No abstract

No abstract

Hybrid materials combine properties of metals, oxides, and polymers by mixing these most different materials at the nanometer level, and strongly rely on interface stabilization. [1][2][3][4] In particular the mechanical incorporation of nanoparticles into engineering thermoplastics (e.g., by melt blending techniques) has offered a continuous challenge to materials science as thermodynamic and kinetic barriers inhibit the dispersal of inorganic nanoparticles with generally high surface energies within hydrophobic polymer matrices. [5][6][7][8][9][10][11] The physical reason for the dispersion difficulties are strong adhesion forces that act between particles with high surface energy, whilst the polymer has a lower surface energy (see Table 1 for a representative overview). The adhesion forces depend on the particle's material properties and the polymer. The free energy of adhesion W a per area between two surfaces of the same material acting in a liquid medium is given bywhere g sl is the interfacial tension between the solid and liquid phase.[17] A low interfacial tension therefore leads to low adhesion forces between particles and, thus, breaking apart of nanoparticle agglomerates and dispersion of primary particles is facilitated. Dispersion of carbon soot in rubber is an example of this class. By contact angle measurements and knowledge about the surface energies of the solid and liquid phase g s and g l , the interfacial energy g sl is given by Young's equation:where u is the wetting contact angle. Low-surface-tension liquids such as hydrophobic polymer melts are able to wet most solid materials (u < 908) from low-energy carbon fibers to highenergy metals (Table 2). Therefore, the interfacial energy g sl and the adhesion energy are small for low-surface-energy solids.[11] Unfortunately, metals have a very high surface energy when compared to polymers or typically used carbon materials (Table 1). This explains the considerable efforts required to disperse metals in polymers as the corresponding metal particle adhesion energies are very high. At present, the most successful preparation of advanced nanocomposites and multifunctional nanomaterials [19] by admixing high-surfaceenergy fillers to polymers has been based on the use of surfactants to overcome the gap between the different surface energies of filler and matrix. [7][8][9][10][11]20] Particularly in the case of metal-polymer hybrid materials, chemical and processing complexity, [21] thermal stability, costs, and health issues of such additives have severely constrained application and development of this fascinating class of materials. The present work investigates the possibility to overcome this dispersion problem by mechanically entrapping metal nanoparticles in a graphenelike carbon shell and, thus, facilitating the contact between the polymer and the particles. Beyond considerable thermal stability, [22] graphenelike carbon coatings on metal nanoparticles have most recently allowed covalent, chemical functionalization of particles [23] which sugges...

No abstract

No abstract