Review: Epoxy

This is the first part of a series in which I will review various glues etc. This is a fairly shallow and boring topic, but systems neuroscience is a field in which we often have to build things and and much frustration and lost time is caused by lack of knowledge in how to properly use adhesives.

The majority of gluing tasks in lab can and should be be solved with epoxy.

Basic properties:

  • Bonds to almost anything.
  • Can fill gaps.
  • No solvent or other outgassing, so it is generally safe to use around optics, plastics, etc.
  • High stiffness, can even be somewhat brittle depending on the type.
  • Makes for amazing composites. Fiberglass / carbon fiber composites are fibers plus epoxy. In the lab, even some strips of lab tape, painted over with epoxy can hold things in place fairly securely. Or tack things in place with hot glue, then cover the hot glue with epoxy.
  • Epoxies with no added fillers (small mixed in particles that improve mechanical strength etc.) can be cut reasonably well with razor blades. As an example, we exploit this when making guide tube arrays for drive implants.

Pro tips:

  • Epoxies are slightly hygroscopic, even when cured. This means they are usually decent insulators, but you can not rely on them being amazing insulators if they are in contact with conductive solutions. This is also why you should keep a cap on the epoxy bottle if you plan on keeping it for a while.
  • Can cure somewhat exothermically, this means that for stress-free precision assemblies you want slow-curing epoxy and thin films.
  • Epoxy retains a little bit of creep for a while, so if you need to hold weight/pressure quickly, dental acrylic might be a better choice. It can also help to use epoxy with fillers.
  • To remove epoxy from small parts, for instance small circuit boards, soak them in ethanol (70% works) for a few days, and you can peel off the, now rubbery, epoxy. Also, be careful when using epoxy in places where it may be exposed to solvents.
  • Most non-filled epoxies break down at high temperatures and can be removed decently well with an old soldering iron tip. This is usually a last resort, but handy.
  • Regular scotch tape releases very well from epoxy. If there’s a space you need to fill, for instance a hole, close if off with tape, fill with epoxy, and remove tape. This can also be used to bridge gaps, etc.

How to use:

  • As always, consider cleaning the surfaces if you need maximal adhesion. Ethanol is ok but has a tendency to just move oils around instead of lifting them away, so its often easier to use an abrasive method. In 99% of cases in lab use, no cleaning is needed.
  • Fix parts to be glued in place, or prepare to do so – its not fun to hold stuff for ~5min.
  • Mix thoroughly in a plastic weigh boat. If your epoxy doesn’t cure right, this likely means you didn’t mix it enough. Watch this video on laminar flow to understand why mixing this stuff takes a while.
  • Apply, fix parts in place.
  • Check if the epoxy in the mixing dish has cured to judge when your part has cured. If you mix large batches, the leftovers could heat up a bit, and cure a bit faster than the part.

What to buy:

  • If you keep one type of epoxy it should be regular 5min epoxy, we like bottles, like the ones from bob smith industries.
  • If you keep two, add a 15min variant for larger jobs where the batch of 5min epoxy would cure while you apply it.
  • Epoxy with fillers, such as JB weld for demanding mechanical bonds and higher stiffness.

Rating: ⭐⭐⭐⭐⭐


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