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Poly(3-hexylthiophene) (P3HT) is one of the most widely studied conjugated polymers for applications in polymer-based photovoltaics and thin-film transistors. The regioregularity index (RR) represented by the mole percentage of the head-to-tail (HT) dyad in the polymer molecule has been considered as a key factor governing both the kinetics and thermodynamics of the self-assembly of P3HT. In this study, we reveal that the configurational sequence beyond dyad plays an equally important role by demonstrating that two P3HT samples bearing almost identical RR value and average molecular weight displayed very different self-assembly kinetics. Counterintuitively, the semidilute xylene solution of the P3HT with slightly smaller RR value exhibited a much faster gelation. In the bulk state, this sample also showed faster crystallization kinetics and higher melting point. Characterization of the configurational structure by nuclear magnetic resonance (NMR) spectroscopy showed that the P3HT with the smaller RR value contained a higher population of HT-HT triad sequence. Therefore, knowledge of this system parameter, which has been omitted prevalently, is essential for the delicate control of the morphological formation of P3HT for enhancing its photophysical properties.

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 investigate the morphology and microstructure of the aggregates, and the gelation behaviour of Poly(3-hexylthiophene) (P3HT) conjugated polymer in xylene solution as functions of P3HT concentration and aging time by the means of ageing time test, wide angle X-ray diffraction (WAXD), scanning electron microscopy (SEM), UV-visible absorption (UV-vis) and photoluminescence (PL) spectra. The result reveals that the gelation time of P3HT/xylene solution decreases markedly with increasing P3HT concentration. The photophysical properties of the P3HT aggregates in P3HT/xylene solution increase as P3HT concentration and ageing time are raised. It indicates that the well soluble P3HT polymer chains in xylene solution present microphase separation and self-assemble into stiff sheetlike structure, which associates by rodlike nanowhiskers of P3HT polymers during aging. Upon prolonged aging, the sheetlike structure of P3HT aggregates to from the three-dimension network that improves the electronic particle mobility in the organic solar cell.

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 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.

The crystallization kinetics and morphology development of pure isotactic polypropylene (iPP) homo- polymer and iPP blended with atactic polypropylene (aPP) at different aPP contents and the isothermal crystallization temperatures were studied with differential scanning calo- rimetry, wide-angle X-ray diffraction, and polarized opti- cal microscopy. The spherulitic morphologies of pure iPP and larger amounts of aPP for iPP blends showed the neg- ative spherulite, whereas that of smaller amounts of aPP for the iPP blends showed a combination of positive and negative spherulites. This indicated that the morphology transition of the spherulite may have been due to changes the crystal forms of iPP in the iPP blends during crystalli- zation. Therefore, with smaller amounts of aPP, the spher- ulitic density and overall crystallinity of the iPP blends increased with increasing aPP and presented a lower de- gree of perfection of the g form coexisting with the a form of iPP during crystallization. However, with larger amounts of aPP, the spherulitic density and overall crystallinity of the iPP blends decreased and reduced the g-form crystals with increasing aPP. These results indicate that the aPP molecules hindered the nucleation rate and promoted the molecular motion and growth rate of iPP with smaller amounts of aPP and hindered both the nucleation rate and growth rate of iPP with larger amounts of aPP during isothermal crystallization. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1093-1104, 2007

The purpose of this study was to research the compatibility and application of polyvinylpyrrolidone (PVP)/chitosan blended polymers. The polymers were synthesized at different weight ratios and tested using techniques such as Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis to evaluate the compatibility of the blended materials. Incompatibility occurred when the quantity of chitosan exceeded 75%. The addition of PVP was beneficial for the thermal stability of chitosan, but resulted in inferior strength performance. Furthermore, the blended polymers did not show a color-enhancement effect, but did show elevated water absorption, chlorine resistance, and colorfastness. In addition, the treated fabrics with a higher chitosan ratio in the blended polymer had antimicrobial properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 885–891, 2006

