1、Designation: E2490 09 (Reapproved 2015)Standard Guide forMeasurement of Particle Size Distribution of Nanomaterialsin Suspension by Photon Correlation Spectroscopy (PCS)1This standard is issued under the fixed designation E2490; the number immediately following the designation indicates the year ofo
2、riginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide deals with the measurement of particle sizedistri
3、bution of suspended particles, which are solely or pre-dominantly sub-100 nm, using the photon correlation (PCS)technique. It does not provide a complete measurement meth-odology for any specific nanomaterial, but provides a generaloverview and guide as to the methodology that should befollowed for
4、good practice, along with potential pitfalls.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regula
5、tory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE1617 Practice for Reporting Particle Size Characterizatio
6、nDataF1877 Practice for Characterization of Particles2.2 ISO Standards:ISO 13320-1 Particle Size AnalysisLaser DiffractionMethodsPart 1: General Principles3ISO 14488 Particulate MaterialsSampling and SampleSplitting for the Determination of Particulate Properties3ISO 13321 Particle Size AnalysisPhot
7、on CorrelationSpectroscopy33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Some of the definitions in 3.1 will differ slightly fromthose used within other (non-particle sizing) standards (forexample, repeatability, reproducibility). For the purposes ofthis Guide only, we utili
8、ze the stated definitions, as they enablethe isolation of possible errors or differences in the measure-ment to be assigned to instrumental, dispersion or samplingvariation.3.1.2 correlation coeffcient, nmeasure of the correlation(or similarity/comparison) between 2 signals or a signal anditself at
9、another point in time.3.1.2.1 DiscussionIf there is perfect correlation (the sig-nals are identical), then this takes the value 1.00; with nocorrelation then the value is zero.3.1.3 correlogram or correlation function, ngraphical rep-resentation of the correlation coefficient over time.3.1.3.1 Discu
10、ssionThis is typically an exponential decay.3.1.4 cumulants analysis, nmathematical fitting of thecorrelation function as a polynomial expansion that producessome estimate of the width of the particle size distribution.3.1.5 diffusion coeffcient (self or collective), na measureof the Brownian motion
11、 movement of a particle(s) in amedium.3.1.5.1 DiscussionAfter measurement, the value is beinputted into in the Stokes-Einstein equation (Eq 1, see7.2.1.2(4). Diffusion coefficient units in photon correlationspectroscopy (PCS) measurements are typically m2/s.3.1.6 Mie region, nin this region (typical
12、ly where the sizeof the particle is greater than half the wavelength of incidentlight), the light scattering behavior is complex and can only beinterpreted with a more rigorous and exact (and all-encompassing) theory.3.1.6.1 DiscussionThis more exact theory can be usedinstead of the Rayleigh and Ray
13、leigh-Gans-Debye approxima-tions described in 3.1.8 and 3.1.9. The differences between theapproximations and exact theory are typically small in the sizerange considered by this standard. Mie theory is needed inorder to convert an intensity distribution to one based onvolume or mass.1This guide is u
14、nder the jurisdiction of ASTM Committee E56 on Nanotech-nology and is the direct responsibility of Subcommittee E56.02 on Physical andChemical Characterization.Current edition approved April 1, 2015. Published April 2015. Originallyapproved in 2008. Last previous edition in 2009 as E2490 09. DOI: 10
15、.1520/E2490-09R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards
16、 Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.7 polydispersity index (PI), ndescriptor of the width ofthe particle size distribution obtained fr
17、om the second and thirdcumulants (see 8.3).3.1.8 Rayleigh-Gans-Debye region, nin this region (statedto be where the diameter of the particle is up to half thewavelength of incident light), the scattering tends to theforward direction, and again, an approximation can be used todescribe the behavior o
18、f the particle with respect to incidentlight.3.1.9 Rayleigh region, nsize limit below which the scat-tering intensity is isotropicthat is, there is no angulardependence for unpolarized light.3.1.9.1 DiscussionTypically, this region is stated to bewhere the diameter of the particle is less than a ten
19、th of thewavelength of the incident light. In this region a mathematicalapproximation can be used to predict the light-scatteringbehavior.3.1.10 repeatability, nin PCS and other particle sizingtechniques, this usually refers to the precision of repeatedconsecutive measurements on the same group of p
