Supramolecular Routes to Hierarchical Structures:  Comb-Coil Diblock Copolymers Organized with Two Length Scales

Abstract

We show that polymeric materials characterized by two length scales are obtained if diblock copolymers are mixed with amphiphilic selective solvents, leading to self-organization which combines the "block copolymer length scale" with a much shorter "nanoscale". In this work, the amphiphilic compound is 3-n-pentadecylphenol (PDP) which is hydrogen-bonded to the pyridine group of polystyreneblock-poly(4-vinylpyridine), i.e., PS-b-P4VP. The molecular architecture resembles comb-coil diblock copolymers A-block-(B-graft-C) but is obtained using the supramolecular assembly route. The structures were determined with a combination of transmission electron microscopy and small-angle X-ray scattering. On the block copolymer scale (300 Å range), the PS blocks are microphase-separated from the P4VP-(PDP) x blocks, where x denotes the ratio between the number of phenol and pyridine groups. For PS-b-P4VP block copolymers having a spherical morphology and P4VP as the minority component, the structure of PS-b-P4VP(PDP)x changes from spherical to hexagonal and further to lamellar as a function of the amount of PDP added. For all comb-coil diblock copolymer morphologies, the P4VP(PDP)x domains are further "nanophase-separated" into lamellar structures due to microphase separation of the comb copolymer-like complex between P4VP and PDP. The morphology diagram is presented for stoichiometric conditions (x ) 1), using a range of different PS-b-P4VP block copolymers.

Incorporation of PPE in Lamellar Self-Assembled PS-b-P4VP(PDP) Supramolecules and PS-b-P4VP Diblock Copolymers

“…Volume fraction was approximated by weight fraction as the densities of the two phases are only slightly different. 36 The experimental results closely follow the theoretical curve for a uniform distribution, even though the molar mass of the PPE homopolymer is larger …”

End-to-End Alignment of Nanorods in Thin Films

“…40,48,49 In thin films, it forms a cylindrical morphology where parallel PS cylinders are embedded in the P4VP(PDP) 1.7 matrix. The PS cylinders are packed in a distorted hexagonal lattice and the NPs, passivated with alkyl ligands, are selectively sequestered in the interstitial region between PS cylinders.…”

Solid state nanofibers based on self-assemblies: from cleaving from self-assemblies to multilevel hierarchical constructs

“…3 nm) takes place. 52 For the present PS-b-P4VP and the nominally stoichiometric amount of DDP or PDP in comparison to P4VP repeat units, and optionally adding PPE (e.g. weight fraction 23% vs PS) one obtains cylindrical self-assemblies.…”

“…weight fraction 23% vs PS) one obtains cylindrical self-assemblies. 17,18,52 In order to have overall alignment, shear flow processing by either large amplitude dynamic rheometry or, more practically, by an extruder allows high overall alignment. 17,19 Finally, the nanofibers forming the self-assembled cylindrical cores can be cleaved by selective polar solvent treatment using ethanol, thus releasing long individualized nanofibers with a PS core and a P4VP corona, see Fig.…”

“…hydrogen bonding or ionic bonding. 4,7,52,61 The self-assembly is based on the ''chemical'' contrast between the three types of constituents. The side-chains can also be rod-like mesogenic, thus incorporating conformation contrast between the constituents to drive towards self-assembling hierarchies.…”