Filler networking is considered as the most important parameter in controlling the mechanical and rheological properties of highly filled systems. Besides, the interparticle distance as a function of filler size and concentration seems to be the main parameter to govern the filler network strength or filler–filler interaction. In this article, considering the importance of filler networking, estimation of the interparticle distance for different values of filler size and concentration, investigation of the architecture of filler network in the nanocomposite for various filler sizes as well as analysis of the effects of filler size and concentration on the dynamic behavior of the filler networks are discussed and atomic force microscopic imaging is used to investigate the filler network parameters. In addition to the proposed filler network structure, the results suggest that the rheological properties of nanocomposites in the linear region could be related to the interparticle distance independent of filler size and concentration. On the other hand, by studying the linear and nonlinear viscoelastic properties of these highly filled systems, the results indicate that an increase in loss and storage modulus would occur by increasing the filler concentration and reducing the filler size.
An accurate prediction of any process is the key to the control of that system. Modeling the rheological properties of nanocomposites would provide us a pattern for prediction of their properties as a function of process and material variables. In this study, the focus is to model and investigate the behavior of highly nanofilled systems, which is controlled by the filler–polymer and filler–filler interactions. In these systems, particles attract each other and form a network, which has a viscoelastic response to the applied stress or strain. Due to the filler–polymer interaction, polymer chains are adsorbed on the filler surface to create a secondary network, parallel with the filler–filler network. The third network in the system is the network of free polymer chains around the adsorbed ones. In this work, the behavior and contribution of these networks in the highly nanofilled systems are described. Furthermore, the relaxation time and the modulus of the filler network are estimated as a function of particle size and concentration. It is observed that the relaxation time and modulus of the filler network are increased with a reduction in particle size and an increase in particle concentration. For studying the parameters of the model, polymer adsorbed layer and available surface area of particles are estimated from the density of the nanocomposites.
Highly filled systems, such as dental materials and tires, have some exceptional properties that make them very special for particular scientists and engineers. In this study, the thermal and dynamic properties of highly nanosilica-filled polystyrene were investigated. Thermal study predicts a phase in the filled system, named as adsorbed polymer, that has a different glass transition temperature (T g ) compared with the neat polymer. The adsorbed polymer seems to be responsible for special thermal properties of the highly filled system. The dynamic properties of the filled system are observed to have a similar trend as the thermal behavior at different particle sizes and concentrations, both increasing linearly with the increase of volume fraction of adsorbed polymer. However, at higher volume fractions or for smaller particles, this trend changes and the filler networking mechanism is considered to be the reason for this change. Effect of the filler network is studied through the Han plot and it is found that the contribution of the filler network to the dynamic behavior of the highly filled system increases by reducing the particle size and increasing the particle loading. Beside the particle size and concentration, the effect of filler surface physics on dynamic and thermal behavior of the highly filled system is investigated and it is found that surface modification of the particle surface with nonpolar groups tends to lower T g and volume fraction for the adsorbed phase and lower strength of the filler network. In this work, the samples were prepared using the method of stabilizing suspension in polymer solution. For viscoelastic investigation, the dynamic rheometry in sweep mode was chosen, also for studying the thermal Downloaded from behavior, differential scanning calorimetric tests were performed. In addition, in order to study the structure of filler in low and highly filled samples, atomic force microscopic imaging was employed.
Morphology of a nanocomposite, which has indisputable effects on its properties, is determined by its dynamic and thermodynamic conditions. While physical properties of the components of a nanocomposite as well as the interaction between them are the parameters controlling the morphology thermodynamically, their dynamic condition is related to the issues like intensity of mixing and geometry of mixer. In this research, we investigate the mixing process of solution casting method by studying the effects of mixing intensity on the dynamics of the particle structure and hereby its morphology using sedimentation test. In these experiments, mixing is performed at various durations, input energies, and energy types for suspensions containing different particle sizes and concentrations as well as diverse polymer concentrations. We found that increasing mixing time and input energy along with using ultrasonic wave decrease the size of aggregates. Sedimentation test revealed improvements of dispersion and distribution states of suspension by using ultrasonic waves and high shear mixing, respectively. Finally, particle-particle interaction data show increase in the probability of restructuring after mixing with reduction in particle size and increase in particle volume fraction.
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