Tuning the Shape and Size of Gold Nanoparticles with Triblock Polymer Micelle Structure Transitions and Environments (original) (raw)
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Micellization of a poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO45-b-P4VP28) copolymer in water during metalation (incorporation of gold compounds and gold nanoparticle formation) with three types of gold compounds, NaAuCl 4, HAuCl4, and AuCl3, was studied using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The transformations of the PEO45-b-P4VP28 block copolymer micelles in water were found to depend on a number of parameters including the thermal history of the as-prepared block copolymer, the type of the metal compound, and the metal loading. For the HAuCl 4-filled PEO45-b-P4VP28 micelles, the subsequent reduction with hydrazine hydrate results in a significant fraction of rodlike micelles, suggesting that slow nucleation (confirmed by the formation of the large gold nanoparticles) and facilitated migration of gold ions yields the ideal conditions for sphere-to-rod micellar transition.
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Double-hydrophilic block copolymers including monomethyl ether of poly(ethylene oxide) and poly(acrylic acid) (MEPEO-b-PAAc) with the different ratios of polymer blocks are synthesized by the matrix block-copolymerization and characterized. The intramolecular complex formation (IntraPC) between polymer blocks in MEPEO-b-PAAc at low pH (protonated MEPEO-b-PAAc) is established. It causes the MEPEO-b-PAAc intense micellization in aqueous solutions at pH 4. Water solutions of MEPEO-b-PAAc copolymers are used for the synthesis of silver nanoparticles. The stabilizing property of MEPEO-b-PAAc solutions by the interaction with the colloid dispersions of silver nanoparticles is shown.
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Synthesis of gold nanoparticles has been examined using triblock copolymer Pluronic P85 (EO26PO39EO26) at different concentrations as a function of hydrogen tetrachloroaureate (III) hydrate (HAuCl4.3H2O) in aqueous solution. The concentration of P85 block copolymer was varied from 0.5 to 2 wt% at fixed temperature (30 oC) in presence of HAuCl4.3H2O in the range of 0.002 to 0.2 wt% for each P85 concentration. The surface plasmon resonance in the time-dependent UV-visible spectra reveals that increase in the block copolymer concentration increases the yield of the gold nanoparticles but decreases their stability. Both small-angle neutron scattering (SANS) and dynamic light scattering (DLS) show that the number density of block copolymer micelles increase almost linearly with the concentration, which is related to result in higher numbers of nucleation centers and therefore increase in the yield of gold nanoparticles. The fact that increase in the number density of nanoparticles also increases the chances of aggregation and this tends to decrease the stability at higher block copolymer concentration. Transmission electron microscopy (TEM) images confirm the larger sizes of the nanoparticles formed in these systems at higher concentrations.
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The yield and stability of synthesis of gold nanoparticles has been examined using triblock copolymer Pluronic P85 (EO26PO39EO26) at varying concentrations as a function of hydrogen tetrachloroaureate (III) hydrate (HAuCl4.3H2O) in aqueous solution. The surface plasmon resonance in the time-dependent UV-visible spectra reveals that increase in the block copolymer concentration increases the yield of the gold nanoparticles but decreases their stability. Small-angle neutron scattering (SANS) suggests that the number density of block copolymer micelles increase almost linearly with the concentration, which is related to result in higher numbers of nucleation centers and therefore increase in the yield of gold nanoparticles. The fact that increase in the number density of nanoparticles also increases the chances of aggregation and this tends to decrease the stability at higher block copolymer concentration. Transmission electron microscopy (TEM) images confirm the larger sizes of the nanoparticles formed in these systems at higher concentrations.
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