Dispersion and characterisation of nanoparticles

Transcription

1 Date Event title Title of Event: Date: June 16 th, 2014 NanoValid Summer School, Tallinn/ Estonia Dispersion and characterisation of nanoparticles Partner representative name: Partner organisation name: Annegret Potthoff, Tobias Meißner Fraunhofer-Gesellschaft (Germany) 1

2 Fraunhofer-Gesellschaft, the largest organisation for applied research in Europe Rostock Itzehoe Lübeck Bremerhaven Hamburg Oldenburg Bremen 66 institutes and independent research units More than 22,000 staff Headquarter in München Berlin Münster Lemgo Gelsenkirchen Dortmund Oberhausen Paderborn Duisburg Kassel Köln Schmallenberg Euskirchen Bonn, Sankt Augustin Aachen Wachtberg Sulzbach Remagen Frankfurt Darmstadt Mannheim St. Ingbert Kaiserslautern Alzenau Wertheim/ Bronnbach Saarbrücken Karlsruhe Pfinztal Ettlingen Stuttgart Hannover Goslar Göttingen Würzburg Braunschweig Erfurt Jena Halle Schkopau Ilmenau Potsdam-Golm Magdeburg Hermsdorf Leipzig Leuna Bayreuth Erlangen, Nürnberg, Fürth Chemnitz Sulzbach-Rosenberg Regensburg Teltow Freiberg Straubing Wildau Cottbus Dresden Zittau Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) in Dresden Delevopment of state-of-the-art advanced ceramic materials Characterisation of materials Powder and suspension characterisation Freiburg Kandern Efringen-Kirchen Augsburg Weßling Freising München, Garching Prien Holzkirchen Fraunhofer

3 Topics Physico-chemical characterisation for toxicologic assessment Relevance of nanomaterial definitions for particle characterisation Dispersion decides Colloid chemical stability of nanoparticles/ analysis of zeta potential Particle size analysis Dynamic Light Scattering (DLS) Comparison to Nanoparticle Tracking (NTA) Applications and examples Powder characterization Dispersion of nanoparticles prior to toxicological tests Proteins natural dispersant aids How to analyze a nanostructured powder? Conclusions 3

4 Physico-chemical characterisation for toxicological assessment Which parameters? Physical description Chemical composition Extrinsic properties When? How often? Batch Time From what? Nanomaterial ISO/TR 13014:2012 4

5 What does it mean nanomaterial? Definition according to ISO/TS :2011 Nanostructured material Material with an nanoscaled (1 nm 100 nm) internal or external structure Nanostructured powder Nanocomposite Solid nanofoam Nanoporous material Fluid nanodispersion Agglomerates, aggregates, nanoparticles 5

6 COMMISSION RECOMMENDATION on the definition of nanomaterial `Nanomaterial` means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm 100 nm. Nanomaterials by EU definition are among nanostructured materials according to ISO norm. EU commission recommends, that about 50 % of particles calculated from a number weighted distribution have to comply with this condition, while there is no similar definition in ISO norm. 2011/696/EU, recommendation of 18 October

7 Materials considered in this presentation Nanostructured material Nanostructured powder Nanocomposite Solid nanofoam Nanoporous material Fluid nanodispersion Agglomerates, aggregates, nanoparticles nanoobjects Independent on amount of nanoscaled material. 7

8 Which pc parameters are the most relevant for toxicological assessment Physical description Particle size/ particle size distribution State of agglomeration and aggregation Particle shape Specific surface area Chemical composition Composition Purity/ impurities Surface chemistry Extrinsic properties Surface charge Solubility Dispersability Nanoparticle Suspending media Solid-liquid interface ISO/TR 13014:2012 8

9 How do they look like Nanostructured powders and nanocomposites Fluid nanodispersions Wikipedia/Nanogold Example: TiO 2 P25 (Evonik) Nanoparticles form aggregates and agglomerates Example: Au dispersion Nanoparticles are separated Particle? Particle size? Particle size analysis? 9

10 How do they occur Surface chemistry? Surface charge? Interactions at the interface? Nel et al.,

11 Prior to any analysis we have to check, what we would like to know! Dispersion decides 11

12 Characterisation of nanomaterials requires information about dispersability Eyjafjallajokull 2010 Natural nanoparticle dispersed in air Oberdörster 2005 Inhalation studies for toxicological testing Dispersion in air Analysis after dry dispersion 12

13 Characterisation of nanomaterials requires information about dispersability Technical nanoparticle dispersed in fluid Preparation prior to toxicological or ecotoxicological testing Dispersion in liquid Analysis after wet dispersion 13

14 Dispersion decides (1) Particle s behaviour Powders in liquids Influencing factors Kind of particle stress Specific energy input (time, intensity) Agglomerates or aggregates and primary particles? 14

