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Research Papers

Light Activated Shape Memory Polymer Characterization

[+] Author and Article Information
Richard V. Beblo

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261rvb2@pitt.edu

Lisa Mauck Weiland1

Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261lweiland@engr.pitt.edu

1

Corresponding author.

J. Appl. Mech 76(1), 011008 (Oct 31, 2008) (8 pages) doi:10.1115/1.2999447 History: Received February 01, 2008; Revised July 10, 2008; Published October 31, 2008

Since their development, shape memory polymers (SMPs) have been of increasing interest in active materials and structures design. In particular, there has been a growing interest in SMPs for use in adaptive structures because of their ability to switch between low and high stiffness moduli in a relatively short temperature range. However, because a thermal stimulus is inappropriate for many morphing applications, a new light activated shape memory polymer (LASMP) is under development. Among the challenges associated with the development of a new class of material is establishing viable characterization methods. For the case of LASMP both the sample response to light stimulus and the stimulus itself vary in both space and time. Typical laser light is both periodic and Gaussian in nature. Furthermore, LASMP response to the light stimulus is dependent on the intensity of the incident light and the time varying through the thickness penetration of the light as the transition progresses. Therefore both in-plane and through-thickness stimulation of the LASMP are nonuniform and time dependent. Thus, the development of a standardized method that accommodates spatial and temporal variations associated with mechanical property transition under a light stimulus is required. First generation thick film formulations are found to have a transition time on the order of 60 min. The characterization method proposed addresses optical stimulus irregularities. A chemical kinetic model is also presented capable of predicting the through-thickness evolution of Young’s modulus of the polymer. This work discusses in situ characterization strategies currently being implemented as well as the current and projected performance of LASMPs.

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Figures

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Figure 1

A (top)—sample exposed to direct laser light: Zone 1 is the high optical stimulus in the laser beam center and Zone 2 is the little optical stimulation away from the beam; B (bottom)—laser diffused with convex cylindrical lens

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Figure 2

Contour plot of optical power, sample location outlined by black rectangle

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Figure 3

Surface plot of optical power as seen in the sample

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Figure 4

Film depicting the laser shadow of a sample during testing

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Figure 5

Example in situ experimental results. Shown are the results of the ten 2 min tests spaced 5 min apart with the loading portion of select curves labeled.

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Figure 6

Time evolution of Young’s modulus for sample exposed to 325–385 nm light

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Figure 7

Time evolution of Young’s modulus for sample exposed to 248–280 nm light

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Figure 8

First generation LASMP absorbance

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Figure 9

Time dependence of absorbance

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Figure 10

Model prediction as compared with experimental data

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Figure 11

Predicted through-thickness evolution of photo activated uncross-linked species

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Figure 12

Predicted evolution of Young’s modulus through sample thickness

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