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Thermodynamic analysis of impurity partitioning in colloidal crystallization

Jun Nozawa ,  Yuhei Naradate ,  Haruhiko Koizumi ,  Kozo Fujiwara ,  Satoshi Uda 

Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan


 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 (keff) were measured at various growth rates. Obtained keff 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((ΔGTr–ΔH)/RT). Here, ΔGTr 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 ΔGTr. It was shown that ΔGTr of w/fluor. is positive whereas PS is zero. This leads to larger ΔGTr–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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Related papers

Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Jun Nozawa
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-03 12:28
Revised:   2013-04-26 02:07