2012 Annual Report
1a.Objectives (from AD-416):
Overall project objectives include: Collecting the best available information on the structures within the cotton fiber; Constructing fundamental models of these structures at different size scales; Providing additional fundamental models that have partial surfaces of hydrophobic molecules; and Monitoring moisture movement through the model structure during molecular dynamics simulations. Specific aspects of this work to be carried out at Tulane include development of coarse-grain (or another suitable approach) modeling of the cellulose in cotton fiber and the execution of molecular dynamics studies to show water movement in the model fiber. (Coarse-grain models group several atoms into a “super-atom” to save computer memory and allow greater speed for large systems.)
1b.Approach (from AD-416):
The main feature of this effort will be to construct realistic coarse grain models that will incorporate specific features of cotton fibers that are likely to affect the movement of moisture and to carry out the molecular dynamics simulations that will depict the movement of moisture. Transport of moisture from one side to the other will also be of interest. Suitable computer software for molecular dynamics studies with either atomistic or coarse-grain modeling will be employed, along with specific models of water that are sufficiently realistic. Data will be collected that will permit moving graphics depictions of the water motions.
This project, new in 2009, has separate efforts at Tulane University and at the University of Georgia (the effort detailed in this report). Both groups have substantial expertise in computerized molecular modeling. ARS scientists at Southern Regional Research Center (SRRC)in New Orleans, LA provide the expertise in cotton cellulose and carry out related research as part of their normally funded project. A foundation for this work is the detailed crystal structure of native cellulose. It provides x, y and z coordinates for each of the atoms.
At Tulane University, models of the different sides of nano-sized cellulose crystals were constructed and a model droplet of water was placed on each surface. Then, the model atoms were given motion that corresponds to room temperature (a molecular dynamics simulation), and the spreading of the water over the surfaces was studied. Besides the surfaces that would be found for native cellulose, surfaces were also constructed with varying amounts of methyl groups that replaced the hydroxyl groups. Those methylated surfaces were devised as a start to understanding treatments of cotton fabrics for moisture management. Work continued along those lines in 2010 but a new effort was directed to understanding dissolution of cellulose fragments in water, a very poor solvent, and N-methylmorpholine-N-oxide, a solvent for cellulose used to make Tencel, or lyocel.
During the final year of the project, the student at Tulane University repeated a substantial amount of the earlier work with improved theory. The student at Tulane University is committed to publishing the results after the formal end of the project.