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Advances in Colloid and Interface Science (v.169, #1)
Adsorption and flocculation by polymers and polymer mixtures by John Gregory; Sandor Barany (pp. 1-12).
Polymers of various types are in widespread use as flocculants in several industries. In most cases, polymer adsorption is an essential prerequisite for flocculation and kinetic aspects are very important. The rates of polymer adsorption and of re-conformation (relaxation) of adsorbed chains are key factors that influence the performance of flocculants and their mode of action. Polyelectrolytes often tend to adopt a rather flat adsorbed configuration and in this state their action is mainly through charge effects, including ‘electrostatic patch’ attraction. When the relaxation rate is quite low, particle collisions may occur while the adsorbed chains are still in an extended state and flocculation by polymer bridging may occur. These effects are now well understood and supported by much experimental evidence. In recent years there has been considerable interest in the use of multi-component flocculants, especially dual-polymer systems. In the latter case, there can be significant advantages over the use of single polymers. Despite some complications, there is a broad understanding of the action of dual polymer systems. In many cases the sequence of addition of the polymers is important and the pre-adsorbed polymer can have two important effects: providing adsorption sites for the second polymer or causing a more extended adsorbed conformation as a result of ‘site blocking’.Cationic polyelectrolyte ‘patches’ acting as adsorption sites for anionic, bridging polymer chains.Display Omitted► Flocculation by adsorbed polymers reviewed. ► Rate of polymer adsorption and re-conformation can have large effect on adsorbed amount. ► Competitive adsorption from polymer mixtures. ► Flocculation by polymer mixtures. ► Dual polymer systems – new adsorption points or ‘site blocking’ effects.
Keywords: Polymeric flocculants; Polymer adsorption; Flocculation; Dual polymer systems
Versatility of cyclodextrins in self-assembly systems of amphiphiles by Lingxiang Jiang; Yun Yan; Jianbin Huang (pp. 13-25).
Recently, cyclodextrins (CDs) were found to play important yet complicated (or even apparently opposite sometimes) roles in self-assembly systems of amphiphiles or surfactants. Herein, we try to review and clarify the versatility of CDs in surfactant assembly systems by 1) classifying the roles played by CDs into two groups (modulator and building unit) and four subgroups (destructive and constructive modulators, amphiphilic and unamphiphilic building units), 2) comparing these subgroups, and 3) analyzing mechanisms. As a modulator, although CDs by themselves do not participate into the final surfactant aggregates, they can greatly affect the aggregates in two ways. In most cases CDs will destroy the aggregates by depleting surfactant molecules from the aggregates (destructive), or in certain cases CDs can promote the aggregates to grow by selectively removing the less-aggregatable surfactant molecules from the aggregates (constructive). As an amphiphilic building unit, CDs can be chemically (by chemical bonds) or physically (by host–guest interaction) attached to a hydrophobic moiety, and the resultant compounds act as classic amphiphiles. As an unamphiphilic building unit, CD/surfactant complexes or even CDs on their own can assemble into aggregates in an unconventional, unamphiphilic manner driven by CD–CD H-bonds. Moreover, special emphasis is put on two recently appeared aspects: the constructive modulator and unamphiphilic building unit.Display Omitted► Crucial roles played by CDs in self-assembly systems of amphiphiles either as a modulator or as a building block. ► CD-induced aggregate growth via selective removing the “less-aggregatable” component in surfactant mixtures. ► Unamphiphilic self-assembly behavior of CDs and their complexes mainly driven by CD-CD H-bonds. ► CDs provide a handful and effective approach to control the self-assembly of amphiphiles.
Keywords: Surfactants; Cyclodextrins; Self-assembly; H-bonds; Unamphiphilic
Reactions of dipolar bio-molecules in nano-capsules — example of folding-unfolding process by A. Sanfeld; K. Sefiane; A. Steinchen (pp. 26-39).
The confinement of chemical reactions in nano-capsules can lead to a dramatic effect on the equilibrium constant of these latter. Indeed, capillary effects due to the curvature and surface energy of nano-capsules can alter in a noticeable way the evolution of reactions occurring within.Nano-encapsulation of bio-materials has attracted lately wide interest from the scientific community because of the great potential of its applications in biomedical areas and targeted therapies.The present paper focuses one's attention on alterations of conformation mechanisms due to extremely confining and interacting solvated dipolar macromolecules at their isoelectric point. As a specific example studied here, the folding–unfolding reaction of proteins (particularly RNase A and creatine kinase CK) is drastically changed when encapsulated in solid inorganic hollow nano-capsules.The effects demonstrated in this work can be extended to a wide variety of nano-encapsulation situations. The design and sizing of nano-capsules can even make use of the effects shown in the present study to achieve better and more effective encapsulation.Display Omitted► Nano-encapsulation is considered as a promising technique for new therapies. ► The nano-capsules material and size can drastically affect reactions within. ► Capilllary pressure alters equilibrium and kinetic constants inside nano-capsules. ► Dipolar interactions also alter protein unfolding kinetics in metal nano-capsules. ► Nano-encapsulation for bio-medical applications can exploit these effects.
Keywords: Proteins folding-unfolding; High pressure; Nano-encapsulation; Reaction kinetics; Dipole moment; Protein-solvent interaction
Capillary condensation of adsorbates in porous materials by Toshihide Horikawa; D.D. Do; D. Nicholson (pp. 40-58).
Hysteresis in capillary condensation is important for the fundamental study and application of porous materials, and yet experiments on porous materials are sometimes difficult to interpret because of the many interactions and complex solid structures involved in the condensation and evaporation processes. Here we make an overview of the significant progress in understanding capillary condensation and hysteresis phenomena in mesopores that have followed from experiment and simulation applied to highly ordered mesoporous materials such as MCM-41 and SBA-15 over the last few decades.Display Omitted► Advances of the modern tools to analyse capillary condensation and evaporation. ► Molecular simulation is a useful in describing condensation and evaporation. ► Better understanding of cavitation and pore blocking.
Keywords: Capillary condensation; Hysteresis; Adsorption; Mesoporous solids; Scanning curves