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We compared the crystallization rate of poly(3-hexylthiophene) (P3HT) in the film cast from the gel (called "gel-cast film") with that in the film cast from the liquid solution (called "solution-cast film") to understand the effect of solution structure on the structural development in the subsequently cast film of conjugated polymer. P3HT was found to form a homogeneous liquid solution with xylene at elevated temperature. When the freshly prepared semidilute solution was allowed to age at room temperature, the solution transformed into a gel in which a significant amount of nanowhiskers formed. The nanowhiskers in the gel were effectively transferred to the corresponding cast film, while the film cast from the freshly prepared solution only contained a small amount of such a morphological entity. The in situ small-angle X-ray scattering (SAXS) measurement and thermal analysis revealed that both the cold and melt crystallization of P3HT in the gel-cast film were much slower than those in the solution-cast counterpart. The retardation of crystallization rate in the gel-cast film was attributed to the abundance of the nanowhiskers. In this case, the crystallization of P3HT occurred predominantly within the individual nanowhiskers and the mesh regions in the networks of the whiskers, where their limited sizes in at least one dimension imposed a strong spatial constraint to the crystal growth and chain motion for crystallization.

In this work, we established the relationship between the thermally induced microstructure development and the photoluminescence efficiency (Ep) of the poly(9,9-dioctylfluorene) (PF8) fibers prepared from the semidilute PF8/chloroform solutions by direct electrospinning. The as-spun (AS) fibers were found to be composed of an amorphous phase and a significant fraction of mesomorphic β-phase, which may promote the Ep of PF8. The temperature-dependent wide-angle X-ray scattering (WAXS) measurement revealed that the PF8 fibers exhibited complex structural transformation on heating from the AS state, and there existed a strong correlation between Ep and the microstructure developed. The AS fibers exhibited the highest Ep value. The Ep decreased progressively on heating at temperatures below the cold crystallization temperature (Tcc), where the microstructure remained unperturbed. The β-phase transformed to γ- or α′-phase (Cγ-/Cα′-crystals) above Tcc, and such a structural transformation led to a reduction of ...

In this study, we explore the orientation of crystals formed within the lamellar domains of a diblock copolymer composed of two crystallizable blocks, that is, poly(l-lactide)-block-polyethylene (PLLA-b-PE). The orientation of both PLLA and PE crystals with respect to the lamellar interface was examined under two types of crystallization condition with a broad range of crystallization temperatures (Tc). The first type was the “two-stage crystallization”, where the PLLA block was allowed to crystallize before PE. The second was the “one-stage crystallization”, where PLLA and PE blocks competed to crystallize. A homeotropic crystal orientation was always observed for the PLLA crystals, with the crystalline stems lying parallel to the lamellar normal regardless of the crystallization condition, except when Tc approached the glass-transition temperature of PLLA, where the orientation became random. A homogeneous crystal orientation with the PE crystalline stems oriented perpendicular to the lamellar normal wa...

A dual-emission nanoprobe that can sense changes in the environmental pH is designed based on the concept of pH-responsive Förster resonance energy transfer induced by the conformational transition of an associating polyelectrolyte, N-palmitoyl chitosan, bearing a donor (Cy3) or an acceptor (Cy5) moiety. We demonstrate that the developed pH-responsive nanoprobe can be used to ratiometrically image and thus discriminate the pH changes in the biological environment at different length scales.

We identified the formation of nanowhiskers of poly(3-hexylthiophene) (P3HT) in the gel with xylene in situ by means of small-angle X-ray scattering (SAXS). In the freshly prepared solution, the rodlike segments of P3HT were found to form local network aggregates characterized by the mass fractal dimension of ca. 2.5. Upon prolonged aging at room temperature, the originally viscous liquid solution transformed into a gel, in which a rodlike entity with the cross-sectional radius of gyration of 7.31 nm was disclosed. Real-space observation of the morphology of the film cast from the gel revealed the presence of long nanowhiskers. The fact that the width and height of these whiskers closely agreed with those of the rodlike entity in the gel deduced from model fitting of the SAXS profile indicated that the nanowhiskers were present in the wet gel. Time-resolved SAXS experiment revealed that the nanowhisker formation was accompanied by the crystallization of P3HT. The ultimate crystallinity attained in the nan...

