What Can AFM Do for Polymer Research?
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Join us for an engaging discussion on the latest in polymeric applications and research. Following presentations from our guest speakers we will have live in-lab demonstrations of the techniques and modes featured.
- Dr. Gregory Meyers, Dow Chemical
- Prof. Dr. Philippe Leclere, University of Mons
- Dr. Bede Pittenger, Bruker
- High-resolution electrical characterization with KPFM and TUNA provide insight into material performance and help to optimize organic photovoltaics and Li-ion batteries.
- Applications of AFM in characterizing the mechanical properties and chemistry for development of new materials and troubleshooting production issues for the polymer materials industry.
- Strengths and weaknesses of common AFM modes when applied to polymers and composites.
- Practical considerations like probe selection and system calibration.
Symposium Introduction by Session Chair | Dr. Thomas Mueller, Bruker
Atomic Force Microscopy in the Polymer Materials Industry| Dr. Gregory Meyers, The Dow Chemical Company
A perspective of AFM capability development coupled with the needs of industrial polymer materials characterization will be described. This will include fundamental studies of polymer behavior, polymer materials development, and troubleshooting issues. For example, AFM has replaced much of our 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.
In particular we have been keenly interested in quantifying mechanical properties in polymer films, blends, composites and interfaces. The local mechanical properties can be helpful to explain bulk performance, for example in revealing weak boundary layers of an adhesive to metal for automotive applications or the ability of an architectural coating to resist pick up of dirt over time. This makes sense considering the exquisite control AFMs provide for force and displacement on the nanoscale. Thermal-mechanical behaviors can also be explored using heated tip technology (NanoTA) for local thermal analysis. Local glass transition or melting temperatures can be helpful in identifying compositions when mechanical contrast alone is not definitive. 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.
Nanoscale Electrical Characterization of Organic and Hybrid Materials for Energy Harvesting Applications| Prof. Philippe Leclere, University of Mons
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 and stop the climate change. To develop efficient and competitive modern electronics from semiconducting (organic, inorganic or hybrid) 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. For instance, for photovoltaic organic devices, we can spatially resolve the surface photo-voltage in high efficiency nanoscale phase segregated photovoltaic blends of conjugated polymers. We show on different examples 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.
For harvesting energy applications, as an example, the morphology and the crystallinity of Poly(lactic acid) electrospun nanofibers have been controlled by thermal post-treatment, leading to improved mechanical and piezoelectrical properties. A complete investigation of pristine and annealed nanofibers was performed using a multi-technique approach. AFM-based methods unveiled interesting results about the changes in crystallinity and the influence of the polymer crystalline phase on local properties.
In fine, for flexible energy storage based on Li-ion batteries, AFM showed that the interlocking frameworks of kinked-silicon nanowires and multi-walled carbon nanotubes exhibit beneficial mechanical properties with a foam-like behavior amplified by the kinks and a suitable porosity for a minimal electrode deformation upon Li insertion.
A Selection of Modes and Methods for SPM Research of Polymers| Dr. Bede Pittenger, Bruker
When studying polymeric materials Scanning Probe Microscopy (SPM) has many benefits over alternative techniques. 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 we will introduce several different SPM modes that are often used in polymer research and describe their strengths and weaknesses. We will discuss 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. We will additionally discuss practical matters of interest to polymer researchers such as the system calibrations needed for quantitative measurements, probe selection and sample preparation methods.
Recent Developments with Live Demonstration | Dr. Senli Guo and Dr. Mickael Febvre, Bruker
Dr. Bede Pittenger is a Senior Staff Development Scientist in the AFM Unit of Bruker's Nano Surfaces Business. He received his PhD in Physics from the University of Washington (Seattle, WA) in 2000, but has worked with scanning probe microscopes for 25 years, building systems, developing techniques, and studying properties of materials at the nanoscale. His work includes more than thirty publications and three patents on various techniques and applications of scanning probe microscopy. Dr. Pittenger's interests span topics from interfacial melting of ice, to mechanobiology of cells and tissues, to the nanomechanics of polymers and composites.