Effect of inorganic additives on solutions of nonionic surfactants VII. Suspension stability

Foam Silica Films Synthesized by Calcium Chloride-Assisted Emulsification

The development of porous films with an accessible high specific surface area is important for designing new adsorbents, sensors, or catalyst supports. Here, we describe a simple method to prepare a silica foam coating using a calcium chloride-assisted evaporation-induced emulsification method. An alcoholic silica sol containing calcium chloride and a poly(ethylene oxide)-based polymer is deposited on a substrate by dipping. The evaporation of the alcohol induces a phase separation between the silica-rich phase and the calcium-rich one. The size of the droplets increases via a coalescence process until the gelation of the sol, which determines the final pore size between 100 nm and 3 μm. Thermal analysis and monitoring of droplet evaporation confirm that the departure of the solvent is delayed by the presence of calcium chloride in the sol. The influence of the nature of the polymer on the porosity is discussed. The use of a block copolymer such as the Pluronic F-127, which strongly stabilizes the emulsion, allows to reach a low pore size (400 nm), while on the contrary, we propose to use a short poly(ethylene glycol) (PEG) such as PEG-400, which weakly stabilizes it, leading to larger pores (2-3 μm). Furthermore, we show that the addition of a zirconium salt (ZrOCl₂·8H₂O) to the silica sol accelerates the condensation step of the silica and leads to the decrease in the pore size.

Clouding phenomenon in amphiphilic systems: A review of five decades

Phase separation in amphiphilic systems is an important phenomenon. The temperature at which an amphiphilic solution phase separates is known as Cloud Point (CP). This article reviews in detail the process of phase separation in various amphiphiles (surfactants, polymers and drugs) and effect of different classes of additives on the CP of these amphiphilic systems. Ions affect the CP of drugs in a different way: kosmotropes and hard bases decrease while chaotropes and soft bases increase the CP of nonionic and cationic surfactants. Anionic surfactants show CP in presence of quaternary salts only. Thus, depending upon the nature and concentration of additive, the CP of an amphiphilic system gets increased or decreased and, hence, properties of the system may be tuned as per the need and use. A system with CP at high concentration can be made to phase separate at lower concentration by simply introducing an appropriate additive in it. This makes the system cost effective. On the other hand, if not required, a low CP can be enhanced with the help of another type of a suitable additive.

Comparing the Surface Chemical Properties and the Effect of Salts on the Cloud Point of a Conventional Nonionic Surfactant, Octoxynol 9 (Triton X-100), and of Its Oligomer, Tyloxapol (Triton WR-1339)

The surface-chemical properties, critical micelle concentrations (CMC), and effect of salts on the cloud points (CP) of octoxynol 9 (Triton X-100) and tyloxapol (Triton WR-1339) were compared. The latter nonionic surfactant is essentially a heptamer of the former. Even though the molecular weight of tyloxapol is 7 times larger than that of octoxynol 9, its area per molecule adsorbed at the air-water interface is only twice as large. This suggests an unusual orientation for molecules of tyloxapol at the surface and is in keeping with a plateau that is less horizontal and has a somewhat higher surface tension than the plateaus of most nonionic surfactants. The CMC of octoxynol 9 was 4.4 times larger than that of tyloxapol. Unexpectedly, the CP of dilute aqueous tyloxapol solutions was 28 degreesC higher than that of octoxynol 9 solutions. The salting-out ions Na+, Cl- and SO2-4 lowered the CP of tyloxapol 29% more than that of octoxynol 9. However, because the blank tyloxapol solution started out with a higher CP value, its CPs in the presence of salts were higher than those of octoxynol 9. Pb2+ and Mg2+ cations salted both surfactants in, raising their CP, Pb2+ more extensively than Mg2+. Copyright 1998 Academic Press.