Thermodynamics parameters of micellization and adsorption
The thermodynamic parameters of adsorption and micellization
of the synthesized cationic surfactants were calculated
according to Gibb’s adsorption equations [20]:DGomic ¼ RT lnðCMCÞDGoads ¼ DGo
mic 6:023 10 2 pCMC AminDSmic ¼ d DGomicDT
DSads ¼ d DGomicDT
DHmic ¼ DGomic þ TDSmic
DHads ¼ DGoads þ TDSads
The thermodynamic parameters of micellization and adsorption
are summarized in Table 2, where theses parameters are
calculated at 25, 40 and 60 8C.
From thermodynamic parameters of micellization Table 2,
change in free energy of micellization (DGo
mic) values are negative
indicating that micellization process is spontaneous. In addition,
DGo
mic increase in the negative direction by increasing both
temperature and hydrophobic moiety, which imply that, the
compound favor micellization [20].
DSmic are positive and increases by increasing hydrophobic
chain length, which be indication on increasing in the randomness
of the system upon transformation of surfactants molecules into
micelle in another means the compounds favor micellization by
increasing hydrophobic character thus CMC be, decreased [21].
From thermodynamic parameters of adsorption it observed
that standard free energys of adsorption (DGo
ads) are negative
which indicate that process of adsorption is spontaneous. In
addition, DGo
ads increase in the negative direction by increasing
both temperature and hydrophobic moiety length, which implies
that the compounds favor adsorption at interface thus lowering
surface and interfacial tension that by expanding force acting
against the contracting force resulting from surface and interfacial
tension [22]. Also it can be observed that DSads are positive and
increase by increasing hydrophobic chain length.
In comparison the thermodynamic parameter of micellization
and adsorption we observed that DGo
ads are more negative than
DGo
mic indicating the tendency of the molecules to adsorb at the
air–water interface until complete surface coverage. Beyond this,
the molecules diffuse to the bulk of their solution to form micelles.
Hence, the thermodynamic aspects govern the micellization and
adsorption processes. The chemical structure of these molecules is
the main factor influencing their thermodynamic aspects. The
DSads values are positive and slightly greater than the DSmic values
for the same compounds. This may reflect the greater freedom of
motion of the hydrocarbon chain at the air-aqueous solution
interface.