Application of Rotational Isomeric State Theory to Ionic Polymer Stiffness Predictions
- PDF / 844,879 Bytes
- 13 Pages / 612 x 792 pts (letter) Page_size
- 72 Downloads / 143 Views
Emily K. Lada Statistical and Applied Mathematical Sciences Institute (SAMSI), Research Triangle Park, North Carolina 27709
Ralph C. Smith Center for Research in Scientific Computation, Department of Mathematics, North Carolina State University, Raleigh, North Carolina 27695
Donald J. Leo Center for Intelligent Material Systems and Structures, Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 (Received 7 February 2005; accepted 12 May 2005)
Presently, rotational isomeric state (RIS) theory directly addresses polymer chain conformation as it relates to mechanical response trends. The primary goal of this work is to explore the adaptation of this methodology to the prediction of material stiffness. This multiscale modeling approach relies on ionomer chain conformation and polymer morphology and thus has potential as both a predictive modeling tool and a synthesis guide. The Mark–Curro Monte Carlo methodology is applied to generate a statistically valid number of end-to-end chain lengths via RIS theory for four solvated Nafion® cases. For each case, a probability density function for chain length is estimated using various statistical techniques, including the classically applied cubic spline approach. It is found that the stiffness prediction is sensitive to the fitting strategy. The significance of various fitting strategies, as they relate to the physical structure of the polymer, are explored so that a method suitable for stiffness prediction may be identified.
I. INTRODUCTION
Ionic polymers comprise the active layer in ionic polymer–metal composites (IPMCs), which were first identified just over a decade ago1–5 and now constitute an emerging class of soft transducers (Fig. 1). Because they generate large strain in response to low electric field stimulation and have high gravimetric energy density, there has been considerable conjecture over the potential applications of these soft transducers2,3,6–8 and considerable fruitful investigations toward these ends.9–11 The high gravimetric energy density is a function of both the electromechanical transduction mechanisms of the ionic polymer layer and the global IPMC stiffness. Most models of the transduction behavior rely on the cluster morphology of the ionic polymer layer, as proposed by Hsu and Gierke,12 where the material has been
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0292 J. Mater. Res., Vol. 20, No. 9, Sep 2005
http://journals.cambridge.org
Downloaded: 25 Mar 2015
solvated with water. In brief, the backbone of the ionic polymer chain is hydrophobic whereas the side chains terminate in hydrophilic ionic groups. Hsu and Gierke propose a clustering of these hydrophilic ionic side groups and the water that has been taken up by the material. The model further suggests an idealized structuring whereby the clusters are of essentially constant radius, uniformly distributed throughout the material, and interconnected by channels. Subse
Data Loading...
