The featured image above is from Formica.com
I dislike many aspects of the kitchen in my house. The previous owners took a well-designed and well-built 1959 house, and basically screwed it up by, among other things, putting in a trendy “designer” kitchen. Amongst the hate-able aspects of that kitchen are the obligatory granite countertops.
Today, as I was housecleaning, scraping little bits of crap off those perpetually-grungy kitchen countertops, I had a flash of insight.
Seems like stuff sticks to these granite countertops to an extent that never happened with our old Formica (r) countertops. It’s almost as if granite countertops are mostly for show, and are a really poor choice if you are actually going to use your kitchen intensively. Heck, I keep a plastic paint scraper at the sink, just for scraping up the most-stuck-on stuff from those countertops. I’m pretty sure I never needed that with Formica (r).
Gunk just seems to glue itself to those granite countertops.
That’s when the light bulb lit. It really isn’t my imagination that granite is tougher to keep clean than Formica (r). My perpetually grungy granite is the flip side of the difficulty of gluing certain types of plastic. If Teflon is at one end of the spectrum, then polished granite is somewhere near the other end.
It’s all about surface energy.
Surface energy
Naively, you might think that the strength of a glue bond is determined by the roughness of the surfaces to be glued. And, to some degree, that’s true. Roughening up a surface can provide more contact area and places for glue to physically wedge itself in place.
But the main determinant of whether or not glue will stick to something is the surface energy of the substance you are trying to glue. Stuff with low surface energy is difficult to glue — think Teflon. Stuff with high surface energy is much easier to glue — most metals fall into that category.
I’m having a hard time finding a plain-language explanation of what, exactly, surface energy is. But in a nutshell, when you take a solid object and cut a surface into it, you disrupt a lot of atomic bonds. That leaves some tag ends of molecules or surfaces of crystals that are not quite happy with their state of being.
Alternatively, even on a smoothly-formed surface (cast plastic, say), the molecules within the solid face balanced forces in all directions. But the molecules on the surface only have those forces on the inside surface, and so they go looking for anything that might counterbalance those forces, on the outside surface.
Those little molecular-level tag ends would be happier if they could latch onto something. Ditto, the surface molecules seeking balance between internal and external forces. The more of those you have, and the “grabbier” they are, the higher the surface energy.
By contrast, if you end up with a surface full of molecules that are quite content with one another, and see no particular need to interact with the outside world, you get low surface energy.
For those of you who have tried to glue plastic to plastic, you know what I’m talking about. If you’re trying to stick two plastic objects together, low surface energy is what makes it next-to-impossible to find a glue that will (e.g.) stick something to HDPE (milk jug) plastic.
In fact, the most common “gluing” of plastic isn’t gluing at all. PVC pipe “cement” isn’t a glue, it’s just a solvent. It dissolves the top layer of the PVC, then evaporates. As a result, when you “glue” PVC together, the process is actually “solvent welding”. When you’re done, there’s nothing but PVC in that pipe joint. Which is good, because almost no glues will reliably stick to PVC.
This is also why you can buy “plastic welding” kits, as an alternative to trying to glue plastic. There, you simply melt the plastic, adding a bit more to fill in any cracks. When you’re done, there’s no glue anywhere, just the original plastic and whatever additional plastic you might have melted into it.
Crazily enough, despite the molecular-level complexity of what surface energy is, physically measuring it is straightforward. Put a drop of water on the clean surface, and see how tightly it beads up.
Surfaces with high surface energy allow the water to spread, producing broad, flat water drops. By contrast, surfaces with low surface energy allow the water’s own surface tension to keep the droplets compact and tall.
Like so: These pictures are from my kitchen. These drops below all contain the same amount of water. All were filmed at just about the same angle. Two are on my polished granite countertops. Two are on a Teflon-coated frying pan.
The low, flat drops reveal that the polished granite is, indeed, a high-surface-energy material. The plump, almost globular droplets on Teflon reveal that it is a low-surface-energy material.
(Surface energy gets quoted in several equivalent units. Sometimes it’s millijoules per square meter. Sometimes it’s ergs per square centimeter. Those are mathematically equivalent because a millijoule is 10,000 ergs, and a square meter is 10,000 square centimeters. (Weirdly, it is sometimes quoted in dynes per something, which makes no sense to me, as dyne is a unit of force, not energy.) In any case, all the common ways of reporting this seem to lead to the exact same quantitative scale. E.g., Teflon is always slightly less than 20.)
Formica (r) behaves a lot more like Teflon than like granite, in this regard. Teflon typically has a surface energy quoted around 19 (see above for units, reference). Melamine — the surface plastic on Formica (f) — seems to be in the neighborhood of 40 (reference), mid-range for most common plastics. But quartz, a principal component of granite, runs from 400 to 1000, on that same scale (reference). Feldspar, the other main component of granite, appears to run 900 to 1100 on that scale (reference).
The upshot of all this is that it isn’t my imagination. Lots of stuff will stick strongly to a smoothly polished granite countertop, but would not be able to adhere, or adhere well, to the melamine top coat of Formica (r).
So coat that granite countertop
The paperwork that came with our kitchen specifically said not to apply sealer to the countertops. They were specially blah-blah-blah with miracle-of-modern-science yada-yada-yada, and so would never need this-that-or-the-other, for as long as we both shall live.
Or something like that.
After 15 years of periodically scraping little bits of crap off those countertops, I think I’m finally ready to ignore the manufacturer’s advice.
Turns out, you have your choice of sealers, most of which have some Teflon-like molecules in them. I have to say, however, these guys, with a different formulation, are speaking my language, emphasis mine:
The molecular bond created with the stone by the STAIN-PROOF sealer changes the surface energy of the stone so that it becomes lower than oil or water. Thus, when you spill something, instead of the stone quickly absorbing the liquid like a hard sponge, it just beads up on top of the stone dramatically delaying absorption for easy cleaning.
I’m not sure what coating or sealer I’m going to use, but I’m completely sure that 15 years is enough.
Still a non-believer? Try Rain-X.
There are probably some readers who still don’t quite believe this story about surface energy. In the back of your mind, you might think that any type of stone sealer is just “filling in the pores in the stone”, and making the surface smoother that way.
Please take a moment to ponder Rain-X.
Rain-X is for use on glass. If you Rain-X your windshield, water will bead up and slide off. The effect is so pronounced that you can drive in the rain, without using windshield wipers, courtesy of a fresh coat of Rain-X on the glass.
I’ve done it. It works, and it’s fun to watch, to boot.
Now, glass is about as physically smooth a material as you will ever come across. So, for sure, Rain-X isn’t “filling in the pores” on your windshield. There aren’t any, on anything above a molecular scale.
Glass has a relatively high surface energy. On the scale where Teflon is 20, and quartz is 1000, common glasses seem to fall into the 100-200 range.
But Rain-X contains siloxanes. A surface coated in siloxane has about the same surface energy as Teflon. Somewhere around 20.
And that’s exactly what the “bead up” part of the Rain-X process is telling you. Rain-X coats the high-surface-energy glass with low-surface-energy siloxanes. In effect, it makes the glass able to bead water as well as Teflon does.
That, plus a little forward motion, and those beaded water droplets simply zip right off the glass. No wipers needed.
So if you still think this is all about smoothness, just ponder the power of Rain-X. That takes a perfectly smooth glass surface that does a poor job of shedding water. And turns it into a surface where water slides right off. That has nothing to do with smoothness. And everything to do with surface energy.
