Rodney S. Ruoff - US grants

Nanorope Mechanics, Rod Ruoff and Wing Kam Liu, Northwestern University

Carbon nanotubes, CNTs, are a multifunctional material that may find applications as a reinforcing component in a variety of composites, where the matrix could be polymer, ceramic, or a metal, including ductile metals such as aluminum. Additionally, CNT's may be applied as a new type of cable material that would exploit the high stiffness and potentially the high strength. There are two types of carbon nanotubes, the "single walled carbon nanotubes," SWCNTs, and the "multiwalled carbon nanotubes," MWCNTs. This grant from the National Science Foundation addresses the mechanics of SWCNT bundles with a combined experimental and modeling effort. In particular, the goal of this project is to develop a detailed understanding of the mechanics of both parallel and twisted SWCNT bundles. Inspiration for this effort comes from the rather well established fields of twisted wire, and textile, mechanics. These disciplines have treated the mechanics of twisted wire structures, or textile fabrics, typically by continuum mechanics. One may expect that twisting a bundle, or achieving a "woven" bundle, of SWCNTs will enhance the load bearing capacity of the SWCNT "rope." The extent of load transfer between individual tubes in the bundle is a crucial aspect of their potential application in structural applications in either composites, as cabling, and even for example, as windings in electromagnets.

Our experimental effort involves the use of a nanomanipulator/testing stage in which we will pick up SWCNT bundles, mount them for tensile loading, and apply twists with a component of this testing stage, which can undergo 1800 individual steps per 360 degree revolution, and can continue to "wind up" a SWCNT bundle through n turns. The stiffness as a function of applied twist, and also the bundle strength as a function of applied twist, will be studied with this tool, which has been previously used to study the tensile loading of individual MWCNT's and of untwisted SWCNT bundles. Our modeling effort involves using a variety of approaches, including molecular dynamics (MD), molecular mechanics (MM), and continuum mechanics, to study such issues as load transfer as a function of both twist and contact length, for both idealized bundles (for example, where every tube in the bundle is identical, such as all tubes being (10,10) tubes with perfect closest-packing) and bundles that might more closely mimic those actually tested in experiment, such as having different diameter tubes in the bundle, without perfect closest packing. There is a close collaboration between the groups doing theory and experiment, and each effort is meant in part to guide the other, and to provide deeper overall understanding.

Abstract.
The US-Swiss 2003: Nano Mechanics and its Application and Single Molecule Research Forum, third in a series of collaborative forums with the Swiss National Science Foundation, is proposed to be held on the campus of the University Basel in Switzerland from the 13th to the 15th of October, 2003. This Forum focuses on the role of nanoscience in mechanics of materials and in single molecule studies.
The Forum will bring together leading scientists from the US and Switzerland who are working in the fields of nanomechanics and single molecule research. Younger researchers (postdoctoral research associates and assistant professors) have been encouraged to attend this exceptional meeting. The format of the meeting will include lectures by leading scientists in the areas of nanomechanics and single molecule research and posters covering on-going research from both US and Swiss research groups. Arrangements for impromptu discussions among participants and opportunities for forming new collaborative networks will be provided.
Rodney S. Ruoff, Professor and Director, NU BIMat Center, Northwestern University, is the US organizer. Hans Leuenberger, Professor of Pharmaceutical Technology, University of Basel, and Vice President of the Swiss Academy of Engineering Sciences, is representing the Swiss contingent. All Swiss participants will be supported by SNF program funds.

NER: Particle Light Valves
PI. Rod Ruoff, Northwestern University

Abstract. This project concerns fabrication of identical disc-shaped particles in the ~300 to 1000 nm diameter size range and of small and uniform thickness (ranging from 10 to 50 nm, approximately), and study of their light scattering when immersed in a liquid and oriented by an AC electric field. Our team includes an expert in particle fabrication and properties measurements (Ruoff), and in electrodynamics and fluid dynamics modeling (Schatz and Patankar, respectively).
The fluid mechanics, electrodynamics, and light scattering studies of this effort are forefront science, and fabrication of the particle size and type in sufficient quantity is a challenging nano-engineering problem. This work will lead to understanding of the electrokinetics of the interaction of an AC field and particles of appropriate size to well scatter visible light, and the interaction of light with such particles. The understanding that will be generated should be of immense interest to the colloid, fluid dynamics, particle fabrication, and light scattering communities.

