Sustainable Design of Structural and Functional Polymers for a Circular Economy.

To achieve a sustainable circular economy, polymer production must start transitioning to recycled and biobased feedstock and accomplish CO2 emission neutrality. This is not only true for structural polymers, such as in packaging or engineering applications, but also for functional polymers in liquid formulations, such as adhesives, lubricants, thickeners or dispersants. At their end of life, polymers must be either collected and recycled via a technical pathway, or be biodegradable if they are not collectable. Advances in polymer chemistry and applications, aided by computational material science, open the way to addressing these issues comprehensively by designing for recyclability and biodegradability. This Review explores how scientific progress, together with emerging regulatory frameworks, societal expectations and economic boundary conditions, paint pathways for the transformation towards a circular economy of polymers.

Hairy surfaces by cold drawing leading to dense lawns of high aspect ratio hairs.

The surfaces of many organisms are covered with hairs, which are essential for their survival in a complex environment. The generation of artificial hairy surfaces from polymer materials has proven to be challenging as it requires the generation of structures with very high aspect ratios (AR). We report on a technique for the fabrication of surfaces covered with dense layers of very high AR nanoscale polymer hairs. To this, templates having pores with diameters of several hundred nanometers are filled with a polymer melt by capillary action. The polymer is then allowed to cool and the template is mechanically removed. Depending on the conditions employed, the formed structures can be a simple replica of the pore, or the polymer is deformed very strongly by cold drawing to yield in long hairs, with hair densities significantly up to 6,6 × 108 hairs/cm2 at AR of much higher than 200. The mechanism of hair formation is attributed to a delicate balance between the adhesion forces of the polymer in the pore and the yield force acting on it during mechanically demolding. We demonstrate how with very little effort and within a timescale of seconds unique topographies can be obtained, which can dramatically tailor the wetting properties of common polymers.

Accelerated discovery of 3D printing materials using data-driven multiobjective optimization.

Additive manufacturing has become one of the forefront technologies in fabrication, enabling products impossible to manufacture before. Although many materials exist for additive manufacturing, most suffer from performance trade-offs. Current materials are designed with inefficient human-driven intuition-based methods, leaving them short of optimal solutions. We propose a machine learning approach to accelerating the discovery of additive manufacturing materials with optimal trade-offs in mechanical performance. A multiobjective optimization algorithm automatically guides the experimental design by proposing how to mix primary formulations to create better performing materials. The algorithm is coupled with a semiautonomous fabrication platform to substantially reduce the number of performed experiments and overall time to solution. Without prior knowledge of the primary formulations, the proposed methodology autonomously uncovers 12 optimal formulations and enlarges the discovered performance space 288 times after only 30 experimental iterations. This methodology could be easily generalized to other material design systems and enable automated discovery.

Hydrophobin-Encapsulated Quantum Dots.

The phase transfer of quantum dots to water is an important aspect of preparing nanomaterials that are suitable for biological applications, and although numerous reports describe ligand exchange, very few describe efficient ligand encapsulation techniques. In this report, we not only report a new method of phase transferring quantum dots (QDs) using an amphiphilic protein (hydrophobin) but also describe the advantages of using a biological molecule with available functional groups and their use in imaging cancer cells in vivo and other imaging applications.

On the lifecycle of nanocomposites: comparing released fragments and their in-vivo hazards from three release mechanisms and four nanocomposites.

Nanocomposites are the dominating class of nanomaterials to come into consumer contact, and were in general assumed to pose low risk. The first data is now emerging on the exposure from nanocomposites, but little is yet known about their hypothetical nanospecific physiological effects, giving ample room for speculation. For the first time, this comprehensive study addresses these aspects in a systematic series of thermoplastic and cementitious nanocomposite materials. Earlier reports that 'chalking', the release of pigments from weathered paints, also occurs for nanocomposites, are confirmed. In contrast, mechanical forces by normal consumer use or do-it-yourself sanding do not disrupt nanofillers (nanoparticles or nanofibers) from the matrix. Detailed evidence is provided for the nature of the degradation products: no free nanofillers are detected up to the detection threshold of 100 ppm. Sanding powders measuring 1 to 80 µm in diameter are identified with the original material, still containing the nanofillers. The potential hazard from aerosols generated by sanding nanocomposites up to the nuisance dust limit is also investigated. In-vivo instillation in rats is used to quantify physiological effects on degradation products from abraded nanocomposites, in comparison to the abraded matrix without nanofiller and to the pure nanofiller. In this pioneering and preliminary evaluation, the hazards cannot be distinguished with or without nanofiller.

Hydrophobin can prevent secondary protein adsorption on hydrophobic substrates without exchange.

