Colloidal crystals are regarded as a promising tool to investigate diverse basic physical phenomena. We have applied this colloidal crystal to impurity partitioning in the melt growth. Since no research has been focused to detail partitioning behavior of colloidal crystals, the objective of the present work is to reveal a partitioning behavior during colloidal crystallization.

 A few amount of impurities (2 percent) were doped to the colloidal dispersion, from which colloidal crystals were grown with convective assembly method. Polystyrene particles (PS) were used for fabricating colloidal crystals, and different sizes of PS and fluorescent bearing PS (w/fluor.) were doped as impurity particles.

In each particle size for two kinds of impurity, effective partition coefficient (k_eff) were measured at various growth rates. Obtained k_eff gives k₀ by using BPS plot. The k₀ is decreased as the difference between the size of the impurity and the 500 nm host particle increased. The k₀ of each w/fluor. was larger than that of the corresponding pure PS. Moreover, the value of k₀ for the 520 nm w/fluor. surpassed unity, whereas the PS is always less than unity.

 We have employed a Thurmond and Struthers (T&S) model (J. Phys. Chem. 57, 831 (1953)) to discuss the difference of k0 for PS and w/fluor. particles. T&S model shows k₀ as; k₀ = exp((ΔG_Tr–ΔH)/RT). Here, ΔG_Tr is free energy difference between the solid and liquid phases of an impurity at the transition temperature, T, ΔH is the excess enthalpy which is caused by incorporation of the impurity into the host material, and R is a gas constant. We have determined the phase transition volume fraction for PS and w/fluor. to evaluate the ΔG_Tr. It was shown that ΔG_Tr of w/fluor. is positive whereas PS is zero. This leads to larger ΔG_Tr–ΔH of w/fluor. than that of PS, which corresponds to larger k₀ of w/fluor., and in a small –ΔH range, k₀ of w/fluor. surpasses unity. We have found the difference of k₀ for different kinds of impurity particles, and succeeded in applying concept of T&S model to partitioning of colloidal crystals.

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