Journal of Physical Chemistry B, Vol.108, No.40, 15503-15510, 2004
Chiral amplification of the structure and viscoelasticity of a supramolecular polymeric system consisting of N,N' N''-tris(3,7-dimethyloctyl)benzene-1,3,5-tricarboxamide and n-decane
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 affect. 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.