By combining several surface analytical tools, we show that an adsorbed layer of the protein H*Protein B prevents the adsorption of secondary proteins bovine serum albumin, casein, or collagen at low-salinity conditions and at pH 8. H*Protein B is an industrially producible fusion protein of the hydrophobin family, known for its high interfacial activity. While applications of hydrophobin have been reported to facilitate adhesion of proteins under different pH conditions, careful analysis by quartz-crystal microbalance and ellipsometry prove that no additional adsorption can be found on top of the H*Protein B layer in this study. Surface analysis by X-ray photoelectron spectroscopy and secondary ion mass spectrometry proves that the hydrophobin layer stays intact even after hours of exposure to solutions of the secondary proteins and that no exchange of proteins can be detected.

Recombinantly produced hydrophobins from fungal analogues as highly surface-active performance proteins.

Hydrophobins are available from natural resources only in milligram amounts. BASF succeeded in a recombinant production process, up-scaled to pilot plant production in kilogram scale. Strain and protein optimization by modulation of gene expression and generation of fusion proteins finally leads to two class I hydrophobins called H*Protein A and H*Protein B. By analytical ultracentrifugation, we confirm that the self-association of H*Proteins in solution is governed by their sequence, because oligomerization is induced by the same mechanisms (pH > 6, temperature >> 5 degrees C, concentration > 0.2 mg/ml) as for the well-known native hydrophobins SC3 and HFB II. Additionally, we established the triggering of structure formation by bridging with divalent ions and the stabilization of dimers and tetramers by monovalent ions or surfactants. This interplay with surfactants can be exploited synergistically: The capacity for emulsification of a 300 ppm standard surfactant solution is boosted from 0 to 100% by the addition of a mere 1 ppm of our new hydrophobins, with H*Protein A and H*Protein B having specific application profiles. This astonishing performance is rationalized by the finding that the same minute admixtures enhance significantly the interfacial elastic modulus, thus stabilizing interfaces against coalescence and phase separation.

Time-resolving molecular vibration for microanalytics: single laser beam nonlinear Raman spectroscopy in simulation and experiment.

A single-beam implementation of coherent anti-Stokes Raman scattering (CARS) allows experimentally very much simplified and flexible approaches to time-resolved vibrational spectroscopy, with the additional benefit of microscopic spatial resolution. To achieve this, a broadband femtosecond laser is combined with a pulse shaper creating tailored pulse sequences by computer control. We discuss the theoretical foundations and technical issues of the technique in detail and show the successful implementation of different schemes for truly femtosecond time-resolved vibrational spectroscopy. Hereby, we elaborate all the details of the method shown earlier in a proof-of-principle study [Von Vacano and Motzkus, Opt. Comm., 2006, 264, 488] and greatly extend it by novel approaches relying on the use of identical double pulses or additional polarization control for background-free spectroscopy with superior robustness and signal-to-noise ratio. Perspectives and applications of the presented schemes for chemical microanalysis and high-contrast chemical imaging are examined.

Molecular discrimination of a mixture with single-beam Raman control.

A single beam of shaped femtosecond pulses is used to coherently control the Raman excitation and to simultaneously observe the resulting vibrations of molecules in a mixture resolved in time. This experimentally simple scheme opens up exciting new possibilities for the selective detection of dangerous chemical or bacterial species, such as spores, and will serve to enhance contrast in nonlinear Raman chemical imaging.

Highly sensitive single-beam heterodyne coherent anti-Stokes Raman scattering.

Single-beam coherent anti-Stokes Raman-scattering (CARS) microspectroscopy achieves a complete CARS scheme with a femtosecond laser. Here, we introduce heterodyne detection in a simple experimental extension: the optical fields driving the CARS process and the local oscillator used for heterodyning are derived from a single beam of ultrashort laser pulses by pulse shaping. The heterodyne signal is amplified by more than 3 orders of magnitude and is linearly dependent on the concentration of Raman scatterers. This dramatically increases the sensitivity of chemically selective detection at microscopic resolution while maintaining the simplicity of the single-beam setup.

In situ broadband pulse compression for multiphoton microscopy using a shaper-assisted collinear SPIDER.

The characterization and control of the phase of broadband femtosecond pulses in nonlinear microscopy are successfully demonstrated with a collinear configuration of spectral shear interferometry for direct electric field reconstruction (SPIDER). A femtosecond-pulse shaper is used as a dispersionless interferometer for the measurement of the spectral phase and to actively compress a broadband supercontinuum from a photonic crystal fiber. This allows in situ online phase management and enables the application of quantum control spectroscopy in microenvironments.

Actively shaped supercontinuum from a photonic crystal fiber for nonlinear coherent microspectroscopy.

The combination of broadband pulses from a photonic crystal fiber (PCF) pumped by a standard 100 fs oscillator and pulse shaping is successfully employed for coherently controlled nonlinear spectroscopy. The pulse shaper manages not only to compress the PCF supercontinuum in a closed-loop optimization scheme but also to manipulate the phase at the same time for quantum control applications. This approach is demonstrated by single-beam coherent anti-Stokes Raman microspectroscopy and should be, due to its simplicity, well suited for general applications in nonlinear microscopy.