It is common practice to form a glass starting from a liquid in a metastable state, by cooling or compressing the system so as to avoid crystallization ('physical vitrification'). However, there exist in nature and technology different ways to form a glass. The hardening of natural and synthetic resins and the formation of most of the materials used in engineering plastics and high-performance composites are based on 'chemical vitrification', a process involving progressive polymerization of initially liquid monomers via the formation of irreversible chemical bonds. Explaining the similarity observed in the slowing down of the dynamics in physical and chemical vitrification constitutes a challenge to general understanding of the glass transition and may disclose its universal nature. Here we use relaxation data from several techniques to show that the similarity between the dynamic behaviours of physical and chemical glass formers originates in a similar evolution of their configurational restrictions and in a similar dynamics-to-thermodynamics correlation. In particular, we derive a relation between relaxation properties and extent of reaction in step polymerization, in remarkable agreement with experimental results.
Configurational entropy and dynamics in chemical vitrification
COREZZI, Silvia
;COMEZ, Lucia;FIORETTO, Daniele
2004
Abstract
It is common practice to form a glass starting from a liquid in a metastable state, by cooling or compressing the system so as to avoid crystallization ('physical vitrification'). However, there exist in nature and technology different ways to form a glass. The hardening of natural and synthetic resins and the formation of most of the materials used in engineering plastics and high-performance composites are based on 'chemical vitrification', a process involving progressive polymerization of initially liquid monomers via the formation of irreversible chemical bonds. Explaining the similarity observed in the slowing down of the dynamics in physical and chemical vitrification constitutes a challenge to general understanding of the glass transition and may disclose its universal nature. Here we use relaxation data from several techniques to show that the similarity between the dynamic behaviours of physical and chemical glass formers originates in a similar evolution of their configurational restrictions and in a similar dynamics-to-thermodynamics correlation. In particular, we derive a relation between relaxation properties and extent of reaction in step polymerization, in remarkable agreement with experimental results.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
