Further, the surface crystals on the 15 lm samples are larger than on the other samples. As can be seen in Fig. 4E and F, after 8 weeks of storage at 23 _C the development of surface crystals was even more pronounced and the difference in frequency could still be observed for the samples with different particle size.
The roughness (Rq) increased over time for all samples and at both storage temperatures, still with varied rates.
The results are reported as the relative increase in roughness compared to the starting value at t = 0, i.e. Rq(t)/Rq(t=0).