The three-dimensional (3D) morphology of particulate fillers embedded in a rubbery matrix was examined by transmission electron microtomography (TEMT). Two types of nanofillers, i.e., carbon black (CB) and silica (Si) nanoparticles, were used as the nanofillers. Although the CB and Si nanoparticles were difficult to distinguish by conventional transmission electron microscopy (TEM), they appeared different by TEMT; the CB and Si nanoparticles appeared to be hollow and solid particles in the cross-sectional images of the TEMT 3D reconstruction, respectively, demonstrating that TEMT itself provided a unique particle-discriminative function. The nanoparticles were found to form aggregates in the matrix. It is intriguing that each aggregate was made of only one species; not a single aggregate contained both the CB and Si nanoparticles. A particle-packing algorithm was developed to estimate the positions of each primary nanoparticle inside the aggregates.

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ABSTRACT:A novel microcellular porous structure, the product of a small proportion of a semi-crystalline thermoplastic elastomer (TPE) and a large proportion of low molecular weight oil, is examined. The structure is formed by the phase separation of a homogeneous mixture of TPE and oil. The system exhibits a unique three-dimensional continuous polymer network consisting of interconnected spherical cells of a few tens of micrometers in diameter. The detailed phase separation process is investigated utilizing optical microscopy, SEM, and DSC. A modulated structure, apparently attributable to spinodal decomposition, is observed in the initial stage of phase separation. However, during its evolution, this structure evolves into a clear network structure of a polymer-rich phase and clusters of a spherical oil-rich phase. Time evolution of D of a typical structure during the phase separation process at constant temperature is estimated to be D ∼ t 1 in the initial stage and D ∼ t 1/3 in the late stage. The character and role of differences in M w of components in the phase separation of the TPE/oil system are discussed in relation to the results of other studies.KEY WORDS Phase Separation / Percolation-to-Cluster Transition / Network Structure / Polymer Solution / Thermoplastic Elastomer / The phase separation process and morphology of polymer blend systems and alloys are both attractive and important from scientific and industrial perspectives, in part because the physical and mechanical properties of such polymer systems are highly dependent on their higher-order structures. Many types of phasecontrolled polymers have been developed and put to practical use over past decades.Despite numerous theoretical approaches, 1-4 most efforts to verify experimentally the kinetics of phase separation and its progress have generally been performed by indirect methods, such as time-resolved light scattering. [5][6][7][8][9] However, in the past five years, several studies have reported on direct observation of phase separation phenomena using laser scanning confocal microscopy, e.g., Ribbe, 10 Jinnai, 11, 12 and Hermansson. 13 Recently, the authors proposed new non-aqueous physical gels prepared with small proportions of semicrystalline thermoplastic elastomers (nearly 10 wt% polymer concentration) and large proportions of oils of low molecular weight. 14, 15 Observed directly with an optical microscope, the systems consist of threedimensional continuous polymer networks, constituted spherical cells of a few tens of micrometers in diameter. Each cell is connected to several other cells. Small openings occur at the connections between the cells: tunnels formed in the walls of the cells. This observation suggests that the oil-rich phases enclosed within the polymer cells are interconnected through the holes, and that the oil-rich phase is also continuous. We call this a "microcellular porous structure." The systems are quite stable thermally and dynamically and are currently used in industrial products as very soft nonaqueous and ...

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