Abstract
The addition of nanoparticles has recently emerged as a clever tool to manipulate the microstructure and, through it, the macroscopic properties of immiscible polymer blends. Despite the huge number of studies in this field, the underlying mechanisms of most of the nanoparticle-induced effects on the blend microstructure remain poorly understood. Among others, the origin of effect of nanoparticles on the transition from distributed (drop-in-matrix) to co-continuous morphology is still controversial. Here we address this issue through a systematic study on a model blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) filled with small amounts of nanoparticles (organo-modified clay) selectively located at the polymer–polymer interface. Extraction experiments with selective solvents prove that the nanoparticles significantly anticipate the onset of co-continuity with respect to the unfilled blend. Morphological analyses reveal that such an effect is a consequence of the interconnection of nanoparticle-coated polymer domains. Such “ginger-like” clusters get into contact at low content due to their irregular shape, thus anticipating the onset of co-continuity.
Highlights
Blending polymers represents an inexpensive route to develop materials with enhanced performances or with new combinations of properties
The use of reliable experimental techniques is mandatory to avoid misinterpretation of the results. In line with these criteria, we have selected a blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) filled with small amounts of an organically-modified clay (Cloisite® 15A), which we know from previous studies to be inclined to accumulate at the polymer–polymer interface [13,14]
The value of φi is a function the weight fraction of “i” in the blend, Φi, and it ranges from 0 to 1 when the morphology passes from a distributed microstructure, made of isolated domains of “i” suspended in the matrix of the second phase, to a co-continuous one, in which both phases are continuous in the space [18]
Summary
Blending polymers represents an inexpensive route to develop materials with enhanced performances or with new combinations of properties. Filippone et al preserved the structural integrity of a blend sample at 75 wt % of high density polyethylene well above its melting temperature by blending it with polyamide 6 and inducing the continuity of that phase by means of nanoclay [11] Extending such an approach to bio-based polymers, Nuzzo et al enhanced the high-temperature mechanical performances of polylactic acid by developing a blend in which the heat-resistant polyamide 11 represents the minor, and yet continuous, phase [12]. The use of reliable experimental techniques is mandatory to avoid misinterpretation of the results In line with these criteria, we have selected a blend of polystyrene (PS) and poly(methyl methacrylate) (PMMA) filled with small amounts of an organically-modified clay (Cloisite® 15A), which we know from previous studies to be inclined to accumulate at the polymer–polymer interface [13,14]. Morphological analyses shed light on the mechanism behind the morphology transition, which appears to be a consequence of a clustering phenomenon between nanoparticle-coated domains of the minor polymer phase
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