title: Surface dilational rheological properties in the nonlinear domain.
abstract: The interfacial tension response to dilational deformation of interfacial area exhibits a (more or less) nonlinear behavior, depending on the amplitude of the deformation. Studies of such observable interfacial properties in the nonlinear domain suggest valuable information about the two-dimensional microstructure of the interfacial layer, as well as about the structure time-evolution. In this article, the emphasis is centered on the available mathematical methods for quantitatively analyzing and describing the magnitude and the characteristics of the nonlinear interfacial viscoelastic properties. Specifically, in periodic oscillation experiments the nonlinear behavior can be represented by the combination of a linear part (the surface dilational modulus), with an additional complementary Fourier analysis parameterizing the nonlinearity. Also asymmetric Lissajous plots, of interfacial tension versus deformation, are useful tools for expanding the response nonlinearity into four distinct components relevant to significant points of the cyclic loop. In connection with the mathematical methods, nonequilibrium thermodynamic formulations provide a powerful theoretical framework for investigating the interfacial dynamic properties of multiphase systems. Experimental results for adsorption layers of complex components, available in the literature, show notable nonlinear interfacial viscoelastic behavior. In particular in this review, data are illustrated for solutions of polymers and of polyelectrolyte/surfactant complexes. The observed nonlinear findings reveal formation of complexes, patches, and other different interfacial structures.
authors.affiliation: Department of Colloid Chemistry, St. Petersburg State University, Universitetsky pr. 26, 198504 St. Petersburg, Russia.
authors.forename: A G
authors.initials: AG
authors.lastname: Bykov
authors.affiliation: CNR-Istituto per l'Energetica e le Interfasi, Via De Marini 6, 16149 Genova, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Liggieri
authors.affiliation: Department of Colloid Chemistry, St. Petersburg State University, Universitetsky pr. 26, 198504 St. Petersburg, Russia.
authors.forename: B A
authors.initials: BA
authors.lastname: Noskov
authors.affiliation: CNR-Istituto per l'Energetica e le Interfasi, Via De Marini 6, 16149 Genova, Italy; Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Firenze, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Pandolfini
authors.affiliation: CNR-Istituto per l'Energetica e le Interfasi, Via De Marini 6, 16149 Genova, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Ravera
authors.affiliation: CNR-Istituto per l'Energetica e le Interfasi, Via De Marini 6, 16149 Genova, Italy; Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Firenze, Italy. Electronic address: giuseppe.loglio@unifi.it.
authors.forename: G
authors.initials: G
authors.lastname: Loglio
keywords: Fourier spectral analysis; Lissajous plots; Nonlinear interfacial rheology; Stress decomposition; Surface dilational modulus; Surface dilational viscoelasticity