Nanoparticle Surface Interactions Research Articles

Substrate directed self-assembly of anisotropic nanoparticles

We present a molecular dynamics study on the self-assembly of anisotropic nanoparticles—triangles and tetrahedrons on a flat surface. We observe ordered and disordered aggregates of nanoparticles depending on the particle–particle and surface–particle interactions. Anisotropic particles induce directionality in the assembly process. In particular, a cross over from the isotropic (spherical) assembly to the anisotropic (non-spherical) assembly of nanoparticles is identified as their size increases for weak nanoparticle–surface interactions. However, at strong nanoparticle–surface interactions, clusters of nanoparticles grow uniformly on the surface. We present phase diagrams that depict all possible structures of triangles and tetrahedrons depending on their size (L) and the nanoparticle–surface interaction strength (εns). We show a disorder to order transition in the L−εns plane, as L and εns increase.

Sorption of Silver Nanoparticles to Environmental and Model Surfaces

The fate of engineered nanoparticles in environmental systems is controlled by changes in colloidal stability and their interaction with different environmental surfaces. Little is known about nanoparticle-surface interactions on the basis of sorption isotherms under quasi-equilibrium conditions, although sorption isotherms are a valuable means of studying sorbate-sorbent interactions. We tested the extent to which the sorption of engineered silver nanoparticles (nAg) from stable and unstable suspensions to model (sorbents with specific chemical functional groups) and environmental (plant leaves and sand) surfaces can be described by classical sorption isotherms. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) qualitative and quantitative analyses were also used to assess the morphology and nanomechanical parameters of the covered surfaces. The sorption of nAg from stable suspensions was nonlinear and best described by the Langmuir isotherm. Langmuir coefficients varied with sorbent surface chemistry. For nAg sorption from an unstable suspension, the sorption isotherms did not follow any classical sorption models, suggesting interplay between aggregation and sorption. The validity of the Langmuir isotherm suggests monolayer sorption, which can be explained by the blocking effect due to electrostatic repulsion of individual nanoparticles. In unstable suspensions, aggregates are instead formed in suspension and then sorbed, formed on the surface itself, or formed in both ways.

Eu2O3-functionalized ZnO/palygorskite

Eu2O3-functionalized ZnO/palygorskite was synthesized in a two-step method, and was thoroughly characterized. Energy was transferred from Eu2O3 to ZnO, but not from ZnO to Eu2O3, in contrast to literature reports. The interaction between Eu2O3 and ZnO directly influenced the energy transfer process. Eu2O3 was sporadically loaded on the ZnO surface, rather than doped in the ZnO crystal lattice as Eu3+ or assembled as a Eu2O3–ZnO core–shell structure as is usually reported. Nanoparticle surface interactions and the ZnO morphology were possible factors affecting energy transfer. Particle-to-particle contact between Eu2O3 and ZnO benefited the energy transfer from Eu2O3 to ZnO. Eu2O3 acted as an ‘energy package’, first absorbing then transferring energy to ZnO. This process increased the number of excited carriers within ZnO, thus enhancing the luminescence and photocatalysis properties.

Light scattering by a magneto-optical nanoparticle in front of a flat surface: Perturbative approach

We develop a perturbative formalism for the interaction of a magneto-optical nanoparticle with a flat surface made of a dielectric or metallic material. The formalism leads to a simple interpretation of the interplay between the purely dielectric and the magneto-optical responses, in terms of excitation of (and radiation by) two orthogonal electric dipoles. We analyze two different routes for the enhancement of the magneto-optical response with respect to the purely dielectric contribution, both based on the nanoparticle-surface interaction. The enhancement is discussed in terms of relevant magneto-optical signals, such as changes in reflectivity, polarization (Kerr) rotation, and ellipticity.

A reptation-based model to the dynamics and rheology of linear entangled polymers reinforced with nanoscale rigid particles

A reptation-based model, that incorporates transient polymer–nanoparticle surface interactions, is proposed to describe the dynamics and rheological behaviors of linear entangled polymers filled with isotropic rigid nanoscale particles. Dispersed nanoparticles are sufficiently small such that even at low volume fractions, the average particle wall-to-wall distance is on the order of the chain size. The model predicts a scaling law in the form, τ d , e f f ∼ τ d ( ϕ a d N + 1 ) 2 , where τ d, eff is the effective reptation time of a chain in the presence of attractive nanoparticles, τ d is its reptation time in the neat polymer, ϕ ad is the fraction of attached monomers per chain, and N is the number of monomers per chain. Hence, the overall relaxation is extremely retarded by attractive nanoparticles in the limit of strongly adsorbed chains. Also, it is found that the effective reptation time, τ d, eff , can be controlled through five main parameters, i.e., the molecular weight of the polymer chain, N, the size of the nanoparticles, d f , the density of attractive site on the nanoparticle surface, n as , the monomer–nanoparticle energetic interaction, ɛ, and the nanoparticle volume fraction, ϕ f . The nonequilibrium dynamics of detachment/re-attachment of monomers from/to nanoparticle surfaces under flow conditions is incorporated in the model to elucidate the effect of monomer–surface interactions on the nonlinear viscoelastic behavior. The resulting model correctly captures the linear dynamical properties and shear rheological behaviors of nanocomposite systems studied. Under very slow shear flow conditions, these filled systems exhibit a strong non-Newtonian behavior and a large enhancement in the viscosity as a certain number of monomers in the chain are attached to nanoparticle surfaces, while at very high shear rates, the neat polymer dominates the shear thinning behavior, suggesting that addition of nanoparticles contributes negligible to the viscosity in strong flows. A picture that is based on transient polymer–particle surface interactions, i.e., the detachment/re-attachment dynamics of monomers from/to nanoparticle surfaces is proposed to interpret the observed huge alteration in rheological properties.

Monodisperse Thioether-Stabilized Palladium Nanoparticles: Synthesis, Characterization, and Reactivity

Size control of monodisperse palladium nanoparticles with sizes ranging from 1.7 to 3.5 nm was accomplished using thioethers as stabilizing ligands, in a one-step procedure. Modulation of the reaction temperature, reaction time, solvent, and carbon chain length of the thioether provided control over the nanoparticle size and size distribution. The resulting Pd nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). 1H NMR spectroscopy provided insight into the thioether−Pd nanoparticle surface interaction. To demonstrate the catalytic activity of the thioether-stabilized Pd nanoparticles, hydrogenation reactions were carried out using the as-synthesized Pd nanoparticles. We observed a trend in the reactivity of the nanoparticles with respect to their size, however, recovery of the nanoparticles following subsequent reactions was rather challenging. Immobilization of the Pd nanoparticles onto commerci...

Towards an accurate description of the capillary force in nanoparticle-surface interactions

We present a method to numerically calculate the exact (non-circular) meniscus profile from the Kelvin equation, and compare the results of the obtained capillary force with different previous approximations and experiments. We show that a circular meniscus profile gives correct results in most cases. We also compare different models of pull-off behaviour and show that the often used approximation of humidity independent capillary force is viable for spherical particles above 1 µm radius, but below that there is a strong humidity dependence, as seen in experiments. At the same length scale the direct surface tension force component becomes important. We also discuss the vanishing of the capillary force at very low humidity, the effect of small initial separation between the particle and the surface and the effects of different particle shapes and contact angles on the capillary force. Finally, calculated results are compared with experimental measurements of the capillary force.