Critical Cooling Threshold Governing Crystallization Pathways in Electrospun‐Derived Poly(ε‐Caprolactone) Studied by Flash DSC

Electrospun poly(ε‐caprolactone) (PCL) nanofibers were analyzed by Flash Differential Scanning Calorimetry (Flash DSC) using ultrafast thermal protocols. Samples were cooled from the melt at rates from 0.1 to 2000 K s −1 and reheated at 500 K s −1 . Because the initial heating step to 120°C at 500 K s −1 erases the thermal history of the as‐spun fibers and melts the fiber geometry, all measurements reported here describe the melt crystallization and cold crystallization behavior of a PCL film on the chip sensor. At slow cooling rates (≤ 30 K s −1 ), crystallization during cooling dominates, yielding a strong melting endotherm and minimal cold crystallization upon reheating. With increasing cooling rate, crystallization during cooling is progressively suppressed, producing a large glass transition step and the emergence of a pronounced cold crystallization exotherm during reheating. A critical cooling threshold near 100 K s −1 is identified, beyond which crystallinity decreases sharply toward zero and cold crystallization becomes the primary crystallization pathway. These findings establish a processing–structure relationship and provide qualitative insight into rate‐dependent crystallization pathways, offering guidance for controlling amorphous phase formation in PCL‐based systems relevant to advanced polymer processing and drug delivery applications.