rus
Issue #1/2016
A.Marakhova, V.Zhilkina, E.Blynskaya, K.Alekseev, Ya.Stanishevskiy
Determination of nanoparticle size in colloidal solutions by dynamic light scattering
Determination of nanoparticle size in colloidal solutions by dynamic light scattering
It was shown, that particle sizes could differ in many times due to the method of analysis. The size distributions for particles in suspension "silver-glycine" and in Protargol was experimentally researched.
Теги: dynamical light scanning low-temperature adsorption scanning electron microscopy динамическое светорассеяние низкотемпературная адсорбция электронная микроскопия
Great interest in the study of nanostructures of different chemical composition, structure and morphology is caused by extraordinary physicochemical, electromagnetic, optical, mechanical and other properties of nanomaterials that opens wide prospects of their practical applications [1–4, 6]. The small size of nanoparticles in the range from 1 to 100 nm determine the uniqueness of their properties [5]. The large number of analytical methods is developed (table 1) to determine the size of nanoparticles.
Each of the methods listed in table.1, has certain advantages and limitations. Scientists of the Reshetnev Siberian State Aerospace University have measured the size of the iron particles in various ways (table.2). Table 2 shows that the most reproducible results were obtained using scanning electron microscopy, low-temperature adsorption and dynamic light scattering (photon correlation spectroscopy). Dynamic light scattering (DLS) has a number of advantages, allowing to determine the effective hydrodynamic radius of the particles in situ in a liquids, and is an effective method of investigation of nano-objects of different origin [9, 11]. This method does not require calibration, the sample preparation is reduced to the dedusting, and often (for strongly scattering systems) this simple, but very time-consuming procedure is not necessary. Modern DLS spectrometers are relatively inexpensive and allow to quickly perform the analysis [2]. The small footprint of the devices allows to use them in express laboratories.
Of course, like other methods, DLS has disadvantages: the dependence on the adequacy of the mathematical model that is in the basis of correlation analysis; in some cases, the complexity of selection of the dispersion medium or the need to know its composition; possible agglomeration of particles in the suspensions [7]. However, in some cases, agglomeration can be avoided by replacing the dispersion medium, adding stabilizer, or the use of dispersion [4]. Thus, significant advantages and minor disadvantages make DLS one of the most popular methods of determination of the size of macromolecules [8, 9, 11].
The determination of particle size by DLS is based on measurement and analysis of fluctuations in time of scattered light intensity in the capacity containing particles in the solvent. Due to random (Brownian) motion of particles caused by uncompensated impacts of the solvent molecules, the intensity of light oscillates about its average value. The frequency of these oscillations one can obtain information about the diffusion coefficient of the particles, which, in turn, depends on their sizes. The frequency of these oscillations allows to estimate the diffusion coefficient of the particles, which, in turn, depends on their size.
When the light beam impinges on the particles, light is scattered due to the interaction of electromagnetic waves with an inhomogeneous medium. The basic assumption of the DLS is that the scattered light has the same frequency as the stimulating light beam [7]. However, an observer perceives optical Doppler effect caused by movement of particles. The frequency of the scattered light is shifted by small changes, which are proportional to the speed of the particles. The intensity of scattered light is not constant, but fluctuates about the mean value. Passing through the medium the beam passes on the way to a huge number of particles moving in all directions with different speeds. The beam passing through the environment, meets the huge number of particles moving in all directions with different speeds. Thus, the result is a continuous spectrum of the probability of frequency shifts, the center of which is the frequency of the exciting beam [7].
To study the size of the nanoparticles the Zetasizer Nano ZS (Malvern Instruments, UK) is often used. It is a highly effective two-angle analyzer of size of particles and molecules (from 0.3 nm to 10 µm) with non-invasive backscatter optics. The device is designed for accurate detection of aggregates and for measurement of small-volume or dilute samples and samples with a very high concentration using DLS method [10, 12, 13].
Another device that allows to measure the size of the particles in a fluid, is the NANOPHOX (Sympatec, Germany) based on photon cross correlation Spectroscopy (PCCS). This method allows the simultaneous measurement of particle size and aggregate stability of opaque suspension or emulsions of nanoparticles in the range from 1 nm up to several micrometers. In PCCS two independent laser beams pass through the same sample volume creating two independent spectral pattern due to multiple scattering on the way to the receiver. The detected signals are similar in profile, but the noise is superimposed on them. The intensity fluctuations are observed by two detectors positioned such that the scattering vectors were the same. The advantage of this method is the possibility to compare signals of scattered light to isolate identical peaks, which are generated by single interactions of scattered photons with the particles in the sample (Fig.4). The specific geometric position of the beams is required to obtain the desired result [5].
In the framework of the present study the comparative analysis of particle sizes in suspensions of silver with glycine and Protargol using Zetasizer Nano ZS and NANOPHOX was carried out. Both devices operate both in automatic and in manual mode. Sample preparation is not required, as the studied samples are liquid. Fig.1 presents distribution of silver nanoparticles in glycine depending on their size obtained using NANOPHOХ device. Fig.2 shows cross-correlation function for the same sample, which reflects the probability that the intensity of scattered light corresponding to a particular configuration of a measured particles, is reliable measured during the correlation time [4]. Presented correlation function allows to estimate the stability of a suspension of silver with glycine.
