Tensile properties for solid films of deoxyribonucleic acid containing hydrated ionic liquids

Mechanical properties of deoxyribonucleic acid (DNA) solid films strongly depend on the water content; from glassy-like to rubbery-like via semi-crystalline-like. Also, the incorporation of intermolecular cross-linking between DNA strands impacts on them. These imply a possibility of DNA solids as an eco-friendly structural material. However, to accelerate such a trend, there exists a challenging problem that water evaporates from the film in a short time, causing a change of the mechanical properties. In this study, aggregation states and tensile properties of the DNA films containing a hydrated ionic liquid, choline dihydrogen phosphate (CDP), were studied. The stress-strain (S-S) curve was strongly dependent on the amount of CDP in the films. A 8-wt% CDP film behaved like a glassy polymer. As the CDP content increased, the shape of S-S curves changed to ductility-like or rubbery-like polymers. In the case of a 23-wt% CDP film, the yield stress decreased more strikingly and the clear strain hardening, like elastomers, was observed. Overall, the breaking point and energy increased, and the Young’s modulus and yield stress decreased with increasing CDP amount. And also, these properties were maintained for more than several days because hydrated CDP could be hardly evaporated.