If this worked could could have a machine that would release hundreds of these things a minute.
The resulting perfect sphere is what you'd need to get that structural element to hold the thing in shape and molten plastic would offer the best material to quickly harden I'd think. That or some kind of two part plastic mixture.-- doctorremulac3, Dec 11 2016 http://physics.stac...-to-exist-in-vacuum [2 fries shy of a happy meal, Dec 11 2016] Something like this guy is doing? http://1.bp.blogspo...an%2B2011%2B002.JPGStill, it's an added weight solution. [doctorremulac3, Dec 12 2016] A dimer, or a thermoset would be best.
But you've set a tough target, creating "vacuum foam". The overall mass of the sphere needs to be lower than the density of air, and still be able to resist 1Bar without collapsing. It needs to be non-porous, rigid, but not brittle.
Wall thickness will be critical; too thin, and the sphere will collapse - too thick, and it will be too heavy.
Rather than a polymer, Titanium might be closer to the mechanical properties you want.-- 8th of 7, Dec 11 2016 I meant to say titanium.
Hey, titanium melts. If you can melt it, you can blow a bubble with it.
But yea, you've got that catch 22 of needing enough wall to hold up to that vacuum without being lighter than the air it's displacing.
Sounds like a job for somebody who knows science 'n stuff with like, math 'n whatever.-- doctorremulac3, Dec 11 2016 It should not be possible to blow bubbles in a vacuum.-- bungston, Dec 11 2016 According to an answer given at the physics stack exchange bubbles could be formed in a vacuum. [link]-- 2 fries shy of a happy meal, Dec 11 2016 I'm struggling to see the advantage here over making a sphere and sucking the air out.
I vaguely remember a lecturer in 1st year proving that the weight of a sphere made out of any currently known material would be too great to allow a vacuum balloon to work, given the material strength. I can't remember exactly as it was a while ago - it should be a fairly simple proof I think.-- TomP, Dec 11 2016 With this you could make several hundred a minute.
If there is a material that would work.-- doctorremulac3, Dec 11 2016 How about making an oblate spheroid with progressively thicker, stronger material at the poles then rotating it at high speed? The centrifugal forces would partially counter- balance atmospheric pressure on the thinner material at the equator.
Someone else can come up with an solution for the atmospheric drag issue.-- AusCan531, Dec 11 2016 Balls-- popbottle, Dec 11 2016 The difference of being able to blow a bubble and pull a bubble with suction from all sides, is probably a universal asymmetry.-- wjt, Dec 12 2016 I was also thinking that the advantage of this over just blowing a balloon, hardening it and sucking the air out is you've got minimum stress on the sphere during the process. You've got no turbulence when sucking the air out therefore no vibration and less stress on the structure of the envelope.
Yes, there is air coming out of the balloon when you open one end to the vacuum to let it out, but since it was blown in a vacuum very little air was needed and the only time you put pressure on the thing is when you let it out of the chamber into the atmosphere. But then any stress on the structure is very even without currents and eddies of airflow buffeting the hole where you're sucking the air out.
Creating a vacuum balloon that is strong enough to hold up to the vacuum yet lighter than the air it's displacing would require some pretty precise manufacturing. This would be one way.
That being said not sure if any material short of diamondium would be able to handle the job so this is more of a look at a different way of manufacturing something than an actual practical idea, despite the word "practical" being in the title.-- doctorremulac3, Dec 12 2016 If you could create some kind of lattice inside the ballon during the process, it might better resist the buckling that tends to be the downfall of vacuum balloons.-- the porpoise, Dec 12 2016 Filled with plastic foam where you evacuate the gas after it hardens?
Or blow multiple bubbles of some sort or another? See link.
I think there's a number that some material would need to achieve, titanium being X meaning strength per pound and to have a bubble that could sustain a vacuum you'd probably need something like 1/10th X.-- doctorremulac3, Dec 12 2016 //The difference of being able to blow a bubble and pull a bubble with suction from all sides, is probably a universal asymmetry.//
No - they're exactly the same thing. To blow a bubble, or to inflate a balloon, the pressure inside must exceed the pressure outside by a certain amount, X. X is the surface tension (of a bubble) or the resilience (of a rubber balloon).
So, you can blow a bubble in a vacuum by supplying just enough internal pressure to overcome surface tension. (It's no different to blowing a bubble in air, except that both the internal and external pressures are reduced by about 15psi in a vacuum.)
There is one difficulty with blowing bubbles: the pressure needed to overcome surface tension decreases as the bubble gets bigger. So, if you provide enough pressure to get the bubble started, and then maintain that same pressure, the bubble will inflate faster and faster and then burst. (Much the same is true of balloons, though the physics is a bit different.) So, you need to inflate a bubble by volume, not by pressure.-- MaxwellBuchanan, Dec 12 2016 Seems to me that to make a vacuum balloon you need to make it out of a material that is resistant to buckling. The skin of a bubble isn't it. I imagine a material like foam board with two high tensile strength skins separated by a low density core that resists compression would be one direction to look. ON second thought, I doubt any type of foam would work because a randomly created foam tends to be compressible to some extent.
I think what would be needed is a truss. To save weight, the members of the truss are probably also small trusses: so a fractal-like truss. A lattice in the balloon sounds good, but needs to be very sparse. I'd say a fractal truss around the surface with a relatively small number of high tensile strength fibers through the center of the sphere to hold the overall shape.
It seems like someone might be able (or has tried and failed) to design such a structure using simulations tools. Once designed, it seems like it would be incredibly difficult to build, but the design itself would be interesting and might inspire someone to figure out how to physically create such a thing.-- scad mientist, Dec 12 2016 What you want is an incredibly stiff material - specifically, a high specific (ie per-weight) Young's modulus. Pure compressive strength isn't an issue - thin shells fail in buckling, as noted.-- MaxwellBuchanan, Dec 12 2016 random, halfbakery