Edwin Peter Kennedy Currie

Tethered polymer chains: surface chemistry and their impact on colloidal and surface properties

In this review the grafting of polymer chains to solid supports or interfaces and the subsequent impact on colloidal properties is examined. We start by examining theoretical models for densely grafted polymers (brushes), experimental techniques for their preparation and the properties of the ensuing structures. Our aim is to present a broad overview of the state of the art in this field, rather than an in-depth study. In the second section the interactions of surfaces with tethered polymers with the surrounding environment and the impact on colloidal properties are considered. Various theoretical models for such interactions are discussed. We then review the properties of colloids with tethered polymer chains, interactions between planar brushes and nanocolloids, interactions between brushes and biocolloids and the impact of grafted polymers on wetting properties of surfaces, using the ideas presented in the first section. The review closes with an outlook to possible new directions of research.

Stuffed brushes: theory and experiment*

The interaction between polymer brushes and mesoscopic particles is investigated both theoretically and experimentally. We present an analytical mean-field theory for a polymer brush (a layer of long polymer chains end-grafted to a substrate) with varying excluded volume interactions between monomer units. This system mimics the reversible adsorption of mesoscopic particles, such as surfactant micelles or proteins, on the grafted chains. The equilibrium structural properties of the brush (the brush thickness and overall degree of complexation) as well as the number of adsorbed particles per unit area, G, are analysed as functions of the affinity between particle and chain, grafting density s and excluded volume interactions. In our model G is found to have a maximum as a function of s. Experimentally the adsorption of BSA on a hydrophobic substrate with grafted PEO chains is measured with reflectometry. In the case of short grafted chains the adsorbed amount of BSA, G, decreases continuously with increasing s, which agrees with previous results and model calculations in the literature. In the case of long PEO chains, however, G is found to have a maximum as a function of s. Qualitatively the experimental dependence of G on s is found to agree with the results of our mean-field model. PEO chains show no affinity for BSA in the bulk, whereas in a grafted conformation an effective attraction is found. Some comments are made on the nature of this affinity, which is not yet fully understood.

Structure of grafted polymers, investigated with neutron reflectometry

Neutron reflectometry is used to investigate the structure of polymers end-grafted to an interface at high grafting densities, so-called brushes. Our system consists of polystyrene-polyethyleneoxide (PS-PEO) diblock copolymers, irreversibly adsorbed at the air/D2O interface. At relatively low grafting densities the density profile of a monodisperse brush is block-like, with a tail region in which the density smoothly decays towards zero. At high grafting density the profile is predominantly parabolic. Bimodal brushes are examined for several length ratios and mixing ratios. At a given grafting density the extension of the long chains is larger in a bimodal brush than in a monodisperse. This additional extension increases with increasing length and fraction of small chains. Good agreement is found between the density profiles obtained from analysis of the neutron reflectometry data and profiles predicted by the Scheutjens–Fleer self-consistent-field model.

Hybrid nanocoatings in the display industry

— In the display industry, there is an increasing use of polymeric coatings comprising inorganic nanoparticles. These particles endow the coatings optical, electrical, or mechanical properties not attainable with organic materials, while the use of an organic binder allows easy processing via, e.g., wet deposition and UV or thermal crosslinking. Nanoparticles are relatively new materials and seem to offer numerous opportunities for new coatings for the display industry. Examples of this are silica nanoparticles in anti-reflection coatings, indium-tin-oxide particles in antistatic coatings, and metallic carbon nanotubes in conductive coatings. Yet the physical interactions that determine the dispersion of nanoparticles in the wet formulation and the resulting morphology in the dry coating can be traced back to classical colloid science. In this paper, we focus on some of these principles and their application to nanoparticles dispersed in organic solvents. We illustrate these principles with several examples of anti-reflection coatings, anti-static coatings, and hardcoats currently in use in the industry.

38.2: High Performance Single Layer Anti‐Reflective Coatings via Wet UV Curing Technology

Here we present a novel manner for preparing single layer anti-reflective coatings with excellent optical properties (<1% reflection) over a broad wavelength regime. The technology is based upon the self-assembly and UV curing of reactive nano-particles, leading to nano-structured coatings with a gradient in refractive index. The single processing step leading to such coatings is fast, robust and cost effective.