Hanging elastomers is something of a artform that one learns through experience.
The best way to minimize making poor elastomers is having all materials prepared ahead of time
- balance
- weighing boat | paper
- glass vial | plastic > 5mL
- glass | plastic transfer pipette
- Teflon film (~20um thick)
- spin casting head
- heated centrifuge | spinning apparatus
- dry-ice | liquid nitrogen
- Tefzel tape (DuPont)
- 15 cm plastic | wood | metal rod for hanging LCE
This material is prepared using a heated centrifuge in a spin casting head. Before
starting material preparation, pre-heat the spin casting head to 60 ~ 65oC.
The first step is preparation of the catalyst solution and reaction solution
- The platinum catalyst solution is prepared as a 1 to 2% weight/weight (w/w) solution
in methylene chloride. Typically, this solution is prepared in quantities of 100 to 200uL in a brown vial and stored
in the refrigerator.
- Example calculation for 1% (w/w)solution: Add 2 mg of the platinum
catalyst to brown glass vial. Add methylene
chloride drop wise until the total mass is 100 mg. This will be enough to prepare 5 batches of LCE
Glass vial used in preparation of catalyst solution. The white crystalline powder
at the front of the vial is the Pt catalyst crystals
- Please use the Excel spreadsheet embedded in the downloadable Word document (top of page) for all calculations. Typically, the amount
of crosslinker is between 5 and 15%
- All materials (crosslinker, mesogen, siloxane polymer, and solvent) are measured using an analytical balance. Try to
measure as precisely as possible. Do not be concerned if a few mg extra of the crosslinker or mesogen are added.
However, the spreadsheet calculations will no longer be accurate. Enter the weighed mass amounts into the spreadsheet
to obtain the correct crosslink density
- Materials are transferred to the glass vial in the following order.
- Siloxane polymer - transferred by pipette. Always use the balance to determine the amount of polymer in the vial,
not the amount dispensed from the pipettor.
Approximately 65 uL of siloxane polymer in glass vial.
- Cross linker
After the addition of the crosslinker
- Mesogen
After the addition of the crosslinker
If too much mesogen is added, it may be very carefully removed using a spatula.
This is not the case for the crosslinker, as it comes in direct contact with the
siloxane polymer.
If too much of a crosslinker is added (> 2% mol) , use the spreadsheet to recalculate the amount of polymer
required and carefully add additional polymer as needed
- Add thiophene free toluene. At room temperature, the materials will spontaneously dissolve in ~60 minutes.
The vial may be heated or gently vortexed to speed up the process. Make sure no materials is left on the side of the vial.
Allow the vial to return to near room temperature before adding the catalyst
After the addition of the crosslinker
- Record the actual amounts of material used in your lab notebook. Enter the values in the Excel spreadsheet to obtain
a more precise estimate of crosslinker density.