Conductive polymer composites CPCs

Smart materials [FEL 11] such as conductive polymer composites (CPCs) could potentially offer such capabilities, and we shall now examine the capacities of rPC/CR mixtures in this domain in greater detail. 

Conductive polymer composites (CPC) exhibit a series of unique features, such as comparatively low room temperature resistivity, percolation phenomenon, resistivity sensitivity to temperature, pressure and gas, and nonlinear voltage-current relationship [1-5]. They found wide industrial applications in the fields of antistatic materials, self-regulating heaters, over-temperature protection devices, and electromagnetic interference shielding. Therefore, fundamental and applied studies of CPC are currently of great interest. 

In order to understand the phenomena behind resistance variations in the conductive polymer composites (CPCs) due to solvent diffiision. Feller et al. [71] have performed sorption exjjeriments with poly (ethylene-co-ethyl acrylate)-carbon black (EEA-CB) and EEA films in the presence of toluene. One main point here was to determine the influence of CB in the diffiision process. The first results showed that, whichever polymer was used, the diffiision coefificiem increased with toluene activity, which indicated plasticization of the material by the solvent. However, it was interesting to note that the plasticization phenomenon was reduced when fillers were introduced into the polymer matrix. It also appeared that the toluene diflfiisivity was about twofold lower in EEA-CB than in EEA, which was certainly due to a hindrance effect of the carbon black particles. In other words, the decrease in toluene solubility was the result of a tortuosity effect due to the morphology of CPC with a dispersion of CB particles, which acted as barrier components and increased the path for toluene molecules inside the composite. 

In this study, the main goal was the elaboration of a thermal conductive CPC (Conductive Polymer Composite) that will be used in thermal solar panel. In fact, the conductive polymer composite was obtained by blending bio-polymer matrix by different percentages of fillers (eGR/CNT). Effect of fillers percentage on thermal conductivity, solar absorbance and total emittance was investigated. 

Unlike the porous membrane, colloidal particles (such as PS or silica particle) are another type of template for the preparation of CPCs (Figure 11.10c). In previous work, core/shell PS/PANI composite particles were prepared by chemical oxidative seeded dispersion polymerization. A conventional coating protocol was employed as follows. The aniline monomer was dissolved in a strongly acidic solution in the presence of the PS seed latex (an alternative method involves using a miscible aniline hydrochloride monomer without external acid). Then polymerization was initiated by the addition of oxidant aqueous solution. The suspended PS particles were coated with PANI by in situ deposition of the formed conducting polymer or oligomer from the aqueous phase. 

From this view, the authors have used a new approach called melt extrusion-hot stretching-quenching to prepare two categories of CPC (isotropic and anisotropic CPC) based on in situ microfibril reinforced polymer-polymer composites. This chapter briefly describes our recent work on several conductive in situ microfibrillar reinforced composites via hot stretching. 

Blending two or above polymers together is an important way to create synergis-tically new physical properties of the composites in the polymer industry. Furthermore, the multiphase separation is produced by polymer blending, and thus, phase morphology of the polymer blends significantly affects the final properties of the composites. When conductive fillers are added to the immiscible polymer blends, the location of conductive fillers in polymer phases may be various and could lead to different electrical properties of CPCs. In another word, conductive fillers can be selectively located in one of the polymer phases or at the phase interfaces [86-88], which can be controlled to constiuct a desirable conductive network structure in CPCs. 

The percolation threshold, cpc, is the fiUer loading level at which the polymer first becomes conductive, which is generally considered to be a value of about 10 S/cm. Comprehensive experimental and theoretical treatments describe and predict the shape of the percolation curve and the basic behaviors of composites as a function of both conductive filler and the host polymer characteristics (36-38). A very important concept is that the porous nature of the conductive carbon powders significantly affect its volume filling behavior. The typical inclusive stractural measurement for conductive carbon powder porosity is dibutyl phthalate absorption (DBF) according to ASTM 2314. The higher the DBF, the greater the volume of internal pores, which vary in size and shape. The crystalhnity of the polymer also reduces the percolation threshold, because conductive carbons do not reside in the crystalhtes but instead concentrate in the amorphous phase. Eq. (2) describes the percolation curve (39). 

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