Figure 1. LEFT : Color contour map of temperature distribution over an aerodynamic model. RIGHT : Schematic of instrumentation for luminescence imaging.
Thin Films for Optical Measurement of
Surface
Temperature, Air Pressure and Mechanical Strain
Kirk S. Schanze
University of Florida at Gainesville
Department of Chemistry
Gainesville, FL 32611
(352) 392-9133
Luminescence imaging is an emerging technology that has wide application in industry. As illustrated below in Figure 1, in this method an object that is coated with a photoluminescent
Figure 1. LEFT : Color contour map of temperature distribution over an aerodynamic model.
RIGHT : Schematic of instrumentation for luminescence imaging.
"adaptive" active layer is illuminated with blue or near-UV light. The
photoluminescence from the coating is imaged with a scientific grade CCD camera that is
equipped with a filter to remove the excitation light. The CCD image data is used to
construct a high-resolution, global map of photoluminescence intensity over the surface of
the object.
The chemistry and materials properties of the "adaptive" active layer comprise the basis for luminescence imaging technology. Researchers in chemistry, physics and engineering have collaborated to develop coatings that display luminescence intensity that responds to temperature and the air pressure that is in equilibrium with the coating. These coatings have been used primarily by aerospace engineers in wind tunnel tests to visualize the air flow and air pressure distributions over aerodynamic models.
The need exists for the development of new "adaptive" materials for use in imaging applications. One area that is of great interest is the development of organic- or organic-inorganic hybrid materials that feature a large change in optical properties (i.e., scattering, absorptivity or luminosity) as a result of mechanical strain on the underlying substrate. Of most interest to the engineering community would be the ability to detect and quantify mechanical strain in the 0 - 2000 microstrain regime-- this is the region over which most structural materials (i.e., aluminum and steel) display elastic deformation. This represents a clear challenge to chemists and materials engineers since 2000 microstrain represents a change in length of only 0.2 % (i.e., @ TEM micrograph of MEH-PPV + PEO/Li + bifunctional additive (octylcyanoacetate) in the ratio 1:1:1 spin cast from cyclohexanone showing the bicontinuous network morphology (1cm =80 nm). The phase seperated network morphology is clearly seen.
In this case the light component is the semiconducting and luminescent polymer [such as MEH-PPV, a soluble derivative of poly (phenylene vinylene)] and the dark component is the polymer electrolyte [PEO containing a suitable concentration of lithium triflate]. The blend was coaxed into the network structure by using a bifunctional ("surfactant-like") additive, octylcyanoacetate, polar on one end and nonpolar on the opposite end. The bifunctional network morphology minimizes the distance required for ionic diffusion from the electrolyte into the polymer during electrochemical doping. The result is faster response (faster turn-on), improved brightness and improved efficiency.
There is much to be learned here, a whole new class of materials to be explored, And much to gained from improved LEC performance. For example, although the reason for the faster response is clear, the origins of the improved efficiency and brightness are not clear. More importantly, we must gain a deeper understanding of the self-assembly of such network microstructured blends rather than proceed by trial and error.
In summary, Bicontinuous Networks as Complex Systems with Adaptive Functionality offer a number of interesting and potentially important opportunities for electro-active polymers, especially in the area of "plastic electronic" devices. The need to utilize two (or perhaps more) incompatible components to achieve the desired material properties leades naturally to phase separated structures. High performance requires bicontinuous networks and a deep understanding of how to create and control the microstructure of such networks in heterogeneous polymer composite materials.