Particle size and stability analysis in turbid suspensions and emulsions with Photon Cross Correlation Spectroscopy, PCCS NANOPHOX

Transcription

1 Particle size and stability analysis in turbid suspensions and emulsions with Photon Cross Correlation Spectroscopy, Basics PCS/PCCS Zeta potential Conclusions PCCS NANOPHOX 11E05A21L1E

2 What is a Nanoparticle? ISO/TS 27687: August 2008 Nanotechnologies - Terminology and definitions for nano-objects nanoparticle, nanofibre and nanoplate General particle definitions in accordance with ISO TC 24/SC 4, TC 146 and TC 209: Particle: Very small piece of substance with defined physical borders Aggregate: Conglomerate of fix bound or fused particles where the resultant surface is considerably smaller than the sum of the calculated single surfaces Agglomerate: Conglomerate of only light bound particles or aggregates where the resultant surface is similar to the sum of surfaces of the single components Nanopartikel: a Nano-Object with three external dimensions in the Nano range from about 1 nm to 100 nm 11E05A21L2E

3 TC 229 "Nanotechnologies" has definied: Nanomaterial (one or more external dimensions or an internal or surface structure on the nanoscale) ISO/NP TS Nano-object (one or more external dimensions on the nanoscale ISO/TS Nano-structured material (inner or surface structure on the nanoscale) ISO/WD TS Nanoparticle (3 ext. dmensions on the nanoscale) Nanotubes (2 ext. dimensions on the nanoscalei) Nanoplates (1 ext. dmension on the nanoscale) Material with nanostructured surface Assembled Nanomaterial Shellstructures Nanocomposite single Nanotubes free Nanoplates fumed silica hollow Al-Shellstructures Nanotubebundle NIST-Goldstandard Silicasolcomposite 11E05A21L3E

4 Size scale and borders of optical measuring principles 11E05A21L4E

5 Particle size analyis in µm - & nm - range micrometre interaction of laser light with particles Diffraction: decreasing particle size increases the diffractionangles as well as the blurring of the diffraction pattern nanometre Scattering: outside low angle light scattering (LALLS) particle diameters, only light scattered at wide angles is available for size measurement 11E05A21L5E

6 Scattered light intensity versus particle size I S Rayleighscattering ~x 6 Fraunhofer diffraction ~x 2 Miescattering x << x ~ x >> x 11E05A21L6E

7 Particles in the nanometre range 1827 the botanist Robert Brown discovered randomly swirling particles under his microscope, which he assumed to being microbes Nano particles in thermal motion, activated by the molecular movement of the continuous liquid The phenomenon was correctly assumed by W. Ramsay in 1876 and proven by A. Einstein and M. von Smoluchowski in 1905/06. 11E05A21L7E

8 Basics of Brownian Molecular movement Due to elastic collisions of the liquid molecules particles are accelerated Speed and radius of the resulting movement are determined through: Mass and size of particles (small particles move fast, large particles only slow) Viscosity of sample (the kinetic energy of the liquid molecules is reversely related to viscosity) Particles dispersed in liquids are always surrounded with a hydrodynamic hull (which sticks to the particle until shear stress limit) In extreme concentration hindered mobility occurs. The hydrodynamic layers influence each other In principle PCS/PCCS instruments only determine hydrodynamic diameters thus being equivalent to shear diameter and Zeta-potential 11E05A21L8E

9 Theoretical background Stokes Einstein relation valid for singular scattered light only! D (x) = k B T/3x D diffusion constant k B T Boltzmann constant absolute temperature viscosity of continuous medium x particle diameter expressed with auto correlation function G (t): G() = I s (,0) I s (,) = I 2 (1 + exp(-2 D(x) q 2 )) I 2 (1 + exp(-2 q 2 k B T /3x)) decay constant ~ diffusion = 1/particle size ( k B T/3 ) 11E05A21L9E

10 Brownian Motion interaction of laser light with particles in the nanometre range Intensity I(t,) I(t, ) t = 0 t = t t = 2t time t the changing short-range order of the particles yields a fluctuating intensity distribution the intensity related to the scattering angle oscillates with time t 11E05A21L10E

11 Determination of particle size NANOPHOX applies a multiple - - evaluation to determine the correlation function This means detecting the similarity while shifting the intensity signal with increasing decay times 11E05A21L11E

