The displacement of adsorbed polymer from silica surfaces by the addition of a nonionic surfactant

The adsorption of polyvinyl alcohol and Synperonic NP8 (nonyl phenol ethoxylate with an average of eight ethylene oxide groups per molecule) on fumed silica has been studied at various pH values. This was followed by an investigation of the competitive adsorption of NP8 and PVA. It was shown that NP8 can displace the polymer from the silica. This was attributed to a higher adsorption energy for the NP8 molecule compared with the value of the individual adsorbed PVA segments. Sediment volume experiments showed that the addition of NP8 to a colloidally stable silica dispersion with adsorbed PVA can induce flocculation as a result of displacement of some or all of the PVA chains from the surface. Initially the adsorption of the NP8 molecules caused an increase in the hydrophobic interaction (resulting in the flocculation) between the alkyl phenol groups which are oriented towards the bulk solution (since the PEO chains preferentially adsorb on the silica surface). Restabilisation at higher NP8 concentrations occur through the formation of bilayers with the PEO chains now dangling in solution.