Interacting nanoparticle systems dynamic properties

In rubber-rubber blend nanocomposites, nanoparticles are incorporated into a blend which can significantly affect the properties of the matrix. The properties of these composites depend on the type of nanoparticles that are incorporated, their size and shape, their concentration and their interactions with the polymer matrix. It is difficult to produce monodispersed nanoparticles in a rubber blend because of the agglomeration of nanoparticles. This problem can be overcome by modification of the surface of the nanoparticles. Surface modification improves the interfacial interactions between the nanoparticles and the polymer matrix. Nanofillers when added to blend systems are known to cause a considerable change in dynamic properties. 

Numerical methods with different time- and length scales are employed and developed to investigate material properties and behaviors. Among them, molecular modeling can predict the molecular behaviors and correlate macroscopic properties of a material with various variables. The most popular techniques include molecular mechanics (MM), MD, and Monte Carlo (MC) simulation. These techniques are now routinely used to investigate the structure, dynamics, and thermodynamics of inorganic, biological, and polymer systems. They have recently been used to predict the thermodynamic and kinetic properties of nanoparticle-matrix mixtures, interfacial molecular structure and interactions, molecular dynamic properties, and mechanical properties. 

ZnO nanoparticles possess greater surface/volume ratio. When used in carboxylated nitrile rubber as curative, ZnO nanoparticles show excellent mechanical and dynamic mechanical properties [41]. The ultimate tensile strength increases from 6.8 MPa in ordinary rabber grade ZnO-carboxylated nitrile rubber system to 14.9 MPa in nanosized ZnO-carboxylated nitrile mbber without sacrificing the elongation at failure values. Table 4.1 compares these mechanical properties of ordinary and nano-ZnO-carboxylated nitrile rubbers, where the latter system is superior due to more rubber-ZnO interaction at the nanolevel. 

These difficulties have stimulated the development of defined model catalysts better suited for fundamental studies (Fig. 15.2). Single crystals are the most well-defined model systems, and studies of their structure and interaction with gas molecules have explained the elementary steps of catalytic reactions, including surface relaxation/reconstruction, adsorbate bonding, structure sensitivity, defect reactivity, surface dynamics, etc. [2, 5-7]. Single crystals were also modified by overlayers of oxides ( inverse catalysts ) [8], metals, alkali, and carbon (Fig. 15.2). However, macroscopic (cm size) single crystals cannot mimic catalyst properties that are related to nanosized metal particles. The structural difference between a single-crystal surface and supported metal nanoparticles ( 1-10 nm in diameter) is typically referred to as a materials gap. Provided that nanoparticles exhibit only low Miller index facets (such as the cuboctahedral particles in Fig. 15.1 and 15.2), and assuming that the support material is inert, one could assume that the catalytic properties of a... 

Molecular dynamics methods afford a unique view of the dynamical feature of non-equilibrium systems as well as the ability to obtain a wide variety of data of physical/chemical properties. We have used this approach to model the equilibrium and kinetic properties of silicon nanoparticles containing up to 1000 atoms (16,17). However for such an analysis to yield even semi-quantitative results requires a knowledge of the interaction potential. For a system as complicated as the one under consideration here, interatomic potentials are beyond the scope of current state of the art. However, one can still, under certain circumstances obtain qualitative information. 

Abstract This chapter describes the influence of three-dimensional nanofillers used in elastomers on the nonlinear viscoelastic properties. In particular, this part focuses and investigates the most important three-dimensional nanoparticles, which are used to produce rubber nanocomposites. The rheological and the dynamic mechanical properties of elastomeric polymers, reinforced with spherical nanoparticles, like POSS, titanium dioxide and nanosdica, were described. These (3D) nanofillers in are used polymeric matrices, to create new, improved rubber nanocomposites, and these affect many of the system s parameters (mechanical, chemical, physical) in comparison with conventional composites. The distribution of the nanosized fillers and interaction between nanofUler-nanofiUer and nanofiller-matrix, in nanocomposite systems, is crucial for understanding their behavior under dynamic-mechanical conditions. 

Nanoparticles, compared with traditional fillers, provide more reinforcement due to the higher interfacial area. Introduction of these particles into the mbber matrix improves many of its properties, in particular tensile strength, thermal stability, elasticity, processability or barrier improvement. The final properties of nanocomposites are determined by the filler-filler and polymer-filler interactions. Therefore, it is very important to have knowledge of the characteristics of nonlinear viscoelastic behavior for mbber reinforced systems, especially an analysis of the low strain dynamic mechanical properties (Payne effect). 

Chapter 4 investigates the rheological and the dynamic mechanical properties of rubber nanocomposites filled with spherical nanoparticles, like POSS, titanium dioxide, and nanosilica. Here also the crucial parameter of interfacial interaction in nanocomposite systems under dynamic-mechanical conditions is discussed. After discussing about filled mono-matrix medium in the first three chapters, the next chapter gives information about the nonlinear viscoelastic behavior of rubber-rubber blend composites and nanocomposites with fillers of different particle size. Here in Chap. 5 we can observe a wide discussion about the influence of filler geometry, distribution, size, and filler loading on the dynamic viscoelastic behavior. These specific surface area and the surface structural features of the fillers influence the Payne effect as well. The authors explain the addition of spherical or near-spherical filler particles always increase the level of both the linear and the nonlinear viscoelastic properties whereas the addition of high-aspect-ratio, fiberlike fillers increase the elasticity as well as the viscosity. 

Force-field molecular dynamics simulations offer the ability to model molecules at the particle level. Often, information from quantum simulations is used to develop the empirical equations (force-field) that are used to govern the interactions between particles. Because force-field molecular dynamics simulations use less detail than the quantum simulations, they are able to model systems that are significantly larger in size ( 10 particles) for a longer period of time (<10 s). Therefore, measuring the structural, mechanical, and/or transport properties of medium to large sized systems (i.e., proteins, functionalized nanoparticles,...) is possible. 

Polymer materials are ubiquitous in our daily life. They often consist of more than one species of polymers and, therefore, can be called multicomponent systems, for example, polymer blends and block copolymers. Because of the repulsive interaction between the constituent polymers, multicomponent polymer materials often show phase separation. Organic-inorganic composites are another class of polymer-based multicomponent materials that have attracted considerable interest from researchers because they often exhibit unexpected properties synergistically derived from the constituents. Nanometer-sized particulate fillers, for example, carbon black (CB) and silica (Si) nanoparticles, are known to form hybrids with organic polymers, which show a significant increase in their static and dynamic moduli, strength, and thermal and electrical conductivities. 

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