The synthesis and processing of nanoparticles consisting of metallic nanocrystal cores and organic monolayer shells promise interesting technological applications. Here, we report the synthesis of gold nanoparticles modified with ionic liquids based on the imidazolium cation. Aggregation-induced color changes of the gold nanoparticles in an aqueous solution were used as an optical sensor for anions via anion exchange of ionic liquid moiety. We also demonstrated the phase transfer of the gold nanoparticles from aqueous media to ionic liquid.
Crystallization of CaCO3 in the presence and the absence of half-generation poly(amidoamine) (Gn.5
PAMAM) dendrimers was carried out by a double jet method to prevent heterogeneous nucleation at glass
walls. The solution was kept at 25 °C under N2 for 4 days with gentle stirring. We found that the crystallization
of CaCO3 in the presence of the anionic dendrimers resulted in the formation of spherical vaterite crystals,
whereas rhombohedral calcite crystals were formed in the absence of additives. As the generation number
of the PAMAM dendrimer increased from G1.5 to G3.5, the particle size of vaterite was decreased from
5.5 ± 1.1 to 2.3 ± 0.7 μm under the constant concentration (0.26 mM) of −COONa unit of the PAMAM
dendrimers. With further increase in the generation number to G4.5, the particle size was not changed.
The relationship between concentration of the dendrimer and the particle size in the same generation
numbers of the PAMAM dendrimer was also studied under the same condition. As concentration of −COONa
increased from 0.26 to 8.33 mM, the particle sizes of spherical vaterite were reduced from 5.5 ± 1.1 to 2.5
± 0.6 μm.
Stable amorphous calcium carbonate (ACC) composite particle with a size-controlled monodispersed sphere was obtained by a new simple carbonate controlled-addition method by using poly(acrylic acid) (PAA) (Mw = 5000), in which an aqueous ammonium carbonate solution was added into an aqueous solution of PAA and CaCl2 with a different time period. The obtained ACC composite products consist of about 50 wt % of ACC, 30 wt % of PAA, and H2O. Average particle sizes of the ACC spheres increased from (1.8 +/- 0.4) x 102 to (5.5 +/- 1.2) x 102 nm with an increase of the complexation time of the PAA-CaCl2 solution from 3 min to 24 h, respectively. The ACC formed from the complexation time for 3 min was stable for 10 days with gentle stirring as well as 3 months under a quiescent condition in the aqueous solution. Moreover, the ACC was also stable at 400 degrees C. Stability of the amorphous phase decreased with an increase of the complexation time of the PAA-CaCl2 solution. No ACC was obtained when the lower molar mass PAAs (Mw = 1200 and 2100) were used. In the higher molar mass case (Mw = 25 000), a mixture of the amorphous phase and vaterite and calcite crystalline product was produced. The present results demonstrate that the interaction and the reaction kinetics of the PAA-Ca2+-H2O complex play an important role in the mineralization of CaCO3.
Formation of an IPN (interpenetrating polymer network) of organic polymer and silica gel in the form of polymer hybrids was accomplished by utilizing the Diels-Alder reaction between maleimide and furan. Maleimide and furan groups were introduced in the side chain of poly(2-methyl-2-oxazoline), respectively. Polymer hybrids were prepared by acid-catalyzed sol-gel reaction of tetramethoxysilane (TMOS) in the presence of these polymers. The progress of the Diels-Alder reaction between maleimide and furan was confirmed by UV and FT-IR spectroscopy. The solvent resistance of the polymer hybrids was improved by the formation of the IPN structure. Retro-Diels-Alder reaction takes place at an elevated temperature, and these reactions can be cycled.
The crystallization of CaCO3 was examined by changing the addition time of poly(acrylic acid) (PAA) to an aqueous solution of calcium carbonate by selectively interacting with the crystal at different stages during the crystal-forming process. The precipitation of CaCO3 was carried out by a double jet method to prevent heterogeneous nucleation on glass walls, and the sodium salt of PAA was added by a delayed addition method. In the initial presence of PAA in an aqueous solution of calcium carbonate, PAA acted as an inhibitor for the nucleation and growth of crystallization. However, it was found that stable vaterite particles were successfully obtained by delaying the addition of PAA from 1 to 60 min. The vaterite particles were stable in the aqueous solution for more than 30 days, and the CaCO3 particles were formed by a spherulitic growth mechanism. It is suggested that PAA strongly binds with the Ca2+ ion on the surface of CaCO3 particles to stabilize the unstable vaterite form effectively. Upon changing the addition time of PAA, we found that CaCO3 particles were formed through different formation mechanisms in selectively controlled crystallization at different stages during the crystallization process.
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