Ingegärd Johansson

Surfactants based on fatty acids and other natural hydrophobes

In the search for environmentally safer surfactants from renewable sources, the interest has lately been focused on new fatty acids and derivatives like ethoxylated fatty acid methyl esters and α-sulfo methyl esters. For the latter more efficient production procedures have been developed opening up for new application areas. In parallel, knowledge about the physico-chemical properties of this group of products has steadily grown. Thus fatty acids and soaps have a high potential to remain the biggest surfactant type especially if their use as raw materials is included.

Polyhydroxyl-based surfactants and their physico-chemical properties and applications

This contribution deals with the physical-chemical properties of surfactants carrying hydroxyl groups in the polar part. Topics discussed include surface and colloid properties, micelles (both single and multi-component), general phase behaviour and microemulsions. A general conclusion is that our understanding of polyhydroxy surfactants is increasing, but that further work is needed to unravel certain aspects of this important class of surfactants. Examples of such aspects are the origin of the liquid-liquid phase separation and the adsorption to solid surfaces of polyhydroxy surfactants.

Mixtures of n-dodecyl-β-d-maltoside and hexaoxyethylene dodecyl ether — Surface properties, bulk properties, foam films, and foams

Mixtures of the two non-ionic surfactants hexaoxyethylene dodecyl ether (C(12)E(6)) and n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) were studied with regard to surface properties, bulk properties, foam films, and foams. The reason for studying a mixture of an ethylene oxide (C(i)E(j)) and a sugar (C(n)G(m)) based surfactant is that despite being non-ionic, these two surfactants behave quite differently. Firstly, the physico-chemical properties of aqueous solutions of C(n)G(m) surfactants are less temperature-sensitive than those of C(i)E(j) solutions. Secondly, the surface charge density q(0) of foam films stabilized by C(n)G(m) surfactants is pH insensitive down to the so-called isoelectric point, while that of foam films stabilized by C(i)E(j) surfactants changes linearly with the pH. The third difference is related to interaction forces between solid surfaces. Under equilibrium conditions very high forces are needed to expel beta-C(12)G(2) from between thiolated gold surfaces, while for C(12)E(6) low loads are sufficient. Fourthly, the adsorption of C(12)E(6) and beta-C(12)G(2) on hydrophilic silica and titania, respectively, is inverted. While the surface excess of C(12)E(6) is large on silica and negligible on titania, beta-C(12)G(2) adsorbs very little on silica but has a large surface excess on titania. What is the reason for this different behaviour? Under similar conditions and for comparable head group sizes, it was found that the hydration of C(i)E(j) surfactants is one order of magnitude higher but on average much weaker than that of C(n)G(m) surfactants. Moreover, C(n)G(m) surfactants possess a rigid maltoside unit, while C(i)E(j) surfactants have a very flexible hydrophilic part. Indeed, most of the different properties mentioned above can be explained by the different hydration and the head group flexibilities. The intriguing question of how mixtures of C(i)E(j) and C(n)G(m) surfactants would behave arises organically. Thus various properties of C(12)E(6)+beta-C(12)G(2) mixtures in aqueous solution have been studied with a focus on the 1:1 mixture. The results are compared with those of the single surfactants and are discussed accordingly.

Environmentally benign nonionic surfactant systems for use in highly alkaline media

The increasing use of surfactants has put more and more emphasis on environmental requirements for the chemicals used. It is also important to follow the whole lifetime of the products and to offer possibilities for efficient wastewater treatment. Good cleaning of oily soil from hard surfaces and efficient separation of the oily soil from the wastewater within the same surfactant system is a challenge. In this article a system is described which, by using the specific cloud-point profile that can be achieved when mixing alkyl ethoxylates with alkyl glucosides, offers a possibility to meet that challenge. Alkyl ethoxylates are known to be good wetting agents, emulsifiers and cleaning agents. They are, however, usually not soluble in concentrated electrolytes and/or alkali, which may be needed in the practical use with different water qualities, etc. The more recently developed nonionic surfactant named alkyl glucoside, which has a polyhydroxyl functionality as its hydrophilic part arising from natural sources such as carbohydrates, offers better solubility as well as strong surface activity. When combining these two categories of surfactants good solubility in, for instance, alkali, is achieved and a special concentration-dependent cloud-point curve results. This phenomenon can be used both to fine-tune the cleaning and wetting efficiency and to stimulate the separation of the emulsified oil from the wastewater.

The effect of polymers on the phase behavior of balanced microemulsions: diblock-copolymer and comb-polymers

The effect of some amphipilic diblock-copolymers and comb-polymers on a balanced Winsor III microemulsion system is investigated with the quaternary system n-octyl-β-d-glucoside/1-octanol/n-octane/D2O as basis system. The diblock-copolymers are polyethyleneoxide-co-polydodecenoxide (PEOxPEDODOy) and polyethyleneoxide-co-polybutyleneoxide (PEOxPEBUy), constituted of a straight chain hydrophilic part and a bulky hydrophobic part. Addition of the diblock-copolymer leads to an enhancement of the swelling of the middle phase by uptake of water and oil; a maximum boosting factor of 6 was obtained for PEO111PEDODO25. Nuclear magnetic resonance diffusometry yields the self-diffusion coefficients of all the components in the system. The diffusion experiments provide information on how the microstructure of the bicontinuous microemulsion changes upon addition of the polymers. The reduced self-diffusion coefficients of water and oil are sensitive to the type of polymer that is incorporated in the film. For the diblock-copolymers, as mainly used here, the reduced self-diffusion coefficient of oil and water will respond to how the polymer bends the film. When the film bends away from water, the reduced self-diffusion of the water will increase, whereas the oil diffusion will decrease due to the film acting as a barrier, hindering free diffusion. The self-diffusion coefficient of the polymer and surfactant are similar in magnitude and both decrease slightly with increasing polymer concentration.