Switchable surfactants

Switchable Surfactants Hydrophobic molecules do not dissolve well in water. Given that water is a very commonly used solvent, this makes certain processes very difficult washing oily food residue off dishes, cleaning up spilled oil, keeping the oil and water phases of salad dressings well mixed, and carrying out chemical reactions that involve both hydrophobic and hydrophilic components. 

There are some situations in which it would be very useful to have a switchable surfactant a molecule that could be reversibly converted between a surfactant and a nonsurfactant. 

Liu et al. describe a prototypical switchable surfactant in their 2006 article Switchable Surfactants. The switching is based on the following reaction ... 

Liu and colleagues produced a switchable surfactant for which R = C16H33. They do not name the molecule in their article for brevity, we ll call it s-surf. 

Jessop and co-workers used the same technology as developed for switchable solvents to obtain switchable surfactants (Scheme 9.1). These have many possible applications, and their use would reduce waste and solvent usage (Table 9.4). 

Scheme 9.1 Switchable surfactant formation from long-chain alkyl amidine, carbon dioxide and water.

Table 9.4 Potential applications of temporary or switchable surfactants.

Crude oil and water mixtures also formed stable emulsions when treated with the switchable amidine carbonate surfactant, and the emulsion could be broken by exposure to argon to give two separate layers. This shows the great potential... 

Figure 9.10 Emulsion switching for a hexadecane-water 2 1 (v/v) mixture containing switchable surfactant, after carbon dioxide treatment and 10 min shaking and (A) 5 min wait period, (B) 30 min wait period and (C) 24 h wait period. (D) After subsequent treatment with argon to turn off emulsification. [Reprinted with permission from Science 2006, 313, 958-960. Copyright 2006 American Association for the Advancement of Science.]...

Some additional examples are given in Table 3.3. Typically, the molar masses range from a few hundreds to several thousands of grams per moles. In depth, discussions of surfactant structure and chemistry can be found in References [50, 54- 56]. A recent review is given by Schramm et al. [57]. A good discussion of the chemistry of commercially available surfactants is given by Myers [58]. Several reviews are available on the toxicity and persistence of surfactants [59-62]. See also the discussion of switchable surfactants in Section 16.3. 

Philip Jessop Queen s University Carbon dioxide triggered switchable solvents and surfactants... 

Schmittel, M., Lai, M., Graf, K., Jeschke, G., Suskec, I. and Salbeckc, J., N, N -Dimethyl-2,3-dialkylpyrazinium salts as redox-switchable surfactants Redox, spectral, EPR and surfactant properties, Chem. Commun., 2005, 5650-5652. 

Jessop PG, Mercer SM, Eldebrant DJ (2012) C02-triggered switchable solvents, surfactants, and other materials. Energy Environ Sci 5 7240-7253... 

Kordel, C., Setaro, A., Bluemmel, P., Popeney, C.S., Reich, S., Haag, R., 2012. Controlled reversible debundling of single-waUed carbon nanotubes by photo-switchable dendritic surfactants. Nanoscale 4, 3029—3031. 

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