Wendy Krause

We intend to create a filter membrane that is superhydrophilic (based on a hydrogel) and can trap water molecules inside its fine nanofibrous network and thus demonstrate high water-holding capacity. With a joint collaborative work between the Department of Forest Biomaterials and the College of Textiles (North Carolina State University), we have already produced a naturally occurring biomaterial that may be an ideal medium for our envisioned work that is known as bacterial cellulose (BC). Bacterial cellulose (BC) is produced from the bacterium Gluconacetobacter xylinus. Due to BC’s high water uptake capacity, it can form gels. It possesses high tensile strength, biocompatibility, and purity, and has been employed in paper and paper-based products, audio components, and soft tissue scaffolds.

To meet the processing challenges from both increased processing speeds, new fibers and new fiber structures, we need to develop a deeper understanding of the physics and chemistry of the polymer surfaces, surface lubrication and surface-lubricant interactions. This project will aid fiber and finish producers in the development of future generations of fibers and fiber lubricants by expanding our fundamental understanding of the mechanisms of hydrodynamic fiber lubrication, including the physics and chemistry of the polymer surfaces, surface lubrication, and surface-lubricant interactions. Therefore, we have been (1) developing model lubricant formulations in conjunction with our industrial contacts; (2) developing nanoindentation-based frictional studies; (3) investigating the rheological behavior of model lubricant formulations with standard stainless steel and custom polymer fixtures; and (4) studying nanotribological properties of the model systems.

To meet the processing challenges from both increased processing speeds, new fibers and new fiber structures, we need to develop a deeper understanding of the physics and chemistry of the polymer surfaces, surface lubrication and surface-lubricant interactions. While extensive work on fiber lubrication was conducted in the 1950s, 1960s and early 1970s by Schick [1-5], Olsen [6,7], and Schlatter [8,9], relatively little work has been published since then [10,11]. We will develop and apply advanced rheological and lubrication testing technology to address a number of fundamental questions of industrial significance in regards to the hydrodynamic lubrication of fibers: ? Why do fibers based on different polymers have different frictional properties in the hydrodynamic region?(This is not as predicted by lubrication theory.) ? What are the variables controling the hydrodynamic frictional behavior of complex lubricant formulations? ? Why does the Streibeck curve (Figure 1) level off and than go down in the high-speed region? ? What are the fluid film thickness, the real shear rates and the extent of heating within the hydrodynamic fluid film during high speed friction?

The objectives of this study include: (1) to characterize the microestructural and surface properties of contact regions between sliding materials relevant to fiber processing; (2) to elucidate the nature of molecular assemblies in boundary films (molecular or nanometric scale) and their relationship with observed macroscopic behaviors; (3) to devise structure-property relationships to assist in the formulation of new additives with improved performance. Key variables to be addressed are those affecting the function of an additive in tribocontact such as the constitution of interfaces, molecular structure, adsorption strength and intermolecular interactions. We also aim at (4) relating the experimental results with predictions from molecular dynamic calculations and, (5) working closely with fiber, textile and lubricant manufacturers to translate this knowledge into testing methodologies relevant to the textile and allied.

The proposed project will address the interplay between strength and toughness as a result of how the nanotube/polymer interface is engineered. For example, the interface between polymer and nanoparticle controls the composite?s strength and toughness. High interfacial strength is desirable to maximize the composite?s strength, while slip between the nanoparticle and matrix (low interfacial strength) is required for maximum toughness. For well-dispersed, oriented nanocomposites, we will quantify: ? The strength of the nanocomposite as a function of interfacial strength; ? The toughness of the nanocomposite as a function of interfacial strength; and ? The optimization of both strength and toughness for the nanocomposite. In this study, we will fabricate carbon nanotube/nylon fibers and films to study the molecular motion, nano- and macroscopic mechanical, electrical, rheological, and processing properties of the composite system of interest. We will combine many analytical techniques to develop a mechanistic understanding of the factors that influence strength and toughness at the nanotube/nylon interface.

To meet the processing challenges from both increased processing speeds, new fibers and new fiber structures, we need to develop a deeper understanding of the physics and chemistry of the polymer surfaces, surface lubrication and surface-lubricant interactions. While extensive work on fiber lubrication was conducted in the 1950s, 1960s and early 1970s by Schick, Olsen, and Schlatter, relatively little work has been published since then. We will develop and apply advanced rheological and lubrication testing technology to address a number of fundamental questions of industrial significance in regards to the hydrodynamic lubrication of fibers: * Why do fibers based on different polymers have different frictional properties in the hydrodynamic region? (This is not as predicted by lubrication theory) * What are the variables controlling the hydrodynamic frictional behavior of complex lubricant formulations? * Why does the Streibeck curve level off and then go down in the high-speed region? * What are the fluid film thickness, the real shear rates and the extent of heating within the hydrodynamic fluid film during high-speed friction?

The objectives of this study include: (1) to characterize the microestructural and surface properties of contact regions between sliding materials relevant to fiber processing; (2) to elucidate the nature of molecular assemblies in boundary films (molecular or nanometric scale) and their relationship with observed macroscopic behaviors; (3) to devise structure-property relationships to assist in the formulation of new additives with improved performance. Key variable to be addressed are those affecting the function of an additive in tribocontact such as the constitution of interfaces, molecular structure, adsorption strength and intermolecular interactions. We also aim at (4) relating the experimental results with predictions from molecular dynamic calculations and, (5) working closely with fiber, textile and lubricant manufacturers to translate this knowledge into testing methodologies relevant to the textile and allied industries.

In this acquisition proposal, we are requesting a state-of-the-art nanoindenter with an integrated atomic force microscope. This instrument is a stand-alone test platform for the quantitative mechanical characterization of materials at the nanoscale. The unique capabilities of the nanoindenter will bring together 16 faculty members from three different colleges at North Carolina State University (NCSU) with a broad range of interests and expertise relevant to materials science based research. General areas critical to the current and future research programs of NCSU will be enabled through this acquisition. They include: Bulk and Thin Film Nanocrystalline Materials, Semiconductors and Ceramics, Nanoscale Organic Materials, Biomaterials.