Experiment 1 - The "Initial" Stamp

The PDMS stamp can be used to transfer many small complex patterns. This experiment may be used to learn about the general idea of the stamp fabrication process and properties.

Materials

• Dull pencil
• Aluminum foil
• Glass slide
• Convection oven capable of reaching 130º C
• Sylgard Elastomer 184, obtained from Ellsworth Adhesive Systems
• Thick-walled tube mold (~ 1 cm I.D. x ~ 3 cm long). A recommended mold is a standard taper 24/40-to-10 Pyrex adapter.
• Ink pad or markers

Procedures

• Take a smooth piece of aluminum foil and place it on a somewhat soft surface like a stack of paper. Using a dull pencil or a ball-point pen, print letters such as your initials onto the foil surface, Figure 1. Deeper letter imprints make better stamps, but DO NOT open holes in the foil with the writing instrument. It may take some practice to obtain uniformly deep lettering.

Figure 1. Impressing initials into aluminum foil.

• Place the foil onto a solid, heat-resistant flat surface such as a glass slide and carefully place the glass tube over the foil. Be careful not to flatten the engraved lettering with the mold while it is being positioned. A recommended mold is a standard taper 24/40-to-10 Pyrex adapter, Figure 2.

Figure 2. Recommended mold for making the "initial" PDMS stamp.

• Pour the freshly mixed PDMS (~1:10 ratio of curing agent to base) into the mold to a depth of approximately 1 cm (typically 1 g will be sufficient for the mold previously mentioned) and set aside for 15 minutes to reduce the amount of bubbles and PDMS clinging to the sides of the mold. After curing at 130º C for 30 minutes and cooling, slowly peel the foil away from the PDMS and mold. Then carefully remove the PDMS from the mold by pressing on the PDMS at a point where it meets the inside mold walls on the end opposite the lettering. Repeat this process while moving around the inside wall until the PDMS pops free of the mold. Excess cured elastomer may be removed carefully with a razor blade.

Explorations

The stamp may be inked by an ink pad or even by markers, Figure 3. Try squeezing the stamp during ink transfer to paper and observe what happens to the size and shape of the letters, Figure 4.

Figure 3. Print from "initial" stamp inked with permanent marker. The length of the "J" (the middle letter of DJC) in the printed image is four millimeters.

Figure 4. Compressing the "initial" PDMS stamp (direction of compression indicated by arrows). The length of the "J" in the printed image (the middle letter of DJC) has increased to five millimeters.

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Experiment 2 - A Flexible Diffraction Grating

Experiment 3 - Bouncing PDMS Balls

Experiment 4 - Surface Treatment of PDMS