Interfacial Phenomena 3 Flashcards
Soluble Surfactant Outline
Micelle Forming
Insoluble Surfactant Outline
Film Forming
Liposome Function
Enter cancer cells to kill them. Coated in polyethylene glycol to prevent immune system detection. Insoluble surfactant
Surfactants Classification
Anionic (negatively charged, damage mammalian membrane ), cationic (positively charged, damage mammalian membranes), zwitterion (either positively/negatively charged) and non-ionic (no charge, less damage to mammalian membranes)
Polysorbate Nomenclature
Name and number in series
Different shape of ionic micelles
spherical, cylindrical, hexagonal/cubic/lamellar phase (surfactant layers with water between)
Classic Micelle Def
Hydrophilic tails point out and hydrophobic heads point in. Hydrophilic continuos phase
Reverse Micelle Def
Hydrophilic tails point in and hydrophobic tails point out. Lipophilic continuos phase
Ionic Surfactants Outline
Smaller micelle then non-ionic. Size and shape influenced by counterion (elongated by high counterion concs). CMCs are higher then non-ionic as repulsive forces between same charged molecules need to be overwhelmed. Counter ion and surfactant form electric double layer. 1 net neutral internal layer and 1 lose counterion layer
Non-ionic surfactants Outline
Hydrophobic core with palisade layer (shear surface) (hydrophobic tails - eg polysorbate). Tails H bond with water entrapment with water molecules
Polymeric Micelles Copolymers Nomenclature
Name, MW of chain (0.01), % of total structure of core (0.1)
Results of increasing temp on poloxamer
poloxamer gel -> micelles -> Gelation
Micellisation Factors
Hydrophobic tail structure, hydrophilic nature, counter ion nature, temp and addition of electrolytes
Hydrophobic Structure Outline
Micelles form more efficently the bigger the lipophilic region. Bigger hydrocarbon tail = lower CMC
Nature of hydrophilic group
Ionic = higher CMC = low aggregation number
Aggregation Number Outline
Amount of surfactant molecules in micelles
Cloud point
Temp at which kinetic energy in system is so high non-ionic surfactants have them stripped out of water, destabiliding micelles
Temp relationship with micelles
As temp increases = micelle formation increases. Until cloud point is met
Hydrophobic-lipophilic balance (HLB) Outline
Categories surfactants, ration of hydrophilic to hydrophobic regions. Low HLB = lipophilic (eg antifoams), High HLB = hydrophilic (eg foaming agents)
Antifoam Outline
Breaks apart foam in more oily emulsions
Surfactant Applications
Antifoam/foam agent, emulsifier, solubilisation, gelling and Anti adherent
Maximum Additive Concentration Outline
Max amount of solubiliser that can be added to a system of fixed volume. Binary: drug + solvent, tertiary: drug + solvent + surfactant, psuedo tertiary: drug + solvent + surfactant + co surfactant
2 sites of drug break down in micelles
core and palisade layer (further away from core in palisade layer is hydrophilic)
Bancrofft Rule
Substance in which emulsifier is soluble in is the continuous phase
How surfactants stabilise suspensions
Surfactants adsorp at interface preventing coagulation, sedimentation and aggregation
Wetting Def
Displacement of gas at the interface of a liquid. Surfactants lower interfacial tension between solid and liquid increasing spreading. Poor wetting is a result of interfacial tensions
Contact Angles in wetting
0 degrees = complete spreading, <90 degrees is good wetting, >90 degrees is poor wetting and >180 degrees is droplet
3 types of wetting as described by young’s modulus
spreading (liquid already in contact), immersional (no original contact to complete spread) and adhesion (liquid not originally in contact, adheres to it)
What surfactant is more likely to cause a wetting
cation. may result in toxicity and foaming
Detergency Outline
Surfactant used to remove substance from interface. Hydrocarbons remove grease, grease spots break off surface and are picked up by detergent anions and small bits of grease are collected in colloidal suspension
Penetration Enhancers Outline
Surfactants that alter the fluidity of lipid layer. Strips away tight junction proteins, allowing passive/facilitated diffusion. Can permanently damage cells.
Surfactants in lipids absorption
oil is immiscible with water in intestine. Lipase breaks oil into disaccharides/monosaccharides and 3 fatty acids. Absorbed into mixed micelle Mixed micelles move across epithelium
Diverse surfactant action
improved wetting, optimise opthalmic delivery, adsorption reduction and improved stability in micelle core
Realtionship between HLB and Toxicity
Higher surfactant HLB = higher lipophilicity = higher toxicity
