Fabrication of organic–inorganic nano-complexes using ABC type triblock copolymer and polyoxotungstates

Abstract

New organic–inorganic nano-complexes were produced from a micelle of tri-block polymers; poly(styrene)-b-poly(2-vinylpyridine)- b-poly (ethylene oxide) (PS-PVP-PEO) and tungsten compounds such as tungstate (W ²⁻₁ ), undecatungstophospate (PW ⁷⁻₁₁ ) and undecatungstosilicate (SiW ⁸⁻₁₁ ) in acidic aqueous solutions. The size and morphology of the complexes were characterized by measurements of dynamic light scattering, atomic force microscopy, and scanning electron microscopy. This complex is assembled mainly by the charge interaction between the inorganic polyanions and the positively charged PVP block in the PS-PVP-PEO molecule, which was confirmed by zeta-potential and fluorescence spectroscopic studies. In the absence of the inorganic anions, the zeta-potential of the micelle was +11 mV at pH 3 due to the positive charge of the PVP block. When the inorganic anion was mixed with the PS-PVP-PEO micelle, decrease in the zeta-potential due to charge neutralization occurred with incorporation of inorganic anions into the PS-PVP-PEO micelle. The minimum zeta-potential was 0, −33, and −35 mV for W ²⁻₁ /PS-PVP-PEO, PW ⁷⁻₁₁ /PS-PVP-PEO, and SiW ⁸⁻₁₁ /PS-PVP-PEO complexes, respectively. Excess negative charge which occurred in the latter two complexes indicates that PS-PVP-PEO molecules bound PW ⁷⁻₁₁ and SiW ⁸⁻₁₁ by forces other than charge interaction. In addition, the incorporation of an inorganic polyanion into the micelle gave a new morphology to the micelle. In the absence of the polyanion, the PS-PVP-PEO micelles showed an extended conformation due to repulsive forces working among the positively charged PVP blocks. Addition of the polyanion caused the formation of shrunken forms of the micelles, since the charge repulsion was cancelled by the polyanion. This feature may be useful in developing a new type of functioning micelle.