What Can AFM Do for Polymer Research?

Scanning probe microscopy (SPM) has many benefits over alternative techniques for studying polymeric materials. The sharp apex and precise force control provided by SPM enables researchers to probe heterogeneous samples with resolution down to the nanometer level where single molecules can be observed. Many different material properties and behaviors can be studied by measuring a signal (e.g., force or current) localized by the probe apex while changing instrumental conditions (e.g., Z position or bias). SPM works over a wide range of temperatures, and in both air and liquid, allowing researchers to select the most interesting environment for their experiments and to do comparisons between measurements under different conditions.

In this talk, the speaker introduces SPM modes that are often used in polymer research and describes their strengths and weaknesses. He discusses methods for measurement of polymer dynamics, high resolution mechanical property mapping, probing the time-dependent viscoelastic behavior of polymers, nano-electrical measurements with data cubes, and temperature-dependent measurements. The speaker additionally discusses practical matters of interest to polymer researchers such as the system calibrations needed for quantitative measurements, probe selection, and sample preparation methods.

In this segment, the speaker presents a perspective of AFM capability development coupled with the needs of industrial polymer materials characterization. This includes fundamental studies of polymer behavior, polymer materials development, and troubleshooting issues. For example, AFM has replaced much of the TEM workflow for sizing of phases in polymer blend development since no heavy metal staining is required. Further time savings come from the ability to automate many of the steps involved in sample preparation, image acquisition, and image analysis. 

A more recent innovation in AFM technology has been chemical functional spectroscopy and mapping using AFM-IR, where AFM is used to detect infrared absorption on the nanoscale via photothermal expansion. This added dimension of chemical contrast now allows AFM to see the chemistry in the morphology.

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The recent development of alternatives to fossil fuels will play a crucial role in global electricity generation and should be one of the global strategies to reduce CO₂ emissions. To develop efficient and competitive modern electronics from semiconducting materials for energy conversion and storage, it is essential to understand the relationships between molecular architecture, supramolecular organization, microscopic morphologies and optoelectronic properties.

Using AFM-derived techniques (such as Conducting AFM, Kelvin Probe Force Microscopy - KPFM), local electrical properties can be measured (together with the morphological and mechanical characterization of the samples) helping to optimize device performance. In this presentation, the speaker presents examples of how the lateral resolution in KPFM and in photo(conducting) AFM can allow a direct visualization of the carrier generation at the donor-acceptor interfaces and their transport through the percolation pathways, among other examples.