Ian Clancy

Pattern formation induced by an electric field in a polymer-air-polymer thin film system†

Strong electric fields produce forces that can overcome the surface tension in thin liquid polymer films and in this way induce an instability of the free surface of the film, that triggers the formation of structures on a micrometer length scale. Here, we study experimentally a polymer–air–polymer system for several combinations of polymer films. These results are accompanied by theoretical considerations based on coupled long-wave time evolution equations for the two free surface profiles. The linear stability and nonlinear time evolution are investigated and compared to the experimental findings. The prediction that the instability always evolves through a mirror mode that couples the two surfaces in an anti-phase manner agrees well with the experimental results. The model describes well the linear (early stage) evolution of the instability. In the non-linear (later stage) evolution, topographical differences in the instability pattern occur if the mobilities of the two layers significantly differ and an unpredicted acceleration of growth is seen in thinner less mobile films. Possible reasons for the mismatch are discussed.

Stability of Ultrathin Nanocomposite Polymer Films Controlled by the Embedding of Gold Nanoparticles

Thin and ultrathin polymer films combined with nanoparticles (NPs) are of significant interest as they are used in a host of industrial applications. In this paper we describe the stability of such films (hpoly ≤ 30 nm) to dewetting, specifically, how the development of a spinodal instability in a composite NP-polymer layer is controlled by the embedding of Au NPs. At working temperatures (T = 170 °C) above the polymer glass transition temperature (Tg ≈ 100 °C) the absence of Au NPs leads to film rupture by nucleation dewetting, while their presence over a large surface area enhances the development of a spinodal instability without destroying the film continuity. When the NPs embed, the surface undulations are suppressed. The dynamics change from an unstable to a stable state, and the thin composite NP-polymer layer returns to a flat configuration, while the wavelength of the pattern remains constant. Moreover, we demonstrate from a thermodynamic perspective that NPs will remain on the surface or embed in the polymer film depending on their free energy, which is determined by the NP interactions with the underlying polymer, the native SiOx layer, and the Si substrate.

Modelling Dual-carriageway Traffic Behaviour as a Complex System: a Proposal for Discussion

This paper outlines the initial developmental stage of a microscopic traffic system model incorporating driver behaviour. The model uses exponential and Gaussian distributions to assign each car its starting time headway and velocity characteristics respectively as expected in real-world traffic [1,2]. Each car may be in one of three distinct regimes (time headway windows), depending upon how close in time the car is to the car in front of it. These time headway windows are developed from previous work carried out by the Centre for Traffic Simulation at the Royal Institute of Technology, Sweden, and correlate with an actual traffic study [3]. The development for assigning time headways and velocities is complete and velocity and position data sets relative to time for both the single lane and multiple lanes for small numbers of cars have also been achieved.