Actuating Porous Polyimide Films

We report a novel method for the fabrication of one-component self-folding polymer films. The approach is based on films with a vertical gradient of porosity and was demonstrated on an example of porous polyimide films. The inhomogeneous porosity of the films was achieved through the implementation of capillary forces and gravity during the drying of a dispersion of colloidal particles in a solution of polymer precursor. As a result, three-layered films were formed. A monolayer of particles comprises the top layer, the second layer is the pure polymer, and the third layer is formed by a mixture of particles and polymer. Etching out the particles leaves polyimide film with inhomogeneous distributed pores. These porous polymer films roll and form tubes in organic solvents as well as their vapors and reversibly unfold in air. The obtained films were used for design of actuators, which are able to capture and release different objects through the reversible folding

Mixed Polymer Brushes with Locking Switching

Mixed polymer brushes, made of two different kinds of polymers randomly grafted to the same solid substrate, were introduced as switchable interfaces for a number of promising applications. The switching properties of the mixed polymer brushes are substantially dependent on grafting density, molecular weight, compatibility of two distinct grafted polymers, and their interaction with the solvent. This work reports the mixed polymer brushes with the property of locking switching. The wetting properties of such a mixed brush can be switched between the wetting properties of individual constituting polymers by appropriate selection of solvent. However, the mixed polymer brushes wetting behavior can be locked in the hydrophobic state. This kinetically frozen methastable state, however, can be unlocked via treatment by proper “unlocking” solvent. This locking and unlocking of the hydrophobic state of the mixed brush with specific solvents could find useful applications for the development of functional materials

Conductive Nanowires Templated by Molecular Brushes

In this paper, we report the fabrication of conductive nanowires using polymer bottle brushes as templates. In our approach, we synthesized poly­(2-dimethylamino)­ethyl methacrylate methyl iodide quaternary salt brushes by two-step atom transfer radical polymerization, loaded them with palladium salt, and reduced them in order to form metallic nanowires with average lengths and widths of 300 and 20 nm, respectively. The obtained nanowires were deposited between conductive gold pads and were connected to them by sputtering of additional pads to form an electric circuit. We connected the nanowires in an electric circuit and demonstrated that the conductivity of these nanowires is around 100 S·m^–1

Surfaces with Self-repairable Ultrahydrophobicity Based on Self-organizing Freely Floating Colloidal Particles

We report an approach for the design of materials with self-repairable ultrahydrophobic properties. The materials are based on highly fluorinated crystalline fusible wax with incorporated colloidal particles. Due to the highly pronounced tendency of the wax to crystallize, the formation of blends with rough fractal surfaces was observed. In order to prove their self-repairing ability, we mechanically damaged them by scratching, which removed most of the particles from the surface. Melting of the damaged blend resulted in reorganization of the particles at the wax-air interface, restoring the initial structure and thus the ultrahydrophobic behavior

Surfaces with Self-repairable Ultrahydrophobicity Based on Self-organizing Freely Floating Colloidal Particles

We report an approach for the design of materials with self-repairable ultrahydrophobic properties. The materials are based on highly fluorinated crystalline fusible wax with incorporated colloidal particles. Due to the highly pronounced tendency of the wax to crystallize, the formation of blends with rough fractal surfaces was observed. In order to prove their self-repairing ability, we mechanically damaged them by scratching, which removed most of the particles from the surface. Melting of the damaged blend resulted in reorganization of the particles at the wax-air interface, restoring the initial structure and thus the ultrahydrophobic behavior

Hybrid Hairy Janus Particles for Anti-Icing and De-Icing Surfaces: Synergism of Properties and Effects

A novel route for the design of functional surfaces with effective anti-icing and de-icing capability based on hybrid Janus particles is presented. The heterogeneous surfaces formed by Janus particles exhibit special surface “edge” morphologies. Water first condenses on the hydrophilic portion of the surfaces, occupying relatively large hydrophilic clusters. It is pinned at the boundary between the hydrophilic and the hydrophobic regions and thus cannot penetrate in the cavities between the particles. Further condensation leads to the fast coalescence of the water clusters, which after freezing yields a fast appearance of large ice crystals, dendrites, in the shape of the agglomeration of sector plates. The mechanism of the dendrite formation is proved experimentally and by Monte Carlo simulations. Moreover, a dry band is formed around the large crystals due to the evaporation of small drops in the vicinity of the large water clusters and the subsequent ice crystals. The synergism of both effects, the area free of ice and the large unstable dendrites at the edges of heterogeneities, leads to an extremely low ice adhesion of ca. 56 kPa. The presented approach opens a new avenue for the rational design of ice-free coatings using Janus particles as building blocks

