asymmetric chemical properties, both in bulk and in surface-confined coatings. [1][2][3][4][5] Referencing their two-faced nature, such asymmetric material properties are often named after the Roman god Janus. In particular, the behavior of membranes, particles, rods, or micelles with two orthogonal sides shows high potential for different applications, such as oil/water separation, droplet manipulation, fog collection, unidirectional water flow design, bubble aeration, ion gating, and energy harvesting. [6][7][8][9][10][11][12] In particular, asymmetrically designed membranes show strong potential for improved transport design and thus improved application performance. Directed oil-water transport in the context of oil-water separation and directed gas-water transport in the context of fuel cell gas diffusion layers are two specific application examples. [13,14] Therefore, enhancing control of material design and reducing the amount of material needed to achieve asymmetric material characteristics such as wettability are still an ongoing challenge. To make this situation even more stimulating, applying biocompatible and degradable materials while retaining needed stability and doing this in simple, ideally single-step, scalable fabrication processes are of increasing demand.Janus materials in general are well known since the Nobel Prize lecture of de Gennes in 1991, but they were first mentioned in 1898 by the group of Veyssié. [15,16] The general definition of Janus materials is diverse and includes all materials with asymmetric surfaces as well as composite bulk materials. In 2016, the group of Xu reshaped the definition of materials having opposing properties at two respective interfaces and proposed three configurations of so-called Janus membranes. [5] One is the "A to B"-type material, which shows a physical and/or chemical gradient across a membrane cross-section. Alternatively, A-to-B or A-and B-type Janus membranes are defined as having a clear interface between the layers. Within the last few years, the Jiang group developed a coating and peeling strategy for the facile preparation of multifunctional Janus membranes based on synthetic polymers such as polyethylene terephthalate (PET)/polytetrafluoroethylene (PTFE). [1] After membrane modification by tannic acid (TA) and diethylenetriamine to form a hydrophilic coating on the surface, peeling off the top PTFE layer from the hydrophilic membrane results in a Janus membrane showing unidirectional water permeation properties at Functional paper-based materials and devices have been increasingly attractive to scientists in the recent past. In particular, the possibility to functionalize the surface of paper fibers with tailor-made coatings has broadened a possible scope of emerging application considerably. This work introduces novel functional paper membranes with adjustable gradient and Janus-type wettability based on gradient and Janus-type silica coating distribution along the paper cross-section. Correlation of CLSM (distribution), thermogravimetric an...

light-triggered changes in the polarity of a material are of interest, as the switching mechanism does not rely on diffusion, as is the case with the pH-or electrolyteinduced switching of polyelectrolytes. [18] However, one of the major challenges of light-responsive spiropyran that has yet to be solved is the rather slow dynamics of the molecular rearrangements (i.e., slow switching behavior) and the oxidative degradation that can occur during the process. Another group of photoresponsive polarity-switching materials are known as donor acceptor Stenhouse adducts (DASAs). DASAs were discovered recently and have gained an increasing amount of attention in a broad range of fields, generating literal toolboxes for the fast implementation into existing systems to add further functionalities. [19][20][21][22][23][24][25][26][27] These compounds are derived from furfural, a commodity chemical and plant by-product, which is a great step toward sustainable building blocks for photoswitchable compounds. Initial studies focusing on the incorporation of the photoresponsive DASA domain into polymer matrices have been carried out, and the products of which displayed a photoinduced change in wetting behavior based around the mechanism displayed in Figure 1a. [28,29] Both studies found that there was no observable back-switching for DASAs on surfaces, which stands in sharp contrast to the fast switching observed for these molecules in solution. A newer study has reported that second-generation DASA-containing polymers could be switched back within hours, triggered by the glass transition of the matrix polymer. [30] Very recently Zheng et al. reported the reversible switching of a silica nanoparticle bound poly dopamine based DASA system, which could, once immobilized on a polydimethylsiloxane substrate, induce a change in water contact angle (WCA) of up to ≈40°. [31] We have been working in the recent past on cellulose-ester and hydroxypropyl cellulose (HPC)-ester polymers, which can be tailored with respect to their thermal behavior (T g ), and such materials can be applied as nanoparticle coatings on planar surfaces. [32,33] When cellulose-or HPC-ester nanoparticles are being coated onto a planar solid or porous (e.g., paper) substrate, superhydrophobic surface properties with WCAs exceeding 150° can be observed through a combination of roughness (a film consisting of nanoparticles) and low surface energy. Through thermal treatment, the nanoparticle structure Recently, donor acceptor Stenhouse adducts (DASAs) have received interest as photoresponsive polarity switches. In this work, a range of DASAs are synthesized and combined with nanoparticles from hydroxypropyl cellulose stearic acid ester to yield a photoresponsive composite material. This composite is spray-coated onto porous paper substrates, forming an interface that is initially superhydrophobic and can be switched by a visible light trigger to become hydrophilic. Subsequently, this hydrophilic state can be switched back to regain a hydrophobic surface by heating abo...

