TY - JOUR
T1 - Bi-modal polymer networks
T2 - Composition-dependent trends in thermal, volumetric and structural properties from molecular dynamics simulation
AU - Sirk, Timothy W.
AU - Karim, Mir
AU - Khare, Ketan S.
AU - Lenhart, Joseph L.
AU - Andzelm, Jan W.
AU - Khare, Rajesh
N1 - Publisher Copyright:
© 2015 Elsevier Ltd. All rights reserved.
Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 2015/2/10
Y1 - 2015/2/10
N2 - Thermal and volumetric properties of mixed epoxy networks were characterized with molecular dynamics simulation. Atomistically detailed models of epoxy networks of diglycidyl ether of bisphenol (DGEBA) cured with stoichiometric binary mixtures of a flexible cross-linker poly(oxypropylene) diamine (POP) and a stiff cross-linker 4,4′-methylenebis(cyclohexylamine) (MCA), having molecular weights of 1987 and 210 g/mol respectively, were prepared. Epoxy networks formed by five different compositions of the cross-linkers ranging from pure POP to pure MCA were constructed, and a network topology analysis was carried out to verify that each network chain was connected to all other chains by a path of bonded molecules. The glass transition temperature (Tg), coefficient of volume thermal expansion (CVTE), heat capacity and thermal conductivity of these network structures were determined as a function of the network composition. The simulated values of these properties are compared with predictions from theories, empirical correlations and experiments from the literature. In general, it is observed that an increase in the mass fraction of MCA leads to an increase in the Tg and a decrease in the CVTE; furthermore, the breadth of the transition as exhibited by the change in the specific volume, CVTE, and heat capacity increases with an increase in the MCA content. The differences in the flexibility of the network components were analyzed using a number of quantitative measures. Using these results, a molecular mechanism is proposed for the observation of the network composition dependence of the breadth of the glass transition in these systems.
AB - Thermal and volumetric properties of mixed epoxy networks were characterized with molecular dynamics simulation. Atomistically detailed models of epoxy networks of diglycidyl ether of bisphenol (DGEBA) cured with stoichiometric binary mixtures of a flexible cross-linker poly(oxypropylene) diamine (POP) and a stiff cross-linker 4,4′-methylenebis(cyclohexylamine) (MCA), having molecular weights of 1987 and 210 g/mol respectively, were prepared. Epoxy networks formed by five different compositions of the cross-linkers ranging from pure POP to pure MCA were constructed, and a network topology analysis was carried out to verify that each network chain was connected to all other chains by a path of bonded molecules. The glass transition temperature (Tg), coefficient of volume thermal expansion (CVTE), heat capacity and thermal conductivity of these network structures were determined as a function of the network composition. The simulated values of these properties are compared with predictions from theories, empirical correlations and experiments from the literature. In general, it is observed that an increase in the mass fraction of MCA leads to an increase in the Tg and a decrease in the CVTE; furthermore, the breadth of the transition as exhibited by the change in the specific volume, CVTE, and heat capacity increases with an increase in the MCA content. The differences in the flexibility of the network components were analyzed using a number of quantitative measures. Using these results, a molecular mechanism is proposed for the observation of the network composition dependence of the breadth of the glass transition in these systems.
KW - Glass transition
KW - Mixed network
KW - Molecular dynamics
UR - http://www.scopus.com/inward/record.url?scp=84921033336&partnerID=8YFLogxK
U2 - 10.1016/j.polymer.2014.12.057
DO - 10.1016/j.polymer.2014.12.057
M3 - Article
AN - SCOPUS:84921033336
VL - 58
SP - 199
EP - 208
JO - Polymer
JF - Polymer
SN - 0032-3861
ER -