How much vacuum is needed to lift? Just like a balloon of Helium lifts about 1.02g for being less dense than the air. Does the same principle applies to vacuum being less dense than air? And if so, how much can a ballon (1L) of vacuum lift? Ignoring the condition that to have a pressure resistant balloon would make it heavier than the whole experiment.
 A: At  101.325 kPa (abs) and 15°C the density of air  is 1.225 kg m$^{-3}$, so a balloon made of massless but very rigid  material will lift  1.225 kg for each cubic meter of volume.
A: Your intuition is correct - with current materials.
Gas based and vacuum based balloon constructions respond to altitude differently.
Any volume of helium always weighs 14% of the displaced amount of air (assuming the same temperature and the same pressure between the air and helium).  If the helium bubble is able to expand at high altitudes, its lift per liter goes down, but its volume goes up - the two effects cancel each other and the total lift is preserved.  If, however, the helium is forced to escape or to compress at higher altitudes, the total lift goes down.  Typical gas balloon constructions therefore aren't terribly sensitive to altitude or elevation which makes them so popular for travel, haulage and even stratosphere exploration.
This is different with vacuum based balloon constructions.  Their rigidity and thus weight has to be optimized for a particular pressure differential; if you assume a near total vacuum on the inside, they have to be optimized for a particular atmospheric pressure.  The higher the balloon sits, the lower the net lift is.
With current envelope materials, helium fares better than vacuum.  Hydrogen fares better than helium (it weighs only 3.5% of the displaced air, and so its lift factor is about 112% over helium).  If and when future envelope materials surpass helium and/or hydrogen, the gas based balloons will still initially retain their ability to climb without gradually losing lift.
However, if vacuum based balloons become practical with future materials, they may be able to offer the practical advantage of lift ratio control through volume control.  Compare this to throw-away ballast used to control buoyancy of gas balloons.
And even if those imaginary envelope materials are infinitely rigid and infinitely light, the vacuum balloon will never be able to achieve more than 104% lift factor over hydrogen.
