Fundamental Properties of Polymers

Left, (from Publication 88) a plot of the heat capacity of silk fibroin measured with DSC (heavy black line) with theoretical calculations of the constituent amino acids (dashed lines). The heat capacity of a material is a fundamental property that is dependent on the specific molecular components. Right, polarized optical microscope image of crystal spherulites in crystalline poly(vinylidene fluoride). Spherulite formation and growth contributes to the overall crystallinity of a polymeric material, and has a large role in the macroscopic properties of the material.

Understanding and describing fundamental polymer properties is one of the main research directions being pursued by the Cebe Research Group. Polymers serve as the basis of a multitude of materials that are commonplace in our everyday lives. The rubber of your car tires is a polymeric material. Your water bottle is made of a polymer. Most of your clothes are made of polymer textiles. Even you are made of polymers, from the DNA in your cells to the cartilage in your joints and everything in between! That is why it is crucial to have a fundamental understanding of how polymers behave.

We are interested in understanding transition phenomena in polymer systems like the glass transition and crystallization/melting, and the role they play in the overall material properties. The glass transition is a transition from a glassy state to a rubbery state without the appearance or disappearance of long range molecular ordering. Crystallization is a transition whereby a material acquires long range molecular ordering (the reverse process is melting). Both transitions can be thermally activated, making them perfect candidates to investigate using thermal analysis and calorimetry.  We investigate both semi-crystalline polymers that partially crystallize, and fully amorphous polymers that do not crystallize in the Cebe Research Group. For semi-crystalline systems we can investigate the effects the crystals have on the system. Not all the material will crystallize in these systems, leaving amorphous domains that are sandwiched between polymer crystals. These crystal structures and interphase regions can be resolved using X-ray diffraction. In addition to this, differential scanning calorimetry (DSC) can be used to quantify the kinetics of crystallization as well as the confinement of the amorphous fraction in the materials. Since amorphous polymer systems will not crystallize, we are interested in investigating the dynamics of the glass transition, using DSC as well as dielectric relaxation spectroscopy. These tools let us see the influence molecular side groups have on the glass transition, and the role the glass transition has in phenomena such as conductivity.


Current Research Interests: Properties of amorphous polyzwitterions, crystallization kinetics in polymorphic systems,  heterogeneous vs homogeneous crystal nucleation in electrospun fibers