Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with increasing alkyl chain length of a particular AO. We conclude with perspectives and prospects.
Abstract. Herein, investigation on synergistic effect during network formation for conductive network constructed with carbon nanofillers in different dimensions is conducted. Multi-walled carbon nanotubes (MWNTs) and carbon black (CB) are employed as conductive fillers in this system. Morphological control of the conductive network is realized by adjusting the ratio between different fillers. Classical percolation threshold theory and adjusted excluded volume theory are used to analyze the electrical percolating behavior of these systems. It is observed that the percolation threshold of hybrid fillers filled conductive polymer composites (CPCs) is much lower than that of MWNTs or CB filled CPCs, and it can be reduced from 2.4 to 0.21 wt% by replacing half of the MWNTs with CB. Possible mechanism of this phenomenon is discussed together with morphological observation. A model is proposed to understand the mechanism of the percolation behavior in the composites containing various proportions of nanofillers. Our work is important for the design and preparation of low cost conductive polymer composites with novel electrical property. Vol.6, No.2 (2012) 159-168 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2012.17 * Corresponding author, e-mail: huadeng@scu.edu.cn © BME-PT PE/MWNTs composites prepared by melt blending. The value is often between 1 to 5 wt% for melt compounded systems and considered as statistical percolation threshold [22]. The mechanism behind this significant difference between kinetic and statistical percolation is the prohibition of re-aggregation between CNTs during melt compounding process [22,24]. It was reported that the re-aggregation process of CNTs within polymer melt can take hours to complete [25]. To achieve better conductivity or lower cost, more than one kind of filler, particularly fillers in different aspect ratios, are used to prepare CPCs. Regarding the formation of conductive network with fillers in different aspect ratios, theoretical study has shown that it is not necessary to build conductive network with high aspect ratio filler alone [26], and the percolation threshold is sensitive to the portion of high aspect ratio filler in a system containing fillers in different aspect ratios [27]. There are a number of investigations reported in the literature on mixed carbon fillers filled CPCs [26,[28][29][30][31]. However, the percolation thresholds of these systems filled with mixed fillers are only simple average of that for systems filled with a particular kind of carbon filler. Therefore, more study is needed to study the true synergistic effect between conductive fillers of different dimensionality in building conductive network. In current study, CPCs based on mixed filler between carbon nanofillers in different dimensions and polypropylene will be fabricated. It is well known that polyolefin is a widely used material and its processability is prominent. Moreover, due to the difference in filler dimension and intrinsic structure, the networ...
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