RIM - Relative Index of Morphology

Quick Start

From a classic γd determination with linear alkanes, followed by a determination of the morphology index IM using isooctane and cyclooctane, a new Relative Index of Morphology (RIM) tells you a lot about what's really happening on your suface.

RIM Surface Analysis


It is highly unlikely that the "real" surface energy of, say, a silica is 100 mN/m. Why? Because measuring any reasonably (molecularly) flat silica gives more normal values in the range of 40-50. The extra measured energy is most likely to come from multiple interactions of the probe alkane with, for examples, pores or nano-rough surfaces. It would be very interesting if we could distinguish genuine high surface energy from this sort of topological surface energy. That's why RIM was developed by Dr Eric Brendlé at Adscientis

Two topological probes

As we know from the Morphology app, a branched alkane such as isooctane will give a lower apparent surface energy on a nano-rough/porous surface simply because it cannot make such perfect contact with the surface(s). For cyclooctane the problem is even greater. So the measured value, IM, is lower than 1 for isooctane and lower than isooctane's value for cyclooctane. The ratio of those two values is the Relative IM, RIM:

RIM = IMcyclooctane/IMisooctane

It is found that we can divide measured surfaces into three zones depending on IMcyclooctane and RIM:

  1. Low IMcyclooctane, low RIM: nano-rough surfaces
  2. High IMcyclooctane: "soft", 3D surfaces
  3. High RIM, IMcyclooctane<1: Mixed surfaces

In the low IM and low RIM zone, the topological probes have no chance to interact strongly with the surface, so these are the hard, clean, nano-rough surfaces, such as highly porous silica. In the high IMcyclooctane zone, both isooctane and cyclooctane can easily interact with whatever is on the surface, so this means that it must be "soft", e.g. with primers/dispersants/sizes into which the probes can easily be lost. In the "mixed" zone, the cyclooctane still has more difficulty in accessing the surface.

Hard knowledge gained easily

The point of RIM is that it gives you hard-to-obtain knowledge relatively easily. With just (say) 4 linear alkanes then the two octanes, you can quickly work out whether, say, your "high γd is really a high surface energy (which it usually isn't) or whether it is due to a porous (zeolite) or nanorough (silica) or strongly angular (crystals) or intercalated (clays) surface.

The IGC apps are based on the inputs kindly provided by Dr Eric Brendlé of Adscientis who are specialists in IGC measurements.