POLYFLUORENE

Conjugated Polyelectrolytes

Conjugated polyelectrolytes possess two important components: pi-conjugated backbones and water-soluble ionic side chains. This interesting class of materials combine the properties of polyelectrolytes with conjugated polymers. Thus the outcome is a material that can coordinate electrostatic forces and exhibit interesting optical and electronic properties.

In our project line, we use alkyl-substituted polyfluorenes due to their highly efficient electroluminescent property. We design the side chains at the level of the conjugated repeat unit and synthesize the polymer in our labs. The structure of their side chains strongly influences the conformation of polymer backbone thus changes the photophysical properties.We investigate the structural and photophysical changes of an anionic polyfluorene upon coating it with a genetically engineered cationic protein. 

In this ongoing project, different combinations of side chain lengths as well as different cationic protein polymers are being studied by using optical methods such as UV-Vis and Fluorescence Spectroscopy, and by using scattering methods such as dynamic light scattering and small angle x-ray scattering. 

Micromechanics of Protein Polymer Gel Network

The nature of the gelation transition in irreversible systems, such as colloidal gels or chemically cross-linked polymer networks, is well established; it typically proceeds as a percolation transition characterised by critical scaling of the elasticity. However, it remains unclear how such a transition is affected by reversibility of the nodes in the network; what happens to the nature of the gelation transition when the nodes can continuously break and reform at new locations? 

Thermo-switchable network forming, collagen-inspired telechelic polypeptides consist of a hydrophilic random coil-like middle block and collagen-like (Pro-Gly-Pro)9 end blocks (See the image on the right (a)). Upon cooling, end blocks assemble into well-defined triple helical nodes and form a gel ((b)& (c))[1]. 

Based on the Brownian motion ofmicron sized tracers in a medium, both the mean-square displacement (MSD) of single particles, so called 1-point microrheology (1P) can be obtained. By using this method, we studied the melting and gelation behavior of well-defined collagen-inspired designer biopolymers expressed by the transgenic yeast P. Pastoris.  We apply the method of time-cure superposition of the mean-square displacement of tracer beads embedded in the biopolymer matrix to study the kinetics and thermodynamics of approaching the gel point from both the liquid and the solid side. The melting point, gel point and critical relaxation exponents are determined from the shift factors of the mean-square displacement and we discuss the use of dynamic scaling exponents to correctly determine the critical transition. Critical relaxation exponents obtained for different concentrations in both systems are compared with the currently existing dynamic models in literature.

Complete study can be read via this link:  Equivalent pathways in melting and gelation of well-defined biopolymer networks on Biomacromolecules 2014, Nov 14 DOI: 10.1021/bm5015014