12 Determination of particle size I The correlation function G() determines the relation between the diffusion coefficient D(x) and the decay time. G( ) I I S A S,0 I, 2 B 1 e 2D(x)q 2 Attention please! It is only vali for single scattered light! I 2 1 e 2q 2 k B T 3 x Decay time ~ Diffusion = 1/Particle size ( k B T/3 ) 11E05A21L12E

13 G()-1 Determination of particle size II 1. Calculation of auto corrolation function G(t) 2. Determination of particle size from slope ln(g(t) -1) the decay constant (correlation/time) decreases with increasing particle size = 0 = 1ms = 2ms Intensity I(t,) 1 0,8 0,6 0,4 0, nm 200nm 100nm 50nm decay rate 1/Particle size 0,001 0,01 0, / ms 11E05A21L13E

14 PCS setup and limitations Only valid for non interacting spherical particles Single scattered laser light Multiple scattering in turbid, concentrated suspensions distorts the result depends on concentration To avoid multiple scattering PCS works at extremely low concentrations only: low scattered light intensity poor signal to noise ratio long measuring times dilution is not only time consuming but often not applicable pollution dust destroys the result stability of a sample? 11E05A21L14E

15 PCCS as improvement of PCS Any possibility for Improvement of the principle? elimination of influence of multiple scattering! a special PCS technology first described by: L.B. Aberle et.al.: Appl. Opt. 37, 6511 (1998), Appl.Phys. 32, 22 (1999) PCCP 1, (1999), Macromol. Symp. 162, (2000) R. Xu, Particle Characteriz.: Light Scattering Methods,Kluwer (2000) P. N. Pusey, Curr. Op. Coll. Interf. Sci. 4, 177(1999), etc. for high solid concentrations in turbid samples enables a new way of stability analysis 11E05A21L15E

16 PCCS setup The initial laser beam is split into two partial beams. The beams intersect in the cuvette. Two detectors detect two series of light intensities: IA(t1),IA(t2) IA(tn) IB(t1),IB(t2) IB(tn) Scattering volume ca. 5.5E-4 µl Only single scattered light contributes to the cross correlation function. Cross correlation function is calculated with the correlator. Cross correlation is a filter for single scattered light The particle size distribution is calculated with a Q3-Matrix from the cross correlation function. 11E05A21L16E

17 PCCS as improvement of PCS Improvement of the principle: elimination of multiple scattering influence scattering vectors have to be equal by direction and amount scattering volumes have to be equal ( 10 µm³) the elimination of multiple scattering allows measurements in much higher concentration only in extreme concentrations when no single scattered information is left after crosscorrelation no result will be presented 11E05A21L17E

18 NANOPHOX Photon-Cross-Correlation-Spectroscopy 11E05A21L18E

19 NANOPHOX evaluation Modes 2ndCumulant very stable only mean particle size and a guess for the width of the distribution Enabled by precise recording and evaluating the progression of the correlation function during measurement and applying robust statistics to it. auto-nnls automated Fit-Range validatable complete particle size distribution Stable NNLS expert mode complete particle size distribution manual selection of a proper Fit-Range for every single measurement (software assisted to the greatest possible extent!) no validation 11E05A21L19E

20 Standard evaluation mode (2nd Cumulant), ISO presumes and requires mono modularity and yields median distribution diameter indication as to the width of distribution (width ± %) Mean diameter: 195 nm Width (2nd Viral Coefficient): ± 10,2% no information regarding internal structure of total distribution 11E05A21L20E

21 NANOPHOX NNLS (Non Negative Least Square) Selection of the best fitting window determines the quality of the evaluation either done automatically by auto-nnls or manually in the NNLS-expert-mode allows for indication of the structure within distribution with correctly set fit-range reliable information on multiple populations in distribution is provided 11E05A21L21E

22 Density distribution q3* Cumulative distribution Q3 / % Correlation / % Resolution and Relevance trimodal Calc. mode Particle size / nm NNLS expert mode manual fit-range optimisation software assisted to the greatest possible extent highest resolution exact relevance control via correlation function limited reproducibility NNLS NNLS Evaluation rule nm:128(log) auto robust nm:128(log) 0, ,773ms -1% x(50 %) nm 43,53 105,38 monomodal Measuring mode Cross correlation Cross correlation Param. 3 n.a. n.a Lag time / ms auto-nnls Param. 1 automated fit-range determination automated computation without manual interaction limited resolution Sympatec Sympatec Calc.Mode very high reproducibility PSD-width reproducible, but peaks wider than expected NNLS NNLS Maximum lag time ms 2,46 0,77 x(50 %) nm 41,52 17,08 Evaluation rule nm:128(log) auto robust nm:128(log) 0, ,773ms -1% 11E05A21L22E

