The potential applications of Atomic Force Microscope (AFM) in measuring the biophysical properties of plants membranes, such as the cuticle of tomato fruits, have been introduced before. However, previous studies on the application of the AFM in surface characterization of polymeric fiber were mainly focused on the AFM capabilities in producing high-resolution topography images of either fiber surface or its cross–section. The main objective of this study was to characterize and compare the surface nanomechanical properties of cotton fibers using various modes of the AFM. To achieve this goal, fifteen fibers were randomly selected from two different cotton varieties that were quite distinct in terms of their macroscale frictional properties. Surface topography and friction images of the fibers were obtained with conventional contact mode (Fig. 1a-b). The nanomechanical property images, such as adhesion and deformation, were obtained with Bruker’s newly developed high-speed force-volume technique, PeakForce QNM<sup>®</sup> (Fig. 1b-c). The experiments were conducted in air, using a silicon nitride tip with radius of curvature of 40 nm and spring constant of 0.06 N/m. In addition to the measured parameters, different contact theories were implemented to estimate the real contact area between the AFM tip and the fibers surface. Our results indicate that the fibers with higher macroscale friction were also associated with higher nanoscale friction, adhesion, and deformation. In fact, cotton fiber cells are covered with a thin cuticular membrane. The cuticle is mostly made of lipids, alcohols, and fatty acids (collectively called ‘cotton wax’). The waxy layer can be 10 to 300 nm thick and imparts hydrophobicity to fiber surface. The differences in nanoscale friction, adhesion, and deformation signals can be attributed to fiber surface hydrophobicity and stiffness, which in turn depend on fatty acids’ hydrocarbon chain length, film viscosity, and the waxy layer thickness.

Nanofriction and surface nanomechanical properties of cotton (Gossypium hirsutum L.) fibers as studied with contact mode and force-distance curve-based AFM

255th National Meeting (2018)

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