A steep upturn at low angles dominates the small-angle neutron scattering profile of low ionic strength polyelectrolyte solutions. This behavior is demonstrated for poly(N-methyl-2-vinylpyridinium chloride) in D 2O by measurements that are extended to low angles not typical of most studies. This behavior is consistent with static and dynamic light scattering measurements performed on the same solutions. Specifically, the upturn at low q and the slow diffusive mode in dynamic light scattering indicate the presence of supramolecular structures, which we interpret as large domains of increased polymer concentration. In these same solutions, a shorter wavelength correlation is evident from the presence of a maximum at finite q in the small-angle scattering experiment. Fluctuations on a short wavelength are also apparent from the existence of the fast mode in the dynamic light scattering. The maximum is interpreted as reflecting a characteristic dimension defined by order within domains, while the fast mode results from electrodynamic coupling of fast moving counterions and portions of chains.
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 intensity [I(q)] with the bare polymer charge density, Γ. Light scattering measurements of the radius of gyration Rg,d of the domains indicate that their size becomes smaller for divalent counterions and with a reduction of Γ. We observe that the “fractal” dimension of the domains measured from the low-angle scaling of I(q) depends on the chemical structure of the polyelectrolyte. Zero average contrast (ZAC) neutron scattering measurements show that the radius of gyration Rg,c of individual polyelectrolyte chains is also reduced for divalent counterions, suggesting that chain rigidity is strongly influenced by Γ*. Charge valency effects on relaxation times are investigated by dynamic light scattering. As usual, two diffusive modes are observed in the light intensity autocorrelation function, G(τ). The “fast” mode becomes slower and the “slow” mode becomes faster for the divalent counterion (Mg2+), relative to the monovalent counterion (Na+). Counterion valence has a large influence on the structure and dynamics of highly charged polyelectrolyte solutions through its influence on Γ*.
The phase separation kinetics of ultrathin deuterated poly(styrene)/poly(butadiene) polymer blend films spun cast onto striped self-assembled monolayer (SAM) substrates is studied by atomic force microscopy (AFM). Fourier transform analysis of the AFM topographic data at various stages of the film pattern development reveals the presence of quantized surface deformation modes. These modes are excited by the phase separation process when the scale of phase separation becomes commensurate with the period of the striped surface pattern. Thus, higher frequency modes become excited at early stages of phase separation, and these excitations decay with time as the phase separation pattern further coarsens. The film ultimately self-organizes into a periodic structure in which the fundamental mode has the largest amplitude. The influence of film thickness on the film morphology in this late stage is also investigated. A decrease in the film thickness leads to surface patterns that match those of the SAM substrates with increasing resolution. However, these film patterns break up into droplet arrays along the SAM stripes if the films are made too thin. This phenomenon is attributed to a capillary wave instability.
Recent theoretical and experimental studies of polyelectrolyte solutions have suggested that hydrophobic interactions between the chain backbone and the solvent lead to some of the essential observations of polyelectrolyte solution scattering. In the current paper we present small angle neutron scattering data on a polyelectrolyte, poly(N-methyl-2-vinylpyridinium chloride) dissolved in ethylene glycol where the hydrophobic effect is not present. This system shows the same general pattern, a peak at finite wavevector and steep upturn at low wavevector, as for those having hydrophobic interactions so that the influences of poor backbone solvation appear to be unessential for explaining the characteristics of polyelectrolyte scattering data. We demonstrate that in the scattering from polyelectrolytes after the addition of salt, the unusual peak and steep upturn are suppressed and the scattering parallels scattering from the neutral chains.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.