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In three sentences, describe how colloids are stabilised by ionic surfactants. Be as concise as possible while conveying maximal information ParagraphFont familyFont sizeB I US A Path: p

Answer 1

Colloidal particles in a dispersion medium always show Brownian motion and hence collide with each other frequently. The stability of colloids is thus determined by the interaction between the particles during such a collision. There are two basic interactions: one being attractive and the other repulsive. When attraction dominates, the particles will adhere with each other and finally the entire dispersion may coalesce. When repulsion dominates, the system will be stable and remain in a dispersed state.

Since there are always strong, long-range attractive forces between similar colloidal particles, it is necessary to provide a long range repulsion between the particles to impart stability. This repulsion should be at least as strong as the attractive force and comparable in range of the attractive interaction. Stability can be obtained by surroundig colloidal particles: · With an electrical double layer (electrostatic or charge stabilization). · With adsorbed or chemically attached polymeric molecules (steric stabilization). · With free polymer in the dispersion medium (depletion stabilization).

Surfactant (surface active agent,detergent) is a substance reducing the interfacial energy of the solution in a contact with other phases.

Surfactants promote dispersion of various phases: emulsification of oils (liquid phase), suspension of solid residuals (solid phase) in the alkaline cleaners and foaming (gaseous phase).

Anionic surfactants dissociate in aqueous solutions into a amphiphilic organic anion (negatively charged ion) and a small inorganic cation (positively charged ion: Na⁺, K⁺).
Anionic surfacants are manufactured in the reaction of an organic substance with sodium/potassium hydroxide.

Examples of anionic surfactants: linear alkylbenzene sulfonates, di-alkyl sulfosuccinate (sulfonic acid salt), sodium lauryl sulfate (alcohol sulfate), phosphoric acid esters, sodium stearate (carboxylic acid salt).
Soaps (salts of fatty acids) are typical anionic surfactants.

Anionic surfacants are generally non-toxic.
Anionic surfactants are most widely used surfactants.

Cationic surfactants dissociate in aqueous solutions into an amphiphilic cation (positively charged ion) and an halide anion (negatively charged halogen ion).
Cationic surfactants are manufactured in the reaction between alkyl halides with fatty amines.
They are are widely used for treatment of synthetic fabrics and proteins molecules of which have negatively charged sites.
Cationic surfactants are effective in acidic solutions and are not effective in alkaline solutions.
As compared to the anionic surfactants the cationic ones are more expensive and more toxic.