Jude Ann Vishnu

PhD Student
Member of the GRK2516
Group: Prof. Friederike Schmid, JGU Physics
Contact: E-mail

Research Project Area D: Microgels – Theory

My research focuses on studying smart polymer gels, which are polymer-gels that respond to an external stimuli like change in pH, temperature or irradiation of light. We focus on two such systems, the thermo-sensitive core-shell microgels and the light driven Feringa gels.
Shell polymer diffusion in core-shell microgels: Core-shell microgels are polymeric particles consisting of a dense core and a soft shell that can be synthesized using various methods such as microfluidic techniques or emulsion polymerization. In our particular case the core is made up of a thermo-sensitive material and hence can undergo a volume phase transition under the change of temperature. Here the shell is just dragged along with core depending on the degree of connectivity between the two phases. These systems prove beneficial in several applications in contrast to the normal thermo-sensitive gels which undergo a change in both adhesiveness and gel-elasticity as temperature changes. Although such particles have been synthesised, no studies have been done to learn how to control the extend of core-shell connectivity. We use coarse grained MD simulation to understand core-shell inter-penetration and the extend of control we can have. We find that there is a direct relationship between concentration of shell-polymers and core-shell connectivity. Further analysis near equilibrium shows how the chains orient near the interface and its effect on the components of diffusion constant. We also see evidence of percolation transition within the system and use cluster analysis to prove this. Finally we have formulated a capillary wave theory for polymer-gel interface and verified it using the simulation data.
Light driven molecular machines: The research group of the Nobel laureate Ben Feringa were the first to produce uni-directionaly rotating light driven molecular motors. Recent experimental work has incorporated these molecules into a polymer matrix creating the Feringa Gels, and thus utilizing the cooperative motion of these molecules to do mechanical work. These gels have potential applications in various fields, such as drug delivery, tissue engineering, and soft robotics. Our collaborators in the Andreas Walther group studies such a system by varying the arm length, side chains and end groups to understand its effect on volume contraction of the gel. We aim to support their research by developing a coarse grained model for the uni-directional rotors and incorporating these to the already existing model for polymer gels used in our previous research. As a first step we study these system by varying the polymer-strand length. We see that volume contraction ratio’s saturates independent of strand-length. We also calculate the work done by the molecular machine which also seem to be affected in a similar fashion. Finally we study the entanglements arising in the system by looking into Gaussian linking number and demonstrate the effect of strand-length on the degree of entanglement.

Fig. a Diffusive interpenetration study: A gel slab (orange) is sandwiched between free polymer
chains (green). The chains permeate into the slab over time.

Fig. b Coarse grained representation of a molecular motor, depicting the four stages of a rotation cycle.