Discovering the Value of Multidisciplinary Approaches to Research: Insights from a Sabbatical

It is NRL policy to maintain a highly competent corps of professional personnel by providing opportunities for employees to keep abreast of advances in their fields. The purpose of the Advanced Graduate Research Program is to permit selected employees to pursue collaborative research in their own or related fields on a full-time basis.

To answer the latter question, I will provide my personal motivation for embarking on this year-long program.

My career with NRL began in May 2000 while a part-time graduate student in computational polymer physics. Although my efforts with NRL were focused on acoustic imagery (Bentrem, 2009b;Bentrem et al., 2006) and sediment classification (Bentrem et al., 2002a(Bentrem et al., , 2006;;Brown et al., 2001;Harris et al., 2008), I completed my doctoral research in simulations for polymer electrocoatings (Bentrem and Pandey, 2005;Bentrem et al., 2000Bentrem et al., , 2002b,c),c). (See Fig. 1). In recent years, I have searched for ways to use my background and expertise in molecular simulations to best serve the missions of both the Marine Geosciences Division and the laboratory as a whole.

Much progress is being made towards understanding the physical properties of geologic sediments in terms of the chemical constituents. However, much remains to be understood regarding the influence of organic matter on mechanical and electrical properties of marine sediments. In particular, how do the polymer components (polysaccharides, biomolecules, etc.) of organic matter affect the flocculation, aggregation, and shear strength of muddy sediment on the seafloor? The Marine Geosciences division is increasing efforts to understand these important issues, which impact Navy interests, such as trafficability, mine burial, and beach morphology, to name a few. Science and Engineering (CBMSE) and their interests in the theory and simulations for polymer systems. In discussions with some CBMSE researchers, we identified areas where my expertise could complement the work they were doing. I was named as an investigator on a proposal to the NRL Nanoscience Institute. The proposal for an innovative type of body armor was one of fifteen selected for presentation before the nanoscience committee, however, it was not selected to go before the Research Advisory Council.

The bond-fluctuation model (BFM) is a computationally efficient simulation method for researching polymer systems at time and length scales not accessible to other methods.

After appropriately assigning the interaction potentials, the BFM has proved successful in reproducing much of the measured polymer structures and dynamics. However, accuracy from the BFM suffers in the highly constrained geometries of dense polymer melts and tightly collapsed chains (as with collapsed PNIPAm globules). I developed an enhancement to the BFM which greatly increased the flexibility in the polymer chains, yet retained the computational efficiency. The resulting polymer coil-globule transition demonstrates the compact collapse (shown in Fig. 2) expected for PNIPAm. This enhanced BFM provides broader capability for the simulation of polymer systems. Colin was taking a computational physics course and asked me for a project idea. He helped me modify the enhanced BFM to simulate a dense polymer melt and analyze the dynamics.

On one occasion, while briefing Wayne and Alina (the PolyRMC directors) on my recent progress at the hallway blackboard, a senior gentleman approached and entered the discussion. His insights into the polymer coil-globule transition research were most welcome. He later visited my office for further discussion on my current simulation technique, and mentioned that years earlier he had worked on polymer simulations with Walter Stockmayer-a well known pioneer in polymer simulations whose research was a forerunner to my current

The second phase of my sabbatical was spent at the Center for Bio/Molecular Science and Engineering in Washington, DC (NRL). I drove to DC with my wife, Amelia, and 3-year-old daughter, Abby, in mid-May 2009 to settle into a modest furnished apartment for a 3-month stay.

A. Micro-and Nano-scale Plastic Spaghetti I continued my work with the center’s senior scientist, and the “nano-Play-Doh group” on the polymerization kinetics in microfluid channels. NRL has developed a microfluidic system with remarkable control of the shape of the microfluid channels. Polymerizing the material in the microfluid channel produces polymer microfibers (Fig. 3) of predetermined shapes.

A potential application for the microfibers is in producing high-strength materials such as FIG. 3 Polymerized microfibers under magnification (Thangawng et al., 2009). body armor. My results for the kinetics of the photopolymerization in the microfluid device were intended to be used as a guide for the design of the apparatus in producing

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