Interested in Dutch related languages? The following link will lead you to the digital bibliography of linguistics of Afrikaans.
With regard to the study of similarities between Dutch related languages, F. Ponelis, 1988. ‘Afrikaans en Taalversteuring’, in: Tydskrif vir Geesteswetenskappe , 28 (2) : 119-149, Jun. is of interest. The full text is also available on the page Scanned publications.