15 Dispersion decides (2) Particle s behaviour in fluids Charges at particle surfaces Influencing factors ph value Electrosteric effects Natural or artificial dispersant aids 15

16 Colloid chemical stabilized? Analysis of zeta potential 16

17 Surface charges and zeta potential Strongly bounded ions are fixed at particle surfaces (= inner and outer Helmholtz layer) Loosely associated ions for charge compensation (= diffuse double layer) Stern model describes conditions in systems with moderate ionic strength ( mol/l). Thickness of diffuse double layer depends on concentration and charge of ions Zeta potential: Difference between potential on shear plane and potential within the fluid (example: negative) starre Fixed Schicht layer Diffuse double layer Shear plane diffuse Schicht 17

18 Colloid chemical stable? Value of zeta potential Repulsive forces between particles Electrostatic stability Agglomeration of particles Value of zeta potential 0 Repulsive forces between particles Electrostatic stability Agglomeration of particles Stable suspensions: suspended or with sedimentation Instable suspensions: flocculation or coagulation (agglomeration) Colloid chemical stable suspensions might be stable against sedimentation, but they do not necessarily have to! 18

19 Analysis of zeta potential Measurement principle Electrophoretic light scattering * Streaming potential Electroosmosis Sedimentation potential Electro sonic amplitude * Concentration Up to 5 vol% Up to 5 vol% Below 0,5 wt% Below 0,5 wt% 1 to 40 vol% ISO norms are available for - sampling and sample splitting and - *-marked measurement principles. 19

20 Electrophoretic light scattering (ELS) measurement principle Acceleration of particles in an electric field Stokes friction acts against particle movement F E Accelerating force F R Retarting force Shifted counter ion cloud Moving particle (negative charge) E F R F E + F R = -6 r v F E = E. q When F E = F R constant particle movement v / E = q / 6 r 20

21 Zeta potential calculation from electrophoresis v / E = q / 6 r v / E = µ e = 2 o r f[ r] / 3 HENRY Equation Small Particle with thick Double Layer Large Particle with a thin Double Layer r < 0.1 r > 100 HUECKEL Equation µ e = 2 r / 3 µ e = r ) / Correction for surface conductivity Correction function for changes of dielectricity and viscosity Correction for particle shape Corrections for high ion and particle concentrations SMOLUCHOWSKI Equation 21

22 Sample preparation finalized successfully Analysis of particle sizes 22

23 Analysis of particle size distributions of dispersed nanomaterials in liquids Measurement principle Measurement range Concentration Dynamic light scattering */ Photon cross correlation spectroscopy * 1 nm 5 µm Up to 5 vol% Nanoparticle tracking 10 nm 1 µm Up to 10 8 particle/ml Ultrasound attenuation * 4 nm 40 µm 1 to 40 vol% Laserlight diffraction * 20 nm 3000 µm Below 0,5 wt% Centrifugal sedimentation * 10 nm 100 µm Below 0,5 wt% ISO norms are available for - sampling and sample splitting - dispersing and - *-marked measurement principles. 23

24 Dynamic light scattering (DLS) measurement principle Laserlight Input Laserlight Output Beam stop Detector Analyzation of scattered light Medium intensity I s Correlator Is 2 Is 2 Fluctuation of scattered light intensity at detector t t Autocorrelation function (depends on diffusion coefficient D) Malvern 24

25 Dynamic light scattering (DLS) measurement principle Small particles: Correlogram G1 vs time G Diffusion velocity high Scattered light intensity low I time t Time(us) Large particles: G1 vs time G Diffusion velocity low Scattered light intensity high I Malvern time t Time(us) Correlation function 25

26 Dynamic light scattering (DLS) result x kbt 3 D Calculation of particle size from diffusion coefficient: x DLS Polydispersity index PI (between 0 and 1) Depending on sample preparation hydrodynamic diameter x DLS may describe diameter of primary particles, aggregates or agglomerates Calculation of intensity-weighted particle size distribution, conversion into volume-weighted particle size distribution possible 26

27 Dynamic light scattering (DLS) Comparison of different approaches Presence of nanoparticles and serum proteins in cell culture medium Analysis using mean particle size and PI (cumulant method) difficult Usage of complex algorithm calculating size distributions Intensity-weighted distribution Volume-weighted distribution Example 1 Example 2

28 Dynamic light scattering (DLS) Comparison of different approaches Presence of nanoparticles and serum proteins in cell culture medium Analysis using mean particle size and PDI (cumulant method) difficult Usage of complex algorithm calculating size distributions Intensity-weighted distribution Volume-weighted distribution Example 1 Example 2 Simultaneous detection of proteins and particles not always possible using DLS scattered light intensity r 6 -dependency Simple cumulant method detects proteins via increased PI, but mean size is error-prone SiO 2 particles appear smaller than they are

