Reversible swelling-shrinking behavior of hydrogen-bonded free-standing thin film stabilized by catechol reaction

Multirole Regulations of Interfacial Polymerization Using Poly(acrylic acid) for Nanofiltration Membrane Development

Effective control of monomer diffusion and reaction rate is the key to achieving a controlled interfacial polymerization (IP) and a high-performance nanofiltration (NF) membrane. Herein, an integration of multirole regulations was synchronously realized using poly(acrylic acid) (PAA) as an active additive in a piperazine (PIP) aqueous phase. Thanks to synergistic interactions, including hydrogen bonding, electrostatic interaction, and covalent bonding between PAA and PIP molecules, together with the increased viscosity of the solution, PIP diffusion was rationally controlled. Moreover, interfacial polycondensation was also restrained via the modestly reduced pH of the aqueous solution. These contribute to the formation of a thinner, looser, more hydrophilic, and higher negatively charged PAA-decorated polyamide selective layer with a unique nanostrand-nodule morphology. The harvested NF-PAA/PIP membrane showed an ∼70% rise in water permeability (up to 23.5 L·m-2·h-1·bar-1) while retaining high Na2SO4 and dye rejections. Furthermore, the optimized NF-PAA/PIP membrane presented a superior fouling resistance capability for typical pollutants, as well as long-term stability during successive filtration. Thus, this work offers a straightforward and impactful approach to regulating IP and promoting NF membrane properties.

Polymer Complex Fiber for Linear Actuation with High Working Density and Stable Catch-State

Fiber-based linear actuators (FLAs) are a key module in microrobots and biomimetic devices. It has been a great challenge to develop linear actuators that can balance output stress and output strain and hence provide high working density. Herein, we report the preparation and performance of a FLA system made from commercially available materials and allowed mass production at relatively low cost. The FLAs can lift up or lay down objects more than 1000 times of its own weight during active contraction and expansion under environmental stimuli. The contraction ratio and output stress can reach 30% and 0.24 MPa, respectively, and the sustainable work density is about 80 J/kg, which is 10 times the typical value of human skeletal muscles. Especially, the FLAs show stable catch-state (lock-up state) with no creeping and no further energy consumption.

Nano/Micro Natural Patterns of Hydrogels against Water Loss

Water loss can be delayed by trapping it within a polymeric network, i.e. hydrogel. However, the dynamic response of natural materials has not been explained to maintain water levels relatively constant against varying environmental conditions. In this study, patterned polymeric materials formed on plant seeds are observed to provide effective water retention ability against repeated dehydration-rehydration procedures. The perpendicular line pattern (layer-by-layer stack) of the polymer films induces lateral line patterns (surface lines) by a typical wrinkling mechanism, which contributes to the characteristic water interaction. The anisotropic line patterns on the seed surface generate more hydrophilic properties over the isotropic patterns against drying-out. The matric potential (Ψ_m) of water through the line patterned gel matrix generally shows higher efficiency over isotropically patterned gels. Anisotropic lines (i.e., wrinkles) are one of the most abundant patterning procedures, thus they are a more advantageous function occurring in natural systems. This study sheds light on material design technologies to control water interaction in porous materials for various applications.

Effect of nanoclay orientation on oxygen barrier properties of LbL nanocomposite coated films

Quantify clay orientation in a layer by layer deposited films. Demonstrate the importance of interfacial region in a high clay loading nanocomposite film, in decreasing permeability.

Salt Water-Triggered Ionic Cross-Linking of Polymer Composites by Controlled Release of Functional Ions

A composite that undergoes ionic cross-linking in the presence of salt water is presented as a viable strategy for the development of chemically responsive materials. The permeation of salt water through the composite activates embedded inorganic fillers, resulting in the release of functional ions and subsequent cross-linking with the functional groups of the polymer matrix. The release of a cross-linking agent from the inorganic filler and composite is evaluated along with the impact of the cross-linking on composite properties. The new methodology is then coupled with a dopamine-functionalized polymer in order to evaluate the potential of this approach for environmentally triggered self-healing materials.

pH-Responsive Janus Film Constructed with Hydrogen-Bonding Assembly and Dopamine Chemistry

Poly(acrylic acid) (PAA) was partially grafted with dopamine (PAA-dopa), and then layer-by-layer assembled with poly(vinylpyrrolidone) (PVPON) to prepare hydrogen-bonded (PVPON/PAA-dopa) _n film. Polydopamine (PDA) was deposited on (PVPON/PAA-dopa) _n film in the presence of oxidant, and hence the whole (PVPON/PAA-dopa) _nPDA film was cross-linked. (PVPON/PAA-dopa) _nPDA could be utilized as a platform to produce the free-standing Janus film because of the easy detaching process and various chemical reactivity of PDA layer. Ag nanoparticles were formed on (PVPON/PAA-dopa) _nPDA film by electroless metallization. 1 H,1 H,2 H,2 H-Perfluorodecanethiol (PFDT) was used to further modify the film through Michael addition. After detaching from the substrate, (PVPON/PAA-dopa)₂₀PDA/Ag/PFDT exhibits reversible swelling-shrinking behavior as the pH value changes. This free-standing film shows Janus character, one side is hydrophobic, whereas the other side is hydrophilic. In addition, the hydrophobic surface exhibits a surface-enhanced Raman scattering effect, whereas the hydrophilic side does not.

Acidity-triggered charge-reversible multilayers for construction of adaptive surfaces with switchable bactericidal and bacteria-repelling functions

Microenvironment acidity of infected sites was utilized to control the surface charge, and therefore, manipulate bacterial behavior.

