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Advances in Colloid and Interface Science (v.162, #1-2)

Editorial Board (pp. iii).

Editorial Board (pp. ifc).

The mechanism of polyelectrolyte-assisted retention of TiO₂ filler particles during paper formation by Ulrich Gesenhues (pp. 1-21).

The mechanism of the retention of TiO₂ filler particles on cellulose fibers has been under discussion for several decades; the diverse models, and the properties of the components relevant to retention, are critically reviewed in the first part of this study. In addition, two new quantitative models of detachment of polyelectrolyte-bonded colloidal particles from the fiber are also examined; one of these is based on DLVO theory for description of the influence of particle charge and polyelectrolyte amount, and should hold true at low shear rates and high bond strengths. The other model applies Kolmogorov's theory of isotropic turbulence in order to relate the work necessary for particle detachment to the turbulent energy of pulp in paper machines, i.e., under high shear rate and low bond-strength conditions. The second model is based on analysis of fluid dynamics in paper machines, and is formulated here for laboratory tests using the Dynamic Drainage Jar (DDJ). A series of laboratory-prepared TiO₂ fillers covering a range of isoelectric points ( ieps) from pH 4.4 to pH 7.5, additionally with poly-(aminoamide)-epichlorohydrin (PAE) and polyethyleneimine (PEI) as retention aids, and commercially milled cellulose, were used in the experimental part of the study. The retention-aid demand of fillers and cellulose for surface neutralization was determined using electrokinetic methods. Filler retention on cellulose was measured in the DDJ for various stirrer speeds and amounts of retention aid, with the amount of filler not exceeding that for a monolayer on the fiber. Without retention aids, neutral filler particles are accordingly completely retained on the negative fiber, whereas negatively charged particles are not. The retention of the latter can, however, be steadily improved by increasing polyelectrolyte concentration. Retention of colloidal particles in paper manufacturing is therefore determined by a delicate balance between H-bridging and van der Waals forces, on the one hand, and Coulomb forces, on the other, resolving the long-enduring debate concerning the relative influence of bridging and patch-charge mechanisms. Results obtained using PAE also indicate that polyelectrolytes initially spread over the filler surface are redistributed into the gap between the filler particle and the fiber during filler attachment.

Keywords: Cellulose; Polyelectrolyte; Titania; Retention; Dynamic drainage jar; Isoelectric point; Turbulence

The environmental applications of activated carbon/zeolite composite materials by K.Y. Foo; B.H. Hameed (pp. 22-28).

Over the past couple of years, the resurgence of placing an effective and sustainable amendment to combat against the auxiliary industrial entities, remains a highly contested agenda from a global point. With the renaissance of activated carbon, there has been a steadily growing interest in the research field. Recently, the adoption of zeolite composite, a prestigious advanced catalyst which formulates the enhancement of adsorption rate and hydrogen storage capability, has fore fronted to be a new growing branch in the scientific community. Confirming the assertion, this paper presents a state of art review of activated carbon/zeolite composite technology, its fundamental background studies, and environmental implications. Moreover, its major challenges together with the future expectation are summarized and discussed. Conclusively, the expanding of activated carbon/zeolite composite represents a potentially viable and powerful tool, leading to the plausible improvement of environmental preservation.

Keywords: Activated carbon; Adsorption; Composite; Hydrogen storage; Zeolite

Self-organization in the flow of complex fluids (colloid and polymer systems). Part 2: Theoretical models by A.V. Subbotin; A.Ya. Malkin; V.G. Kulichikhin (pp. 29-38).

Flow induced transitions in complex fluids are usually accompanied by changes in the internal media structure and the flow symmetry. In this review paper, we discuss the theoretical models and approaches that have been used for the analysis of different types of flow instabilities and flow patterns. The main attention is focused on the basic fluid models which reveal vortex and banding flow structures at high shear rates. The Oldroyd-B fluid is one of such models. The Reynolds and the Weissenberg (or Deborah) numbers are the parameters governing its flow behavior. For this model, the secondary flow patterns arising in viscometric flows of different geometries at the bifurcation point are described. Complex fluids which are able to exist in multiple states can form coexisting bands of different structures with different rheological properties and flowing with different shear rates at the same shear stress. Shear banding is typical for fluids demonstrating non-monotonous flow curves described by such models as the diffusive Johnson–Segalman fluid model, for example. Recent progress in exploring this phenomenon is discussed.

Keywords: Rheology; Constitutive equations; Instability; Secondary flow; Shear banding; Elasticity

Kinetics of adsorption of metal ions on inorganic materials: A review by Susmita Sen Gupta; Krishna G. Bhattacharyya (pp. 39-58).

