The phrase "a complex mixture of particles" is correct and usable in written English.
It can be used in scientific or technical contexts to describe a combination of different types of particles, such as in chemistry or physics.
Example: "The solution contained a complex mixture of particles, including ions, molecules, and larger aggregates."
Alternatives: "a diverse blend of particles" or "a complicated assortment of particles."
Diesel exhaust is a complex mixture of particles (< 1.0 μm in diameter) and combustion gases.
Air pollution is a complex mixture of particles, gases and liquids, mainly derived from the combustion of fossil fuels.
Particulate matter is a complex mixture of particles and liquids, traffic and non-traffic components, and varies in composition across geographic regions [ 1].
Ambient PM is a complex mixture of particles with distinct physical and chemical characteristics that arise from various primary (hydrocarbon combustion) and secondary (photochemical smog) sources.
Ambient PM is a complex mixture of particles of varying size that are classified as coarse (PM2.5 10; 10 µm > PM > 2.5 µm in aerodynamic diameter), fine (PM2.5; PM < 2.5 µm), and ultrafine (PM0.1; PM < 0.1 µm) particles.
Naturally occurring particles smaller than 0.45 μm are not clearly defined spherical particles but rather a complex mixture of particles of different shapes and possibly agglomerates of very small particles.
These dust samples demonstrate a complex mixture of coarse particles and fibers consisting of relatively larger particles (> 90% of dust particle mass was > 10 μm in diameter) (Lioy et al. 2002).
Space radiation is a complex mixture of charged particles from solar and galactic origins.
Particulate matter (PM) is a complex mixture of small particles and liquid droplets.
Environ Health Perspect 123:737–742; http://dx.doi.org/10.1289/ehp.1408121 Air pollution is a complex mixture of solid particles and gases.
Arey (2004) appropriately recognized that diesel exhaust particulates are a small category of emissions in what is truly a complex mixture of ambient particles.
