Intermediate Nanoparticles Research Articles

Enhancement and modulation of three-body near-field radiative heat transfer via anisotropic hyperbolic polaritons

Anisotropic hyperbolic polaritons (HPs) provide novel opportunities to control light at nanoscale because of their promising ability of subdiffractional confinement, low losses, and polarization sensitivities. However, it has not been explored in the modulation of many-body near-field radiative heat transfer (NFRHT). In this work, we investigate the NFRHT in an α-phase molybdenum trioxide three-body nanoparticles (NPs) system. The results show that the near-field radiative conductance (NFRHC) can be significantly enhanced by adding the third NP between two NPs due to the excitation of the localized hyperbolic polaritons (LHPs). The enhancement effect can be actively modulated by rotating the intermediate NP, which is attributed to the high directionality of the LHPs. In addition, the effects of interparticle distance and vertical displacement on the NFRHC are also studied. We achieved an enhancement ratio of over 20,000 when the interparticle distance and vertical displacement is 4 times and 1.2 times the radius, 38 times higher than that of previous works. This work demonstrates the potential of anisotropic HPs in NFRHT modulation within the many-body system.

Intermediate Structures of Pt-Ni Nanoparticles during Selective Chemical and Electrochemical Etching.

Both chemical and electrochemical etching are effective methods for tailoring the surface composition of Pt-based catalytic bimetallic nanoparticles (NPs). However, the detailed nanoscale etching mechanisms, which are needed for achieving fine control over the etch processes, are still not understood. Here, we study selective chemical and electrochemical Ni etching of Pt-Ni rhombic dodecahedron NPs using in situ liquid-phase transmission electron microscopy. Our real-time observations show that the intermediate NP structures evolve differently in the two cases. Chemical etching of Ni starts from localized pits on the NP surface, in contrast to the uniform dissolution of Ni during the electrochemical etching. Our study reveals how oxidative etching participates in the removal of a non-noble metal and the subsequent formation of noble-metal-rich NPs. The mechanistic insights reported here highlight the role of a native surface oxide layer on the etching behavior, which is important for the design of NPs with specific surface composition for applications in electrocatalysis.

Hydrothermal synthesis of tin-doped indium oxide nanoparticles using pamoic acid as an organic additive and their photoluminescence properties

We report a facile hydrothermal method using the disodium salt of pamoic acid (Na2PA) as an organic additive, In(NO3)3·xH2O as an indium precursor, and SnCl2·2H2O as a tin precursor for preparation of ITO nanoparticles (NPs) at low temperature (200 °C). After drying at 110 °C, the as hydrothermally synthesized materials were found to be monodisperse spherical NPs with diameters in the range of ca. 30–40 nm as an intermediate NP product, as confirmed by field emission scanning electron microscopy, transmission electron microscopy and XRD analysis. The XRD analysis confirmed the presence of InOOH in the intermediate NPs. For comparison, the formation of the intermediate NPs under the same reaction conditions was also examined using two analogs of PA instead of Na2PA, i.e., 3-hydroxy-2-naphthalene carboxylic acid (3H2NA) or 2-naphthol (2NP). These additives yielded spherical NPs but with different sizes and different homogeneities compared to the NPs formed using Na2PA. In terms of size and homogeneity of the intermediate NPs, the additives followed the order Na2PA > 2NP > 3H2NA. However, in photoluminescence (PL) studies, the intermediate prepared using 3H2NA showed the highest intensity followed by the intermediates formed using Na2PA and 2NP. After calcination at 420 °C, only the NPs obtained with Na2PA were converted to ITONPs; the other NPs remained in the InOOH form. These results correlated with the corresponding TGA analysis. Interestingly, the ITONPs prepared using Na2PA did not change their morphology during calcination at 420 °C. The morphology of the ITONPs prepared using Na2PA was found to be comparable in terms of homogeneity and shape to that of a commercially available ITO nanopowder. However, the ITONPs prepared using Na2PA showed superior PL intensities compared to the commercial ITONPs.

