PDMS phase behavior

Phase Behavior of Short-Chain PDMS- -PEO Diblock Copolymers and Their Use as Templates in the Preparation of Lamellar Silicate Materials... 

Summary PDMS-6-PEO short-chain diblock copolymers were prepared via anionic ring-opening polymerization of cyclosiloxanes. Applying this method, various well-defined block copolymers with different compositions were synthesized and their phase behavior was investigated. The polymers predominantly showed lamellar phases in aqueous solutions. At small surfactant concentrations, vesicles were formed, as observed via cryogenic TEM. The aggregates of the diblock copolymers were used for the formation of lamellar thin films, applying the evaporation-induced self-assembly approach. 

Phase Behavior of Short-Chain PDMS-h-PEO Diblock Copolymers 821... 

As indicated by Figure 16, which shows the positions of the brine-oil interface for two PDM experiments as functions of t1, the oil phase grew in volume with time. This solubilization of brine into the oil contrasts with the behavior at lower salinities where the oil phase was consumed by the microemulsion. Based on equilibrium phase behavior, one can conclude that conversion of oil to a water-in-oil microemulsion was occurring above the brine interface. Also, as shown in Table IV, the position of the interface between brine and this oil-continuous phase varied as the square root of time, indicating no extensive convection in these samples. 

Polysiloxane-containing amphiphilic block copolymers have been prepared by different approaches. Coupling of an end-functionalized polydimethylsiloxane with a functionalized poly(ethylene oxide) led to the formation of PDMS- -PEO diblock copolymers. The sequential anionic ring-opening polymerization of tetramethyltetravinylcyclotetrasiloxane and hexamethylcyclotetrasiloxane resulted in the formation of a vinyl-substituted diblock copolymer, the vinyl groups of which could be modified by further reactions so as to import amphiphilic character. The phase behavior of short-chain PDMS-Z -PEO diblock copolymers revealed the preferred formation of lamellar phases by this type of amphiphile... 

YAN Yang, J., Wegner, G., and Koningsveld, R., Phase behavior of ethylene oxide-dimethylsiloxane PEO-PDMS-PEO triblock copolymers with water, Colloid Polym. ScL, 270, 1080, 1992. 

When the methacrylate monomer was pol)mierized within an already crosslinked PDMS phase, the resulting product displayed a co-continuous two-phase morphology and exhibited a leathery type behavior. 

Hu et al. [48] studied the addition of PS-h-PDMS diblock copolymer to the PS/PDMS blend. A maximum interfacial tension reduction of 82% was achieved at a critical concentration of 0.002% diblock added to the PDMS phase. At a fixed PS homopolymer molecular weight, the reduction in interfacial tension increases with increasing the molecular weight of PDMS homopolymer. Moreover, the degree of interfacial tension reduction was found to depend on the homopolymer the diblock is mixed with when the copolymer was mixed into the PS phase, the interfacial tension reduction was much less than that when the copolymer was blended into the PDMS phase. This behavior suggested that the polymer blend interface may act as a kinetic trap that limits the attainment of global equilibrium in these systems. 

As the aramid phase is less permeable compared with the PDMS phase, the continuous PDMS phase can be obtained in the copolymer containing a 0.43 volume fraction or more of PDMS. In the PASs with PDMS volume fractions ranging from 0.43 to 0.61, both the PDMS and aramid phases seem to exist in cocontinuous phases with lamellar structures that are also indicated by the modulus behaviors. On the other hand, in the PAS with 75 wt% of PDMS, the PDMS phase exists as the continuous phase, with the aramid phase present as discrete domains, judging from the dynamic thermomechanical results. 

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