Suspension (chemistry): particulate dispersions in fluids

Characteristics and behavior

Key properties include particle size distribution, density differences between phases, and the viscosity of the continuous phase. These factors determine whether solids settle quickly or remain dispersed. Brownian motion, electrostatic repulsion, and steric effects can slow settling or prevent aggregation. Practical details are discussed in sources such as particle stability and rheology.

• Particle size — larger particles tend to settle faster.
• Density difference — greater contrast between dispersed and continuous phases speeds sedimentation.
• Viscosity — higher viscosity of the fluid retards particle motion.
• Interparticle forces — attraction leads to aggregation, repulsion favors dispersion.

Types and related systems

Closely related classes depend on the phases involved. When a liquid is dispersed in a liquid the system is typically called an emulsion; milk is a familiar example. When a liquid or solid is dispersed in a gas the system is termed an aerosol; mist and smoke are common aerosols. For readable comparisons see emulsions, milk and aerosols.

Examples and uses

Everyday suspensions include sand in water, flour in water, and many paints and certain pharmaceutical syrups. Industries that work with suspensions include wastewater treatment, ceramics manufacturing, paint and coatings, and food processing. Biological fluids such as blood are often treated as suspensions of cells in plasma for diagnostic and laboratory procedures. See further reading on industrial uses and medical contexts.

Stability and separation

Stability is often adjusted by adding dispersants or surfactants, altering pH or ionic strength, or increasing the continuous phase viscosity. Common separation techniques include filtration, sedimentation and centrifugation; each is chosen according to particle size and density. For practical methods and protocols consult separation techniques and stabilization strategies.