Capillary Wave Studies of Multiblock Polypeptide Copolymers at the Air/Water Interface

• Published in: Langmuir 1997-10, Vol.13 (22), p.5933-5940
• Main Authors: Gandhi, J. V, Maher, J. V, Shaffer, K. A, Chapman, T. M
• Format: Article
• Language: English
• Subjects: Aminoacid polymers; Applied sciences; Exact sciences and technology; Physicochemistry of polymers; Synthetic biopolymers
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la970519h

To observe the changes in the mechanical properties of copolymer interfacial films when controlled changes are imposed on molecular architecture, we have studied capillary waves in spread monolayers of triblock and pentablock copolymers of γ-benzyl-l-glutamate and d,l-glutamic acid having similar molecular weights and hence different block sizes. Using the mechanically generated capillary wave method and the capillary wave dispersion relation, we have extracted the values of viscoelastic parameters including surface pressure, transverse viscosity, longitudinal elasticity, and longitudinal viscosity of copolymer monolayers at the air−water interface, as a function of the interfacial number density of molecules of the triblocks and the pentablocks. The surface pressure, π, shows a clear saturation as a function of the number density for both copolymers. The saturation surface pressure of the pentablocks is not dramatically larger than that of the triblocks, in contradiction to expectations from a steric blocking argument. The longitudinal elasticity increases at a larger rate as the function of the interfacial number density for the pentablocks as compared to the triblocks. We observe negligibly small values of the transverse and the longitudinal viscosity at all number densities of the two copolymers.