Null‐Scattering Hybrid Particles Using Controlled Radical Polymerization

Abstract

The particular properties of nanometer-sized inorganic materials are of central importance to the design of modern composite materials such as polymer composites, coatings, or cosmetic products where particle additives are used to improve mechanical, thermal, transport, or optical properties. [1][2][3][4][5][6][7] However, in many instances the improvement of some performance characteristic is compromised by a loss in transparency that results from the scattering of visible light by the embedded particle inclusions -a consequence of the significantly different refractive index n of most inorganic materials and the organic embedding medium. For applications that capitalize on optical transparency, the scattering of particle inclusions presents severe limitations to the maximum concentration of filler particles as well as the design possibilities of the organic-matrix composites. For optically isotropic particles with linear dimensions significantly less than the wavelength of light, the particle scattering cross-section is given by C sca ∼ V p 2 (Da) 2 (with V p denoting the particle volume and Da the polarizability of the particle within the embedding medium). [8,9] Since Da ∼ (e p -e m )/(e p + 2e m ) >> 0 (with e i = n i 2 denoting the dielectric constant of medium 'i'; 'p', and 'm' represent the particle and embedding medium, respectively) for most inorganic/organic material combinations, significant scattering can arise even for small particle sizes.In this Communication we demonstrate that the scattering of inorganic particles can efficiently be suppressed by grafting of polymers of appropriate composition, molecular weight, and grafting density from the particles' surface such as to match the effective dielectric constant of the resulting coreshell particle to the dielectric constant of the embedding medium. Key to the presented approach is the observation that for core-shell particles with a size less than the wavelength of light the optical properties are approximately equal to those of a homogeneous particle with an effective dielectric constant that depends on the optical properties and volume fractions of the respective constituents.[10] In particular, for a core-shell particle at wavelengths larger than the particle dimension the particles' effective dielectric constant is given by Maxwell-Garnett theory as e eff e shell 1 3 fx 1 À fx 1Here, x = 1/3 (e core -e shell )/(e core -1/3 (e core -e shell )), e core and e shell represent the dielectric constant of the particle-core and shell, respectively, and f = V core /(V core + V shell ) is the relative particle-core volume. [11][12][13][14][15][16] Scattering will be suppressed if the effective dielectric constant of the core-shell particle equals the dielectric constant of the embedding medium. [10,17] Equation 1 thus provides a design criterion for the synthesis of quasi-transparent particle additives, i.e., by grafting a shell with a dielectric constant greater than (less than) the one of the embedding media to a particle core that has a dielectri...

High-Transparency Polymer Nanocomposites Enabled by Polymer-Graft Modification of Particle Fillers

“…particles to the reduced solubility in the absence of PS-grafts that has been reported before and that also was corroborated by dynamic light scattering [35]. Since C sca ~ V p 2 , the total scattering of a number of particles increases upon aggregate formation.…”

Polymer-Tethered Nanoparticle Materials—An Emerging Platform for Multifunctional Hybrid Materials

“…3.4b. In this case, the distribution of active and inactive centers across the particle surface is generally thought to be stochastic (Bombalski et al 2007).…”

Null Extinction of Ceria@silica Hybrid Particles: Transparent Polystyrene Composites

“…5 However, there is often a trade-off between the development of one or more novel optical features and the optical transparency. 6 Because of the sharp refractive index (RI) at the interface of particles and polymers, transparency suffers from strong light scattering and absorption, and eventually transparency is deteriorated. 5−13 The reduction of size of the scatterers (individual particles and particle domains) has been the most common approach for suppressing optical scattering.…”

“…Previously, Bockstaller and Matyjaszewski demonstrated the minimization of scattering for polystyrene-grafted SiO 2 nanoparticles in liquid state (toluene). 6 The precise control of the SiO 2 layer thickness is essential for the design. Optimum polymer-graft composition for the shell is obtained using atom transfer radical polymerization (ATRP) for a well-defined coating on the SiO 2 core with a controlled graft density, molecular weight, and appropriate composition.…”