Stable polydiacetylene/ZnO nanocomposites with two-steps reversible and irreversible thermochromism: the influence of strong surface anchoring

The influence of pH value on gold nanoparticle production in the presence of Pluronic stabilizers is systematically investigated. The reactions are studied as a function of pH and at fixed concentrations of the two reactants, HAuCl(4) and P123 block copolymer. Results indicate that the reaction pathway during the nanoparticle formation can be controlled by varying pH. The nanoparticles synthesized at pH=11.12 have an average diameter of 9.6 nm with a narrow size distribution, and the Pluronics are adsorbed on individual gold particle surfaces to form core-shell structures via hydrophobic interactions. The present work provides an economic way to improve the dispersion and stabilization of gold nanoparticles and throws further light on the understanding of gold nanoparticle production using block copolymers.     

Conformational change,intrachain aggregation and photophysical properties of regioregular poly(3‐octylthiophene) in alkanes

This study explores the role of segmental solubility of regioregular poly(3‐octylthiophene) (rr‐P3OT) on chain organization and its photophysical properties. In good solvent chlorobenzene (CRB), rr‐P3OT chain adopts an extended conformation, allowing long conjugation length of π‐electrons. Cyclohexane is a good solvent for octyl side chain but a poor solvent for the thiophene backbone. The selective segmental interactions of rr‐P3OT with this solvent induce conformational change of the polymer. Addition of cyclohexane into the CRB solution leads to chain coiling, which in turn causes significant decrease of the conjugation length. Absorption and photoluminescence spectra of the rr‐P3OT in cyclohexane exhibit a blueshift of about 16 nm compared to those of the CRB solution. The change of chain conformation is also detectable by monitoring the variation of quantum yield upon increasing cyclohexane ratio. The quantum yield drops from 0.17 ± 0.01 to 0.11 ± 0.01 when the extended rr‐P3OT chain transforms into coiled conformation. Hexane is a nonsolvent for rr‐P3OT due to its relatively low solubility parameter. The addition of hexane into rr‐P3OT solution in cyclohexane forces dense packing of thiophene rings within the coiled chain. An intrachain aggregation occurs in this system, leading to the appearance of three distinct redshift peaks in absorption spectra and the drastic drop of quantum yield. Correlation between the growth of redshift peaks and the decrease of quantum yield is clearly observed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1288–1297     

Effects of chain conformation and chain length on degree of aggregation in assembled particles of conjugated polymer in solvents–nonsolvent: A spectroscopic study

This article explores photophysical properties and aggregation behaviors of conjugated polymer, poly[2‐methoxy, 5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene](MEH?PPV), in various solvent–nonsolvent systems by utilizing UV/vis absorption and photoluminescence (PL) spectroscopy. The isolated chains of MEH‐PPV dispersed in solvents including dichloromethane, chloroform, and tetrahydrofuran adopt either extended or collapsed conformations depending on local polymer–solvent interactions. Aggregation of the MEH‐PPV in these solvents is induced by addition of a poor solvent, cyclohexane. The formation of aggregates is indicated by the appearance of distinct red‐shift peaks in the absorption and PL spectra. The degree of aggregation in each solvent–nonsolvent system is compared by means of absorbance and PL intensity of the aggregate bands. In early stage of the aggregation, the amount of aggregates in system is controlled by the solubility of polymer. When the polymer chains are forced to densely pack within assembled particles by increasing ratio of cyclohexane to 99 v/v %, the conformation of individual chain plays important role. We have found that the extended chains facilitate the aggregation in the assembled particles. Increasing chain length of polymer promotes the aggregation in early stage and densely packed particles. Size distribution of the assembled particles is also found to depend on the choice of solvent. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 894–904, 2010