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Title: Stress effects on the elastic properties of amorphous polymeric materials

Brillouin light scattering measurements have been used to study the stress induced modification in the elastic properties of two glass forming polymers: polybutadiene and epoxy-amine resin, prototypes of linear and network polymers, respectively. Following the usual thermodynamic path to the glass transition, polybutadiene has been studied as a function of temperature from the liquid well into the glassy phase. In the epoxy resin, the experiments took advantage of the system ability to reach the glass both via the chemical vitrification route, i.e., by increasing the number of covalent bonds among the constituent molecules, as well as via the physical thermal route, i.e., by decreasing the temperature. Independently from the particular way chosen to reach the glassy phase, the measurements reveal the signature of long range tensile stresses development in the glass. The stress presence modifies both the value of the sound velocities and their mutual relationship, so as to break the generalized Cauchy-like relation. In particular, when long range stresses, by improvise sample cracking, are released, the frequency of longitudinal acoustic modes increases more than 10% in polybutadiene and ∼4% in the epoxy resin. The data analysis suggests the presence of at least two different mechanisms acting on different lengthmore » scales which strongly affect the overall elastic behaviour of the systems: (i) the development of tensile stress acting as a negative pressure and (ii) the development of anisotropy which increases its importance deeper and deeper in the glassy state.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [2]
  1. Istituto Officina dei Materiali del CNR (CNR-IOM) - Unità di Perugia, c/o Dipartimento di Fisica e Geologia, Perugia I-06100 (Italy)
  2. Dipartimento di Fisica e Geologia, Università di Perugia, Via A. Pascoli, I-06100 Perugia (Italy)
  3. (Istituto dei Sistemi Complessi), c/o Università di Roma “LaSapienza,” Piazzale A. Moro 2, I-00185 Roma (Italy)
  4. NiPS Laboratory, Dipartimento di Fisica e Geologia, Università di Perugia, Via A. Pascoli, I-06100 Perugia (Italy)
Publication Date:
OSTI Identifier:
22413282
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 141; Journal Issue: 21; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; AMINES; ANISOTROPY; CHEMICAL BONDS; CRACKING; DATA ANALYSIS; ELASTICITY; EPOXIDES; GLASS; LIGHT SCATTERING; LIQUIDS; MOLECULES; RESINS; STRESSES; TEMPERATURE DEPENDENCE