Exploring the adhesive mechanics of single polymers

The physics of adhesion and stiction of synthetic biopolymers such as polyisocyanides is of great interest for the study of biological adhesion and the development of nanoelectronics and composites. Peeling long stiff molecules from substrates involves a strong coupling between elasticity, friction, adhesive and entropic forces. These forces can be measured with an atomic force microscope (AFM) which is commonly used for measuring the mechanical properties of cells, proteins and polymers by pushing or pulling at surfaces or molecules.

In this project we want to measure desorption of a variety of polyisocyanides under different conditions. In order to peel the polymer from the surface it has to be attached to the AFM tip. The simplest way to achieve this is by probing a surface with loose polymers and wait until one adsorbs strongly to the tip. Although this method offers limited control, it was successfully applied in a proof of principle study (figure 1).

Figure 1. (a) Schematic representation of the setup in which a polymer is desorbed form a solid substrate. (b) Analyzed force curve. (c) Length of desorbed polymers vs. curve number showing grouped events. (d) Distribution of the desorption forces.

We want to start the project by further investigating the desorption of different polyisocyanides under various conditions. The next step will be to identify polymers based on their desorption forces and use this to map the composition of block copolymers and other compounds. During this project, the student will learn several techniques including operating an AFM at an advanced level, polymer and surface chemistry, programming and data analysis.