Temperature sensitive underwater glues

Bsc/Msc thesis -Synthesis of temperature sensitive, charged polymers

Ilse van Hees, Anton Hofman, Marleen Kamperman (Physical Chemistry and Soft Matter, PCC)

Underwater adhesion remains a challenging task to humans, while nature has already found an answer to this problem. Sandcastle worms (figure 1 left) are small marine organisms that build protective shells from sand grains and pieces of shell found in their surroundings. Analysis has revealed that the adhesive proteins of the sandcastle worms contain high amounts of hydrophobic and charged amino acids. For mimicking these underwater adhesives, we use two oppositely charged block copolymers that are functionalized with temperature sensitive blocks (TSB) ( figure 1 middle A). Oppositely charged polymers attract each other, and can phase separate from water upon mixing in the right conditions (figure 1 right), resulting in water insoluble complex coacervates. However, a glue also needs to set, or harden. This is obtained by introducing the TSB, that is water soluble at room temperature, but water insoluble at high temperature. Upon increasing the temperature, the TSB will form domains in the complex coacervates that form cross-links which strengthen the material (figure 1 middle B).

In this thesis you will synthesize block-copolymers using reversible addition chain transfer (RAFT) polymerization. During the polymerization, a RAFT-agent controls the radical concentration leading to polymers with a monodisperse distribution, and a well-controlled length. Some of these RAFT-agents are commercially available, but for making triblock copolymers in two steps (figure 1 middle A) divalent RAFT-agents are needed, which are synthesized in our lab as well.

BSc/MSc thesis – Analysis of temperature sensitive underwater glues

Ilse van Hees, Anton Hofman, Marleen Kamperman (Physical Chemistry and Soft Matter, PCC)

Underwater adhesion remains a challenging task to humans, while nature has already found an answer to this problem. Sandcastle worms (left figure) are small marine organisms that build protective shells from sand grains and pieces of shell found in their surroundings. Analysis has revealed that the adhesive proteins of the sandcastle worms contain high amounts of hydrophobic and charged amino acids. For mimicking these underwater adhesives, we use two oppositely charged block copolymers that are functionalized with temperature sensitive blocks (TSB) (figure 1 middle A).

Oppositely charged polymers attract each other, and can phase separate from water upon mixing in the right conditions (figure 1 right), resulting in water insoluble complex coacervates. However, a glue also needs to set, or harden. This is obtained by introducing the TSB, that is water soluble at room temperature, but water insoluble at high temperature. Upon increasing the temperature, the TSB will form domains in the complex coacervates that form cross-links which strengthen the material (figure 1 middle B).

In this thesis you will analyse underwater adhesives by rheology, adhesion testing, or light scattering techniques. Rheology is used to investigate the flow behaviour of the glue both at room and elevated temperatures. The flow behaviour is important for obtaining an optimum contact area with the surface, without flowing away. Furthermore, we are curious for the effect of different block lengths and ratios, salt concentrations and temperatures on the adhesive strength.

MSc thesis – SCF modelling of PNIPAM functionalized polyelectrolyte micelles

Ilse van Hees, Frans Leermakers, Marleen Kamperman (Physical Chemistry and Soft Matter, PCC)

Underwater adhesion remains a challenging task to humans, while nature has already found an answer to this problem. Sandcastle worms (figure 1 left) are small marine organisms that build protective shells from sand grains and pieces of shell found in their surroundings. The adhesive proteins of the sandcastle worms contain high amounts of hydrophobic and charged amino acids. For mimicking these underwater adhesives, we are using two oppositely charged block copolymers (figure 2), cationic (figure 2A, red) poly-[N-isopropylacrylamide]-b-poly[dimethylaminoethylmethacrylate] and anionic (figure 2A, blue) PNIPAM-b-poly[acrylic acid]-b-PNIPAM, where PNIPAM mimics the hydrophobic block. In dilute conditions, mixing of these polymers results in the formation of micelles. At low salt concentrations, complex coacervate core micelles (C3M) (figure 2B), with a water soluble PNIPAM shell and a water insoluble polyelectrolyte core, can be formed. At high salt, the micelles are inverted into PNIPAM cored micelles (PCM) (figure 2C) with a water soluble polyelectrolyte shell. This conversion happens when the polyelectrolyte charges are screened by the salt, preventing complexation between the opposite charges, while the PNIPAM becomes water insoluble because of a salting out effect. Also, when increasing the temperature, the micelles show a salt dependent phase separation from aqueous solution. In this thesis, we are using self-consistent field (SCF) modelling to obtain details on the interactions between the solvent and the polymer, between the polyelectrolytes, and between the different blocks of the polymer. This information will provide us with a better physical understanding of the origin of the micelle behaviour.