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- 1. PSA 2011 1 1 Joint Research Centre (JRC) IRMM - Institute for Reference Materials and Measurements Geel - Belgium http://irmm.jrc.ec.europa.eu/ http://www.jrc.ec.europa.eu/ Analysis of the dynamic light scattering data from the characterisation study of two nanoparticle reference materials K. Franks, A. Braun, T.P.J. Linsinger, G. Roebben PSA 2011 1
- 2. PSA 2011 2 2 What is Nano? 1 m 1 cm 1 mm 100 µm 100 nm 1 nm 0.1 nm Human Body Human Hair Virus Atom Nanomaterials 1 µm
- 3. PSA 2011 3 3 SAXS (Small-Angle X-ray Scattering) ISO/TS 13762 • Detects and assesses size of structures (e.g. particles) via scattering of x-rays at interfaces between two phases with different electron densities DLS (Dynamic Light Scattering) ISO 22412 + 13321 • Measures velocity of particles and everything which sticks to them moving through random Brownian motion in a suspension CLS (Centrifugal Liquid Sedimentation) ISO 13318-1/2 • Measures sedimentation rate of particles moving in a specific direction under centrifugal force (directed) EM (Electron Microscopy) via ISO 13322-1 • Uses images resulting from interaction between electron and particles. Less compact layers not easily detectable Main Nanoparticle Size Measuring Methods Introduction
- 4. PSA 2011 4 4 • Signal reporting: mean, median or modal • Distribution base Number Volume Light scattering Intensity Reporting of Results nm
- 5. PSA 2011 5 5 ISO 22412:2008 Particle size analysis Dynamic Light Scattering (DLS) a.) Correlation Function Analysis (cumulants method and other methods) b.) Frequency Analyses Both methods are based on the same fundamental measurement principle should give same particle diameter
- 6. PSA 2011 6 6 Correlation Function Analysis • Scattered light intensity of particles – correlated with the delayed value of itself and expressed as a function of delay time t = 0 t = ∞Time Perfect Correlation Correlation Small particles = moving quickly Large particles = moving slowly0 1
- 7. PSA 2011 7 7 Correlation Function Analysis • Theoretical shape of function is fitted e.g. cumulants method (other methods exists too e.g. CONTIN, NNLS) Diameter (nm) Amplitude NNLS Cumulants
- 8. PSA 2011 8 8 Frequency Analysis • Scattered light intensity of particles – frequency spectrum is obtained and expressed as a function of time • Information is transformed to power spectrum Particle size
- 9. PSA 2011 9 9 Frequency Analysis Time 0Light Fluctuation Signal Fast Fourier Transform Volt Frequency ω Intensity Power Spectrum
- 10. PSA 2011 10 10 Frequency ω Intensity Power Spectrum Spectrum Analyser Correlator Correlation Correlation Function Laser Detector Amplitude Diameter [nm] Time ISO 22412:2008 Particle size analysis Dynamic Light Scattering (DLS) = nominally equal methods
- 11. PSA 2011 11 2009-2011 JRC – organisation of interlaboratory comparison study (ILC) Materials and Methods Study material • 2 candidate reference material (20nm and 40nm) • higher and lower polydispersity TEM – by MVA, USA (2009) e.g. ERM® -FD100
- 12. PSA 2011 12 12 • 35 competent laboratories participated • 2 different silica nanoparticles used – ERM-FD100 (nominal particle diameter of 20 nm) – Material B (nominal particle diameter of 40 nm) • Wide range of instruments have been covered • Particle size determination by various methods – 21 data sets for DLS method evaluated • Analysed the influence of: – Analytical method, sample temperature, cuvette material, sample viscosity, optical system, scattering angle, distribution metric (intensity, volume, number), polydispersity of material
- 13. PSA 2011 13 13 Results DLS method, frequency and correlation function analysis, intensity weighted 15 20 25 30 Labno5 Labno6 Labno10a Labno10b Labno11 Labno13 Labno14 Labno15 Labno16 Labno17a Labno17b Labno18a Labno18b Labno19 Labno20 Labno21 Labno22 Labno23 Labno25 Labno26 Labno27 Intensity-weightedharmonicmean diameter[nm] Figure 1+2: DLS data set of Intensity-weighted harmonic mean diameter [nm]. The red lines are marking the calculated expanded uncertainty UCRM. ERM-FD100 Material B DLS method, frequency and correlation function analysis, intensity weighted 40 45 50 55 Labno5 Labno6 Labno10a Labno10b Labno11 Labno13 Labno14 Labno15 Labno16 Labno17a Labno17b Labno18a Labno18b Labno19 Labno20 Labno21 Labno22 Labno23 Labno25 Labno26 Labno27 Intensity-weightedharmonicmean diameter[nm]
- 14. PSA 2011 14 14 Table 1: additional measurement information
- 15. PSA 2011 15 15 DLS data analysis – in more detail Instrument Analysis Type Particle Sizing System, Nicomp DLS CC Beckman Coulter, Nanosizer N 4+ COM Horiba, LB-550 FA Malvern, Zetasizer Nano ZS CC ALV, CGS-3 CC Microtrac, Nanotrac FA Sympatec, Nanophox CC Sympatec, Nanophox COM Malvern, HPPS CC Precision Detectors, PDEXPERT COM CC = Correlation function analysis with cumulants method COM = Correlation function analysis with other methods FA = Frequency analysis Table 2: Instruments used
- 16. PSA 2011 16 16 DLS method, frequency and correlation function analysis, intensity weighted 15 20 25 30 [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [COM] [COM] [COM] [COM] [FA] [FA] [FA] [FA] Intensity-weightedharmonicmean diameter[nm] Figure 3+4: DLS data set of Intensity-weighted harmonic mean diameter [nm]. The red lines are marking the calculated expanded uncertainty UCRM. CC = correlation function analysis, cumulants method COM = correlation function analysis, other methods FA = frequency analysis DLS method, frequency and correlation function analysis, intensity weighted 40 45 50 55 [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [CC] [COM] [COM] [COM] [COM] [FA] [FA] [FA] [FA] Intensity-weightedharmonicmean diameter[nm] ERM-FD100 Material B
