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Advances in Colloid and Interface Science (v.153, #1-2)

Editorial Board (pp. iii).

Streaming potential studies of colloid, polyelectrolyte and protein deposition by Z. Adamczyk; K. Sadlej; E. Wajnryb; M. Nattich; M.L. Ekiel-Jeżewska; J. Bławzdziewicz (pp. 1-29).

Recent developments in the electrokinetic determination of particle, protein and polyelectrolyte monolayers at solid/electrolyte interfaces, are reviewed. Illustrative theoretical results characterizing particle transport to interfaces are presented, especially analytical formulae for the limiting flux under various deposition regimes and expressions for diffusion coefficients of various particle shapes. Then, blocking effects appearing for higher surface coverage of particles are characterized in terms of the random sequential adsorption model. These theoretical predictions are used for interpretation of experimental results obtained for colloid particles and proteins under convection and diffusion transport conditions. The kinetics of particle deposition and the structure of monolayers are analyzed quantitatively in terms of the generalized random sequential adsorption (RSA) model, considering the coupling of the bulk and surface transport steps. Experimental results are also discussed, showing the dependence of the jamming coverage of monolayers on the ionic strength of particle suspensions. In the next section, theoretical and experimental results pertaining to electrokinetics of particle covered surfaces are presented. Theoretical models are discussed, enabling a quantitative evaluation of the streaming current and the streaming potential as a function of particle coverage and their surface properties (zeta potential). Experimental data related to electrokinetic characteristics of particle monolayers, mostly streaming potential measurements, are presented and interpreted in terms of the above theoretical approaches. These results, obtained for model systems of monodisperse colloid particles are used as reference data for discussion of experiments performed for polyelectrolyte and protein covered surfaces. The utility of the electrokinetic measurements for a precise, in situ determination of particle and protein monolayers at various interfaces is pointed out.

Keywords: Colloid deposition; Nanoparticle deposition; Particle covered surfaces; Polyelectrolyte deposition; Protein deposition; Streaming potential of covered surfaces

Factors governing partial coalescence in oil-in-water emulsions by Eveline Fredrick; Pieter Walstra; Koen Dewettinck (pp. 30-42).

The consequences of the instability mechanism partial coalescence in oil-in-water food emulsions show a discrepancy. On the one hand, it needs to be avoided in order to achieve an extended shelf life in food products like sauces, creams and several milk products. On the other hand, during the manufacturing of products like ice cream, butter and whipped toppings partial coalescence is required to achieve the desired product properties. It contributes to the structure formation, the physicochemical properties (stability, firmness,…) and the sensory perception, like fattiness and creaminess of the final food products. This review critically summarises the findings of partial coalescence in oil-in-water emulsions in order to provide insight in how to enhance and retard it. Next to the pioneering work, a large set of experimental results of more recent work is discussed. First, the general mechanism of partial coalescence is considered and a distinction is made between partial and ‘true’ coalescence. The main differences are: the required solid particles in the dispersed oil phase, the formation of irregular clusters and the increased aggregation rate. Second, the kinetics of partial coalescence is discussed. In more detail, potential parameters affecting the rate of partial coalescence are considered by means of the encounter frequency and capture efficiency of the fat globules. The flow conditions, the fat volume fraction and the physicochemical properties of continuous aqueous phase affect both the encounter frequency and capture efficiency while the actual temperature, temperature history and the composition and formulation of the emulsion mainly affect the capture efficiency.

Keywords: Partial coalescence; Emulsions; Cream; Fat crystals; Tempering; Interfacial composition

Ordered mesoporous silica (OMS) as an adsorbent and membrane for separation of carbon dioxide (CO₂) by Thiam-Leng Chew; Abdul L. Ahmad; Subhash Bhatia (pp. 43-57).

Separation of carbon dioxide (CO₂) from gaseous mixture is an important issue for the removal of CO₂ in natural gas processing and power plants. The ordered mesoporous silicas (OMS) with uniform pore structure and high density of silanol groups, have attracted the interest of researchers for separation of carbon dioxide (CO₂) using adsorption process. These mesoporous silicas after functionalization with amino groups have been studied for the removal of CO₂. The potential of functionalized ordered mesoporous silica membrane for separation of CO₂ is also recognized. The present paper reviews the synthesis of mesoporous silicas and important issues related to the development of mesoporous silicas. Recent studies on the CO₂ separation using ordered mesoporous silicas (OMS) as adsorbent and membrane are highlighted. The future prospectives of mesoporous silica membrane for CO₂ adsorption and separation are also presented and discussed.

Keywords: Carbon dioxide; Adsorption; Ordered mesoporous silica; Gas separation; Membrane

GENERIC model for multiphase systems by Leonard M.C. Sagis (pp. 58-69).

GENERIC is a nonequilibrium thermodynamic formalism in which the dynamic behavior of a system is described by a single compact equation involving two types of brackets: a Poisson bracket and a dissipative bracket. This formalism has proved to be a very powerful instrument to model the dynamic behavior of complex bulk phases. In this paper we review the basic principles of the GENERIC formalism, and show how it can be applied to multicomponent multiphase systems with interfaces displaying viscous stress deformation behavior. The generalization of the GENERIC formalism to multiphase systems provides a powerful tool to model nonlinear dynamic behavior of complex interfaces in for example emulsions or foam. Adding several interfacial contributions to the standard two-bracket formulation we derive the conservation laws for mass, momentum, and energy for the bulk phases of the system. We also derive the jump balance equations for the surface mass density, surface momentum, and surface energy. In addition to these balance equations we obtain constitutive equations for the extra stress tensor, energy flux vector, and mass flux vectors in the bulk phase, and the surface extra stress tensor, the surface energy flux vector, and surface mass flux vectors of the interface. The GENERIC formalism also allows us to derive constitutive equations for the transport of mass, momentum, and energy from the bulk phase to the interface. The resulting set of equations is compared to those derived using the rational thermodynamic and classical irreversible thermodynamic formalisms, and is in good agreement with the balance equations derived using these formalisms.

Keywords: Nonequilibrium thermodynamics; Interfaces; Surface rheology; GENERIC formalism; Poisson brackets; Dissipative brackets

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Advances in Colloid and Interface Science (v.153, #1-2)

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Advances in Colloid and Interface Science (v.153, #1-2)