1 Chemistry for Engineering Logistics DISPERSED SYSTEMS 1. Definition and classification of the dispersed systems 2. Structure and interaction between colloid particles Assoc. Prof. V. Grozev Department “ORGANIC CHEMISRTY AND TECHNOLOGY”

1. Definition and classification of the dispersed systems 1.1. Definition The term "Disperse System" refers to a system in which one substance (the dispersed phase) is distributed, in discrete units, throughout a second substance (the continuous phase, medium). Examples: suspension – the continuous phase is liquid, dispersed phase – solid substance. Emulsions – mixture from two insoluble liquids Classification of desperse systems according to state of the continuous (medium) and dispersed phases Each phase of the dispersed systems can exist in solid, liquid or gaseous state. 2

1.2. Classification of desperse systems according to state of the continuous (medium) and dispersed phases 3 Dispersion medium Dispersed phase Example Gas Gas mixture: air (oxigen and other gases in nitrogen) Liquid Aerosol: fog, mist, vapor, hair spray; Aerosol Solid Solid aerosol: smoke, dust Liquid Gas Solution: oxygen in water; Foam: whipped cream, shaving cream; Foam Liquid Solution: alcoholic beverages; Emulsion: microemulsion; Emulsion: milk, mayonnaise Solid Solution: sugar in water; Sol: pigmented ink, blood; Suspension: mud (soil, clay or silt particles are suspended in water), chalk powder suspended in water Solid Gas Solution: hydrogen in metals; Solid foam: aerogel, styrofoam Solid Solution: metal alloys; Solid sol: cranberry glass.

1.2. Classification of desperse systems according to state of the continuous (medium) and dispersed phases Suspension - heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Dispersion is made by mechanical agitation (sand in the water). Aerosol - a suspension of liquid droplets or a suspension of fine solid particles in a gas (smoke, air pollution, smog). Emulsion - a mixture of two or more immiscible liquids. Prepared by shaking – oil/water (milk), water/ oil (butter). Foam - a substance that is formed by trapping pockets of gas in a liquid or solid. 4 Soap foam bubbels

1. Definition and classification of the dispersed systems ClassRange of particle size, d Characteristics of system Coarse dispersion d> 0.5 μm (>0, m) Don't diffuse, visible under microscope (Suspension & emulsion) Colloidal dispersion 1.0 nm 0.5 μm (0, ÷10 -9 m) Diffuse slowly, visible in electron microscope, ultramicroscope (colloidal Ag sol) Molecular dispersion (true solutions) d<1.0 nm ( m) Rapid diffusion, invisible in electron microscope (Ordinary ions) Classification of the the dispersed systems according to their particle size:

6 2. Structure and interaction between colloid particles + Potential determing ions Kernel of the colloid particle Opposite ions Kernel of the colloid particle Oppositely ions (counter- ions) Potential determining ions The ions form electrical double layer. The charge of the counter - ions determine the charge of the colloid particle. Colloidal particles carry an electrical charge and therefore attract or repel each other. The colloidal system is stabilized by electrostatic repulsion between particles. repulsion

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