The scalable and sustainable manufacture of thick electrode films with high energy and power densities is critical for the large-scale storage of electrochemical energy for application in transportation and stationary electric grids. Two-dimensional nanomaterials have become the predominant choice of electrode material in the pursuit of high energy and power densities owing to their large surface-area-to-volume ratios and lack of solid-state diffusion1,2. However, traditional electrode fabrication methods often lead to restacking of two-dimensional nanomaterials, which limits ion transport in thick films and results in systems in which the electrochemical performance is highly dependent on the thickness of the film1-4. Strategies for facilitating ion transport-such as increasing the interlayer spacing by intercalation5-8 or introducing film porosity by designing nanoarchitectures9,10-result in materials with low volumetric energy storage as well as complex and lengthy ion transport paths that impede performance at high charge-discharge rates. Vertical alignment of two-dimensional flakes enables directional ion transport that can lead to thickness-independent electrochemical performances in thick films11-13. However, so far only limited success11,12 has been reported, and the mitigation of performance losses remains a major challenge when working with films of two-dimensional nanomaterials with thicknesses that are near to or exceed the industrial standard of 100 micrometres. Here we demonstrate electrochemical energy storage that is independent of film thickness for vertically aligned two-dimensional titanium carbide (Ti3C2T x ), a material from the MXene family (two-dimensional carbides and nitrides of transition metals (M), where X stands for carbon or nitrogen). The vertical alignment was achieved by mechanical shearing of a discotic lamellar liquid-crystal phase of Ti3C2T x . The resulting electrode films show excellent performance that is nearly independent of film thickness up to 200 micrometres, which makes them highly attractive for energy storage applications. Furthermore, the self-assembly approach presented here is scalable and can be extended to other systems that involve directional transport, such as catalysis and filtration.

Thickness-independent capacitance of vertically aligned liquid-crystalline MXenes.

The nonlinear viscoelastic properties for a series of intercalated nanocomposites of an organically modified montmorillonite and a disordered styrene−isoprene diblock copolymer are reported. The li...

Nonlinear viscoelastic properties of layered-silicate-based intercalated nanocomposites

Recent Advances in Functional 2D MXene-Based Nanostructures for Next-Generation Devices

Nonsymmetric dimers derived from naturally occurring cholesterol represent an exemplary and emerging class of chiral liquid crystals. They are formed by linking the pro-mesogenic cholesterol moiety to one of the termini of aromatic/aromatic-alicyclic/supramolecular mesogenic core through a flexible spacer of varying length and parity. Hitherto, over 300 dimers comprising fourteen different mesogenic cores have been reported. The stabilization of a variety of highly frustrated fluid structures, reentrant phases and unprecedented phase sequences clearly illustrates their unique molecular structural characteristics. Besides, the employed fragments facilitate modulating the properties of technologically important fluid phases. Thus, they are immensely significant in both fundamental science and practical applications. In this Feature Article an overview of these chiral dimers is provided.

Cholesterol-based nonsymmetric liquid crystal dimers: an overview

We present a calorimetric study of the phase behavior of octylcyanobiphenyl (8CB) liquid crystal confined to a controlled-pore glass (CPG). We used CPG matrices with characteristic void diameters ranging from 400 to 20 nm. In bulk we obtain weakly first-order isotropic to nematic (I-N) phase transition and nearly continuous character of the nematic to smectic-A (N-SmA) phase transition. In all CPG matrices the I-N transition remains weakly first order, while the N-SmA one becomes progressively suppressed with decreasing CPG pore radius. With decreased pore diameters both phase transition temperatures monotonously decrease following similar trends, but increasing the stability range of the N phase. The heat-capacity response at the weakly first order I-N and continuous N-SmA phase transitions gradually approaches the tricritical-like and three-dimensional XY behavior, respectively. The main observed features were explained using a bicomponent single pore type phenomenological model.

Calorimetric study of octylcyanobiphenyl liquid crystal confined to a controlled-pore glass.

Surface-Induced Discrete Smectic Order in the Isotropic-Phase of 12Cb in Cylindrical Pores

Small-angle neutron scattering was employed to study the effect of shear flow on the nematic (N) and lamellar (Lα) phases in aqueous solutions of cesium perfluoro-octanoate. Shear rates as high as ~ 4000 s-1 were used. The N phase was found to align with the director in the direction of the gradient velocity. The Lα phase oriented with lamellae parallel to the shear plane. This change in equilibrium orientation is attributed, primarily, to changes in the value of the Ericksen viscosity parameter α2. Subtle shear-rate-dependent director reorientations were also observed in the proximity of the N-to-Lα phase transition.

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Discotic Micellar Nematic and Lamellar Phases Under Shear-Flow

Small angle neutron scattering was used to investigate the orientational ordering of a lyotropic mixture of cesium-perfluoro-octanoate (CsPFO) in water under simple Couette and oscillatory shear. The discotic-liquid-crytstal micelles were found to orient mostly parallel to the moving shear cell walls (i.e., vertically). A partial ``flipping'' of the orientation was observed in the smectic phase, whereby lamellae were seen to orient horizontally. Oscillatory shear produced orientational effects as well as shear-induced shifts of the phase transition boundaries. Interesting competing ``bulk'' and ``wall'' effects were also observed.

Shear-Induced Orientational Effects in Discotic-Liquid-Crystal Micelles

The orientation of the smectic-A and -C* layers, inside 25 μm pores of glass capillary arrays, has been studied by high-resolution x-ray diffraction. The pores were coated with lecithin in order to ensure perpendicular anchoring of molecules at the surface. A chevron-like layer structure was seen in the smectic-A phase of 8CB, while a uniform structure was found in the smectic-C* phase of, both, ZLI-3041 and CBC.

Smectic Layer Orientation in Confined Geometries

High-resolution x-ray scattering measurements of 23.0 and 28.4 mole % mixtures of TBBA in DB6 have led to the observation of a true incommensurate phase in a liquid crystal system. The phase is characterized by two primary quasi-Bragg reflections at incommensurate wave vectors. X-ray scattering measurements of a freely suspended film in the new phase have revealed that it possesses sixfold in-plane symmetry, suggesting it to be an incommensurate crystal- $B$ or - $E$ phase.

Joseph T. Mang

Papers

Surface-Induced Discrete Smectic Order in the Isotropic-Phase of 12Cb in Cylindrical Pores

Discotic Micellar Nematic and Lamellar Phases Under Shear-Flow

Shear-Induced Orientational Effects in Discotic-Liquid-Crystal Micelles

Smectic Layer Orientation in Confined Geometries

True incommensurate phase in mixtures of two polar liquid crystalline materials.