13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- of our current model is that thermal conductivities at each density were 5 times higher than experimental aerogels. The most significant reason is that our model is unable to attain micropores. This can be seen in the pore size distribution of samples of increasing aerogel length scales. Shown in Fig. 6, these plots are calculated using PSDsolv [23], which determines the relative probability of finding pores of different sizes. At a density of 0.3g/cm3, we generate two different samples with system lengths of 180Å (our current system length at 0.3g/cm3), and 277Å. Figure 6. Pore size distribution (PSD) at density of 0.3g/cm3, at system length scales of a) 180Å, and b) 277Å The largest pore sizes accessible increase from 27.5Å to 32Å in diameter, as the system length scales increase. The pore sizes attainable are nowhere near the micron-sized diameters in bulk experimental silica aerogels. 3.4. Young’s modulus Using the method discussed in Section 2, the Young’s modulus of silica aerogel with different densities ranging from 0.3g/cm3 to 1.0g/cm3 are obtained through MD simulation as shown in Fig. 7. A power-law fitt can be used to describe the relationship between Young’s modulus and density of samples [9]. From Fig. 7, the exponent of the relationship between Young’s modulus and density can obtained and the exponent value is about 2.4313. This value has slightly difference with the result from Murillo et al. [9] which was 3.11, while the magnitude of the constant of Young’s modulus is almost the same. The discrepancy mainly results from the different interactive potential. Figure 7. Relation between Young’s Modulus and density. (Red line refers to the power-law fitting line, and the blue dots refers to the simulation data.)
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