Hierarchical Assemblies of Block-Copolymer-Based Supramolecules in Thin Films

Abstract

The hierarchical assemblies of supramolecules, which consisted of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with 3-pentadecylphenol (PDP) hydrogen-bonded to the 4VP, were investigated in thin films after solvent annealing in a chloroform atmosphere. The synergistic coassembly of PS-b-P4VP and PDP was utilized to generate oriented hierarchical structures in thin films. Hierarchical assemblies, including lamellae-within-lamellae and cylinders-within-lamellae, were simultaneously ordered and oriented from a few to several tens of nanometers over macroscopic length scales. The macroscopic orientation of supramolecular assembly depends on the P4VP(PDP) fraction and can be tailored by varying the PDP to P4VP ratio without interfering with the supramolecular morphologies. The lamellar and cylindrical microdomains, with a periodicity of ∼40 nm, could be oriented normal to the surface, while the assembly of comb blocks, P4VP(PDP), with a periodicity of ∼4 nm, were oriented parallel to the surface. Furthermore, using one PS-b-P4VP copolymer, thin films with different hierarchical structures, i.e., lamellae-withinlamellae and cylinders-within-lamellae, were obtained by varying the ratio of PDP to 4VP units. The concepts described in these studies can be potentially applied to other BCP-based supramolecular thin films, thus creating an avenue to functional, hierarchically ordered thin films.

Nanostructured Organic Semiconductors via Directed Supramolecular Assembly

“…Thus, solvent-annealed PS-b-P4VP(4T) 1.5 does not form a well-ordered lamellae-within-lamellae morphology in thin films as previously found with other BCPbased supramolecules. 41,43 We speculate that, after solvent annealing, PS-b-P4VP(4T) 1.5 may form morphologies similar to that shown in Figure 4b, where a significant fraction of 4Ts organize into lamellae bridging the BCP lamellae in different grains to provide a pathway to transport charges between P4VP(4T) r lamellae. Upon thermal annealing, 4Ts are incorporated within P4VP(4T) r microdomains, which resulted in an increase in BCP periodicity.…”

“…39Ϫ43 Experimentally, by adjusting the loading of the small molecules, the BCP microdomains can be aligned perpendicular to the surface. 41,43 Within BCP microdomains, lamellar assemblies from the comb block, several nanometers in size, are oriented parallel to the surface and small molecules are aligned perpendicular to the surface. 41,43 Blending organic semiconductors with inert polymers was shown to be effective for improving the solution processability of the semiconductor.…”

“…41,43 Within BCP microdomains, lamellar assemblies from the comb block, several nanometers in size, are oriented parallel to the surface and small molecules are aligned perpendicular to the surface. 41,43 Blending organic semiconductors with inert polymers was shown to be effective for improving the solution processability of the semiconductor. 44 The supramolecular approach provides a new avenue to solution process organic semiconductors as well as to assemble them into nanoscopic structures in thin films.…”

Thin films of complexed block copolymers

“…140 In the case of P2VP-b-PEO hydrogen bonded with mesogenic groups, also able to form structures-within-structures, the preferred orientation of the liquid crystalline layers parallel to both interfaces stabilized a perpendicular orientation of the microdomains, comparable to the covalent counterparts in ref. 101-104.…”

“…Thin films of PS-b-P4VP(PDP) supramolecules have been investigated by van Zoelen et al and Tung et al [138][139][140] In a study on solvent annealed systems of high molecular weight asymmetric comb copolymers with a small P4VP(PDP) block on silicon, the presence of PDP induced enough mobility to induce structure formation in the high molecular weight ($320 000 g mol À1 ) block copolymer. Furthermore, it was found that as opposed to pure PS-b-P4VP diblock copolymers, which exhibit asymmetric wetting conditions (PS wets the surface and P4VP the substrate), the P4VP(PDP) comb wetted both the substrate and the air interface due to the low surface energy of PDP, which shielded P4VP from the surface.…”