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The filler dispersion is an essential rubber compound characteristic. Traction, treadwear, and rolling resistance are affected by filler dispersion. The quantification of dispersion is a length scale phenomenon. The existing experimental tools, which are capable of measuring dispersion, for example transmission electron microscopy (TEM), mechanical scanning microscopy (MSM), optical microscopy, and reflectometry, have limitations and the information they provide may not probe the relevant scale length. The recent advance in instrumentation allows one to include electrical measurements in the arsenal of tools available to quantify the dispersion. This paper reviews the range of dispersion measurements and the correlation with compound dynamic properties is presented.

A high frequency viscoelasticity spectrometer, using the state-of-the-art ultrasonic technology, was constructed. The longitudinal and shear waves characteristics were measured in rubber compounds to obtain the attenuation coefficient, α, and sound velocity, v Preliminary results were obtained for a number of filled and unfilled polymers. The grade of carbon black used, filler loading, crosslinking density and filler dispersion were varied during the study. Temperature sweepS from −100°C to +60°C were also studied. It was found that the polymer type had a greater influence on α and v than did the grade of carbon black, loading or dispersion. The experimental data show that shear waves do not propagate in the rubbery state. Above the glass transition temperature, Tg, the longitudinal wave measurements could be sufficient to determine the high frequency dynamic properties of filled and unfilled polymers to characterize a tire tread compound. The temperature sweep measurements allowed the determination of the Tg of polymers at high frequency. It is proposed that the described method of measuring α and v be used as a laboratory tool for potential tire traction prediction.

26,754 STRAWA ET AL.: CARBONACEOUS AEROSOL AND STRATOSPHERIC PHOTOCHEMISTRY focused on conditions of continuous solar exposure, especially the effect on nitrogen radicals (NOx) which are central to ozone depletion. The goal of this paper is to assess the role of BCA in stratospheric ozone chemistry using data obtained during the POLARIS mission and computer simulations. The critical role of sulfuric acid aerosol in stratospheric ozone depletion is well established [cf. Fahey et al., 1993; Gao et al., 1997]. Chemical reactions that take place on the sulfuric acid aerosol, in particular, the hydrolysis of N205, transfer nitrogen out of the reactive nitrogen species, NOx, and into the HNO3 reservoir species. One of the most effective means of studying nitrogen partitioning is by examining the ratio of NOx within the total reactive nitrogen reservoir, NOy (= NOx + NO 3 + HNO3 + C1ONO2 + 2N205 + ...). including heterogeneous reactions on sulfate aerosol in computer models has generally brought better agreement between measured and computed NOx / NOy ratios. The impact of BCA on ozone depletion is felt through heterogeneous reactions that modify the partitioning between reactive and reservoir nitrogen species and that involve ozone directly. BCA may transfer nitrogen out of the reservoir HNO3 species and into NOx through the re-noxification reaction; (R ) H7½ > NO, H,O This reaction acts in opposition to the heterogeneous sulfate reactions.in the laboratory, Thlibi and Petit [1994] found that the reduction of HNO3 to NO occurred on carbon. Rogaski et al. [1997] found that the major products of the heterogeneous reaction of HNO3 with BCA were H20, NO2, and NO and reported an uptake coefficient of 3.8 x 10 •. They measured two NOx molecules produced for every three HNO3 molecules adsorbed. More recently, however, Choi and Leu [1998] investigated the uptake and decomposition of HNO3 on carbon black surfaces. Observations were made under stratospheric conditions of P(HNO3) -102 Torr and T = 220 K. Carbon black (Degussa FW2), graphite, hexane soot and kerosene soot samples were used as surrogate black carbon aerosol surfaces. They found that all black carbon samples tested at stratospheric conditions showed no reactivity towards nitric acid, but only limited physical absorption. NO2 can be reduced on carbon aerosol to produce NO: (R2) NO• sc• ,•NO Further reaction of NO can lead to indirect ozone depletion. [Lary et al., 1997] This reaction is independent of sunlight and can occur whenever carbon aerosol is present. Tabor et al. [ 1993,1994] report an uptake coefficient for NO 2 of 4.8 x 10 '2. Thlibi and Petit [1994] also found that NO 2 was reduced on solid amorphous carbon to yield NO. Rogaski et al. [ 1997] measured the uptake coefficient for NO 2 as 0.11-+ 0.04. Tabor et al. [1994] reported 0.064_+0.02 and observed production of NO with initial conversion of 100%, but uptake of NO 2 and percent conversion to NO decreased with time. Ozone losses may also occur through more direct interaction of ozone with BCA through...