OIA1008 W7 SURFACTANTS

Surfactant: substance that when present at low conc. in a system, has property of adsorbing onto surface/ interfaces

Used to alter/ lower to marked degree the surface tension/ interface tension, between liquid-liquid, gas-liquid or liquid-solid

May act as wetting agents, emulsifiers, detergents, dispersants & etc.

Usually amphiphilic organic compounds (contain both hydrophobic tail & hydrophilic head) -> water-insoluble & water-soluble component

At air-water surface: strong cohesive force btwn water molecules -> high water surface tension

Surfactants absorb they break/ weaken these interactions & lower surface tension

Interface (contact surface btwn 2 liquids) - surfactants gather at this interface

Hydrophilic part in water & hydrophobic part in oil -> create bond between 2 liquids -> reduce interface tension

[Surfactant] high -> form micelles at critical micelle conc.

Type of surfactants - depend on charges

(A) Nonionic

Combine uncharged hydrophilic & hydrophobic group -> effective in wetting, spreading & act as emulsifiers & foaming agents

Hydrophilic component based largely on polyethylene oxide (petroleum-derived)

High stability

Good compatibility w anionic, cationic or amphoteric surfactants

E.g., polyoxyethylene (20) sorbitan monolaurate

(B) Anionic: -ve charged hydrophilic polar group

Best - remove dirt, clay & oily stains

MOA: ionises & have -ve charge -> bind to +ve charged particles

Common anionic surfactants have RCOO-, RSO4(2-), sulfonate RSO3- & RPO4(2-) polar groups w counter ions (Na+ & K+ - water solubility //Ca2+ & Mg2+ - oil solubility)

E.g., Sodium lauryl sulfate (SLS) - cleansing & emulsifying properties & sodium dodecyl sulfate (SDS)

(C) Cationic: +ve charged functional group

E.g., quaternary ammonium salts, long chain amine salts

Has +ve charged end - ideal in antistatic formulae

Has antimicrobial characteristic: found in hard-surface disinfectants & cleaners

E.g., cetylpyridinium chloride - antiseptic which effective in preventing dental plaque & reduce gingivitis

(D) Zwitterionic (Amphotenic)

Surfactant simultaneously carry anionic & cationic hydrophilic group - able to form cation/ anion depend on pH & ambient conditions

Cationic part: amine salt/ quaternary ammonium hydrophilic gp

Anionic part: carboxylate, sulfonate, phosphate hydrophilic gp

Aqueous solution has various dissociation degrees w various pH value

*Low toxicity, antibacterial properties, excellent resistance to hard water, excellent compatibility w various surfactants

E.g., cocamidopropyl betaine - personal care

Hydrophile-Lipophile Balance (HLB)

Describe relationship btwn water-soluble & oil-soluble parts of surfactant

HLB = 1 -> very oil soluble; HLB = 15 -> water soluble

Measure percent of ethoxylation in surfactant: ethoxylation portion is water soluble component of compound; greater ethylene oxide (EO) content, surfactant more water soluble

Hydrophilic surfactants used for solubilization, detergency & readily dilute w water

Lipophilic surfactants used to couple water-soluble materials into nonaqueous oil-based system

Combine hydrophilic & lipophilic -> oil-in-water & water-in-oil emulsions

Micelles - aggregate (5-100nm) of surfactant molecules dispersed in liquid colloid

Consist of molecules contain 2 complete different regions having opposite affinites against water

Core: hydrophobic fragments; shell: hydrophilic fragments

Micellar amphiphilic molecules at low conc. exist separately in aqueous medium; if conc. increase, aggregation occur

Critical Micelle Concentration (CMC): conc. of monomeric micellar amphiphile starts aggregate & micelles appear

Critical Micelle Temperature (CMT): temperature where aggregates appear & below which micellar molecules exist as monomers

Aggregation of amphiphiles & formation of micelles as hydrophobic fragments removed from aqueous environment & reconstiution of H bonds in water -> reduce free energy of system

Micelle shape & size controlled by chemical structure, temperature, overall surfactant conc., surfactant composition, ionic strength & pH

Micelle growth controlled by surfactant heads: 1D & 2D growth need to bring surfactant heads closer - reduce available area per surfactant molecule at micelle surface

Micelle size increase as counter ion changed according to series (Cationic: Cl- < Br- < I-; Anionic: Na+ < K+ < Cs+)

Micelle solubilization - increase in solubilty of a poorly water-soluble substance w surfactants

Involve trapping (adsorbed/ dissolved) molecules in micelles & formation of colloidal aggregation at CMC

CMC: minimum surfactant conc. to start solubilization of insoluble molecule

Increase in conc. of micelle -> increase drug solubilty

E.g., polysorbate 20/40/80, monopalmitate, polyoxyethylated substance of fatty acid & sorbitan