Molla Islam - Preclusion of nano scale self-assembly in block-selective non-aqueous solvents for rod-coil and coil-rod-coil macromolecular surfactants based on perylene tetracarboxylic diimide.

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      Publication Details (including relevant citation   information): Islam, Molla Rafiquel, Dahan, Elianne,   Saimani, Sundar, Sundararajan, Pudupadi R., Eur. Polym.   J., 2012, 48 (9), pp 1538-1554

      Abstract: Self-assembly of amphiphilic mols.   ranging from simple surfactants to block copolymers in a solvent   depends on one part of the mol. (one block in block copolymers)   being sol., and the other not. The aggregation of the insol.   segment in the block-selective solvent leads to the self   assembly. In this paper, we describe a system of amphiphilic   rod-coil and coil-rod-coil mols., which do not show self assembly   in block-selective non-aq. solvents. We prepd. rod-coil mols.   based on hydrophilic propylene oxide/ethylene oxide copolymer   (PO-EO copolymer) (Jeffamine) as the flexible segment and   photo-conducting large arom. perylenediimide (PTCDI) as the rod.   PO-EO copolymer was attached either to one side of PTCDI   (MJ-PTCDI) or both sides (DJ-PTCDI). The former can be considered   an inverse macromol. surfactant, since the tail is hydrophilic   and the head is hydrophobic. The DJ-PTCDI is a pseudo Gemini   surfactant. Because of the presence of the chromophore, UV-Vis   and fluorescent spectra could be used to study the self assembly   of these amphiphilic rod coil polymers in soln. PTCDI forms   π-interaction mediated aggregates in aq. soln. and these are   H-stacked in MJ-PTCDI and J-stacked in DJ-PTCDI. Variable temp.   UV and NMR spectra show that the assembly is stable over a large   temp. range in water. The aggregates are also stable up to a pH   of 12. However, when a non-aq. solvent is used, no aggregation   occurs. This is attributed to the solvation of the π-system of   the PTCDI. With the addn. of water, such solvation seems to be   interrupted and aggregation occurs when water becomes a major   component. We find that the mole percentage of the aggregates in   acetone/water mixts. increases almost linearly with the concn. of   water, providing a route to control the extent of aggregation of   the chromophores. Due to the long, waxy PO-EO copolymer, MJ-PTCDI   and DJ-PTCDI do not show liq. cryst. behavior or nanorod   morphol., which were seen with short side chains. The optical   microscopy of the bulk material shows aggregated crystals of   PTCDI in the waxy matrix, showing that even in the presence of   PO-EO copolymer, the mol. assembly of PTCDI takes place in the   bulk. Secondary assembly was seen, in that upon ageing of the aq.   solns., the drop cast films show that the spherical aggregates   one-dimensionally coalesced into long fibers. Although UV-Vis   spectra indicated no aggregation in non-aq. solvents, drop-cast   films of these solns. show needle-like aggregates and Lego-like   assemblies. [on SciFinder(R)]

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