|M.Sc Student||Klein Riki|
|Subject||Molecular Modeling and Investigation of Thermo-Mechanical|
Properties of Epoxy Resin Using Molecular Dynamic
|Department||Department of Chemical Engineering||Supervisor||ASSOCIATE PROF. Simcha Srebnik|
Epoxy resins are important thermosetting polymers in industry. They display a unique set of properties and are available in a wide variety of forms, which makes them suitable for different applications and processes. They are cheap, strong, have water and electrical resistance and have great adhesion to different substrates, and thus are useful as adhesives, coatings, encapsulates, casting materials, potting compounds, binders and composites. Their properties derive from their chemical structure and so it is important to study their molecular structure and changes at a molecular and microscale level. Using computer simulations reduces the need for expensive and time consuming experiments and enables to predict and understand different phenomena that cannot be understood through experiments. Molecular dynamics (MD) is a computational method of solving classical equations of motions for systems of which interatomic potentials are known. These days the technology is developed enough to perform case studies of large systems in relatively short time. We constructed a DGEBA based epoxy resin cured with a TETA based curing agent in different temperatures and crosslinking degrees and measured mechanical properties of the system in different measuring methods while comparing the results to experiments. The Glass transition temperature (Tg) was extracted from the discontinuity in the slope of the volume-temperature curve during both heating and cooling. We found a difference in the results of the two methods which indicated that a longer equilibration should have been performed and a slower heating/cooling rate should have been used, although both of the results were within the range reported in the literature. The coefficient of thermal expansion (CTE) was extracted from the slope of the volume-temperature curve for both the glassy and rubbery states and was in good agreement with the literature. The bulk modulus was measured from volume fluctuations as well as compression simulations. We found that the value obtained from volume fluctuations highly depended on the duration of equilibration, while the compression simulations were more simple to execute and produced better results in a shorter amount of time, but did not guarantee that the initial system was well equilibriated. The bulk modulus was found to increase with increase of crosslinking degree. The Young's modulus was consistent with values in the literature and showed an increase with increasing crosslinking degree, but revealed no dependence on the temperature. The Poisson's ratio was measured at different temperatures and showed no obvious trend as well. The shear modulus was found to be consistent with experiment, with a clear dependence on the temperature. The different mechanical properties were also calculated according to the theory of linear elasticity and their value differed from those calculated from simulations due to the small system size and since the system was is truly homogeneous. All the results indicate that the model we established is consistent with the literature, and emphasize the importance of sufficient equilibration of the system prior to mechanical and thermal deformation. Furthermore, a number of independent crosslinked configurations should be examined to establish sufficient sampling.