Patterning the Stiffness of Elastomeric Nanocomposites by Magnetophoretic Control of Cross-linking Impeder Distribution

Suvojit Ghosh; Mehran Tehrani; Marwan S Al-Haik; Ishwar K Puri

doi:10.3390/ma8020474

Patterning the Stiffness of Elastomeric Nanocomposites by Magnetophoretic Control of Cross-linking Impeder Distribution

Materials (Basel). 2015 Jan 30;8(2):474-485. doi: 10.3390/ma8020474.

Authors

Suvojit Ghosh^{1

2}, Mehran Tehrani³, Marwan S Al-Haik⁴, Ishwar K Puri^{5

6}

Affiliations

¹ Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. sghosh@mcmaster.ca.
² Department of Engineering Science and Mechanics, Virginia Tech, 495 Old Turner Street, Blacksburg, VA 24061, USA. sghosh@mcmaster.ca.
³ Department of Mechanical Engineering, University of New Mexico, Albuquerque, NM 87131, USA. mtehrani@unm.edu.
⁴ Department of Engineering Science and Mechanics, Virginia Tech, 495 Old Turner Street, Blacksburg, VA 24061, USA. alhaik@vt.edu.
⁵ Department of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. ikpuri@mcmaster.ca.
⁶ Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. ikpuri@mcmaster.ca.

Abstract

We report a novel method to pattern the stiffness of an elastomeric nanocomposite by selectively impeding the cross-linking reactions at desired locations while curing. This is accomplished by using a magnetic field to enforce a desired concentration distribution of colloidal magnetite nanoparticles (MNPs) in the liquid precursor of polydimethysiloxane (PDMS) elastomer. MNPs impede the cross-linking of PDMS; when they are dispersed in liquid PDMS, the cured elastomer exhibits lower stiffness in portions containing a higher nanoparticle concentration. Consequently, a desired stiffness pattern is produced by selecting the required magnetic field distribution a priori. Up to 200% variation in the reduced modulus is observed over a 2 mm length, and gradients of up to 12.6 MPa·mm^-1 are obtained. This is a significant improvement over conventional nanocomposite systems where only small unidirectional variations can be achieved by varying nanoparticle concentration. The method has promising prospects in additive manufacturing; it can be integrated with existing systems thereby adding the capability to produce microscale heterogeneities in mechanical properties.

Keywords: functional grading; magnetic nanoparticles; nano composites; nanoindentation.