Polyelectrolyte Multilayers Containing Triblock Copolymers of Different Charge Ratio

Multilayers formed by the sodium salt of poly(4-styrenesulfonate), PSS, and triblock copolymers of the form PDMAEMA−PCL−PDMAEMA (PDMAEMA corresponding to poly[2-(N,N-dimethylamino)ethyl methacrylate), and PCL to poly(ε-caprolactone) have been built by layer-by-layer self-assembly from the aqueous polyelectrolyte solutions. Two types of block copolymers have been used which differ on the type of the amino groups, either hydrochloride or quaternized. This leads to changes in the charge density of the chains for the same content of amino groups. The growth of the multilayers has been followed using dissipative quartz crystal microbalance and ellipsometry techniques. The results show that, independently of the conditions used in the assembling, the film thickness grows linearly with the number of layers. The comparison of the thickness values obtained from D-QCM and ellipsometry has allowed us to calculate the water content of the polymer film. The analysis of the D-QCM data also provides the shear modulus, whose values are typical of a rubber-like polymer system. The analysis of the mass adsorbed calculated by the ellipsometric measurements indicated that the nature of the charge compensation mechanism is extrinsic for all the studied systems, although the degree of extrinsic compensation is strongly dependent on the copolymer used and the concentration in solution. Finally, it was found that the adsorption kinetic of the layers is bimodal for all the films built. Even though the characteristic adsorption times depend on the specific copolymer used, no dependence on the number of layers has been found for a given multilayer.This work was supported in part by MICINN under grants FIS2009-14008-C02-01, by CAM under grant INTERFASES S05-MAT-227, and by ESA under grant MAPAO-00-052. E.G. was supported by a FPU fellowship from MICINN. The authors are grateful to the UIRC of the CAI of Spectroscopy of Complutense University for the use of the ellipsometer