National Textile Center
Year 8 Proposal
Project No.: M98-C01
Competency: Material Science
Chameleon Fibers: Color Tunable Molecular & Oligomeric Devices
Project Team:
Leader R. V. Gregory Expertise Polymer and Materials Science
Email: Richar6@Clemson.edu Phone: 864-656-5961
Members: R. J. Samuels Ga. Tech. Polymer Science and Engineering
T. W. Hanks Furman Uni. Synthetic Chemistry
Objective:
The overall objective of this study is to provide the textile and fiber industry with a series of new "smart" materials that can quickly change their color, hue, depth of shade, or optical transparency by application of an electrical or magnetic field. This work, started six months ago with NTC funding, is already identifying, characterizing, and producing electroactive and magnetoactive oligomeric molecules with unique abilities to change their absorption and/or reflection of electromagnetic radiation in the infrared, visible, and ultraviolet frequency ranges. Molecules and oligomers identified in the initial phase of this research that possess these "tunable" properties are being introduced into fiber forming polymeric matrices. These are being formed into fibers and films (films provide ease of study by a variety of spectroscopic methods) and their optical properties evaluated under differing electrical, magnetic and thermal stress.
Relevance to NTC Mission:
Simply put, color sells textiles. Fibers with unique optical, magnetic, and electrical properties are being widely studied in Japan and Europe for use in both military and commercial applications. Little is reported in the American scientific or patent literature on fiber applications of photonic materials. Chameleon fibers with unique tunable coloration properties spanning the visible, infrared and ultraviolet region of the electromagnetic spectrum will have wide application to a variety of new products. These new materials will also allow penetration into markets normally not dependent on textile materials. Textiles markets will include floor and wall covering, billboards where specific areas can be programmed with different colors or wording, and materials with infrared or ultraviolet shielding capabilities. New markets will include biosensors, detector applications for textile materials, and "smart materials".
State of the Art:
This work employs the expertise developed and reported in the literature over the last several years at Georgia Tech. and Clemson in previous collaborative efforts on structure property relationships of electroactive materials. In this new recently funded NTC work the expertise of the Furman laboratory is employed to synthesize new derivatized monomers and oligomers. Several potential target monomers and oligomers have already been identified and are or have been synthesized, processed into fiber and film form, and evaluated during the first six months of this study (funding and work began 5/1/98). This work is considered the leading edge of the current field of knowledge in this area as evidenced by invited talks at national and international meetings scheduled for the spring of 1999 which include American Chemical Soc. (invited), Chemtronics (invited), SEAM (invited), and several other meetings of note.
Approach:
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At the time of this writing this project is six months into year one funding. Substantial progress has been made toward the goals stated in the year one proposal. Recent synthetic successes at Furman have produced molecules that are highly polarizable. This research has a two pronged attack strategy to produce dynamic color change materials. The first area involves identifying and synthesizing individual molecules that are highly polarizable, while the second area investigates the use of photonic polymers. These are not isolated focus areas but are highly interactive and synergistic. Incorporation of polarizable molecules onto or into the chain matrix of a photonic polymer may provide the desired results. Understanding of the mechanism of structural and/or electronic change in these materials leading to dynamic color change is paramount in this effort.
Initially the focus of research efforts in the Furman lab has been on identifying and synthesizing chromophores, which will respond controllably to the application of electric or magnetic fields such as those in Figure 1. Towards these ends, we have begun to explore highly polarizable, highly conjugated compounds. Several intensely colored compounds, which are highly polarizable and field responsive, have been prepared. The compounds were designed to undergo a dramatic change in their molecular dipole moment upon application of an electric field. Each can be dissolved within a polymer, or covalently bound to it. These complexes are designed to work with conventional fiber systems, such as the polyesters or polyamides as described in the annual report to the National Textile Center on this project.
