Molecular-scale assessment

Imaging is a common technique for assessing materials. For example, airliner structural materials are often X-ray-imaged to check for hairline cracks or other signs of imminent failure. In scientific applications, advances in nanotechnology have produced a parallel need for improved methods of imaging nanomaterials on the molecular scale. 

Molecular-scale approaches to assess sorption-desorption 111... 

MOLECULAR-SCALE APPROACHES TO ASSESS SORPTION-DESORPTION... 

On a molecular scale, the accurate and controlled application of inter-molecular forces can lead to new and previously unachievable nanostructures. This is why molecular self-assembly (MSA) is a highly topical and promising field of research in nanotechnology today. With many complex examples all around in nature, MSA is a widely perceived phenomenon that has yet to be completely understood. Biomolecular assemblies are sophisticated and often hard to isolate, making systematic and progressive analyzes of their fundamental science very difficult. What in fact are needed are simpler MSAs, the constituent molecules of which can be readily synthesized by chemists. These molecules would self-assemble into simpler constmcts that can be easily assessed with current experimental techniques [37, 38]. 

The study of chemistry depends heavily on measmement. For instance, chemists use measurements to compare the properties of different snbstances and to assess changes resulting from an experiment. A number of common devices enable us to make simple measurements of a substance s properties The meterstick measures length the buret, the pipet, the graduated cylinder, and the volrrmetric flask measure volume (Figure 1.6) the balance measures mass the thermometer measures temperature. These instruments provide measurements of nuicroscopic properties, which can be determined directly. Microscopic properties, on the atomic or molecular scale, must be determined by an indirect method, as we will see in Chapter 2. 

Ab initio methods allow the nature of active sites to be elucidated and the influence of supports or solvents on the catalytic kinetics to be predicted. Neurock and coworkers have successfully coupled theory with atomic-scale simulations and have tracked the molecular transformations that occur over different surfaces to assess their catalytic activity and selectivity [95-98]. Relevant examples are the Pt-catalyzed NO decomposition and methanol oxidation. In case of NO decomposition, density functional theory calculations and kinetic Monte Carlo simulations substantially helped to optimize the composition of the nanocatalyst by alloying Pt with Au and creating a specific structure of the PtgAu7 particles. In catalytic methanol decomposition the elementary pathways were identified... 

Figure 5. Schematic description of a multi-technique approach to the assessment of molecular mobility inside swollen polymeric frameworks as a phenomenon dependent on their morphology at the nanometric scale [14, 21, 22, 108].

To assess homogeneity, the distribution of chemical constituents in a matrix is at the core of the investigation. This distribution can range from a random temporal and spatial occurrence at atomic or molecular levels over well defined patterns in crystalline structures to clusters of a chemical of microscopic to macroscopic scale. Although many physical and optical methods as well as analytical chemistry methods are used to visualize and quantify such spatial distributions, the determination of chemical homogeneity in a CRM must be treated as part of the uncertainty budget affecting analytical chemistry measurements. 

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