Yvonne A. Akpalu Assistant Professor Physical Polymer Chemistry Cogswell 321 518.276.6648 akpaly@rpi.edu

Prior to joining the faculty at RPI, Dr. Akpalu was a Guest Researcher with Eric J. Amis at the National Institute of Standards and Technology, Gaithersburg, MD. She obtained a Ph. D. in Polymer Science and Engineering in 1998 from the University of Massachusetts at Amherst and a B. A. in Chemistry and Physics from Smith College in 1992. At Rensselaer, she teaches courses in general chemistry, organic chemistry and polymer chemistry. In 1999, she was awarded the Paul Schmidt Award for her work in small-angle x-ray scattering.

Elucidating the Structure and Function of Macromolecules

Our interest in this area is on biomacromolecules and synthetic macromolecules (polymers) with applications in coatings, renewable energy and in medicine.

Solution structure of macromolecules

Many biological functions depend on the assembly of molecules into networks, complexes or crystals. To understand the detailed molecular mechanism underlying the structure and function of macromolecules involves characterizing structure on sizes that range from a few nanometers to several microns. Using a seven angle static light scattering instrument available in our laboratory, synchrotron x-ray scattering (Brookhaven National Laboratory (BNL), Beamline X6A) and neutron scattering (NIST Center for Neutron Research) we are characterizing the size, shape, conformation and aggregation behavior of macromolecules as a function solution conditions (e.g., pH, salt, macromolecule concentration). This approach is also being used to understand chain conformation, aggregation behavior of polymer exhange membranes for fuel cells and polysaccharide metal ion complexes for medical imaging an sensing.

Structure of polymer films

In the solid state, the structure of polymer films has important technological and scientific ramifications. Interest in polymer films range from applications such as optics, automobile manufacturing, biomedical devices, electronics, and food packing to fundamental studies of the structure and properties of polymeric materials. Since the properties (e.g., optical, physical, mechanical and electrical) of these materials largely depend on their structure, understanding the mechanisms that govern structure and its formation is of major importance.

At RPI my main focus is to facilitate the rapid determination of structural and thermodynamic variables for developing fundamental structure-property correlations for multicomponent polymer blends and composites. To this end we have constructed a small-angle light scattering (SALS) instrument with unique capabilitie for measuring absolute light scattering intensities consistent with model predictions for semicrystalline polymers [1]. Quantitative characterization of nanocomposite structure is also possible because SALS scattering from nanoparticles and polymer crystals can be resolved and separated [2].

We use an integrated SALS and synchrotron x-ray scattering (BNL, Beamline X10A) approach [3] to determine structural and thermodynamic variables for materials of interest. Several techniques are used to augment the information obtained from scattering measurements. These include: differential scanning calorimetry, atomic force, electron and optical microscopy. We also perform measurements to correlate mechanical, optical and electrical properties with the structure and morphology.

*Denotes graduate students

1. Ying Li*, Youyu Lin* and Yvonne A. Akpalu, “Determining Absolute Small-Angle Light Scattering Intensities for Semicrystalline Polymers, Journal of Polymer Science Polymer Physics”, in press
   
2. Dongling Ma*, Yvonne A. Akpalu, Ying Li*, Richard W. Siegel and Linda S. Schadler, “Effect of Titania Nanoparticles on the Morphology of Low Density Polyethylene”, Journal of Polymer Science Part B Polymer Physics, 2005, 43, 488-497.
   
3. Ying Li* and Yvonne A. Akpalu, “Probing the melting behavior of a homogeneous ethylene/1-hexene copolymer by small-angle light scattering”, Macromolecules, 2004, 37, 7265-7277.
   
4. Yvonne A. Akpalu and Youyu Lin*,“Multivariable structural characterization of semicrystalline polymer blends by small-angle light scattering”, Journal of Polymer Science Polymer Physics Edition, 2002, 40, 2714 – 2727.
   
5. Yvonne A. Akpalu, Alamgir Karim, Sushil Sajita and Nitash Balsara, "Suppression of lateral phase separation in polyolefin thin blend films", Macromolecules, 2001, 34, 1720-1729.
   
6. Franziska Groehn, Barry J. Bauer, Yvonne A. Akpalu, Catheryn L. Jackson, Eric J. Amis, "Dendrimers as nanotemplates for the formation of inorganic colloids", Macromolecules, 2000, 33: 6042-6050.
   
7. Yvonne A. Akpalu and Eric J. Amis, "Effect of polydispersity on the evolution of density fluctuations to lamellar crystals in linear polyethylene", Journal of Chemical Physics, 2000, 113: 392-403.
   
8. Yvonne A. Akpalu and Eric J. Amis, "Evolution of density fluctuations to lamellar crystals in linear polyethylene", Journal of Chemical Physics,1999, 111: 8686-8695.
   
9. Y. Akpalu, L. Kielhorn, B.S. Hsiao, R.S. Stein, T.P. Russell, J. van Egmond, and M. Muthukumar, "An investigation of the early stages of structure development during isothermal melt crystallization of homogeneous copolymers of ethylene and 1-octene: Time-resolved synchrotron x-ray and SALS", Macromolecules 1999, 32: 765-770.