We study the surface behavior of Langmuir films of highly concentrated interfacial colloids composed of flocculated silver nanoparticles located at the liquid−liquid interface of water and dichloromethane. Pressure/area isotherms and UV−visible absorption−reflection spectra are acquired in situ simultaneously. The behavior is discussed in terms of the colloid particle size and concentration. A reversible buckling of the film is observed at about 20−22 erg/cm2, with a creased three-dimensional phase replacing the smooth two-dimensional phase. The temperature dependence of the π/A curves is measured and discussed, particularly in relation to the buckling of the film. This work bridges over the size gap between the behavior of monoparticulate films of nanoparticles and those of micron-size glass and latex particles.

We study 2-(p-N-hexadecyl-N-methylamino)benzylidene-1,3-indandione (1a) as a model compound for the preparation of nonlinear optically (NLO) active Langmuir-Blodgett (LB) layers. The pressure-area (π-A) isotherm of (1a) at the air-water interface is investigated. A limiting area of 0.60 ( 0.02 nm 2 per molecule is found. The alternate-layer LB deposition of compound (1a) and an inert spacer, cadmium stearate, at different surface pressures is performed. The effects of temperature and delay time between spreading of the Langmuir film and the deposition of the LB films are studied. An increase of collapse pressure from 20 to 30 mN/m is observed as the delay time increases. UV-vis spectra indicate a uniform transfer of (1a) and show compressioninduced changes as a function of the deposition conditions. A split of the absorption maximum is observed for LB films deposited at higher pressures and lower temperatures. The two bands can result from two different molecular electronic transitions, affected by the aligning influence of the surface, and the different environments in the film compared to solution. Alternatively, these two bands can be associated with (at least) two different conformers. The orientation of the transition moments is evaluated on the basis of polarized UV-vis spectra at different angles of incidence, and found to be 40-44°. Significant second harmonic (SH) generation by the LB films is observed. Analysis of the SH response gives a tilt angle of 44°, in agreement with the finding from UV absorbance.

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