Macroscopic characterization/properties

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

Despite these arguments and the conceptual attractiveness of the procedure which is sketched in Fig. 1 convincing evidence for the relevance of a particular gas phase adsorption experiment can only be obtained by direct comparison to electrochemical data The electrode potential and the work function change are two measurable quantities which are particularly useful for such a comparison. In both measurements the variation of the electrostatic potential across the interface can be obtained and compared by properly referencing these two values 171. Together with the ionic excess charge in the double layer, which in the UHV experiment would be expressed in terms of coverage of the ionic species, the macroscopic electrical properties of the interracial capacitor can thus be characterized in both environments. 

Most important macroscopic transport properties (i.e., permeabilities, solubilities, constants of diffusion) of polymer-based membranes have their foundation in microscopic features (e.g., free-volume distribution, segmental dynamics, distribution of polar groups, etc.) which are not sufficiently accessible to experimental characterization. Here, the simulation of reasonably equilibrated and validated atomistic models provides great opportunities to gain a deeper insight into these microscopic features that in turn will help to develop more knowledge-based approaches in membrane development. 

Analytical characterization includes measurement of absolute sizes and concentrations of species present in the catalyst. For the purpose of clarity, these techniques have been organized, starting with the bulk macroscopic properties, down to the component, microscopic features. The underlying goal of analytical characterization is to provide information about the sample which will allow research personnel to relate the properties measured to some aspect of a catalyst s performance, either in the field or in the evaluation laboratory. Macroscopic characterization includes both chemical compositions and physical properties such as particle size, density and total surface area. Chemical analysis techniques are well... 

The key challenge for the successful use of NMR velocity-imaging techniques to characterize fluid flow properties is the interpretation of the measured parameters. Different experimental strategies provide information about flow processes at different spatial and dynamic scales in porous media. In principle, the flow velocity can be probed either as a local quantity with an image resolution below the pore level,2425 or as a macroscopic flow property corresponding to local volume and temporal averages of fluid molecular displacements.26 One must develop a suitable methodology to correctly determine the parameters that best describe the properties of interest. 

Overall, the regime of linear viscoelasticity is characterized by reasonable success in establishing structure-property relationships. The properties themselves are unambiguously and simply specifiable. The relevant structural features are largely recognizable aspects of molecular structure. Molecular theories exist that provide a bridge between the molecular structure and the macroscopic viscoelastic properties. 

Characterization of porous media based on the pore (microscopic) level is carried out for the purpose of understanding, modeling, and sometimes controling the macroscopic behavior and properties of the medium. The macroscopic (bulk) properties needed to relate to the pore description are porosity, permeability, tortuosity, and connectivity. When one examines a sample of a porous medium, for example, sandstone, it is obvious that the number of pore sizes, shapes, orientations, and interconnections is enormous. Furthermore, even the identification of a pore is not unique. Because of this complexity, pore structure is often characterized based on an idealized model. A true description is not realistic for a natural porous medium. 

Orientational order of LCPs is conveniently described in terms of two differoit order parameters, characterizing the average orientation of the mesogenic units within a molecular domain (microorder) and the macroscopic alignment of the domains (see Fig. 3) [10,35]. The measurement of these parameters is important for relating macroscopic physical properties of LCPs to their molecular structure. Various methods have been used to measure order parameters in these systems, including the use of X-ray diffraction [128-130], birefringence [103, 104], and linear dichroism [104,131], but these methods can not essentially separate the two types of orientational order. 

A metamaterial is a type of artificially engineered material that typically features a pattern or periodic arrangement of a material. Metamaterials are characterized by the fact that they take on specific macroscopic physical properties based on their structure or the pattern in which the material is arranged, but not necessarily the composition of the material. Another way to say this is that the elemental makeup of a metamaterial is not as important as the interned structure of the metamaterial. By relying on the structure of the material to influence its properties, metamaterials have been able to achieve properties... 

The following sections describe the preparation and characterization of supramolecular polymer networks, particularly emphasizing their physical-chemical features with regard to the type and strength of physical chain cross-linking and the resulting macroscopic material properties. Furthermore, recent work on the formation and characterization of supramolecular hydrogels based on synthetic and natural precursors is summarized with a focus on their application and potential in biomedicine. 

