Nanoscale Res Lett (2009) 4:420–430 increase in amount of crosslinking. SBS0.5 has an E0 value of 0.8 MPa, which increases by more than threefold to 2.63 MPa for SBS3. Similar observations are also noted for NR gels; however, the level of increment in modulus val- ues is less as compared to SBR gels. These nanogels were subsequently used as viscoelastic ﬁllers for the inter mixing study i.e. NS gels were added to SBR matrix and SBS gels were mixed with NR at a given concentration, to investigate their effect on the morphol- ogy, mechanical, dynamic mechanical and thermal properties of raw SBR and NR. Morphology of the Gel Filled Rubbers EDX or energy dispersive X-ray sulfur mapping is a useful technique to check the distribution of gel particles in the rubber matrix. Figure 3a–d shows representative EDX images of 4 and 16 phr gel loaded SBR and NR matrices. It is quite apparent that at 4 phr loading, the gels are very well distributed irrespective of the nature of the gels or the matrix. For example, both SBNS1/4 and NRSBS1/4 (Fig. 3a and c) show good distribution of NS and SBS gels in the neat SBR and NR, respectively. However, the scenario changes completely in the case of 16 phr gel ﬁlled samples. Both the SBNS1/16 and the NRSBS1/16 show (Fig. 3b and d) considerable agglomeration of gel particles. EDX study also clearly demonstrates that aggregation in nanosized SBS1 gel ﬁlled system is more than that in NS1 gel ﬁlled system. The surface morphology of the gel ﬁlled samples has been investigated with atomic force microscopy in tapping Fig. 3 EDX-sulfur mapping showing gels distribution in matrix for a SBNS1/4, b SBNS1/16, c NRSBS1/4, and d NRSBS1/16 425 mode by magnifying a small region of the surface. These are shown in Fig. 4a–d. In this mode, more rigid compo- nent appears as the brighter spots on the phase image and the darker regions correspond to a less rigid component [24]. Although taken at a much smaller scan size of 5 l, these AFM images are perfectly in line with the earlier EDX observation. In Fig. 4a, NS1 gels at 4 phr loading in SBR matrix can be seen as dark colored circular and semi- circular dispersed domains. Individual gel particles are fairly uniformly distributed (circular) with occasional one or two gel agglomerate (semi-circular). The domain sizes of most of the single gel particles range from 130 to 360 nm, which corroborates the earlier DLS and AFM ﬁndings. For NRSBS1/4, as shown in Fig. 4b, again homogeneous distribution of nanogels (brighter circular spots) in NR matrix is observed. Most of the gel particles have sizes ranging from 70–130 nm. This again shows good correlation with the PSD data obtained from the DLS measurements. However, it can be seen that, nano SBS1 gels at even 4 phr loading in NR show some sign of agglomeration, with circular domains of aggregated parti- cles of 250–350 nm. At 16 phr loading, both SBNS1/16 and NRSBS1/16 display regions having agglomerated gel par- ticles with domain size much larger than the individual particles (Fig. 4c–d). In the case of SBNS1/16 system (Fig. 4c), NS1 gel agglomerates having dispersed domains ranging from 500 to 770 nm in length can be detected easily. These are comprised of at the most 2–3 individual gel particles. It may be noted here that the tendency of NR gels to form agglomerates is much less compared to the nano sized SBR gels as shown in Fig. 4d for NRSBS1/16 system. This has been shown earlier also with the help of EDX study. In 16 phr nano SBS gel loaded NR matrix, almost all the nanogels are in agglomerated state having dispersed gel domains of 300 to 1500 nm in length. This implies that unlike NR gels, several nano sized gel particles take part in forming very large cluster of gel agglomerates. This type of agglomerating behavior of nanogel particles at comparatively higher loading is very similar to that of the nanoﬁllers reported in literature [25]. Section analysis of representative 4 phr gel loaded samples corroborates the AFM ﬁndings about the gel domain sizes and also gener- ates some interesting features (see Figure S1 of Supple- mentary Information). It shows that NR gels are embedded in the SBR matrix (less rough surface), whereas SBR nanogels appear mostly on the surface of NR matrix (more rough surface), which could be due to the differences in the gels moduli. It may be pointed out here that the AFM morphology of nanogel ﬁlled elastomers is possibly being reported for the ﬁrst time. Transmission electron microscopy (TEM) was per- formed to elucidate the bulk morphology of the represen- tative gel ﬁlled samples. These are presented in Fig. 5a–d. 123