Among the next-generation solar cells, in particular, organic photovoltaics are gaining impact as a promising alternative to conventional silicon-based solar cells because they promise significantly shorter energy payback times. However, despite big achievements in terms of power conversion efficiencies in the last years, with champion efficiencies approaching the 20% limit, it remains an unresolved challenge to fabricate large-area organic solar cells without sacrificing efficiencies. Large-area deposition of the conjugated polymer donor and small molecule acceptor blends via printing is key in the device upscaling. Another issue calling the attention of scientists is the fabrication of environmentally friendly organic solar cells. To become environmental-friendly, the used solvents are a key factor. Today, still the most used solvents are halogenated solvents such as chloroform, chlorobenzene, and dichlorobenzene. These chemicals would harm the human body and can cause environmental pollution during the device fabrication process and waste solvent treatment. Accordingly, we investigate the printing of donor-acceptor blend films out of different solvents for use as active layers in organic solar cells with advanced in-situ scattering methods. We use grazing incidence small and wide-angle X-ray scattering (GISAXS and GIWAXS) in situ during printing to gain a fundamental understanding of the underlying film formation processes. Different examples of polymer donors and small molecule acceptors are presented, and the resulting morphologies are correlated with solar cell device performance. A special emphasis is put on the shift towards more environmentally friendly solvents, which will also be a prerequisite to promote the large-scale production of organic solar cells.

Dynamic light scattering (DLS) has become a routine characterization technique used mostly for the size determination of various objects in liquid dispersions. This contribution shall address more complex polymer systems on two levels:
1. Handling of "difficult" samples such as systems containing dust or large particles, systems exhibiting multiple light scattering, systems with superposition of diffusive and relaxation behavior of decay rate, systems with a combination of weakly and strongly scattering objects, systems with multiple relaxation modes. The techniques used are the software/hardware dust filter, subtraction method [1], multiangle data analysis [2], 3-dimensional analysis of DLS correlation functions [3],[4].
2. Applications of DLS to several complex systems such as internal dynamics of block copolymers in solutions, collective diffusion in concentrated polymer solutions, DLS from polymers under zero-average contrast conditions, critical behavior and correlation lengths in polymer blends and in bicontinuous microemulsions, density fluctuations in polymer melts, and detection of undulation modes in polymer systems with lamellar morphology.
DLS is a very versatile technique that can provide valuable detailed information on polymer dynamics in very complex systems.

Acknowledgment:
Support by the Ministry of Education, Youth and Sports of the Czech Republic (grant #LM2023053).

nano-FTIR correlation nanoscopy for organic material analysis

Adrian Cernescu; Suman Paul

neaspec – attocube systems AG, Haar-Munich, Germany
adrian.cernescu@attocube.com; suman.paul@attocube.com


Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) is a scanning probe approach to optical microscopy and spectroscopy, bypassing the ubiquitous diffraction limit of light to achieve a spatial resolution below 20 nanometers. s-SNOM employs the strong confinement of light at the apex of a sharp metallic atomic force microscopy (AFM) tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties of the sample directly below the tip and yields nanoscale resolved images simultaneous to topography. In addition, the technology has been advanced to enable Fourier-Transform Infrared Spectroscopy on the nanoscale (nano-FTIR) using broadband radiation from the visible spectral range to THz frequencies.

Recently, the combined analysis of complex nanoscale material systems by correlating near-field optical data with information obtained by other scanning probe microscopy (SPM)-based measurement methodologies has gained significant interest. In addition, the nano-FTIR spectroscopy enables not only nano-chemical identification and to explore local distribution of polymer blends, but it also offers information about local orientation of polymer chains in crystalline organic semiconductors and in polymer monolayers. Various examples of s-SNOM measurements on different polymer samples will be presented.

Keywords: nano-FTIR, s-SNOM, organic semiconductors, correlation nanoscopy

The primary purpose of industrial coatings for metals is to prevent corrosion of the substrate. The barrier effect, primarily driven by the pigment volume concentration (PVC) in the dry coating, plays a critical role in preventing corrosion species from penetrating through the coating film. While well-known PVC formulas are based on theoretical assumptions, experimentally verified the PCV value in the coating remains challenging.

In this study the film formation process in waterborne (WB) epoxy coatings is studied using electrochemical impedance spectroscopy (EIS) measurements and dynamic mechanical analysis (DMA). Ten epoxy coatings with different pigment volume concentration (PVC) were prepared on standard steel substrates and carefully monitored over four weeks (30 days). It is shown that impedance spectroscopy can serve as a very sensitive tool for accurate experimental detection of the critical pigment volume concentration (KPVC).
We also show that the optimal film formation process and corrosion stability of coatings are greatly affected by the coating PVC value. As a whole, the study confirms that the optimization of coating protection ability needs to take into account both maximization of the barrier effect as well as maximization of the degree of epoxy-amino cross-linking.

This research investigates the adhesion properties of multilayer paint coatings, with a particular emphasis on marine coatings and antifouling paints. A comprehensive suite of analytical techniques, including Dynamic Mechanical Analysis (DMA), Fourier Transform Infrared Spectroscopy (FTIR), Shaft-loaded blister test, and nano-indentation, was employed to evaluate the adhesion characteristics. The coatings were formulated under varying temperature and humidity conditions to elucidate the correlation between these environmental factors and the adhesion performance. Understanding the mechanisms of adhesion failure, such as substrate and intercoat adhesion failures, is crucial for improving coating durability and performance. By identifying and mitigating the risks associated with adhesion failure, we can significantly shorten the development time for new paint formulations, leading to more efficient and reliable production processes. Potential solutions to mitigate adhesion risks include optimizing the formulation of primers and topcoats, ensuring proper surface preparation, and controlling the application environment to maintain consistent temperature and humidity levels. The results of this study aim to advance the understanding of adhesion mechanisms in multilayer coatings, thereby contributing to the development of more robust and durable marine coatings.

The strength of Pulsed Field Gradient Nuclear Magnetic Resonance (PFG-NMR) for polymer research lies in its ability to separate molecules by hydrodynamic radius while simultaneously resolving chemical structures [1,2]. The latest generation of benchtop NMR systems offers these capabilities in a compact, user-friendly, and cost-effective manner, making the technique a viable alternative to established methods like size exclusion chromatography.
In this study, benchtop PFG-NMR was employed for molecular weight (MW) determination using Diffusion-Ordered Spectroscopy (DOSY) at 80 MHz. Self-diffusion coefficients (D) of polystyrene (PS) and polymethyl methacrylate (PMMA) standards in deuterated chloroform were measured and correlated with MW, achieving measurement times below 10 minutes—significantly improving throughput compared to Size-Exclusion Chromatography (SEC).
To assess accuracy, DOSY-derived MW values were validated against end-group analysis for polyphenylsulfone (PPSU), demonstrating strong concordance. A similar validation for polysiloxanes further confirmed DOSY’s robustness for MW determination. Additionally, DOSY analysis of lignin revealed a well-defined D-MW correlation, highlighting its applicability to both synthetic and natural polymers. Preliminary investigations on chitosan further support its relevance for biopolymer analysis.
Beyond MW determination, PFG-NMR was used to monitor end-group functionalization of poly(ε-caprolactone) (PCL) via the Pulsed Field Gradient-Stimulated Echo (PGSTE) method. This approach effectively resolved reactants and functionalized polymer species, even in cases of spectral overlap, eliminating the need for extensive purification.
Benchtop PFG-NMR provides a compact, cryogen-free platform for rapid, solvent-flexible polymer characterization, offering a viable alternative to high-field NMR for both synthetic and natural macromolecules.