Composite system comprising a polymer matrix and core-shell nanoparticles, process for preparing it and use thereof

A light diffuser comprising a composite system comprising a polymer matrix that contains a plurality of nanoparticles, wherein a material used for preparing the polymer matrix is a material that is transparent;

• wherein the nanoparticles are core-shell nanoparticles, and a core of the nanoparticles:
• is made of a material that is different from the polymer matrix, that does not absorb light, and has a refractive index that is different from the refractive index of the polymer of the matrix,
• to thereby provide a scattering of white visible light transmitted through the diffuser so as to chromatically separate white visible light into at least two chromatic components:
• one in which the blue component is dominant and one in which the blue component is low;
• wherein the nanoparticles are uniformly and randomly distributed within the polymer matrix and the minimum distance between the surfaces of the cores of any two neighbouring nanoparticles is at least 10 nm and at least 0.2 times the nanoparticle size;
• and
• wherein the light diffuser is a Rayleigh-like diffuser in that the composite system or at least a portion of the composite system produces a haze, as defined in the ASTM Designation E284-09a, which is at least 1.5 times larger for an impinging light in the spectral interval 400-450 nm than in the interval 600-650 nm.

A process for preparing a light diffuser comprising a composite system configured to provide a scattering of white visible light transmitted through the composite system so as to chromatically separate white visible light into a least two chromatic components, one in which the blue component is dominant and one in which the blue component is low;

• the composite system comprising a polymer matrix in which a plurality of nanoparticles is dispersed, the polymer matrix being prepared from a polymer material that is transparent and is made of a material that does not absorb light, the process comprising:
• preparing a plurality of nanoparticle cores of a material B;
• providing the nanoparticle cores with at least one shell obtained starting from a monomer or a polymer to obtain a first shell comprising a polymer A thereby giving a core-shell nanoparticle, wherein the material B of the core of the nanoparticle is different from the monomer or polymer used for obtaining the matrix and has a refractive index that is different from the refractive index of the matrix;
• cross-linking the polymer of the first shell;
• providing the core-shell nanoparticle with an additional shell, the additional shell being obtained starting from a monomer or polymer to comprise a polymer that is not cross-linked;
• dispersing the core-shell nanoparticles into the monomer or polymer from which the matrix will be obtained, the monomer or polymer used to obtain the matrix being the same as or being compatible with the monomer or polymer used to obtain the additional shell, so as to obtain a dispersion of the nanoparticles in the matrix before polymerization;
• and
• polymerizing the matrix;
• wherein the light diffuser is a Rayleigh-like diffuser in that the composite system or at least a portion of the composite system produces a haze, as defined in the ASTM Designation E284-09a, which is at least 1.5 times larger for an impinging light in the spectral interval 400-450 nm than in the interval 600-650 nm.