What Causes an Enveloped Vius to Become Nonviable?

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We keep seeing that certain viruses survive X amount of hours on different surfaces; so what actually happens to them that causes them to be no longer viable?

Does the mucus protect the capsid and then when the mucus dries up, the capsid cracks?

Flu survives in water for days; does the pH finally damage the shell enough to "kill" it?

Or is it something entirely different?

 

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Re: What Causes an Enveloped Vius to Become Nonviable?

This helped a little to answer my questions. We know that fat hardens in the cold. Apparently the coat is a soft shell instead of a hard one?

A false-color image of an influenza virus, or virion, taken with transmission electron micrography. The flu's protein-laced fatty coat (orange) toughens up in cold weather, helping it survive. Credit: CDC/Cynthia Goldsmith



http://www.livescience.com/health/090426-sr-flu-basics.html