Ion conductivities of layer-by-layer (LBL) assemblies of solid thin film polyelectrolyte systems involving poly (ethylene oxide) (PEO) and poly(acrylic acid) (PAA) were found to be a strong function of the number of bilayer stacks, n, with conductivities approaching 10(-7) S/cm for n < 10, compared to 10(-9) Sian for n >= 10 and 10(-10) S/cm for bulk PEO. Increased ion conductivity for low LBL stack numbers (n<10) originated to part from an effective suppression of the PEO crystallization via PEO/PAA blending, which could be inferred from local glass transition temperature measurements involving shear modulation force microscopy. Another phenomenon responsible for high conductivity in thin films was found in the in-plane phase heterogeneity of PEO and PAA. Increased ion conductivity for larger LBL stacks (n >= 10) were attributed to low concentration autoblending caused by PEO-PAA hydrogen bonding, and an average layer thickness of noticeably less than 100 nm. The effect of interfacial constraints was evident in the degree of intermixing, addressed by a thin film extended Fox blend analysis, in the glass and melting transitions of PEO and PAA pure film components. While the glass transition value of PAA decreased by 55% to 46 degrees C for an 8 nm film, the melting transition for PEO decreased by 15% to 64 degrees C caused by surface tension effects. (C) 2011 Elsevier B.V. All rights reserved.