Which size particles behave like a gas and are affected by Brownian Motion?

Brownian Motion describes the random movement of particles that are suspended in a fluid (liquid or gas). This phenomenon is particularly significant for very small particles, typically in the range of less than 1 micron.

When particles are smaller than 0.1 microns, they behave similarly to gas molecules, allowing random collisions with the surrounding fluid molecules to significantly influence their motion. In this size range, the particles are so small that they are heavily influenced by thermal energy and can experience greater random motion compared to larger particles, which can settle rapidly due to gravity or are less affected by these collisions.

Particles less than 0.1 microns are also important in various applications, such as in filtration efficiency, air quality, and aerosol science, as their behavior impacts how they can be filtered or their effects on health.

Larger particles or those in different size ranges do not behave like gases and do not exhibit Brownian Motion to the same extent, since gravitational forces and inertial effects become more prominent, impacting their movement and behavior in a fluid medium.