Search

The properties of colloids are considerably affected by particles' surface morphology. In this work, for understanding the mechanism of roughness formation in polymeric core-shell (CS) particles, the surface morphology of synthesized CS particles through seeded dispersion polymerization (SDP) in the presence of poly(methyl methacrylate) seeds was investigated. The results revealed that shell polymers with higher solubility parameters (δ) and glass transition temperatures (Tg) had a rougher surface. These parameters directly affect the time needed for chain deformation, which is a critical parameter in controlling the final morphology. We suggested a relation based on these parameters to predict the surface morphology (smoothness or roughness) of CS particles synthesized through SDP in water.

The one-pot synthesis of hybrid hollow nanoparticles of symmetric and asymmetric shapes is a challenging task and has rarely been reported. This work proposes a method for a high-yield synthesis of hybrid hollow carbon particles. In the first step, hexadecane/styrene (HD/St) is encapsulated in a silica shell. Then, by the polymerization of St, a silica/polystyrene double shell is formed. Finally, hollow carbon particles with bowl-like and crumpled shapes are obtained by carbonization. The results show that the ratio of diameter to thickness (D/H) for obtaining crumpled particles is ∼4-12, whereas this ratio is ∼7-18 for bowl-like particles. We study the effects of HD and St concentrations on the D/H ratio and the composition of hybrid particles. In contrast to suspensions of hollow carbon spheres, the suspensions of hybrid nanoparticles show shear-thinning behavior over the examined range of shear rates, which is attributed to their enhanced packing. The shape effect of hybrid particles also increases their adsorption on human mesenchymal stem cells (hMSCs) compared to the hollow carbon spheres.

Along with the rising trend of stringent fire safety regulations, demands for reduction in the fire hazard caused by highly combustible materials such as textiles and polymers have become a matter of significant importance. Therefore, numerous attempts have been made to improve the flame retardation of textiles for a variety of applications. The present paper aims to review the recent developments in the flame retardant nanocomposites of natural and synthetic textile polymers. We survey the application of different nanoparticles or a combination of nanoparticles and conventional flame retardants. Furthermore, a comprehensive discussion on mechanisms and optimized conditions of flame retardation and thermal stability is presented.

The effects of several factors (i.e., nanoclay content (NC), melt temperature, screw speed, and feeding rate), on morphology, rheology, thermodynamics, and thermal stability of PA6/NC samples produced in a co-rotating twin-screw extruder were studied. We discuss how changes in the level of these factors can vary diffusion or imposed shear, how these variations in diffusion and/or shear can affect NC dispersion, and how the changes in the state of NC dispersion can influence several properties of the samples. Samples with low NC content, below percolation threshold, showed exfoliated/intercalated structure with negligible sensitivity to changes in the level of the factors; whereas, samples with high NC content, above percolation threshold, showed intercalated with sporadic flocculated structures and noticeable sensitivity to the changes in the level of the factors. Moreover, NC dispersion was found to be mostly diffusion-controlled: changes that resulted in higher diffusion or residence time (i.e., high melt temperature or low screw speed) also eventuated in better NC dispersion. What is more, percolation threshold was seen to move to lower NC contents as diffusion rate was increased. Moreover, as NC content increased, opposite thermal stability behaviors were observed at above and below the percolation threshold. J. VINYL ADDIT. TECHNOL., 2014. © 2014 Society of Plastics Engineers