Toward exploiting the attractive mechanical properties of cellulose I nanoelements, a novel route is demonstrated, which combines enzymatic hydrolysis and mechanical shearing. Previously, an aggressive acid hydrolysis and sonication of cellulose I containing fibers was shown to lead to a network of weakly hydrogen-bonded rodlike cellulose elements typically with a low aspect ratio. On the other hand, high mechanical shearing resulted in longer and entangled nanoscale cellulose elements leading to stronger networks and gels. Nevertheless, a widespread use of the latter concept has been hindered because of lack of feasible methods of preparation, suggesting a combination of mild hydrolysis and shearing to disintegrate cellulose I containing fibers into high aspect ratio cellulose I nanoscale elements. In this work, mild enzymatic hydrolysis has been introduced and combined with mechanical shearing and a high-pressure homogenization, leading to a controlled fibrillation down to nanoscale and a network of long and highly entangled cellulose I elements. The resulting strong aqueous gels exhibit more than 5 orders of magnitude tunable storage modulus G' upon changing the concentration. Cryotransmission electron microscopy, atomic force microscopy, and cross-polarization/magic-angle spinning (CP/MAS) 13C NMR suggest that the cellulose I structural elements obtained are dominated by two fractions, one with lateral dimension of 5-6 nm and one with lateral dimensions of about 10-20 nm. The thicker diameter regions may act as the junction zones for the networks. The resulting material will herein be referred to as MFC (microfibrillated cellulose). Dynamical rheology showed that the aqueous suspensions behaved as gels in the whole investigated concentration range 0.125-5.9% w/w, G' ranging from 1.5 Pa to 105 Pa. The maximum G' was high, about 2 orders of magnitude larger than typically observed for the corresponding nonentangled low aspect ratio cellulose I gels, and G' scales with concentration with the power of approximately three. The described preparation method of MFC allows control over the final properties that opens novel applications in materials science, for example, as reinforcement in composites and as templates for surface modification.

Ruokolainen, J.; M"kinen, R.; Torkkeli, M.; Makela, T.; Serimaa, R.; ten Brinke, G.; Ikkala, O.; Makinen, R

Although remarkable success has been achieved to mimic the mechanically excellent structure of nacre in laboratory-scale models, it remains difficult to foresee mainstream applications due to time-consuming sequential depositions or energy-intensive processes. Here, we introduce a surprisingly simple and rapid methodology for large-area, lightweight, and thick nacre-mimetic films and laminates with superior material properties. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. They are forced to rapidly self-assemble into aligned nacre-mimetic films via paper-making, doctor-blading or simple painting, giving rise to strong and thick films with tensile modulus of 45 GPa and strength of 250 MPa, that is, partly exceeding nacre. The concepts are environmentally friendly, energy-efficient, and economic and are ready for scale-up via continuous roll-to-roll processes. Excellent gas barrier properties, optical translucency, and extraordinary shape-persistent fire-resistance are demonstrated. We foresee advanced large-scale biomimetic materials, relevant for lightweight sustainable construction and energy-efficient transportation.

We show that polymeric materials characterized by two length scales are obtained if diblock copolymers are mixed with amphiphilic selective solvents, leading to self-organization which combines the "block copolymer length scale" with a much shorter "nanoscale". In this work, the amphiphilic compound is 3-n-pentadecylphenol (PDP) which is hydrogen-bonded to the pyridine group of polystyreneblock-poly(4-vinylpyridine), i.e., PS-b-P4VP. The molecular architecture resembles comb-coil diblock copolymers A-block-(B-graft-C) but is obtained using the supramolecular assembly route. The structures were determined with a combination of transmission electron microscopy and small-angle X-ray scattering. On the block copolymer scale (300 Å range), the PS blocks are microphase-separated from the P4VP-(PDP) x blocks, where x denotes the ratio between the number of phenol and pyridine groups. For PS-b-P4VP block copolymers having a spherical morphology and P4VP as the minority component, the structure of PS-b-P4VP(PDP)x changes from spherical to hexagonal and further to lamellar as a function of the amount of PDP added. For all comb-coil diblock copolymer morphologies, the P4VP(PDP)x domains are further "nanophase-separated" into lamellar structures due to microphase separation of the comb copolymer-like complex between P4VP and PDP. The morphology diagram is presented for stoichiometric conditions (x ) 1), using a range of different PS-b-P4VP block copolymers.

Binary nanoparticle superlattices are periodic nanostructures with lattice constants much shorter than the wavelength of light and could be used to prepare multifunctional metamaterials. Such superlattices are typically made from synthetic nanoparticles, and although biohybrid structures have been developed, incorporating biological building blocks into binary nanoparticle superlattices remains challenging. Protein-based nanocages provide a complex yet monodisperse and geometrically well-defined hollow cage that can be used to encapsulate different materials. Such protein cages have been used to program the self-assembly of encapsulated materials to form free-standing crystals and superlattices at interfaces or in solution. Here, we show that electrostatically patchy protein cages--cowpea chlorotic mottle virus and ferritin cages--can be used to direct the self-assembly of three-dimensional binary superlattices. The negatively charged cages can encapsulate RNA or superparamagnetic iron oxide nanoparticles, and the superlattices are formed through tunable electrostatic interactions with positively charged gold nanoparticles. Gold nanoparticles and viruses form an AB(8)(fcc) crystal structure that is not isostructural with any known atomic or molecular crystal structure and has previously been observed only with large colloidal polymer particles. Gold nanoparticles and empty or nanoparticle-loaded ferritin cages form an interpenetrating simple cubic AB structure (isostructural with CsCl). We also show that these magnetic assemblies provide contrast enhancement in magnetic resonance imaging.

Properly selected hydrogen bonding suffices to induce mesomorphic structures in mixtures of flexible polymers and nonmesogenic surfactants. For poly(4-vinylpyridine)-3-pentadecylphenol (P4VP-(PDP)x) complexes, the long period of the lamellar structure decreases as x -1 (x is the number of PDP molecules per P4VP repeat unit) in complete contrast to similar polyelectrolyte systems. Upon cooling from 80 °C to the room temperature, the long period gradually increases and levels off at around 30 °C at a value which is approximately 4 Å above the starting value. After an induction time, a structural transformation occurs in the highly complexed samples, due to the crystallization of the alkyl side chains. It is accompanied by a sudden decrease in the long period of approximately 5 Å. However, the structure is not stable and after an additional induction time both structures are present in the samples. Arguments to explain most of the observed phenomena will be given.

tetraoctylammonium carboxylate in dry THF were added at once. A color change from orange to light yellow could be observed and the solution started to turn black due to colloid formation. After 4 h the solvent was removed in vacuo [10]. [4] It is not straightforward to assess or to compare the relative reducing power of such different reductants as H 2 , NaBH 4 , [Et 3 BH] ± [R 4 N] + , hydrazine or alcohols used in metal colloid syntheses [1]. [5] J. S. Bradley in Clusters and Colloids: From Theory to Applications (Ed.: G. Schmid), VCH, Weinheim 1994, p. 459. [6] In our electrochemical method for the formation of stabilized metal colloids, current density plays a certain role [2j], but other parameters such as electrode distance, temperature and solvent polarity are more important [M. T. Reetz, M. Winter, unpublished]. [7] The variation of alcohols as reductants of certain transition metal salts leads to metal colloids of different sizes, although the range is rather small. Moreover, opposite trends are observed, depending upon the nature of the metal: a) G. W. Busser, J. G. von Ommen, J. A. Lercher in [8]The reduction of metal salts in micelles allows for an elegant way to control particle size in many cases: a) M.

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