For the first time, pristine graphene can be controllably crumpled and unfolded. The mechanism for graphene is radically different than that observed for graphene oxide; a multifaced crumpled, ...dimpled particle morphology is seen for pristine graphene in contrast to the wrinkled, compressed surface of graphene oxide particles, showing that surface chemistry dictates nanosheet interactions during the crumpling process. The process demonstrated here utilizes a spray‐drying technique to produce droplets of aqueous graphene dispersions and induce crumpling through rapid droplet evaporation. For the first time, the gradual dimensional transition of 2D graphene nanosheets to a 3D crumpled morphology in droplets is directly observed; this is imaged by a novel sample collection device inside the spray dryer itself. The degree of folding can be tailored by altering the capillary forces on the dispersed sheets during evaporation. It is also shown that the morphology of redispersed crumpled graphene powder can be controlled by solvent selection. This process is scalable, with the ability to rapidly process graphene dispersions into powders suitable for a variety of engineering applications.
The morphological transition of 2D graphene nanosheets to 3D crumpled particles is achieved via a scalable spray‐drying technique. In‐situ microscopy shows that factors such as nanosheet elasticity and surface chemistry affect the crumpling process, such that the crumpling mechanism differs between pristine graphene and graphene oxide. Unfolding of crumpled graphene upon rewetting depends on nanosheet–solvent interactions.
We demonstrate a simple and effective technique for dispersing pristine (unfunctionalized) graphene at high concentrations in a wide range of organic solvents by use of a stabilizing polymer ...(polyvinylpyrrolidone, PVP). These polymer-stabilized graphene dispersions are shown to be highly stable and readily redispersible even after freeze-drying. This technique yields significantly higher graphene concentrations compared to prior studies. An excellent increase in the thermal conductivity of the fluid by the addition of pristine graphene is also demonstrated. These well-dispersed pristine graphene sheets were then used as a strong and conductive nano-filler for polymer composites. Graphene/PVP composites were produced by the bulk polymerization of
N-vinylpyrrolidone loaded with dispersed graphene, resulting in excellent load transfer and improved mechanical and electrical properties.
We demonstrate a novel in situ polymerization technique to develop localized polymer coatings on the surface of dispersed pristine graphene sheets. Graphene sheets show great promise as strong, ...conductive fillers in polymer nanocomposites; however, difficulties in dispersion quality and interfacial strength between filler and matrix have been a persistent problem for graphene-based nanocomposites, particularly for pristine graphene. With this in mind, a physisorbed polymer layer is used to stabilize graphene sheets in solution. To create this protective layer, we formed an organic microenvironment around dispersed graphene sheets in surfactant solutions, and created a nylon 6, 10 or nylon 6, 6 coating via interfacial polymerization. Technique lies at the intersection of emulsion and admicellar polymerization; a similar technique was originally developed to protect luminescent properties of carbon nanotubes in solution. These coated graphene dispersions are aggregation-resistant and may be reversibly redispersed in water even after freeze-drying. The coated graphene holds promise for a number of applications, including multifunctional graphene–polymer nanocomposites.
In this paper, we demonstrate a facile technique to disperse pristine few-layer graphene (FLG) in water utilizing a triphenylene based stabilizer (C10) that non-covalently functionalizes the surface ...without micelle formation. The yield of FLG in the final dispersion (0.2 mg FLG/mg C10) is much higher than comparable surfactants and polymers stabilizers. This dispersion is reversible in response to pH changes unlike conventional stabilizers. The C10-stabilized FLG dispersion is also stable against heat and lyophilization. This non-covalent functionalization does not disrupt the pristine structure of the graphene sheets; instead, these coatings allow for stable, aggregation-resistant FLG dispersion, as characterized through TEM. To demonstrate the utility of such dispersions, we prepared pristine FLG-loaded poly (vinyl alcohol) (PVA) composites by a simple solution casting process. This is the first example of PVA composites based on pristine graphene. These composites have enhanced electrical properties at relatively low filler fraction (0.26 vol% FLG). Moreover, these composites exhibit improved mechanical properties established by tensile and hardness tests results; these data suggest anisotropic reinforcement caused by graphene alignment.
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In delineating the painful experiences of LGBTQ individuals after the introduction of Section 377 of the Indian Penal Code R Raj Rao’s works look into the struggle of these people to survive the ...onslaught of normative sexual discourses. Given the fact that Queer sexuality has been continuously questioned, suspected and tormented prior to its legitimate recognition in 2018, Rao draws attention to the nuances of gay urban life in India. The paper critically analyses the representation of gay subculture in the cities of India as reflected in select works of Rao. It demystifies how gay people share the urban space, manage to make room for their pleasure in the cities, and pose a threat to the dominant understanding of sexuality. The ultimate objective of this paper is to understand the role of the city in the (un)making of a subcultural identity. Textual analysis, with reference to certain theoretical frameworks, would be used as a qualitative research method.
