear rates experienced by drilling fluids in the critical annulus region, all rheograms appeared fairly linear and the Bingham plastic model fitted well all data. The Bingham yield stress, from the low shear rate data, increased linearly with temperature, while the plastic viscosity decreased with temperature, in a manner very similar to the decrease of water viscosity with temperature. The plastic viscosity and Bingham yield stress data, from the low shear rate range, can be fitted well by an Arrhenius-type equation, with the activation energy for the plastic viscosity very similar to the activation energy for water viscosity, while for the Bingham yield stress, the activation energy is equal but opposite in sign to that of the plastic viscosity. A hypothesis is stated for the the observed linear increase of the yield stress with temperature, in the temperature range studied. One should be concerned when non-standard preparation and measurement procedures are followed which makes extremely difficult to understand any differences observed when reporting rheological data of water bentonite dispersions. A standard methodology is proposed, complementary to API, which can give very consistent results.

Transparent titania coatings have self-cleaning and anti-reflection properties (AR) that are of great importance to minimize soiling effect on photovoltaic modules. In this work, TiO2 nanocolloids prepared by polyol reduction method were successfully used as coating thin films onto borosilicate glass substrates via adsorptive self-assembly process. The nanocolloids were characterized by transmission electron microscopy and x-ray diffraction. The average particle size was around 2.6 nm. The films which have an average thickness of 76.2 nm and refractive index of 1.51 showed distinctive anti soiling properties under desert environment. The film surface topography, uniformity, wettability, thickness and refractive index were characterized using x-ray diffraction, atomic force microscopy, scanning electron microscopy, water contact angle measurements and ellipsometry. The self-cleaning properties were investigated by optical microscopy and UV-Vis spectroscopy. The optical images show 56% reduction of dust deposition rate over the coated surfaces compared with bare glass substrates after 7 days of soiling. The transmission optical spectra of these films collected at normal incidence angle show high anti-reflection properties with the coated substrates having transmission loss of less than 6% compared to bare clean glass.

Metal−organic frameworks (MOFs) provide highly versatile platforms to stabilize molecular catalysts that are not readily accessible under homogeneous conditions, thus enabling access to a new set of catalytic materials. Herein, we describe a recyclable and highly active nickel catalyst immobilized on MOF for Suzuki−Miyaura coupling reaction, which operates under mild conditions. This mixed ligand catalyst forms from the combination of 1 equiv of MOFimmobilized ligand, 1 equiv of nickel source, and 1 equiv of PPh 3 . The nature of the catalyst was verified through a series of analytical tests and catalysis experiments. The immobilized catalyst was reusable for at least up to 7 cycles without decrease in the yield of the coupled product. We also verified that this reaction does not work under homogeneous conditions and that the reaction is truly heterogeneous through "hot filtration" experiments. We identified that the reaction is first order in arylborane concentration and negative order in arylbromide concentration through the effect of substrate concentrations on the initial rate. This informed us to conduct the catalysis under slow addition of the arylbromide and reduce the catalyst loading to 1% from 3%, without detriment to the yield or rate of the reaction. The catalyst gave good to excellent isolated yields with a range of functionalities, including heterocycles on aryl bromide with widely varying electronic properties.