Scaling Description of Two-Dimensional Chain Conformations in Polymer Monolayers

It is shown how the molecular weight dependence of the radius of gyration $R_{F2\mathrm{}}$ of two-dimensional polymeric chains can be derived from surface-pressure isotherms in Langmuir monolayers. $R_{F2\mathrm{}}$ scales as $N^{\nu }$ with $\nu =0.56\mathrm{}$ for polymethylmethacrylate and 0.79 for polyvinylacetate. These values are in agreement with the scaling predictions for tricritical and excluded-volume behaviors, respectively. The crossover between the dilute and the intermediate regimes is also clearly observed in one case.