rubber matrix. When MoS2loading is increased to 3 phr, the sil-ica dispersion is further improved (Fig. 1c). The higher resolutionimage (Fig. 1e) shows that the diameter of the dispersed silica par-ticles is about 30 nm, which is consistent with the value for theprimary silica particles, indicating that the silica is finely dispersedas individual particles with the inclusion of MoS2. Besides, MoS2sheets are homogeneously dispersed as nanoplatelets. If the con-tent of MoS2is further increased (5 phr), some MoS2plates start toaggregate into thicker nanoplatelets in the composite (Fig. 1d andf).Dynamic-mechanical measurements were conducted on theuncured compounds to examine the filler networking. Fig. 2 showsthe dependence of the elastic modulus (G) of uncured NR/silicacompounds with various MoS2contents on the strain. It can be seenthat the initial Gvalues of the compounds increase with increas-ing MoS2content, especially when the MoS2content is higher than1 phr, which is due to the formation of a more developed filler net-work in the presence of MoS2. The Gvalues for all the compoundssharply decrease with increasing strain, which is known as Payneeffect and is mainly related to collapse of the filler network andrelease of the trapped rubber in the filler network on applicationof an oscillatory shear [29]. In addition, compared with the controlsample, the Gvalues for the compounds with MoS2are more sen-sitive to strain, indicating that the three-dimensional filler networkis more developed in compounds with MoS2.To shed light onto the mechanism for the improved dispersion ofsilica, we prepared the aqueous solutions of the model silica/MoS2compounds with various ratios. The particle size of silica in thesolution is investigated by light scattering method. As shown inFig. 3, the silica has a particle size of 430 nm in the absence ofMoS2. This value is significantly higher than that for the individual silica particle, as silica is arranged in chains or three-dimensionalnetworks in aqueous solution, leading severe aggregation of sil-ica [30]. The silica particle size sharply decreases to about 260 nmwhen the weight ratio of silica/MoS2is 30/1. The silica particle sizecontinuously decreases with increasing MoS2content. The signifi-cantly increased suspension stability of silica by MoS2can also beverified visually, as shown in the inset in Fig. 3. With the same sil-ica concentration, silica particles are precipitated in a few hoursand that with MoS2is still stable in the same standing time. This ispresumably caused by the improvement of electrostatic repulsiveforces in the system by adding negatively charged MoS2plates.As is well documented, silica is negatively charged in water dueto the deprotonation of silanol groups [30–32]. Meanwhile, duringthe exfoliation of LiMoS2in water, the initially neutral MoS2layersare converted to a complex solution containing negatively charged(MoS2)x−layers, hydroxide anions, and lithium cations, and thusthe chemically exfoliated MoS2layers are negatively charged [33].But on account of both with different charge, the charge transferwill happen between silica and MoS2, which gives rise to chargerepulsion between silica. Therefore, we propose that MoS2canimprove silica particle dispersion as a result of charge transferinteraction between them [34].Fig. 4 shows the UV–vis spectra of the aqueous solutions of themodel silica/MoS2compounds with various the weight ratios. Foreach sample, the background of silica (with the same concentra-tion of silica) is subtracted. The spectrum of the aqueous solutionsFig. 4. UV–vis spectra of MoS2dispersed in water at various silica contents, afterthe subtraction of the corresponding silica background (in the same silica concen-tration).Fig. 5. Raman spectra of freeze-dried MoS2solution at various silica contents (fixedMoS2mass).of the model silica/MoS2compounds has clear characteristic peaksat 256 and 305 nm, which belong to characteristic peaks of MoS2.The intensities of characteristic peaks along the increase in silicaare compared in Fig. 4. As shown, with the increasing of silica, theintensities of the characteristic peaks at 255 and 307 nm of MoS2are substantially decreased. It is well-known that the charge trans-fer interaction of single-walled carbon nanotube (SWCNT) withelectron acceptors or donors will reduce the characteristic peak ofSWCNT [35,36]. Matsuda et al. [37] studied the charge interactionbetween SWCNT and nanosilicas by the optical absorption spec-tra. The presence of nanosilica decreases significantly the intensityof the characteristic peak of SWCNT, which can be ascribed to thecharge transfer interaction between SWCNT and nanosilica. In thepresent study, the decreases in the intensities of the characteris-tic peaks of MoS2are reasonably attributed to the charge transferinteraction between silica and MoS2.Fig. 5 shows Raman spectra of freeze-dried the aqueous solu-tions of the model silica/MoS2compounds with various the weightra