PhD Student
Member of the GRK2516
Group: Prof. Sebastien Seiffert, JGU Chemistry
Contact: E-mail, Web

Research Project Area D: Microgels – Experiments
Core-shell interfacial interpenetration control forms microgels with switchable elasticity

Thermo-responsive gels can controllably swell and deswell via a change of the surrounding temperature. These transitions change the elastic and Young’s moduli of the gels, as well as their adhesiveness. In order to decouple these two effects core-shell particles with a thermo-responsive core and a thermo-insensitive shell are synthesized, thereby maintaining the advantages of a thermo-responsive gel while the adhesiveness of the particle remains constant. For the creation of the core-shell particles, droplet based microfluidics are used. In a first step the thermo-responsive cores (Fig. 1, orange circles) made of poly(N-isopropylacrylamide) (pNIPAAm) with a size of around 120 μm in diameter are synthesized, as well as the thermo-insensitive shell polymer made of polyacrylamide. In a second step the thermo-responsive cores and an aqueous solution of the thermo-insensitive shell polymer are used in a droplet based microfluidic setup seen in Fig. 1 c) to create the core-shell particles. The interconnection of the core and the shell is determined by the time elapsed until the core-shell droplet is exposed to UV-light. Up until the point of irradiation the uncrosslinked shell polymer can interpenetrate into the core. UV exposure almost instantly after the creation of the core-shell droplet results in core-shell particles with a negligible interconnection between the two, as can be seen in Fig. 1a). If UV exposure is delayed, the uncrosslinked thermo-insensitive shell polymer will interpenetrate into the core creating a more pronounced interconnection between the core and shell (Fig. 1 b). Depending on the interconnection between the core and the shell the core-shell particles Young’s module changes. In the case of negligible interconnections between the core and shell the core shrinking results in empty space into which the shell polymer can swell, thereby decreasing the Young’s modulus. If however the core is interconnected with the shell the core shrinking will pull on the shell polymer as well resulting in an increase of the Young’s modulus (Fig. 1 a,b).

Fig. 1(a) Increasing the temperature leads to shrinkage of the thermo-sensitive core without pulling the shell. The shell swells into the free volume, thereby decreasing the Young‘s modulus. Due to the interconnection of the core and shell in (b) the shrinking of the core also leads to a shrinking of the shell, leading to an increase of the Young‘s modulus. (c) Schematic of the microfluidic setup used in the synthesis of the core-shell particles with a thermo-sensitive core and a non-thermo-sensitive shell.