150 WORD PROJECT SUMMARY

A major challenge in nanotechnology is wafer-scale assembly of nano/bio molecules with the high packing density Understanding and modeling the mechanics of the cell is one of the major challengesin current nanotechnology.. A composite electric field and the forces induced on molecules to achieve their assembly, will be will be analyzed with the inmmersedImmersed FEM method. Imaging methods will be accompaniedcombinedused to investigate the assembly results. , and yet probably most rewarding, tasks of the present centurynext few decades. The task is complex, for the mechanical behavior emerges through an interaction of a hierarchy of scales, and it is essential for models to reflect these scales so that they can eventually become "first-principles" models that enable predictions of a large variety of mechanical behavior. The intellectual merits will beare the following3D simulation tools to be developed will span three scaless: (1) wafer-scale assembly of nano/bio molecules; (2) mechanics of bio-filament suspensions; and development of imaging tools to enable imaging by for SEM,, AFTEM, and AFM; (3) development of modeling simulation tools for assembly process modeling; and (4) understanding of electric field driven forces. coarse-grained models of the entire cell. An hierarchical modeling approach will be taken bewhere: a) material properties of bio-filaments will be passed from the atomic scale to the bio-filament suspension scale, and b) the effective properties of the active cell material will be passed on to the continuum scale simulations of cell migration by coarse graining the bio-filament suspension simulations. Concurrent multiscale coupling schemes will be developed at two levels: a) . Although information will be transferred between the scales primarily by passing property information, concurrent coupling schemes linking continuum mechanics to molecular mechanics will be developed that enable direct coupling of atomistic motions to biofiber properties in some applications, and b) a new hybrid simulation scheme that solves the continuum equations for cell motion and concurrently resolves the local cytoskeletal structure by performing bio-filament suspension simulations.Individual molecular devices will be developed and tested foras bio/chemical sensors.A novel NEMS device to measure cellular forces, being fabricated in our group, will be used for the measurements of traction forces and the simultaneous imaging of the fibrous structure of the cell. This will initiate the development of molecular scale bio/chemical sensors in a massthat ultimately could be mass-producedproducible way.
the simulation of cell motility.. Also, at a larger scale, we will develop new models to obtain coarse-grained active stresses from mechanical models of bio-filament suspensions, thereby accounting for bio-fluid-structure effects, electrostatic interactions, thermal behavior and polymerization and depolymerization.

This award supports a project that will improve instrumentation used for patch-clamp measurements for recording the electrical potential of individual cells. The patch-clamp method is the most widely used method for this purpose; 26,000 research publications have cited the method since 1975, half of these appearing in the last five years. Despite this widespread use, the method has a number of well known limitations that arise from the equipment used. In particular, it is difficult to obtain and to sustain more than one recording at a time, making studies of the electrical activity of individual members of cellular networks difficult. Moreover, the quality of recordings deteriorates with time, and the recording bandwidth is limited. Through the development of new instrumentation undertaken with the support of this award, long-duration, multiple-site recordings will be easier to obtain, and high bandwidth signals will be more accessible. Traditional patch clamp systems employ a glass pipette to contact the cell with an Ag/AgCl electrode located at a fixed position far from the pipette tip. Introduction of any cellular or other debris near the tip interferes with reliable measurement. In the device to be developed, a movable nanoelectrode can be advanced forward and through the tip to clear such debris. This modification alone is expected to alleviate most of the current patch clamp limitations. While the proposed device will be more complex than a standard patch clamp electrode, the project's goal is development of a device that will integrate easily into existing patch clamp systems. This approach of adapting the design to systems currently in use should encourage rapid acceptance of the new tool among electrophysiologists, significantly increasing the likely impact it will have on the progress of biological research over the next decade. The PI has been active in development of new curricula and other activities that serve both neuroscience and bioengineering. Because of the extensive use of the patch-clamp in a variety of areas of neuroscience and cell biology, successful development of the proposed device can be expected to have a broad impact on biological research.

ABSTRACT. Fracture Mechanics of Nanowires and Nanostructures
Rod Ruoff 8-3-2006 (241 words by word count)

The strength of an ideal crystal has long been of interest but 'real' materials have lower strengths because they have defects. Nanostructures can fail differently from larger structures, so studies of how nanostructures will break (fracture) provide an opportunity to connect the 'real' to the 'ideal'. This study of fracture in nanowires having novel structures that are important due to their electrical, thermal, and mechanical properties includes collaborators in the United States, Sweden, and South Korea who will provide nanowires for mechanical testing. A new microelectromechanical ('MEMS-based') mechanical loading stage that can operate inside a transmission electron microscope with sub-nanometer resolution will be used along with other tiny testing devices to find out what makes nanowires break.

Nanowires may be used in nanoelectronics (as logic and memory and interconnect elements), as chemical sensing elements due to their high surface to volume ratio and exceptional sensitivity to surface interactions, in nanoelectromechanical systems (NEMS; as mechanical components, electromechanical components, actuators, strain gauges, flow sensors, others), and in structural composites where the crystalline perfection of nanowires is expected to confer exceptional stiffness, strength, and toughness. It is thus important to understand the detailed mechanics of single crystal nanowires so a base of knowledge can be available for their subsequent use in diverse applications where mechanical stress will be present. This effort includes research programs for graduate students and postdoctoral fellows, summer research training for undergraduate students and high school teachers, and other educational activities.

The conformational states of low-dimensional carbon nanostructures will be studied in an integrated program involving experiment and simulation. The conformational states influence critical properties such as the packing and stacking, surface energy, deformation energy, stiffness, strength, electronic/thermal transport, and chemical reactivity. Developing understanding of why one-dimensional and two-dimensional carbon nanostructures adopt such conformations is essential for applications such as nanocomposites, nanoscale sensors/actuators (NEMS), and for use as components for nanoelectronics, among others. Our proposed effort is motivated by the current lack of a computational and experimental framework to represent, model, and simulate on the one hand, and on the other to experimentally measure the conformational states. A multi-scale modeling/simulational framework will be integrated with experimental measurements of the 3-dimensional geometry of individual carbon nanostructures using scanning and transmission electron, and atomic force, microscopy.

The proposed topic represents an opportunity to pursue an important new direction of research. Graduate and undergraduate students will have the opportunity to do forefront scientific research of practical importance and should grow into future leaders by performing discovery-based research, contributing important scientific papers, and by giving presentations at international conferences. The proposal also includes a significant outreach program, including research for graduate and undergraduate students, summer training for undergraduate (including minority) students and high school teachers, additions to course materials being offered in engineering courses, K-12 summer science camps, and curriculum development for grades 7-12.