Structures of the cylindrical and vesicular micelles of an P4VP-longer asymmetric PS-b-P4VP

Abstract

IntroductionThe control of the self-assembled micellar morphology of amphiphilic block copolymers in a selective solvent has engrossed substantial interests in the theoretical and applied research fields. [1][2][3] The micellar morphology of the block copolymers can be controlled by solvent selectivity and block copolymer composition. 4 There are three main factors for controlling these morphologies, i.e., the stretching of core blocks, the repulsive interaction among corona chains, and the surface tension of the core/corona interface at the onset of micellization. 5,6 The block copolymer can selfassemble into spherical, cylindrical, and vesicular micelles in a given solution. 4 Among those micelles, the vesicle has fascinated scientists because of its diverse applications such as drug delivery diagnostics, 7 electronics (chip nanopatterning), 8 and catalysis (enzyme entrapment). 9 Vesicles (generally kinetically trapped and non-equilibrium) 10 are usually formed by low molecular materials such as surfactants or lipids.Wittmann et al. for the first time reported the polymeric vesicles of poly(styrene-b-isoprene) (PS-b-PI) and poly(styrene-b-ethylene oxide) (PS-b-PEO) in a mixture of ethyl benzene (a selective solvent for both blocks) and n-decane (a PI and PEO selective solvent). 11 Schrage et al. investigated vesicular morphologies of quaternized poly(1-methyl-4-vinyl pyridine-b-styrene) and poly(1,2-butadiene-b-(cesium methacrylate)) which were self-assembled in THF (nonselective for PS and poly(1,2-butadiene) but selective for charged blocks). 12 Kesselman et al. also studied the change in the vesicular morphologies of PS-b-PI by controlling solvent selectivity in diethyl phthalate (less PS-selective) and dimethyl phthalate (highly PS-selective) mixtures. 13 Putaux et al. investigated the vesicular morphologies of PS-b-PI in n-heptane and n-decane, both of which are selective solvents for PI. 14 The PS-b-P4VP vesicles have been observed when the P4VP blocks were complexed with other small molecules. [15][16][17][18][19] The vesicles of PS-b-P4VP in chloroform were observed when perfluorooctanoic acid (PFOA) was added to be complexed with P4VP. 18 Peng et al. also reported another interesting research on the vesicular morphology of PS-b-P4VP in a complex form with low molecular-weight aliphatic acids (stearic acid, decanoate, acetic acid, and formic acid) in chloroform (non-selective for PS-b-P4VP and aliphatic acids but selective in a complex form). 20 But, PS-b-P4VP vesicles without complexation were rarely observed. The cylindrical morphology of an asymmetric PS(19600)-b-P4VP(5100) (PS longer) in P4VP selective solvents was reported. However, the vesicles with asymmetric PS-b-P4VPs (P4VP longer) in PS selective solvents have not been reported. The block length of P4VP of the PS-b-P4VP is of prime importance because a number of valuable metals or small molecules could be complexed with the P4VP core of micelles (in the PS selective solvents) which is utilized as a nanoreactor.The screening of the solvent sel...

Amphiphilic Block Copolymer Micelles in Selective Solvents: The Effect of Solvent Selectivity on Micelle Formation

“…While our previous reports dealt with functionalization of PS-b-P4VP nanofibers and spherical micelles, the present work is addressed to a fundamental understanding of micellization process taking place upon dispersion of PS-b-P4VP BCPs in P4VP-selective solvents, and the role of temperature and solvent selectivity on micelle formation and their characteristics. Alcohols are generally considered to be P4VP-selective solvents for PS/P4VP pair, which are governed by their polar nature and potential for interacting with P4VP units via hydrogen bonding [7,11,12]. The only example on solution assembly of PS- b -P4VP containing longer P4VP block, which we found in literature, deals with toluene/ethanol mixtures as an environment [12].…”

“…Alcohols are generally considered to be P4VP-selective solvents for PS/P4VP pair, which are governed by their polar nature and potential for interacting with P4VP units via hydrogen bonding [7,11,12]. The only example on solution assembly of PS- b -P4VP containing longer P4VP block, which we found in literature, deals with toluene/ethanol mixtures as an environment [12].…”

“…The ability of pyridine units to undergo hydrogen bonding and coordinate with electron-deficient species largely simplifies the functionalization process and diversifies synthetic strategies, which can be implemented to achieve desired materials. Micellization of symmetric and asymmetric PS- b -P4VP BCP was studied in the past by several research groups, focusing on different aspects of micelle formation and morphological transformation processes [8,9,10,11,12,13,14,15].…”

“…Surprisingly, most of the literature reports related to PS- b -P4VP micellar systems have focused on either symmetric or asymmetric BCP compositions with longer PS block where the solution self-assembly was studied in PS-selective conditions. The PS- b -P4VP micellar systems comprising longer P4VP blocks are scarce and less explored [12]. Such micelles comprising an inner PS core and outer P4VP corona can be obtained with the aid of P4VP-selective solvents, for instance, alcohols.…”

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4′-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate))

“…The conformation of the polyelectrolyte primarily depends on the electrostatic interactions between the charged groups of the polyelectrolyte. Highly charged polyelectrolytes lead to an increase in osmotic pressure, which causes the chains to adopt an expanded, rigid, rod-like conformation [5][6][7][8][9]. Therefore, the pH of the solution also controls the chain conformation through protonation (or deprotonation) of weak polyelectrolytes.…”