Interacting nanoparticle systems models

This nanoparticle sample exhibits strong anisotropy, due to the uniaxial anisotropy of the individual particles and the anisotropic dipolar interaction. The relative timescales (f/xm) of the experiments on nanoparticle systems are shorter than for conventional spin glasses, due to the larger microscopic flip time. The nonequilibrium phenomena observed here are indeed rather similar to those observed in numerical simulations on the Ising EA model [125,126], which are made on much shorter time (length) scales than experiments on ordinary spin glasses [127]. 

Main recent developments in magnetic nanoparticle systems Measurements on single magnetic nanoparticles Synthetic model systems ofmagnetic nanoparticles Inter-particle interactions and collective behavior Noteworthy attempts at dealing with nanoparticle complexity Interpreting the Mossbauer spectra of nanoparticle systems Needed areas of development... 

In biological applications we need to consider the nanoparticle system (composition, size and structure, surface substitution), the given in vitro or in vivo biologic system (media, serum, cells, tissues, animal model, etc), and the mechanisms, through which they interact. We have to determine the properties that are biologically relevant. Some of the physical properties of nanoparticles are easy to measure, but irrelevant from a biological point of view, and vice versa. As an example, low ethylenediamine contamination of technical PAMAM materials is not easy to measure, but this data is very significant in toxicity experiments. 

Simulations of physical properties of realistic Pt/support nanoparticle systems can provide interaction parameters that are used by molecular-level simulations of self-organization in CL inks. Coarse-grained MD studies presented in the section Mesoscale Model of Self-Organization in Catalyst Layer Inks provide vital insights on structure formation. Information on agglomerate formation, pore space morphology, ionomer structure and distribution, and wettability of pores serves as input for parameterizations of structure-dependent physical properties, discussed in the section Effective Catalyst Layer Properties From Percolation Theory. CGMD studies can be applied to study the impact of modifications in chemical properties of materials and ink composition on physical properties and stability of CLs. 

In the previous Sections (2.1-2.3) we summarized the experimental and computational results concerning on the size-dependent electronic structure of nanoparticles supported by more or less inert (carbon or oxide) and strongly interacting (metallic) substrates. In the following sections the (usually qualitative) models will be discussed in detail, which were developed to interpret the observed data. The emphasis will be placed on systems prepared on inert supports, since - as it was described in Section 2.3 - the behavior of metal adatoms or adlayers on metallic substrates can be understood in terms of charge transfer processes. 

Summing up this section, we would like to note that understanding size effects in electrocatalysis requires the application of appropriate model systems that on the one hand represent the intrinsic properties of supported metal nanoparticles, such as small size and interaction with their support, and on the other allow straightforward separation between kinetic, ohmic, and mass transport (internal and external) losses and control of readsorption effects. This requirement is met, for example, by metal particles and nanoparticle arrays on flat nonporous supports. Their investigation allows unambiguous access to reaction kinetics and control of catalyst structure. However, in order to understand how catalysts will behave in the fuel cell environment, these studies must be complemented with GDE and MEA tests to account for the presence of aqueous electrolyte in model experiments. 

Unfortunately, the author has not come so far across any publication on concerning inorganic semiconductor surfaces (2D) or linear ID systems. The problem of correct measurement of local densities or distances between PCs in nanostructured low-dimensional systems is even more complicated. Indeed, using modem EPR technique, one can measure 1/T2 values up to 5-6 nm [124]. But it is the very size of colloidal and aggregated nanoparticles Is it possible to use the pure 2D model in this case, or is it necessary to take into consideration an input of 3D interaction Our group is working on this problem now, trying to understand where is a border between 3D and 2D cases in terms of quantitative analysis of dipole-dipole interaction. 

Figure 4.4.1 Schematic representation of the model systems discussed within the chapter (A) nanoparticle growth influenced by dopants in the support, (B) nanoparticle deposition from solution, (C) strong metal support interaction, and (D) photochemistry at supported nanoparticles as a function of size.

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