Application of mean-field theory to the spin casting of polystyrene and poly(methyl methacrylate) blend films from toluene

The Flory-Huggins free energy of mixing is shown to be appropriate for the analysis of the temporal evolution of a ternary blend of polystyrene and poly (methyl methacrylate) during spin-coating from toluene using an in-situ light scattering technique. For the range of concentrations studied, both the onset of film instability and the observation of a scattering ring occur at the same toluene volume fraction. The success of Flory-Huggins theory indicates that polymer chains retain random walk characteristics during spin-coating. It is also concluded that the thermodynamics of phase separation during film formation is independent of the initial solvent concentration

From spin coating to roll-to-roll: investigating the challenge of upscaling lead halide perovskite solar cells

Spin coating, typically used to achieve nanometre thick films, is the established method for depositing perovskite precursors at lab scale for use in solar cells. This study investigates the dynamics of spin coating perovskite. By combining experimental measurement with a semi-empirical model the evaporation rate of the dimethylformamide solvent during the spin coating of a mixed lead halide precursor is determined to be 1.2 × 10 –8 m/s. When K-bar coating the same precursor the solvent does not significantly evaporate during the deposition process and when this film is crystallised on a hot plate a rough film results which gives a power conversion efficiency (PCE) of less than 2%. By increasing the airflow of the K-bar coated perovskite film during crystallisation to 2.7 × 10 –4 m/s the PCE increases significantly to 8.5% through an improvement in short-circuit current and fill factor

Dynamics of polymer film formation during spin coating

Standard models explaining the spin coating of polymer solutions generally fail to describe the early stages of film formation, when hydrodynamic forces control the solution behavior. Using in situ light scattering alongside theoretical and semi-empirical models, it is shown that inertial forces (which initially cause a vertical gradient in the radial solvent velocity within the film) play a significant role in the rate of thinning of the solution. The development of thickness as a function of time of a solute-free liquid (toluene) and a blend of polystyrene and poly(methyl methacrylate) cast from toluene were fitted to different models as a function of toluene partial pressure. In the case of the formation of the polymer blend film, a concentration-dependent (Huggins) viscosity formula was used to account for changes in viscosity during spin coating. A semi-empirical model is introduced, which permits calculation of the solvent evaporation rate and the temporal evolution of the solute volume fraction and solution viscosity

Seismic Retrofitting of Typical Illinois Bridges by Response Modification

The impact of seismic retrofitting of typical Illinois bridges, via response modification using friction pendulum bearings (FPB), on the state economy is studied. For this purpose, two typical bridges with distinct characteristics were selected by Illinois Department of Transportation (IDOT). The seismic analyses of the bridges revealed that the bearings, wingwalls and substructures are vulnerable and need to be retrofitted. Conventional retrofitting strategies are developed for the bridges and the retrofitting costs are estimated. The same bridges are further studied to develop appropriate techniques for upgrading their seismic capacity using FPB and the seismic analyses are repeated. It is observed that the FPB effectively mitigated the seismic forces and eliminated the need for retrofitting of the substructures of the bridges. This resulted in a considerable reduction in the seismic retrofitting costs of the bridges

Dynamics of polymer film formation during spin coating

\ua9 2014 Author(s).Standard models explaining the spin coating of polymer solutions generally fail to describe the early stages of film formation, when hydrodynamic forces control the solution behavior. Using in situ light scattering alongside theoretical and semi-empirical models, it is shown that inertial forces (which initially cause a vertical gradient in the radial solvent velocity within the film) play a significant role in the rate of thinning of the solution. The development of thickness as a function of time of a solute-free liquid (toluene) and a blend of polystyrene and poly(methyl methacrylate) cast from toluene were fitted to different models as a function of toluene partial pressure. In the case of the formation of the polymer blend film, a concentration-dependent (Huggins) viscosity formula was used to account for changes in viscosity during spin coating. A semi-empirical model is introduced, which permits calculation of the solvent evaporation rate and the temporal evolution of the solute volume fraction and solution viscosity

IImpact of friction pendulum bearings on the seismic retrofitting cost of typical bridges with wall type piers in the state of illinois

The economical efficiency of friction pendulum bearings (FPB) for seismic retrofitting of typical Illinois bridges with wall type piers is studied. A typical bridge with heavy wall piers was carefully selected by Illinois Department of Transportation (IDOT) for the purpose of this study. The seismic analysis of the bridge revealed that the bearings, and substructures of the bridge are vulnerable and need to be retrofitted. A conventional retrofitting strategy is developed for the bridge and the cost of retrofit is estimated. Next, the bridge is further studied to develop appropriate techniques for upgrading its seismic capacity using FPB and the seismic analysis is repeated. It is observed that the FPB effectively mitigated the seismic forces and eliminated the need for retrofitting of the substructures of the bridge