Last year’s STSM at the Faculty of Sciences of the University of Lisbon left a strong impression on me, not only because of the science I learned but also because of the collaborative spirit of the group that welcomed me. Coming back this year felt less like arriving in a new place and more like reconnecting with familiar faces, while also stepping into new territory scientifically. This time, my work revolved around the polymorphism of metacetamol, a benchmark compound for the BEST-CSP COST Action. In materials science, isolating a metastable polymorph is a well-known challenge, often likened to capturing a ghost. My mission was precisely this: to characterize the stable, predictable Form I, and then to hunt for its fleeting, elusive alter-ego, Form II.

The first phase of my work was to establish a solid foundation. This involved purifying commercial metacetamol via sublimation to obtain a high-purity reference sample of Form I. With this pristine material, I was able to perform a series of experiments, including detailed solubility measurements and precise calorimetry using a Thermal Activity Monitor (TAM) to determine its enthalpy of solution. Then, the chase for Form II began. Using a delicate melt-quench approach, by melting the stable Form I and rapidly cooling it to trap the molecules in their high-energy, metastable state.

The method was a success, and form II appeared, confirmed by its distinct melting peak in the DSC. However, this new form was incredibly fragile in most cases; the slightest scratch would cause it to instantly revert to Form I, vanishing before my eyes. The real puzzle emerged from the TAM data, which suggested an energy difference between the forms that was too high to be plausible. This unexpected result wasn’t a failure, but a crucial clue, prompting a deeper inquiry into the true nature of the quenched sample.

Overall, this STSM grant proved invaluable. It not only advanced our understanding of the metacetamol system but also allowed me to deepen my practical skills in advanced calorimetry and solubility analysis. Discussing these puzzling results with the host group was a fantastic exercise in collaborative science and has clarified the path forward. I am sincerely grateful to my hosts at the Faculty of Sciences of the University of Lisbon. I want to extend my deepest thanks to Professor Manuel Minas da Piedade for his warm welcome and for generously sharing his profound knowledge, and to Dr. Carlos Bernardes for his invaluable scientific guidance throughout my stay. A special thank you is also due to Inês Feliciano, whose help in the lab was instrumental to the success of my experiments. I must also thank my supervisor at UPC Barcelona, Professor Michela Romanini, whose encouragement was key in motivating me to pursue this opportunity.

This month in Lisbon has been a significant step forward in my PhD journey. The STSM has not only enabled me to generate crucial data for the BEST-CSP benchmark molecule, metacetamol, but it has also been a remarkable opportunity for personal and scientific growth. The knowledge gained, the connections forged, and the scientific puzzles uncovered here will undoubtedly have a lasting influence on my future work. Based on this experience, I strongly encourage anyone interested in exploring new techniques or contributing to the BEST-CSP project to apply for an STSM. It is a unique and powerful opportunity to engage in pioneering science and forge meaningful connections with researchers across the globe