- 17. PSA 2011 17 17 -3 -2 -1 0 1 2 3 4 5 6 7 -4 -2 0 2 4 6 8 10 Deviation from average Material B [nm] DeviationfromaverageERM-FD100[nm] Youden plot Data DLS Method Figure 5: Youden plot shows data from 2 ILCs; 1 point/lab; x = results for Material B, y = results on ERM-FD100 CC = correlation function analysis, cumulants method COM = correlation function analysis, other methods FA = frequency analysis
- 18. PSA 2011 18 18 • 21 data sets were evaluated for DLS • Influence on result: – Distribution base (intensity, volume, number) – Polydispersity of the test material analysed – Analytical Method Correlation Function Analysis Frequency Analysis • No significant influence on result: – Sample temperature, scattering angle, cuvette material, sample viscosity, optical system
- 19. PSA 2011 19 19 Take-home message Particle size determination is dependent on •Distribution base (intensity, volume, number) •Signal reporting (mean, mode, modal) •Polydispersity of the test material Analytical Method •Level of Proficiency
Editor's Notes
- Nanoparticles are particles with external dimensions between 1nm to 100 nm, that exhibit unique properties due to their size. In order to understand the different properties of nanoparticles, reliable size and size distribution measurements are needed. Milliardstlel meter Nano 10 -09
- For the measurement set up it is important to determine the distribution (Verteilung) base in number, volume, intensity Explain equal number (4) for each particle size – in terms of number Volume, Light scattering: because of different volume, bigger particles are more scattered, with higher intensity as smaller particles. Mode – peak of distribution Median – middle of the middle of the distribution Mean - average of the distribution
- The time dependent signals is generally processed by one of two methods: time-based correlation function of frequency-based power spectrum. The two methods are mathematically related
- Correlation between two points in time , temporal distance between 2 points Correlator = relationship, context Correlator basically measures the degree of similarity between two signals over a period of time If two intensity signals are compared from one moment of time to the next moment of time a very short time later, two signals would be almost identical, perfectly correlated. Another moment of time later, the signal at that moment would be more different to the original signal and the correlation would reduce in time. It also depends whether the particle is large (moving slowly) or small (moving quickly) How on earth does one get a particle size out of this correlation function?
- Algorisms ((datenabfolge) are used to extract the decay time and to produce the particle size distribution One very common method to fit experimental data to the theoretical shape of the measured Correlation function is the cumulants method which is a polynominal series, often truncated after the quatratic term, which results in a robust method with high reproducibility. A most strict analysis approach is use of a Laplace inversion but it has its own problems. To overcome these, various data analysis methods have been developed e.g. CONTIN, NNLS. For later However, noise in the scattered intensity signal and the dependance of the scattered intensity makes resolution of broad or multimodal PSD difficult regardless of the data analysis method used. Because of these limitations, simple data analysis methods e.g. method of cumulants often estimate the particle size distributions as well as the more complex inversion methods.
- The information is then transformed into the particle size diameter via a power spectrum
- Silica nanoparticle in aqueous solution (commercially available silica) ERM-FD100 (20 nm) and ERM-FD304 (40 nm) Not perfectly spherical = “equivalent spherical” Higher polydispersity (bimodal particle size distribution)
- UCRM= Sqrt uchar2+ ubb2+ults2+ usts2 Uncertainty stadev/ squar(n)
- Diese Daten hatten wir zusaetzlich gefragt, wie auch natuerlich die Instrumente (damit dann auch deeren analytische Methode) Mein talk ist dann ueber die Auswertung der dieser Daten
- Measures the deviation from the mean value (absolut values or procent) What do we see? 45 degree line give the systematic bias, everything else is a random bias. Point at -2 is double the time deviation, at -4 four time the deviation and so on, same on the positive scale What is also very nice to see, all cumulatns methods (blue fit in very nicely, all together) the red one, other methods are widely overlapping with the method of cumulants however one outlier, and the green points representing the frequency does not overlap with the other two methods used. missed die Abweichungen vom Mittelwert es braucht 2 ringversuche mit 2 materialien die zur gleichen Zeit vermessen worden sind Die Abweichugn des einen materials weren auf der xAchese, die des anderen auf der yAchse aufgetragen. was man hier sieht sind das cumulants und andere methoden gut zusammenpassen, freuquency passt uebrehaupt nicht ins bild, liegt auch nicht auf der 45°Achse In diesem Fall gut fuer die ISO documentation, falls es zu einer Abaenderung kommt. Hier wird deutlich gezeigt, dass zumindest fuer dieses Material beide Analysenmethoden, correlation fkt mit cumulants oder anderen Methoden nicht zu dem gleichen Ergebnis gruen = random errow blau/red = systematical errow