Monomolecular blades

[cptbutton]

Originally Posted by AlexanderHowl

One possibly realistic alternative though would be a triangular carbon nanotube wire with sides one hundred micrometers long. It would be strong enough to be a weapon and you could actually see it. Each point of the triangle could be 1 nanometer in thickness.

The utility of the weapon would be in the creation of a superior lasso rather than the creation of a superior blade or lasso. When the carbon nanotube wire wraps around a target, it would cut into the target until the target was cut in half. Of course, untangling it afterwards would be nearly impossible, so the wire would have to be disposable (and would presumably have something that would allow it to decay to prevent hazardous conditions).

Walter Jon Williams had something like that in Voice Of The Whirlwind. it is explicitly noted that this is a weapon that can be more dangerous to the wielder than the opponent if you don't know what you are doing.

[malloyd]

Originally Posted by mr beer

When does that start happening? I've seen a couple of pop-sci articles about super-sharp glass scalpels and the like that implied they're superior to steel in some ways because of their sharpness, although obviously not as durable. So I guess there's a cut-off somewhere between the sharpness of a steel razor and atomic scale widths?

Not so much that. Glass knife edges aren't much narrower than steel ones, maybe a factor of 2 or 3. What they are is less irregular in the other direction. If you pushed them both into a material edge on, there's probably little difference in performance, it's mostly when you make a draw cut there are fewer irregularities on the part a little back from the edge that can get caught on the cut tissue and tear some of it.

Edit: for some applications, glass is also harder than steel, so it doesn't deform as easily. The downside there being when a steel edge deforms it gets dull, where a glass one *breaks*. That probably doesn't matter so much for modern scalpels, which are essentially single use tools, though.

[Anaraxes]

Originally Posted by cptbutton

I think they were in A Gift From Earth (1968), if not earlier.

Yes to both. The SF Encyclopedia's earliest reference is a 1963 Randall Garrett story, "Thin Wire", unless you count the 1951 film "The Man in the White Suit" (in which I don't think it was a weapon, just a monofilament super-nylon wonder material).

Originally Posted by malloyd

Glass knife edges aren't much narrower than steel ones, maybe a factor of 2 or 3.

Numbers I turned up yesterday put steel at 50 nm, with obsidian at around 3. Maybe they were underestimating the steel, though, or comparing something like a typical commercial razor to best possible scalpel.

It's interesting that those edges are already only around ten atoms thick, so "one atom wide" isn't nearly as much of an improvement as it sounds like.

[AlexanderHowl]

If I remember correctly, the reason why glass scalpels are better is because they cause less damage to the surrounding tissue because they are sharper, they are easier to clean during a procedure, and they do not suffer from corrosion (even a tiny amount of corrosion will adversely effect the performance of a steel scalpel). Their hardness also keeps them from becoming dull during a procedure, which can be useful during complex and long procedures.

[lwcamp]

Originally Posted by mr beer

When does that start happening?

For ductile metals like steel and aluminum, at about a few hundred nanometers (this is the radius over which ductile deformation is happening at the crack tip. For plastics it is more like a few tens to hundreds of microns. For glass, it really is all happening at only an atom or two in radius.

For a rough dimensional analysis of the distance over which the strain is occurring around the crack tip, divide the strain energy release rate by Young's modulus (you can look up both of these quantities for most commonly used materials).

Luke

[Extrarius]

Originally Posted by malloyd

[...]Edit: for some applications, glass is also harder than steel, so it doesn't deform as easily. The downside there being when a steel edge deforms it gets dull, where a glass one *breaks*. That probably doesn't matter so much for modern scalpels, which are essentially single use tools, though.

It depends on the tempering. Steel can vary in properties in many ways, in hardness it can range from soft iron to so-hard-it's-fragile ceramics. There are, of course, many other factors, such as the contents of the steel (there are so many different alloys and mixtures).
Tapping extremely hard steel against another metal produces a sound very much like tapping a glass rod, and the first time I witnessed that is was a kind of strange experience. The link between metals and ceramics makes many interesting materials possible even without modern 'meta-material' science.
Fully hardened steel is essentially a ceramic, and might be just as good as (or better than) glass in many respects, but it is more resource intensive (materials, labor, time, and more) to produce and it isn't easy to work with (because it is harder than common abrasives, grinding requires more expensive materials and tools).

[mr beer]

Originally Posted by lwcamp

For ductile metals like steel and aluminum, at about a few hundred nanometers (this is the radius over which ductile deformation is happening at the crack tip. For plastics it is more like a few tens to hundreds of microns. For glass, it really is all happening at only an atom or two in radius.

For a rough dimensional analysis of the distance over which the strain is occurring around the crack tip, divide the strain energy release rate by Young's modulus (you can look up both of these quantities for most commonly used materials).

Luke

Thank you. I had no idea that's how it works - always cool to learn something new.

[Johnny1A.2]

Originally Posted by evileeyore

For me it was shigawire in Dune... though the first time it was called monofilament wire for me was in Stand on Zanzibar.

Technically, though, IIRC shigawire isn't monomolecular, it's a weird biological product that is extremeluy fine and tough and strong, more so than anything we have today but not a single molecule.

[Johnny1A.2]

Originally Posted by Anthony

Incidentally, monomolecular in Niven applies to more than blades. A General Product hull is "an artificially-generated giant molecule, with the inter-atomic bonds artificially strengthened".

I still suspect that Niven retroactively came up with that explanation for what they were in order to give them that special vulnerability to antimatter.

(In Niven's stories, the GP hulls are actually more vulnerable to antimatter than ordinary hulls are, though the Puppeteers don't advertise this. That is, an amount of antimatter than an ordinary hull would hold together amidst will destroy a GP hull.)

[evileeyore]

Originally Posted by Johnny1A.2

Technically, though, IIRC shigawire isn't monomolecular...

Correct, it can be as fine as the finest human hair, so around 10 microns at it's thinnest.

I included it as the wiki article on monomolecular wire included it.