Composite gels modulus

From the experimental results, the ER effect in polymer gels is explained as follows (Fig. 8). When an electric field is applied, the particles electrically bind together and cannot slip past each other. Larger shear forces are needed in the presence of an electric field. Thus, the electric field apparently enhances the elastic modulus of the composite gel. The difference in ER effects between an oil and a gel is that the polarized particles necessarily cannot move between the electrodes to produce the ER effect in a gel. In order for the ER effect to occur, it is important to form migration paths before application of an electric field. 

In this section, we discuss theoretically the influence of microscopic interaction between polarized particles on the macroscopic mechanical properties of the composite gel, in particular, the elastic modulus. 

Let us now discuss the shear modulus of the composite gel under a magnetic held which is applied parallel to the path of a dispersed particle. Shear strain is applied so as to cross the path of a particle. The assumptions are as follows ... 

We have called composite gels which vary in elastic modulus in electric or magnetic fields ER or MR gels. In this section, the viscoelastic properties of some ER or MR gels are presented... 

The dynamic viscoelasticity of particulate gels of silicone gel and lightly doped poly-p-phenylene (PPP) particles has been studied under ac excitation [55]. The influence of the dielectric constant of the PPP particles has been investigated in detail. It is well known that the dielectric constant varies with the frequency of the applied field, the content of doping, or the measured temperature. In Fig. 11 is displayed the relationship between an increase in shear modulus induced by ac excitation of 0.4kV/mm and the dielectric constant of PPP particles, which was varied by changing the frequency of the applied field. AG increases with s2 and then reaches a constant value. Although the composite gel of PPP particles has dc conductivity, the viscoelastic behavior of the gel in an electric field is qualitatively explained by the model in Sect. 4.2.1, in which the effect of dc conductivity is neglected. 

Figure 2-15 Modulus of the Composite Gel (Gq) Plotted Against Volume Fraction of Component y (G = 10,000). When the weaker component (x, G = 1,000 Pa) dominates and becomes the continuous phase, Gc follows the lower bound isostress limit, with increasing fraction of r, there will be a phase inversion and Gc reaches the upper bound limit, path indicated by open circles.

Elastomer (a) Name Composition % Gel % Swell Tensile 300% Modulus Elongation Heat Build-up 212°F. 

Name Composition Gel Swell Tensile 300% Modulus Elongation 212°F. 

The parameters which characterize the thermodynamic equilibrium of the gel, viz. the swelling degree, swelling pressure, as well as other characteristics of the gel like the elastic modulus, can be substantially changed due to changes in external conditions, i.e., temperature, composition of the solution, pressure and some other factors. The changes in the state of the gel which are visually observed as volume changes can be both continuous and discontinuous [96], In principle, the latter is a transition between the phases of different concentration of the network polymer one of which corresponds to the swollen gel and the other to the collapsed one. 

Silicon carbide CVD Sol-gel High strength High modulus High cost High-temp composites... 

The elastic modulus of laminated composite plate in which an ER silicone gel of carbonaceous particles is sandwiched between two PVC sheets also changed under the influence of an electric field. It was found that an electric field of 1.17 kV/mm caused a gain in the elastic modulus of the gel of 13% [57]. 

The effect of polymer-filler interaction on solvent swelling and dynamic mechanical properties of the sol-gel-derived acrylic rubber (ACM)/silica, epoxi-dized natural rubber (ENR)/silica, and polyvinyl alcohol (PVA)/silica hybrid nanocomposites was described by Bandyopadhyay et al. [27]. Theoretical delineation of the reinforcing mechanism of polymer-layered silicate nanocomposites has been attempted by some authors while studying the micromechanics of the intercalated or exfoliated PNCs [28-31]. Wu et al. [32] verified the modulus reinforcement of rubber/clay nanocomposites using composite theories based on Guth, Halpin-Tsai, and the modified Halpin-Tsai equations. On introduction of a modulus reduction factor (MRF) for the platelet-like fillers, the predicted moduli were found to be closer to the experimental measurements. 

The effect of the microstructure of acrylic copolymer/terpolymer on the properties of silica-based nanocomposites prepared by the sol-gel technique using TEOS has been further studied by Patel et al. [144]. The composites demonstrate superior tensile strength and tensile modulus with increasing proportion of TEOS up to a certain level. At a particular TEOS concentration, the tensile properties improve with increasing hydrophilicity of the polymer matrix and acrylic acid modification. 

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