Effect of the type of oil on a vinaigrette's texture? When I prepare vinaigrette, I always use the same basic technique: first the vinegar (or another acid liquid like lemon juice), some salt, a spoonful of Dijon mustard and then I add oil little by little (not as carefully as with mayonnaise – in that case I use an electric whisk – but not all at once), whisking or even simply mixing it with a spoon or fork.

Usually, that's enough to obtain a nice emulsion but in some cases the oil and vinegar never seem to mix properly and the texture isn't right. It's merely anecdotal but I have the feeling that the type of oil I use is the key factor here. Olive, walnut or pumpkin seed oil all seem to work very well, sunflower oil not so much.

My question is: Is it really the case? Does the type of oil have a well documented effect on how easy it is to get a good emulsion? And if that's the case, is there some “neutral” oil I could use instead of sunflower oil if I want to avoid the strong flavour of olive or walnut oil?
Add egg yolk or lecithin to your mixture and whisk it again.

Here is some theory:

To make an emulsion (consistent, not separating oil–water mixture), we rely on emulsifiers – long organic molecules that on one end bind with water, and another with oil. They play role of a glue that does not let molecules of water and oil separate.

The most common emulsifier is a lecithin – compound found in egg yolks.
There is a more complete list of them I found on this website:

Emulsifiers in food