If you were to inflate a balloon with a vacuum inside it, several things would occur. However, it's important to note that creating a perfect vacuum is practically impossible, so we'll assume you're referring to a highly evacuated balloon.
Balloon Expansion: Initially, the balloon would remain collapsed since there is no pressure inside it. However, as the vacuum is introduced, the external atmospheric pressure would push against the balloon's walls, causing it to expand.
Balloon Stretching: As the balloon expands, the elastic material of the balloon would stretch to accommodate the increasing volume. The degree of stretching would depend on the material's elasticity and the strength of the balloon.
Structural Integrity: Balloons are typically designed to contain air or other gases that exert pressure from the inside. In the absence of internal pressure, the balloon's structural integrity might be compromised as it stretches. If the balloon material is not strong enough or is unable to withstand the stretching forces, it could rupture or burst.
Lack of Tension: Normally, when a balloon is filled with air or gas, the pressure inside creates tension in the balloon's material, which gives it a firm and inflated shape. In the case of a vacuum-filled balloon, there would be no internal pressure to create tension, resulting in a floppy or saggy balloon.
External Pressure Effects: The absence of pressure inside the balloon means that the only force acting on it would be the external atmospheric pressure. As you ascend to higher altitudes, where atmospheric pressure decreases, the balloon would appear to expand further due to the pressure differential. Conversely, at lower altitudes with higher atmospheric pressure, the balloon would appear slightly compressed.
In summary, if you could somehow create a highly evacuated balloon, it would initially collapse and then expand due to the external atmospheric pressure. However, without internal pressure, the balloon would lack tension and could potentially stretch or rupture depending on its material strength.