Micro and macrocomposites are opaque because of light scattering produced by the filler. Such problems can be avoided using a reinforcement phase of extremely reduced size (< 50 nm). Nanocomposites are optically homogeneous materials with modified optical properties. To prepare useful materials, it is required to employ, thermoplastic hydrophobic polymers as matrix. Usually, poly(methylmethacrylate) is adequate because it has very good mechanical properties and a refractive index similar to the glass. The nanometric filler is made by spherical monodispersed particles obtained by homogeneous phase precipitation of inorganic oxides. For the introduction of particles into the matrix it is required the full water removal. However, it is not possible the addition of particle as powder because for the high surface free energy they aggregate if dry, compromising the transparency. A possible solution is to make compatible the particle surface with the polymeric matrix. Such operation is easy to perform in the case of polymer coloration, because some watersoluble organic dyes have a full nonpolar molecule, with the exception of the reactive group. After dye absorption, the particles become hydrophobic, aggregate and flocculate, but washing the system with solvents of decreasing polarity, it is possible the water removal, achieving a new particle dispersion into a medium able to dissolve the polymer matrix. Also pyridine can be used to transfer hydrophilic particles into a hydrophobic polymer matrix without aggregation. The pyridine is an aromatic compound , which polarity is fully located on the nitrogen atom. The compound results miscible with water and highly soluble into a number of organic solvents. The first step of the process is to transfer the particles into a pyridine medium (pyridine addition to the aqueous silica suspension and water distillation). Then, because of the pyridine solubility into methylmethacrylate monomer, the addition of a convenient amount of activated monomer can follow. The pyridine present in the composite at the end of polymerization can be totally removed by washing nanocomposite films in hot water.
Transparent Organic-Inorganic Nanostructured Materials: Preparation Methods
Nicolais L
2000
Abstract
Micro and macrocomposites are opaque because of light scattering produced by the filler. Such problems can be avoided using a reinforcement phase of extremely reduced size (< 50 nm). Nanocomposites are optically homogeneous materials with modified optical properties. To prepare useful materials, it is required to employ, thermoplastic hydrophobic polymers as matrix. Usually, poly(methylmethacrylate) is adequate because it has very good mechanical properties and a refractive index similar to the glass. The nanometric filler is made by spherical monodispersed particles obtained by homogeneous phase precipitation of inorganic oxides. For the introduction of particles into the matrix it is required the full water removal. However, it is not possible the addition of particle as powder because for the high surface free energy they aggregate if dry, compromising the transparency. A possible solution is to make compatible the particle surface with the polymeric matrix. Such operation is easy to perform in the case of polymer coloration, because some watersoluble organic dyes have a full nonpolar molecule, with the exception of the reactive group. After dye absorption, the particles become hydrophobic, aggregate and flocculate, but washing the system with solvents of decreasing polarity, it is possible the water removal, achieving a new particle dispersion into a medium able to dissolve the polymer matrix. Also pyridine can be used to transfer hydrophilic particles into a hydrophobic polymer matrix without aggregation. The pyridine is an aromatic compound , which polarity is fully located on the nitrogen atom. The compound results miscible with water and highly soluble into a number of organic solvents. The first step of the process is to transfer the particles into a pyridine medium (pyridine addition to the aqueous silica suspension and water distillation). Then, because of the pyridine solubility into methylmethacrylate monomer, the addition of a convenient amount of activated monomer can follow. The pyridine present in the composite at the end of polymerization can be totally removed by washing nanocomposite films in hot water.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
