Ben ReynoldsGraduate Student, Ph.D. Programco-advised by Nitash Balsara and Clay Radke
University of Canterbury, 1999
Research Interest:
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Research Summary
In most binary polymer blends, phase separation of the constituent polymers is the equilibrium state and unfavorably affects the properties of the blend. The properties of the blend are determined not only by the polymers themselves but by the morphology and length-scale of the dispersion and by the properties of the interface. By adding interfacially active polymers such as diblock copolymers to the blend, the interfacial tension can be reduced and in some cases may be sufficiently lowered to allow the formation of a microemulsion or ordered structure. Understanding the dynamics of both the phase separated dispersions and the thermodynamically stable microemulsions, is largely a question of understanding the dynamics of the interfaces.
We use an A / A-B / B ternary polymer blend to study interfacial dynamics, where A is saturated polybutadiene with 63% 1,2 addition and B is saturated polybutadiene with 90% 1,2 addition. The equilibrium properties of the interface are investigated using 450 nm thick homopolymer trilayers (A | B | A), created by spincoating. The top layer is in fact a blend of homopolymer A and the diblock copolymer A-B, however after several days at room temperature the diblock copolymer has diffused throughout the trilayer and reached an equilibrium concentration profile. The diblock copolymer is labeled with deuterium so that the concentration profile through the film can be measured using dynamic secondary-ion mass spectroscopy. By making various films with different amounts of the diblock copolymer, we construct an adsorption isotherm for the system. The equilibrium behavior is found to be predicted very well using self-consistent field theory, where the c parameter and the statistical segment lengths are determined from small-angle neutron scattering experiments.
We are currently investigating the dynamic behavior of the diblock copolymers at the interface, specifically the rate of adsorption/desorption. The films were prepared in the manner described earlier, however rather than letting the films come to equilibrium the secondary-ion mass spectroscopy measurements were made a set amount of time after the sample was prepared, ranging from 12 minutes to 5 days. In this way the time dependence of the concentration profile is found.