We demonstrate that functionalized pyrene derivatives effectively stabilize single- and few-layer graphene flakes in aqueous dispersions. The graphene/stabilizer yield obtained by this method is ...exceptionally high relative to conventional nanomaterial stabilizers such as surfactants or polymers. The mechanism of stabilization by pyrene derivatives is investigated by studying the effects of various parameters on dispersed graphene concentration and stability; these parameters include stabilizer concentration, initial graphite concentration, solution pH, and type and number of functional groups and counterions. The effectiveness of the pyrene derivatives is pH-tunable, as measured by zeta potential, and is also a function of the number of functional groups, the electronegativity of the functional group, the counterion, the relative polarity between stabilizer and solvent, and the distance from the functional group to the basal plane. Even if the dispersion is destabilized by extreme pH or lyophilization, the graphene does not aggregate because the stabilizer remains adsorbed on the surface. These dispersions also show promise for applications in graphene/polymer nanocomposites (examined in this paper), organic solar cells, conductive films, and inkjet-printed electronic devices.
Recent developments in the exfoliation, dispersion, and processing of pristine graphene (i.e., non‐oxidized graphene) are described. General metrics are outlined that can be used to assess the ...quality and processability of various “graphene” products, as well as metrics that determine the potential for industrial scale‐up. The pristine graphene production process is categorized from a chemical engineering point of view with three key steps: i) pretreatment, ii) exfoliation, and iii) separation. How pristine graphene colloidal stability is distinct from the exfoliation step and is dependent upon graphene interactions with solvents and dispersants are extensively reviewed. Finally, the challenges and opportunities of using pristine graphene as nanofillers in polymer composites, as well as as building blocks for macrostructure assemblies are summarized in the context of large‐scale production.
Recent developments in the exfoliation, dispersion, and processing of pristine graphene are described. Quantitative metrics are outlined to describe both graphene quality and graphene‐processing techniques. Finally, the major challenges are detailed regarding industrial scale‐up of pristine graphene production and processing into multifunctional materials, as well as the associated quality/quantity tradeoffs.
Biosurfactants are naturally occurring, surface-active chemicals generated by microorganisms and have attracted interest recently because of their numerous industrial uses. Compared to their chemical ...equivalents, they exhibit qualities that include lower toxic levels, increased biodegradable properties, and unique physiochemical properties. Due to these traits, biosurfactants have become attractive substitutes for synthetic surfactants in the pharmaceutical industry. In-depth research has been done in the last few decades, demonstrating their vast use in various industries. This review article includes a thorough description of the various types of biosurfactants and their production processes. The production process discussed here is from oil-contaminated waste, agro-industrial waste, dairy, and sugar industry waste, and also how biosurfactants can be produced from animal fat. Various purification methods such as ultrafiltration, liquid–liquid extraction, acid precipitation, foam fraction, and adsorption are required to acquire a purified product, which is necessary in the pharmaceutical industry, are also discussed here. Alternative ways for large-scale production of biosurfactants using different statistical experimental designs such as CCD, ANN, and RSM are described here. Several uses of biosurfactants, including drug delivery systems, antibacterial and antifungal agents, wound healing, and cancer therapy, are discussed. Additionally, in this review, the future challenges and aspects of biosurfactant utilization in the pharmaceutical industry and how to overcome them are also discussed.
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Enhancement of toughness in nanomaterial-based hydrogels is a critical metric for many of their engineering applications. Pristine graphene-polyacrylamide (PAM) hydrogels are synthesized via in situ ...polymerization of acrylamide monomer in PAM-stabilized graphene dispersion. In-situ polymerization leads to the uniform dispersion of the graphene sheets in the hydrogel. The graphene sheets interact with the elastic chains of the hydrogel through physisorption and permit gelation in the absence of any chemical cross-linker. This study represents the first report of pristine graphene as a physical cross-linker in a hydrogel. The properties of the graphene-polymer hydrogel are characterized by rheological measurements and compressive tests, revealing an increase in the storage modulus and toughness of the hydrogels compared to the chemically cross-linked PAM analogues. The physically cross-linked graphene hydrogels also exhibit self-healing properties. These hydrogels prove to be efficient precursors for graphene-PAM aerogels with enhanced electrical conductivity and thermal stability.
High‐strength conductive pristine graphene/epoxy composites are prepared by two simple processing methods – freeze dry/mixing and solution processing. PVP‐stabilized graphene is aggregation‐resistant ...and allows for excellent dispersion in both the resin and final composite, as confirmed by optical microscopy and SEM images. The superior dispersion quality results in excellent nanofiller/matrix load transfer, with a 38% increase in strength and a 37% improvement in modulus for 0.46 vol% graphene loading. The composites have a very low electrical percolation threshold of 0.088 vol%. Despite the effectiveness of both methods, the freeze‐drying method is more promising and versatile enough to be used for graphene dispersion in a wide range of other composite precursors.
High‐strength, low‐percolation conductive pristine graphene/epoxy composites are prepared. Two processing methods are used for nanofiller loading: freeze‐dry mixing and solution processing. The freeze‐dry mixing method is versatile enough to be used for graphene dispersion in a wide range of other composite precursors.
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