Chemical Compatibility of Microfluidic Plastics: COC, COP, PMMA, PC, PDMS

Why chemical compatibility matters more at the microscale

In a microchannel the surface-area-to-volume ratio is very high, so interactions between the fluid and the channel wall are amplified. A reagent that a bulk plastic part would shrug off can, in a thin-walled micro-feature, cause enough swelling or softening to distort channel geometry, or leach plasticisers and unreacted monomers into a tiny sample volume. The failure modes worth keeping in mind are swelling, surface crazing, stress-cracking, leaching of additives, and absorption of the very molecules you are trying to measure. Any one of these can ruin a device or quietly bias an assay.

Chemical compatibility at a glance

COC and COP

Cyclic olefin copolymer (COC) and cyclic olefin polymer (COP) are the workhorses when chemistry is demanding. Both typically offer broadly excellent resistance to acids, bases, alcohols and aqueous buffers, and they take on very little water — useful for dimensional stability and optical work. Compare the two in our COC vs COP vs PMMA guide.

Their standout weakness is non-polar and aromatic organic solvents. Toluene, hexane and some chlorinated solvents can swell COC and COP, so they are not the right choice if your protocol involves those liquids at any meaningful concentration. For most aqueous and alcohol-based chemistry, though, they are generally more solvent-resistant than PMMA or polycarbonate.

PMMA (acrylic)

PMMA is cheap, optically clear and easy to mould, which makes it a popular prototyping and production material. It is typically fine with dilute aqueous solutions and weak acids and bases. Its limitation is organics: PMMA is attacked or stress-cracked by many of them — ketones such as acetone, chlorinated and aromatic solvents, and esters — and it is prone to crazing with alcohols such as isopropanol when the part is under stress.

This makes cleaning-solvent choice surprisingly important. A wipe-down with the wrong solvent on a stressed PMMA part can craze a polished optical window or seed cracks near a bond line. If you are bonding PMMA, the bonding chemistry itself matters too — see our bonding methods overview.

Polycarbonate (PC)

Polycarbonate is tough and heat-resistant, which makes it attractive where mechanical robustness or thermal cycling matters. Chemically, though, it is one of the weaker options: it can be hydrolysed or attacked by strong bases, and it is notoriously prone to stress-cracking with many solvents, including isopropanol. As with PMMA, parts under residual moulding stress are the most vulnerable, so a solvent that looks harmless in a soak test can still crack a loaded feature.

PDMS

PDMS is the default for soft-lithography prototyping, but its chemistry is distinctive. It swells substantially in non-polar solvents — toluene, hexane and chloroform are classic examples — while remaining perfectly happy with water and mild aqueous reagents. It also absorbs small hydrophobic molecules such as drugs and dyes, which can deplete them from solution and confound quantitative work.

Both behaviours can be managed to a degree with surface chemistry. See our deeper treatments of PDMS in microfluidics and surface treatment for the trade-offs.

Glass: the inert benchmark

When the chemistry is genuinely aggressive, glass is the safe answer. It is essentially inert to nearly all solvents, acids and bases. The practical exceptions are hydrofluoric acid, which etches it, and slow attack by strong hot alkali. For harsh organic solvents or strong oxidisers, a glass chip sidesteps the swelling and cracking concerns that affect the plastics entirely.

Environmental stress cracking

A recurring theme above is that a material can pass a relaxed soak test yet fail in service. The mechanism is environmental stress cracking: the combination of mechanical stress (often residual stress frozen in during moulding, or assembly stress at a bond) and a marginally aggressive solvent produces cracks that neither would cause alone. Bonding and adhesives can also introduce their own incompatibilities — a solvent or adhesive used to join parts may attack the substrate or leave a reactive residue, so the joint chemistry deserves the same scrutiny as the reagents. Our bonding methods guide covers the solvent-free options.

Practical guidance

• Pick the material by chemistry first. Decide what your most aggressive reagent is, then choose a substrate that tolerates it — it is far cheaper than discovering an incompatibility after tooling.
• Test with your actual reagents. Generic compatibility charts are a starting point only; validate with the real fluids at the concentration and temperature your protocol uses, ideally on stressed parts.
• Consider coatings or a different substrate. Surface coatings can mitigate absorption or wetting issues; where chemistry is severe, switching to glass removes the problem rather than managing it. See our surface treatment notes.
• Mind the assembly chemistry. Cleaning solvents, adhesives and bonding processes all touch the part — check those too, and review the material parameters for the candidates.

If you are unsure which substrate suits your chemistry, our DFM advice can help narrow it down — upload a design and we will factor material compatibility into the quote.

Frequently asked questions