The Chemistry of Consumer Products Topic 2 Surfactants The Chemistry of Consumer Products Topic 2

Amphophiles Greek roots Ampophilic - two parts Amphi – ‘double’ ‘from both sides’ Filos – friend Ampophilic - two parts Polar group – contains O, S, P, or N Non-polar group – contains C, H

Amphophiles Hydrophilic or hydrophile Hydrophobe or lipophile Likes water Hydrophobe or lipophile Fears water or likes grease

Amphophiles Not at ease in any solvent Migrate to surfaces or interfaces Surface – boundary between a condensed and gas phase Interface – boundary between two condensed phases

Surface – Active – Agent Surfactant Short for Surface – Active – Agent Properties Lower surface tension Wetting agent Emulsifier Foaming agent others

Surfactant types Anionic Nonionic Cationic Amphoteric / zwitterionic

Anionic Surfactants Dissociate in water to give an amphophilic anion and acation (generally Na+, or K+) Sodium Dodecyl Sulfate

Anionic surfactants Most common type Examples: Alkylbenzene sulfonates (detergents) Fatty acid soaps Laury sulfate (foaming agent) Di-alkyl sulfo succinate (wetting agent) Lignosulfanates (dispersants)

Nonionic Surfactants Do not dissociate in water An alcohol ethoxylate and an alkylphenol ethoxylate. The poly(ethylene oxide) chain forms the water soluble surfactant "head". alkyl polyglycosides – contain one or more sugar groups

Nonionic Surfactants Second largest classification Most have a hydrophilic group comprise of a polyethylene glycol chain produced by the condensation of ethylene oxide Sugar based head groups are also used – low toxicity

Cationic Surfactants Dissociate in water to give an amphophilic cation and an anion – usually a halogen Fatty amine salts were the first style of cationic surfactant The development of alkyl pyridinium and quaternary ammonium salts provided excellent surfactants that could be used over a vast range of conditions

Cationic Surfactants Generally more expensive than anionics Used to target negatively charged substrates

Amphoteric / zwitterionic Surfactants A zwitterionic surfactant has both an anion and a cation in one molecule chemically joined together. Zwitterionic surfactants are also called amphoteric surfactants as they often comprise a base coupled to an acid. Three zwitterionic surfactants: an ammonium carboxylate, an ammonium sulfate and an amine oxide

Hybrid Surfactants combines a nonionic surfactant with an anionic head group. improves the behavior of the surfactants in hard water. increases the range of temperatures over which the nonionic surfactants are soluble. Sodium laureth sulfate

Saponification The saponification reaction is the hydrolysis of fatty esters. The saponification reaction typically refers to the reaction that is carried out by a strong base. Historically, this was done with potash (potassium hydroxide) rather than sodium hydroxide, although nowadays we can obtain sodium hydroxide from the hydrolysis of seawater.

Properties of Solutions Adsorption Surface tension reduction Self assembly

Adsorption Adsorption is the tendency for a surfactant molecule to collect at an interface. (Adsorption is very different to absorption - don't get them confused!)

Adsorption Surfactant molecules tend to adsorb to the surface of oil droplets. The hydrophilic heads stick out into the water phase, while the hydrophobic tails happily stick into the oil phase.

Reduction in surface tension

Self Assembly Self-assembly is the tendency for surfactant molecules to organize themselves into extended structures in water. This includes the formation of micelles, bilayers and liquid crystals. These structures are formed when the hydrophobic tails of the surfactants cluster together, forming small aggregates such as micelles, or large layer structures (bilayers) which are similar to a cell wall.

Self assembly Surfactants can aggregate to form micelles. There is usually between a few dozen to a couple of hundred surfactant molecules in a micelle Surfactants also aggregate to form extended structures in water, such as surfactant bilayer, or rods

Micelle Formation Micelles will begin to form when the concentration of the surfactant exceeds a limit known as the critical micelle concentration.

Detergency