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Paper
gelation behaviour of the amide amphiphiles. The manifesta-
tion of the role of H-bonding interactions can also be seen in the
ribbon-like aggregate structures whose aspect ratio increases
with the increase of strength of the intermolecular H-bond
between head-groups of two gelator molecules. Relatively
stronger H-bonding as with –COOH group favours 1D growth of
the gel aggregates. The results of this investigation suggests that
thermal stability as measured by Tgs value, mechanical strength
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00
y
Fig. 6 Variation of storage modulus (G ) and loss modulus (G ) of the as measured by s value and morphology of the organogels are
p-Ph(Me)
2
organogels of NAT and NHT with the applied shear stress (s) correlated with the gelator–gelator and gelator-solvent
at a constant frequency of 1 Hz at 298 K.
H-bonding interactions. In general, the thermal as well as
mechanical stability and gel morphology are connected to
strength of molecular interactions. However, strong molecular
interactions lead to precipitation/crystallization of the gelator
molecules. This means only noncovalent interactions of
moderate strength are required for physical gelation.
produced sufficiently stronger gel as indicated by the higher
values of G compared to G . A small dependence of G and G
on frequency and small values of G compared to G in the case
of NHT gelator, is indicative of weak gel formation. The rheo-
logical response of the gels to the applied shear stress was also
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0
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00
Acknowledgements
0
00
examined at a constant frequency. The plots of G and G versus
applied shear stress at a frequency of 1 Hz are presented in
Fig. 6. As can be seen, above a critical stress value the G -value
exhibits a rapid fall indicating ow of the organogel. This crit-
The authors acknowledge Indian Institute of Technology,
Kharagpur for nancial support of this work. RDM thanks CSIR,
India for a research fellowship. We thank Mr Kiran Patruni,
Department of Agricultural Science, IIT Kharagpur, for his help
with the rheological measurements.
0
ical stress is termed as yield stress (s
obtained from the corresponding plots are 4, 191, and 9445 Pa
for NHT, NAT, and NCT organogels, respectively. The highest s
y y
). The s values as
y
value of the NCT organogel compared to NAT and NHT indi-
cates its highest mechanical strength. On the other hand, the
Notes and references
NHT organogel has the lowest s value and hence it is the
y
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2
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4
or –N(CH
observe that the –NH
3
)
2
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2
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2
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–
2
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7764 | RSC Adv., 2014, 4, 7760–7765
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