Advances in Colloid and Interface Science (v.166, #1-2)

This paper presents a review of the published articles related to froth stability and its importance in mineral flotation. Froth structure and froth stability are known to play a significant role in determining the mineral grade and recovery achieved in a flotation operation. Froth stability is depending not only on the type and concentration of the frother but also on the nature and amount of the particles present in the system. To date, there is no specific criterion to quantify froth stability although a number of parameters are used as indicators of froth stability. Linking froth stability to the metallurgical performance is also challenged.Froth stability has a significant role in determining the mineral grade and recovery achieved in a flotation operation. Froth stability is depending not only on the type and concentration of the surfactant used but also on the nature and concentration of the particles present in the system. To date, there is no specific criterion to quantify froth stability although a number of parameters are used as indicators of froth stability.Display Omitted► The importance of froth stability in mineral flotation was reviewed. ► Froth stability determines mineral grade and recovery in flotation operations. ► Froth stability is depending on the concentration and type of frother and particles. ► There is no specific criterion to quantify froth stability.
Keywords: Froth; Frother; Froth stability; Froth flotation; Flotation performance;

Magnetic fluid hyperthermia: Focus on superparamagnetic iron oxide nanoparticles by Sophie Laurent; Silvio Dutz; Urs O. Häfeli; Morteza Mahmoudi (8-23).
Due to their unique magnetic properties, excellent biocompatibility as well as multi-purpose biomedical potential (e.g., applications in cancer therapy and general drug delivery), superparamagnetic iron oxide nanoparticles (SPIONs) are attracting increasing attention in both pharmaceutical and industrial communities. The precise control of the physiochemical properties of these magnetic systems is crucial for hyperthermia applications, as the induced heat is highly dependent on these properties. In this review, the limitations and recent advances in the development of superparamagnetic iron oxide nanoparticles for hyperthermia are presented.Magnetic fluid hyperthermia has been developed through the testing of different superparamagnetic nanoparticles in vitro and in vivo, and has now reached the stage of clinical trials for the treatment of many different cancer types.Display Omitted► Size and surface modified SPIONs enable a safe and reproducible application to the tumor. ► SPIONs can be magnetically targeted and concentrated in the tumor tissue. ► Optimized SPIONs show a heating efficiency sufficient for a hyperthermia tumor therapy. ► Cancer specific binding agents on the SPIONs surface makes this therapy very selective. ► First clinical trials with SPION hyperthermia were carried out and showed promising results.
Keywords: Superparamagnetic iron oxide nanoparticles; Physiochemical properties; Cancer; Hyperthermia; Theragnostics;

Electro-optic properties of organic nanotubes by Stoyl P. Stoylov; Svetla Stoilova-McPhie (24-35).
In this review article the theoretical and experimental possibilities of applying EO-methods for estimation of the physico-chemical properties of the organic nanotubes (ONTs) are studied. The ONTs are highly organized nanostructures of strongly elongated, anysometric, and hollow cylinders with a size range of 1 nm to 10,000 nm, e.g. in aqueous solutions they could behave as colloid (disperse) particles. They have high interaction ability due to their extremely large curved, rolled-up external surfaces (bilayers of membrane walls) and unique properties because of their specific electric charge distribution and dynamics that make possible the functionalization of their surfaces. Thus they could template guestsubstances such as membrane proteins and protein complexes on the exterior surfaces and in the membrane. We performed our investigations for the case of ONT aqueous colloid suspension. Following our earlier proposition of the general expression for the electro-optic (EO) effect we derived equations for the evaluation of the electric properties of ONT particles such as mechanism of electric polarization and identification of their most important electric Dipole Moments (DM), permanent (pDM) and induced (iDMs). Further we recommend ways for the calculation of their magnitude and direction. Also we evaluated some geometrical properties such as length of the ONT particles and their polydispersity.The knowledge that we provided about the ONT properties may enable us to elucidate and predict their biological activity. Templating biological active ligands (such as membrane proteins and protein complexes) on the inner and outer surfaces as well as in the surface membrane creates their potential usefulness as carrier and deliverer of biopharmaceuticals in bio-nanodevices.The theoretical equations were compared with the experimental data for ONTs such as (lipid) LNT, Tobacco Mosaic Virus (TMV) and microtubules (MT). Comparison of EO methods with other methods used till now shows that the EO methods are faster, not invasive and do not alter the studied particles.Display OmittedDispersion curve of the steady-state electro-optic (EO) effect dependence of the applied electric field frequency (ν), showing the critical frequencies corresponding to the different dipole moments of organic nanotubes (ONT). Inset: cryo-electron micrograph of A. Single bilayer lipid nanotubes (LNT) frozen-hydrated and suspended in a hole of 2 μm in diameter. B. Magnified view, scale bar = 100 nm.► A correct theoretical consideration of the electro-optic (EO) effect of nanotubes has been made. ► A simple equation for the identification of permanent dipole moment has been derived. ► Recommendations for the rapid electro-optic (EO) characterization of organic nanotubes (ONT) have been proposed. ► The agreement between theory and experimental results for organic nanotubes (ONT) has been found to be satisfactory.
Keywords: Colloids electro-optics; Organic nanotubes; Permanent and induced dipole moments; Optical anisotropy; Surface charge; Polarization;

