You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Impurity partitioning during colloidal crystallization. We have found that an impurity partitioning takes place during growth of colloidal crystals, which was recognized by the fact that the impurity concentration in the solid (CS) was different from that in the initial solution (C0). The effective partition coefficient keff (=CS/C0) was investigated for pure polystyrene and polystyrene dyed with fluorescent particles by changing the ratio of particle diameters dimp/dcryst and growth rate V. At each size ratio for the polystyrene impurity, keff was less than unity and increased to unity with increasing V, whereas at a given growth rate, keff increased to unity as dimp/dcryst approached unity. These results were consistent with the solute behavior analyzed using the Burton, Prim, and Slichter (BPS) model. The obtained k0, equilibrium partition coefficient, from a BPS plot increased as dimp/dcryst approached unity. In contrast, while the fluorescent particles also followed the BPS model, they showed higher k0 values than those of the same size of polystyrene particles. A k0 value greater than unity was obtained for impurities that were similar in size to the host particle. This behavior is attributed to the positive free energy of fusion associated with the incorporation of the fluorescent particles into the host matrix. Such positive free energy of fusion implies the presence of the enthalpy associated with interaction between particles.
{"Chemical": ["polystyrene"]}