Order and dynamics of poly(styrene-b-1,4-isoprene), P(S-b-I), diblock copolymersin nanometer thin layers with different isoprene volume fractions(fPI) and identical molecular weight ofthe styrene blocks are studied by a combination of grazing-incidencesmall-angle X-ray scattering (GISAXS), atomic force microscopy (AFM),and broadband dielectric spectroscopy (BDS). GISAXS and AFM revealrandomly oriented lamellar structures in the films and a parallelorientation at the top surface, respectively. Using BDS, three wellseparated relaxation processes are detected: (i and ii) the dynamicglass transitions (segmental mode) in the styrene and isoprene blocks,respectively, and (iii) the normal mode relaxation representing fluctuationsof the isoprene chain as a whole or parts of it. While the first two do not show any thickness dependence in their spectral positions,the latter becomes faster with decreasing sample thickness. This reflectsthe difference in the length-scale on which the molecular fluctuationstake place. [ABSTRACT FROM AUTHOR]