Dynamics and thermodynamics of diblock copolymers at polymer/polymer interfaces

The adsorption of an AB diblock copolymer surfactant to an A/B polymer/polymer interface was measured, where A is saturated polybutadiene with 90% 1,2 addition (sPB90), and B is saturated polybutadiene with 63% 1,2 addition. Thin trilayer films were constructed, consisting of first a layer of the homopolymer sPB90, followed by a layer of sPB63, and finally by a layer of a blend of sPB90 and deuterium labeled sPB90-sPB63 diblock copolymer. The films were annealed at ambient temperature before the concentration profiles of diblock copolymer through the films were measured using dynamic secondary-ion mass spectrometry.; The adsorption isotherm of the diblock copolymer at the polymer/polymer interface was measured by constructing films with different amounts of diblock copolymer and annealing them until equilibrated. The amount of surfactant adsorbed was then determined from the measured concentration profiles. These measurements were compared with the predictions of self-consistent field theory (SCFT). All necessary inputs for the theory were independently determined so that no adjustable parameters were required. The agreement between theory and experiment was good.; Dynamics of adsorption and desorption of the diblock copolymer to the interface were measured by annealing the films for periods of times ranging between 0.2 h and 108 h and by comparing the various transient concentration profiles produced. The diblock-copolymer transport was modeled as diffusion in an external field, generated from SCFT, and the diffusion coefficients were measured in independent experiments. This proposed field-theoretic diffusion model neglects the dynamics of molecular conformational change. Nevertheless, agreement between theory and experiment is good. The absence of slow conformational dynamics, and the absence of an energy barrier to adsorption means that adsorption and desorption are diffusion limited down to the length scale of the interfacial width.