Wettability of anisotropic and porous particles adsorbed to fluid interfaces

The wettability of particles and the way they attach to liquid interfaces is important for many technologies where powders are mixed with liquids or used as emulsifiers. Most such powders are highly agglomerated into larger aggregates that are highly porous. The attachment of such porous particles to liquid–fluid interfaces has not been studied in detail, especially in cases where the porous particles are impregnated with another fluid phase. The overall aim of the thesis is to study the behaviour of particles at the liquid–fluid interface with an emphasis on non– spherical and porous solid particles. We study the orientation of anisotropic microparticles and measure the contact angle of smooth and porous microparticles with the gel–trapping technique (GTT) to find the wettability of microparticles adsorbed in fluid interfaces. This technique allows us to obtain micrographs by scanning electron microscopy (SEM) for particles resting on polydimethylsiloxane (PDMS), which replicates the non–polar phase and allows for measuring the particle contact angle. We show the results of the typical attachment and orientation of needle–like (aragonite), rhombohedra–like (calcite) microcrystals and ethyl cellulose micro–rods, as well as highly porous hydrophilic and hydrophobic silica microparticles at these liquid interfaces. The importance of these results is in gaining an understanding of the adsorption behaviour and demonstrating actual information on anisotropic particles which have potential applications in industrial formulations and products. We also investigate how carboxylate modified latex (CML) microparticles adsorb at liquid surfaces and the preferred type of emulsion they can stabilise depending on the particle size and the surface density of carboxylic groups. We also study, both theoretically and experimentally, the effect of salt in the aqueous phase on the contact angle of such microparticles. The main finding is that the wettability of CML microparticles is governed by the carboxylic group density on the particle surface rather than their ionisation. We demonstrate that the type of Pickering emulsions is governed by the wettability of microparticles at the oil–water interface. We study the effect of the initial impregnation of porous particles with polar or non–polar phases on their attachment at liquid interfaces both theoretically and experimentally. Model supra–particles have been prepared by using building blocks of smaller colloid particles packed in a spherical aggregate. The particles were produced by drying latex particle suspensions of various particle volume fractions and concentrations, followed by partial fusion of the particles achieved by thermal annealing. We have studied the particle surface morphology and porosity and showed how the annealing temperature, the initial particle volume fraction of sulphate latex suspension and the evaporation temperature can be used to control the supra–particle final structure and porosity. Furthermore, we have investigated the link between the wettability of the porous supra–particle building blocks, i.e. sulphate latex particles, and the macroscopic (apparent) contact angle of the porous supra–particle when attached to liquid surfaces. The contact angles of porous supra–particles infused with water at the oil–water interface were found to be much bigger than those at the air–water interface as expected. We also show how the type of liquid filling the pores of the supra–particle affects its macroscopic contact angle at the oil–water interface

Occurrence and germination of dinoflagellate cysts in surface sediments from the Red Sea off the coasts of Saudi Arabia

AbstractThe distribution and abundance of dinoflagellate cyst assemblages were investigated in surface sediments from south-western Red sea coasts of Saudi Arabia at six sites during March 2010. A total of 19 taxa of dinoflagellate cysts were identified from all sites. The sampling sites showed a similar cyst assemblage, but they differed in total cyst abundance (3 to 4083 cysts g−1 dry weight). Cyst abundance was strongly correlated with sediment characteristics, the highest numbers being recorded in sediments with large contents of organic carbon, silt and clay. Cyst assemblages were dominated by cysts of potentially toxic species, including Cochlodinium polykrikos, Prorocentrum minimum, Dinophysis acuminata, Alexandrium catenella and Scrippsiella trochoidea. Most cysts germinated successfully at different rates at 15 and 25° C. This study suggests that surface sediments from all Saudi Red Sea coasts should be monitored for the presence of dinoflagellate cysts to give ample warning of the presence and abundance of toxic species in a given area

Direct Enantiomeric Resolution of Betaxolol with Application to Analysis of Pharmaceutical Products

A high-performance liquid chromatographic (HPLC) method has been developed for the separation and determination of S- and R-enantiomers of betaxolol in tablets and ophthalmic preparations. Baseline resolution was achieved by using teicoplanin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic T with fluorescence detection at excitation/emission wavelengths 275/305 nm. The polar ionic mobile phase (PIM) consists of methanol-glacial acetic acid-triethylamine, (100:0.020:0.025, v/v/v) has been used at a flow rate of 1.5 ml/min. All analytes with S-(–)-atenolol as internal standard were conducted at ambient temperature. The method is highly specific where another coformulated compounds did not interfere. The stability of betaxolol enantiomers under different degree of temperature also studied. The results showed that it is stable for at least 7 days at 70°C. The method validated for its linearity, accuracy, precision and robustness. Experimental design was used during validation to evaluate method robustness. Using the chromatographic conditions described, S- and R-betaxolol were well resolved with mean retention times of 11.3 and 12.6 min, respectively. Linear response (r > 0.997) was observed over the range of 10–500 ng/ml of betaxolol enantiomers, with detection limit of 5 ng/ml. The recoveries of S- and R-betaxolol from tablets and ophthalmic preparation ranged from 97.4 to 101.4% and 98.0 to 102.0%, respectively. The mean relative standard deviation (R.S.D.%) for both enantiomers were 1.1–1.4% and 1.3–1.7% in tablets and ophthalmic solution, respectively

Induced voltages on fence wires and pipelines by AC powertransmission lines

A method is developed for calculating the induced voltages on fence wires/pipelines underneath AC power transmission lines. The method is based on the charge simulation technique and takes into account the disturbances of the electric field and potential due to the presence of the fence wire/pipeline underneath the line. The calculated values of the induced voltage on fence wires are compared with those measured before. Induced voltages on pipelines underneath 230- and 380-kV lines are measured, correlated to the calculated values and discussed in the light of electric field induction on objects adjacent to AC power transmission line

Induced voltages on fence wires and pipelines by AC powertransmission lines

A method is developed for calculating the induced voltages on fence wires/pipelines underneath AC power transmission lines. The method is based on the charge simulation technique and takes into account the disturbances of the electric field and potential due to the presence of the fence wire/pipeline underneath the line. The calculated values of the induced voltage on fence wires are compared with those measured before. Induced voltages on pipelines underneath 230- and 380-kV lines are measured, correlated to the calculated values and discussed in the light of electric field induction on objects adjacent to AC power transmission line

Combined method based on inversion and charge simulation forcalculating electric stresses in three-core belted cables

A combined method based on inversion and charge-simulation techniques for calculating the electric field everywhere in three-core belted cables is developed. A small number of simulation charges is required for accurate field determination. The set of equations which describe the potential and field is solved only once with direct determination of the electric potential and field values at any time instant. All of this achieved higher accuracy with a drastic saving in computer time in comparison with previous method

Calculation of electric stresses in three-core belted cables

The authors present a combined method based on inversion and charge-simulation techniques for calculating the electric field in three-core belted cables. Numerical techniques have been developed based on the charge-representation, charge-simulation and successive-imaging methods. The set of equations which describe the potential and field is solved only once with direct determination of the electric potential and field values at any time instant. This achieved higher accuracy with a very large saving in computer time in comparison with previous method

Harmonic signals in Saudi Arabia industrial plants

Results of a preliminary survey of harmonic levels within the Saudi Arabian power network and industrial facilities are presented. The major industries are petrochemical related and a number of arc furnaces. The voltage and current harmonic levels are within the IEEE 519-1992 standard. The results indicate a growing level of harmonics as more and more petrochemical industries are connected to the network