Wavefront kinetics of plasma oxidation of polydimethylsiloxane: limits for sub-μm wrinkling.
Soft matter 10:8 (2014) 1155-1166
Abstract:
We investigate the surface plasma oxidation of polydimethylsiloxane (PDMS) elastomers and its implication for the morphologies attainable by wrinkling of glassy-elastomer 'bilayers'. The kinetics of glassy skin formation is found to follow a logarithmic dependence with plasma exposure time t and, for various plasma intensities I, the relevant control variable is shown to be dose (≡I × t). We model the mechanism and kinetics of glassy film formation by plasma oxidation with a frontal propagation coarse-grained model, describing the spatio-temporal evolution of a conversion order parameter (ϕ) orthogonal to the film surface. The model is validated by X-ray reflectivity experiments, which confirm the logarithmic growth and quantify the initial growth of a transient, incomplete, skin layer during the early stage of plasma exposure. Three regimes are identified as (I) induction, (II) formation and (III) propagation with a combination of X-ray and wrinkling experiments. The simultaneous increase in thickness and skin mechanical modulus is found to be responsible for an unexpected minimum wavelength λmin attainable, which depends on critical strain εc and is ultimately limited by mechanical failure of the elastomer (λmin ≃ 140 nm is demonstrated at ε = 200%). We conclude by establishing a 1D surface morphology diagram, in terms of wavelength λ and amplitude A, limitations and capabilities for producing highly ordered (sub-)micropatterns over macroscopic areas using plasma oxidised PDMS under uniaxial strain.Polythiophenes with vinylene linked ortho , meta and para -carborane sidechains
Polymer Chemistry Royal Society of Chemistry (RSC) 5:21 (2014) 6190-6199
Interfacial molecular order of conjugated polymer in P3HT:ZnO bilayer photovoltaics and its impact on device performance
Applied Physics Letters AIP Publishing 103:15 (2013) 153304
Controlling the interaction of light with polymer semiconductors.
Advanced materials (Deerfield Beach, Fla.) 25:35 (2013) 4906-4911
Abstract:
In this study, a generally applicable strategy is described to manipulate the optical properties of a wide range of polymer semiconductors in the solid state. Blending these materials with a non-conjugated, polar polymer matrix is found to be the processing key to a drastic change and red-shift of the absorption characteristics.Paper No 19.2: Large‐Area Printed Transparent Electrodes for Flexible Organic Light‐Emitting Diodes
SID Symposium Digest of Technical Papers Wiley 44:S1 (2013) 282-284