Tunable Interfacial Properties Research Articles

Multi-Interface Engineering of MXenes for Self-Powered Wearable Devices.

Self-powered wearable devices with integrated energy supply module and sensitive sensors have significantly blossomed for continuous monitoring of human activity and the surrounding environment in healthcare sectors. The emerging of MXene-based materials has brought research upsurge in the fields of energy and electronics, owing to their excellent electrochemical performance, large surface area, superior mechanical performance, and tunable interfacial properties, where their performance can be further boosted via multi-interface engineering. Herein, a comprehensive review of recent progress in MXenes for self-powered wearable devices is discussed from the aspects of multi-interface engineering. The fundamental properties of MXenes including electronic, mechanical, optical, and thermal characteristics are discussed in detail. Different from previous review works on MXenes, multi-interface engineering of MXenes from termination regulation to surface modification and their impact on the performance of materials and energy storage/conversion devices are summarized. Based on the interfacial manipulation strategies, potential applications of MXene-based self-powered wearable devices are outlined. Finally, proposals and perspectives are provided on the current challenges and future directions in MXene-based self-powered wearable devices.

Facile Bond Exchanging Strategy for Engineering Wet Adhesion and Antioxidant/Antibacterial Thin Layer over a Dynamic Hydrogel via the Carbon Dots Derived from Tannic Acid/ε-Polylysine.

Adhesive hydrogels, playing an essential role in stretchable electronics, soft robotics, tissue engineering, and so forth, upon functioning often need to adhere to various substrates in wet conditions and simultaneously exhibit antibacterial/antioxidant properties while possessing the intrinsic stretchability and elasticity of the hydrogel network intact. Therefore, simple approaches to conveniently access adhesive hydrogels with multifunctional surfaces are being pursued. Herein, a facile strategy has been proposed to construct multifunctional adhesive hydrogels via surface engineering of a multifunctional carbon dot (CD)-decorated polymeric thin layer by dynamic bond exchange. By this strategy, a double cross-linked network hydrogel of polyacrylamide (PAM) and oxidized dextran (ODA) was engineered with a unique dense layer over the Schiff base hydrogel matrix by aqueous solution immersion of PA-120, versatile CDs derived from tannic acid (TA) and ε-polylysine (PL). Without any additional agents, the PA-120 CDs with residual polyphenolic/catechol and amine moieties were incorporated into the surface structure of the hydrogel network by the combined action of the Schiff base and hydrogen bonds to form a dense surface layer that can exhibit high wet adhesive performance via the amine-polyphenol/catechol pair. The armor-like dense architecture also endowed hydrogels with considerably enhanced tensile/compression properties and excellent antioxidant/antibacterial abilities. Besides, the single-sided modified Janus hydrogel and completely surface-modified hydrogel can be flexibly developed through this approach. This strategy will provide new insights into the preparation and application of surface-modified hydrogels featuring multiple functions and tunable interfacial properties.

Amphiphilic Nanointerface: Inducing the Interfacial Activation for Lipase.

Graphene-based materials are widely used in the field of immobilized enzymes due to their easily tunable interfacial properties. We designed amphiphilic nanobiological interfaces between graphene oxide (GO) and lipase TL (Thermomyces lanuginosus) with tunable reduction degrees through molecular dynamics simulations and a facile chemical modulation, thus revealing the optimal interface for the interfacial activation of lipase TL and addressing the weakness of lipase TL, which exhibits weak catalytic activity due to an inconspicuous active site lid. It was demonstrated that the reduced graphene oxide (rGO) after 4 h of ascorbic acid reduction could boost the relative enzyme activity of lipase TL to reach 208%, which was 48% higher than the pristine GO and 120% higher than the rGO after 48 h of reduction. Moreover, TL-GO-4 h's tolerance against heat, organic solvent, and long-term storage environment was higher than that of free TL. The drawbacks of strong hydrophobic nanomaterials on lipase production were explored in depth with the help of molecular dynamics simulations, which explained the mechanism of enzyme activity enhancement. We demonstrated that nanomaterials with certain hydrophilicity could facilitate the lipase to undergo interfacial activation and improve its stability and protein loading rate, displaying the potential of the extensive application.

