Multilevel structure of reinforcing silica and carbon

Abstract

Using small‐angle x‐ray (SAXS), neutron (SANS), x‐ray diffraction and light scattering, we study the structure of colloidal silica and carbon on length scales from 4 Å < q−1 < 107 Å where q is the magnitude of the scattering vector. These materials consist of primary particles of the order of 100 Å, aggregated into micron‐sized aggregates that in turn are agglomerated into 100 µ agglomerates. The diffraction data show that the primary particles in precipitated silica are composed of highly defective amorphous silica with little intermediate‐range order (order on the scale of several bond distances). On the next level of morphology, primary particles arise by a complex nucleation process in which primordial nuclei briefly aggregate into rough particles that subsequently smooth out to become the seeds for the primaries. The primaries aggregate to strongly bonded clusters by a complex process involving kinetic growth, mechanical disintegration and restructuring. Finally, the small‐angle scattering (SAS) data lead us to postulate that the aggregates cluster into porous, rough‐surfaced, non‐mass‐fractal agglomerates that can be broken down to the more strongly bonded aggregates by application of shear. We find similar structure in pelletized carbon blacks. In this case we show a linear scaling relation between the primary and aggregate sizes. We attribute the scaling to mechanical processing that deforms the fractal aggregates down to the maximum size able to withstand the compaction stress. Finally, we rationalize the observed structure based on empirical optimization by filler suppliers and some recent theoretical ideas due to Witten, Rubenstein and Colby.

Determination of Filler Structure in Silica-Filled SBR Compounds by Means of Saxs and Afm

“…The fitting parameters of this model are the average radius of gyration of the primary particles p g R , , its fractal surface dimension of the primary particles d p , the average cluster radius of gyration cl g R , and its mass fractal dimension d cl . In addition, the four pre-factors H [1][2][3][4] are also free fitting parameters. As introduced here, these pre-factors have no distinct physical meaning, however the relationship H 1 = N p,B H 3 is often used in the literature, which serves for the estimation of the average number of particles per cluster, N p,B 19 .…”

“…For automobile tires SBR rubbers are often reinforced by the addition of fillers such as carbon black or silica particles [1][2][3][4][5][6] . In particular, activated silica reinforcement plays an important role in improving the properties of the SBR compounds [7][8][9][10] .…”

“…Small-angle scattering and high-resolution microscopy techniques are very suitable for the study of filler morphologies in filled rubber compounds 3,[12][13][14] . In particular, by combining two independent techniques like atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS), a detailed structural analysis of the silica filled rubbers can be carried out.…”

Analysis of structures of rubber-filler systems with combined scattering methods

“…[72][73][74][75][76][77] Silica rubber systems also form hierarchical structures consisting of agglomerates, aggregates and particles and the size of each structure can be estimated from the scattering function. Moreover, we can estimate the size distribution of silica particles.…”

“…Moreover, we can estimate the size distribution of silica particles. 74 Schaefer et al 76 investigated the hierarchical structures of the precipitated silica prepared by the acidification of water glass using light scattering, USAXS, SAXS and WAXS, which cover the range from 3 Â 10 À6 to 50 nm À1 , as shown in Figure 7. By fitting four levels of the unified Guinier/power-law equation to the scattering function at 3 Â 10 À6 oqo4 nm À1 , they found that the hierarchical structure consists of agglomerate level 2 (R g ¼ 115 mm, D m ¼ 1.9, mass fractal), agglomerate level 1 (R g ¼ 0.9 mm, D s ¼ 2.8, rough surface), aggregates (R g ¼ 66 nm, D m ¼ 1.8, mass fractal) and particles (R g ¼ 4.7 nm, D s ¼ 2 or Porod law, smooth surface).…”