Colloids and Surfaces A: Physicochem. Eng. Aspects 343 (2009) 96–103 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Structure of poly (sodium 4-styrenesulfonate) (PSS) in electrolyte solutions: Theoretical modeling and measurements Z. Adamczyk ∗ , B. Jachimska, T. Jasi ´ nski, P. Warszy ´ nski, M. Wasilewska Institute of Catalysis and Surface Chemistry Polish Academy of Sciences, Niezapominajek 8, 30-239 Cracow, Poland article info Article history: Received 30 September 2008 Received in revised form 5 January 2009 Accepted 30 January 2009 Available online 5 April 2009 Keywords: Polyelectrolyte Viscosity Electrophoretic mobility Conformation of polyelectrolyte abstract In this work, the structure of poly (sodium 4-styrenesulfonate) (PSS) molecules in electrolyte solutions obtained from theoretical simulations was compared with experimental data derived from dynamic light scattering (PCS), electrophoretic and dynamic viscosity measurements. Simulations and experiments were carried out for polymer having molecular weight of 15.8 kD and for various ionic strength of the sup- porting electrolyte (NaCl). It was predicted from molecular dynamic simulations that for the entire range of electrolyte concentration studied (I = 10 -3 to 0.15 M) the molecule behaved as a flexible rod. Its effective length L ef varied from 12.5 to 8.5nm, which corresponds to 0.79–0.56 of the contour length L ext = 16 nm predicted for fully extended polymer chain. Thus, for electrolyte concentration of 0.15M, a significant folding of the molecule was predicted, whose shape resembled a semi circle (torus). These predictions were compared with PCS measurements of the diffusion coefficient of the molecule, which allowed one to calculate its hydrodynamic radius R H . It was found that R H varied between 3.1 for I =5 × 10 -3 M and 4 nm for I = 0.15 M. These R H values were in a good agreement with theoretical predictions stemming from Brenner’s theory, approximating the true particle shape by prolate spheroids, bent to various forms. Using these R H values and electrophoretic mobility data derived from microelectrophoresis, the average number of uncompensated (free) charges on the PSS molecule and the effective ionization degree were calculated. The number of free charges was determined to be 14–16 (decreasing slightly with ionic strength), which gives the ionization degree of 18–20%, which was comparable with theoretical predictions. Additional shape information was derived from the dynamic viscosity measurements of dilute PSS solutions using a capillary viscometer. The intrinsic viscosity derived from these measurements varied between 28.3 and 8 for the ionic strength 10 -3 to 0.15M. It was shown, after introducing the correction for hydration, that the experimental results were accounted well by the Brenner’s viscosity theory for slender particle sus- pensions. The effective lengths derived from viscosity measurements using this theory was comparable with values predicted from the molecular dynamic simulations. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Polyelectrolytes or polyions are molecules composed of a large number of covalently linked ionizable subunits. They are abundant in nature and essential for biological systems, just to mention DNA. Polyelectrolytes are often used in pharmaceutical, cosmetic and food industries, in ternary oil recovery, papermaking, for regulating rheological properties of suspensions. Another important field of polyelectrolyte applications is preparing multilayer films on solid substrates of a desired com- position and functionality [1–4], which is often realized by layer-by-layer (LbL) deposition of anionic and cationic polyelec- trolytes. Such films can be used as convenient supports for proteins ∗ Corresponding author. E-mail address: ncjachim@cyf-kr.edu.pl (Z. Adamczyk). and nanoparticles, which can be easily embedded into the poly- meric layer. A controlled formation of such polymeric films requires a throughout knowledge of the structure of macromolecules, their shape and charge in relation to its molecular weight, ionic strength and pH of solutions. One of the efficient ways of learning about structural aspects of polyelectolytes is the rheological measurements, which have been performed extensively over the decades [5–8]. However, because of the variety of parameters influencing polyelectrolyte viscosity, these results are often misinterpreted using for example, the scaling theories of de Genes et al. [9], applicable for high molecular weight polyelectrolytes in solutions with no added salt only. A better description of viscosity of polyelectrolytes in real solu- tions can be attained using the electrostatic wormlike chain theory developed by Odijk [10] and Skolnick and Fixman [11], known as the Odjik–Skolnick–Fixman (OSF) theory. This approach was based on the persistence length L p concept, whose electrostatic contribution 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.01.035