I was just wondering if, when discussing professors who would be interesting to work with as PhD advisers in the statement of purpose, one can also mention a professor who is an affiliate of the department but primarily a professor in another department?
It may be difficult to have an affiliate professor as your sole adviser if he or she is not a professor housed in your main department. Administratively, it can be a challenge to have graduate students matriculated in one department but being advised by another.
However, if the professor is an affiliate of the department, he/she likely has someone who is full-time in your target department that they work with. You could say something such as
I am interested in working with Professors Carl McCauley [in main department] and Demelza Fordham [affiliate]. Their research on the decomposition of rubber aligns closely with the work I did on rubber composites while at the University of ZYX.
If you tie them into a professor in your target department, being associated with an affiliated professor can actually be a good thing. It will give you more diversity and networking opportunities. It may also fulfill requirements for outside committee members on your dissertation committee.