PREPARATION AND CHARACTERIZATION OF MONOP ARTICULATE LAYERS COMPOSED OF PARTIALLY HYDROPHOBIC GLASS AND SILICA PARTICLES - A LANGMUIR FILM BALANCE STUDY .1.

Monoparticulate layers of partially hydrophobic (silanized) glass and silica beads (2R = 75 +/- 5 and 3 +/- 1 mu m, respectively) were studi ed in Langmuir film balance. Surface pressure vs. surface area isother ms were determined which permitted some conclusions concerning particl e-particle (p-p) and particle-subphase (p-s) interactions. 1, Methods were suggested a, for the determination of the p-p distance in the sec ondary potential energy minimum as well as the p-p repulsive interacti on energy as a function of interparticle distance for weakly cohesive monoparticulate layers and b, for the approximation of p-p adhesion en ergy for (strongly) cohesive monoparticulate layers. Interparticle dis tances between particles of weakly cohesive monoparticulate layers in their secondary interaction energy minimum have been assessed to be 49 0 nm by method a,. This distance is in fair agreement with that calcul ated by the DLVO theory, augmented by capillary interaction. However, the calculated total (repulsive) interaction energies (E(rep) = (0,5 - 1,3)10(-13) J) between these particles are some two orders of magnitu de greater than expected (10(-16) - 10(-15) J). This discrepancy is no t completely understood at present. The particle-particle adhesion ene rgies for the strongly cohesive layers of the most hydrophobic particl es (Theta = 90 degrees, 2R = 75 mu m and 3 mu m) were approximated by method b,. They were in good agreement with each other (85 - 100 mJm(- 2) for the larger and 111-133 mJm(-2) for the smaller particles, respe ctively) and with the ''pull-off'' energy obtained earlier for silaniz ed glass surfaces (41). 2, The p-s interaction was examined by compari ng the energy which is necessary for particle removal from the monopar ticulate layer, E(r), determined via II vs. A isotherms, with the adhe sion work, W-r, determined by in situ contact angle measurements. Sati sfactory agreement between E(r) and W-r was obtained for the monoparti culate layers which were prepared from the more hydrophobic particles (Theta = 90 degrees, 2R = 75 mu m and 2R = 3 mu m). Significant discre pancies between E(r) and W-r for the monoparticulate layers which were prepared from the less hydrophobic (Theta = 72 degrees and Theta = 55 degrees) particles were interpreted in terms of contact angle hystere sis, dynamic wetting, and distortion of the electric double layer arou nd the interfacial particles.