the procedure described by Hoffman

the procedure described by Hoffman and Weeks (23). Thus, the
relationship between Tand the apparent melting temperature
of TP in the PS/sesame oil solutions (T
M
′) was established plotting T
M
′vs T. The T
M
′value was determined from the melting
thermograms (heating rate of 1 K/min) after the corresponding
crystallization according to the isothermal conditions described
previously. Thus, the experimental T
M
′ vs. Tplot provided a
straight line whose crossing point with the line T
M
′ = Trepresented T
M
o
(Fig. 2). The T
M
o
value is defined as the temperature where the smallest aggregation of molecules (i.e., unstable
crystal nucleus) is in equilibrium with the molecules in the
melt. This concept is particularly utilized in polymers (24).
Thus, small aggregations of molecules without the correct tridimensional arrangement to develop a stable crystal nucleus will
melt below T
M
o
. Finally, from the slope, s, of the linear regression of log[T
i
T] vs. 1/T(∆T)
2
the calculation of ∆Gc
was performed since ∆Gc
=sk/(∆T)
2
.
Measurements of viscosity. The viscosity of the PS/sesame
oil solution was determined under isothermal conditions at a
shear rate of 15.82 s
−1
utilizing a Brookfield LVDV-III viscosimeter (Brookfield Instruments, Stoughton, MA) with a
cone and plate geometry with the cup CP-41. In all cases the
volume of the sample was 0.5 mL and the temperature control
was ± 0.1 K (Brookfield TC-500).
The solution in the sample container of the viscosimeter was
heated at 353 K for 30 min. Afterward, the system was cooled
(1.0 K/min) until the desired temperature was achieved. The
equilibrium time for the recording of the viscosity was 25 s.
The value of viscosity for each PS/sesame oil solution was plotted as a function of the effective supercooling and the T
i
.
RESULTS AND DISCUSSION
The fatty acid profile of the sesame oil and PS used are presented in Table 1. As previously indicated, sesame seed oil has
a high degree of unsaturation, mainly provided by the high concentrations of oleic and linoleic fatty acids.
The triglyceride composition of PS was as follows, where
M = myristic, P = palmitic, L = lauric, O = oleic, and St =
stearic: MMM, 0.16 ± 0.01; MMP, 0.14 ± 0.01; MPL, 1.47 ±
0.11; PPP, 16.46 ± 0.17; PPO, 36.91 ± 0.12; PPSt, 3.39 ± 0.06;
POSt, 31.21 ± 0.03; StOSt, 0.06 ± 0.02; OOO, 8.00 ± 0.11; and
unknown, 1.58 ± 0.77 wt%. That is, the main constituents of
PS were, in decreasing order of concentration, PPO, POSt, PPP,
and PPSt, with TP as the triglyceride with the highest melting
temperature (14,25). Thus, TP must affect the crystallization
kinetics and polymorphic behavior of the PS/sesame oil solutions in a significant way. From the concentration of TP in the
PS (16.46%), the effective TP concentrations for the 26, 42, 60,
and 80% PS/sesame oil solutions were 4.27, 6.90, 9.85, and
13.14% (wt/vol), respectively.
The corresponding DSC cooling (Fig. 3) and heating (Fig.
4) dynamic thermograms pointed out the high degree of unsaturation of sesame oil. Sesame oil had a crystallization peak
with a maximum at ≈256 K, a melting peak with maximum at
≈258.5 K, and melting was completed at ≈266 K. Although,