Anna Marie Ritcey

This study explores the self-assembly of bimetallic core-satellite nanostructures, which have potential applications in photocatalysis and sensing. More specifically, the Langmuir-Blodgett technique is used to prepare composite thin films composed of palladium nanoparticles (PdNPs), gold nanoparticles (AuNPs), and a block copolymer, poly(styrene-b-2-vinylpyridine). First, PdNPs of different sizes and shapes, capped with alkanethiols of various lengths, are prepared. When assembled alone with PS-b-P2VP, the arrangement of PdNPs within the composite films depends on the NP size and the length of the capping agent. By cospreading 5.4 nm PdNPs coated with octadecanethiol and 6 nm AuNPs capped with octanethiol with poly(styrene-b-2-vinylpyridine) at the air-water interface, bimetallic core-satellite nanostructures (NSs) are obtained. These NSs are composed of satellite AuNPs assembled into a ring, which surrounds PdNP islands that constitute the core. The substrate-supported core-satellite NSs were immersed in a growth solution containing a gold precursor and a reducing agent. This treatment resulted in a doubling of the size of the AuNPs, whereas the size of the PdNPs remained unchanged. Further investigation demonstrates that the preferential growth of the AuNPs is kinetically controlled. Optical extinction spectra of the core-satellite NSs suggest that the surface plasmons of the AuNPs and PdNPs behave independently. The absence of coupled plasmonic modes can be attributed to the small size of the PdNPs. Nevertheless, this work presents an effective way to prepare substrate-supported hybrid core-satellite NSs over macroscopic surface areas for potential applications in photocatalysis and sensing.

Uniform hollow carbon nanoparticles (CNPs) of different shapes were prepared by a reverse microemulsion polymerization method. The main advantage of this method is the ability to control the precise shape...

The optical properties of lanthanide-doped nanoparticles depend on the location of dopant ions. Doped (H3O)Y3F10@(H3O)Y3F10 core@shell nanoparticles were synthesized in a one-pot inverse microemulsion involving multiple additions of precursors, leading to the isolation of the lanthanide ions in the core or the shell. This synthesis provides excellent control of shell growth without secondary nucleation. Elemental analysis, electron microscopy, and electron spectroscopy revealed the doping level and ion localization. Heavier lanthanide ions, such as Er3+, can completely replace Y3+ in the host matrix (H3O)Y3F10 without crystal structure modification; (H3O)Er3F10 can be prepared either as a shell or a core material. Lighter lanthanide ions, such as Eu3+, however, are only tolerated in the (H3O)Y3F10 matrix up to ∼15%. Eu-doped (H3O)Y3F10 nanoparticles show well-defined emission spectra, consistent with high crystallinity. The emission intensity varies with Eu doping levels, even after normalization for Eu content. The addition of an undoped shell to Eu-doped cores increases luminescence, which varies significantly with the core doping level. Luminescence decay curves, fitted as biexponentials, yield lifetimes on the order of 2 and 4 ms. For 5% Eu cores, the relative contribution of the shorter lifetime to overall emission decreases upon the addition of an undoped shell, consistent with the protection of emissive surface sites from environmental quenching. Even with uniform, well-defined shells, lighter lanthanide dopant segregation is hampered by potential ion migration. This work demonstrates not only the importance of developing syntheses permitting the controlled localization of doping ions but also the necessity of validating ion distribution in nanoparticles.

A bottom-up approach, the Langmuir-Blodgett technique, is used for the preparation of composite thin films of gold nanoparticles and polymers: poly(styrene-b-2-vinylpyridine), poly-2-vinylpyridine, and polystyrene. The self-assembly of poly(styrene-b-2-vinylpyridine) at the air-water interface leads to the formation of surface micelles, which serve as a template for the organization of gold nanoparticles into ring assemblies. By using poly-2-vinylpyridine in conjunction with low surface pressure, the distance between nanostructures can be increased, allowing for optical characterization of single nanostructures. Once deposited on a solid substrate, the preorganized gold nanoparticles are subjected to further growth by the reduction of additional gold, leading to a variety of nanostructures which can be divided into two categories: nanocrescents and circular arrays of nanoparticles. The optical properties of individual structures are investigated by optical dark-field spectroscopy and numerical calculations. The plasmonic behavior of the nanostructures is elucidated through the correlation of optical properties with structural features and the identification of dominant plasmon modes. Being based on a self-assembly approach, the reported method allows for the formation of interesting plasmonic materials under ambient conditions, at a relatively large scale, and at low cost. These attributes, in addition to the resonances located in the near-infrared region of the spectrum, make nanocrescents candidates for biological and chemical sensing.

