Controllable Nanostructure Formation through Enthalpy-Driven Assembly of Polyoxometalate Clusters and Block Copolymers

Abstract

The coassembly of block copolymers (BCPs) with nanoscale inorganic objects is an important route to fabricate nanostructured polymer composites. However, the immiscibility of inorganic/polymeric interface is a recurring challenge to overcome, particularly for inorganic clusters, such as the polyoxometalates (POMs)/BCPs system. In this paper, we present a general method to incorporate POMs into BCP matrices, in which a POM cluster is embedded as a core in a supramolecular star polymer (SSP) whose arms possess the same chemical composition as a BCP segment. Because of the enthalpic interaction between SSP arms and BCP segments, the SSP can carry POM into BCP matrices to realize their coassembly. By this way, we successfully localize a Keggin-type POM cluster [CoW 12 O 40 ] 6− modified with polystyrene (PS) arms into the PS domain of poly(styrene-b-ethylene oxide) micelles, which induces the formation of a series of hybrid micelles with spherical, toroidal, and bicontinuous structures. The morphological transition of micelles can be adjusted by the length of PS arms and the content of cluster cores. The mechanism is studied by both experimental methods and simulations. An unconventional mechanism for toroid formation is disclosed for the first time, which follows a sphere− rosary−toroid pathway. Furthermore, the electrostatically bonded structure of SSP is found to play a crucial role on this pathway. These results not only pave the way for fabricating cluster−polymer nanocomposites with controllable structures but also provide new insights into comprehending the self-assembly behavior of complex polymer systems.

Inorganic‐Macroion‐Induced Formation of Bicontinuous Block Copolymer Nanocomposites with Enhanced Conductivity and Modulus

“…[16,19] Such structures are stable under thermal annealing at 120 8 8C for 48 h. Notably,t he phase transition is accompanied by adecrease in the P2VP/SiW domain distances,which are 61.8, 45.8, and 32.9 nm for SVP97K-1, -3, and -5, respectively ( Figure S5 b-d), which reflects an increase in the interfacial areas between the PS domain and the P2VP/SiW domain that is due to the SiW-induced electrostatic cross-linking of the P2VP chains.T he cross-linking is also indicated by the vanished glass transition of P2VP ( Figure S12). [41] Moreover,a th igher concen- trations of 0.1 to 1mgmL À1 (Figure 3d-f), the fusion of micelles is more and more enhanced, and they are linked into disordered networks similar to the bicontinuous structures of dry SVP97K-5 nanocomposites.T hese results demonstrate that the formation of disordered bicontinuous structures is ar esult of the fusion of micellar precursors.A salogical extension, if we could precisely shield the strong electrostatic cohesion between the POMs and BCPs by replacing the protons of the POMs with cationic organic or polymeric ligands, [34] other structures aside from bicontinuous phases would also be accessible. Such al arge f value is favorable for fabricating conductive materials.…”

“…[1,22,23] However,p hase transitions induced by multi-charged ions,p articularly the formation of bicontinuous structures,h ave been rarely reported, although multi-charged ions are preferable for achieving as trong electrostatic cohesion. [26][27][28][29][30][31][32][33][34][35][36][37][38] Moreover,POMs are typical inorganic macroions [39] owing to their very high negative charges from 2t o more than 40 and nanoscale dimensions with diameters from 0.5 to 6nm. [26][27][28][29][30][31][32][33][34][35][36][37][38] Moreover,POMs are typical inorganic macroions [39] owing to their very high negative charges from 2t o more than 40 and nanoscale dimensions with diameters from 0.5 to 6nm.…”

Role of High‐Molecular‐Weight Homopolymers on Block Copolymer Self‐Assembly: From Morphology Modifier to Template

“…In such a situation, the adjacent PS globules are easier to fuse with each other forming rod‐like aggregates upon water addition. In fact, fusion of polymer particles into new morphologies has already been reported in several works . Further increasing f HP produces large globules (in the scale of 100 nm) which act as templates for the PS 15k ‐ b ‐PEG 5k BCPs.…”

“…As illustrated in Scheme , the self‐assembly process can be divided into two successive steps. With adding water to the initial solution of the polymer mixtures, PS 52k HPs first collapse and form globules which are stabilized by PS 15k ‐ b ‐PEG 5k BCPs . Subsequently, with further adding water, the pre‐formed PS globules would cooperative self‐assemble with PS 15k ‐ b ‐PEG 5k BCPs.…”

“…When f HP is lower, the size of the pre‐formed PS globules is small (in the scale of 10 nm). In the further cooperative self‐assembly, the small globules could increase the volume fraction of hydrophobic blocks, leading to the formation a morphology transition from spherical to vesicle with a less curved interface (Scheme a) . With increasing f HP , rod‐like aggregates can be produced (Scheme b).…”