20、articles andis normally expressed as a relative standard deviation (RSD) orcoefficient of variation (C.V.).3.1.10.1 DiscussionThe repeatability value reflects thestability (instrumental, but mainly the sample) of the systemover time. Changes in the sample could include dispersion(desired?) and settl
21、ing.3.1.11 reproducibility, nin PCS and particle sizing thisusually refers to second and further aliquots of the same bulksample (and therefore is subject to the homogeneity or other-wise of the starting material and the sampling method em-ployed).3.1.11.1 DiscussionIn a slurry system, it is often t
22、helargest error when repeated samples are taken. Other defini-tions of reproducibility also address the variability amongsingle test results gathered from different laboratories wheninter-laboratory testing is undertaken. It is to be noted that thesame group of particles can never be measured in suc
23、h asystem of tests and therefore reproducibility values are typi-cally be considerably in excess of repeatability values.3.1.12 robustness, na measure of the change of therequired parameter with deliberate and systematic variations inany or all of the key parameters that influence it.3.1.12.1 Discus
24、sionFor example, dispersion time (ultra-sound time and duration) almost certainly will affect thereported results. Variation in pH is likely to affect the degree ofagglomeration and so forth.3.1.13 rotational diffusion, na process by which the equi-librium statistical distribution of the overall ori
25、entation ofmolecules or particles is maintained or restored.3.1.14 translational diffusion, na process by which theequilibrium statistical distribution of molecules or particles inspace is maintained or restored.3.1.15 z-average, nharmonic intensity weighted averageparticle diameter (the type of dia
26、meter that is isolated in a PCSexperiment; a harmonic-type average is usual in frequencyanalyses) (see 8.9).3.2 Acronyms:3.2.1 APDavalanche photodiode detector3.2.2 CONTINmathematical program for the solution ofnon-linear equations created by Stephen Provencher and ex-tensively used in PCS (1).43.2.
27、3 CVcoefficient of variation3.2.4 DLSdynamic light scattering3.2.5 NNLSnon-negative least squares3.2.6 PCSphoton correlation spectroscopy3.2.7 PMTphotomultiplier tube3.2.8 QELSquasi-elastic light scattering3.2.9 RGBRayleigh-Gans Debye4. Summary of Guide4.1 This Guide addresses the technique of photo
28、n correla-tion spectroscopy (PCS) alternatively known as dynamic lightscattering (DLS) or quasi-elastic light scattering (QELS) usedfor the measurement of particle size within liquid systems. Toavoid confusion, every usage of the term PCS implies that DLSor QELS can be used in its place.5. Significa
29、nce and Use5.1 PCS is one of the very few techniques that are able todeal with the measurement of particle size distribution in thenano-size region. This Guide highlights this light scatteringtechnique, generally applicable in the particle size range fromthe sub-nm region until the onset of sediment
30、ation in thesample. The PCS technique is usually applied to slurries orsuspensions of solid material in a liquid carrier. It is a firstprinciples method (that is, calibration in the standard under-standing of this word, is not involved). The measurement ishydrodynamically based and therefore provide
31、s size informa-tion in the suspending medium (typically water). Thus thehydrodynamic diameter will almost certainly differ from othersize diameters isolated by other techniques and users of thePCS technique need to be aware of the distinction of thevarious descriptors of particle diameter before mak
32、ing com-parisons between techniques. Notwithstanding the precedingsentence, the technique is widely applied in industry andacademia as both a research and development tool and as a QCmethod for the characterization of submicron systems.6. Reagents6.1 In general, no reagents specific to the technique
33、 arenecessary. However, dispersing and stabilizing agents often arerequired for a specific test sample in order to preserve colloidalstability during the measurement. A suitable diluent is used toachieve a particle concentration appropriate for the measure-ment. Particle size is likely to undergo ch
34、ange on dilution, asthe ionic environment, within which the particles are dispersed,changes in nature or concentration. This is particularly notice-able when diluting a monodisperse latex. A latex that is4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.