Interfacial defect engineering and photocatalysis properties of hBN/MX 2 (M = Mo, W, and X = S, Se) heterostructures

Van der Waals (VDW) heterostructures have attracted significant research interest due to their tunable interfacial properties and potential applications in many areas such as electronics, optoelectronic, and heterocatalysis. In this work, the influences of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX 2 (M = Mo, W, and X = S, Se) are studied using density functional theory calculations. The results reveal that the band alignment of hBN/MX 2 can be adjusted by introducing vacancies and atomic doping. The type-I band alignment of the host structure is maintained in the heterostructure with n-type doping in the hBN sublayer. Interestingly, the band alignment changed into the type-II heterostructrue due to VB defect and p-type doping is introduced into the hBN sublayer. This can conduce to the separation of photo-generated electron–hole pairs at the interfaces, which is highly desired for heterostructure photocatalysis. In addition, two Z-type heterostructures including hBN(BeB)/MoS2, hBN(BeB)/MoSe2, and hBN(VN)/MoSe2 are achieved, showing the decreasing of band gap and ideal redox potential for water splitting. Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX 2 heterostructures via interfacial defects.

A pH-responsive polyelectrolyte multilayer film with tunable interfacial properties

We report a facile and versatile approach to fabricate polyelectrolyte multilayer (PEM) films with a chemically modifiable outer surface. A PEM film was prepared by layer-by-layer assembly of poly (2-aminoethyl methacrylate) (PAMA) and polymethacrylic acid (PMAA), terminated with a partially tert-butyloxycarbonyl (Boc)-protected random copolymer (PAMA-co-PBocAMA) as the final layer. The obtained PEM film was then cross-linked and the free amino groups in the PEM film were quenched using EDC/NHS chemistry. The outer layer of the film was then treated via a deprotection reaction, affording free amino groups selectively located at the film surface. As a proof of concept study, these functional groups were used to modify the film surface with two model hydrophilic and hydrophobic compounds, which tuned the wettability of the PEM.

Lubricant-Impregnated Surfaces for Mitigating Asphaltene Deposition.

Asphaltenes are heavy aromatic components of crude oil. Their complex chemical makeup-an aromatic core surrounded by aliphatic side chains-enables them to adhere to most surfaces. Their buildup in pipes can result in clogging and lead to interruption of production operations and expensive mechanical cleaning. We demonstrate the use of liquid-impregnated surfaces (LIS) to prevent asphaltene deposition and buildup on substrates. Indeed, these surfaces expose a liquid interface to the working fluid, which combines the benefits of a dynamic defect-free surface and tunable interfacial properties. In contrast to bulk additives that are typically mixed into the oil phase, the impregnating liquid also provides the great benefit of protecting the underlying solid surface with a stable and minimal layer of lubricant, thereby reducing costs and eliminating the need for subsequent downstream removal. We first select and confirm the thermodynamic stability of a suitable lubricant and its lack of interaction with asphaltenes. By using a carefully selected system composed of a textured and functionalized solid substrate in conjunction with a fluorinated lubricant, we show that asphaltene adsorption is prevented over long time scales. We further demonstrate the possibility of building such a system with representative industrial materials such as aluminum and expose the resulting substrate to an external shear flow to simulate pipe flow conditions.

Tunable Interfacial Properties in Silk Ionomer Microcapsules with Tailored Multilayer Interactions.

Microencapsulation techniques represent a critical step in realizing highly controlled transport of functional materials in multiphase systems. The first demonstration of microcapsules prepared from minimally grafted silk ionomers (silk fibroin modified with cationic/anionic charge groups) are presented here. These tailored biomacromolecules have shown significantly increased biocompatibility over traditional polyelectrolytes and heavily grafted silk ionomers, but the low grafting density had previously limited attempts to fabricate stable microcapsules. In addition, the first microcapsules from polyethylene-glycol-grafted silk ionomers are fabricated and the corresponding impact on microcapsule behavior is demonstrated. The materials are shown to exhibit pH-responsive properties, with the microcapsules demonstrating an approx. tenfold decrease in stiffness and an approx. threefold change in diffusion coefficient when moving from acidic to basic buffer. Finally, the effect of assembly conditions of the microcapsules are shown to play a large role in determining final properties, with microcapsules prepared in acidic buffers showing lower roughness, stiffness, and an inversion in transport behavior (i.e., permeability decreases at higher pH).

Bottom-Up Electrochemical Fabrication of Conjugated Ultrathin Layers with Tailored Switchable Properties.

A bottom-up electrochemical process for fabricating conjugated ultrathin layers with tailored switchable properties is developed. Ultrathin layers of covalently grafted oligo(bisthienylbenzene) (oligo(BTB)) are used as switchable organic electrodes, and 3,4-ethylenedioxythiophene (EDOT) is oxidized on this layer. Adding only a few (less than 3) nanometers of EDOT moieties (5 to 6 units ) completely changes the switching properties of the layer without changing the surface concentration of the electroactive species. A range of new materials with tunable interfacial properties is created. They consist of oligo(BTB)-oligo(EDOT) diblock oligomers of various relative lengths covalently grafted onto the underlying electrode. These films retain reversible redox on/off switching and their switching potential can be finely tuned between +0.6 and -0.3 V/SCE while the overall thickness remains below 11 nm.