Industrial wastes, such as, fly ash, blast furnace slag and sludge, black liquor lignin, red mud, and waste slurry, etc. are currently being investigated as potential adsorbents for the removal of the heavy metals from wastewater. It was found that modified industrial wastes showed higher adsorption capacity. The application of low-cost adsorbents obtained from the industrial wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. The adsorption mechanism, influencing factors, favorable conditions, and competitive ions etc. on the adsorption of heavy metals have also been discussed in this article. From the review, it is evident that certain industrial waste materials have demonstrated high removal capacities for the heavy metals laden with wastewater. However, it is to be mentioned that adsorption capacities of the adsorbents vary depending on the characteristics of the adsorbents, the extent of chemical modification and the concentration of adsorbates. There are also few issues and drawbacks on the utilization of industrial wastes as low-cost adsorbents that have been addressed. In order to find out the practical utilization of industrial waste as low-cost adsorbents on the commercial scale, more research should be conducted in this direction.Industrial wastes, such as, fly ash, blast furnace slag and sludge, black liquor lignin, red mud, and waste slurry, etc. are currently being investigated as potential adsorbents for the removal of the heavy metals from the wastewater. It was found that the modified industrial wastes showed higher adsorption capacity. The application of low-cost adsorbents obtained from the industrial wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. From the review, it is evident that certain industrial waste materials have demonstrated high removal capacities for the heavy metals laden with wastewater. The figure shows the adsorption capacities of Zn(II) on various industrial wastes adsorbents.Display Omitted► Industrial wastes have been investigated for heavy metals removal from wastewaters. ► Fly ash, waste slurry, red mud, lignin, sugar beet pulp, blast furnace slag, tea industry waste, and sugar cane bagasse have been proven to be a promising material. ► For efficient utilization of these industrial wastes as potential adsorbents newer technology should be developed. ► To find out the practical utilization, more research should be conducted in this direction.
Keywords: Industrial wastes; Fly ash; Sludge; Red mud; Metals; Adsorption; Adsorbent; Wastewater treatment;

Surfactant influence on rivulet droplet flow in minitubes and capillaries and its downstream evolution by Mohamed E. Labib; Stanislav Dukhin; Joseph Murawski; Yacoob Tabani; Richard Lai (60-86).
During our investigations of two-phase flow in long hydrophobic minitubes and capillaries, we have observed transformation of the main rivulet into different new hydrodynamic modes with the use of different kinds of surfactants. The destabilization of rivulet flow at air velocities < 80 m/s occurs primarily due to the strong branching off of sub-rivulets from the main rivulet during the downstream flow in the tube. The addition of some surfactants of not-so-high surface activity was found to increase the frequency of sub-rivulet formation and to suppress the Rayleigh and sinuous instabilities of the formed sub-rivulets. Such instabilities result in subsequent fragmentation of the sub-rivulets and in the formation of linear or sinuous arrays of sub-rivulet fragments (SRFs), which later transform into random arrays of SRFs. In the downstream flow, SRFs further transform into large sliding cornered droplets and linear droplet arrays (LDAs), a phenomenon which agrees with recent theories. At higher surface activity, suppression of the Rayleigh instability of sub-rivulets with surfactants becomes significant, which prevents sub-rivulet fragmentation, and only the rivulet and sub-rivulets can be visualized in the tube. At the highest surface activity, the bottom rivulet transforms rapidly into an annular liquid film. The surfactant influence on the behavior of the rivulets in minitubes is incomparably stronger than the classic example of the known surfactant stabilizing influence on a free jet. The evolution of a rivulet in the downstream flow inside a long minitube includes the following sequence of hydrodynamic modes/patterns: i) single rivulet; ii) rivulet and sub-rivulets; and iii) rivulet, sub-rivulets, sub-rivulet fragments, cornered droplets, linear droplet arrays, linear arrays of sub-rivulet fragments and annular film. The formation of these many different hydrodynamic patterns downstream is in drastic contrast with the known characteristics of two-phase flow, which demonstrates one mode for the entire tube length. Recent achievements in fluid mechanics regarding the stability of sliding thin films and in wetting dynamics have allowed us to interpret many of our findings. However, the most important phenomenon of the surfactant influence on sub-rivulet formation remains poorly understood. To achieve further progress in this new area, an interdisciplinary approach based on the use of methods of two-phase flow, wetting dynamics and interfacial rheology will be necessary.Surface flow entities on the image are: rivulet, two sub-rivulets, linear array of sub-rivulet fragments, linear array of droplet and random dropletsDisplay Omitted► Effect of surfactants on rivulet flow in minitubes. ► Hydrodynamic modes of two-phase flow in minitubes. ► Instabilities of liquid in high-velocity air in narrow tubes. ► Visualization of two-phase flow in narrow lumens. ► Wetting and de-wetting in minitubes.
Keywords: Surfactant; Marangoni stress; Wetting dynamics; Interfacial rheology; Two-phase flow; Rivulet; Sub-rivulet; Sub-rivulet fragment; Sliding droplet; Cornered droplet; Linear droplet array; Rayleigh instability; Sinuous instability; Minitube cleaning; Meandering; Two-phase flow maps;

