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The Marangoni effect induced by the mass transfer between
two immiscible liquid phases upon the characteristics of phase
inversion is experimentally investigated in this article.As the
solutes are transferd from the dispersed phase to the continuous
phase,the Marangoni effect increases the coalescene rate of the
drops,while it retards the drops to coalesce when the type of
mass transfer is C->D.Experiments were carried out by changing
the directins of mass transfer C->D and D->C, with two kinds of
solute (acetic acid and acetone) to study the effect of solute
concentration、density、viscosity and temperature upon the phase
inversion characteristics.
The phase inversion of W/O->O/W for a system with solute acetone
is more difficult to happen than that for a system with solute
acetic acid.With the same solute,the solute concentrations and
the directions of mass transfer affect the phase inversion hold-
up insignificently.Both solutes can make the phase inversion
hold-up of O/W(s)->W/O higher than that for the systems without
adding solutes.And higher the solute concentrations,more
difficult for the phases to invert.This is because both solutes
have the characteristics of surfactants,and this makes the water
likely to be the continuous phase. It was found that Marangoni
effect has the greatest influence on the phase inversion of O(
s)/W->W/O .Because of the speeding coalescence of the drops,both
solutes make this system unstable,until the phase inversion is
completely established,then the system becomes stable W/O
dispersion.Also the delayed inversion time for this system is
almost zero.When the density difference between the two
immiscible liquids becomes small ,both solutes lower the
inversion hold-up of the W/O(s)->O/W、W(s)/O->O/W and O/W(s)->W/
O systems.For the phase inversion of the O(s)/W->W/O system,it
will have significant local phase inversion with acetic acid as
the solute,but adding acetone wouldn''t have the same situation.
Raising the viscosity of the oil phase,even acetic acid is
added,the phenonmena of serious local phase inversion will no
longer happen.In addition,as the direction of mass transfer is
O->W,the faster the stirred speed,the wider the ambivalence
range.When the temperature of the system is raised to 40℃,the
inversion hold-up of this system,W(s)/O->O/W,will be lowered and
the phase inversion of the O(s)/W->W/O is still unstable as the
solute is acetic acid.The coalescence time of the drops (for
both oil and water drops) for the systems with solutes are
longer than those without adding solutes.This is due to the fact
that both acetic acid and acetone can reduce the interfacial
tension,and make the dispersed drops smaller.Higher temperature
can reduce the value of Tc,and this is helpful to the separation
of the system.The delayed invrsion time for the systems with
mass transfer,C->D,is longer than that for the systems with mass
transfer,D->C.
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