Modified asphalts using polymeric additives, such as isotactic polypropylene (iPP) and maleated polypropylene (MPP), for asphalt binders were prepared and characterized for potential usages in pavement construction. The differential scanning calorimetry (DSC) studies show that most of the crystallinity of iPP remains intact in the asphalt binders, but MPP exhibits more interaction with the asphalt due to the increase of the amorphous region of MPP. The phase distributions and rheological properties of the modified asphalts were examined by scanning electron microscope (SEM) and dynamic shear rheometer (DSR), respectively. The images of SEM show that the MPP-rich phase is larger than the iPP-rich phase in asphalt blends, which contributes to more dispersion of the polymer into the asphalt phase in the asphalt/MPP blend. From the rheological studies, the asphalt blends containing iPP exhibit higher viscosity in terms of higher temperature to get Newtonian behavior and have a higher performance grade for rutting resistance at high temperature and frequency. POLYM. ENG. SCI., 45:1152–1158, 2005. © 2005 Society of Plastics Engineers

An assay of biomarkers consisting of alpha-fetoprotein (AFP) is reported. Real-time measurements of the effective relaxation timeτeff, when the biofunctionalized magnetic nanoparticles (BMNs) were conjugating with biotargets, were made. The BMNs are anti-alpha-fetoprotein (antiAFP) coated onto dextran-coated iron oxide nanoparticles labeled as Fe3O4-antiAFP. It was found that the effective relaxation time,τeff, increases as the association of AFP and Fe3O4-antiAFP evolves. We attribute this to the enhanced Brownian motion of BMNs when magnetic clusters are present during the conjugation. We found that saturation magnetization,Ms, increases when the concentration of AFP increases. This is due to the fact that more magnetic clusters are associated in the reagent, and therefore theMsincreases when the concentration of AFP increases. The change of effective relaxation time and saturation magnetization shows a behavior of logistic function, which provides a foundation for assaying an unknown amount of biomolecules. Thus, we demonstrate sensitive platforms for detecting AFP by characterizingτeff. The detection platform is robust and easy to use and shows promise for further use in assaying a broad number of biomarkers.

In this work, the network structure and chain mobility of dried polyvinyl chloride/dioxane (PVC/DOA) gels prepared by the freeze-drying method are studied by SEM, FT i.r., WAXD, EDTA and pulsed NMR analyses. The results of FT i.r. and WAXD show no remarkable change in the crystallinity of either dried or wet PVC gels; however, the elasticity of wet gels and the gelation time of semi-dilute solutions exhibit remarkable changes with increasing concentration, C and molecular weight, M w of the polymer. From SEM results, the dried gel morphology consists of a fibril-like structure and the mesh size of the gel network decreases, resulting in the glass transition temperature ( T g ) shifting to higher temperatures with increasing M w and C . The results of pulsed NMR (CPMG method) for wet gels show that spin–spin relaxation time, T s 2 and T l 2 , respectively, related to the immobile and mobile components decrease, and the fractional amount of the immobile component, f l increases, while that of the mobile component, f f decreases with increasing M w and C . On the other hand, similar results are also found in freeze-dried gels from the pulsed NMR experiment (FID method). These facts in both wet and dried gels are considered to be due to the reduction of chain mobility related to the increase in the aggregation of polymer chains or the number of junction points in the gel network. The change in elasticity of PVC/DOA gels must be mainly related to the chain mobility of the network structure but not to the crystallinity of gels.

