Spherical Polymer Brushes in Solvents of Variable Quality: An Experimental Insight by TEM Imaging

Abstract

The spherical micelle and vesicle composed of [PW12O40](3-) and poly(styrene-b-4-vinylpyridinium methyl iodide) are regarded as a model system to study spherical polymer brushes (SPBs) in solvents of various quality. The pure repulsions occur for the brush chains in the chloroform solution and chloroform/methanol mixture with a methanol volume ratio of 9.1%, where the grafted polystyrene chains have a relatively extended conformation. Further increase in the methanol concentrations leads to the presence of the intra/inter-brush van der Waals attractions. Transmission electron microscopy studies show that there is a coexistence of isolated and oligomeric SPBs and multi-SPB aggregates (MSAs) with the methanol content from 17% to 23%. Only MSAs are detected with the increasing methanol content. Both the corona and core shrink significantly in the isolated and oligomeric SPBs and MSAs. The full interpenetration of the grafted chains is observed between the cores in the oligomeric SPBs and MSAs.

Self-Assembly of Star Micelle into Vesicle in Solvents of Variable Quality: The Star Micelle Retains Its Core–Shell Nanostructure in the Vesicle

“…The present feature of interstar (micelle) van der Waals attractions agreed well with the previous TEM observations of the interpenetrations between the grafted chains of spherical polymer brushes (SPBs) and between the internal chains of the vesicle of polyoxometalatebased supramolecular polymers and the grafted chains of SPBs obtained in the solvents of weakening quality. 25,26 It should be highlighted that the present assignments of intra-and interstar van der Waals attractions were essentially consistent with the previously theoretical insights of star polymers in solvents of variable quality as briefly described in the Introduction, although only single-and two-star systems are concerned there. 1,8,9 However, the formation of the vesicles implied that many-star interactions actually occurred in the real solutions with weakening solvent quality even under this dilute condition.…”

Tunable Interactions of Polyoxometalate-Based Brushlike Hybrids in Solvents of Variable Quality: From Self-Recognition to Supramolecular Recognition

“…The DLS pattern of the dispersion of PSP-4 and SVP-6 in the chloroform/methanol mixture with a methanol volume ratio of 43% provided a hydrodynamic diameter (D h ) of 116 nm ( Figure S1a), which was smaller than those of both PSP-4 (150 nm, Figure S1b) and SVP-6 (230 nm) 18 in the same solvent mixtures with the same concentrations. The mixture dispersion was cast onto a carbon-coated copper grid for both BF-TEM (Figure 2a,b) and HAADF-STEM (Figure 2c) observations.…”

“…Among these different structures, the spherical POM-based polymeric hybrids have been regarded as a good model system for studying the intrabrush and interbrush interactions of SPBs in solvents of various quality because they can be directly imaged by transmission electron microscopy (TEM) without any other staining. 17,18,21 For example, POM-based supramolecular star polymers (PSPs) formed by the electrostatic combination of a Keplerate cluster of [Mo 132 O 372 (CH 3 COO) 30 (H 2 O) 72 ] 42− (Mo 132 , d = 3 nm) with quaternary-ammonium-terminated polystyrenes (S n + ) are highly soluble in good solvents chloroform, toluene, and tetrahydrofuran as a result of the purely repulsive intra-PSP and inter-PSP interactions ( Figure 1a). 21 In this case, the core diameter is much smaller than the unperturbed end-to-end distances of the S n + chains (R 0 = 0.456n 0.595 ).…”

“…POM-based nanocomposites formed by poly-(styrene-b-4-vinylpyridinium methyl iodide) (S n -b-V m ) and POMs ([PW 12 O 40 ] 3− anions) (SVPs) can form spherical micelles and vesicles with a polystyrene corona and a POMbased ionic hybrid core in solvents with very low polarity, such as toluene, chloroform, and dichloromethane ( Figure 1d). 17,18 Unlike PSPs, the core diameters of SVPs are comparable to or larger than the R 0 values of the S n chains. The polystyrene chains show a relatively stretched conformation in the chloroform/methanol mixtures with low methanol volume ratios as a result of the repulsive interactions.…”

“…The polystyrene chains show a relatively stretched conformation in the chloroform/methanol mixtures with low methanol volume ratios as a result of the repulsive interactions. 17,18 The increase in the volume ratio of methanol leads to the decrease in solvent quality and thus the direct observation of isolated and oligomeric SPBs and multi-SPB aggregates by TEM imaging, where both the corona and core shrink significantly ( Figure 1e,f). The compact corona is assigned to the presence of strong intrabrush van der Waals attractions.…”