Abstract
The glass transition of an amorphous material is a fundamental property characterized by an abrupt change in viscosity. Its very knowledge was a conundrum as no satisfying theory existed at the molecular level. We herein relate this complex phenomenon to events occurring at the molecular scale. By studying conformational transitions in the carbon-chain polymer of polyethylene, we clearly establish a relation between local dynamics and the classical dihedral potential energy diagram of a carbon-carbon bond. This methodology is applied to a carbon-chain polymer with a side-group, polystyrene. A direct link is proved between activation energy and glass transition temperature. This work thus provides the cornerstone for linking molecular structure to macroscopic polymer properties, and in particular, the glass transition temperature.
Highlights
Numerous systems such as polymers exhibit a glass transition
Due to very rapid cooling rate, molecular dynamics simulation leads to a spread in the glass transition domain bordered by a lower coefficienthaenrmd aalneuxpppanersi(oTngua)ntedmthpeerhaetautrceasp
the graph of Ea (Tg) from atomistic simulation, as it corresponds to an intersection between two linear fits in the dilatometry simulation, www.nature.com/scientificreports not to a change in physical properties
Summary
Numerous systems such as polymers exhibit a glass transition. As the temperature is decreased they turn from an amorphous state of low viscosity to a supercooled liquid with very high viscosity[1]. The main reason is that no experiments or theories can grasp its entire domain of dynamic ranging from nanoseconds to years (ageing) These recent years, molecular simulation became an additional and powerful technique to complement existing data or current theories[3]. The intersection between two linear fits at low and high temperatures gives Tg. we recently showed that due to the extremely rapid cooling rate, molecular dynamics (MD) simulation leads to a spreading of the glass transition domain, in order of 160 K11. Behind the measurement of Tg from MD, the meaning of these two extra temperatures during the glass transition process must be investigated To unravel their significance, computing the activation energy (Ea) is a very attracting avenue as it depicts local dynamics[12,13]. The activation energy corresponds to the energy necessary to go from one potential energy minimum to www.nature.com/scientificreports/
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