Deformation of and Interfacial Stress Transfer in Ti3C2 MXene-Polymer Composites

Mechanical reinforcement from two-dimensional nanofillers: model, bulk and hybrid polymer nanocomposites

Thanks to their intrinsic properties, multifunctionality and unique geometrical features, two-dimensional nanomaterials have been used widely as reinforcements in polymer nanocomposites. The effective mechanical reinforcement of polymers is, however, a multifaceted problem as it depends not only on the intrinsic properties of the fillers and the matrix, but also upon a number of other important parameters. These parameters include the processing method, the interfacial properties, the aspect ratio, defects, orientation, agglomeration and volume fraction of the fillers. In this review, we summarize recent advances in the mechanical reinforcement of polymer nanocomposites from two-dimensional nanofillers with an emphasis on the mechanisms of reinforcement. Model, bulk and hybrid polymer nanocomposites are reviewed comprehensively. The use of Raman and photoluminescence spectroscopies is examined in light of the distinctive information they can yield upon stress transfer at interfaces. It is shown that the very diverse family of 2D nanofillers includes a number of materials that can attribute distrinctive features to a polymeric matrix, and we focus on the mechanical properties of both graphene and some of the most important 2D materials beyond graphene, including boron nitride, molybdenum disulphide, other transition metal dichalcogenides, MXenes and black phosphorous. In the first part of the review we evaluate the mechanical properties of 2D nanoplatelets in "model" nanocomposites. Next we examine how the performance of these materials can be optimised in bulk nanocomposites. Finally, combinations of these 2D nanofillers with other 2D nanomaterials or with nanofillers of other dimensions are assessed thoroughly, as such combinations can lead to additive or even synergistic mechanical effects. Existing unsolved problems and future perspectives are discussed.

MXene-Based Elastomer Mimetic Stretchable Sensors: Design, Properties, and Applications

Flexible sensors based on MXene-polymer composites are highly prospective for next-generation wearable electronics used in human-machine interfaces. One of the motivating factors behind the progress of flexible sensors is the steady arrival of new conductive materials. MXenes, a new family of 2D nanomaterials, have been drawing attention since the last decade due to their high electronic conductivity, processability, mechanical robustness and chemical tunability. In this review, we encompass the fabrication of MXene-based polymeric nanocomposites, their structure-property relationship, and applications in the flexible sensor domain. Moreover, our discussion is not only limited to sensor design, their mechanism, and various modes of sensing platform, but also their future perspective and market throughout the world. With our article, we intend to fortify the bond between flexible matrices and MXenes thus promoting the swift advancement of flexible MXene-sensors for wearable technologies.

Water-induced strong isotropic MXene-bridged graphene sheets for electrochemical energy storage

Graphene and two-dimensional transition metal carbides and/or nitrides (MXenes) are important materials for making flexible energy storage devices because of their electrical and mechanical properties. It remains a challenge to assemble nanoplatelets of these materials at room temperature into in-plane isotropic, free-standing sheets. Using nanoconfined water-induced basal-plane alignment and covalent and π-π interplatelet bridging, we fabricated Ti3C2Tx MXene-bridged graphene sheets at room temperature with isotropic in-plane tensile strength of 1.87 gigapascals and moduli of 98.7 gigapascals. The in-plane room temperature electrical conductivity reached 1423 siemens per centimeter, and volumetric specific capacity reached 828 coulombs per cubic centimeter. This nanoconfined water-induced alignment likely provides an important approach for making other aligned macroscopic assemblies of two-dimensional nanoplatelets.

Engineering Photo-Cross-Linkable MXene-Based Hydrogels: Durable Conductive Biomaterials for Electroactive Tissues and Interfaces

Light-cured conductive hydrogels have attracted immense interest in the regeneration of electroactive tissues and bioelectronic interfaces. Despite the unique properties of MXene (MX), its light-blocking effect in the range of 300-600 nm hinders the efficient cross-linking of photocurable hydrogels. In this study, we investigated the photo-cross-linking process of MX-gelatin methacrylate (GelMa) composites with different types of photoinitiators and MX concentrations to prepare biocompatible, injectable, conductive, and photocurable composite hydrogels. The examined photoinitiators were Eosin Y, Irgacure 2959 (Type I), and lithium phenyl-2,4,6-trimethylbenzoyl phosphinate (Type II). The light-blocking effect of MX strongly affected the thickness, pore structure, swelling ratio, degradation, and mechanical properties of the light-cured hydrogels. Uniform distribution of MX in the hydrogel matrix was achieved at concentrations up to 0.04 wt % but the film thickness and curing times varied depending on the type of photoinitiator. It was feasible to prepare thin films (0.5 mm) by employing Type I photoinitiators under a relatively long light irradiation (4-5 min) while thick films with centimeter sizes could be rapidly cured by using Type II photoinitiator (<60 s). The mechanical properties, including elastic modulus, toughness, and stress to break for the Type II hydrogels were significantly superior (up to 300%) to those of Type I hydrogels depending on the MX concentration. The swelling ratio was also remarkably higher (648-1274%). A conductivity of about 1 mS/cm was attained at 0.1 mg/mL MX for the composite hydrogel cured by the Type I photoinitiator. In vitro cytocompatibility assays determined that the hydrogels promoted cell viability, metabolic activity, and robust proliferation of C2C12 myoblasts, which indicated their potential to support muscle cell growth during myogenesis. The developed photocurable GelMa-MX hydrogels have the potential to serve as bioactive and conductive scaffolds to modulate cellular functions and for tissue-device interfacing.

Interface plasmon damping in the Cd33Se33/Ti2C MXene heterostructure

MXenes, a class of two-dimensional materials, have shown immense potential in various applications such as energy storage, electromagnetic shielding, solar cells, smart fabrics, optoelectronics, and plasmonics. In this study, we employ first-principles density functional theory (DFT) and time-dependent DFT calculations to investigate a semiconductor-metal heterostructure composed of a Cd33Se33 cluster and Ti2C MXene monolayer flakes. Our research focuses on the formation and damping of localized surface plasmon resonances (LSPRs) within this heterostructure. We discover that the Cd33Se33/Ti2C interface gives rise to a Schottky barrier. Importantly, this interface formation results in the damping of the Ti2C LSPR, thereby facilitating the transfer of electrons into the Cd33Se33 cluster. By directly visualizing the LSPR damping phenomenon, our study enhances our understanding of the semiconductor-MXene interface and provides novel insights for the design of MXene-based photocatalysts.