Chemically identical gels I – under-crosslinked networks

Do materials prepared from identical compositions of constituting ingredients always exhibit similar mechanical properties? The answer is negative for most structural materials, as has been demonstrated by extensive studies on various factors such as the effects of processing and microstructures. However, the same question has seldom been addressed in the case of polymeric gels. In this work, by using a simple chemically crosslinked hydrogel as a model system, the mechanical properties, including elastic stiffness , fracture toughness , and fatigue threshold, of gels with identical chemical compositions are systematically investigated. The distinct material properties are then rationalized and quantitatively correlated to synthesis conditions and manufacture processes through scaling laws derived from basic physics. Different scaling laws are identified between samples prepared from swelling and deswelling. Extreme mechanical properties, such as the remarkable fracture energy of hydrogels prepared by deswelling from highly swollen samples, are observed and attributed to the structural characteristics of the polymer network , and further correlated to the synthesis processes. This study provides insights into the synthesis-property correlations of polymeric gels, which may have profound influences on the design of new polymeric materials and their applications in various fields.