Tickling soft polymers at the nanoscale

The results of the research published in Nano Letters
AFM of nanovesicles on a surface

Due to their excellent stability, polymers are widely utilized as coatings or packing materials in modern cutting-edge techniques, such as nanoimprint lithography, microelectromechanical systems (MEMS), and semiconducting devices. Among diverse mechanics parameters, the elastic moduli of the polymer nanofilms are not only paramount for their effective utilization but also the key parameter to explore the size-related physical quantities at small scales. The conventional method for measuring the elastic modulus is to deform the thin material to a nanometer-scale depth using a sharp indenter, and the elastic modulus can be extrapolated from the acquired load–displacement curve. In fact, a hybrid modulus of the film–substrate system rather than the intrinsic modulus of the film is obtained, and for softer, thinner films, more significant substrate effects emerge.

To eliminate the substrate effects, freestanding strategies in the form of either cantilever microbeams, or suspended membranes, etc, are developed. However, most of the methods require elaborate sample preparation, handling, and/or transfer, restricting their applications in practical scenarios. Therefore, a simple but accurate method is urgent for the nanofilm characteristics.

In a joint effort, an international team of researchers from the University of Electronic Science and Technology (UESTC), China, led by Yakang Jin and Longquan Chen, and the Department of Materials Science of the University of Milano-Bicocca (UNIMIB), Italy, led by Carlo Antonini, recently investigated the nanomechanics of nanoblisters, naturally forming in water between a polymeric nanofilm and a rigid substrate, using atomic force microscopy (AFM). The researchers investigated the size effect on nanoblister stiffness and proposed a theoretical model with the help of energy analyses, offering a simple method for accurately measuring the elastic modulus of polymeric nanofilms. The study led to the journal publication “Interfacial Nanoblisters Formed in Water Serving as Freestanding Platforms for Measuring Elastic Moduli of Polymeric Nanofilms” in the international peer-reviewed journal Nano Letters (Impact Factor 11.189, Journal Citation Report, Clarivate Analytics, 2021).

The method does not only avoid complicated sample preparation, but also eliminates the substrate effects in conventional tests, so it is anticipated to be highly helpful in both fundamental and applied research of polymeric nanomechanics and nanomaterials.