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Advances in Colloid and Interface Science (v.175, #)

Editorial Board (pp. ifc).

Superhydrophobicity and liquid repellency of solutions on polypropylene by R. Rioboo; B. Delattre; D. Duvivier; A. Vaillant; J. De Coninck (pp. 1-10).

The sliding of drops of aqueous solutions of organic liquids over a superhydrophobic polypropylene (SH-PP) surface has been studied experimentally. The multi-scale roughness of this surface is intrinsically inhomogeneous. Careful analysis of the wettability of each solution enables us to establish the statistics of the advancing and receding contact angles. We consider a threshold value of the receding static contact angle, above which drop sliding and rebound are facilitated as the criterion for superhydrophobicity. The percentage of receding contact angles greater than this threshold is then used as a practical index of superhydrophobicity (SHI). The variation of the SHI is compared with surface tension of the solution and various wetting parameters. A linear correlation is found between the SHI and the work of wetting defined by γ_LGcos θ₀ where γ_LG is the surface tension of the solution and θ₀ is the static contact angle of the solution over the corresponding smooth surface. Such a correlation can be used as a predictive tool of the superhydrophobicity of a given surface with various liquids.Display Omitted► The methods to characterize superhydrophobicity are critically reviewed ► We construct a superhydrophobicity index adapted to random-like roughnesses ► Using organic liquids solutions we analyze transition to superhydrophobicity ► Surface tension is not the relevant liquid-related measure for superhydrophobicity ► The work of wetting is linear with the superhydrophobic index

Keywords: Superhydrophobicity; Measurement techniques; Wetting; Roughness; Homogeneity; Liquid repellency

Colloidal interactions in liquid CO₂ — A dry-cleaning perspective by Soumi Banerjee; Stevia Sutanto; J. Mieke Kleijn; Maaike. J.E. van Roosmalen; Geert-Jan Witkamp; Martien A. Cohen Stuart (pp. 11-24).

Liquid CO₂ is a viable alternative for the toxic and environmentally harmful solvents traditionally used in dry-cleaning industry. Although liquid CO₂ dry-cleaning is being applied already at a commercial scale, it is still a relatively young technique which poses many challenges. The focus of this review is on the causes of the existing problems and directions to solve them. After presenting an overview of the state-of-the-art, we analyze the detergency challenges from the fundamentals of colloid and interface science. The properties of liquid CO₂ such as dielectric constant, density, Hamaker constant, refractive index, viscosity and surface tension are presented and in the subsequent chapters their effects on CO₂ dry-cleaning operation are delineated. We show, based on theory, that the van der Waals forces between a model soil (silica) and model fabric (cellulose) through liquid CO₂ are much stronger compared to those across water or the traditional dry-cleaning solvent PERC (perchloroethylene). Prevention of soil particle redeposition in liquid CO₂ by electrostatic stabilization is challenging and the possibility of using electrolytes having large anionic parts is discussed. Furthermore, the role of different additives used in dry-cleaning, such as water, alcohol and surfactants, is reviewed. Water is not only used as an aid to remove polar soils, but also enhances adhesion between fabric and soil by forming capillary bridges. Its role as a minor component in liquid CO₂ is complex as it depends on many factors, such as the chemical nature of fabrics and soil, and also on the state of water itself, whether present as molecular solution in liquid CO₂ or phase separated droplets. The phenomena of wicking and wetting in liquid CO₂ systems are predicted from the Washburn–Lucas equation for fabrics of various surface energies and pore sizes. It is shown that nearly complete wetting is desirable for good detergency. The effect of mechanical action and fluid dynamic conditions on dry-cleaning is analyzed theoretically. From this it follows that in liquid CO₂ an order of magnitude higher Reynold's number is required to exceed the binding forces between fabric and soil as opposed to PERC or water, mainly due to the strong van der Waals forces and the low viscosity of CO₂ at dry-cleaning operational conditions.Display Omitted► Challenges in liquid CO₂ dry-cleaning are discussed from the colloidal aspects. ► Particle removal in liquid CO₂ based on dispersive interactions is discussed. ► Role of water in enhancing soil-fabric adhesion in liquid CO₂ is highlighted. ► Poor mechanical action in liquid CO₂ is explained at relevant operating conditions. ► Critical comments on surfactant design in liquid CO₂ have been made.

Keywords: Liquid CO; ₂; Environmentally friendly CO; ₂; dry-cleaning; Soil–fabric interaction; Surfactants; Hydrodynamics; Detergency in apolar media

Surface chemistry of porous silicon and implications for drug encapsulation and delivery applications by Karyn L. Jarvis; Timothy J. Barnes; Clive A. Prestidge (pp. 25-38).

Porous silicon (pSi) has a number of unique properties that appoint it as a potential drug delivery vehicle; high loading capacity, controllable surface chemistry and structure, and controlled release properties. The native Si_ySiH_x terminated pSi surface is highly reactive and prone to spontaneous oxidation. Surface modification is used to stabilize the pSi surface but also to produce surfaces with desired drug delivery behavior, typically via oxidation, hydrosilylation or thermal carbonization. A number of advanced characterization techniques have been used to analyze pSi surface chemistry, including X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry. Surface modification not only stabilizes the pSi surface but determines its charge, wettability and dissolution properties. Manipulation of these parameters can impact drug encapsulation by altering drug–pSi interactions. pSi has shown to be a successful vehicle for the delivery of poorly soluble drugs and protein therapeutics. Surface modification influences drug pore penetration, crystallinity, loading level and dissolution rate. Surface modification of pSi shows great potential for drug delivery applications by controlling pSi–drug interactions. Controlling these interactions allows specific drug release behaviors to be engineered to aid in the delivery of previously challenging therapeutics. Within this review, different pSi modification techniques will be outlined followed by a summary of how pSi surface modification has been used to improve drug encapsulation and delivery.Display Omitted► Porous silicon (pSi) has significant potential as a drug delivery vehicle. ► The hydride terminated surface can be passivated via oxidation and hydrosilylation. ► Surface modification can be used to tailor drug–pSi interactions. ► By controlling drug crystallinity within pSi pores, drug dissolution is enhanced. ► Techniques such as XPS and ToF-SIMS provide insight into modification and loading.

Keywords: Porous silicon; Surface modification; Surface chemistry; Drug loading; Drug delivery

Ordered mesoporous phenolic resins: Highly versatile and ultra stable support materials by Ilke Muylaert; An Verberckmoes; Jeroen De Decker; Pascal Van Der Voort (pp. 39-51).

Ordered mesoporous phenolic resins and carbons – an advanced class of ultra-stable mesoporous materials – offer potential applications in the field of catalysis, electrodes and adsorbents. This review gives an extensive overview of the main principles and the recent progress made in the synthesis of these innovative materials using the soft-template method. Furthermore, the versatility towards functionalization and the incorporation of hetero-atoms in the organic framework of the mesoporous resins and carbons are considered. Finally, the broad range of potential applications is discussed and future perspectives in the field of mesoporous polymers and carbons are given.► Main synthesis principles of phenolic resins using the soft-template method. ► Thermally and mechanically stable support materials. ► Functionalization and incorporation of metals in mesoporous resins and carbons. ► Versatile use in catalysis, adsorption and electrochemistry.

Keywords: Ordered mesoporous materials; Phenolic resins; Carbons; Soft-template synthesis; Catalysis

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Advances in Colloid and Interface Science (v.175, #)