Brett D. Ermi

Influence of counterion valency on the scattering properties of highly charged polyelectrolyte solutions

Light and neutron scattering measurements on highly charged polyelectrolyte solutions have recently provided firm evidence for the existence of “domain structures” containing many chains, even at rather low-polymer concentrations. In the present paper, we systematically investigate the influence of counterion charge valency Zc on the scattering properties of sulfonated polystyrene (PSS) solutions in water with monovalent and divalent counterions. This study is part of a larger effort to identify essential factors governing polyelectrolyte domain formation and the geometric properties of these transient structures. Neutron scattering measurements indicate that the interchain correlation length ξd within the domains becomes larger by a factor of 1.5–2 for divalent relative to monovalent counterions. This observation is consistent with the Manning model estimate of the change in effective polymer charge density Γ* with Zc and with previous observations linking ξd [from the peak position in the scattering int...

Formation and dissolution of phase‐separated structures in ultrathin blend films

ABSTRACT: The phase separation of ultrathin polymer blend films of deuterated poly-(styrene)/poly(vinylmethylether) leads to a variety of film morphologies, dependingon polymer composition. Phase-separation measurements are made at a constant tem-perature difference from the critical temperature, leading to a bicontinuous spinodaldecomposition pattern for near-critical blend compositions and to ‘‘mounds’’ and ‘‘holes’’for PVME-rich and dPS-rich off-critical mixtures, respectively. Reverse temperaturejumps of the phase-separated blend films into the one-phase region result in dissolutionof the undulating surface patterns, confirming the phase-separation origin of the filmpatterns. q 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 191–200, 1998 Keywords: ultrathin films; polymer blends; phase separation; atomic force microscopy INTRODUCTION than1 mm. 1 Moreover,thiseffectissubstratedepen-dent, shifting to higher temperatures with decreas-Polymer blends have been the focus of decades of ing film thickness on gold and to lower tempera-research owing to their technological and scien- tures on glass.