You can buy a VIX based ETF but it will constantly go down.
It's called "Theta".
Volatility as measured via VIX (or implied options volatility) is measured accross multiple expiries and strikes, and the theoretical value of the VIX can move for free from one expiry to the next because it is a theoretical value (no transaction costs). On the other hand, VIX ETFs have to deal with options or swaps or similar stuff depending on the product, and those always decay in value due to theta (relative to underlying price).
In other words, you can't be always long volatility because as future approaches the present,it becomes more certain.
You can keep buying OTM puts though, and hope that one day a volatility explosion will pay off all the $ that theta took...