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In your recent Energy and Fuels article you quote one my articles on asphaltenes (reference 5) as a reference to the formation of a solid gel at the interface.
This is actually the opposite to my conclusions: in the quoted article we have demonstrated asphaltenes (petroleum, oil, synthetic) follow a Langmuir equation of state with a molecular area corresponding to their aromatic core size.
In another article (Pauchard, Vincent, Jayant P. Rane, and Sanjoy Banerjee. "Asphaltene-laden interfaces form soft glassy layers in contraction experiments: a mechanism for coalescence blocking." Langmuir 30.43 (2014): 12795-12803.)
we have demonstrated that the transition from a fluid interface to a solid one occurs when coverage reaches close packing, i.e. it is rather a glass transition.
It happens that the Soft Glass rheology model actually yields the same frequency dependence as the phenomenological observations from Winter and Chambon without restricting it to the very gel point (which is an issue with the critical gel rheology model: it should only be observed over a limited period of time, not at any arbitrary long time).
Finally a systematic rheological study (Samaniuk, Joseph R., et al. "Soft-Glassy Rheology of Asphaltenes at Liquid Interfaces." Journal of Dispersion Science and Technology 36.10 (2015): 1444-1451.) demonstrated that shear rheology of asphaltenes covered interfaces follow all predictions of the Soft glass rheology model (frequency sweep, amplitude sweep, steady state flow and creep).
the difference might seem at first glance of theoretical importance only but in fact it really has practical consequences:
if asphaltenes slowly formed a gel like interface preventing coalescence, they should not be able to cause emulsion stability after short mixing times as actually observed.
to the contrary if glass transition is the cause of emulsion stability in enables conciliating all observations:
with a static interface (e..g. pendant droplet), evolution of surface coverage is slow due to diffusion and steric hindrance, hence fluid solid transition is delayed.
within an emulsion, coalescence and subsequent reduction in interfacial area lead to a fast increase in surface coverage until it reaches close packing and blocks further coalescence (see Pauchard, Vincent, and Tirthankar Roy. "Blockage of coalescence of water droplets in asphaltenes solutions: A jamming perspective." Colloids and Surfaces A: Physicochemical and Engineering Aspects 443 (2014): 410-417.)
You might not agree with this view, but at least I wanted to make sure it is not confused with the main stream theory about asphaltenes and emulsion stability. |