The Gel Trapping Technique – A Novel Method for Characterization of the Wettability of Microparticles and Replication of Particle Monolayers

We have developed a novel gel trapping technique (GTT) which allows the three-phase contact angle of microparticles to be determined at an air-water or an oil-water interface. The method is applicable for particle diameters ranging from several hundred nanometers to several hundred micrometers. We also used the GTT for replicating of particle monolayers at liquid surfaces and for preparation of unsymmetrically coated particles. RESULTS AND DISCUSSION Characterization of the wettability of microand nanoparticles has been a long-standing challenge in materials science. Although several methods exist for characterization of the contact angle of macroscopic surfaces [1] or powder plugs [2], a reliable and robust technique for determination of the wettability [3] of individual microparticles and nanoparticles was not available until recently [4]. We have developed a “gel trapping technique” [4] which is based on spreading of colloid particles on air-water or oil-water surface and subsequent gelling of the water sub-phase with a suitable non-adsorbing hydrocolloid (see Figure 1). Gellan [5] was used as a gelling agent as it has been demonstrated that the presence of gellan in the water phase does not change the interfacial tension of both the air-water and the oil-water interface [4]. We also showed that the contact angle of water drops on hydrophobic substrates (polystyrene slides) is insensitive to the gellan concentration up to 2%wt. The particle monolayer trapped on the gel Figure 1. Schematic diagram of the “gel trapping technique” for determination of the contact angle θ of microparticles at the oil-water (A-F) and the air-water (C-F) interface. Mat. Res. Soc. Symp. Proc. Vol. EXS-2 © 2004 Materials Research Society M8.25.1