Characterization Equipment and Techniques
X- Ray diffraction (XRD)
X-ray diffraction is a common technique to study the crystal structures and atomic spacing of the materials. It is based on interference of monochromatic rays and a crystalline sample. The X-ray is generated by bombarding a metal target (usually Cu or Mo) with a beam of electrons emitted from a hot filament (usually tungsten).The interaction of the incident rays with the sample produces a diffracted ray which satisfies the Bragg's Law (đλ = 2đ sin Ξ , where n is an integer, λ is the wavelength of the X-ray radiation, and Ξ is the angle at which the scattered beam was observed). This law relates the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in a crystalline sample.
X-ray diffraction (XRD) was used to confirm the identity of magnetite and silica-coated magnetite nanoparticles. The X-ray diffraction patterns were obtained with a Inel Equinox 2000 powder diffractometer equipment using CuKα radiations (1.5418 Ă ). The samples were dried overnight in an oven set at 80ÂșC. The dry samples were ground into a fine powder and packed into X-ray sample holder ensuring smooth surface with no visible cracks.
Transmission Electron Microscopy (TEM)
Transmission Electron Microscopy (TEM) is a common technique to study the morphology and size of nanoparticles. Electron beams are used in TEM to illuminate the specimen and consequently creates an image. TEM consists of on electron gun (usually a tungsten filament) which produces electron beam which are then accelerated by a voltage in the anode, a condenser system (magnetic coils) that focus the beam onto the specimen, objective lenses which focus the electrons passing through the sample to form a magnified image and a fluorescent screen and a digital camera for viewing the image. A higher anode voltage will give the electrons a higher speed.
TEM images of the samples were recorded using a JEOL JEM2000EX (JEOL, Japan) instrument operating at an accelerating voltage of 200 kV. The micrographs were recorded using digital camera and Gatan Digital Micrograph software. 400 mesh carbon coated copper grids (Agar Scientific, UK) were used. TEM samples were prepared by placing approximately 5 ”L of diluted nanoparticles suspension on the carbon coated copper grid. The grids were left to dry in air at room temperature.
The TEM images were processed using ImageJ software 1.50b and Gatan Digital micrograph 3.01.598 to obtain average particle sizes. Examples of the processed images are shown in Appendix A.
Nitrogen Gas Adsorption-Desorption
Gas adsorption-desorption analysis is commonly used to evaluate the surface area and porosity of the materials.The Brunauer, Emmet and Teller (BET) technique is the most common method for determining the surface area of the powders and porous materials. Nitrogen gas is commonly used as the probe molecule. The material is exposed to the nitrogen at liquid nitrogen conditions (i.e.
77 K). The surface area of the solid is calculated considering the amount of gas used to form the monolayer on the solid surface as well as the dimensions and the number of the molecules (Naderi, 2015). Adsorption isotherm is obtained measuring the amount of gas adsorbed onto the solid sample across a range of relative pressure. The type of the isotherms indicate the pore types in the materials.
To perform the surface area evaluation of the nanoparticles, nanoparticles were dried overnight in an oven at 50°C. Prior to analysis, the nanoparticles were degassed at 100°C for 24 hours.
Analysis was performed using a Micromeritics ASAP 2010 Autopore, USA (Accelerated Surface Area and Porosimetry System). The Micromeritics ASAP 2010 software was used to perform automatic BET analysis.
Dynamics Light Scattering (DLS)
Dynamic light scattering (DLS) is typically used for sizing of nanoparticles dispersed or dissolved in a liquid. DLS principle is based on the fact that small particles in a suspension experience random thermal motion known as Brownian motion. The sample is illuminated by a laser beam, the Brownian motion of particles in a suspension causes laser light to be scattered at different intensities. The fluctuations of the scattered light are detected at a known scattering angle Ξ by a fast photon detector. This random motion is used for particle sizing using the Stokes-Einstein equation.
DLS was performed to estimate the particles size (mostly for polymeric micelles and liposomal formulations) using a Zetasizer Nano, Malvern Instruments, UK at 23°C. Nanoparticles were suspended in water at a dilute concentration, consequently, 1 mL of the nanoparticle suspension were placed in a 12 mm (OD) square polystyrene cuvettes for measurements.
Vibration Sample Magnetometry (VSM)
Vibrating Sample Magnetometer (VSM) is commonly used to measure the magnetic properties of a material as a function of magnetic field. VSM operates based on Faraday's Law of Induction, which states that a changing magnetic field will produce an electric field. In the measurement setup, the sample is fixed to the sample rod which is connected to an oscillator. The oscillator provides a sinusoidal signal that is translated by the transducer assembly into a vertical vibration.
