Nanoscale DMA with the Atomic Force Microscope: A New Method for Measuring Viscoelastic Properties of Nanostructured Polymer Materials

Abstract

We introduce nanoscale dynamic mechanical analysis (DMA) based on atomic force microscopy (AFM), a new mode for quantitative viscoelastic analysis of heterogeneous polymer materials at the nanoscale (AFM-nDMA). AFM-nDMA takes advantage of the exquisite force sensitivity, small contact radius, and nanoscale indentation depth of the AFM to provide dynamic mechanical analysis with 10 nm spatial resolution at rheologically relevant frequencies and variable temperature. This novel, non-resonant measurement is embedded in a force curve and typically occurs at a series of frequencies to provide spectra of storage modulus, loss modulus, and loss tangent. By using tailored probes and mitigating the effect of contact radius changes throughout the measurement, quantitative results are obtained that tie directly to bulk DMA and allow for time-temperature superposition analysis. The combination of quantitative results and 10 nm spatial resolution holds promise for the investigation of previously inaccessible microscopic domains, confinement effects, and interphases.

Nanomechanical mapping of soft materials with the atomic force microscope: methods, theory and applications

“…348 This result is in conflict with the other studies that compared nanoscale with either micro-scale or macroscopic measurements. 86,108,317,346,347,349 The stress applied on AFM-based measurements is between one and two orders of magnitude higher than the one applied on bulk measurements. It has been noted that, for certain materials, the stress applied on AFM could be in a nonlinear stress-strain regime, in particular when using sharp tips.…”

“…108,316 The same conclusion was reached for FV measurements of the elastic, storage and loss tangent values of several polymers and polymers blends. 86,346,347 One study performed on polyurethane and polystyrene samples reported that the agreement between rigidity modulus measured by FV and DMA macroscopic measurements was only possible for AFM experiments performed with dull tips (R 4 800 nm). 348 This result is in conflict with the other studies that compared nanoscale with either micro-scale or macroscopic measurements.…”

Measuring Viscoelastic Master Curves at the Nanoscale in Polymer Composites

“…In designing a technique for the nanoscale measurement of viscoelastic properties (AFM-nDMA), there are some key considerations that need to be incorporated [5][6][7][8]. First, the AFM tip-sample interaction must be operated at low, well-controlled loads.…”

“…Bruker AFM-nDMA addresses this by adding a relaxation segment just after applying the preload. Additionally, reference segments at a given frequency are collected periodically throughout the measurement to allow for later estimation of contact radius evolution [8].…”

On the Nanomechanical and Viscoelastic Properties of Coatings Made of Recombinant Sea Star Adhesive Proteins

“…This technique is a new mode for quantitative viscoelastic analysis of heterogeneous polymer materials at the nanoscale. AFM-nDMA takes advantage of the exquisite force sensitivity, small contact radius, and nanoscale indentation depth of the AFM to provide dynamic mechanical analysis with 10 nm spatial resolution at rheologically relevant frequencies and variable temperature (Pittenger et al, 2019).…”