(4cy) Polymer-Based ‘Soft' Materials: Coacervate Assemblies, Carbon Nanotube Nanocomposites

The intelligent use of processes such as self-assembly, combined with the ability to manipulate the chemical structure of polymers, can lead to a wide array of materials. Such functional materials could be a solution to many of the challenges that the modern world faces, including engineering improved biomedical devices and strategies for renewable energy. During this poster session I will highlight examples from my graduate and postdoctoral research that demonstrate how these two elements can be utilized for the development of novel polymer-based soft materials. I will also describe how based on past experience I plan to create an independent research program at the interface of chemistry and materials engineering.

During my doctoral studies in the groups of Professor Nikos Hadjichristidis and Professor Jimmy Mays (at the Universities of Athens and Tennessee respectively) my attention was focused in the design of polymer-carbon nanotube (CNT) nanocomposites. These unique materials have great potentials as they combine the physicochemical properties of polymers and the extraordinary properties of the CNTs, such as mechanical strength and electrical conductivity. My research was centered on the development of a CNT polymer functionalization strategy that helps circumvent CNTs’ inherent insolubility, and considerably widens the scope of nanocomposite materials that can be produced. The strategy involved covalent attachment of substituted benzocyclobutenes to CNTs. With a judicious choice of substitution, initiators for most popular polymerization techniques were attached onto the CNT surface.^1,2 Complete control over grafting percentage of initiator and surface-initiated polymerizations allowed synthesis of nanocomposite materials with desired compositions, which is essential for any application. The resulting nanocomposite materials exhibited improved mechanical and thermal properties when compared to pure polymers.³

In 2010 I accepted a postdoctoral scholar position from the Bioengineering Department of the University of California Berkeley (in the group of Professor Matthew Tirrell). There I initiated a project aimed at exploring a liquid-liquid phase separation phenomenon, referred to as complex coacervation. Using polypeptides as a model system I studied many aspects of complex coacervation through a number of collaborations. I identified the external parameters that affect coacervation,⁴ explored the thermodynamics of coacervate formation,⁵ and studied the rheological⁶ and interfacial properties⁷of polypeptide coacervates. Building on this work I am currently exploring, at the Institute for Molecular Engineering of the University of Chicago, how complex coacervation can be used for the development of other polyelectrolyte self-assembly structures. More complex molecular design can be utilized, wherein polyelectrolyte domains are connected to neutral polymer blocks. These neutral domains stabilize microphase separation of the coacervate phase. Mixing of oppositely charged block-copolymers results in the formation of new self-assembly structures such as micelles or hydrogels.

My research is driven by a strong curiosity to develop and study new materials and target specific applications by bridging knowledge from various disciplines (i.e. chemistry, materials, physics, bioengineering). In the past few years I have successfully organized and collaborated on various research efforts that have resulted in a number of peer-reviewed publications (including 10 first author and 4 corresponding author articles). By working at the interface of different subjects areas, and with the use of my expertise in chemistry, polymers and material design I can make unique and lasting contributions to chemistry and material engineering.

Selected-Related References:

1.  Priftis D., Sakellariou G., Baskaran D., Mays J.W., Hadjichristidis N., ‘Polymer Grafted Janus Multi-Walled Carbon Nanotubes.’ Soft Matter, 2009, 5, 4272-4278.

2.  Priftis D., Petzetakis N., Sakellariou G., Pitsikalis M., Baskaran D., Mays J. M., Hadjichristidis N., ‘Surface initiated titanium mediated coordination from catalyst-functionalized single and multi-walled carbon nanotubes.’ Macromolecules, 2009, 42, 3340-3346.

3.  Priftis D., Sakellariou G., Lorenzo A. T., Müller A. J., Hadjichristidis N., ‘Surface modification of multi-walled carbon nanotubes with biocompatible polymers via ring opening and living anionic surface initiated polymerization. Kinetics and crystallization behaviour.’J. Polym. Sci. Part A: Polym. Chem, 2009, 47, 4379-4390.

4.  Priftis D.,* Tirrell M., ‘Phase Behaviour and Complex Coacervation of Aqueous Polypeptide Solutions.’Soft Mater 2012, 8, 9396-9405.

5.  Priftis D., Farina R., Tirrell M., ‘Interfacial Energy of Polypeptide Complex Coacervates Measured via Capillary Adhesion.’ Langmuir 2012, 28,8721-8729.

6.  Priftis D.,* Megley K., Laugel N., Tirrell M., ‘Phase Behavior and Complex Coacervation of Polyethyleneimine /Polypeptide Solutions.’J. of Colloid and Interface Science 2013, 398, 39-50.

7.  Priftis D.,* Laugel N., Tirrell M., ‘Thermodynamic Characterization of Polypeptide Complex Coacervation.’ Langmuir 2012, 28, 15947-15957.

*Corresponding author