why does the fragrance of the perfume last longer if we spray it on the part of our body where we have applied non fragrant lotion or vaseline? 

I'm not sure it does, but if we assume this is true then almost certainly it's because the lotion or petroleum jelly do a better job of holding on to the volatile scent compounds and molecules than bare skin does. They evaporate off the bare skin more rapidly than the lotion or vaseline where they're more likely to remain "caught."

3 minutes ago, iNow said:

I'm not sure it does, but if we assume this is true then almost certainly it's because the lotion or petroleum jelly do a better job of holding on to the volatile scent compounds and molecules than bare skin does. They evaporate off the bare skin more rapidly than the lotion or vaseline where they're more likely to remain "caught."

could you be more specific? like how do alcohol and oil work together? 

I'm not sure I can, no. I am curious why you'd focus on the alcohol as opposed to the olfactory compounds, though

2 hours ago, iNow said:

I'm not sure it does, but if we assume this is true then almost certainly it's because the lotion or petroleum jelly do a better job of holding on to the volatile scent compounds and molecules than bare skin does. They evaporate off the bare skin more rapidly than the lotion or vaseline where they're more likely to remain "caught."

Yes, that's the same function as ambergris in expensive perfumes.

3 hours ago, mundane said:

could you be more specific? like how do alcohol and oil work together? 

Here's my theory: The components of a perfume that smell good might be mainly lipophilic (I think essential oil are used often, and those are lipophilic). If they are sitting on your skin, they are directly exposed to influences like warmth and oxygen, causing them to break down or evaporate quite fast. If they are applied onto a lipophilic base, they can diffuse into this base and probably also partially into the skins top layer (as this is lipophilic to)?

On 4/30/2020 at 10:31 AM, Aconitin said:

Here's my theory: The components of a perfume that smell good might be mainly lipophilic (I think essential oil are used often, and those are lipophilic). If they are sitting on your skin, they are directly exposed to influences like warmth and oxygen, causing them to break down or evaporate quite fast. If they are applied onto a lipophilic base, they can diffuse into this base and probably also partially into the skins top layer (as this is lipophilic to)?

Yup, this is a sound hypothesis

Do their molecules bind or something?

I think those perfumes don't really last long on our bodies but rather in our clothes... these clothes are holding them until they are washed