Showing papers by "Kenneth R. Shull published in 1992"

Mean-field theory of block copolymers: bulk melts, surfaces, and thin films

Abstract: A quantitative mean-field treatment of inhomogeneous polymer systems is applied to bulk diblock copolymer melts, as well as to surfaces and thin films of these melts. Equations for a set of polymer chain probability distribution functions are solved numerically in a manner that requires no further approximation to the fundamental mean-field treatment. Results for symetric block copolymer meld are in quantitative agreement with previous predictions which are valid only near the critical point or in the strong segregation regime

Homopolymer distributions in lamellar copolymer/homopolymer blends

Abstract: A quantitative mean-field treatment, based on the representation of polymer chain statistics by probability distribution functions, is applied to lamellar blends of an AB diblock copolymer with an A homopolymer. We work in the strong segregation limit, where the interface between A and B microdomains is narrow and the A homopolymer segregates exclusively to the A domain. Copolymer blocks are modeled as end-adsorbed «brushes» which are anchored to opposing sides of a microdomain. Numerical solution of the mean-field equations can be used to determine homopolymer and copolymer profiles for all blend compositions

Interfacial segment density profiles of end-anchored polymers in a melt

Abstract: The segment density profile of end-functionalized deuterated polystyrene (EF-dPS) polymers anchored in a surrounding melt of hydrogenated polystyrene (hPS) to an interface with silicon was determined by neutron reflectometry. Thin films of mixtures with various volume fractions of the EF-dPS and hPS were spun cast from toluene solutions onto the silicon. These films as cast were uniform as a function of depth. After heating to 184 C for approximately 1 day to allow equilibrium segregation to be achieved in the films, neutron reflection measurements were performed. The EF-dPS segment density profiles ({phi})z needed to fit the reflectivity data showed a high {phi} at the silicon interface which increased to a maximum approximately 10 nm away from the interface and then fell monotonically to the bulk segment density [illegible]. The interface excess determined by integration of these profiles was in excellent agreement with that directly determined by forward recoil spectrometry on the same samples. The form of the profiles is consistent with the predictions of a self-consistent mean field theory if, in addition to a large attachment free energy of the end group to the silicon, there is a weak preferential attraction of the silicon for the more polarizable hPS segmentsmore » relative to the less polarizable dPS segments.« less

Morphologies of discontinuous gold films on amorphous polymer substrates

Abstract: Transmission electron microscopy was used to analyze the effects of annealing treatments on the morphologies of discontinuous gold films evaporated onto polystyrene or poly(2‐vinylpyridine) substrates. For polystyrene substrates the average size of discrete gold particles increases significantly during a long‐term annealing treatment at 179 °C. The size distribution is well approximated by a log normal distribution function, consistent with a coalescence mechanism for particle growth. The fluid character of the polymer substrates at the annealing temperature of interest allows us to control this coalescence rate, thereby providing a unique method for controlling the microstructure of discontinuous metal films. Cross‐sectional transmission electron microscopy showed that the coalescence rate for gold particles in a poly(2‐vinylpyridine) matrix is much less than the coalescence rate for gold particles in a polystyrene matrix, indicating that polymer/metal interactions play an important role in the determina...

Vanishing interfacial tension in an immiscible polymer blend

Abstract: The properties of the interface between polystyrene (PS) and a random copolymer of polystyrene and poly(parahydroxystyrene) (PPHS) were modified by addition of a diblock copolymer of deuterated polystyrene (dPS) and poly(2‐vinylpyridine) (PVP). Segregation of diblock copolymer chains to the interface between the immiscible blend components is driven by the compatibility of the dPS block with the PS phase and by a strong favorable interaction between the PVP block and the PPHS units of the random copolymer. Forward recoil spectrometry was used to measure the equilibrium excess of copolymer chains at the interface as a function of the copolymer volume fraction in the bulk PS phase. A dramatic increase in the interfacial adsorption is identified with the formation of emulsified ‘‘droplet’’ phases which appear when the interfacial free energy between the immiscible blends becomes vanishingly small. Dynamic secondary‐ion mass spectrometry was used to characterize these emulsified phases, and to verify our pict...