Particle formation

Measured time-resolved particle size distribution data was used to develop a coagulational growth model which accounts for the growth of fractal IOP's with open, low density structures as observed in laboratory work on IOP's, whilst taking into account inter-particle, short-range van der Waals interactions and hydrodynamic forces (Saunders and Plane, 2006).

An example of the model fits to a time series of size distribution data is shown in Figure 1. The best-fit procedure allowed for estimation of the parameters of fractal dimension (D_f) and primary particle size (r₀) used to characterise all fractal forms.

Figure 1. Comparison of model fits (lines) to the measured distributions (discrete points) at the coagulation times indicated. Best-fit parameter values were as follows; r₀ = 3.3 nm (all times), D_f = 2.2 (20 s), 2.4 (45 s) and 2.5 (70, 95 and 120 s). For all fits, particle density was calculated from the relevant r₀ and D_f values and coagulation started at r_n=1 = 0.30 nm, corresponding to the size of a single I₂O₅ molecule - Figure taken from Saunders and Plane (2006)

The modelled value of D_f = 2.5 at the longest growth times is consistent with the particle-cluster diffusion limited aggregation (DLA) mechanism.

References

Saunders, R.W., and J.M.C. Plane, Fractal growth modelling of I₂O₅ nanoparticles. J. Aerosol Sci., 2006, 37, 1737.