35、E2490 09 (2015)2measured as 60 nm in110-3M NaCl can have a hydrody-namic diameter of over 70 nm in110-6M NaCl (close todeionized water). In order to minimize any changes in thesystem on dilution, it is common to use what is commonlycalled the “mother liquor”. This is the liquid in which theparticles
36、 exist in stable form and is usually obtained bycentrifuging of the suspension or making up the same ionicnature of the dispersant liquid if knowledge of this material isavailable. Many biological materials are measured in a buffer(often phosphate), which confers the correct (range of) condi-tions o
37、f pH and ionic strength to assure stability of the system.Instability (usually through inadequate zeta potential (2) canpromote agglomeration leading to settling or sedimentation ina solid-liquid system or creaming in a liquid-liquid system(emulsion). Such fundamental changes interfere with the sta-
38、bility of the suspension and need to be minimized as they affectthe quality (accuracy and repeatability) of the reported mea-surements. These are likely to be investigated in any robustnessexperiment.7. Procedure7.1 Verification:7.1.1 The instrument to be used in the determination shouldbe verified
39、for correct performance, within pre-defined qualitycontrol limits, by following protocols issued by the instrumentmanufacturer. These confirmation tests normally involve theuse of one or more NIST-traceable particle size standards. Inthe sub-micron ( 60 nm)the light starts to be scattered towards th
40、e forward angleinlaymans terms it becomes egg-shaped with more forward thanback-scatterand up to /2 ( 300 nm for a He-Ne laser at632.8 nm) then the Rayleigh-Gans-Debye approximationworks well as there is little structure to the observed polarpattern of scattering. Thus, in the 100 nm present in the
41、sample (and thusthe distribution is broader than “monodisperse”). The situationis likely to be simpler (smaller values of polydispersity index)for samples that are 100 % 100 nm and therefore not relevant to this Guide) there isthen a variation in scattering intensity with angle (the scatteringis non
42、-isotropic in contrast to the sub-100 nm (approximate)regime. Any angular variation in scattering can be used (alongwith the known optical properties of the particulate system), intheory at least, to obtain particle size distribution information.This area (0.1 m and higher) is now the preserve of “l
43、aserdiffraction” (for example, see ISO 13320-1) where lightscattering is involved and a range of other non-optical tech-niques (for example, sedimentation, sieves, electrical sensingzone) dependent on the size range of the system.8.4 Carrying Out the Measurement:8.4.1 A generic diagram is shown in F
44、ig. 3.8.4.2 Fig. 3 shows the “classic” design where scattered lightis detected at a variable angle (often 90), although for dilutesmall systems ( 0.7) then the sample is unlikely to be suitable forPCS and is not likely to give a stable distribution with time.E2490 09 (2015)108.10 Conversion of the I
45、ntensity Distribution to OtherParticle Size Distributions:8.10.1 In mathematical terms, this deconvolution is termedill-posed or ill-conditioned that means, in practical terms that itis ill advised. Small changes in collected data can give rise toenormous changes in derived result and as such treat
46、anyderived result with caution and skepticism. To convert fromintensity to volume distribution would involve the manipula-tion of perfect noise-free experimental data with accuratelymeasured refractive indices using Mie theory. A further con-version to number should never be attempted. If a numberdi
47、stribution is desired then an instrument that collects suchinformation should be used in the first place.8.10.2 The wider the initial distribution the more serious arethe errors in the conversion, and we have previously shownthat the given solution(s) are derived from ill-posed mathemati-cal problem
48、s and thus possibly subject to unbounded errors.8.10.3 Notwithstanding the above caveats and cautions,conversion to a volume-weighted distribution can often pro-vide an indication of the relative importance (prominence) oftwo or more reported peaks. A common situation is to see anapparently dominant
49、 large-size peak virtually disappearing anda low-intensity smaller-sized peak becoming the primary modeafter conversion to volume weighting. This conversion tends tobe relatively insensitive to the refractive index (the additionalparameter required for the conversion) except when the particleand medium have very similar values for the real refractiveindex ( 0.03).9. Report9.1 See Practice E1617.9.2 As a minimum the following need reporting in additionto graphical and tabular information:9.2.1 The instrument type and manufacturer a
