Sticky when wet: Adhesives for wet environments

Ilse van Hees, Aljosha Filippov, Marco Dompe, Anton Hofman, Marleen Kamperman (PCC)

Thesis in polymer science at the laboratory of Physical Chemistry and Soft Matter (PCC), as part of a BSc/MSc in the programs of Molecular Life Sciences or Biotechnology.

Glues are used everywhere, in your shoes, your books or the post-its on your desk. Most glues only stick to dry, clean surfaces and should not get wet before the glue has hardened. But which glue do you use if you want to stick surfaces in a wet environment, like the inside of your body? This research focuses on the development of an adhesive that can be applied and harden in a humid or wet environment. We used the Sandcastle worm, Phragmatopoma californica, as a source of inspiration. Sandcastle worms are small marine organisms that stick pieces of sand together to make a protecting shell while they are underwater, see Fig. 1.

The adhesive proteins from the sandcastle worms have two important properties; some parts of the proteins are hydrophobic and some parts have electrostatic characteristics. We will make 2 types of polymers with an ABA block structure. The A-blocks, grey in Fig. 2, will mimic the hydrophobic parts of the proteins and the B-blocks, red and blue in Fig. 2, will mimic the electrostatic, hydrophilic parts of the adhesive proteins. The difference between the two polymer types will be the charge on the electrostatic B-block which will be either positive, Fig. 2 (b), or negative, Fig. 2 (c).

Fig 1
Fig 1
Fig 2
Fig 2

Mixing of the two types of polymers might result in a nanostructured complex as shown in Fig. 2 (a). There are two types of domains visible in the complex. At first there is a polyelectrolyte domain caused by complex coacervation of the oppositely charged middle blocks, while the second domain in the complex of Fig. 2 (a) originates from aggregation of the hydrophobic blocks. We expect that the combination of these different blocks will lead to materials with interesting mechanical properties.

A thesis in this project can focus on two different topics: a) polymer synthesis or b) material characterization. A synthesis thesis will involve the preparation of polymers using RAFT (reversible addition-fragmentation chain transfer) polymerization. We will focus on the synthesis of ABA polymers with varying block lengths or on different B-block chemistries. A characterization thesis will include studying the phase behaviour of the polymers in various conditions using techniques like light scattering and rheology. Furthermore, we are interested in the self-assembly behaviour of solutions with either one polymer type or both.