Fast scanning chip calorimetry coupled with synchrotron SAXS: an easy-to-use plug-in setup for standard SAXS...

A custom-built experimental setup combining in situ fast scanning chip calorimetry (FSC) with small-angle X-ray scattering (SAXS) is presented. The setup enables synchronized calorimetric and structural measurements with millisecond acquisition times and heating or cooling rates of up to several thousand kelvin per second. Its capabilities were demonstrated using the ultra-long monodisperse n-alkane n-C₃₉₀H₇₈₂, a model compound for linear polyethylene. Varying the cooling rate from the melt over nearly five orders of magnitude produces pronounced changes in lamellar thickness, corresponding to different non-integer-folded chain configurations, from approximately the F₅ form after rapid quenching to F₂-F₃ configurations after slow cooling. During subsequent in situ heating at 1000 K s^-1, SAXS revealed a pronounced increase in the average crystalline lamellar thickness from values characteristic of the F₅ form toward those expected for the F₄ form, consistent with rapid structural reorganization during the onset of melting. These results demonstrate that significant structural reorganization can occur even under ultrafast heating conditions and highlight the potential of the combined FSC-SAXS approach for probing transient and kinetically controlled structural transformations in polymers and other soft-matter systems.