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The action of dispersants on the aggregation of carbon black (CB) particles, chosen as model for diesel soot present in lubricants, and their interactions with polymeric additives are investigated using Light Scattering techniques. The study of an ashless dispersant in a basestock shows that polyisobutylene (PIB) succinimides are associated in aliphatic media. The effect of PIB succinimides on the aggregation of CB suspensions is followed in 100 Neutral solutions of dispersant and non-dispersant polymethacrylate viscosity index improvers (respectively DPMA and PMA). The results show that ashless dispersants slow down the aggregation of CB suspensions without polymer or with non-dispersant PMA. The dispersant effect of DPMA is not improved by addition of ashless dispersant, in contrast to the case of the non-dispersant polymer.