Silanization has rendered spherical (75 ± 5 μm diameter) glass particles to be weakly (sample A, ϑ = 55°), moderately (sample B, ϑ = 72°), and highly (sample C, ϑ = 90°) hydrophobic. Nonequilibrium surface pressure (Π) vs surface area (A) isotherms have been determined for monoparticulate layers which were prepared from samples A, B, and C at water−air interfaces in a Langmuir film balance. The effect of hydrophobicity on the particle−particle interaction and on the energy (E r) which is necessary for the removal of a particle from the water−air interface (particle−subphase interaction) has been elucidated. Contact cross-sectional areas (CCSA), surface coverages (SC), and collapse energies (E c), evaluated from Π vs A isotherms, provided semiquantitative information on the structural strength. Monoparticulate layers which were formed from the most hydrophobic glass spheres (sample C) had a structural strength which was almost 5 times greater than that of those which were formed from the least hydrophobic sample (sample A), as revealed by the E c values which were elucidated for these systems. Long-term stability, determined by time-dependent surface-pressure measurements, was only found for sample C. The energy of a particle−particle contact was calculated, for the strongly cohesive layer of sample C, to be (1.2−1.4) × 10-10 J. The weakly cohesive layer, prepared from sample A, had a 490-nm interparticle distance at the secondary energy minimum and a total repulsive interaction energy in the range of (0.5−1.3) × 10-13 J between two beads at an interparticle distance of 1−200 nm. Values for adhesion work (W r) were calculated from in situ contact-angle measurements and compared to corresponding E r values which were obtained experimentally by the isotherms. The significant discrepancies between the W r and E r values which were found for sample A or sample B were rationalized in terms of contact-angle hysteresis, dynamic wetting, and distortion of the electric double layer around the interfacial beads.

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The association behavior of a maleic anhydride grafted and pyrene labeled ethylenepropylene random copolymer was studied using fluorescence spectroscopy. The labeling was achieved with 1-pyrenebutanoic acid hydrazide via the grafted anhydride groups. The resulting polar grafts induced intra-and intermolecular associations among the polymer chains in apolar solvents. This association process was studied using steady-state and time-resolved fluorescence spectroscopy as a function of polymer concentration. Due to the high complexity of the polymer system, an improved approach of handling the time-resolved fluorescence data had to be introduced. Thus, the quantitative analysis of the fluorescence decays was carried out using a novel model in which the polymer network is divided into blobs among which the chromophores distribute themselves randomly, according to a Poisson distribution. Results show that, as the polymer concentration is increased, the number of polar group aggregates increases. However, the local concentration of aggregated polar groups in the polymer network does not change. This indicates that as polymer concentration is increased, either that there are only a few polymer aggregates in the solution that increase in size and keep the concentration of polar junctions constant throughout the polymeric network or that more polymer aggregates are formed. This latter process would be reminiscent of micelle formation. This behavior is observed until the overlap concentration (c* ) 10-20 g/L), above which newly formed polar aggregates contribute to increasing the local aggregate concentration.