The sample rode is placed at the centre of two pole pieces of an electromagnet that generates a
magnetic field and, stationary pickup coils are mounted on the poles of the electromagnet. When a magnetic sample is placed under the magnetic field, the magnetic domains will be aligned with the field which creates a magnetic field around the sample. Since the sample moves vertically in the field, the magnetic field generated by the sample changes as a function of time and can be sensed by the pickup coils. This alternating magnetic field causes an electric field in the pick-up coils which is proportional to the magnetization of the sample.
VSM measurements were performed at room temperature using a 7 kOe vibrating sample magnetometer and data were collected using a home built computer software. The samples were prepared by drying and grinding of nanocomposites into a fine powder. The powder was then packed into plastic tubes with length of 10 mm and internal diameter of approximately 2 mm.
Differential Scanning Calorimetry (DSC)
Differential scanning calorimetry (DSC) is a thermoanalytical technique which monitors the heat effects related with phase transitions of a sample as a function of temperature. The main application of DSC is in studying melting point, crystallisation and glass transitions. A DSC measuring cell consists of a furnace and an integrated sensor with designated positions for the sample and reference pans and the sensors are connected to thermocouples. The basic principle underlying this technique is that, when the sample undergoes a physical transformation such as phase transitions, the heat flow to the sample is affected and is higher or lower than the reference sample depending on whether the process is exothermic or endothermic.
The melting temperature of the polymer was measured using DSC Nano, TA instruments under a flow of nitrogen at a scanning rate of 5°C/min. The thermograms covered from â20 to 60°C.
Samples were prepared by placing the solid sample in a hermetic aluminium DSC pan and sealing the lids using an encapsulating press, an empty pan was sealed and used as reference sample.
Scanning Column Magnetometry (SCM)
Scanning column magnetometer (SCM) is used to measure concentration profiles of columns of magnetic dispersions and stability of the magnetic suspensions. The SCM plots the changes in the frequency (âđ) as a function of distance from the bottom of the column. The principle underlying this technique is that changes in the inductance of a coil in an LC oscillatory circuit result in corresponding changes in the frequency. On that basis a column containing magnetic dispersion is driven through the core of the detection coil, which is a part of a Colpitts oscillatory circuit.
The inductance of the coil is directly related to the concentration of the magnetic suspension, as a result variation in the suspension concentration is translated to a change in induction and consequently a change in the oscillator frequency.
SCM measurements were performed using a built in-house SCM with a sample-free frequency of 1MHz. The LabVIEW software is used for operating the system. The samples for the SCM were
prepared by sonication of the magnetic suspension using titanium horn sonicator for 4 minutes followed by placing up to 10 mL of the suspension into the SCM column.
Contact Angle Measurements
Contact angle measurement is performed to determine the hydrophilicity of a sample. Contact angle is conventionally measured through the liquid, where a liquidâvapor interface encounters a solid surface. The wettability of a solid surface is quantified by the Young equation (Yuan and Lee, 2013).
Contact angle measurements were performed by using a FTA contact angle/surface tension at room temperature. Samples were packed to small tablets with smooth surface with no visible cracks. A drop of Milli-Q water was placed on the sample surface and the evolution of the droplet shape was recorded with a video camera. An image analysis software (drop Shape Analysis v2) was used to determine the contact angle.
Gas Chromatography (GC)
Gas chromatography (GC) is an analytical technique that measures the content of various components in a sample. A GC consist of a mobile phase (Helium or nitrogen is commonly used as the carrier gas.) and a stationary phase. When a sample is injected into the GC, it instantaneously vaporized at the column inlet. Mobile phase then carry the vaporized sample through the column. Passing through the column, each component in the sample is adsorbed or partitioned to the stationary phase according to its characteristic. Identification of the compounds is based on the strengths of this interactions between the compounds and the stationary phase.
Stronger interaction translate to longer time required for the compound to migrate through the column which in turn result in longer retention time. A detector at the end of the column measures the quantity of the components as they exit the column.
Gas chromatography (GC) was used to identify and quantify the products of the catalytic hydrolysis of cis-3,5-diacetoxy-1-cyclopentene. Analysis was performed by injecting a 1 ”L aliquot of the reaction mixture into a Varian Inc CP-3380 Gas Chromatograph with nitrogen as the carrier gas. Chromatograms were interpreted using Varian Star Integrator software version 4.51. Temperature program was set to start at 50ÂșC and increase to 200ÂșC at a 10ÂșC per minute rate. A Supelco ÎČ-DEX 110 fused silica capillary column specifically designed to separate chiral compounds with the length of 30 m, internal diameter of 0.25 mm and film thickness of 0.25 ”m was used (Sigma-Aldrich, 2016).
