title: Effect of Interfacial Bonding on Interphase Properties in SiO2/Epoxy Nanocomposite: A Molecular Dynamics Simulation Study.
abstract: Atomistic molecular dynamics simulations have been performed to explore the effect of interfacial bonding on the interphase properties of a nanocomposite system that consists of a silica nanoparticle and the highly cross-linked epoxy matrix. For the structural properties, results show that interfacial covalent bonding can broaden the interphase region by increasing the radial effect range of fluctuated mass density and oriented chains, as well as strengthen the interphase region by improving the thermal stability of interfacial van der Waals excluded volume and reducing the proportion of cis conformers of epoxy segments. The improved thermal stability of the interphase region in the covalently bonded model results in an increase of ∼21 K in the glass transition temperature (Tg) compared to that of the pure epoxy. It is also found that interfacial covalent bonding mainly restricts the volume thermal expansion of the model at temperatures near or larger than Tg. Furthermore, investigations from mean-square displacement and fraction of immobile atoms point out that interfacial covalent and noncovalent bonding induces lower and higher mobility of interphase atoms than that of the pure epoxy, respectively. The obtained critical interfacial bonding ratio when the interphase and matrix atoms have the same mobility is 5.8%. These results demonstrate that the glass transitions of the interphase and matrix will be asynchronous when the interfacial bonding ratio is not 5.8%. Specifically, the interphase region will trigger the glass transition of the matrix when the ratio is larger than 5.8%, whereas it restrains the glass transition of the matrix when the ratio is smaller than 5.8%.
authors.affiliation: College of Science, China University of Petroleum , Qingdao 266580 Shandong Province, P. R. China.
authors.forename: Zhikun
authors.initials: Z
authors.lastname: Wang
authors.affiliation: College of Science, China University of Petroleum , Qingdao 266580 Shandong Province, P. R. China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Lv
authors.affiliation: College of Science, China University of Petroleum , Qingdao 266580 Shandong Province, P. R. China.
authors.forename: Shenghui
authors.initials: S
authors.lastname: Chen
authors.affiliation: College of Science, China University of Petroleum , Qingdao 266580 Shandong Province, P. R. China.|Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong (China University of Petroleum) , Qingdao 266580 Shandong Province, P. R. China.
authors.forename: Chunling
authors.initials: C
authors.lastname: Li
authors.affiliation: College of Science, China University of Petroleum , Qingdao 266580 Shandong Province, P. R. China.|Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong (China University of Petroleum) , Qingdao 266580 Shandong Province, P. R. China.
authors.forename: Shuangqing
authors.initials: S
authors.lastname: Sun
authors.affiliation: College of Science, China University of Petroleum , Qingdao 266580 Shandong Province, P. R. China.|Key Laboratory of New Energy Physics & Materials Science in Universities of Shandong (China University of Petroleum) , Qingdao 266580 Shandong Province, P. R. China.
authors.forename: Songqing
authors.initials: S
authors.lastname: Hu
keywords: epoxy; glass transition; interphase; molecular dynamics simulation; nanocomposite