Posted in Исследования

Zeta potential measurement principle (Laser Doppler Electrophoresis)

Many nanoparticles or colloidal particles have a surface charge when they are suspension. When an electric field is applied, the particles move due to the interaction between the charged particle and applied field. The direction and velocity of the motion is a function of particle charge, the suspending medium, and the electric field strength. Particle velocity is then measured by observing the Doppler shift in the scattered light. The particle velocity is proportional to the electrical potential of the particle at the shear plane which is zeta potential. Thus, this optical measurement of the particle motion under an applied field can be used to the determine zeta potential.

Particle motion under an applied electric field is known as electrophoresis. The method used by SZ100 is known as laser Doppler electrophoresis. Sample particles are suspended in a solvent af known refractibe index n, velocity η and dielectric constant ε. The sample is irradiated with laser light of wavelength λ. An electric field with strength E is applied. Due to the electric field, the particles are moving. Since the particles are moving, the scattered light at angle ϑ is measured and the particle velocity V is determined from the frequency shift. Mobility is then readily obtained as the radio of velocity to electric field strength V/E. Zeta potential is then found mobility using a model, the most common of which is the Smulochowski model.

The following equation is used for the relationship between the calculated electrical mobility and zeta potential.

where ζ – Zeta potential, U – Electrical mobility, E – Electric field strength, ε – Solvent dielectric constant, n – Solvent refraction index, η – Solvent viscosity, f(ka) – henry coefficient

Overviews and methods

Under construction

Equipment

Laser particle analyzer SZ100

Contacts

The Leading Researcher in optical systems Alexandr Shimko

Specialist in spectroscopy and granulometry Anastasia Povolotckaia

Specialist in optical systems Alexandra Mikhaylova

Posted in Исследования

Absorption spectroscopy

Absorption spectroscopy is used to obtain the absorption spectra (transmission), diffuse scattering and measurement of the optical density of matter in different states of aggregation in the ultraviolet, visible and near-infrared regions of the spectrum. This method is used to the vast majority of information about the structure of the material at the atomic and molecular level, how atoms and molecules behave when combined in condensed matter. Feature of optical spectroscopy compared to other types of spectroscopy is most structurally organized matter (larger atoms) interacts resonantly with the electromagnetic field in an optical frequency range. Therefore, optical spectroscopy is widely used for studying matter.

Also absorption spectroscopy is used:

- qualitative and quantitative analysis of the substance on the changes in the position, intensity and shape of the absorption bands;

- measurement of the reflectance spectra of samples;

- determination of the optical characteristics of the glass with a high absorption coefficient, optical elements with antireflection coatings, narrow-band (DWDM) filters, fiber optical communication components of flat panel displays, solar cell elements and their coatings, paints, color printing, etc.

Being a fairly simple and straightforward technique, absorption spectroscopy can give important information about the spatial structure of nano-objects.

Transmission spectra of filters SZS7, SZS8 and SZS9

Overviews and methods

Under construction

Equipment

UV/Vis/NIR spectrophotometer Lambda 1050

Contacts

The Leading Researcher in optical systems Alexandr Shimko

Specialist in optical systems Alexandra Mikhaylova

Posted in Исследования

Luminescence spectroscopy

ОFluorescent spectroscopy differ from other spectroscopic techniques because of the recorded spectral dependence is a function of two variables - the excitation wavelength λ_ex and emission wavelength λ_em. If λ_ex is kept constant and λ_em is scanned, the measured luminescence spectrum is emission (spectral dependence of the luminescent intensity on the wavelength). If you are scanning λ_ex at constant λ_em, you measure excitation spectrum (spectral dependence of the excitation efficiency on the excitation wavelength).

Luminescence methods include studies using fluorescence and phosphorescence. Fluorescent measuring are the most widely used as methods for analysis and monitoring of chemical and biochemical reactions and kinetic studies for the fast reactions of electron-excited molecules.

Applications of luminescence spectroscopy for analytical purposes embrace identification of substances, detection of low concentrations of substances, control the changes of studied matter, determination the purity of compounds. Also luminescence studies are used to measure kinetics of conventional chemical reactions. The high sensitivity allows detecting the small degree of substances conversion and sometimes it is possible to establish the mechanism of chemical reaction.

Luminescent methods are used in biology, in particular for the study of protein structure by fluorescent probes and labels. Also they are successfully applied in the study of fast reactions of electronically excited molecules. Such reactions are accompanied by decreasing of fluorescence intensity due to fluorescence quenching. Quenching processes compete with the deactivation of the excited molecules by other mechanisms. Since the fluorescence decay time of about 10^-8s, fluorescent methods are commonly used to study the kinetics of fast reactions of excited molecules that occur during a 10^-7–10^-10s.

Luminescence spectrum of YVO₄:Eu 8 at.% nanopowder (λ_ex = 300 nm)

Overviews and methods

Under construction

Equipment

Modular spectrofluorometerFluorolog-3

Fluorescence spectrometer Lumina

Contacts

The Leading Researcher in optical systems Alexandr Shimko

Specialist in spectrofluorimetry Ilya Kolesnikov

Specialist in spectroscopy and granulometry Anastasia Povolotckaia

Specialist in optical systems Alexandra Mikhaylova

Posted in Исследования

The Fourier Transform Infrared Spectroscopy (FT-IR)

FT-IR spectroscopy (FT-IR) is a well-known and proven technology for analysis and identification of unknown chemicals. The method is based on a microscopic interaction between infrared light and a chemical substance by a process of absorption and results in a set of ranges, called the spectrum (the spectrum is unique for chemical substance and serves as a "molecular fingerprint"). Despite the fact that FT-IR - is widely applicable method, it uses the analysis of the chemical substances’ intrinsic properties, thanks to that FT-IR is very suitable for comparison with the spectral library. With the use of an extensive database, the comparison with the spectral library makes it possible to quickly identify thousands of chemicals on the base of their unique "molecular fingerprint".

Besides the absorption is the characteristic of the individual groups of atoms, its intensity is directly proportional to their concentration. Thus, by measuring the absorption intensity after a simple calculation provides the amount of this component in the sample.

In their capability method is almost universal. FTIR spectroscopy is used for determining the content of organic and inorganic substances and compounds in solid, liquid and gaseous samples (foods, soil, metals and their alloys, polymers, etc.).

The absorption spectrum of the polyethylene glycol, filmed by FT-IR spectrometer Nicolet 8700

Reviews and methods

Under construction

Equipment

FT-IR spectrometer Nicolet 8700

Contacts

The Leading Researcher in optical systems Alexandr Shimko

Specialist in spectroscopy and granulometry Anastasia Povolotckaia