Surface Coverage Of Nanoparticles Research Articles

Effect of Areal Chain Density on the Location of Polymer-Modified Gold Nanoparticles in a Block Copolymer Template

A strategy for controlling the location of gold nanoparticles within block copolymer domains through varying the surface coverage of gold nanoparticles by end-attached polymer ligands is described. Gold nanoparticles coated by short thiol end functional polystyrene homopolymers (PS-SH) (Mn = 3.4 kg/mol) are incorporated into a poly(styrene-b-2-vinylpyridine) diblock copolymer template (PS-b-P2VP) (Mn = 196 kg/mol), the P2VP block of which has a more favorable interaction with a bare gold particle surface than does the PS block. The areal chain density of the PS-SH ligands on gold particles is varied by changing the mole ratio of PS-SH chains to gold atoms. It is found that the areal density of PS chains on the gold particles is critical to controlling their location in block copolymer templates. PS-coated gold nanoparticles with PS chain areal density higher than 1.6 chains/nm2 are dispersed in PS domains of PS-b-P2VP while they are segregated along the interface between PS and P2VP domains of PS-b-P2VP for PS chain areal density <1.3 chains/nm2. Even at extremely low grafting densities of polymer ligands, gold nanoparticles can be stabilized in solution, and self-assembly of these nanoparticles can be controlled within the block copolymer template.

금 나노입자 박막의 분광전기화학적 연구

아미노실리케이트로 안정화한 금 콜로이드 용액으로부터 산화인듐주석(ITO) 위에 전해석출법으로 금 나노입자의 박막을 만들고, 이 박막을 순환 전압전류법(CV), 주사전자현미경법(SEM), 자외선-가시선 및 에너지분산 X-선 분광법(EDXS)으로 조사하였다. 박막 위 금 나노입자의 표면덮힘율은 1.2 나노몰/cm2였다. 금 박막을 0.10 M HClO4 용액에 든 0.1mM anthraquinone-2,6-disulfonic acid, disodium 염(AQDS) 용액에 20시간 이상 담가서 AQDS의 자체조립 단막층을 생성하였다. 그 결과 690 nm에서 다중층(AQDS/금박막/ITO)의 새로운 흡수 봉우리가 얻어졌다. 또한, +0.5V에서 -0.5V까지 전위를 변화시키는 시간전류법과 자외선-가시선 분광법으로 다중충의 표면 플라스몬 흡수를 측정하였다. 음의 전위를 걸어주었을 때 550 nm에서 나타나는 최대 표면 플라스몬 흡수띠가 감소하였다. 흡광도의 변화와 AQDS의 표면덮힘율과의 상관관계로부터 AQDS층의 유사용량 표면상태가 음전위를 걸어줄 때 플라스몬 띠의 에너지준위와 연관되어 있음을 알았다. films of gold nanoparticles were formed on indium tin oxide (ITO) by an electrodeposition method from an aminosilicate stabilized gold colloid solution. The thin films were examined by cyclic voltammetry (CV), scanning electron microscopy (SEM), UV-visible, and energy dispersive X-ray spectroscopy (EDXS). The surface coverage of gold nanoparticles on the thin film was estimated to 1.2 nanomole/cm2. An anthraquinone-2, 6-disulfonic acid, disodium salt (AQDS) self-assembled layer was generated by immersing gold thin film into 1mM of AQDS in 0.1M HClO4 solution for over 20 hours. As a result, a new absorbance peak from the multi-layers (AQDS/thin film of gold /ITO) was obtained about at 690 nm. Also, the surface plasmon absorption of multi-layers was measured by UV-Visible spectrometer along with chronoamperometry by applying the various potentials from +0.5V to -0.5V. The maximum surface plasmon absorption band at 550 nm was decreased by applying negative potentials. The change of absorbance was correlated with the surface coverage of the AQDS indicating the pseudo-capacity surface state of the AQDS layer was coupled to the energy level of the plasmonband by applied negative potentials.

Decomposition of Monolayer Coverage on Gold Nanoparticles by UV/ozone Treatment

Abstract Au nanoparticles, covered with cationic dichain surfactant on the whole surface, were treated with UV/ozone. FT-IR spectra of the Au nanoparticles with bottom-, upper-, and fully covered surfactant monolayers revealed a variable decomposition rate. The sum frequency generation spectra of the treated nanoparticles showed that the surface coverage of gold nanoparticles lose the centrosymmetric structure, implying asymmetric distribution of the protected surfactant molecules. The UV–vis electronic absorption spectra suggested stable nanoparticle monolayer film structure after UV/ozone irradiation.