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Cellulose derivate phase separation in thin films was applied to generate patterned films with distinct surface morphology. Patterned polymer thin films are utilized in electronics, optics, and biotechnology but films based on bio-polymers are scarce. Film formation, roughness, wetting, and patterning are often investigated when it comes to characterization of the films. Frictional properties, on the other hand, have not been studied extensively. We extend the fundamental understanding of spin coated complex cellulose blend films via revealing their surface friction using Friction Force Microscopy (FFM). Two cellulose derivatives were transformed into two-phase blend films with one phase comprising trimethyl silyl cellulose (TMSC) regenerated to cellulose with hydroxyl groups exposed to the film surface. Adjusting the volume fraction of the spin coating solution resulted in variation of the surface fraction with the other, hydroxypropylcellulose stearate (HPCE) phase. The film morphology confirmed lateral and vertical separation and was translated into effective surface fraction. Phase separation as well as regeneration contributed to the surface morphology resulting in roughness variation of the blend films from 1.1 to 19.8 nm depending on the film composition. Friction analysis was successfully established, and then revealed that the friction coefficient of the films could be tuned and the blend films exhibited lowered friction force coefficient compared to the single-component films. Protein affinity of the films was investigated with bovine serum albumin (BSA) and depended mainly on the surface free energy (SFE) while no direct correlation with roughness or friction was found. BSA adsorption on film formed with 1:1 spinning solution volume ratio was an outlier and exhibited unexpected minimum in adsorption.

To improve the reactivity of lignin for incorporation into high value polymers, the introduction of amines via Mannich reaction is a commonly used strategy. During this functionalization reaction, intra- as well as intermolecular lignin–lignin crosslinking occurs, which can vastly change the elastic properties of the lignin, and therefore, the properties of the resulting polymer. Therefore, the molecular structure of the amine that is used for such a lignin functionalization may be of great importance. However, the relationship between the molecular structure of the amine and the elastic properties of the lignin-based polymer that is generated thereof, has not been fully understood. Herein, this relationship was investigated in detail and it was observed that the molecular flexibility of the amines plays a predominant role: The use of more flexible amines results in an increase in elasticity and the use of less flexible amines yields more rigid resin material. In addition to the macroscopic 3-point bending flexural tests, the elastic modules of the resins were determined on the nanometer scale by using atomic force microscopy (AFM) in the PeakForce tapping modus. Thus, it could be demonstrated that the intrinsic elasticities of the lignin domains are the main reason for the observed tendency.

Chemistry, geometric shape and swelling behavior are the key parameters that determine any successful use of man-made polymeric networks (gels). While understanding of the swelling behavior of both water-swellable hydrogels and organogels that swell in organic solvents can be considered well-advanced with respect to fossil fuel-based polymer networks, the understanding, in particular, of wood-derived polymers in such a network architecture is still lacking. In this work, we focus on organogels derived from hydroxypropyl cellulose (HPC) ester. The latter polymer was functionalized with saturated and unsaturated fatty acids, respectively. Due to their tailored chemical constitution, we demonstrated that such polysaccharide can be crosslinked and simultaneously surface-bound by using a photo-induced radical reaction using a photo-initiator. Based on the choice of fatty acid used in the design of the HPC ester, and by controlling the degree of substitution (DS) obtained during the esterification of the polysaccharide, modular manipulation of the physical properties (e.g., polarity) of the resulting gel is possible. Depending on the initiator employed, different wavelengths of light, from UV to visible, can be utilized for the crosslinking reaction, which facilitates the deployment of a range of light sources and different lithographic methods. Additionally, we showed that altering of the illumination time allows to tailor the netpoint density, and thus, the degree of linear deformation in equilibrium and the swelling kinetics. Finally, we performed a proof-of-principle experiment to demonstrate the application of our material for the generation of spatially resolved polymer patches to enrich organic molecules from a solution within a microfluidic channel.

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