Sagheer A. Onaizi

Flocculation and viscoelastic behavior of industrial papermaking suspensions

The effects of the surface charge type and density C496, C492 and A130LMW polyacrylamides (PAMs) on the rheological behavior of real industrial papermaking suspensions were quantitatively related to the degree of flocculation for the same industrial papermaking suspensions. The floc sizes were larger but less dense when anionic PAM was used, and this due to the repulsive forces between the anionic PAM and colloidal particles, leading to the development of open structure flocs of less density. On the other hand, rheological measurements showed that the papermaking suspension is thixotropic with a measurable yield stress. The results showed that the magnitude of the critical stress, τc, complex viscosity, η*, elastic modulus, G′, and viscous modulus, G″, depend on the number of interactions between the PAM chains and particle surface and the strength of those interactions. Cationic PAM showed higher values of η*, G′, G″ and τc compared to anionic PAM. This behavior is in good agreement with Bingham yield stress, τB, adsorption and effective floc density results. Similar to oscillatory measurements, creep measurements also showed that the deformation was much lower for the cationic PAM based suspensions than for the anionic PAM based suspensions. Furthermore, the results revealed that increasing the cationic PAM surface charge decreases the floc size but increases the adsorption rate, elasticity and effective floc density proposing differences in the floc structures, which are not revealed clearly in the Bingham yield stress measurements.

Adsorption of an anionic surfactant at air-liquid and different solid-liquid interfaces from solutions containing high counter-ion concentration

The self-assembly (adsorption) of the anionic surfactant, sodium dodecylbenzenesulphonate (SDBS), at air-liquid and different (octadecanethiol, β-mercaptoethanol, α-lipoic acid) solid-liquid interfaces from aqueous solutions containing high concentrations of counter-ion has been investigated. SDBS adsorption at the solid-liquid interfaces was obtained using surface plasmon resonance (SPR) while its adsorption at the air-liquid interface was extracted from surface tension measurements. The results have demonstrated that SDBS packing at the air-liquid interface is similar to its packing at the hydrophobic octadecanethiol-liquid interface. Additionally, SDBS packing at the three solid-liquid interfaces increases with increasing surface hydrophobicity, irrespective whether the surface is neutral or negatively charged. Nonetheless, SDBS adsorption is always within monolayer coverage (no evidence of bilayer or admicelle formation). The results have also revealed that SDBS affinity for the solid-liquid interfaces increases with increasing surface hydrophobicity. Furthermore, SDBS affinity for the air-liquid interface is more than 10-fold its affinity for the solid-liquid interfaces.

Lysozyme binding to tethered bilayer lipid membranes prepared by rapid solvent exchange and vesicle fusion methods

Abstract Tethered bilayer lipid membranes (tBLMs) are important tools for studying protein–lipid interactions. The widely used methodology for the preparation of these membranes is the fusion of phospholipid vesicles from an aqueous medium onto an anchored phospholipid layer. The preparation of phospholipid vesicles is a long and tedious procedure. There is another simple method, rapid solvent exchange, for preparing lipid membranes. However, there is a lack of information on the effects of the preparation method of tBLMs on their interactions with proteins. Therefore, we present in this paper a comparative study on the binding of lysozyme onto tBLMs prepared by the abovementioned methods. The prepared tBLMs have either zwitterionic or anionic characteristics. The results show that lysozyme binding onto the prepared tBLMs is unaffected by the preparation method of the tBLMs, suggesting that the tedious fusion method might be replaced by the simple rapid solvent exchange method without altering the level of protein–lipid interactions.

Effect of the degree of template removal from mesoporous silicate materials on their adsorption of heavy oil from aqueous solution

The key aim of this study is to evaluate the adsorption of heavy oil from aqueous solutions with different oil contents over mesoporous silicate materials having different surfactant template contents. The mesoporous silicate materials have been synthesized from tetraethylorthosilicate as a silica precursor and cetyltrimethylammonium bromide as a template using the sol-gel technique. Four samples were prepared by (1) totally removing the template using the calcination process, (2) partially removing the template via ethanol extraction, (3) partially removing the template via water extraction, and (4) keeping the template as synthesized, respectively. These four samples have been characterized using X-ray diffraction, nitrogen adsorption, thermal gravimetric analysis and Fourier transformed infrared. The effect of the degree of template removal of these mesoporous materials for the oil removal has been investigated. The oil removal is inversely proportional to the surfactant content in the mesoporous material, being highest for the calcined sample but lowest for the as-synthesized sample. The kinetic of oil adsorption over the calcined material has been also studied and the data obtained fit well a second-order model.