| Abstract
| - Polyion complex formation at the air−water interface between carboxymethylcellulose and a series oftriethylammonium-functionalized amphiphiles containing the 4-nitro-4‘-alkoxy azobenzene chromophorehas been investigated. Surface pressure−area isotherms are found to exhibit a systematic dependence onsubphase concentration up to a certain critical concentration, which depends on the chromophore spacerlength. However, UV−visible, polarized FT-IR, and X-ray reflectivity measurements indicate no significantdifferences in molecular density, molecular orientation, or film thickness for Langmuir−Blodgett (LB)films transferred at a given surface pressure from different polyion subphase concentrations. LB filmsprepared at different polyion concentrations thus appear to have essentially identical structures, despitethe differences in the recorded surface pressure−area isotherms. Isotherm dependence on subphaseconcentration is therefore attributed to partial loss of the soluble amphiphile into the water subphase atlower polymer concentrations. These results imply that isotherms obtained below the critical subphaseconcentration give false (or apparent) molecular areas, which may lead to erroneous conclusions.
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