23 Density distribution qint* Cumulative distribution Qint / % Density distribution q3* Cumulative distribution Q3 / % Density distribution q0* Cumulative distribution Q0 / % Different presentation stiles Q3 volume distribution Particle size / nm intensity distribution 11E05A21L23E Calc. mode NNLS NNLS Evaluation rule nm:128(log) auto robust nm:128(log) 0, ,773ms -1% x(50 %) nm 43,53 105,38 Measuring mode Cross correlation Cross correlation Param. 3 n.a. n.a Calc. mode Particle size / nm NNLS NNLS Q0 number distribution Calc. mode Particle size / nm Evaluation rule nm:128(log) auto robust nm:128(log) 0, ,773ms -1% x(50 %) nm 43,53 105,38 Measuring mode Cross correlation Cross correlation Param n.a n.a NNLS NNLS Evaluation rule nm:128(log) auto robust nm:128(log) 0, ,773ms -1% x(50 %) nm 43,53 105,38 Measuring mode Cross correlation Cross correlation Param. 3 NNLS expert mode auto-nnls n.a. n.a

24 Results key principle: 3D-cross correlation Selection of only single scattered light 2 measured parameters: 1. Amplitude ~ single scattered part Mutation of sample change in amplitude potential for stability analysis 2. slope ~ 1/particle size In the Rayleigh - Area (particles << wave length) the scattered light intensity increases proportional to the particle diameter by 10 6! PCCS provides exact information from turbid samples (particle >> wave length -> up to 10 2.) 11E05A21L24E

25 Interactions between particles dispersed in polar fluids particles adsorb negative ions (anions) directly on their surface concentration of anions causes attraction of hydrated counter-ions (cat-ions) from the outer fields electrical double layer is built up the shear plane (slipping plane) is an imaginary surface seperating the thin layer of liquis bound to the solid surface and showing elastic behaviour from the rest of liquid showing normal viscous behaviour Zeta-potential z is defined at the shear plane of fixed and diffuse ionic shell 11E05A21L25E

26 state of suspension dispersion agglomeration ideal dilution Zeta-potential attraction energy repulsion energy Balance of forces resulting particle potential repulsion ER + attraction EA the state of suspensions (dispersion agglomeration) depends on the sum of Zeta-potential (repulsion) and VAN DER WAALS forces (attraction) + 0 distance from particle surface rejection ER (Zeta potential) attraction EA (V.D. WAALS forces) resulting particle potential ER+EA agglomeration dispersion + - concentration of counter-ions The Zeta-potential of a suspension depends on concentration and changes with dilution! concentration of counter-ions Thus real Zeta-potential can be measured in original concentration only. This is impossible in instruments based on scattered light technique! 11E05A21L26E

27 PCCS versus Zeta-potential As the measurement basis of PCCS as well as of Zeta-potential is the hydrodynamic diameter there is no need to measure both ways! Especially because of the strong dependence of Zeta-potential on concentration its results are mostly not reliable because the samples have to be diluted by far. The calculation of Zeta-potential based on PCS is calculated using 2 nd Cumulant only and by that is totally wrong for multimodal samples. Further the influence of the thickness of the hydrodynamic layer is very roughly approximated by the Huckle factor: 1,0 < 200nm > 1,5 The combination of multiple long known measuring principles in one instrument may price wise look as a benefit, but in the end cannot cope with one superior setup like NANOPHOX that has been especially developed to overcome the concentration weaknesses of former PCS and related methods. 11E05A21L27E

28 Conclusion NANOPHOX opens a new dimension with respect to high concentration for reliable and reproducible analysis of particle size distributions in the nano meter area. The singular Sympatec specific auto-nnls evaluation mode together with automated measuring time determination, enables to run the instrument in a push button mode and enables instrument validation. The NNLS-expert-mode together with the relevance control via the correlation function reveals singular deep insights by highest resolution. NANOPHOX represents a new and superior class of powerful analytical instruments for particle size and stability measurement in the nanometer area, that can be applied to a broad range of applications while it is widely independent of concentration. 11E05A21L28E