Ag core/poly

Ag Core/Poly(DCHD)-Shell Hybridized Nanocrystals. 154... 

The improved co-reprecipitation and microwave-irradiation method is an effective process to fabricate Ag core/poly(ADA)-shell hybridized NCs [30,45, 50], Ag NPs in an aqueous dispersion liquid were prepared by reducing silver nitrate (AgN03) with trisodium citrate [106], The size of the resulting Ag NPs was ca. 45-50 nm, which is larger than that in Sect. 3.2. 

Figure 5 displays the SEM and TEM images of Ag core/poly(ADA)-shell hybridized NCs [50], Actually, Ag core was clearly covered with almost uniform poly(ADA) shell. The thickness of the shell was about 5 nm, and the morphology of the core/shell nanostructure in the present hybridized NCs was dependent remarkably on microwave irradiation conditions [50], For example, the above-mentioned microwave irradiation condition is the most desirable, and the core/shell nanostructure could not be formed successfully when the irradiation condition was 500 W, 20 s or 200 W, 40 s. After co-reprecipitation, the dispersion liquid is considered to be a mixture of Ag NPs and ADA NCs. The heated ADA NCs were probably partially melted by microwave irradiation, and may easily collide and fuse with Ag NPs at the elevated temperature. As a result, molten ADA monomer could adsorb effectively on the surface of Ag core, and was then recrystallized to form solid-state polymerizable ADA shell during the cooling process after microwave irradiation [50]. The present co-reprecipitation and microwave-irradiation method is available for the fabrication of another type of metal-core/ji-conjugated polymer-shell hybridized NCs [107]. 

The extinction spectrum of Ag core/poly(ADA)-shell hybridized NCs dispersion liquid is shown in Fig. 6 [50]. The main peak at ca. 450 nm is assigned to ESP of Ag core [108], and was red-shifted and broadened because of the large size and its distribution of Ag core [109-111]. The small shoulder peak at 540 nm may come from the EAP of poly(ADA) shell [112], and the inset in Fig. 6 also displays the differential spectrum before and after solid-state polymerization. The obtained extinction spectrum could be reproduced by spectrum simulation on the basis of Mie scattering theory [113], assuming spherical Ag core (radius = 45 nm)/poly(ADA) shell (thickness = 5 nm) type hybridized NC. In Fig. 7, both main peaks around 450-500nm is attribute to ESP (Frohlich mode) of Ag core, and the two sharp peaks at 380 and 400 nm are the quadrupole mode of ESP [108]. 

Anyway, the LSP still appears in Ag core/poly(ADA)-shell hybridized NCs, which will be one of the promising nanomaterials for photonic device application in the near future. 

In addition, the MW Auger peak (kinetic energy = 351.6eV) from Ag core, corresponding to short observation depth, appeared in the hybridized NCs, which suggests the existence of interspace between poly(DCHD)-shell and some part of Ag core [49]. The present interspace is due to difficulty in stacking poly(DCHD) shell closely on a steeply curved surface of Ag core, because poly(DCHD) is onedimensional conjugated and rigid chain in the crystal state of PDA sheU [91-93]. 

One can imagine from these experimental results that PDA chains inside poly(DCHD)shell may contact with some points on the surface of Ag core [47,49]. These contact points at hetero nano-interface might be anchors to disturb and depress the plasma oscillation, and then diminish the mean-free-path of conduction free electrons in VB of Ag core. In other words, the LSP of Ag core would damp simply without changing the resonance frequency, owing to the reduction of electronic conductive domain induced by locally and strongly physicochemical interaction at the core/shell interface in the hybridized NCs [103,105]. 

The acetone solution (5mM, 200 JL) of ADA was injected into vigorously stirred Ag NPs dispersion liquid at room temperature. Afterwards, the mixed dispersion liquid was poured into a Teflon vessel, sealed-up, irradiated by microwave (2.45 GHz, 500 W, 40 s), and then was cooled down again to room temperature. After UV-irradiation for solid-state polymerization to convert ADA into poly(ADA) [91-93], the resulting dispersion liquid was centrifuged for 15 min at 8,000rpm to remove residual poly(ADA) NCs having no Ag core. 

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

As mentioned above, metal/CPs with core-sheath structure can be prepared by the template method. However, the approach based on the template technique is complicated and non-economical because of the need to remove the templates. In fact, metal/CPs with core-sheath structure can be fabricated via a one-step chemical polymerization [83-87]. Niu and co-workers demonstrated that Au/PANI coaxial nanocables could also be fabricated by the redox reaction between chloroauric acid and aniline in the presence of d-CSA [85]. In that case, CSA acted not only as a dopant, but also as a surfactant or a soft template. In addition to Ag/PPy and Au/PANI nanocables, cable-like Au/poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructures have been synthesized in the absence of any surfactant or stabilizer through one-step interfadal polymerization of EDOT dissolved in dichloromethane solvent and HAuCl dissolved in water [86]. Microscopy studies showed (Figure 13.6) that the outer and inner diameters of Au/PEDOT nanocables were aroimd 50 and 30 nm, respectively. 

Interestingly, Smeenk et al. could realize similar structures with a protein-polymer conjugate. For that purpose, a central high-molecular-weight p-sheet-tum protein (poly[(AG)3EG] with n = 10 or 20) was flanked on both terminal sides with PEO blocks. The resulting PEO-protein ABA conjugate shows self-assembly into well-defined fibrils with a protein p-sheet core with a distinct fine stmcture and PEO shell. 

Poly(styrene) composite particles consisting of thermosensitive core-shell of pNIPAM in which Ag nanoparticles are embedded. 

Dong H, Nyame V, Macdiarmid AG, Jones WE (2004) Polyaniline/poly(methyl methacrylate) coaxial fibers the fabrication and effects of the solution properties on the morphology of electrospun core fibers. J Polym Sci B Polym Phys 42 3934-3942... 

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