Fourier Transform Infrared Spectroscopy (FT-IR)
Fourier transform infrared spectroscopy (FT-IR) is commonly used to identify the presence of certain functional groups in a molecule by monitoring the bond vibration. FT-IR operates based
on the principle that when an IR radiation is passed through a sample, some of the infrared radiation is absorbed by the sample. The probability of a particular IR frequency being absorbed depends on the actual interaction between this frequency and the molecule. In general, a frequency will be strongly absorbed if its photon energy coincides with the vibrational energy levels of the molecule. This absorption corresponds specifically to the bonds present in the molecule. The frequency range are measured as wave numbers typically over the range 4000 to 350 cm-1. The resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample.
Infrared spectra of the samples were recorded over the frequency range of 350 to 4000 cm-1 using a JASCO FT/IR 410 Fourier transform infrared spectrophotometer, where the dry samples were directly cast over the FT-IR diamond crystal for analysis. To analyse the liquid samples, 10 ”L of sample was cast over a low-e slides and left to dry overnight in room temperature after which it was placed directly against the FT-IR diamond crystal and analysed.
Small Angle X-Ray Scattering (SAXS)
Small Angle X-ray Scattering (SAXS) measurements were performed using S3-Micro, HECUS X-RAY SYSTEMS, GMBH GRAZ instrument with Geni Xenocs software in order to investigate structure of the particles. The powered samples were packed in a 1.5 mm dimeter quartz capillaries. Scattering curves were monitored in a q-range from 0.01 to 0.5 Ă â1.
Magnetic Heating Experimental Method and Procedure
Magnetic heating, specific power absorption (SPA) and Intrinsic loss power (ILP) of the nanoparticles were evaluated using a commercial AC field applicator, DM2, with a system controller DM100 by nB nanoscale Biomagnetics, Spain. All the experiments were performed at frequency of 406 kHz and the temperature was monitored using a fibre optic temperature sensor and controlled by adjusting the magnetic field strength. The maximum filed strength was 15.8 kA/m. System embedded software, MaNIaC, was used to control the experiments and collect the data. Experiments were performed by placing 1 ml of a magnetic suspension in a glass vial in the centre of the DM2 applicator coil. Experiments using cells were performed by placing the T-25 flask directly in the DM2 field applicator.
Nuclear Magnetic Resonance (NMR) Spectroscopy
Nuclear Magnetic Resonance (NMR) spectroscopy is based on the nuclear magnetic resonance phenomenon. The NMR is a characteristic of the nucleus of an atom, related to the nuclear spin (I), the intramolecular magnetic field around an atom in a molecule changes the resonance frequency, consequently providing information about the molecular structure. The NMR
spectroscopy can determine an entire structure of an organic compound using one set of analytical tests (RSC, 2016).
H-NMR spectra were obtained using a Bruker fourier 300 (300MHz) spectrometer with CDCl3
and D2O as solvents at 25°C. The 5 mm outer diameter NMR tubes were used with and polyethylene cap.
Energy Dispersive X-Ray Spectroscopy (EDS)
Energy dispersive X-ray spectroscopy (EDS or EDX) is an analytical technique used to study the elemental composition of a sample. EDS is commonly combined with imaging tools such as scanning electron microscopy (SEM) or TEM. The EDS is based on interactions of the X-ray and a sample, where the impact of the electron beam on the sample produces x-rays. When the electron beam reaches the sample, electrons are ejected from the atoms leaving vacancies, these vacancies are subsequently filled by electrons from a higher state, resulting in an x-ray emission to balance the energy difference between the two electrons' states. Each element emits a unique set of peaks on its X-ray emission spectrum during bombardment by an electron beam. EDS can be used to determine the elemental composition of individual points or to map the distribution of elements in a sample (EAG, 2016).
The EDS analysis was performed to investigate the existence and distribution of elements in nanocomposites. Measurements were carried out by moving the electron beam to different positions and examine different particles. An Oxford Instruments INCA X-Sight EDS combined with TEM, operating on Microanalysis Suite, INCA version 4.15 were used for elemental analysis of the samples. The samples were prepared using 400 mesh carbon coated copper grids.