Assembly of Silica Nanoparticles for Two-Dimensional Nanomaterials

To realize the great potential of nanoparticles as new materials for biomedical applications, the nanoparticles will have to be assembled in such a way that the newly created assembly will have unique properties that conventional materials do not possess. This will enable nanomaterials to be used for many novel applications. We have attempted to assemble silica nanoparticles to create a two-dimensional nanomaterial, which might be useful for biosensor and biochip production. The silica nanoparticles are synthesized and assembled in a monolayer fashion through the use of halogenated silanes. Photolithography techniques are used to pattern the glass surface prior to nanoparticle attachment. The concentration of the silica nanoparticles in the solution controls the surface coverage of nanoparticles on the glass surface. Different patterned silica arrays can be made with controlled surface coverage. The nanoparticle-covered surface is successfully tested for surface-enhanced enzymatic reactivity for the detection of a neurotransmitter, glutamate. This report demonstrates the feasibility of assembling nanoparticles for biosensor development.

The Distance-Dependence of Colloidal Au-Amplified Surface Plasmon Resonance

Au nanoparticle-amplified surface plasmon resonance (PA-SPR), like traditional SPR, is typically used to detect binding events at a thin noble metal film. Here we describe the use of SiO2-overcoated Au films as a substrate for PA-SPR. Changes in SPR angle shift upon Au nanosphere binding were investigated as a function of the SiO2 thickness. In these experiments, a submonolayer of Au nanoparticles was immobilized atop a thin Au film separated by an intervening SiO2 layer. Although SPR is an evanescent wave technique, the observed SPR angle shift does not decrease monotonically with increasing Au nanoparticle−Au surface separation, but rather increases to a maximum at ∼32 nm separation before decreasing. In contrast to the previously proposed electromagnetic coupling between the metal particles and the surface as the main cause for the observed distance-dependent SPR response, we propose and have demonstrated qualitatively that the energy modulating capability of the SiO2 spacing layer is the main contributor. The impact of the particle size, composition, and surface densities on this maximum in SPR angle shifts was also examined. The results indicate that the optimal SiO2 thickness was independent of Au nanoparticle surface coverage for coverage less than 10%. This work extends the use of PA-SPR to monitoring binding events at glass interfaces and points to a route for increased sensitivity, as evidenced in an PA-SPR assay for human immunoglobin G in a sandwich immunoassay format.

Nano-CaCO3/polypropylene composites made with ultra-high-speed mixer

In polymer-based nanocomposites, because of the large fraction of the nanoparticle atoms that reside at the interface, there would be a strong interface interaction between filler and polymer. The mechanical properties of nanocomposites would improve significantly at a low filler content if the ultrafine phase dimension was retained [1]. However, the homogeneous dispersion of nonaparticles is very difficult because nanoparticles with high surface energy are easy to agglomerate. To break up the agglomerates, studies have been carried out on the approaches of in situ polymerization of monomers in the presence of nanoparticles [2–4] and other intercalation polymerization techniques [5]. Although nanoparticles can be dispersed uniformly, the methods with complex processes, special conditions and high cost are limited to laboratory scale. Melt blending nanoparticles with polymer is the best compounding technique in the case of mass production of nanocomposites with low cost. In the literature [6–9], it is reported that the problem of melt blending is that nanoparticles tend to agglomerate due to their high surface energy during mixing even when the nanoparticle content in the composites is small. The key is to decrease the surface energy of the nanoparticles, however, the uniform surface coverage of nanoparticles is hard to realize by simply physical and mechanical means. In order to resolve this problem, an ultra-high-speed mixer has been designed to treat the surface of the nanoparticles [10]. The mixer has high speed (6000 rpm), special rotors that are designed to deal with nanoparticles. Under high shear force, the nanoparticle surface is modified with coupling agent, which is added by means of an atomizer. The purpose of this letter is to show how efficiently the mechanical performance of the nanocomposites can be improved by the above approach. Isotactic polypropylene (PP) homopolymer (melting flow index (MI) = 5g/10 min) was used as matrix and CaCO3 (diameter = 70 nm, density = 2400 kg/m3) was selected as the filler. Stearic acid was used as coupling agent. Nano-CaCO3 and stearic acid were mixed in the high speed mixer for 5 min. Because of high shear force, the temperature of mixtures could increase to 140 ◦C, and the powders were ready for compounding. PP and fillers were melt mixed in a twin-screw extruder at 200 ◦C and 100 rpm. The specimens for

Dependence of the Raman Intensity on the Surface Coverage of Nanoparticles in SERS-ctive Gole Nanoparticulate Films

Dependence of the Raman Intensity on the Surface Coverage of Nanoparticles in SERS-ctive Gole Nanoparticulate Films

PH-Dependent Adsorption of Gold Nanoparticles on p-Aminothiophenol-Modified Gold Substrates

Colloidal Au nanoparticles were assembled on a gold substrate via a p-aminothiophenol coupling layer. The surface coverage of Au nanoparticles was found to be closely related to the pH value of gol...