Viscoelastic behavior of supramolecular polymeric systems, so-called organogels, consisting of N,N
‘,N‘ ‘-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide (DO3B) and n-alkanes (C
n
) such as decane (n = 10), dodecane
(n = 12), and tetradecane (n = 14) was examined varying the concentration of DO3B (c) with temperature
ranging from 20 to 50 °C. It is widely accepted that DO3B forms long columnar supramolecular structure in
nonpolar solvents like C
n
due to intermolecular hydrogen bonding between amide groups. The obtained storage
and loss moduli as functions of frequency for DO3B/C
n
were simple and well described with a Maxwell
model possessing only one set of a relaxation time (τ) and strength (G
N) just like those in aqueous threadlike
micellar systems formed by some surfactants. The value of G
N is proportional to c
2 as observed in fully
entangled linear flexible polymer systems. The value of τ slightly decreases with increasing the value of c
contrary to the behavior of the polymer systems. The activation energy of τ was determined to be 32 ± 2 kJ
mol-1 irrespective of the sort of solvents and was different from those of the viscosity for each solvent.
These strongly suggest that columnar, flexible supramolecular polymeric structure is generated in DO3B/C
n
and densely entangles each other to show the pronounced viscoelasticity as well as in the polymer systems,
whereas a mechanism for entanglement release is not similar to that in the polymer systems, but to that in
aqueous threadlike micellar systems.
The influence of a chiral gelator molecule, N,N
‘,N
‘
‘-tris-(S)-(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide
((S)DO3B), on the structure in the formation of supramolecular polymers and viscoelasticity was examined
in an organogel system consisting of a racemic mixture of the gelator molecule, N,N
‘,N
‘
‘-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide (DO3B), and n-decane. In the absence of the chiral gelator, equal amounts were
observed of the right- and left-handed helicities of the formed columnar supramolecular polymers. Addition
of (S)DO3B markedly induced one helicity in excess, due to the Majority
Rule
effect. Although there are two
possibilities, (1) left- and right-handled helices within single supramolecular polymers and (2) mixtures of
homochiral supramolecular helical polymers, the viscoelasticity of the system supports the former. Without
(S)DO3B, 60% of the amide groups of the gelators formed hydrogen bonding in the system; upon increasing
the relative (S)DO3B composition (relative to the total gelator concentration), the amount of amide groups
that formed hydrogen bonding increased up to 90%. The viscoelasticity of the organogel system was described
using the Maxwell model, with only one set of relaxation time and strength irrespective of the relative
composition of (S)DO3B. Relaxation strength was proportional to the square of the total gelator concentration
as observed in entangled flexible polymer solutions, and was barely dependent on the relative composition of
(S)DO3B. Relaxation time was less dependent on the total concentration of gelators; slightly longer relaxation
times were observed with increasing relative compositions of (S)DO3B. Changes of the structure of the formed
supramolecular polymers induced by the addition of (S)DO3B did not influence the molecular weight between
the entanglement points whatsoever, whereas the relaxation time (corresponding to the lifetime of entanglement
points) was affected.
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