NOVELTY - Particle treatment method for disaggregating, deagglomerating, exfoliating, cleaning or functionalizing particles, in which the particles for treatment are subject to plasma treatment in a treatment chamber comprising multiple electrically-conductive solid contact bodies or contact formations, the particles being agitated with the contact bodies or contact formations and in contact with plasma in the treatment chamber.    USE - The method is useful for particle treatment for disaggregating, deagglomerating, exfoliating, cleaning or functionalizing particles (claimed).    ADVANTAGE - The methods are found to effectively deagglomerate nanoparticles, and to exfoliate graphitic material to produce very thin (few-layer or monolayer) graphitic sheets showing graphene-type characteristics. The invention is advantageous in using safe, dry and moderate conditions to achieve a high degree of deaggregation or exfoliation compared with previous aggressive chemical methods such as acid treatment.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a method of preparing a particle dispersion or a composite material, comprising: (a) treating particles by the particle treatment method, and (b) dispersing the treated material in a liquid vehicle or matrix material;    (2) particulate carbon material obtained or obtainable by the method, comprising discrete graphitic platelets and/or carbon nanotubes;    (3) a particle dispersion or a composite material comprising particulate carbon material dispersed in a liquid vehicle or matrix material; and    (4) an article or device comprising an electrically-conductive element or layer comprising the composite material, or obtained by the method, such as a photovoltaic device, field emission device, hydrogen storage device, battery or battery electrode.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a treatment vessel.    Electrode (3)    Cylindrical glass vessel (4)    Lid (5)    Fine filter disc (32)    Front opening (41)    Drum wall (42)    Integral glass rear end wall (43)    Axially-extending rib formations (44)    Fluid injection port (51)    Peripheral sealing skirt (53)