Surfactant and Micelle Formation PDF

2. Non ionotropic / nonionic surfactant Ø Its hydrophilic part carries no charge ØThey derive their polarity from having an oxygen-rich portion of the molecule at one end and a large organic molecule at the other end ØThe oxygen component is usually derived from short polymers of ethylene oxide or...

2. Non ionotropic / nonionic surfactant Ø Its hydrophilic part carries no charge ØThey derive their polarity from having an oxygen-rich portion of the molecule at one end and a large organic molecule at the other end ØThe oxygen component is usually derived from short polymers of ethylene oxide or propylene oxides such as; alcohol ethoxylates, polyoxyethylene, alcohols, and ethylene oxide/propylene oxide 3. Cationic surfactant ØThese are positively charged molecules usually derived from nitrogen compounds ØThey are not commonly used as cleaning agents in hard surface cleaners ØMany cationic surfactants have sanitizing properties that are useful in creating disinfectants that leave a cationic disinfectant film on the surface Amphoteric / zwitter surfactants ØThese surfactants change their charge with pH. ØThey can be anionic, nonionic or cationic depending on the pH. ØFor amphoteric surfactants the charge of the hydrophilic part is controlled by the pH of the solution ØThey can act as anionic surfactants in an alkalic solution or cationic surfactant in an acidic solution ØUsually, any one amphoteric can be any two of the three charge states  Micelles Definition üWhen surfactants are added to water, they self-assemble into little sphere called micelles with the hydrophilic head facing out and hydrophobic tail pointing in üThey are made out of amphipathic molecules üA micelle is a ball that forms when amphipathic molecules are put in a liquid Micelles üThe liquid can be polar like water or non polar like butane or octane üMicelles will form because only one end of the amphipathic molecules will be compatible with the liquid Formation of micelle In aqueous system, the high interfacial energy between the water molecules and the hydrocarbon chains of the surfactant is the primary factor in the process, while in a nonpolar system the attractive interaction between the polar parts serves as the force governing the association process The micellization in aqueous solutions may be perceived as a phase separation that is modified through geometrical restrictions, while the corresponding phenomenon in oils is a chemical equilibrium similar to that of alcohols in such media The consequence of this difference is that, the process in water is highly cooperative and the designation of a critical micellization concentration (CMC) is justified Formation of micelle CMC is the concentration of surfactant at which micelles first form in solution or the concentration above which micelles will form spontaneously. The higher the concentration, the more micelles there are. In the nonpolar environment, on the other hand, the association process is gradual and the term CMC is not warranted. In this case the interactions leading to the micellization are amenable to analysis by spectroscopic methods Formation of micelle Micelles form when the polar head and the nonpolar tails are arranged specially. They are usually driven to arrange either with the polar heads out (oil in water) or with the polar heads in (water in oil). Micelles only form when the concentration of surfactant is greater than the critical micelle concentration. The surfactant is any surface active material that can part the surface upon entering. The CMC is the concentration of surfactant at which micelles first form in solution or the concentration above which micelles will form spontaneously. The higher the concentration, the more micelles there are. Formation of micelle Micelle formation is also dependent on the krafft temperature. This temperature is when surfactants will form micelles. If the temperature is below the krafft temperature, then there is no spontaneous formation of micelles. As the temperature increases, the surfactant will turn into a soluble form and be able to form micelles from a crystalline state. The hydrophobic effect is also a driving force that needs to be taken into account. This effect is characterized by the fact that it likes to form intermolecular aggregates in aqueous substances and in intramolecular molecules. Micelle formation can be summed up by thermodynamics, driven by entropy and enthalpy