Copper-graphene composite is synthesized by electrochemical deposition of copper in graphene quantum dot (GQD, 5% w/v) bath and is characterized by electrochemical and spectroscopic techniques. The electrochemical formation of the composite has been investigated by cyclic voltammetry that reveals the oxidation of the composite produces convection at the electrode. From the interaction of GQD with cupric ion the life time of the excited state of GQD has been estimated to be 4.1 × 10−9 s. The morphology of the composite is having a string like structure as compared to normal cauliflower like copper deposition. Energy Dispersion Analysis X-ray spectrum (EDAX) shows distinct peaks at 0.25 eV and 8.1 keV that are identifiable as due to carbon and Cu of the composite. The copper-graphene composite gave a critical heat flux (CHF) of 216 W/cm2 and a heat transfer coefficient (HTC) of 86 kW/m2C in pool boiling experiments. High speed images were taken using a Photron fastcam for determining the bubble departure diameter. The graphene-copper composite resulted in a 66% increase in CHF over a plain copper surface suggesting it to be an attractive option for pool boiling enhancement. The improved performance has been attributed to the higher thermal conductivity of the graphene layers arising from the porous nature of the surface with an increased surface area.
The objective of this paper was to investigate the viscosity‐temperature relationship of lipid‐based materials (fatty alcohol, fatty acid, fatty ester and glycerides) amenable for spray congealing. The flow properties and viscosity–temperature relationship of cetyl alcohol, stearic acid, myristyl myristate, glyceryl monostearate, glyceryl dibehenate, hydrogenated soybean oil, hydrogenated vegetable oil and hydrogenated cottonseed oil were investigated using continuous ramping and temperature ramping tests. The viscosity–temperature data obtained was fitted into two existing viscosity–temperature models as well as a series of mathematical functions. The peak melting points of the materials were established by differential scanning calorimetry. Morphology and size of the spray‐congealed microparticles were analysed by scanning electron microscopy and laser diffractometry. Correlation analyses were conducted to explore the relationship between viscosity and microparticle median size. When molten, all eight lipid‐based materials used were Newtonian liquids. Viscosity of these materials decreased in a biphasic manner with increasing temperature which fitted a simple biexponential equation. The viscosity–temperature curves showed distinct transition points, from which mathematical manipulations generated a new rheological parameter termed Tp. Compared to the conventionally used viscosity values at spraying temperature, the Tp values of materials showed a stronger correlation with the median size of spray‐congealed microparticles produced. Practical applications: From this work, a new temperature‐independent constant (Tp) unique to each lipid‐based material was derived and found to have good correlation with the resultant spray‐congealed microparticle median size. This work aims to introduce Tp as a viable parameter of the rheology of lipid‐based materials for optimisation of formulation in spray congealation. Besides spray congealing, the application of Tp may be extended to other melt processes, such as melt granulation, melt extrusion and hot melt coating. (A) A typical biexponential temperature ramping curve showing the location of the characteristic transition point (Tp). (B) Graph of median size (μm) of spray‐congealed microparticles against Tp values.
Zinc-graphene composite has been electrolytically produced for the first time using a graphene quantum dot (GQD) electrode. The electrochemical reduction of zinc ion at a GQD electrode is shifted to a lesser negative potential with the complimentary anodic peak due to the oxidation of the composite shifted towards a positive potential as compared to zinc ion reduction in the GQD bath. The coulombic efficiency of the composite represents a gain of nearly 10% over the conventional Zn/Zn 2+ in the energy storage systems. In galvanostatic electrolysis, the deposition of zinc-graphene composite is carried out under neutral and acidic conditions. The Xray diffraction of the electrolytically prepared composite shows distinct features of 2 theta reflection at 8 o due to (001) plane of graphene, in addition to the characteristic reflections at 38.9 o ,43.2 o , 54.3 o , 70.1 o and 90 o arising from Zn at (002), (100), (101), (102) and (110). A large scale preparation of the zinc-graphene composite has been achieved at a zinc plate as the working electrode in the GQD bath. The composite is stable up to 250 o C. Scanning electron microscopic (SEM) and energy dispersion X-ray analysis (EDAX) shows a string like structure with peaks for carbon and zinc in EDAX.
This study was used to find solid state characteristics of ibuprofen loaded spray-congealed solid lipid microparticles (SLMs) by employing simple lipids as matrices, with or without polymeric additives, and the impact of solid drug-matrix miscibility on sustaining drug release. Solid miscibility of ibuprofen with two lipids, cetyl alcohol (CA) and stearic acid (SA), were investigated using differential scanning calorimetry (DSC). SLMs containing 20% w/w ibuprofen with or without polymeric additives, PVP/VA and EC, were produced by spray congealing, and the resultant microparticles were subjected to visual examination by scanning electron microscopy (SEM), thermal analysis using DSC, and hot-stage microscopy. Intermolecular interactions between lipids and drug as well as additives were investigated by Fourier-transformed infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). X-ray diffractometry (XRD) was utilized to study polymorphic changes of drug and matrix over the course of a year. Ibuprofen was found to depress the melting points of CA and SA in a colligative manner, reaching maximum solubility at 10% w/w and 30% w/w for CA and SA, respectively. Drug encapsulation efficiencies and yields of spray-congealed SLMs containing 20% w/w ibuprofen were consistently high for both lipid matrices. CA and SA were found to adopt their stable γ- and β-polymorphs, respectively, immediately after spray congealing. The spray congealing process resulted in ibuprofen adopting an amorphous or poorly crystalline state, with no further changes over the course of a year. SEM, DSC, and hot stage microscope studies on the SLMs confirmed the formation of a solid dispersion between ibuprofen and CA and a solid solution between ibuprofen and SA. SA was found to sustain the release of ibuprofen significantly better than CA. PVP/VA and EC showed some interactions with CA, which led to an expansion of unit cell dimensions of CA upon spray congealing, whereas they showed negligible interactions with SA. PVP/VA and EC both hastened drug release in both CA and SA matrices, despite PVP/VA being hydrophilic and EC being hydrophobic. CA and SA are useful as lipid matrices that do not exhibit polymorphism when spray-congealed. Sustained release of ibuprofen was achieved with the formation of a solid solution with SA. Solid miscibility of drug in lipid matrix has a large impact on the ability of the SLMs to sustain the release of a drug. Polymeric additives generally disrupted structural integrity of SLMs and led to faster drug release.
Spray congealing is efficient for producing drug-loaded SLMs. It induces polymorphic changes in GB. The latter incorporated 20%, w/w IBU as a solid solution and polymeric additives exerted contrasting effects on the GB polymorphic conversion.
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