The distribution in volume depending on the particle size of Protargol is presented in Fig.3, and Fig.4 shows the correlation function for this sample. The analysis of the correlation function indicates the absence of aggregation or sedimentation in the Protargol.
Graphical interpretation of the results obtained using the Zetasizer device for silver particles with glycine, is represented in Fig.5. The results of determination of particle size in the samples are given in table.3.
The obtained data allow to conclude about the adequate convergence of results. Herewith the NANOPHOХ device is characterized by a more user friendly software and interpretation of results with better speed of measurement. The studied samples have a size of particles above the nano-level in its classical sense.
Each of the methods listed in table.1, has certain advantages and limitations. Scientists of the Reshetnev Siberian State Aerospace University have measured the size of the iron particles in various ways (table.2). Table 2 shows that the most reproducible results were obtained using scanning electron microscopy, low-temperature adsorption and dynamic light scattering (photon correlation spectroscopy). Dynamic light scattering (DLS) has a number of advantages, allowing to determine the effective hydrodynamic radius of the particles in situ in a liquids, and is an effective method of investigation of nano-objects of different origin [9, 11]. This method does not require calibration, the sample preparation is reduced to the dedusting, and often (for strongly scattering systems) this simple, but very time-consuming procedure is not necessary. Modern DLS spectrometers are relatively inexpensive and allow to quickly perform the analysis [2]. The small footprint of the devices allows to use them in express laboratories.
Of course, like other methods, DLS has disadvantages: the dependence on the adequacy of the mathematical model that is in the basis of correlation analysis; in some cases, the complexity of selection of the dispersion medium or the need to know its composition; possible agglomeration of particles in the suspensions [7]. However, in some cases, agglomeration can be avoided by replacing the dispersion medium, adding stabilizer, or the use of dispersion [4]. Thus, significant advantages and minor disadvantages make DLS one of the most popular methods of determination of the size of macromolecules [8, 9, 11].
The determination of particle size by DLS is based on measurement and analysis of fluctuations in time of scattered light intensity in the capacity containing particles in the solvent. Due to random (Brownian) motion of particles caused by uncompensated impacts of the solvent molecules, the intensity of light oscillates about its average value. The frequency of these oscillations one can obtain information about the diffusion coefficient of the particles, which, in turn, depends on their sizes. The frequency of these oscillations allows to estimate the diffusion coefficient of the particles, which, in turn, depends on their size.
When the light beam impinges on the particles, light is scattered due to the interaction of electromagnetic waves with an inhomogeneous medium. The basic assumption of the DLS is that the scattered light has the same frequency as the stimulating light beam [7]. However, an observer perceives optical Doppler effect caused by movement of particles. The frequency of the scattered light is shifted by small changes, which are proportional to the speed of the particles. The intensity of scattered light is not constant, but fluctuates about the mean value. Passing through the medium the beam passes on the way to a huge number of particles moving in all directions with different speeds. The beam passing through the environment, meets the huge number of particles moving in all directions with different speeds. Thus, the result is a continuous spectrum of the probability of frequency shifts, the center of which is the frequency of the exciting beam [7].
To study the size of the nanoparticles the Zetasizer Nano ZS (Malvern Instruments, UK) is often used. It is a highly effective two-angle analyzer of size of particles and molecules (from 0.3 nm to 10 µm) with non-invasive backscatter optics. The device is designed for accurate detection of aggregates and for measurement of small-volume or dilute samples and samples with a very high concentration using DLS method [10, 12, 13].
Another device that allows to measure the size of the particles in a fluid, is the NANOPHOX (Sympatec, Germany) based on photon cross correlation Spectroscopy (PCCS). This method allows the simultaneous measurement of particle size and aggregate stability of opaque suspension or emulsions of nanoparticles in the range from 1 nm up to several micrometers. In PCCS two independent laser beams pass through the same sample volume creating two independent spectral pattern due to multiple scattering on the way to the receiver. The detected signals are similar in profile, but the noise is superimposed on them. The intensity fluctuations are observed by two detectors positioned such that the scattering vectors were the same. The advantage of this method is the possibility to compare signals of scattered light to isolate identical peaks, which are generated by single interactions of scattered photons with the particles in the sample (Fig.4). The specific geometric position of the beams is required to obtain the desired result [5].
In the framework of the present study the comparative analysis of particle sizes in suspensions of silver with glycine and Protargol using Zetasizer Nano ZS and NANOPHOX was carried out. Both devices operate both in automatic and in manual mode. Sample preparation is not required, as the studied samples are liquid. Fig.1 presents distribution of silver nanoparticles in glycine depending on their size obtained using NANOPHOХ device. Fig.2 shows cross-correlation function for the same sample, which reflects the probability that the intensity of scattered light corresponding to a particular configuration of a measured particles, is reliable measured during the correlation time [4]. Presented correlation function allows to estimate the stability of a suspension of silver with glycine.
The distribution in volume depending on the particle size of Protargol is presented in Fig.3, and Fig.4 shows the correlation function for this sample. The analysis of the correlation function indicates the absence of aggregation or sedimentation in the Protargol.
Graphical interpretation of the results obtained using the Zetasizer device for silver particles with glycine, is represented in Fig.5. The results of determination of particle size in the samples are given in table.3.
The obtained data allow to conclude about the adequate convergence of results. Herewith the NANOPHOХ device is characterized by a more user friendly software and interpretation of results with better speed of measurement. The studied samples have a size of particles above the nano-level in its classical sense.
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