Grants

Eastman Chemical Company(1/01/16 – 3/31/17)

Phase change materials (PCMs) constitute a broad class of chemical compounds that typically undergo a first-order phase transition (e.g., melting/freezing or evaporation/ condensation) at a temperature that lies near a target value for a given application. Associated with this thermodynamically-reversible transition is a latent heat that must be overcome before a rise or fall in temperature proceeds. In this fashion, the PCM can be used effectively to extract heat from (and thus cool) a warm body or provide heat to a cool body. For illustrative purposes, consider a PCM that is heated from a temperature below its transition temperature. Initially, the temperature of the PCM increases according to its heat capacity, which is a material property that relates a change in heat to the corresponding change in temperature. Once the PCM reaches its transition temperature, however, it remains isothermal until it fully undergoes its phase transition. Beyond this temperature, the PCM continues to change temperature with a new, higher heat capacity. This series of events is schematically depicted in Figure 1. As is evident from this heating scenario, an effective PCM must possess (1) a target-specific transition temperature, (2) a relatively high latent heat to absorb/emit heat under isothermal conditions, and (3) relatively high heat capacities to absorb heat without changing temperature significantly above and below the transition temperature. Another consideration is the extent of thermal expansion at temperatures lower than and above the thermal transition, as well as at the transition itself. For this reason, while high latent heats can be best achieved with PCMs designed to possess an evaporation/condensation transition, the associated volume increase and likelihood of losing PCM vapor from a reusable thermal comfort system preclude such materials from further consideration. Challenges in the use of PCMs that activate upon melting/freezing include incorporating the mass required to achieve adequate performance under target conditions, heat transfer limitations and the degree of cooling required to induce freezing (along with crystallization kinetics). To avoid complications due to melting of the PCM, we intend to use a technology derived from thermoplastic elastomers wherein the PCM is incorporated into the matrix of the TPE. In this manner, melting of the PCM results in a thermodynamically stable gel that does not flow. To improve heat transfer, the PCMs will be modified with thermally conductive nanoparticles at concentrations above the percolation threshold to expedite thermal conduction. For this reason, we refer to these hybrid nanomaterials as Phase-Change Elastomer Nanocomposites (PCENs). Promising and economically viable conductive nanoparticles for use in this design include high-aspect-ratio silver nanowires, which tend to possess relatively low percolation thresholds (ca. 1 wt%). Analysis of these materials sandwiched between polymers of interest to Eastman (e.g., Tritan) will be conducted to ascertain the cooling/heating efficiency of such laminates for use in homes and/or automobiles.

National Science Foundation (NSF)(8/01/15 – 7/31/18)

Textiles constitute an obvious choice as multifunctional platforms, since they are worn and used to cover and drape over many of the surfaces around us. They are commonly used to provide protection in hostile environments. The present work proposes a systematic investigation into sensory characteristics of textile structures assembled from multicomponent fibers to produce fiber-based sensory textiles that are capable of generating measurable electrical response under various stimuli.

All-American Hose, LLC(6/01/14 – 12/23/14)

The objectives of this project are to:

• Develop a portable pneumatic splicing system for heavy denier continuous filament yarns
• Optimize the pneumatic splice configuration that provide the least structure changes of woven fabrics

NCSU National Textile Center Program(5/01/10 – 4/30/12)

Fiber actuators are capable of changing their dimensions (length, diameter etc) as well as generate a force when activated using appropriate electric field. Our objective is to fabricate fiber actuators from electroactive polymers, specifically dielectric elastomers. Through appropriate experimental design and theoretical analysis we plan to understand the critical parameters in the design of the fiber actuator. For the analysis we plan on using finite element modeling (using ABAQUS) of the deformation of the actuator under electrostatic stress.

NCSU National Textile Center Program(5/01/09 – 7/31/11)

The objective of the proposed research is to fabricate fiber actuators from electroactive polymers, specifically, dielectric elastomers (DE) using multi-component fiber extrusion technologies. The fiber actuators are fibers that are capable of changing their dimensions (length, diameter, etc.) as well as generate a force when activated using appropriate electrical field. Muscle-like fiber actuators capable of mimicking biological muscles have many potential applications including medical assist devices, and next generation humanoid robots. In textiles, the fibers can be used for porosity control and fabric bulk control among many other potential applications. The work is motivated by successful demonstration of the concept in a recently completed limited study and the simplicity of the principle of working of DE actuators as well as the tremendous potential offered by the current fiber forming technologies to fabricate these.

Northrop Grumman Corporation(4/01/09 – 11/30/09)

The proposed research is to adapt various preparatory and weaving technologies to weave carbon nanotube (CNT) yarns. The challenge is to develop an optimal process to weave very thin CNT yarns (ca. 2.8 tex) along both warp and filling to form a fabric.

US Dept. of Education (DED)(10/01/07 – 9/30/10)

An integrated, low-cost Braille reader will be developed using micromachining techniques and polymer actuator technologies.

National Science Foundation (NSF)(4/01/07 – 12/31/11)

Polymeric nanocomposites that are filled with conducting nanoparticles have attracted considerable scientific and commercial interest in recent years because of their wide ranging potential and availability as new functional materials. The objective of the proposed research is to fabricate lightweight, conformable sensory materials that are compatible with electronic textile products including body-worn sensors. The proposal aims to use screen-printing to fabricate an elastic and conductive nanocomposite layer of plastisol, plasticized poly(vinyl chloride) (PVC), and carbon nanofiber (CNF) on existing textile fabrics to produce a piezoresistive strain-sensing fabric. Our overarching objective of developing a fabric sensor composite (FSC) is based on the hypothesis that an elastomeric layer containing conducting nanoparticles printed on fabric substrates can yield a flexible, piezoresistive coating that can be tailored for specific applications. The objective is also based on the premise that lightweight sensory materials can be produced by controlling the volume fraction of CNF relative to the percolation threshold at which the insulating polymer layer transitions into a conducting medium. The novelty of the proposed research lies in the use of PVC in the form of plastisol and CNF. Plastisol is a commercially available dispersion of PVC resin in a plasticizer that provides unique and tunable print properties. Fractionated CNFs, on the other hand, are well-suited to the fabrication of FSCs since they are more easily dispersed, less expensive and less rigid than their carbon nanotube (CNT) analogs. In addition, the proposed method of application, screen-printing, is a well understood process that can be readily adapted to the general development of conformable self-monitoring systems and, more specifically, FSCs. The scope of the project proposed here includes the following: (1) dispersion of CNFs in plasticized PVC by reported and novel methods, (2) characterization of CNF/PVC nanocomposites varying in CNF diameter, aspect ratio, concentration and dispersion route to determine the percolation threshold and piezoresistive response, (3) application and drying of the CNF/PVC nanocomposites on fabric surfaces to determine adhesion, wettability and electro-mechanical properties, and (4) examination of the resultant FSCs by advanced microscopy methods to elucidate the distribution and orientation of the CNFs under the same conditions listed in (2).