I've grown accustomed to there almost always being an article before nouns, even if that article is contracted with another word. I know that there are exceptions, such as proper nouns and negations. But I didn't expect there to be an exception in this sentence.
Si tu avais assez d'argent, voyagerais-tu?
I would have expected to see the partitive article: either du argent or de l'argent. Why is the article lost?
You've likely already encountered “beaucoup de” or “peu de” used without an article many times. “Assez de” is similar, but unlike the former I don't think it can ever be used with an article.
“De” is a preposition in these constructs and the partitive (du, de la, and even the indefinite plural des) is always omitted after it. You can think about other cases like:
Il a besoin d'eau.
Il parle de moments difficiles.
Some other examples:
recueillir un maximum d'informations
une poignée de données non confidentielles
envoyer un grand nombre de photos
As you can see, words that denote a quantity, such as "assez / suffisamment / beaucoup / maximum / poignée", to name but a few, have a noun immediately follow "de" without a definite article in between.