It is necessary to establish the rate law of adsorbate–adsorbent interactions to understand the mechanism by which the solute accumulates on the surface of a solid and gets adsorbed to the surface. A number of theoretical models and equations are available for the purpose and the best fit of the experimental data to any of these models is interpreted as giving the appropriate kinetics for the adsorption process. There is a spate of publications during the last few years on adsorption of various metals and other contaminants on conventional and non-conventional adsorbents, and many have tried to work out the kinetics. This has resulted from the wide interest generated on using adsorption as a practical method for treating contaminated water. In this review, an attempt has been made to discuss the kinetics of adsorption of metal ions on inorganic solids on the basis of published reports. A variety of materials like clays and clay minerals, zeolites, silica gel, soil, activated alumina, inorganic polymer, inorganic oxides, fly ash, etc. have been considered as the adsorbents and cations and anions of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn as adsorbate have been covered in this review. The majority of the interactions have been divided into either pseudo first order or second order kinetics on the basis of the best fit obtained by various groups of workers, although second order kinetics has been found to be the most predominant one. The discussion under each category is carried out with respect to each type of metal ion separately. Application of models as given by the Elovich equation, intra-particle diffusion and liquid film diffusion has also been shown by many authors and these have also been reviewed. The time taken for attaining equilibrium in each case has been considered as a significant parameter and is discussed almost in all the cases. The values of the kinetic rate coefficients indicate the speed at which the metal ions adsorb on the materials and these are discussed in all available cases. The review aims to give a comprehensive picture on the studies of kinetics of adsorption during the last few years.The review discusses the kinetics of adsorption of metal ions on inorganic solids based on publications of last ten years. Materials like clays and clay minerals, zeolites, silica gel, soil, activated alumina, inorganic polymer, inorganic oxides, fly ash, etc. have been used as sorbents for As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn. The majority of the interactions have been reported as following either pseudo first order or second order kinetics. Application of Elovich equation, intra-particle diffusion and liquid film diffusion kinetics has also been reviewed. The kinetic rate coefficients indicate the speed at which the metal ions are taken up by the materials.Second order plots for Cr(VI) adsorbed on natural and modified kaolinite (experimental conditions: adsorbent 2gL−¹, Cr(VI) 50mgL−¹, pH 4.6, and temperature 303K).Display Omitted► Kinetics of adsorption of metal ions on inorganic solids done during last ten years is reviewed. ► Clays, zeolites, silica gel, alumina, oxides, fly ash, etc., are considered as sorbents. ► Most interactions are reported as following pseudo first order or second order kinetics. ► Application of Elovich, intra-particle and liquid film diffusion models are also reviewed. ► The rate coefficients for sorption of metal ions on various materials are given and discussed.

Keywords: Inorganic adsorbents; Metal ions; Kinetics; Adsorption

Clouding behaviour in surfactant systems by Partha Mukherjee; Susanta K. Padhan; Sukalyan Dash; Sabita Patel; Bijay K. Mishra (pp. 59-79).

A study on the phenomenon of clouding and the applications of cloud point technology has been thoroughly discussed. The phase behaviour of clouding and various methods adopted for the determination of cloud point of various surfactant systems have been elucidated. The systems containing anionic, cationic, nonionic surfactants as well as microemulsions have been reviewed with respect to their clouding phenomena and the effects of structural variation in the surfactant systems have been incorporated. Additives of various natures control the clouding of surfactants. Electrolytes, nonelectrolytes, organic substances as well as ionic surfactants, when present in the surfactant solutions, play a major role in the clouding phenomena. The review includes the morphological study of clouds and their applications in the extraction of trace inorganic, organic materials as well as pesticides and protein substrates from different sources.Cloud point behaviour of nonionic surfactant systems has wide applications in separation technology.Display Omitted► Clouding behavior and basic principles of clouding in surfactant systems. ► Clouding in anionic as well as cationic surfactants. ► Role of additives on clouding phenomenon. ► The morphological study of clouds. ► Applications in the extraction of trace inorganic, pesticides and proteins.

Keywords: Surfactant; Cloud point technology; Micelles; Microemulsions; Preconcentration; Extraction; Phase behaviour

Electro-optic effects of colloidal crystals by Tsuneo Okubo; Akira Tsuchida; Maria Stoimenova (pp. 80-86).

Many kinds of electro-optic effects of colloidal crystals are observed and discussed on the basis of the fundamental properties of colloidal crystals themselves. Several electro-optic effects of colloidal crystals have been found by the authors mainly by use of light-scattering, reflection- and transmitted-light intensity measurements in an electric field, (a) waveform deformation, (b) phase-shift effects, (c) second-order harmonics generation, (d) self-resonance frequency generation (characteristic frequency and harmonic oscillation), (e) peak wavelength-shift effects and (f) waveform transformation. These electro-optic responses are explained successfully by the resonance-, visco-elastic- and structural relaxation-parameters of colloidal crystals.Giant single crystals and self-resonance effects of colloidal crystals.Display Omitted►Why colloidal crystallization takes place is reviewed. ►Fundamental properties of colloidal crystals relating the electro-optics are reviewed. ►Wave-form deformation and phase-shift effects of colloidal crystals are discussed. ►Harmonics generation and self-resonance effects of colloidal crystals are discussed.

Keywords: Electro-optics; Colloidal crystal; Electrical double layer; Structural relaxation time; Visco-elasticity

Understanding protein adsorption phenomena at solid surfaces by Michael Rabe; Dorinel Verdes; Stefan Seeger (pp. 87-106).

Protein adsorption at solid surfaces plays a key role in many natural processes and has therefore promoted a widespread interest in many research areas. Despite considerable progress in this field there are still widely differing and even contradictive opinions on how to explain the frequently observed phenomena such as structural rearrangements, cooperative adsorption, overshooting adsorption kinetics, or protein aggregation. In this review recent achievements and new perspectives on protein adsorption processes are comprehensively discussed. The main focus is put on commonly postulated mechanistic aspects and their translation into mathematical concepts and model descriptions. Relevant experimental and computational strategies to practically approach the field of protein adsorption mechanisms and their impact on current successes are outlined.Display Omitted► We discuss the latest findings on mechanistic details of protein adsorption. ► Important effects: cooperative adsorption, overshootings, relaxation, and aggregation. ► Experimental, mathematical, and computational concepts are reviewed.

Keywords: Protein adsorption mechanisms; Cooperative protein adsorption; Overshooting adsorption kinetics; Protein aggregation; MD- and MC-simulation

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Advances in Colloid and Interface Science (v.162, #1-2)