The Clemson and Ga. Tech. laboratories will continue their extensive collaborative efforts working closely to characterize and quantify the structure /property relationships of films and fibers either cast or spun from photonic polymers, such as poly-paraphenylenevinylene (PPV) and its derivatives. Derivatives of the photonic polymers are prepared with the aid of the synthesis group at Furman and involve students from all three schools working in laboratories of the other universities from time to time particularly in the summer months. Photonic polymers and their derivatives demonstrate a strong potential for use as field responsive materials and undergo changes in their molecular polarizability and structure upon the application of an electric or magnetic field. Changes in molecular polarizability and/or structure upon application of an electric field will be quantified and the results used by the Furman laboratory to aid in the design and synthesis of new dynamic color change materials. Molecular modeling provides a powerful tool to determine the most likely candidate and synthetic targets for stable dynamic color change materials
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Several classes of materials will be investigated to effect dynamic color change. In addition fibers formed of polymeric materials capable of charge delocalization are ideal candidates for grafting field responsive oligomers to the surface. It is unclear at this time whether one specific oligomer can be designed and be capable of being tuned over the entire visible spectrum. Oligomers with different absorption coefficients at certain field strengths may be necessary to achieve a broad band material. It is therefore important that the optical properties and the structure/property relationships of the host polymer be understood and quantified as well. These relationships are and will be characterized in the Clemson and Ga. Tech. laboratories during year two and three. Optical property measurements on films (initially films are formed rather than fibers due their ease of study) have already yielded new results on PPV films. PPV film has been measured for the first time in the near infrared region (1550 nm) in our wave guide coupler system [see Figure 2]. This was used for preliminary testing of a new theoretical approach more completely detailed in the annual report. The in-plane values were measured. The refractive index value determined was Np=1.9988, while the attenuation coefficient Kp=0.0109. We are currently doing independent experiments to confirm these results. Refinement and expansion of the technique in years two and three will provide a straight forward method of evaluating the optical properties of new photonic polymers. Methodologies currently being developed in this present work will provide the necessary knowledge base for application of these polymers to a broad variety of fiber and film products in the coming years .
A set of test devices for applying a controled electric field have been constructed at the Clemson laboratory and will used at all three universities on a variety of new materials synthesized in year two and three. These materials will include photonic polymers derivatized with pendent groups which either inject charge or withdraw it depending on the field strength. As we have already demonstrated this changes the absortion coefficient and therefore alters the color of the light reflected The test devices allow for the application of electric fields of varying strengths while observing and quantifying the color change results of films prepared from field responsive polymers.
During year two, fibers will be prepared which either have the field responsive oligomers grafted on to the surface, or have molecular field responsive moeities contained within the fiber matrx. These materials will then be tested in order to determine the range of color change and their ability to be repeatably cycled from color to color.
This work has already established a strong multi-disciplinary team systems approach utilizing expertise from three universities to produce materials which will lead to new textile products containing "smart materials". This will establish new markets for high technology fibers, films, and textile structures which incorporate these materials.
This Year’s Goal:
The objectives for year two will build on the success of year one.
a) Work will continue to model, synthesize, and characterize the molecular structure and intrinsic properties of highly polarizable molecules, PPV and its derivatives, and other polymers such as polyethylene –dioxythiophene (PEDOT). Results obtained from these studies will aid in the design and characterization of new molecules and oligomers containing charge injection or withdrawing pendent groups which change the reflection coefficients and hence the color upon application of an electric field.
b) The three dimensional optical properties of the new systems will be characterized by wave guide coupling techniques developed at Ga. Tech. New theoretical methods developed last year will be applied to these systems and tested. This includes determining the effect of processing on the molecular anisotropy produced.
c) Fibers as produced are always anisotropic. Thus it is essential to understand the effect of molecular anisotropy on charge delocalization with respect to field direction and strength. Films allow a direct measurement of this effect both alone or as measurable coatings. Techniques will be developed for producing and measuring electrical field strength in films during analytical measurements. This technique will allow measurement of both the molecular structural anisotropy and the properties as a function of field strength simultaneously. These measurements will include such techniques as wave guide coupling, other polarized optical methods (UV/vis, NIR and midIR) and x-ray diffraction.
Outreach to Industry:
Interactions are already established with Milliken and Co., Allied Signal, Hoechst-Celanese, I.B.M., Kemet Electronics, Granitville Industries, and Monsanto for exploration of unique applications of electroactive polymers. These interactions will continue and strengthen under the proposed work. Several fiber producer and textile companies involved in the production wall and floor covering materials have expressed interest in chameleon fibers.
New Resources Required:
The laboratories of Clemson, Georgia Tech, and Furman have substantial resources and expertise to carry out the studies outlined in this proposal. Resources include, atomic force microscopy, scanning tunneling microscopy, nuclear magnetic resonance, electron spin resonance, infrared, ultraviolet, near infrared, and visible spectrometers. For optical studies a prism optical waveguide, specular reflectance cells, infrared polarizers, electron and optical microscopes. For polymer structural studies all three campuses are equipped with x-ray, TGA, DSC, and a variety of other characterization tools including electrical and electronic characterization. The only major new equipment purchase is an inert atmosphere glove box for storage of synthetic precursor materials.