Piezoelectric excitation and acoustic detection of thin film polymer membrane vibrations.

A simple method of measuring the vibrational response of a thin film membrane was developed. Piezoelectric excitation and acoustic detection (using a microphone) allowed the vibrational spectra of thin membranes to be measured in the kHz range. Vibrational frequencies were used to determine Young's modulus in thin (µm) solvent tensioned films of polydimethylsiloxane and to measure tension in ultrathin polystyrene films. Simulations of membrane motion generated vibrational spectra that agreed with the results of experiments for different membrane shapes.

Thickness dependence of telephone cord blister formation in solvent swollen films of polydimethylsiloxane.

The thickness dependence of telephone cord blister formation in thin films of solvent swollen polydimethylsiloxane (PDMS) was studied using a simple imaging setup. Chloroform was deposited on top of PDMS that had been spin coated on to glass slides coated with a thin wax layer. After an initial thickness dependent nucleation time, straight-sided blisters were observed to form on the films. These later developed into sinusoidal telephone cord blisters. Movies of the growing telephone cord blisters were recorded at 200 fps for PDMS films with thickness values in the range 38 < h ≤ 223 µm. Software written in Python was used to analyse the movies and to extract the thickness dependence of the width of the telephone cord blisters as well as the wavelength of the sinusoidal corrugations and the blister growth rates. Data were interpreted in the context of theories of buckling and dynamic fracture mechanics.