Many plastics around us are made up of a large number of polymer chains that are aggregated together.In the process of solidifying plastic, polymer chains interfere with each other, resulting in an irregular molecular arrangement like a window glass instead of a regular molecular arrangement like crystals. Why are so many polymers? It has not been clarified from the molecular level of its properties whether it becomes hard like window glass when chains are gathered.
A joint research group of Osaka University, the University of Tokyo, and the University of Tsukuba reproduced the process of vitrification of polymer chain aggregates by computer simulation, and when the polymer chains were gradually hardened, what was the property of the entire aggregate? We analyzed in detail how it changes.
First, the magnitude of the force generated inside was measured by applying a strain called shear deformation, and the hardness against shear deformation was quantified. As a result, as one polymer chain became harder, the entire aggregate also became harder.However, as a result of non-affin deformation peculiar to glass in which each polymer chain is greatly deformed after straining, it was found that the hardness of the entire system is relatively extremely soft with respect to the hardness of one chain. rice field.
Next, when the vibrational state density that characterizes the molecular vibrational state in the polymer chain was calculated, it was found that the vibrational excitation called boson peak observed in many glass materials is also observed in the terahertz wave region in the polymer glass. discovered.It was also clarified that the frequency of the boson peak changes depending on the hardness of the polymer chain and can be explained by an extremely simple relational expression that depends only on the shear modulus, which is an index of the hardness against shear deformation.
This means that it is possible to perform non-destructive inspection of mechanical properties such as the difficulty of shear deformation of plastics using terahertz waves, and it can be said that this is an important finding in terms of application.It is expected that this result will accelerate the theoretical progress toward the elucidation of the "glass transition" phenomenon in which polymers vitrify.
Paper information:[Scientific Reports] Boson peak, elasticity, and glass transition temperature in polymer glasses: Effects of the rigidity of chain bending