As in the case of the statistical mechanics of a fluid, these Boltzmann factors contain more information than is necessary in order to characterize the experimental properties of polymer systems. We therefore focus attention upon reduced distribution functions in order to make contact with the macroscopic observable properties of polymers. In the usual many-body problems encountered in statistical mechanics, the reduced distribution functions are the solutions to coupled sets of integro-differen-tial equations. - On the other hand, because a polymer is composed of several atoms (or groups of atoms) that are sequentially joined together by chemical bonds, these reduced distributions for polymers will obey difference equations. Therefore, by employing the limit in which a polymer molecule is characterized by a continuous chain, these reduced probability distributions can be made to obey differential, instead of difference, equations. This limit of a continuous chain then enables the use of mathematical analogies between polymers and other many-body systems. The use of this limit naturally leads to the use of the technique of functional integration. 

Cure is illustrated schematically in Figure 1 for a material with co-reactive monomers such as an epoxy-diamine system. Reaction in the early stages of ciu-e (a to b in Fig. 1) produces larger and branched molecules and reduces the total number of molecules. Macroscopically, the thermoset can be characterized by an increase in its viscosity r] (see Fig. 2 below). As the reaction proceeds (lb to Ic in Fig. 1), the increase in molecular weight accelerates and all the chains become linked together at the gel point into a network of infinite molecular weight. The gel point coincides with the first appearance of an equilibrium (or time-independent) modulus as shown in Figure 2. Reaction continues beyond the gel point (Ic to Id in Fig. 1) to complete the network formation. Macroscopically, physical properties such as modulus build to levels characteristic of a fully developed network. 

In nanotechnology numerical simulation can help to predict properties of new materials that do not yet exist in reality. And it can help to identify the most promising or suitable materials. The trend is towards virtual laboratories in which materials are designed and studied on a computer. Simulation offers the possibility of determining mean or average properties for the material macroscopic characterization. At... 

Liquid crystals as anisotropic fluids exhibit a wide range of complex physical phenomena that can only be understood if the appropriate macroscopic tensor properties are fully characterized. This involves a determination of the number of independent components of the property tensor, and their measurement. Thus a knowledge of refractive indices, electric permittivity, electrical conductivity, magnetic susceptibilities, elastic and viscosity tensors are necessary to describe the switching of liquid crystal films by electric and magnetic fields. Development of new and improved materials relies on the design of liquid crystals having particular macroscopic tensor properties, and the optimum performance of liquid crystal devices is often only possible for materials with carefully specified optical and electrical properties. 

The analysis of the statistical or preferred orientation of the crystallites in solid polycrystaUine materials is commonly referred to as texture analysis. Again, the diffraction technique allows the definition of the relationship between a microscopic property, i.e. the orientation of the crystallites defined as coherent diffraction domains, and the macroscopic physical properties of the crystal aggregate. Texture studies are of course crucial in the characterization of oriented synthetic materials such as cold-rolled metals or oxide thin films, but they are also of great relevance in the study of the formation processes of mineral assemblages. As an example, the texture features of olivine or pyroxene minerals in meteoritic chondrules yield information on the early condensation sequence... 

We have considered in 2 a system of prescribed temperature, volume and composition (that is for a given number of molecules Ni, Nz.. For some purposes it will be more convenient to use instead the independent variables T, V and chemical potentials fn, jwa. ..). It is shown in all textbooks of statistical mechanics that the macroscopic equilibrium properties of such a system are obtained by averaging all accessible quantum stat of the stem characterized by the energy Er and the numbers of molecules Ni, JVa..., attadaing to each state the statistical weight... 

Several papers recently addressed the importance of studying the relationship existing between the basic macroscopic electrochemical properties of boron-doped diamond electrodes and their characterization at the microscopic level, in order to understand which factors influence the electrochemical reactivity [4, 5]. It was found that the boron doping level in the diamond and the presence of graphitic impurities play a major role in the basic... 

In continuum electrodynamics, an optical system is represented as a collection of discretization grids, each of which is characterized by its electric permittivity and magnetic permeability which are uniquely determined by the material properties. By solving Maxwell s equations or the coupled dipole-field equations in either the time or frequency domain, any macroscopic optical property of interest can be numerically determined subject to the desired boundary conditions. Since the continuum models are typically scale invariant, they are applicable to arbitrarily large systems. However a limitation in the description of metal nanoparticles is that grid sizes on the order of a few nanometers are necessary for convergence of the numerical methods, so this places an... 

Material Properties. The properties of materials are ultimately deterrnined by the physics of their microstmcture. For engineering appHcations, however, materials are characterized by various macroscopic physical and mechanical properties. Among the former, the thermal properties of materials, including melting temperature, thermal conductivity, specific heat, and coefficient of thermal expansion, are particularly important in welding. 

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