Surfactants

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Surfactants

• The Chemistry of Consumer Products
• Topic 2

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Amphophiles

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

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Amphophiles

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

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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

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Surfactant

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

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Surfactant types

• Anionic
• Nonionic
• Cationic
• Amphoteric / zwitterionic

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Anionic Surfactants

• Dissociate in water to give an amphophilic anion
  and acation (generally Na, or K)

Sodium Dodecyl Sulfate
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Anionic surfactants

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

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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
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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

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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
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Cationic Surfactants

• Generally more expensive than anionics
• Used to target negatively charged substrates

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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
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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
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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.

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Properties of Solutions

• Adsorption
• Surface tension reduction
• Self assembly

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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!)

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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.
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Reduction in surface tension
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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.

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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

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