Based on the definition provided by the International Union of Pure and Applied Chemistry (IUPAC), polymer structure analysis is categorized in characterization of the architecture/topology of the individual macromolecules such as chemical composition or molar mass, and characterization of the macromolecular assemblies thereof, i.e. their bulk and surface/interface properties like crystallinity or transparency. Lately, local structural characterization especially at interfaces became very important for the contemporary R&D fields like circular plastic, light weight mobility, additive manufacturing or printable electronics.
The high-resolution microscopy techniques Transmission Electron and Atomic Force Microscopy (TEM/AFM) have demonstrated their capabilities to characterize the local morphology of polymer materials with (sub-) nanometer spatial resolution. Moreover, recent technological developments allow for connecting the morphological information with additional structural features and properties as defined above. Especially the acquisition of local chemical information based on various spectroscopic techniques integrated in TEM/AFM became mature.
Here, I will present an overview of state-of-the-art TEM/AFM-based methodologies highlighting some recent amazing results. I will focus on Scanning TEM (STEM), which offers staining-free contrast creation between different polymer phases, e.g. different rubbers or even between the amorphous and crystalline phases in a semi-crystalline polymer like polyethylene, and in combination with Energy-Dispersive X-ray spectroscopy (EDX) or Electron Energy Loss Spectroscopy (EELS) allows for elemental and, in part, molecular distribution mapping. Moreover, I will present recent developments of AFM-based nearfield Infrared spectroscopy, which allows for local chemical identification of polymers and other organic compounds with high energy- and nanometer spatial resolution.

Novel high-tech materials share a common denominator: a careful design at the nanometer range. From functional polymer composites to wearable electronics or selective membranes, local variations in mechanical and electrical properties dictate the macroscopic properties. A focus on progressively smaller structures increases the demand for analytical methods that offer sufficient resolution. Here, atomic force microscopy provides analytic insights beyond mere topography.
In this talk, we demonstrate several state-of-the-art modes of the broad family of Atomic Force Microscopy (AFM) to analyze polymer surfaces on the nanometer scale.
Park Systems’ PinPoint mode measures high-speed force-distance curves for each pixel which allows for the study of the mechanical properties like Young’s modulus, adhesion, or mechanical energy dissipation on a local scale. Moreover, PinPoint mode enables facile integration of other modes such as conductive atomic force microscopy or piezo force microscopy and thus offers a holistic approach to nanoscale characterization. Additionally, it will be explained how Kelvin Probe Force Microscopy (KPFM) is a valuable tool, for example, to study local perturbances in the electronic structure of surfaces.
Lastly, we show how Photo-induced Force Microscopy (PiFM) integrates IR lasers with AFM to characterize local physical and chemical features.
This talk emphasizes the versatility of AFM-based techniques to provide a comprehensive analytical toolbox for various types of samples.

Nanoscale-resolved infrared imaging and spectroscopy (nano-IR) enables detailed chemical analysis and compositional mapping at a spatial resolution of 10-20 nm and below [1]. The high spatial resolution is achieved by illuminating a metallic atomic force microscopy (AFM) tip with IR radiation - creating a nanofocus below the tip. The sample is scanned below the tip to obtain simultaneous mechanical (AFM) and optical (nano-IR) images. Nano-IR spectroscopy is enabled by employing broadband or tunable IR laser sources (such as wOPO laser covering 570-7000 cm-1). The sample’s local IR response is detected either via photothermal expansion forces (AFM-IR) or light scattering (nano-FTIR, s-SNOM), depending on the measurement goals. Notably, the nano-FTIR phase and AFM-IR amplitude both closely resemble IR spectra known from FTIR absorption spectroscopy. To date, a plethora of polymer properties were probed using nano-IR (Figure 1).

Here we present an overview of key polymer properties probed by nano-IR; (i) a brief introduction to chemical nano-identification and compositional mapping of organic contaminants [1]; followed by probing of molecular orientation, conformation, and crystallinity of sub-20 nm thin polyethylene-oxide layers [2, 3]; and quantification of material composition in cross-sections of individual core-shell-shell nanoparticles [4].

Figure description: nano-IR absorption images and spectra with 10-20 nm spatial resolution.
Center: Chemical identification of PMMA and PS via nano-IR (near-field) and FTIR (far-field) spectra. Further, clockwise: PS-PMMA blend; 3-component polymer blend; polyamide layers cross-section; PS-PMMA block co-polymer; all-polymer core-shell-shell nanoparticles; α-helix/β-sheet reveals virus in protein mixture; molecular orientation in PEO monolayer; phase-coexistence in pentacene; crystallinity of PEO.

Polyurethane foams are extensively used in thermal insulation applications, the control and reduction of their pore size are critical for enhancing their insulation performance. Our recent findings on the role of entrained air bubbles challenge conventional views on pore size control in rigid polyurethane (PU) foams [1,2]. Although fluorinated alkanes (FCs) have long been employed to reduce the pore size, the exact mechanism behind their action remained unclear. Our studies demonstrate that FCs primarily act by increasing the number of entrained gas bubbles, which act as heterogeneous nucleation sites during the foaming step [3].
We show that once a critical FC concentration is reached, further additions of FCs no longer impact the pore size, indicating a saturation effect. We establish a direct relationship between the air bubble density in the initial reactive mixture and the final foam morphology. By carefully controlling the air entrainment step during processing, we can precisely tune the final pore size, without changing the chemical formulation [1]. Corelating cryogenic scanning electron microscopy and surface tension measurements, we further reveal the formation of interfacial films induced by FCs, influencing foam stabilization and growth dynamics [4]. These findings do not only advance our understanding of reactive PU foaming but also propose a paradigm shift: rather than structural changes occurring during foam aging, key modifications are initiated during the pre-mixing phase. This new perspective opens up opportunities for more advanced process control in PU foaming, enabling the design of tailored foam structures that enhance thermal insulation and material performances.