Elastic properties of symmetric liquid-liquid interfaces

The mean (κ) and Gaussian (κ) bending rigidities of liquid-liquid interfaces, of importance for shape fluctuations and topology of interfaces, respectively, are not yet established: Even their signs are debated. Using the Scheutjens Fleer variant of the self-consistent field theory, we implemented a model for a symmetric L-L interface and obtained high-precision (mean-field) results in the grand-canonical (μ,V,T) ensemble. We report positive values for both moduli when the system is close to critical where the rigidities show the same scaling behavior as the interfacial tension γ. At strong segregation, when the interfacial width becomes of the order of the segment size, κ turns negative. The length scale λκ/γ remains of the order of segment size for all strengths of interaction; yet the 1/N chain length correction reduces λ significantly when the chain length N is small.