Graphene quantum dot doped viscoelastic lyotropic liquid crystal nanocolloids for antibacterial applications

Graphene quantum dots (GQDs) are prepared and characterized via X-ray diffraction (XRD), UV-Visible spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM) and photoluminescence (PL). GQDs are doped (5 mg and 10 mg) in the lyotropic liquid crystalline (LLC) lamellar and hexagonal phases to prepare GQD/LLC nanocolloids. Polarizing optical microscopy and X-ray diffraction measurement reveals that GQDs do not affect the lamellar and hexagonal LLC structures and may organize on their interface. Pure LLC phases and nanocolloids are studied for steady and dynamic rheological behavior. LLC phases and GQD/LLC nanocolloids possess shear thinning and frequency dependent liquid viscoelastic behavior. A complex moduli study of LLCs and GQD/LLC nanocolloids is carried out which indicates the gel to viscous transition in LLCs and GQD/LLC nanocolloids as a function of frequency. LLC phases and GQD/LLC nanocolloids are tested for antibacterial activity against Listeria ivanovii. The effect of surfactant concentration, LLC phase geometry and GQD concentration has been studied and discussed. A probable mechanism for the strong antimicrobial activity of LLCs and GQD/LLC nanocolloids is presented considering intermolecular interactions. The viscoelastic behavior and strong antibacterial activity (inhibition zone 49.2 mm) of LLCs and GQD/LLC nanocolloids make them valuable candidates for lubrication, cleaning, cosmetics and pharmaceutical applications.

Ferrihydrite nanoparticles entrapped in shear-induced multilamellar vesicles

HYPOTHESIS

Ferrihydrite (Fh) nanoparticles are receiving considerable scientific interest due to their large reactive surface areas, crystalline structures, and nanoparticle morphology. They are of great importance in biogeochemical processes and have the ability to sequester hazardous and toxic substances. Here, the working hypothesis was to entrap fractal-like Fh nanoparticles, with a radius of gyration of 6.2 nm and a primary building block of polydisperse spheres with a radius of 0.8 nm, in a shear-induced multilamellar vesicle (MLV) state using a 40 wt% polyethylene glycol dodecyl ether surfactant.

EXPERIMENTS

Small- and Wide- Angle X-ray scattering revealed the equilibrium state of the non-ionic planar lamellar phase, the Fh dispersion, and their mixture. The MLV state was induced by using a shear flow in a Taylor-Couette geometry of a rheometer.

FINDINGS

The nonionic surfactant initially exhibited a lamellar gel phase with two distinct d-spacings of 11.0 and 9.7 nm, which collapsed into the MLV state under shear flow. The Fh nanoparticles induced bilayer attraction by suppressing lamellar layer undulations, decreasing the d-spacing. These results are helpful in the understanding of the relationship between nanoparticle size and nanoparticle-bilayers interactions and provides insight on Fh encapsulations in a kinetically stable MLVs state.

Improved ordering and lubricating properties using graphene in lamellar liquid crystals of Triton X-100/CnmimNTf2/H2O

Graphene has been studied extensively owing to its excellent lubricity performance. However, when used as lubricant additives, graphene layers tend to agglomerate and precipitate; further, poor dispersion will reduce the lubrication performance. Herein, graphene was evenly dispersed in Triton X-100/1-alkyl-3-methylimidazole ditrifluorosulfonylimide (CnmimNTf2)/H2O (n = 8, 12, and 16) lamellar liquid crystals (LLCs). The effects of the graphene concentration on the microstructures of the LLCs are detected by 2H NMR and small angle X-ray scattering measurements and their rheological and tribological performance are investigated in detail. The addition of 0.30 mg mL-1 graphene into the Triton X-100/C16mimNTf2/H2O LLC system led to a 15% reduction in the friction coefficient and 65% reduction in the wear volume when compared with the pure LLCs. The synergistic effect of the graphene and LLC hybrid system efficiently improved the lubrication performance, which is attributed to the higher order of the amphiphilic molecules and the thicker amphiphilic bilayer. The generated tribofilm formed by the physical adsorption and the tribochemical reaction of LLCs on the surface of steel is conducive to lubricity protection from abrasion. This study reveals that with the understanding of the microstructure change mechanism, the combination of graphene and LLCs could provide a new path to the design of a novel lubricant that can be utilized in nanostructures for energy saving applications.

