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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.


Optical microscope images of PS/PTFE dissolved in GBL and mixed for different time periods. Longer mixing times result in good dispersion of PTFE particles and the formation of bar-like particles.
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Figure 1: Optical microscope images of PS/PTFE dissolved in GBL and mixed for different time periods. Longer mixing times result in good dispersion of PTFE particles and the formation of bar-like particles.

Mentions: The PS/PTFE needed for the mold is prepared by first dissolving PS in gamma-Butyrolactone (GBL) in a 25:75 wt% ratio (PS:GBL). GBL was chosen as the solvent for two main reasons: GBL does not swell or attack PDMS, and GBL can be evaporated completely in a fume hood at a relatively moderate temperature [13]. The PS/GBL mixture is kept in a shaker for 48 h to allow a complete dissolution of the PS particles. The resulting solution can be stored for several months at room temperature. The unique easy-release feature of the resulting mold is achieved by adding PTFE to the PS/GBL solution. PTFE powder (Zonyl MP 1000, DuPontTM, Wilmington, USA) is added in a 5:1 wt% ratio of PS:PTFE, by adding 4.76 wt% to the PS/GBL solution. The antisticking effect of the PTFE increases when a good dispersion of the PTFE powder or a partial unwinding of PTFE crystallites, creating fibrils, is achieved. The creation of fibrils is also referred as fibrillation [14]. To avoid agglomerates and to achieve a good dispersion of the PTFE when stirring the mixture, high shear forces are needed. In this work, a custom-made mixing head [15] was used to stir at 2000 rpm for 30 min, leading to a high degree of dispersion when the PTFE powder is ground up between the mixing head and the walls of the mixing beaker. Figure 1 shows microscopic images of PS/PTFE solutions mixed for different time periods. At longer mixing times, the PTFE particles are ground up and transformed into small, bar-like particles.


Highly elastic conductive polymeric MEMS
Optical microscope images of PS/PTFE dissolved in GBL and mixed for different time periods. Longer mixing times result in good dispersion of PTFE particles and the formation of bar-like particles.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Optical microscope images of PS/PTFE dissolved in GBL and mixed for different time periods. Longer mixing times result in good dispersion of PTFE particles and the formation of bar-like particles.
Mentions: The PS/PTFE needed for the mold is prepared by first dissolving PS in gamma-Butyrolactone (GBL) in a 25:75 wt% ratio (PS:GBL). GBL was chosen as the solvent for two main reasons: GBL does not swell or attack PDMS, and GBL can be evaporated completely in a fume hood at a relatively moderate temperature [13]. The PS/GBL mixture is kept in a shaker for 48 h to allow a complete dissolution of the PS particles. The resulting solution can be stored for several months at room temperature. The unique easy-release feature of the resulting mold is achieved by adding PTFE to the PS/GBL solution. PTFE powder (Zonyl MP 1000, DuPontTM, Wilmington, USA) is added in a 5:1 wt% ratio of PS:PTFE, by adding 4.76 wt% to the PS/GBL solution. The antisticking effect of the PTFE increases when a good dispersion of the PTFE powder or a partial unwinding of PTFE crystallites, creating fibrils, is achieved. The creation of fibrils is also referred as fibrillation [14]. To avoid agglomerates and to achieve a good dispersion of the PTFE when stirring the mixture, high shear forces are needed. In this work, a custom-made mixing head [15] was used to stir at 2000 rpm for 30 min, leading to a high degree of dispersion when the PTFE powder is ground up between the mixing head and the walls of the mixing beaker. Figure 1 shows microscopic images of PS/PTFE solutions mixed for different time periods. At longer mixing times, the PTFE particles are ground up and transformed into small, bar-like particles.

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.