The gelation behavior of the solution of a conjugated polymer, poly(9,9-dioctylfluorene) (PF8), with a poor solvent, methylcyclohexane (MCH), induced by aging at room temperature has been investigated. Light scattering and optical microscopy revealed that the gelation was driven by a macrophase separation occurred through a spinodal decomposition mechanism. Although the spinodal decomposition could proceed to the late stage, the interconnected morphology was arrested to give rise to the gel property of the system. The phase-separated gel was composed of an isotropic phase and a PF8-enriched liquid crystalline phase. The liquid crystalline phase was further found to consist of sheetlike aggregates (as revealed by small-angle X-ray scattering) in which a fraction of the PF8 chains formed the β-phase (as disclosed by the optical spectra) which dominated the photoluminescence spectrum of the gel. The PF8/MCH gel could be disintegrated by moderate heating to ca. 70 °C. This gel-to-sol transition was accompanie...

The crystallization behavior of the blends of two crystalline−amorphous diblock copolymers bearing chemically different crystalline block has been studied. A series of lamellae-forming blends of a ...

We probed the gelation and its effect on the photophysical property of a conjugated semiconducting polymer, poly(9,9-dioctylfluorene-2,7-diyl) (PF8), in toluene. The conformational structure characterized by the radius of gyration and the persistence length of PF8 in the dilute toluene solution depended strongly on temperature, where the conjugated chains exhibited a more extended conformation as the temperature was raised. The interchain interaction above the overlap concentration induced aggregation of PF8 to form network clusters in the solution. Gelation took place when the semidilute PF8 solutions were cooled and subsequently aged at −20 °C. The gel composed of the dynamically arrested PF8-enriched phase and the isotropic phase due to the occurrence of a macrophase separation at the subambient temperature. The PF8-enriched phase was mesomorphic, consisting of sheetlike aggregates or membranes. A fraction of the PF8 chains or segments within these sheetlike aggregates formed the β-phase which dominate...

The structure of poly(9,9-dioctylfluorene-2,7-diyl) (PF8) in deuterated toluene solutions at concentrations ranging from 0.60% to 7.0% (w/v) has been investigated by means of small-angle neutron scattering (SANS) and nuclear magnetic resonance (NMR) spectroscopy. PF8 chains exhibited aggregation above 1.0%, where the corresponding SANS profiles were characterized by the superposition of an aggregate component and a dynamic component associated with the transient network formed by interchain overlap. The 1H NMR resonance lines for both the polymer as well as for the residual protons in the solvent showed large upfield shift at higher concentrations, indicating strong polymer−solvent interaction. At a higher concentration (4.5%) an additional resonance line was observed in the aromatic regions of both the 1H and the 2H spectra that has been attributed to a residual anisotropic chemical shift of the solvent molecules. The later phenomenon is suggestive of the existence of magnetically anisotropic aggregate d...

Semirigid conjugated polymers have received much scientific and technological interest due to their unique electrical and photonic semiconducting properties. Spectroscopic studies have indicated that these polymers underwent interchain aggregation in the solution state even at large dilution; however, the origin of this event and the structure of the resultant aggregates remained the crucial issues to be resolved. In the present study, we revealed that the interchain aggregation of a conjugated polymer, poly(2,3-diphenyl-5-hexyl-1,4-phenylenevinylene) (DP6-PPV), in solutions with chloroform and toluene generated network aggregates with the hydrodynamic radii of several micrometers. Small angle neutron scattering (SANS) demonstrated that the internal structure of these aggregates could be characterized by the mass fractal dimensions of 2.2-2.7. The networks were looser in chloroform but became highly compact in the poorer toluene solvent due to severe segmental association. Increasing the temperature alleviated the segmental association in toluene while largely retaining the mass fractal dimension of the aggregates. However, the interchain aggregation was never completely dissipated by the heating, suggesting the existence of two types of segmental association with distinct stability. The highly stable segmental association that could neither be solvated by chloroform nor be disrupted thermally in toluene was attributed to the pi-pi complex already present in the DP6-PPV powder used for the solution preparation. The chains tied firmly by this complex formed network aggregates in the solution and hence reduced the entropy of mixing of the polymer. In the poorer toluene solvent, further segmental association took place within the preexisting aggregates, making the networks more compact. This type of segmental association could be disrupted by moderate heating, and its occurrence was ascribed to the poor affinity of the aliphatic side chains of DP6-PPV for toluene.