Kenneth R. Shull

Theory of end‐adsorbed polymer brushes in polymeric matrices

A detailed self‐consistent field theory is used to calculate the properties of end‐adsorbed polymer chains, or polymer ‘‘brushes,’’ in equilibrium with a blend of adsorbing B polymer and nonadsorbing A polymer. The brush properties depend on χab, Na/Nb and β, where χab is the Flory interaction parameter characterizing the thermodynamic interaction between the A and B polymers, Na and Nb are the respective degrees of polymerization of the A and B polymers and kBTβ is the net attractive interaction between the adsorbing chain end and the surface. For χab=0, β≫1 and Na/Nb≫1 an asymptotic limit is reached where the brush properties are completely specified by z*/Rbg, where z* is the integrated surface excess of the adsorbing polymer and Rbg is its unperturbed radius of gyration. In this strong adsorption, dry brush regime the volume fraction of adsorbing polymer at the surface increases rapidly from 0.0 to 0.96 as z*/Rbg increases from 0.0 to 1.6. For z*/Rbg>1.6 the surface volume fraction of the adsorbing po...

Morphologies of discontinuous gold films on amorphous polymer substrates

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 179u2009°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

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...

Improved technique for cross-sectional imaging of thin polymer films by transmission electron microscopy

Abstract An improved method for obtaining cross-sectional images of thin polymer films by transmission electron microscopy is described. Two examples are described in order to demonstrate the simplicity and flexibility of the technique. In the first example, the structure of a highly ordered block copolymer on a solid surface is examined. In the second example, the behaviour of colloidal gold particles at the interface between immiscible polymers is considered.

NEUTRON-SCATTERING BY MULTIBLOCK COPOLYMERS OF STRUCTURE (A-B)(N)-A

Multiblock copolymers were prepared by anionic copolymerization of deuterated and classical styrene monomers. The use of bifunctional initiators gives copolymers with an odd number of sequences. Neutron scattering experiments were performed on these samples in order to check the existing theories which are extended in the first part to multiblock copolymers with an odd number of blocks. The agreement between theory and experiment is excellent and, surprisingly, the height of the maximum of the curves: scattered intensity versus scattering angle, does not depend on the number of blocks.