CHARACTERIZING POLYMERS WITH AN IMPINGING JET

The impinging jet is a well-established technique to study the deposit ion of colloidal particles onto a solid surface (a collector) under we ll-defined hydrodynamic and physicochemical conditions. The presence o f polymers, in solution, adsorbed onto the colloidal particles or onto the collector surface, can have a large effect on the deposition kine tics of the particles. In this study we show that it Is possible to ch aracterize polymers by using colloidal particles as probes. By choosin g experimental conditions under which a competition takes place betwee n polymer adsorption and particle deposition on the solid surface, the kinetics of particle deposition is governed by the properties of the polymers. Under conditions for which particle deposition is absent whe n both the particles and the solid surface are coated by polymer, the impingement of a mixture of polymers and polymer-coated particles will cause an initial deposition of polymer-coated particles which stops w hen the solid surface is coated by polymers in solution. The time at w hich particle deposition stops equals the time tau(ads) at which the s olid surface is coated by polymers. This time depends on the polymer c oncentration, c, and molecular weight, M. Thus, in principle, measurin g tau(ads) yields information about c and/or M. Here we show that adso rption isotherms can be obtained for a polyelectrolyte (polyethylenimi ne) adsorbing on TiO2 particles, by measuring c with the impinging jet technique. The obtained isotherm closely resembles the one obtained b y classical methods (colloid titration), The advantage of the present method is that the technique can be applied for very low polymer conce ntrations, typically in the range 10 ppb to 1 ppm. (C) 1996 academic p ress, Inc.