A bit of historyThe key role of surfaces for many material properties as well as for many biological processes has been recognized now. Therefore, new strategies aim at the tailoring of the material's surface only -or of a thin surface layer, respectively -, while preserving the bulk properties of the underlying support. Particular emphasis has been given to the surface modification by polymers, in an attempt to extend the known versatility of polymer bulk materials to ultrathin films and coatings, and to prepare bulk-surface composite materials. The self-organization of polymers has been increasingly explored for the preparation of well-defined surfaces and interfaces in recent years, extending the use of the established methods of low molar mass compounds (for comparative reviews, see ref. 1-3)). With such techniques, polymer films are formed spontaneously on substrates, due to balanced interactions between substrate, polymer (or its precursor) and medium. Typically, very thin, often monomolecular layers are produced. Repetitive deposition steps provide a precise control over the total thickness of the coatings, in the range from a few angstroms up to the micrometer range. Moreover, the step-by-step procedures allow for a fine structuring in the third dimension. In addition to the preparation of uniform and homogeneous coatings, gratings, gradients or steps of defined height in molecular dimensions can be easily constructed.The most recent of the self-organization techniques is the alternating physisorption of oppositely charged polyelectrolytes, the so-called "layer-by-layer" method or "electrostatic self-assembly" (ESA) [3][4][5][6][7][8][9][10] . Although some early, singular studies of self-assembly by alternating adsorption of oppositely charged polyions are reported [11][12][13] , a practical method for ESA was developed Feature Article: The article presents the state-of-the-art of alternating physisorption of oppositely charged polyelectrolytes, the so-called "layer-by-layer" method or "electrostatic self-assembly" (ESA), for the preparation of thin polymer coatings. In comparison to other, more established self-organization techniques, this recent method is distinguished by its simplicity, versatility, and speed. In particular, the tendency for self-healing is unique. Emphasis is given to the role of the molecular structure of the polyelectrolytes, and to the nature of the support. Also, various parameters for the preparation of multilayer films are highlighted, which are very important due to the kinetic control of the build-up process. The structure of the resulting coatings, their quality and stability, chemical reactions in the films, and potential applications are discussed.Macromol. Rapid Commun. 21, No. 7

Apolipoprotein AI (apoAI) is the principal protein constituent of high density lipoproteins and it plays a key role in human cholesterol homeostasis; however, the structure of apoAI is not clearly understood. To test the hypothesis that apoAI is organized into domains, three deletion mutants of human apoAI expressed in Escherichia coli were studied in solution and in reconstituted high density lipoprotein particles. Each mutant lacked one of three specific regions that together encompass almost the entire 243 aa sequence of native apoAI (apoAI ⌬44-126, apoAI ⌬139-170, and apoAI ⌬190-243). Circular dichroism spectroscopy showed that the ␣-helical content of lipid-free apoAI ⌬44-126 was 27% while the other mutants and native apoAI averaged 55 ؎ 2%, suggesting that the missing N-terminal portion contains most of the ␣-helical structure of lipid-free apoAI. ApoAI ⌬44-126 exhibited the largest increase in ␣-helix upon lipid binding (125% increase versus an average of 25% for the others), confirming the importance of the C-terminal half of apoAI in lipid binding. Denaturation studies showed that the N-terminal half of apoAI is primarily responsible for ␣-helix stability in the lipid-free state, whereas the C terminus is required for ␣-helix stability when lipid-bound. We conclude that the N-terminal half (aa 44-126) of apoAI is responsible for most of the ␣-helical structure and the marginal stability of lipid-free apoAI while the C terminus (aa 139-243) is less organized. The increase in ␣-helical content observed when native apoAI binds lipid results from the formation of ␣-helix primarily in the C-terminal half of the molecule.

The evolution of structural parameters characterizing the semicrystalline morphology of poly(ary1-ether-ether-ketone) (PEEK), and its blends with poly(ary1-ether-imide) (PEI), has been determined as a function of temperature by means of small-angle (SAXS) and wide-angle (WAXS) X-ray scattering studies, using synchrotron radiation. By comparing the behavior of initially amorphous samples continuously heated in the beam and samples heated and cooled below and above their annealing temperature, a complete picture is drawn of the morphological changes occurring during the cold crystallization and subsequent heating-cooling of PEEK. Upon crystallization of an amorphous sample, new lamellae are progressively inserted in the free space left between existing ones. No decrease of the lamellar thickness is evident during this insertion mechanism. When the polymer is cooled below its last annealing temperature T,, only reversible morphological changes occur, which can be explained quantitatively by the effects of thermal expansion, provided one takes into account the existence of strains in the crystalline lamellae created by their coupling to the noncrystalline interlamellar regions. When the polymer is heated above T,, "irreversible" changes occur in the average thickness of the lamellar crystals and of the interlamellar noncrystalline regions, in the perfection of the crystals, and in the crystalline density. Cold-crystallized samples are shown to comprise a single lamellar population which undergoes a rapid melting-recrystallization process above T,. The double melting behavior of coldcrystallized PEEK results from this melting-recrystallization mechanism. IntroductionThe morphology and properties of a semicrystalline polymer depend on its thermal history. Therefore, when studying the morphology, changes in the structure as a function of the crystallization conditions and subsequent thermal treatments must be considered. Moreover, any

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The PEEK glass transition ( -relaxation) is studied as a function of polymer semicrystalline morphology, characterized by small-angle X-ray scattering. An inverse relationship is observed between glass transition temperature and amorphous interlayer thickness. This is interpreted in terms of configurational entropy differences in the amorphous regions of semicrystalline samples, as compared to a bulk amorphous sample. The existence of so-called rigid amorphous fractions is shown to result partly from these entropy differences. The PEEK subglass transitions have also been studied. The highly-localized wagging of the polar bridges corresponding to the -relaxation is insensitive to ageing history and details of the semicrystalline morphology. The combination of the -wagging with phenyl flips results in the appearance of the 0-relaxation.