Document Type

Student Presentation

Presentation Date

4-16-2018

College

College of Engineering

Department

Materials Science and Engineering

Faculty Sponsor

Peter Müllner

Abstract

With the recent advent of magnetic shape memory alloys (MSMA), such as martensitic Ni-Mn-Ga, researchers focused studies about these materials on properties such as magnetic-field-induced deformation. Currently, some of the properties of interest include, but are not limited to: twin boundary deformation, strain, stress, magnetic and thermal activation, operating temperatures, magnetic permeability, and electric resistivity. Given some of these properties, materials such as Ni-Mn-Ga have been used as actuators, channels, and membranes in pumps. While these pumps are currently at the stage of sub-microliter medical application, they have also been shown to possess great accuracy in delivery as well as strength in pumping against relatively high back pressures. In this system, given the small size of the pump, a typical O-ring cannot provide the same effective seal as it would in a regular impeller pump. However, using a Polydimethylsiloxane (PDMS) gel has proven to be a useful sealant for these MSMA pumps. The interaction of the sealant against the Ni-Mn-Ga itself, in particular adhesion and detachment, take on a critical role in the pumping process. That is to say that as the "channel", created by the twin boundary shift, moves, the PDMS must adhere to the alloy up to a specific limit and then detach. This adhesion-detachment must be controlled and repeatable. This simulation study aims to quantify the interaction of PDMS and Ni-Mn-Ga, as it pertains to the adhesivity of the former to the latter, in order to better determine how best to cure PDMS for optimal adhesion and separation. In order to study these PDMS-MSMA surfaces, GPUs in the XK nodes of the Blue Waters Supercomputer, at the University of Illinois, Urbana-Champaign, were used in conjunction with the HOOMD-blue particle simulation kit to render them and study the molecular dynamics between these two materials. The PDMS models for this simulation were based on a united atom (UA), Lennard-Jones potential modified from previous studies(1) , utilizing 20-mer chains. While the Ni-Mn-Ga surface was based on an M1 matrix developed at Boise State. The MSMA surface his modeled as a rigid lattice structure without twin boundary movement, the motion is instead replaced by simulating a pulling force on the PDMS surface up to where it detaches from the MSM surface. By utilizing these constraints we can begin to study the effects that the curing time of PDMS has on this interaction with Ni-Mn-Ga, how the MSMA’s lattice structure reacts in this scenario, and how best to continue incorporating further constraints into these simulation studies, such as simulated twin boundary movement.

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