Hydrogen-Bonded Polymer Complex Thin Film of Poly(2-oxazoline) and Poly(acrylic acid)

The hydrogen-bonded polymer complex thin film of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA) was fabricated with layer-by-layer (LbL) assembly. The film shows exponential growth at early stage and transfers to linear growth after 10 assembling cycles, and the stable thickness increment per assembling cycle in the linear region could be higher than 100 nm. The film growth should be related with polymer chain diffusion during LbL assembly. The effects of assembling time, rinsing time, temperature, pH value, concentration and molecular weight on the thin film growth were investigated. Increasing the assembly time, the temperature and the concentration is favorable to produce the thick film. Prolonging rinsing time is good for preparing smooth film. The film can be constructed below pH 4.5 while the prepared film will not completely dissolve until pH value elevates to 7.0. Molecular weight has a subtle effect on the PEOX/PAA film growth. The PEOX-PAA pair that has a big molecular weight contrast shows fast film growth in the linear region.

Improvement of Interfacial Adhesion by Bio-Inspired Catechol-Functionalized Soy Protein with Versatile Reactivity: Preparation of Fully Utilizable Soy-Based Film

The development of materials based on renewable resources with enhanced mechanical and physicochemical properties is hampered by the abundance of hydrophilic groups because of their structural instability. Bio-inspired from the strong adhesion ability of mussel proteins, renewable and robust soy-based composite films were fabricated from two soybean-derived industrial materials: soluble soybean polysaccharide (SSPS) and catechol-functionalized soy protein isolate (SPI-CH). The conjugation of SPI with multiple catechol moieties as a versatile adhesive component for SSPS matrix efficiently improved the interfacial adhesion between each segment of biopolymer. The biomimetic adherent catechol moieties were successfully bonded in the polymeric network based on catechol crosslinking chemistry through simple oxidative coupling and/or coordinative interaction. A combination of H-bonding, strong adhesion between the SPI-CH conjugation and SSPS matrix resulted in remarkable enhancements for mechanical properties. It was found that the tensile strength and Young's modulus was improved from 2.80 and 17.24 MPa of unmodified SP film to 4.04 and 97.22 MPa of modified one, respectively. More importantly, the resultant films exhibited favorable water resistance and gas (water vapor) barrier performances. The results suggested that the promising way improved the phase adhesion of graft copolymers using catechol-functionalized polymers as versatile adhesive components.

Vapor-based synthesis and micropatterning of Janus thin films with distinct surface wettability and mechanical robustness

Janus polymer thin films with distinct surface wettability and mechanical robustness were synthesized using a facile, one-step, vapor-deposition process.

Antimicrobial efficiency of PAA/(PVP/CHI) erodible polysaccharide multilayer through loading and controlled release of antibiotics

The adhesion of bacteria and subsequent formation of biofilm on the surface of implants greatly affect the long-term use of the implants. The low molar mass gentamicin (GS) cations could hardly be directly incorporated into the multilayer films through alternately deposition with a polyanion. Herein, we have designed and constructed a (poly(acrylic acid)/(polyvinylpyrrolidone/chitosan))_n ((PAA/(PVP/CHI))_n) multilayer films through layer-by-layer self-assembly method. Through increasing the pH to destroy hydrogen bonding between PAA and PVP, PVP released into the solution and GS simultaneously combined with PAA through electrostatic interactions. The loading dosage of GS into the (PAA/(PVP/CHI))₁₀ multilayer film was up to 153.84±18.64μg/cm² and could be precisely tuned through changing the thickness of the films. The release behaviour of GS in phosphate buffer saline could also be regulated through thermal cross-linking of the films. The drug-loaded multilayer films displayed efficient against three kinds of Gram-positive and three kinds of Gram-negative bacteria and one kind of fungi, and good biocompatibility towards human lens epithelial cells. GS-loaded multilayer films-coated polydimethylsiloxane (PDMS) were compared with pristine PDMS in the rabbit subcutaneous S. aureus infection model. The antimicrobial-coated implants yielded a much lower degree of infections than pristine implants at day seven.

Highly Elastic Fibers Made from Hydrogen-Bonded Polymer Complex

In this letter, we put forward an approach to prepare hydrogen-bonded complex fibers. First, a spinnable fluid is obtained by restricting hydrogen bonds, and then it is extruded through a spinneret into a coagulation bath where hydrogen bonds are built to induce fiber formation. The hydrogen-bonded poly(acrylic acid)/poly(ethylene oxide) (PAA/PEO) complex was prepared into fibers. PAA/PEO fiber shows excellent elastic behavior and can be drawn to more than 12× its original length without breaking, which is much higher than Spandex fiber or natural rubber fiber. In the fiber, PAA and PEO are miscible in the molecular level. Dynamic hydrogen bonding between PAA and PEO restricts the crystallization of PEO, retains flexibility of polymer chains, and also provides recovery forces when removing stress.

Catechol-based layer-by-layer assembly of composite coatings: a versatile platform to hierarchical nano-materials

Inspired by the marine mussel's ability to adhere to surfaces underwater, an aqueous catechol-based dip coating platform was developed. Using a catechol-functionalized polyacrylamide binder in combination with inorganic nanoparticles enables the facile fabrication of robust composite coatings via a layer-by-layer process. This modular assembly of well-defined building blocks provides a versatile alternative to electrostatic driven approaches with layer thickness and refractive indices being readily tunable. The platform nature of this approach enables the fabrication of hierarchically ordered nano-materials such as Bragg stacks.