Morphology, nanomechanical and thermodynamic surface characteristics of nylon 6/feather keratin blend films: an atomic force microscopy investigation

Abstract

The surface structure and nanomechanical properties of solution-cast nylon 6 (NY6)/feather keratin (FK) blend films were investigated using a combination of tapping-mode atomic force microscopy (AFM) phase imaging and nanoscale indentation. A tendency for a nanoscale phase separation between NY6 and FK in their various blends was judged based on the blend phase images. The surface topography and roughness analysis of the AFM height images revealed that FK-rich blends had coarser surfaces than NY6-rich ones, possibly due to the heterogeneous nature of the FK chemical structure. Amplitude–phase–distance measurements involving the assignment of the darker and brighter regions of the phase images to NY6-rich and FK-rich, respectively, or vice versa led to the recognition of a phase inversion in the blend containing 40 wt% FK. The occurrence of the phase inversion phenomenon was related to the significant difference between the molecular weights of the blend constituents. Analysis of nanoindentation data showed that blending FK and NY6 at various ratios resulted in mixtures with modified mechanical and adhesion features. On the one hand, the NY6 component was responsible for an enhanced elastic modulus and stiffness of the blends, and on the other hand, the FK component provided higher pull-off force and work of adhesion for the samples. A new approach is also proposed to directly determine the surface energy (γ) values of samples from the nanoindentation data. The excellent consistency between the calculated γ values and the results obtained from contact angle measurements lends credence to the proposed approach. Copyright © 2012 Society of Chemical Industry