Stuart Leadley

Surface characterization of micrometre-sized, polypyrrole-coated polystyrene latexes: verification of a ‘core–shell’ morphology

Micrometre-sized, polypyrrole-coated polystyrene latexes with various conducting polymer loadings have been extensively characterized using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), Raman and UV–VIS reflectance spectroscopy, scanning force microscopy (SFM) and scanning electron microscopy (SEM). Both XPS and TOF-SIMS studies are consistent with relatively uniform, chloride-doped polypyrrole overlayers. Raman studies also indicated a ‘core–shell’ morphology since only bands attributable to polypyrrole were observed; no evidence was found for the underlying polystyrene component even at the lowest polypyrrole loadings. This is most likely due to remarkably efficient attenuation of the polystyrene bands by the highly absorbing polypyrrole overlayer. UV–VIS reflectance spectroscopy studies confirmed that a coated latex had a much lower reflectance (higher absorbance) than a heterogeneous admixture of polypyrrole and polystyrene with a similar polypyrrole content. High-resolution images of the polypyrrole overlayer nanomorphology were obtained using SFM. At low polypyrrole loadings (1.0 mass%) the overlayer was relatively smooth and uniform, but higher loadings (8.9 mass%) resulted in a rougher, more globular morphology. Finally, the underlying polystyrene latex ‘core’ was quantitatively removed by solvent extraction. SEM studies of the polypyrrole residues revealed a ‘broken egg-shell’ morphology, thus providing irrefutable evidence for the ‘core–shell’ morphology of the original polystyrene/polypyrrole particles.

Adsorption isotherms of PMMA on a conducting polymer by ToF-SIMS

Adsorption isotherms of PMMA onto conducting hydrogensulfate-doped polypyrrole (PPyHSO4) from chloroform and CCl4 have been determined by means of time-of-flight secondary ion mass spectroscopy (ToF-SIMS). PMMA adsorption is of the Langmuir-type in both solvents. CCl4 yields a much stronger adsorption of PMMA, a result that is discussed in terms of acid–base properties of PMMA, PPy and the solvent as well as the solvent power.

Atmospheric Pressure Plasma Polymerised Primer to Promote Adhesion of Silicones

By combining a liquid primer and a plasma jet system, a new route to improved adhesion on various substrates has been developed. The liquid primer is introduced as an aerosol into a plasma jet and the resultant active species are deposited as a polymer coating on adjacent surfaces. Careful control of the plasma parameters produced a dry polymerised coating with functional chemistry designed to enhance the adhesion of silicone sealants to two substrates. This paper describes the surface chemistry and adhesion properties of various coatings on both a plastic and a metal substrate. Selected surface analysis techniques were coupled to both wet and dry adhesion testing to characterise the factors that control adhesion within the system. Mechanical testing indicates that adhesion was improved by several orders of magnitude.

Chapter 14 – Fundamental aspects of adhesion technology in silicones

Publisher Summary This chapter reviews the general structures and properties of silicone polymers. It describes the cross linking chemistry and the properties of the cross linked networks. It then discusses the promotion of adhesive and cohesive strength. The buildup of adhesion and the loss of adhesive strength are explained in the light of the fundamental theories of adhesion. The chapter illustrates the use of silicones in various adhesion applications and leads to the design of specific adhesive and sealant products. The surface of the substrate, the silicone/substrate interface, and the bulk properties of silicones play significant and influential roles that affect practical adhesion and the performance of the silicone. The design of silicone adhesives, sealants, coatings, encapsulants, or any products where adhesion property is needed requires the development chemist to have a thorough understanding of both silicone chemistry and adhesion phenomena. The chapter presents a detailed review of the theories that are proposed for the mechanisms of adhesion. The various theories underlying each mechanism is briefly outlined and qualitatively illustrated in the chapter with specific examples.

Surface Analysis of Silicones

As many of the desirable performance differences of silicones are related to their surface properties, it is important to be able analyze their surfaces effectively. This chapter presents an overview of key surface analysis techniques that can provide information on the surface morphology, chemical composition and surface physical properties of silicone materials. These techniques are X-ray photoelectron spectroscopy, secondary ion mass spectrometry, scanning electron microscopy and scanning probe microscopy. Both fundamentals and applications to the analysis of silicones are covered. It is evident from a consideration of key examples that in many cases it is a combination of these analytical techniques that provides a clearer picture of the surface properties of silicones.