Thermo-mechanical Behavior of (Meth)Acrylate Shape-Memory Polymer Networks
- PDF / 282,892 Bytes
- 7 Pages / 432 x 648 pts Page_size
- 22 Downloads / 182 Views
Thermo-mechanical Behavior of (Meth)Acrylate Shape-Memory Polymer Networks Carl P. Frick1, Nishant Lakhera1 and Christopher M. Yakacki2,3 1
Mechanical Engineering, University of Wyoming, Laramie, Wyoming, USA MedShape Solutions, Inc., Atlanta, Georgia, USA 3 School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, USA 2
ABSTRACT Our overall approach is based on developing a photocrosslinkable polymer network with a favorable shape-memory response, using polymer chemistry and crosslinking density to control thermo-mechanical properties. Three polymer networks were created and thermo-mechanically tested, each from tert-Butyl acrylate linear builder co-polymerized with a poly(ethylene glycol) dimethacrylate cross-linker. By systematically altering the molecular weight and the weight fraction of the cross-linker, it was possible to create three polymers that exhibited the same glass transition temperature, but varied by almost an order of magnitude in rubbery modulus. Therefore, the mechanical stiffness could be tailored to suit a given application. Recovery behavior of the polymers was characterized over a range of deformation temperatures. It has been implicitly assumed a linear relationship between Free-Strain (i.e. no actuation force) and Fixed-Stress (i.e. maximum actuation force), however, this has never been confirmed experimentally. The energy per unit volume performed by the shape-memory polymer was quantified, and observed to be a function of strain recovered. The maximum recoverable work was shown to increase with cross-linking density, although the overall efficiency is similar for all materials tested. INTRODUCTION Shape-memory polymers (SMPs) have attracted increased attention over the last several years due to their ability to temporarily store a deformed shape, and subsequently recover the deformation upon exposure to heat. This capability has led to several proposed applications, including self-deployable structures for biomedical and space applications, among others [1-4]. Inherent advantages include high recovery strain, low density, and low cost. For example, in comparison with NiTiNOL shape-memory alloys that can recover approximately 4% to 8% of applied displacement, whereas SMPs can recover strains on the order of 50% to 500% [5, 6].
Figure 1: Schematic illustration of the Shape-Memory Effect. The material is mechanically deformed, cooled to store the deformed shape, and then heated to elicit shape recovery.
The shape-memory effect in polymers is schematically outlined in Figure 1. The polymer is first synthesized into a permanent shape by standard polymer processing techniques. Subsequently, the polymer is heated above a critical temperature, such as the glass transition temperature, Tg, and thermo-
111
mechanically deformed into a temporary shape, a process known as shape storage. The polymer will remain in the stored shape until it is reheated in the vicinity of its glass transition temperature, upon which it will experience controlled shape recovery. Thermopl
Data Loading...