In this study, the relationship between the polymer-solvent interaction and the network structure of poly(vinyl alcohol) (PVA) gels prepared with organic solvents such as N-methylpyrrolidone (NMP) and ethylene glycol (EG) are investi- gated. The values of the intrinsic viscosity (h) and Huggins constant k* of dilute PVA solutions indicate that the attractive interaction between PVA and NMP is higher than that between PVA and EG. The X-ray result shows that PVA-EG gels have a (101) diffraction peak of PVA crystal that appeared at about 2uA 197, while PVA-NMP gels only show a broad amorphous scattering peak. On the other hand, Fourier transform infrared results of PVA/EG gels also clearly show an intense peak at 1141 cm 01 due to the crystalline absorption. The results of H 1 pulsed nuclear magnetic resonance show that the spin-spin relaxation time, T s and T l, respectively, related to the poly- mer-rich and polymer-poor components decrease, and the fractional amount of the polymer-rich component, f s , increases, while that of the polymer-poor component, f l , decreases with an increase in the concentration of polymer. At a given concentration, the value of f s in the PVA-EG gel is larger than that in the PVA-NMP one. These facts indicate that the crystallinity in the PVA-EG gel is higher than that in the PVA- NMP gel, implying that the aggregation of PVA chains is much easier in the poor solvent, EG, than in the good solvent, NMP. The structural change with aging time in the PVA-EG gel is very remarkable because of the significant syneresis, indicating that the opaque PVA-EG gel with higher crystallinity has a comparatively heteroge- neous and unstable network structure than the PVA-NMP gel does. q 1998 John Wiley &

In this work, the structure and physical properties of polyvinyl chloride (PVC) gels prepared from the solutions of bromobenzene (BrBz) and dioxane (DOA) under different gelation conditions are studied. The average size of the junction point for PVC gels in the initial gelation state are the combination of ca. two to three chains in width and ca. six to eight syndiotactic sequences in length to form a fibril-like network structure, irrespective of the species of solvents used, the molecular weight and the concentration of the polymer. Because the size of the junction point/microcrystal is too small, the results of wide angle X-ray diffraction (WAXD) shows only a broad intensity peak, implying that the crystallinity is very low for PVC gels. However, the X-ray intensity peak of amorphous scattering in PVC/DOA gel is sharper than that in PVA/BrBz gel, indicating that PVC/DOA gel has a thicker network structure due to a larger degree of polymer aggregation. The morphology of the gel is investigated from the observation of dried gel prepared from the freeze-drying method using electron microscopy. The results show that the gel morphology consists of a fibril-like structure and the mesh size of the network decreases with increasing polymer concentration. The difference in physical properties, such as the modulus of gels, may be considered to be mainly due to the aggregation degree of amorphous chains related to the solvent type, the concentration and molecular weight of polymer.

The conformational structure and the interchain aggregation behavior of a semirigid conjugated polymer bearing a decyl side chain, poly(2,3-diphenyl-5-decyl-1,4-phenylenevinylene) (DP10-PPV), in solutions with chloroform and toluene have been investigated by means of small-angle neutron scattering (SANS), static light scattering (SLS) and dynamic light scattering (DLS). The radius of gyration, persistence length, and the second virial coefficient of the polymer in dilute solution as determined by SLS were higher in chloroform than in toluene; consequently, the polymer assumed a more extended wormlike chain conformation in the former. The difference in the strength of interaction in the two solvents gave rise to contrasting aggregation behavior of the polymer in the semidilute regime. While only a minor fraction of the polymer underwent segmental association in chloroform, a considerable fraction of it formed clusters (microgels) with several micrometers in size in toluene. These clusters were further found to consist of sheetlike nanodomains. Compared with the DP-PPV bearing a shorter hexyl side chain, DP6-PPV, the aggregates of DP10-PPV in toluene were weaker as they could be easily disrupted by moderate heating. This was attributed to a lack of strong pi-pi interaction between the DP10-PPV segments due to the greater steric hindrance imposed by the longer decyl side chains.

Segments of conjugated polymers display the propensity to aggregate in solutions with common organic solvents. Here we revealed that the segmental aggregation of a conjugated polymer, poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl), (PF2/6), in toluene was stabilized by the polymer-solvent complex formation through pi-pi stacking induction of solvent molecules and polymer segments. In this case, a portion of the solvent was trapped inside the aggregate domains upon bringing the system to the subambient temperatures. The residence time of these associated solvent molecules became long enough to yield a separate upfield-shifted NMR resonance. The line-shape of this resonance revealed alignment of the polymer segments in the aggregates. A portion of the solvent was frozen in the compact structure due to the formation of strong polymer-solvent complex.