Enhancement of DNA compaction by negatively charged nanoparticles. Application to reversible photocontrol of DNA higher-order structure

We report for the first time that negatively charged silica nanoparticles (NPs) enhance the ability of cationic surfactants to induce genomic DNA compaction. Single-chain compaction of duplex DNA molecules was studied by fluorescence microscopy in the presence of dodecyltrimethylammonium bromide (DTAB) and NPs. We found that very small amounts of NPs (∼10−4 to 10−2 wt%) significantly decreased the concentration of the surfactant at which DNA is compacted. This effect was maximal at intermediate NP concentration (here, 1.5 × 10−3 wt%) where the concentration of DTAB necessary for DNA compaction was 5-fold smaller than that in the absence of NPs. As a possible mechanism, we suggest that negatively charged NPs, by inducing the aggregation of DTAB molecules through electrostatic interactions, promote cooperative binding to DNA and thus enhance the ability of DTAB to compact DNA. By applying this phenomenon to a photosensitive cationic surfactant (AzoTAB), we could achieve reversible control of DNA higher-order structure using light at a much lower AzoTAB concentration than what has been reported up to now.

Tunable Wetting of Nanoparticle-Decorated Polymer Films

In this paper, amine-modified silica nanoparticles (NPs) with diameters (d) from 15 to 230 nm are covalently linked to poly(styrene-random-acrylic acid) (P(S-ran-AA)) films, and wettability is studied as a function of diameter and NP surface coverage. During attachment, films swell and exhibit long and short scale roughness, consisting of a ridged, honeycomb structure, approximately 1 mum wide and 45-50 nm deep, which encircles nanoscale features 10-15 nm high and approximately 50 nm apart. A maximum NP coverage of approximately 70% was achieved for d less than or nearly equal to the nanoscale roughness induced by surface swelling. For d several times greater than this nanoscale roughness, the maximum coverage was limited by interparticle repulsion and reached only approximately 30%. For NPs with diameters of 15-106 nm, the water contact angle increased from 75 degrees to 120 degrees as NP coverage increased from 0 to 70%. At low and high NP coverage, the Wenzel and Cassie models, respectively, accurately describe the data. However, at intermediate NP coverage, neither model is satisfactory. An increase in surface roughness alone cannot account for this discrepancy. Atomic force microscopy (AFM) studies show that the NPs partially embed into the swollen P(S-ran-AA) surface, suggesting that the amine-coated NPs are wet by the copolymer, exposing low surface energy styrene. These studies demonstrate that control over surface properties of coatings, such as wetting, can be achieved by selecting NP sizes that complement film roughness.

Tetanus toxoid loaded nanoparticles from sulfobutylated poly(vinyl alcohol)-graft-poly(lactide-co-glycolide): evaluation of antibody response after oral and nasal application in mice.

Aim of the study was the evaluation of the potential of novel tetanus toxoid (TT) loaded nanoparticles (NP) for electing an immune response in mice against TT. Six week-old female Balb/c mice were immunized by oral (p.o.), nasal (i.n.) and intraperitoneal (i.p.) application of TT NP loaded by adsorption. As polymer a novel polyester, sulfobutylated poly(vinyl alcohol)-graft-poly(lactide-co-glycolide), SB(43)-PVAL-g-PLGA was used. Blood samples were collected 4 and 6 weeks after immunization and assayed for serum IgG- as well as IgA antibody titers by ELISA. NP formulations varying in size and loading were compared to alum adsorbates as well as to TT solutions. Both, p.o. and i.n. administration of TT associated NP increased serum titers up to 3 x 10(3) (IgG) and 2 x 10(3) (IgA). While small NP induced significantly higher titers then larger ones after oral administration, intermediate NP induced antibodies after nasal application. Of the mucosal routes investigated, i.n. seems to be more promising compared to p.o. immunization. Antigen loaded NP prepared from surface modified polyesters combined with CT show considerable potential as a vaccine delivery system for mucosal immunization. The results warrant further experiments to explore in more detail the potential use of NP as mucosal vaccine delivery system.