29 Volume-weighted or number-weigthed concentration? 95 % below 100 nm V tennis balls! = V medicine ball Nano? 40 % below 100 nm x tb x mb x tb x mb Number-weighted 10 distribution 100 Volume-weighted 1000 distribution Particle size [nm] 29

30 Dynamic Light Scattering vs. Nanoparticle Tracking Analysis Analysed particle property Analysis of particle velocity Calculated result DLS Brownian motion Time dependent light scattering Diffusion coefficient from Einstein equation Hydrodynamic diameter NTA Brownian motion Video analysis of particle tracking Diffusion coefficient from Einstein equation Hydrodynamic diameter Particle size range 1 nm 5 µm 10 nm 1 µm Results x DLS, PI; intensity or volume weighted distribution Number weighted particle size distribution, concentration Concentration Up to 5 vol% Up to 10 8 particle/ml Compatibility ISO/TS :2011 EU commission

31 Advantages and limitations DLS NTA Limitation due to sedimentation of large (or high-aggregated!) particles, especially for high-density materials Good for fluid nanodispersions and for well-dispersable nanostructured powders and nanocomposites (narrow PSD) Few small particles very difficult to detect in presence of large particles Detection of time stability of PSD possible (including agglomeration processes) Small particles detectable in presence of large particles Detection of time stability of PSD should be possible Analysis in physiological and in ecotoxicological relevant media possible Particle concentrations as often tested in in-vitro tests Particle concentrations as often tested ecotoxicological tests

32 Tools for sample preparation and particle size analysis available Applications and examples 32

33 Example 1: Powder characterisation Particle size = size of aggregates and primary particles = smallest dispersable unit Requirements for dispersion Colloid chemical stability high = high value of zeta potential dosage of dispersant necessary Complete deagglomeration = high specific energy input dispersion by ultrasound (sonotrode) Dispersion strategy prior to powder characterisation is described in ISO 14887:2000 Comparison to BET ~ 45 m²/g x BET ~ 21 nm 500 nm TiO 2 P25 Size from SEM or TEM image 33

34 Example 1: Comparison of results for particle size analysis 500 nm TiO 2 P25 Analysis in water containing polyphosphate ZP Smoluchowski > 60 mv DLS measurement BET ~ 45 m²/g (x BET ~ 21 nm) Size from SEM or TEM image Well dispersable powder, which consists of small aggregates (x DLS > x BET ) Complementary results from different measurement methods 34

35 Example 2: Dispersion the main challenge Dispersion of nanomaterials for toxicological testing No standardized procedure for dispersion available!!! Results strongly depend on sample preparation. Recommendation for Dispersion SOP will be developed within NanoValid project. 35

36 Decision of principle considerations Under relevant/ possible conditions Accept agglomeration Yes Disperse directly in media Yes No No Worst-case scenario Predispersion in water Smallest dispersable unit Disperse directly in media No Specify dispersant aid Yes Specify energy input Characterisation, i. e. by DLS Predispersion in water 36 Origin: D4.32 (NanoValid project)

37 Comparison of results Example: TiO 2 NP in PBS Smallest dispersable unit x DLS remains constant during testing Time-dependent analysis Specify concentration of BSA, which acts as a dispersant aid 37

38 Comparison of results Example: TiO 2 NP in DMEM + FBS Smallest dispersable unit Reduced agglomeration Increase Energy-input-dependent analysis Specify specific energy input 38

39 First results of a round-robin test 500 nm BET: 50 m²/g x BET ~ 40 nm Silica OX50 SOP with detailed specification of concentration, dispersion, energy input etc. 4 out of 7 partners receive similar results 39

40 Example 3: Zeta potential analysis in toxicological tests Challenge: Analysis of zeta potentials in physiological media Conductivity compression of electric double layer low values of zeta potential zeta potential [mv] tungsten carbide (WC) lysozyme (LSZ) WC + LSZ Analysis of solid-liquid interface ph Due to adsorption of proteins nanoparticles change their behaviour in presence, i. e. of LSZ. Proteins may act as dispersant aids x DLS remains constant. 40

41 Example 4: How to analyze a nanomaterial? 1 µm 200 µm Nanostructured powder according to ISO/TS :2011 Bad dispersability aggregates are micron-scaled and settle down very fast DLS does not meet all requirements! 41

42 Example 4: How to analyze a nanomaterial? Use same dispersion procedure as for nanoparticles Analysis by laserlight diffraction aggregates of up to 100 µm in size! 42

43 Conclusions Dispersion decides, but is not yet standardized for nanotoxicological testing Nanomaterial or not sometimes a question of definition Zeta potential - a tool for stability analysis DLS or NTA? DLS + NTA + BET + SEM/TEM + = results are complementary DLS a tool for analysis in physiological and in ecotoxicological relevant media Particle size analysis of nanostructured materials sometimes requires devices other then DLS As particle properties change depending on time, batch or surrounding behaviour, they always need to be investigated prior, while and after toxicological testing. 43

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