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Highly elastic conductive polymeric MEMS

View Article: PubMed Central - PubMed

ABSTRACT

Polymeric structures with integrated, functional microelectrical mechanical systems (MEMS) elements are increasingly important in various applications such as biomedical systems or wearable smart devices. These applications require highly flexible and elastic polymers with good conductivity, which can be embedded into a matrix that undergoes large deformations. Conductive polydimethylsiloxane (PDMS) is a suitable candidate but is still challenging to fabricate. Conductivity is achieved by filling a nonconductive PDMS matrix with conductive particles. In this work, we present an approach that uses new mixing techniques to fabricate conductive PDMS with different fillers such as carbon black, silver particles, and multiwalled carbon nanotubes. Additionally, the electrical properties of all three composites are examined under continuous mechanical stress. Furthermore, we present a novel, low-cost, simple three-step molding process that transfers a micro patterned silicon master into a polystyrene (PS) polytetrafluoroethylene (PTFE) replica with improved release features. This PS/PTFE mold is used for subsequent structuring of conductive PDMS with high accuracy. The non sticking characteristics enable the fabrication of delicate structures using a very soft PDMS, which is usually hard to release from conventional molds. Moreover, the process can also be applied to polyurethanes and various other material combinations.

No MeSH data available.


Resistance-strain measurement for a 200-μm thin layer of C-PDMS. Different elongation cycles are shown, starting with cycle 2 after the first preload cycle.
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Figure 5: Resistance-strain measurement for a 200-μm thin layer of C-PDMS. Different elongation cycles are shown, starting with cycle 2 after the first preload cycle.

Mentions: C-PDMS. Figure 5 shows the results of the C-PDMS measurements. The base resistance of the strip was measured before stretching to be at a distance of 34 mm, leading to a conductivity of 5.1 Sm−1. After the first preload cycle, the conductive particles inside the PDMS rearranged, and the resistance increased to at 0% strain. The measurement results of five representative curves are shown in the figure. The material shows a non linear behavior when stretched and a fairly linear behavior when released, leading to a relatively strong hysteresis. The hysteresis and the absolute values of the resistance decrease slightly with each consecutive cycle. The resistance after 2500 cycles is decreased to at 0%, strain, thus showing a reduction of 28.6 % after 2500 elongation cycles, in comparison to the resistance after preloading. Possible reasons for the systematic variation of the measurement results during the cycles are a rearrangement of particles during stretching and relaxation, and the viscoelastic behavior of the filled polymer.


Highly elastic conductive polymeric MEMS
Resistance-strain measurement for a 200-μm thin layer of C-PDMS. Different elongation cycles are shown, starting with cycle 2 after the first preload cycle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036488&req=5

Figure 5: Resistance-strain measurement for a 200-μm thin layer of C-PDMS. Different elongation cycles are shown, starting with cycle 2 after the first preload cycle.
Mentions: C-PDMS. Figure 5 shows the results of the C-PDMS measurements. The base resistance of the strip was measured before stretching to be at a distance of 34 mm, leading to a conductivity of 5.1 Sm−1. After the first preload cycle, the conductive particles inside the PDMS rearranged, and the resistance increased to at 0% strain. The measurement results of five representative curves are shown in the figure. The material shows a non linear behavior when stretched and a fairly linear behavior when released, leading to a relatively strong hysteresis. The hysteresis and the absolute values of the resistance decrease slightly with each consecutive cycle. The resistance after 2500 cycles is decreased to at 0%, strain, thus showing a reduction of 28.6 % after 2500 elongation cycles, in comparison to the resistance after preloading. Possible reasons for the systematic variation of the measurement results during the cycles are a rearrangement of particles during stretching and relaxation, and the viscoelastic behavior of the filled polymer.

View Article: PubMed Central - PubMed

ABSTRACT

Polymeric structures with integrated, functional microelectrical mechanical systems (MEMS) elements are increasingly important in various applications such as biomedical systems or wearable smart devices. These applications require highly flexible and elastic polymers with good conductivity, which can be embedded into a matrix that undergoes large deformations. Conductive polydimethylsiloxane (PDMS) is a suitable candidate but is still challenging to fabricate. Conductivity is achieved by filling a nonconductive PDMS matrix with conductive particles. In this work, we present an approach that uses new mixing techniques to fabricate conductive PDMS with different fillers such as carbon black, silver particles, and multiwalled carbon nanotubes. Additionally, the electrical properties of all three composites are examined under continuous mechanical stress. Furthermore, we present a novel, low-cost, simple three-step molding process that transfers a micro patterned silicon master into a polystyrene (PS) polytetrafluoroethylene (PTFE) replica with improved release features. This PS/PTFE mold is used for subsequent structuring of conductive PDMS with high accuracy. The non sticking characteristics enable the fabrication of delicate structures using a very soft PDMS, which is usually hard to release from conventional molds. Moreover, the process can also be applied to polyurethanes and various other material combinations.

No MeSH data available.