Lead free solders are increasingly being used in electronic applications. Eutectic Sn–Cu solder alloy is one of the most favored lead free alloys used for soldering in electronic applications. It is inexpensive and principally used in wave soldering. Wetting of liquid solder on a substrate is a case of reactive wetting and is accompanied by the formation of intermetallic compounds (IMCs) at the interface. Wettability of Sn–0.7Cu solder on metallic substrates is significantly affected by the temperature and the type of flux. The wettability and microstructural evolution of IMCs at the Sn–0.7Cu solder/substrate interfaces are reviewed in the present paper. The reliability of solder joints in electronic packaging is controlled by the type and morphology of interfacial IMCs formed between Sn–0.7Cu solder and substrates. The formation and growth mechanisms of interfacial IMCs are highlighted. Mechanical behavior of bulk solder alloy and solder joint interfaces are analyzed. The characteristics of the IMCs which have marked effect on the mechanical properties and fracture behavior as well as reliability of solder joints of the alloy are discussed. An attempt has also been made to discuss the effect of cooling rate and strain rate on shear strength, tensile properties and creep resistance of the solder alloy. It is recommended that future work should focus on evolving a standard procedure involving sequential assessment of wetting behavior, evolution of IMCs and mechanical properties.Wettability and the formation of IMCs at the interface are very much interrelated and cannot be separately studied. The reactive wetting between eutectic Sn–0.7Cu solder alloy and metallic substrates is reviewed in the present paper. The evolution and growth of intermetallic compounds (IMCs) and their role in solder joint reliability is highlighted.Display Omitted► Review of wettability of Sn–0.7Cu solder and the type and morphology of interfacial IMCs. ► Discussion of IMC characteristics that have a marked effect on solder joint reliability. ► Need for developing a microstructure dependent model for predicting interface damage in solder joint. ► Importance of sequential assessment of wetting behavior, evolution of IMCs and mechanical properties.
Keywords: Reactive wetting; Sn–0.7Cu lead-free solder; Contact angle; IMC;

Utilization of metallic nanoparticles in various biotechnological and medical applications represents one of the most extensively investigated areas of the current materials science. These advanced applications require the appropriate chemical functionalization of the nanoparticles with organic molecules or their incorporation in suitable polymer matrices. The intensified interest in polymer nanocomposites with silver nanoparticles is due to the high antimicrobial effect of nanosilver as well as the unique characteristics of polymers which include their excellent structural uniformity, multivalency, high degree of branching, miscellaneous morphologies and architectures, and highly variable chemical composition. In this review, we explore several aspects of antimicrobial polymer silver nanocomposites, giving special focus to the critical analysis of the reported synthetic routes including their advantages, drawbacks, possible improvements, and real applicability in antibacterial and antifungal therapy. A special attention is given to “green” synthetic routes exploiting the biopolymeric matrix and to the methods allowing preparing magnetically controllable antimicrobial polymers for targeting to an active place. The controversial mechanism of the action of silver against bacteria, fungi and yeasts as well as perspectives and new applications of silver polymeric nanocomposites is also briefly discussed.The intensified interest in polymer nanocomposites with silver nanoparticles is due to the high antimicrobial effect of silver. The effort to stabilize the particles in order to be applicable for the antibacterial treatment of the medicinal and other instruments resulted in an enormous expansion of synthetic routes toward silver polymeric nanocomposites. In this review, we critically discuss their advantages, drawbacks and real applicability as antimicrobial and disinfection agents.Display Omitted► Synthetic routes toward silver–polymer nanocomposites are classified and critically reviewed. ► Advantages, drawbacks and applicability in antimicrobial and disinfection treatments. ► “Green” synthetic approaches. ► One-step approaches to polymers with attached silver, without the use of any extra reducing agent. ► Magnetic silver–polymer nanocomposites enabling targeted antimicrobial action and consequent removal.
Keywords: Silver nanoparticle; Polymer nanocomposite; Antimicrobial agent; Composite material; Nanobiotechnology;