Tuning the response selectivity of graphene oxide fluorescence by organometallic complexation for neurotransmitter detection

It is of great interest to design nanomaterial biosensors that can selectively detect target molecules without the use of fragile and expensive antibodies. Here, we report a chemical approach to modulate the response selectivity of graphene oxide (GO) fluorescence for neurotransmitters, in order to design an optical biosensor for the selective detection of dopamine without using antibodies. To this end, GO was functionalized with six different amino acids, followed by the immobilization of seven metal ions, resulting in the production of forty-two different GO nanohybrids (denoted GO-AA-MI derivatives). The fluorescence response of GO-AA-MI derivatives to dopamine, norepinephrine, and epinephrine was modulated by varying the type of amino acids and metal ions introduced. Tyrosine-modified GO with Fe2+ ions (GO-Y-Fe) exhibited selective quenching of its fluorescence in the presence of dopamine whereas lysine-modified GO with Au3+ ions (GO-K-Au) showed a selective increase in fluorescence upon addition of norepinephrine. The GO-Y-Fe sensor developed was able to differentiate dopamine from similar structures of norepinephrine and epinephrine, as well as abundant interferents such as ascorbic acid and uric acid, without the use of antibodies. In addition, the GO-Y-Fe sensor successfully detected dopamine secreted from living neuron cells in a rapid and simple manner.

Graphene Oxide Liquid Crystals: Discovery, Evolution and Applications

The discovery and relevant research progress in graphene oxide liquid crystals (GOLCs), the latest class of 2D nanomaterials exhibiting colloidal liquid crystallinity arising from the intrinsic disc-like shape anisotropy, is highlighted. GOLC has conferred a versatile platform for the development of novel properties and applications based on the facile controllability of molecular scale alignment. The first part of this review offers a brief introduction to LCs, including the theoretical background. Particular attention has been paid to the different types of LC phases that have been reported thus far, such as nematic, lamellar and chiral phases. Several key parameters governing the ultimate stability of GOLC behavior, including pH and ionic strength of aqueous dispersions are highlighted. In a relatively short span of time since its discovery, GOLCs have proved their remarkable potential in a broad spectrum of applications, including highly oriented wet-spun fibers, self-assembled nanocomposites, and architectures for energy storage devices. The second part of this review is devoted to an exclusive overview of the relevant applications. Finally, an outlook is provided into this newly emerging research field, where two well established scientific communities for carbon nanomaterials and liquid crystals are ideally merged.

Non-covalent modification of reduced graphene oxide by a chiral liquid crystalline surfactant

In order to effectively disperse reduced graphene oxide (RGO) in functional materials and take full advantage of its exceptional physical and chemical properties, a novel and effective approach for non-covalent modification of RGO by a chiral liquid crystalline surfactant (CLCS) consisting of chiral mesogenic units, nematic mesogenic units with carboxyl groups and non-mesogenic units with a polycyclic conjugated structure is firstly established. The polycyclic conjugated structure can anchor onto the RGO surface via π-π interactions, the chiral mesogenic units possess affinity for chiral materials by joining the helical matrix of chiral material and the carboxyl groups in nematic mesogenic units are supposed to form coordination bonds with nano zinc oxide (ZnO) to fabricate functional nano hybrids. The transmittances of CLCS-RGO hybrids exhibit S-shaped nonlinear increase with the increase of wavelength, but the total transmittances from 220 nm to 800 nm show a linear decreasing trend with the increase of RGO content in the CLCS-RGO hybrid. Due to the superior thermal properties of RGO and the interactions between RGO and CLCS, the dispersed RGO can improve the glass transition and increase the thermal stability and decomposition activation energy of CLCS. The intercalation of RGO can decrease the thermochromism temperature and improve the pitch uniformity of CLCS. Furthermore, CLCS can promote the dispersion of RGO in chiral nematic liquid crystals (CNLCs), and the CNLC-RGO-CLCS hybrids present decreased driving voltage and accelerated electro-optical response. The CLCS non-covalently modified RGO can strengthen the photocatalytic degradation of ZnO by suppressing the aggregation of ZnO and RGO.

Covalent modification of reduced graphene oxide by chiral side-chain liquid crystalline oligomer via Diels–Alder reaction

RGO was dispersed in the CSLCO matrix via DA reaction, and the composites have excellent properties.

Hierarchical spatial heterogeneity in liquid crystals composed of graphene oxides

We demonstrate herein a hierarchical heterogeneity, which forced particles to diffuse in an anisotropic manner, in a liquid crystal composed of graphene oxides.

Incorporation of graphene oxide into C12E4/C12mimBr hybrid lyotropic liquid crystal and its thermo-sensitive properties

Schematic illustration of the formation of GO/C₁₂E₄/C₁₂mimBr lamellar and hexagonal LLC composites.