Presented by: Sharanjeet Kaur

Surface Active Agents

Hydrophilic: A liquid/surface that has a high affinity to water.

Hydrophobic: A liquid/surface that has very low affinity to water

Lipophilic: A liquid/surface that has a high affinity to oil.

Lipophobic: A liquid/surface that has a very low affinity to oil.

BASIC TERMINOLOGY

A molecule that contains a polar portion and a non polar portion is called surface active agent/ surfactant.

A surfactant can interact with both polar and non polar molecules.

A surfactant increases the solubility of the otherwise insoluble substances.

In water, surfactant molecules tend to cluster into a spherical geometry non polar ends on the inside of the sphere polar ends on the outside .These clusters are called micelles

Surface active agents?

Surfactants have amphipathic structure tail or hydrophobic group little affinity for bulk solvent.

Usually hydrocarbon (alkyl/aryl) chain in aqueous solvents.

Can be linear or branched. Head or hydrophilic group strong

affinity for bulk solvent. Can be neutral or charged.

Structure of a surfactant

Surfactants reduce the surface tension of water by adsorbing  at the liquid-gas interface.

Many surfactants can also assemble in the bulk solution into aggregates. Examples of such aggregates are vesicles and micelles. 

Thermodynamics of the surfactant systems are of great importance, theoretically and practically.

Surfactants play an important role as cleaning, wetting, dispersing, emulsifying, foaming 

and  anti-foaming agents in many practical applications and products

Properties

1. Anionic2. Cationic3. Non- Ionic4. Amphoteric or Zwitterionic

Classification of Surfactants

Based on permanent anions or pH-dependent anions .

These are categorised as:1. Sulfates: Alkyl sulfates, Alkyl ether sulfates2. Sulfonates: Sulfonate fluorosurfactants,

Alkyl benzene sulfonates3. Phosphates: Alkyl aryl ether phosphate,

Alkyl ether phosphate4. Carboxylates: Alkyl carboxylates,

Carboxylate fluorosurfactants(~ 60% of industrial surfactants)

Anionic Surfactants

Based on pH-dependent primary, secondary or tertiary amines i.e. primary amines become positively charged at pH < 10, secondary amines become charged at pH < 4.

Examples:Cetylpyridinium chloride (CPC)Polyethoxylated tallow amine (POEA)Benzalkonium chloride (BAC)Benzethonium chloride (BZT)5-Bromo-5-nitro-1,3-dioxaneDimethyldioctadecylammonium chloride

Cationic Surfactants

Amphoteric surfactants are characterized by the fact that these surfactants can carry a positive charge on a cationic site and a negative charge on an anionic site. The use of amphoteric terminology is still restrictive: The charge of the molecule must change with pH, showing a zwitterionic form at an intermediate pH

Examples: Amino acidsImino acidsBetaines lecithin

Amphoteric or Zwitterionic

They doesnt include any charged head. These are categorised as:

1. Fatty Alcohols2. Polyoxyethylene glycol3. Polyoxypropylene gylcol4. Glucoside5. Polyoxyethylene glycol octylphenol ethers6. Sorbitan alkyl esters7. Polyoxyethylene glycol sorbitan alkyl esters

Non Ionic

The hydrophilic-lipophilic balance (HLB) of a surfactant reflects its partitioning behavior between a polar and non-polar medium.

HLB number, ranging from 0-40, can be assigned to a surfactant, based on emulsification data.

Semi-empirical only. 

What is HLB Scale?

No dispersibility in water 0 antifoaming agents 2Water –in- oil emulsifier 6Wetting agent 8 Milky dispersion 10Oil-in-water emulsifier 12Clear solution 14Detergent 16Solubilizer 18A value of 10 represents a “mid-point” of HLB.

Cont..

For non ionic surfactantsHLB = E/5 HLB = 20(1-S/A)Where ;E= percentage by weight of ethylene oxideS= saponification number of esterA= Acid number of the fatty acid

Calculation of HLB ‘s

Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solutions. The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic regions (polar head groups) as well as hydrophobic regions.

 Micelles contain polar head groups that usually form the outside as the surface of micelles. They face to the water because they are polar. The hydrophobic tails are inside and away from the water since they are nonpolar.

Micelles Formation

 Micelles contain polar head groups that usually form the outside as the surface of micelles. They face to the water because they are polar. The hydrophobic tails are inside and away from the water since they are nonpolar.

Micelles form spontaneously in water, as stated above this spontaneous arrangement is due to the amphipatic nature of the molecule. 

when the lipids form micelles the hydrophobic tails interact with each other, and this interaction releases water form the hydrophobic tail and this increases the disorder of the system, and this is increase in entropy is favorable.

Cont..

The polar heads out (oil in water) or with the polar head in (water in oil).

Micelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC). 

 The CMC is the concentration above surfactant when micelles will form spontaneously.

Micelle formation also depend on the Krafft temperature. This temperature is when surfactants will form micelles. 

As the temperature increases, the surfactant will turn into a soluble form and be able to form micelles from a crystalline state.

DetergentsFabric softenersEmulsifying agents in EmulsionsPaintsAdhesivesInksAnti-fogsSuspending agents in suspensions Laxatives

Uses of Surface active agents