Effect of Triton X-100 on the stability of titania nanoparticles against agglomeration and sedimentation: A masked depletion interaction

•Nonionic surfactant micelles introduce significant depletion forces causing flocculation of titania particles.•Micellar depletion effects can be masked by the higher solution viscosity caused by the micelles.•Depletion effects cause fast flocculation and then faster sedimentation of dense particles.•A new model of agglomeration and sedimentation establishes the basis of the hidden depletion effect.

The sedimentation half-times ts of suspensions of polydisperse titania particles in aqueous Triton X-100 (TX100) solutions with concentrations cTX100 ranging from 0.05 to 250 mM were measured. Three regions of TX100 concentrations with different settling behavior were observed. In region A, or for cTX100 below its cmc (ca. 0.24 mM in water at 25 °C), the ts-values increase with increasing surfactant concentration. In region B, or for cmc≤cTX100

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