Multilayers formed by the sodium salt of poly(4-styrene sulfonate), PSS, and poly(diallyldimethylammonium) chloride, PDADMAC, have been built by electrostatic self-assembly from polyelectrolyte aqueous solutions of different ionic strengths. The growth of the multilayers has been followed using dissipative quartz crystal microbalance and ellipsometry. Neutron reflectometry and XPS data indicate that the PSS and PDADMAC layers interpenetrate leading to an almost homogeneous polymer film. The results show that on increasing [NaCl] the growing process changes from a linear to a non-linear regime. The comparison of the thickness values obtained from QCM and ellipsometry has allowed us to calculate the water content of the polymer film. The results agree with those obtained by neutron reflectometry. The analysis of the QCM data has provided values of the complex shear modulus, which are typical of a rubber-like polymer system. The analysis of the mass adsorbed calculated by the ellipsometry measurements indicated that the charge compensation mechanism changes from intrinsic at low ionic strengths to mainly extrinsic at high ionic strengths. Finally, it was found that the response of a polymer film to a change in [NaCl] is rather different for films grown at low or at high ionic strengths.

Trisiloxane surfactants also known as “superspreaders” are characterized by a critical wetting concentration (CWC) which has been determined by Svitova et al [T. Svitova, R.M. Hill, Y. Smirnova, A. Stuermer, G. Yakubov, Langmuir 14 (1998) 5023–5031]. CWC is a concentration above which a transition from partial wetting to complete wetting occurs at spreading over moderately hydrophobic surfaces, hence, the CWC is associated with the beginning of the superspreading. The latter shows that the knowledge of the CWCs is important for many wetting/spreading applications. We suggest a new method, which allows determining CWCs for a range of trisiloxanes using wetting behaviour of aqueous trisiloxane solutions on highly hydrophobic smooth Teflon AF coated silicon wafers. Using the new method the CWCs for trisiloxane surfactants, T n with a wide range in the number ( n = 4–9) of ethylene oxide units have been measured. The critical aggregation concentration (CAC) for trisiloxane surfactants has been measured using the surface tension methods. Additionally, spreading kinetics of all trisiloxane surfactants studied over moderately hydrophobic substrates has been investigated. It has been found that for all trisiloxanes studied the CWCs are several times higher than their corresponding CAC values. The CWCs for T 6 and T 8 trisiloxanes obtained according to our approach are in agreement with those measured by Svitova et al. [T. Svitova, R.M. Hill, Y. Smirnova, A. Stuermer, G. Yakubov, Langmuir 14 (1998) 5023–5031] for the case of complete wetting. It has been verified that indeed at CWCs estimated according to our approach trisiloxane surfactant solutions demonstrate superspreading behaviour on moderately hydrophobic surfaces with the exception of trisiloxane T 4 , which still shows only partial wetting. Thus, the CWC does not depend on the degree of hydrophobicity of substrates and could be considered as a distinct property of surfactants that characterize the highest limit of their spreading capability. Keywords Trisiloxane Spreading Critical wetting concentration