Effect of atmosphere on reductions in the glass transition of thin polystyrene films

We have used nulling ellipsometry to measure the glass transition temperature, T g , of thin films of polystyrene in ambient, dry nitrogen, and vacuum environments. For all environments, the measured T g values decrease with decreasing film thickness in a way that is quantitatively similar to previously reported studies in ambient conditions. These results provide strong reinforcement of previous conclusions that such reduced T g values are an intrinsic property of the confined material. Furthermore, the results are in contrast to recent reports which suggest that the T g reductions measured by many researchers are the results of artifacts (i.e. degradation of the polymer due to annealing in ambient conditions, or moisture content)

Adhesion and membrane tension of single vesicles and living cells using a micropipette-based technique

The fundamental study of the adhesion of cells to each other or to a substrate is a key research topic in cellular biophysics because cell adhesion is important to many biological processes. We report on the adhesion of a model cell, a liposome, and a living HeLa cell to a substrate measured with a novel experimental technique. The cells are held at the end of a micropipette mounted on a micromanipulator and brought into contact with a surface. The adhesion energy and membrane tension are measured directly using the deflection of the micropipette when binding or unbinding the cell from the substrate. Since the force applied on the cells is known throughout the experiment, the technique presented enables the measurement of dynamics such as changes in the adhesion, elasticity, and membrane tension with time

Measurement of adhesion energies and Young's modulus in thin polymer films using a novel axi-symmetric peel test geometry

We present a novel method of probing adhesion energies of solids, particularly polymers. This method uses the axi-symmetric deformation of a thin spincast polymer membrane brought into contact with a flat substrate to probe the work of adhesion. The use of a thin membrane minimizes uncertainty in the radius of contact, while the use of spincast films provides very smooth surfaces by means of a very simple method. The experimental profile of the deformed membrane shows good agreement with the expected logarithmic profile. The experimental setup enables the measurement of Young's modulus and the solid-solid work of adhesion for thin films. The value obtained for Young's modulus of polystyrene (PS) was found to be in agreement with other conventional measurement techniques. In addition, measurement of the work of adhesion at the PS/silicon oxide interface was possible. The apparatus is well suited to studying the dependence of Young's modulus, work of adhesion and fracture energy on membrane thickness, temperature, pulling rate, and ageing of the interface, and can readily be modified to study biologically relevant samples

Substrate Remote Control of Polymer Film Surface Mobility

Polymer segments at the surface of glassy polymer films remain mobile at temperatures below the glass transition temperature, Tg. This mobility, which is usually attributed to the access to a larger free volume by segments at the surface, opens pathways for polymer surface structuration by the effect of a destabilizing force. By studying the destabilization of polystyrene films under the influence of ions dissolved in degassed water at temperatures well below Tg, we have observed that this mobility can be strongly affected by a substrate buried down distances of the order of the chain size below the film surface. This effect is particularly important if there is a strong interaction between the polymer and the substrate or in the presence of pinning points for the polymer chains. These results can be qualitatively interpreted in terms of the sliding model for Tg reduction in thin polymer films. This effect allows remotely controlling the structuration of the polymer surface