Discoloration of wood coatings due to fungal growth negatively affects the aesthetic properties of the coatings, and new ways to control fungal growth on coatings are needed. For this reason, silver nanoparticles (AgNPs) have been incorporated in acrylic latexes as antifungal agents. Using miniemulsion polymerization, latexes were prepared with two types of initiators (hydrophilic and hydrophobic) to assess the influence of the initiator type on AgNPs dispersion, both within the latex particles and the dry film. In addition, the impact of NP dispersion on resistance to black-stain fungi (Aureobasidium pullulans) was also evaluated. Inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis indicates that acrylic latexes prepared with azobisisobutyronitrile (AIBN) as the initiator contain more AgNPs than those prepared with potassium persulfate (KPS). Cryo-TEM and SEM analyses show that the distribution of the AgNPs within the polymer particles is influenced by the nature of the initiator. When AIBN, a hydrophobic initiator, is used, the AgNPs appear to be closer to the surface of the polymer particles and more evenly distributed. However, the antifungal efficiency of the AgNPs-embedded latexes against A. pullulans is found to be higher when KPS is used, despite this initiator leading to a smaller amount of incorporated AgNPs and a less uniform dispersion of the nanoparticles.

Polymerization of acetylene using a Glaser-Hay dispersion polymerization was achieved, yielding spherical CNPs. UV irradiation of these CNPs makes them fluorescent in the blue region.

Polydimethylsiloxane (PDMS)/iron oxide magnetic nanoparticle (NP) composites with tailored mechanical properties are prepared for use in magnetically actuated soft devices based on their controlled deformation by the application of an external magnetic field. This investigation reports the synthesis and functionalization of iron oxide NPs, the preparation of the PDMS/NP composites, the evaluation of NP dispersion using scanning electron microscopy (SEM) and optical microscopy, and the mechanical characterization of the composite films. Characterization includes rheological measurements as well as stress‐strain curves to obtain the Young modulus and elongation at break. SEM is used to probe individual NP dispersion, whereas optical microscopy provides rapid access to quantitative information about the size and distribution of particle aggregates. Results for nonfunctionalized (nf), oleic acid (OA)‐coated, and stearic acid (SA)‐coated iron oxide NPs and their blends are presented. PDMS elastomers containing both OA‐ and SA‐coated iron oxide NPs are found to have very low Young moduli with substantially higher resistance to failure than neat PDMS. For example, a formulation containing 2.5 wt% OA‐coated NPs and 2.5 wt% SA‐coated iron oxide NPs has a modulus of 0.15 MPa (compared with 0.24 MPa for neat PDMS), while it can withstand an elongation of about 1.5 times its initial length compared with only 0.3 times for neat PDMS. As a comparison, the modulus of the most commonly used commercial PDMS elastomer (Sylgard 184) is an order of magnitude higher than that of the composites prepared here, whereas maximum elongation is similar for the two. The formulations developed in this work could be used in applications where high deformability is required with limited magnetic field strength and/or NP loading.

Quasi-monodisperse populations of (H₃O)Y₃F₁₀·xH₂O nanocrystals of varying size are prepared in Igepal-stabilized microemulsions. Correlations between microemulsion composition, micelle hydrodynamic radius, and final nanoparticle size are established and shed light on the mechanism of particle size control. Under the conditions considered here, size control appears to be primarily governed by the number of micelles and the quantities of precursor ions. More specifically, the number of NPs formed can be successfully correlated with the number of micelles present and final NP size is, in turn, determined by the number of nuclei and the total amount of material available for nanocrystal formation. This insight into nanoparticle formation facilitates the selection of appropriate synthetic conditions for the preparation of populations of a targeted size.