Surfaces with Self-repairable Ultrahydrophobicity Based on Self-organizing Freely Floating Colloidal Particles

We report an approach for the design of materials with self-repairable ultrahydrophobic properties. The materials are based on highly fluorinated crystalline fusible wax with incorporated colloidal particles. Due to the highly pronounced tendency of the wax to crystallize, the formation of blends with rough fractal surfaces was observed. In order to prove their self-repairing ability, we mechanically damaged them by scratching, which removed most of the particles from the surface. Melting of the damaged blend resulted in reorganization of the particles at the wax-air interface, restoring the initial structure and thus the ultrahydrophobic behavior

Reversibly Actuating Solid Janus Polymeric Fibers

It is commonly assumed that the substantial element of reversibly actuating soft polymeric materials is chemical cross-linking, which is needed to provide elasticity required for the reversible actuation. On the example of melt spun and three-dimensional printed Janus fibers, we demonstrate here for the first time that cross-linking is not an obligatory prerequisite for reversible actuation of solid entangled polymers, since the entanglement network itself can build elasticity during crystallization. Indeed, we show that not-cross-linked polymers, which typically demonstrate plastic deformation in melt, possess enough elastic behavior to actuate reversibly. The Janus polymeric structure bends because of contraction of the polymer and due to entanglements and formation of nanocrystallites upon cooling. Actuation upon melting is simply due to relaxation of the stressed nonfusible component. This approach opens perspectives for design of solid active materials and actuator for robotics, biotechnology, and smart textile applications. The great advantage of our principle is that it allows design of non-cross-linked self-moving materials, which are able to actuate in both water and air, which are not cross-linked. We demonstrate application of actuating fibers for design of walkers, structures with switchable length, width, and thickness, which can be used for smart textile applications

Hybrid Hairy Janus Particles for Anti-Icing and De-Icing Surfaces: Synergism of Properties and Effects

A novel route for the design of functional surfaces with effective anti-icing and de-icing capability based on hybrid Janus particles is presented. The heterogeneous surfaces formed by Janus particles exhibit special surface “edge” morphologies. Water first condenses on the hydrophilic portion of the surfaces, occupying relatively large hydrophilic clusters. It is pinned at the boundary between the hydrophilic and the hydrophobic regions and thus cannot penetrate in the cavities between the particles. Further condensation leads to the fast coalescence of the water clusters, which after freezing yields a fast appearance of large ice crystals, dendrites, in the shape of the agglomeration of sector plates. The mechanism of the dendrite formation is proved experimentally and by Monte Carlo simulations. Moreover, a dry band is formed around the large crystals due to the evaporation of small drops in the vicinity of the large water clusters and the subsequent ice crystals. The synergism of both effects, the area free of ice and the large unstable dendrites at the edges of heterogeneities, leads to an extremely low ice adhesion of ca. 56 kPa. The presented approach opens a new avenue for the rational design of ice-free coatings using Janus particles as building blocks

Enhanced Activity of Acetyl CoA Synthetase Adsorbed on Smart Microgel: an Implication for Precursor Biosynthesis

Acetyl coenzyme A (acetyl CoA) is an essential precursor molecule for synthesis of metabolites such as the polyketide-based drugs (tetracycline, mitharamycin, Zocor, etc.) fats, lipids, and cholesterol. Acetyl CoA synthetase (Acs) is one of the enzymes that catalyzes acetyl CoA synthesis, and this enzyme is essentially employed for continuous supply of the acetyl CoA for the production of these metabolites. To achieve reusable and a more robust entity of the enzyme, we carried out the immobilization of Acs on poly­(<i>N</i>-isopropylacrylamide)-poly­(ethylenimine) (PNIPAm-PEI) microgels via adsorption. Cationic PNIPAm-PEI microgel was synthesized by one-step graft copolymerization of NIPAm and <i>N</i>,<i>N</i>-methylene bis-acrylamide (MBA) from PEI. Adsorption studies of Acs on microgel indicated high binding of enzymes, with a maximum binding capacity of 286 μg/mg of microgel for Acs was achieved. The immobilized enzymes showed improved biocatalytic efficiency over free enzymes, beside this, the reaction parameters and circular dichroism (CD) spectroscopy studies indicated no significant changes in the enzyme structure after immobilization. This thoroughly characterized enzyme bioconjugate was further immobilized on an ultrathin membrane to assess the same reaction in flow through condition. Bioconjugate was covalently immobilized on a thin layer of preformed microgel support upon polyethylene terephthalate (PET) track etched membrane. The prepared membrane was used in a dead end filtration device to monitor the bioconversion efficiency and operational stability of cross-linked bioconjugate. The membrane reactor showed consistent operational stability and maintained >70% of initial activity after 7 consecutive operation cycles