Understanding the effect of hydrophobic protecting blocks on the stability and biopassivity of polymer brushes in aqueous environments: A Tiramisù for cell-culture applications

Abstract Despite the wide range and versatility of polymer-grafting methods to produce biopassive interfaces, commonly applied polymer brushes suffer from an intrinsic lack of long-term stability when incubated in aqueous media under physiological conditions. The robustness of brush films in such environments can be greatly improved by applying a hydrophobic, “protecting” layer between the supporting substrate and the interfacial, biopassive brush. Block-copolymer brushes synthesized by sequential surface-initiated atom transfer radical polymerization (SI-ATRP) forming well-defined bilayered architectures can produce coatings with tunable interfacial properties and improved stability when subjected to cell-culture conditions. Three poly(n-alkyl methacrylates) (PAMA), exhibiting different mechanical properties, have been tested as protecting layers. A biopassive, hydrophilic brush is chosen to constitute the interfacial layer in all three cases. On the one hand, the structure of the interfacial layer clearly regulates film biopassivity, as well as its nanomechanical and nanotribological properties, as determined by atomic force microscopy (AFM) techniques. On the other hand, the composition and the mechanical properties of the polymer constituting the substrate-bound layer govern the stability of the entire bilayered film in the aqueous cell-culture environment. Precise control of bilayered brush architecture thus determines the film’s applicability for cell manipulation or biomaterials surface engineering.

Design and characterization of chitosan-based composite particles with tunable interfacial properties

Composite nano-microparticles were prepared in aqueous solution that contain chitosan or modified (carboxymethyl) chitosan with polyanion species such as alginate or tripolyphosphate, respectively. Several types of particles were prepared and characterized by 1H/31P NMR spectroscopy, IR spectroscopy, and DLS. According to DLS, the particle size was observed to increase as the concentration of the aqueous urea solution increased. The average size and polydispersity index (in parentheses) vary and are reported for the chitosan-based particles from 243.0±1nm (0.28) to 424±14nm (0.33), according to DLS measurements at ambient conditions. Thus, the particles are herein referred to as nano-microparticles (NMPs) due to the relative size range. The stability of the NMPs is related to the particle composition and the aqueous solution conditions, as evidenced by variable NMP stability on the order of two weeks or more at different ionic strength.

The electronic structures of group-V-group-IV hetero-bilayer structures: a first-principles study.

Recent findings of group-V nanosheets provide new building units for van der Waals hetero-nanostructures. Based on first-principles calculation, we investigate the structural and electronic properties of bilayer hetero-sheets composed of group-V (arsenene/antimonene) and group-IV (graphene/silicene) layers. These hetero-sheets exhibit typical van der Waals features with small binding energies and soft interlayer elastic constants. In the hetero-sheets, the Dirac characteristics of the group-IV layer and the semiconducting feature of the group-V one are well preserved, which causes a Schottky contact at the metal-semiconductor interface. The Schottky barriers are always p-type in the Si-based hetero-sheets, whereas in the C-based ones, the interfacial feature is sensitive to the interlayer distance. A tensile strain would induce a p-type-to-n-type Schottky barrier transition for the As-C hetero-sheet, while a compressive strain can cause a Schottky-to-ohmic contact transition in the Sb-C one. Moreover, due to the inhomogeneous charge redistribution, a sizeable band gap is opened at the Dirac point of the Sb-Si hetero-sheet, which could be linearly modulated by perpendicular strains around the equilibrium site. The versatile electronic structures and tunable interfacial properties enable the group-V-group-IV hetero-bilayer structures to have many potential applications in nano-devices and nano-electronics.

Tunable interfacial properties of epitaxial graphene on metal substrates

We report on tuning interfacial properties of epitaxially-grown graphenes with different kinds of metal substrates based on scanning tunneling microscopy experiments and density functional theory calculations. Three kinds of metal substrates, Ni(111), Pt(111), and Ru(0001), show different interactions with the epitaxially grown graphene at the interfaces. The different interfacial interaction making graphene n-type and p-type doped, leads to the polarity change of the thermoelectric property of the graphene/metal systems. These findings may give further insights to the interfacial interactions in the graphene/metal systems and promote the use of graphene-based heterostructures in devices.