Penn State Chemical Engineering Faculty, Janna K. Maranas Research

Faculty

Introduction

The Maranas group has state-of the-art computational and experimental programs. As a student in the Maranas group, this offers you the chance to become proficient in two main research tools: molecular simulation and neutron scattering. Computational work is done in our computational lab at Penn State. Experiments in our group require a nuclear reactor - and thus are done off site at the National Institute for Standards & Technology [NIST] in Gaithersburg, MD. In the paragraphs below, I discuss our main interests and methodology.

Computation and Nanoscience

Does the shape of a nanoparticle influence the way its atoms pack together? This question would be extremely difficult to answer using experiments. Making particles on the order of 1-2 nm is difficult to begin with, and making controlled shapes would be even more so. What experiment would we use to assess the molecular arrangement of the atoms on the surface and in the interior of the particle? In the Maranas group we are using molecular simulation to answer this type of question. Molecular simulation is a means to sample various properties of a collection of atoms or molecules on a computer.

It allows us to calculate properties difficult to assess experimentally. The realm of nanoscience is easy for simulations. We made nanoparticles of boron oxide - the main ingredient in pyrex glass - in various shapes: sphere, cube, rectangles of various dimensions. We then analyzed the packing of atoms in these shapes and found that it varies quite significantly between particles. Why is this important? Nanoscience is strongly influenced by surfaces because the surface to volume ratio of such small objects is so large. In our case, the arrangement of atoms at the surface was quite different between shapes - which could completely alter the behavior of any device formed with the particles.

Simulations such as these will be extremely important as nanoscience is developed. Consider a polymer matrix [imagine a plastic milk carton for example] that is embedded with particles like those described above. This could completely alter the mechanical properties of the polymer. Some people even think it could make that polymer as strong as steel - but it would still be light and flexible. There are many choices to be made about the nanofiller - what should it be made of? What size should it be? What shape? It will be nearly impossible to test all of the possibilities in the lab. It is difficult and time consuming to make these materials. Computation can and will be used as a screening tool by companies producing these products - to identify the most promising candidates for additional study.

Nuetron scattering and polymer motion

Why would the properties of a polymer filled with nanosize particles change so dramatically? One reason is that the particles influence the motion of the chains. I'm not talking about diffusion - this motion involves portions of a chain backbone twisting or bending. These motions influence the physical properties of the polymer dramatically. If they are active, the polymer is flexible and is used for things like plastic bags. If they are not, the polymer is rigid - more like the outside of a CD case. In our group we use dynamic neutron scattering to study these motions in polymers. Neutron scattering is a powerful experimental technique because various molecules or parts of molecules can be "hidden" by replacing their hydrogen atoms with deuterium. It just so happens that neutrons scatter far more [about 80 times stronger] from hydrogen than from deuterium. In our group we are investigating what happens to these motions in blends, or mixtures, of polymers. How does the addition of polymer A affect the motion of polymer B? The answer can be found by hiding polymer A, so that the experiment yields only the motion of polymer B in the blend.

Dr. Maranas and two group members at the High Flux Backscattering Spectrometer at N.I.S.T.

The Neutron Spin Echo Spectrometer at N.I.S.T.

Why worry about polymer motion in blends?
Well, in order to form polymers into objects, they must be heated to a temperature high enough that these motions are active. Otherwise, the material cannot be processed. Consider the polymer - poly(methyl methacrylate) or PMMA for short. You may know PMMA as plexiglass. In order to make something from PMMA, it must be heated to above 220 ^oC. But at around 240 ^oC, PMMA begins to degrade. This leaves only a 20 degree window in which to operate while processing. If a second polymer was added to PMMA that lowers the temperature to which it must be heated - in other words activating motion at lower temperatures - the 220 ^oC could be shifted downwards thus widening the temperature window for processing.