National Textile Center

Year 8 Proposal

Project No.: M98-G08

Competency:

MOLECULAR SPINNERETS FOR POLYMERIC FIBERS

Project Team:

Leader Karl I. Jacob Expertise Polymer Physics, Molecular Modeling

Email: jacob@moose.tfe.gatech.edu Phone: (404) 894-2541

Name/school/expertise

Members: Malcolm Polk Georgia Tech Synthetic Chemistry

Bobby Sumpter Oak Ridge National Lab Nanotechnology

Mike Ellison Clemson Fiber Processing, Nano-Structures

William Goddard III(Consultant) Beckman Institute-Caltech Nano-Tech

Objective:

(1) Investigate, design, and synthesize a revolutionary molecular spinning machine with discotic molecules which can be shaped in the form of membranes that can produce highly engineered fibers with significantly reduced size and energy requirements compared to conventional spinning machines.

(2) Using state-of-the art theoretical, computational, synthetic, and experimental tools investigate, synthesize, and characterize discotic assemblies that can produce fibers with precise control of the structure, geometry, and hence properties, making the drawing step unnecessary.

(3) Design molecular hooks to connect large number of separate discotic molecules as a column.

(4) Identify and characterize the rotation of discotics under a rotating magnetic field, using scanning probe microscopy (SPM), scanning tunneling microscopy (STM), and molecular imaging.

(5) Develop the technology to custom design molecular spinning machines for nylon 6 and nylon 6,6 by characterizing the interactions between the end groups of discotic molecules and polymer segments.

(6) Investigate the possibility of using this material spinning machine to produce nanofibers.

(7) Finally, combine polymerization and spinning in the same process, by designing appropriate discotic membranes.

Relevance to NTC Mission:

This is fundamental cutting edge research with the objective of applying advances in nanotechnology to textiles. If we can synthetically develop a molecular spinning machine, it will be a revolutionary development in the fiber spinning area. Entire spinning units and associated systems can be made to fit in a small room. Fibers with custom designed structures and properties can be spun with extreme precision using this system. The energy requirements will be diminished by an order of magnitude. The drawing step can be eliminated altogether. Start up and transition time for spinning different polymers will be reduced significantly. We envision that polymerization and spinning can be combined into a small unit. The results will be diminished cost of manufacturing fibers, development of new fibers and fibers with improved properties. From the advances made in 1998, we are more confident that such a machine can be designed. Most of all, this work will produce a wealth of very useful new technical information.

State of the Art:

The basic idea behind nano-machines has been to tailor a material to function like a machine. Molecular interactions are the basic building blocks of this technology. Nanotechnology has been increasingly applied to inorganic systems especially in micro-electronics. Oak Ridge National Laboratory and Beckman Institute have been involved in this area. Bobby Sumpter (Oak Ridge) has been designing machines with nano-gears, nano-rods, and nano-bearings, some of which are similar to the discotics needed for the molecular fiber spinning machine. Extraordinary advances have been made in the last few years to synthesize "discotic" supramolecules, which are the building blocks for nanospinning technology.

Using Scanning Tunneling Microscopy, researchers at the IBM Zurich research Lab. showed that a single supramolecule, similar in structure to the structures we will use for our work rotates in a specific direction due to thermal energy alone (SCIENCE, Vol. 281, July 1998, pp. 531—533). We have synthesized a candidate discotic molecule and the rotational characteristics of this molecule are being investigated using the new state-of-the-art instruments available at Georgia Tech (NMR, SPM, and STM). Progress made in the first nine months of this project has convinced us that a molecular machine can be a reality.

Approach:

The nano-spinning "machine" we envision consists of a membrane containing discotics (large ring like columnar organic molecular structures) positioned at designed locations. Discotics are a recent development in synthetic polymer chemistry (V. Percec, et. al., Polymer reprints, March 1996). As the discotic molecular columns are made to rotate in a synchronized fashion, they will pull polymer molecules supplied at the top surface of the membrane, organize and orient them to develop the required structure, and release the fiber at the bottom surface (Figure). This can be achieved through precise sequential interactions between discotic end groups and polymer molecular segments. The discotics must be designed and positioned such that they can attract and pull certain segments of polymer molecules in the prescribed sequence. The size and the nature of the end groups of the discotics must be designed specifically for each polymer fiber and for each required fiber structure. The rotational synchronization of discotic molecules is achieved by using molecular hooks, which will connect several discotics as a column. The rotation of the discotics will be achieved by the application of a rotating magnetic field. For combined polymerization and spinning, the discotics must be designed for reversible exchange reactions with pre-polymer components and the end-groups of discotics.

