Nanoscale rheology: Dynamic Mechanical Analysis over a broad and continuous frequency range using Photothermal Actuation Atomic Force Microscopy

TL;DR

This paper introduces a novel AFM-based method using photothermal actuation to measure nanoscale viscoelastic properties of polymers over a broad frequency range, enhancing understanding of their time-dependent mechanical behavior.

Contribution

The paper develops and validates a new AFM technique that quantifies nanoscale viscoelasticity across five orders of magnitude in frequency, integrating it with existing AFM methods for comprehensive analysis.

Findings

Successfully measured nanoscale loss tangent, storage, and loss modulus.

Extended viscoelastic measurement range up to 20,200 Hz.

Demonstrated synergy with existing AFM techniques for broader frequency coverage.

Abstract

Polymeric materials are widely used in industries ranging from automotive to biomedical. Their mechanical properties play a crucial role in their application and function and arise from the nanoscale structures and interactions of their constitutive polymer molecules. Polymeric materials behave viscoelastically, i.e. their mechanical responses depend on the time scale of the measurements; quantifying these time-dependent rheological properties at the nanoscale is relevant to develop, for example, accurate models and simulations of those materials, which are needed for advanced industrial applications. In this paper, an atomic force microscopy (AFM) method based on the photothermal actuation of an AFM cantilever is developed to quantify the nanoscale loss tangent, storage modulus, and loss modulus of polymeric materials. The method is then validated on a styrene-butadiene rubber (SBR), demonstrating the method's ability to quantify nanoscale viscoelasticity over a continuous frequency range up to five orders of magnitude (0.2 Hz to 20,200 Hz). Furthermore, this method is combined with AFM viscoelastic mapping obtained with amplitude-modulation frequency-modulation (AM-FM) AFM, enabling the extension of viscoelastic quantification over an even broader frequency range, and demonstrating that the novel technique synergizes with preexisting AFM techniques for quantitative measurement of viscoelastic properties. The method presented here introduces a way to characterize the viscoelasticity of polymeric materials, and soft matter in general at the nanoscale, for any application.