Wearing a scarf after applying minoxidil?

In my opinion it is doubtful that a scarf would disrupt much of the absorption of minoxidil into the scalp. Chances are you are giving the minoxidil enough time to adhere from when you apply it to when you don the scarf.  

The results of minoxidil will not be affected by the scarf. I would suggest leaving a few minutes between applying the minoxidil and putting on the scarf so it has time to absorb. 

A scarf is not going to affect minoxidil results. However, it is possible that a small amount of minoxidil could be transferred to the scarf. This is of no consequence unless minoxidil coated regions of scarf comes in contact with the skin and thereby promotes a bit of hair growth. All in all, the use of a scarf will not affect results of minoxidil.