Spinodal decomposition of two homopolymers with their block copolymer: A comparison of models

The dynamics of phase separation in the presence of a diblock copolymer have been studied using ternary and quaternary models of spinodal decomposition. The ternary model treats the block copolymer as a third component that is compatible with each of the mutually incompatible homopolymers. The quaternary model treats the block copolymer as a pair of specially constrained homopolymers. Both models predict core-shell morphologies with the copolymer concentrated at the interface. Both models predict larger domain sizes and less sharp phase boundaries in the early stages of spinodal decomposition. In the late stages, domain sizes are largest for the system of homopolymers without copolymer and smallest when a system containing copolymer is modeled as a quaternary blend. The scaling exponent observed for the quaternary model was s = 0.25 ± 0.02 compared to s ≅ 0.3 for the homopolymers without copolymer and for the ternary model. The quaternary model predicts internal phase separation within a pure diblock copolymer, whenever the corresponding homopolymers are sufficiently incompatible. © 1996 John Wiley & Sons, Inc.     

Effects of bisphenol monomer structure on the surface morphology and reverse osmosis (RO) performance of thin-film-composite membranes composed of polyphenyl esters

Four reverse osmosis (RO) composite membranes, in which thin-film active layers were polyphenyl esters, were prepared by interfacial polymerization of a series of bisphenol monomers and trimesoyl chloride (TMC). An atomic force microscope (AFM) was used to investigate the surface morphology and RO experiments were carried out to measure the rejection and flux characteristics of the membranes. Correlations between the inherent chemical nature of bisphenols possessing structural variations in the middle of phenyl rings and the surface morphology/RO performance of the membranes were studied. Polarity of the connectors between two phenyl rings of bisphenols played an important role in determining the surface morphology and RO performance. Nonpolar bisphenol gave a morphology of uniform, distinct nodular corrugation and a superior RO rejection but a relatively low flux, while the polar one resulted in an irregular, ambiguous nodule structure and a high flux. The size of the bisphenol connectors was also found to be important; the smaller one was more favorable for the formation of membrane with better salt rejection, while the larger one contributed to higher flux. © 1996 John Wiley & Sons, Inc.     

On phase equilibria,interfacial tension and phase growth in ternary polymer blends

A gradient squared free energy functional of the Landau-Ginzburg type is combined with Flory-Huggins theory to calculate minimum domain sizes, concentration profiles and interfacial tensions in ternary polymer blends. The dynamic equations governing spinodal decomposition are linearized to show that the minimum size for growth is identical to the thermodynamic minimum on phase volume. It is shown that unseparated, third components are enriched at the interface, reduce interfacial tension, increase stability and increase the minimum domain sizes. Enrichment of the third component at the interface causes concentrations at the major components to lie outside their binodal limits at a distance from the interface. Although the effects are most pronounced when the third component is a compatibilizer, the general phenomena remain true even when the third component is relatively incompatible. Generalizations to blends of N components are presented, and a robust method for calculating multicomponent phase diagrams is described.     

Photoisomerization and Emission Properties of trans‐ and cis‐Poly(dimethylsilylenephenylenevinylene)s

The photoirradiation of trans‐ and cis‐poly(dimethylsilylenephenylenevinylene)s gave cis‐rich mixtures at equilibrium states. The degree of the photoisomerization could be exactly evaluated by comparing the UV spectra of the photoirradiated solutions with those of the trans and cis polymers. The geometric configuration of the trans and cis polymers was thermally stable and hardly changed even though they were heated. The trans and cis polymers exhibited different emission properties; e.g., trans polymer: λ_max = 400 nm, quantum yield = 3.4×10^–3; cis polymer: λ_max = 380 nm, quantum yield = 1.5×10^–3.     

A New Photoluminescent Conjugated Poly(1‐hexyl‐3,4‐dimethyl‐2,5‐pyrrolylene): Synthesis,Properties and Characterization

Oxidative coupling reaction of 1‐hexyl–3,4‐dimethylpyrrole affords a conjugated conducting poly(1‐hexyl‐3,4‐dimethyl‐2,5‐pyrrolylene) (PHDP), which is completely soluble in common organic solvents. The luminescence of PHDP is comparable to that of poly(N‐vinylcarbazole) (PVK), which has been widely used in electroluminescence devices. The quantum efficiency of PHDP is 2.5 times higher than that of PVK. A rationalization is presented relating the conductivity of PHDP to its polymer structure.     

High-Performance Near-Infrared Chlorinated Rylenecarboximide Fluorophores via Consecutive C−N and C−C Bond Formation

A new class of near-infrared (NIR) fluorophores, PAI , is obtained by consecutive C−N/C−C bond formation between diphenylamines and 9,10-dibromoperylenecarboximide. Owing to the rigid structure, extended π-conjugation and pronounced push-pull substitution, these fluorophores show emission maxima up to 804 nm and large Stokes shifts. The extraordinarily high fluorescence quantum yields from 47 % to 70 % are attributed to chloro substitution in the bay positions of the perylene core. These characteristics, together with high photostability, qualify them as useful NIR emitters for applications as biomarkers and security inks.     

Benzotrithiophene-based Covalent Organic Framework Photocatalysts with Controlled Conjugation of Building Blocks for Charge Stabilization

Covalent organic frameworks have recently shown high potential for photocatalytic hydrogen production. However, their structure-property-activity relationship has not been sufficiently explored to identify a research direction for structural design. Herein, we report the design and synthesis of four benzotrithiophene (BTT)-based covalent organic frameworks (COFs) with different conjugations of building units, and their photocatalytic activity for hydrogen production. All four BTT-COFs had slipped parallel stacking patterns with high crystallinity and specific surface areas. The change in the degree of conjugation was found to rationally tune the rate of photocatalytic hydrogen evolution. Based on the experimental and calculation results, the tunable photocatalytic performance could be mainly attributed to the electron affinity and charge trapping of the electron accepting units. This study provides important insights for designing covalent organic frameworks for efficient photocatalysts.