Warning: the following is a little long, but the question is interesting to me.
I have been looking at some of the literature on viscosity index improvers, pour point depressants, and base oil waxes. From what I can gather, some VIIs can interact with waxes and PPDs (and solvent for that matter) such that the VIIs would crystallize at very different temperatures in different base oils (waxes and solvent) or in the presence of different PPDs. So, it seems that you could mix two fully formulated oils and get a very different viscosity than you would predict from measurement of the two oils separately. From what I can tell, this differences could sometimes be seen at temperatures as high as 40 C. As a general observation, it seems that for these types of interactions, the resulting viscosity would be higher than predicted. In addition, it could take several days of the oil being undisturbed for the co-crystals to form (from patent discussion, US 5460739 A).
On the other hand, when VIIs are mixed within otherwise identical oils, the resulting cold temperature performance is reduced viscosity (eg. Journal of Polymer Science 2013, 3(3):35-45). This phenomenon appears to be due to VIIs interacting with each other (as opposed to interacting with waxes, PPDs, or solvent).
So the question is, has anyone seen commercial formulations of PCMO that act differently when mixed than would predicted from viscosity measures of each separately? It seems as though the likely combinations would be fairly polar (RedLine maybe) with some of the less polar (heavy PAO). Alternatively, when a high-quality synthetic with very low wax content is mixed with a lower quality mineral with heavy wax content, there could be problem. The high quality synthetic could be formulated with the assumption that the selected VIIs would not encounter waxes.
Similarly, are any of the blenders willing to share examples of where they have stumbled upon combinations that act unexpectedly?
I have been looking at some of the literature on viscosity index improvers, pour point depressants, and base oil waxes. From what I can gather, some VIIs can interact with waxes and PPDs (and solvent for that matter) such that the VIIs would crystallize at very different temperatures in different base oils (waxes and solvent) or in the presence of different PPDs. So, it seems that you could mix two fully formulated oils and get a very different viscosity than you would predict from measurement of the two oils separately. From what I can tell, this differences could sometimes be seen at temperatures as high as 40 C. As a general observation, it seems that for these types of interactions, the resulting viscosity would be higher than predicted. In addition, it could take several days of the oil being undisturbed for the co-crystals to form (from patent discussion, US 5460739 A).
On the other hand, when VIIs are mixed within otherwise identical oils, the resulting cold temperature performance is reduced viscosity (eg. Journal of Polymer Science 2013, 3(3):35-45). This phenomenon appears to be due to VIIs interacting with each other (as opposed to interacting with waxes, PPDs, or solvent).
So the question is, has anyone seen commercial formulations of PCMO that act differently when mixed than would predicted from viscosity measures of each separately? It seems as though the likely combinations would be fairly polar (RedLine maybe) with some of the less polar (heavy PAO). Alternatively, when a high-quality synthetic with very low wax content is mixed with a lower quality mineral with heavy wax content, there could be problem. The high quality synthetic could be formulated with the assumption that the selected VIIs would not encounter waxes.
Similarly, are any of the blenders willing to share examples of where they have stumbled upon combinations that act unexpectedly?