3.3. Characterization of NR/SiO2 Nanocomposites
3.3.1. SEM Observation. In recent work, NR/SiO2 nanocomposite was prepared with a constant mixture rate (NR/SiO2 =98/2). Because SiO2 has been surface-functioned with MPSand MMA, the compatibility is improved between SiO2nanoparticles and NR matrix, and, moreover, SiO2-PMMAnanoparticles with an average size ranged from 60 nm to100 nm are uniformly dispersed in the matrix as individual spherical core-shell structure (Figure 5(c)). Whereasunmodified SiO2 in NR matrix (Figures 5(a) and 5(b))aggregate significantly and the size of the SiO2 clusters
reaches to more than 200 nm. These results illustrate thatthe excellent compatibility between the SiO2-PMMA and
NR-PMMA enhances the interaction between SiO2 and NR,and thus improves the adhesion and morphological structureof NR/SiO2 nanocomposites. The preparation method ofpolymer/SiO2 composites has been widely reported, suchas melt compounding [31] and other physical blending[32], however, the process presented in this paper possessessignificant advantages, for instance, the compatibility withNR is excellent and the size of SiO2 is approximately 80 nm.
3.3.2. Dynamic Thermal Mechanical Analysis. Dynamic thermal mechanical analysis (DTMA) can characterize the
reaction between polymer molecular chains and inorganicparticles and the transformation from glass state to viscoelastic state. It can be seen from Figure 6 that peaks ofcurves move to the direction of high temperature with
the enhancement of compatibility which can be seen fromSEM images (Figure 5). The glass-transition temperature(Tg ) can be calculated from the peak of tand-T curve.Tg of NR-PMMA/SiO2-PMMA is obviously higher thanthat of the others (Figure 6), which reaches to −48◦C. Itcould be attributed to the well-dispersed core-shell SiO2-
PMMA nanoparticles in NR-PMMA matrix. PMMA play animportant role in the molecular interaction between SiO2
and NR chains, declining the thermal motion of the NRmolecule [33]. Therefore, the adapting temperature range
of rubber products has been expanded with the loading of2 wt% core-shell SiO2-PMMA nanoparticIn addition, NR-PMMA composite filled with core-shell SiO2-PMMA nanoparticles has a higher storage modulus han the others at the temperature ranged from −100◦C to −50◦C (Figure 7). When the temperature is below Tg ,the core-shell SiO2-PMMA nanocomposites possess a high storage modulus, which is caused by introducing rigidnanosilica particles [34]. The increasing storage modulusattributes to the friction between the core-shell SiO2-PMMA nanoparticles and the NR-PMMA molecules whenthe nanosilica particles are thoroughly dispersed in the NR
matrix.