There are a few barriers in our research. Theoretically designing molecular hooks to connect discotics in the membrane, and synthesizing them in a membrane is one of them. Secondly, the discotics must be designed such that they will rotate in the specified direction with the specified speed. In light of recent advances (Science, cited above), we believe we can overcome this difficulty. In spite of these barriers, if the work is successful the benefits are enormous.

Computational Approaches

Since the synthesis and characterization of discotic molecules will be very time consuming, it will be guided by theoretical design. Molecular modeling will be applied in the design and positioning of the discotics (which are key to success), since such "virtual" molecular machines can be designed and characterized on a computer with good precision. Discotics must spin polymer molecular assemblies by means of the non-bonded interactions with them. Using molecular dynamics, these interactions can be simulated. Chemical compositions of the discotics can be adjusted for improving specific interaction sequences with the polymers, the location and size of discotics can be changed until the spun polymer molecules attain the desired structure. Kinetics of exchange reactions will be accounted for in addition to non-bonded interactions for designing discotics for combined polymerization and spinning. The candidate discotic structures from molecular modeling analysis will be synthesized and tested.

Synthetic Approaches

We have synthesized the first synthetic model which is poly [2-(2-(2-methacryloyl-oxyethoxy)ethoxy)ethyl 3,4,5- tris(p- dodecyloxybenzyloxy)benzoate] (details in annual report). These systems have been shown to form tubular supramolecular architectures involving a columnar mesophase, and they self-assemble to form almost identical supramolecular tubular architectures because of the presence of the tapered exo-receptors attached to the polymethacrylate backbones. Exo-molecular recognition generated by the similar sized and shaped surfaces results in spontaneous self-organization to form cylindrical-shaped assemblages remarkably similar in shape to molecular rotors.

Films of the rotor-like columnar structures will be studied to determine whether they will undergo rotation on exposure to a rotating magnetic field of the correct field strength. A magnetically oriented sample of poly((image not available)-benzyl glutamate) has been shown to undergo reorientation on rotation about some angle. The movement of polymeric nematic liquids in a rotating magnetic field has been used for measurement of the twist viscosity. If the columnar mesophase undergoes rotation in a rotating magnetic field, then a nanofiber of poly(methacrylic acid) may be produced in a rotating magnetic field by hydrolyzing the polyester bonds.

Since incorporation of metals can facilitate controlled rotation of discotics in a rotating magnetic field, columnar polymeric phthalocyanines which contain metals such as copper, zinc, cobalt, nickel and lead will be synthesized with required end groups to act as molecular hooks.

Discotic Supramolecule A Candidate Molecular Spinning Machine.

Image not available.

This Year’s Goal:

(1) Investigate of the rotational characteristics of the synthesized discotic poly [2-(2-(2-methacryloyl-oxyethoxy)ethoxy)ethyl 3,4,5- tris(p- dodecyloxybenzyloxy)benzoate], using NMR, and possibly using the newly acquired scanning probe and scanning tunneling microscopes (these instruments are currently being installed). Characterize both thermal rotation and rotation under an applied rotating magnetic field.

(2) Investigate and design molecular hooks for the above discotic molecules in a columnar mesophase.

(3) Identify molecular interactions between the end-groups of rotating discotics and polymer segments. Using this result design a discotic structure for spinning nylon 6,6 polymer.

(4) Investigate the possibility of spinning polymer molecules through this machine by performing computer simulations and animations of spinning. Study the formation of structures during the "virtual" spinning process.

(5) Synthesize the additional columnar structure (guided by molecular studies) and determine the effect of exposure to a rotating magnetic field. Concurrently design new polymer systems (e.g. biphenyl systems) which should rotate in a rotating magnetic field.

(4) Study the properties of endo- and exo-recognition systems involving hydogen bonding.

Outreach to Industry:

We are working with the DuPont Corporation.

New Resources Required:

A device to generate rotating magnetic field.