HLD (Expert Mode)
The HLD page laid out the basics. For those who want a little more power and understand HLD, read on.
The basic HLD app provides an introduction to calculating HLD. However, expert users require two extra functionalities.
- The ability to choose salts other than NaCl
- The ability to tune HLD via alcohols
There are two forms of salt correction. The first takes into account the MWt of the salt. The same weight of LiCl provides more salinity than NaCl and KCl provides less salinity. The correction is simple: S=58/MWt*g/100ml. So if you have 1g/100ml of LiCl (MWt=42) that is equivalent to 58/42= 1.38g/100ml.
The second correction takes into account divalent or trivalent salts. The approximation is that a divalent salt is equivalent (after the MWt correction) to 0.666 of a monovalent equivalent and a trivalent salt is equivalent to 0.5. This could probably be handled better via an Ionic Strength calculation, but I'm not aware that it has been validated.
This section on alcohols is preserved for historical reasons. It is now recognised that the interactions of alcohols with the whole system are too complex to be described in a simple theory. It was a great idea at the time and there was good evidence for some simple alcohol effects, but more data have revealed fundamental issues. We await a superior theory that can handle alcohols and polar oils.
We can rewrite the HLD formula as
HLD = F(S) - k.EACN - α(T-25) + F(A) + Cc
where F(A) is a function of the % Alcohol added to the system. It would be wonderful if there were a universal formula for F(A). It is generally agreed that sec-BuOH has no influence on HLD (so it is a useful additive to help break emulsions during EACN or Cc measurements) and that PrOH and EtOH decrease HLD (i.e. make the system more hydrophilic, which is obvious). BuOH probably is F(A)=+0.1 and pentanol etc. will have higher values. Unfortuntely by the time you reach something like octanol it's unclear if that is a bad alcohol or a poor surfactant or, indeed, a hydrotrope or co-surfactant. In short, there is no coherent language for describing alcohol effects in terms of HLD. Had the surfactants community been using HLD consistently over the past 30+ years we would no doubt have a much clearer idea about the F(A).
To calculate HLD use the same inputs as before but choose the MWt of the salt and whether it is mono-, di- or tri-valent. Then enter your % alcohol with your estimate of F(A) which might vary from -0.4 for EtOH, -0.2 for PrOH, 0.1 for BuOH and maybe 0.3 for Pentanol.
If anyone from industry or academia can provide better estimates for the salt or alcohol effects it will be easy to update this app and acknowledge the source of the information!