It is well-known that surface activity and solubilising power of surfactants, two important features in application, increase by increasing the length of the hydrophobic chain. As a consequence, long chain, water-soluble surfactants are desirable. Unfortunately, with increasing chain length the solubility of the surfactant decreases, which leads to higher Krafft-temperatures. For this reason, sodium alkylsulfates, which are commonly used surfactants in household products, are only applied with a chain length of 12 C-atoms (commercial name: sodium lauryl sulfate). The longer chain alkylsulfates exhibit Krafft-temperatures above room-temperature.
In many papers the decrease of the Krafft-temperature of sulfate- and carboxylate-surfactants is described by using a quaternary ammonium-ion as a counter-ion. The problem is that these ammonium-ions are toxic and consequently inappropriate for application. Choline, also a quaternary ammonium-ion, is a green, non-toxic alternative, which shows the same effect and could be used in formulations.
In the present contribution we will focus on choline hexadecylsulfate (C16) and its Krafft-temperature below room-temperature. As a result of the excellent water solubility, it will be possible to use long chain alkylsulfates (up to C16 and more) in household products, which are applied at room-temperature. This should lead to improved application properties compared to products containing only sodium lauryl sulfate (C12).
Finally, an approach is presented to decrease the Krafft-temperature of longer chain alkylsulfates (C18) below room-temperature, by adding different alcohols as a co-surfactant.
werner.kunz@ur.de
