Abstract
The synthesis, morphological transformation, and photophysical properties of a rod-coil block copolymer, poly[2,7-(9,9-dihexylfluorene)]-block-poly(2-vinylpyridine) (PF-b-P2VP), with P2VP coils of various lengths in a mixed methanol/tetrahydrofuran (MeOH/THF) solvent are reported. Various morphological structures of PF-b-P2VP aggregates, including spheres, short worm-like structures, long cylinders, and large compound micelles (LCMs), were observed after varying the coil length of PF-b-P2VP and the selectivity of mixed solvents. These aggregated structures demonstrated considerable variation with regard to optical absorption, fluorescence, and the PL quantum yield of rod-coil copolymers. The degree of hypsochromic spectral shift was enhanced as the length of P2VP coils and the content of poor solvent increased. This study reveals the influence of coil length and selectivity of solvents on the morphology and the optical characteristics of rod-coil amphiphilic copolymers.
Highlights
dynamic light scattering (DLS) cannot provide the real morphologies of micellar aggregation. e selectivity of solvents can be manipulated by selecting solvents with various solubility parameters. e solubility of photoluminescence spectra of (PF) and P2VP is in the range of 18.62–19.02 MPa0.5 and 27.6 MPa0.5, respectively. e solubility of THF and MeOH is 18.6 and 29.7 MPa0.5, respectively. us, THF is a suitable solvent for PF and a selective solvent for P2VP
Spherical micelles with a diameter ranging from 50–80 nm were observed in pure THF solution. is is because THF acts as a good solvent for PF, but as a poor solvent for P2VP, resulting in a spherical morphology with a core of P2VP and a corona of PF
A further increase in the MeOH content to 50 vol.% resulted in the formation of two morphological structures of PF-b-P2VP aggregate: a spherical micelle with a core of PF and a corona of P2VP and a cylinder with a diameter of 50–100 nm and a length of approximately 300–500 nm. is transformation was due to the expansion of the P2VP core following an increase in MeOH, because MeOH is a good solvent for P2VP, and the increased selectivity enhances the ππ-ππ stacking of the PF segment, resulting in a cylindrical morphology [22]
Summary
E self-assembly of amphiphilic block copolymers (ABCs) is considered a promising approach to synthesize nanostructured or hierarchical materials with novel morphological and physical properties for advanced applications in areas such as electronics, optoelectronics, biotechnology, and environmental technology [1,2,3,4,5,6,7,8,9,10,11,12,13]. e morphology of amphiphilic block copolymers can be manipulated using different driving forces, including relative block length, block polarity, volume fraction, and temperature [14,15,16]. Amphiphilic rod-coil diblock copolymers [17, 18] have attracted considerable attention, as they produce novel self-organizing structures in the form of stiff rod-like segments, such as helical [19] and ππ-conjugation polymers [20,21,22,23,24,25]. E high immiscibility and stiffness asymmetry between rigid conjugated rods and exible coil segments signi cantly in uence the molecular packing of polymers, leading to self-organized aggregation. E importance of the morphological transformation of rod-coil poly[2,7-(9,9dihexyl uorene)]-block-poly(2-vinylpyridine) (PF-b-P2VP) via selective solvents on optical characteristics has been demonstrated [22]. Is paper reveals the in uence of the ratio of poor/good solvents on the morphological and photophysical properties of these diblock copolymers with various coil lengths as well as the spectral stability of PF-b-P2VP. Transmission electron microscopy (TEM), atomic force microscopy (AFM), UVvis optical absorption, and photoluminescence (PL) spectroscopy were employed to investigate the correlation between optical characterization and morphology
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