Sofia Martinez
PDMS, or polydimethylsiloxane, is a silicon-based organic polymer that is widely used in research and industry due to its unique properties, including optical transparency, biocompatibility, and flexibility. However, one common challenge faced by those working with PDMS is its tendency to stick to surfaces, particularly plastic and glass. This can cause issues during the fabrication process, such as difficulty in removing PDMS from moulds or stamps, as well as leakage and bonding problems. To address this issue, various techniques have been proposed, including the use of coatings or treatments such as sigmacote, hair oils, Pluronic F127, silanisation, and oxygen plasma treatment. Adjusting the curing process, such as curing time and temperature, as well as the polymer-to-curing agent ratio, can also influence the stickiness of PDMS.
Characteristics and Values
| Characteristics | Values |
|---|---|
| Polymer:curing agent ratio | Determines stickiness of PDMS |
| Baking time | Determines stickiness of PDMS |
| Tricloroperfluorooctyl silane | Used to prevent PDMS from sticking to silicon |
| Pluronic F127 | Used to prevent cells from sticking to PDMS |
| Talcum powder | Used to prevent PDMS from sticking to glass |
| Hair oil | Used to prevent PDMS from sticking to glass |
| Plasma treatment | Used to help PDMS stay adhered |
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What You'll Learn
Try a different curing method
Curing PDMS at room temperature for 24 hours is a commonly suggested method to prevent stickiness. However, some users have reported that this method does not always work, and they have experienced stickiness even after curing for this duration.
One user recommends a different approach: mix the PDMS base and curing agent in a 1:10 ratio, mix for 10 minutes, pour, and cure overnight at 50°C. This method resulted in non-sticky PDMS devices.
Another user suggests a similar method: mix the PDMS base and curing agent in a 1:20 ratio, leave it overnight at 37°C, and expect it to be sticky the next day. However, this user encountered issues with the PDMS not sticking perfectly to their dishes, allowing the cell solution to sneak underneath and causing detachment.
It is worth noting that the polymer-to-curing agent ratio and baking time can influence the stickiness of PDMS. Adjusting these parameters may be necessary to find the optimal conditions for your specific application.
Additionally, pre-treating the PDMS with Pluronic F127 is recommended by some users as a simple solution to reduce stickiness in digital microfluidics applications.
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Use a different PDMS product
Using a different PDMS product can help prevent PDMS from sticking to plastic. Different PDMS products have varying levels of stickiness, so choosing a less sticky option may be beneficial. For instance, one user reported that their PDMS product worked perfectly and could be cured after mixing the elastomer base and hardener, but when they purchased the same product again, it did not cure under the same conditions.
Additionally, the polymer-to-curing agent ratio in PDMS products determines their stickiness. Adjusting this ratio can help reduce stickiness. For example, one user reported that decreasing the polymer-to-curing agent ratio in their PDMS product made it less sticky.
Another factor that influences the stickiness of PDMS is the baking time. By altering the baking time, you can affect the stickiness of the PDMS product.
Furthermore, some specific PDMS products, such as Pluronic F127, can be used as a pre-treatment to reduce the stickiness of PDMS. This product is available at Sigma and is relatively inexpensive.
Additionally, using a Mylar® film between the rigid plate and PDMS can help prevent adhesion. PDMS does not stick to Mylar®, so it can be easily peeled off after fabrication. This method also eliminates the need for surface treatment and protects the plates from scratches.
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Use a different coating
To prevent PDMS from sticking to plastic, you can use a different coating. Here are some suggestions:
Sigmacote
You can coat your wafers with a thin layer of sigmacote to prevent adhesion. This will create a barrier between the PDMS and the plastic surface, reducing the likelihood of sticking.
Hair Oil
Coating the plastic surface with a thin layer of hair oil before applying PDMS can make it easier to remove the PDMS once it is cured. This method has been used successfully in the past, although it may not work for all types of plastic.
Pluronic F127
Soaking your plastic surface in a solution of Pluronic F127 can help prevent sticking. This method is simple and inexpensive, but it may not be effective for all applications. For example, one user reported that Pluronic F127 did not completely prevent cells from adhering to a PDMS surface.
Tricloroperfluorooctyl Silane
This chemical can be used in a process called silanisation to prevent PDMS from sticking to silicon. It is applied through vapor deposition, either in a desiccator or a custom deposition chamber. This method may be more complex and require specialised equipment.
Perfluorooctyltrichlorosilane
This chemical has been suggested as an alternative to hexamethyldisilizane (HMDS) to prevent sticking. It may be worth trying this substitute if HMDS is not effective for your specific application.
Teflon
A thin layer of teflon film, similar to household cling film, can be stretched over the plastic surface before applying PDMS. This creates a barrier that allows for easy removal of the PDMS after curing.
It is important to note that the effectiveness of these coatings may vary depending on the specific materials and conditions you are working with. It may be necessary to experiment with different coatings and conditions to find the most effective solution for your particular application.
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Adjust the polymer:curing agent ratio
Adjusting the polymer-to-curing agent ratio is a critical step in preventing PDMS from sticking to plastic. PDMS, or polydimethylsiloxane, is a silicone polymer that is widely used for its ease of moulding, gas permeability, optical transparency, flexibility, and biocompatibility.
The polymer-to-curing agent ratio determines the stickiness of the PDMS material. By decreasing the ratio, that is, using less curing agent relative to the amount of polymer, you can make the PDMS less sticky. This is because a lower ratio results in a lower rate of cross-linking, producing a softer elastomer.
The specific ratios used will depend on the type of PDMS being used and the desired mechanical properties. Common mixing ratios for the base polymer and curing agent include 10:1, 10:2, and 10:3. It is important to note that increasing the amount of curing agent will reduce the tensile strength of the PDMS.
In addition to adjusting the ratio, other factors such as curing time and temperature play a role in the final properties of the PDMS. PDMS can be cured at room temperature, but this will take a longer time. Typically, PDMS is cured at temperatures between 65°C and 80°C for a few hours.
By carefully controlling the polymer-to-curing agent ratio and curing conditions, you can prevent PDMS from sticking to plastic and achieve the desired mechanical and surface properties for your specific application.
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Try a different cleaning method
PDMS residue can be challenging to remove from surfaces. One method to prevent adhesion is to coat your wafers with a thin layer of sigmacote. Another option is to use hair oil on the surface before coating with PDMS; the PDMS will then come off easily after curing.
If you are using a stainless steel mould, you can try curing at room temperature for 24 hours. If you want a 'soft' PDMS, bake the system at 65°C for at least 3 hours. For a harder PDMS, curing at a higher temperature of 50°C overnight will prevent stickiness.
If you are using a 3D-printed mould, you can try mixing a 1:10 base-to-curing agent ratio, mixing for 10 minutes, and then curing overnight at 50°C.
To clean PDMS from a silicon master, you can use solvents like acetone and dry under airflow.
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Frequently asked questions
To prevent PDMS from sticking to plastic, you can try using silicon grease around the inlets. Alternatively, you can coat your wafers with a thin layer of sigmacote to prevent adhesion.
You can try silanizing your masters with a tridecafluoro-silane using vapor deposition. Another option is to coat the surface with a thin layer of hair oil before coating with PDMS.
You can try spreading PDMS over a precision polished aluminium surface and stretching a thin Teflon film over it to allow for easy peel-off after curing.
