Tingying Zeng

Self-assembled flexible electrodes on electroactive polymer actuators

Thin film metal/polymer composite electrodes with electrical conductivities on the order of those of bulk metals have been formed on electroactive polymer actuator elements using a novel self-assembly technique. The electrodes exhibit good flexibility and mechanical performance.

High-Performance Photovoltaic Behavior of Oriented Purple Membrane Polymer Composite Films

The photovoltaic behavior of films in which bacteriorhodopsin molecules are embedded in a polyvinyl alcohol matrix has been investigated by using both pulsed laser excitation and regular light illumination. Response times as short as milliseconds, photocurrents as great as 120 micro A/cm(2), and photovoltages as large as 3.8 V have been obtained. A theoretical model has been developed and used to extract several physical parameters and fit the experimental results. Some important intrinsic parameters have been obtained. Theoretical results indicate that the average displacement of the excited protons is on the order of several tens of microns. Other curve fits show that photocurrent and photovoltage increase linearly with external field, but increase exponentially with flash power. These theoretical models and results can be extended to other kinds of photoactive polymeric materials.

Ultrathin film actuators fabricated by layer-by-layer molecular self-assembly

Polymer/metal cluster nanocomposite thin films as new types of electroactive polymer (EAP) material have been synthesized by the layer-by-layer (LBL) electrostatic self-assembly process. A self-assembled 11-bilayer poly-S-119/Pt nanocluster film, with a thickness of approximately 30 nm and a Pt content of 0.49 at.%, exhibited an actuation response similar to that of conventional ionic polymer-metal composite films for low applied voltage in air, but nonlinear bending behaviour in response to a slightly higher applied voltage. The film has a uniform nanostructure with the Pt nanoclusters dispersed within the multiple molecular layers, as confirmed by atomic force microscopy. The self-assembled electroactive films may have different actuation mechanisms from those of traditional piezoelectric materials, and from other EAP materials, due to the quite different LBL laminated structure. Further studies concerning the principles governing the novel processing of the films and applications are underway.

Characterization of electrostatically self-assembled nanocomposite thin films

Multilayer thin films of metallic nanoclusters, polymers and other molecules have been formed using a novel electrostatic self-assembly method and analysed by multiple characterization techniques. Nanocluster size measurements, ellipsometry and UV-visible absorption spectroscopy have been used to confirm the linear build-up of the thin film thickness with the number of deposited nanocluster, polymer and other molecular layers. Auger electron spectroscopy allowed verification of the distribution of molecular species through thick films with multilayer segments containing different elements. Field emission scanning electron microscopy and atomic force microscopy permitted visualization of the morphologies of the outermost layers of the deposited films. Together, such characterization allows improved understanding and the basis for the design of multilayer thin film materials engineered to have specific molecular level structures and macroscopic functionalities.

Piezoelectric ultrathin polymer films synthesized by electrostatic self-assembly processing

Ultrathin piezoelectric composite films composed of poly(sodium 4-styrenesolfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) were synthesized using the electrostatic self-assembly (ESA) process. The ESA-processed PSS/PDDA films have a layer-by-layer laminated structure, and exhibit a piezoelectric response directly without electric field poling. The measured piezoelectric coefficient d33 = 6.0 pC N-1. The molecular self-assembly process plays a very important role in molecular alignment, resulting in a net macroscopic polarization of the layer-by-layer structured ultrathin film, although the process is quite different from that used to form conventional piezoelectric materials. Further study concerning the principles governing the novel ESA processing of piezoelectric and other functional films is on-going.

Space-radiation-induced effects in polymer photodetectors

Self-assembled polymer photo-detectors (PPDs) composed of ruthenium complex N3 and PPDs based on thin films of poly(p-phenylene vinlyene) with sulfonated polystyrene are examined for their ability to function in a simulated space radiation environment. Examination of the PPD pre- and post- response data following gamma-ray irradiation ranging in total dose from 10 krad(Si) to 100 krad(Si) are examined. The output photovoltage was observed to decrease for all irradiated devices. The brief study was performed at room temperature and a discussion of the preliminary data and results are presented.

Radiation-resistant polymer-based photonics for space applications

Empirical data regarding the radiation induced responses of Mach Zehnder interferometric electro-optic polymer based modulators (PBMs) operating at 1310 and 1550 nm and broadband InP quantum dot (QD) polymer photodetectors (PPDs) operating into the near infrared (NIR) are reported. Modulators composed of spun-on materials and hybrid electostatically self assembled (ESA) and spun-on NLO materials are examined for changes to their half-wave voltage and insertion losses following a gamma-ray total dose of 163 krad(Si) and irradiation by 25.6 MeV protons at a fluence of ~1011 cm-2. Pre- and post- irradiation responses of ESA grown polymer detectors using InP QDs are examined for photovoltage degradation and aging effects. The data indicates and excellent potential for developing polymer based photonic (PBP) devices with increased radiation resistance suitable for transition to photonic space applications.

Modeling the electro-static self-assembly process using stochastic cellular automata

The electro-static self-assembly (ESA) process has proved to be extremely successful in creating multilayer coatings with properties that can be tailored for particular applications. In this process, almost any surface with charged functional groups can be used as a substrate. Alternate dipping in solutions having ions of opposite charge builds up the layers through ionic bonding. One particular application of this process could be to form multi-functional biocompatible coatings on microelectromechanical systems devices intended for use in vivo. In this paper, we describe two different models of the process based on the cellular automata techniques used in the field of artificial life. The output of the models consists of three parameters as a function of layer: ionic coverage, film height and film roughness. The results of the models are compared to experimental data to determine which of them more accurately describes the ESA process.

Electrostatically self-assembled electro-optic materials and devices

Thin film electro-optic materials have been synthesized by a novel electrostatic self-assembly (ESA) method. This method allows the molecular-level, layer-by-layer formation of multilayer thin and thick films of alternating anionic and cationic molecules and other materials. We have found that during the adsorption of dipolar molecules from solution to form a single molecular layer, the dipoles align themselves. In a multilayered material, this leads to multiple functionalities that require a noncentrosymmetric molecular structure, such as active optical properties and piezoelectric behavior. Such properties are usually achieved in other materials by electric field poling. In this paper, we describe the precursor molecular chemistries that we have developed to make electro-optic thin films by this method, how the films are formed, the resulting molecular orientation within the film, and measured electro- optic coefficients to date.

Polymer-based photonic technologies for aerospace and space applications

This paper presents a brief overview examining the recently reported research and development of polymer based modulators and photodetectors that have been advanced for aerospace and space applications, and discusses the reported radiation resistance of several device technologies. Preliminary results of focused investigations to develop polymer based photonic technologies capable of surviving in the naturally occuring near-earth space ionizing radiation environment environment as well as the expected performance of these technologies on elevated radiation environments are presented.