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Understanding particle size distributions – Nanometrology at NMI

Understanding particle size distributions – Nanometrology at NMI  
Are particulate materials critical to your business?  Could you improve your quality control and processes if you gained a better understanding of how to interpret particle size distribution data? Are you struggling to meet international regulatory requirements in trade? Helping you to tackle the issues underlying these and many other questions is the focus of a new course currently under development at the National Measurement Institute (NMI): “Making critical assessments of particle size distribution data”. The course is being developed by NMI’s Nanometrology Section in response to stakeholders asking for help with this issue. A recent survey to test market interest confirmed this need and helped to guide the focus and structure of the new course.

NMI established a dedicated area for nanometrology, the science of measurement at the nanoscale, in 2007 to support Australia’s emerging nanotechnology industry. Nanotechnology is driving a new generation of innovative products, ranging from the latest in consumer electronics (the current feature size in new processor chips is just 14 nm – that’s 14 billionths of a metre or 500 times smaller than a red blood cell) to novel cancer diagnostics and therapies. Products containing nanotechnology are innovative and will drive some of the high-tech, high-value industries that will help position Australia for the future.

Nanometrology at NMI
NMI Nanometrology supports the responsible and safe development of nanotechnology by providing Australia with infrastructure for traceable, comparable and trusted nanoscale measurements. This is achieved primarily by the development of a primary standard for nanoscale dimensional measurement, based on atomic force microscopy, which is linked directly to the International System of units (SI) via the realisation of the SI metre at NMI. This instrument is called the metrological scanning probe microscope (mSPM) and was designed and built at NMI. It can be used to calibrate transfer artefacts, which in turn can be used to calibrate other atomic force and electron microscopes. The mSPM can also measure the properties of nanoscale objects that can then be used to validate practical measurements of nanoparticles made with other laboratory instrumentation in industry and elsewhere. In addition to the mSPM, Nanometrology operates a comprehensive particle characterisation laboratory where we can measure nanomaterial properties such as size, surface charge, agglomeration and aggregation state and shape. These are characteristics that need to be taken into consideration when developing or using nanomaterials: in product development, scale-up, process or quality control, and in studies of health and environmental effects.

The challenge of characterisation
One of the big challenges facing nanotechnology is the lack of universally applicable, validated methodology and instrumentation for the comprehensive characterisation of the properties of nanomaterials. Characterisation is important for the development and manufacture of products containing nanoparticles or other nanomaterials. Industry especially needs such methods for measurements of particle size and size distribution. Size is often closely linked to novel properties of these materials and thus also influences their transport, environmental fate, and regulation. Many techniques for measuring particle size and size distribution are available, all with different strengths and limitations in their ability to representatively measure the size distribution of nanomaterials. Challenges arise particularly when such materials have broad or multi-value size distributions, variations in shape, composition, high or low particle concentration, or when they are present in anything other than a simple medium such as water or air. In addition, different techniques measure size distributions that are weighted differently – some are sensitive to particle volume or mass, others measure according to the light scattering properties of a sample, and others measure on a particle-by-particle basis and return number-weighted distributions.  These different types of distributions need to be understood when interpreting particle size distribution data, especially when comparing measurements made with different instruments based on different weightings, and when making decisions based on particle size distribution.  As an example, European regulations that require labelling of cosmetics products incorporating nanomaterials rely on a definition for ‘nanomaterial’ that includes a cut-off based on the number of particles below a certain size.  In contrast, measurement limits for particles in air are typically based on particle mass (PM) concentrations (PM10, for example, is the mass of particles in an air sample with a size below 10 µm).

Standards
Standards provide agreed references to ensure that the particle characterisation results obtained from different measurement methods are comparable both between techniques and between different operators using the same technique. Such standards can come in the form of both physical “measurement” standards and documentary standards, Developing appropriate standards is critical to ensure the open, reproducible, safe and responsible development of nanotechnology. Standards are also essential for lowering technical barriers to trade, for ensuring individual, community and environmental safety, and in the development and implementation of legislation and regulation.

Physical standards help ensure that measurements are comparable. NMI’s mSPM is one example of a physical standard, reference materials (RMs) are another. RMs can be used to verify and calibrate measurement equipment. Appropriate reference materials with properties that are similar to the system under test can also help industry to validate and have confidence in their measurement methods. Such reference materials for nanotechnology, which include nanoparticles and other nanostructures, are still under development, with only a limited number of certified reference particles available. It is important that industry has access to appropriate nanoscale RMs of relevant size, size distribution, shape, concentration and composition. NMI Nanometrology contributes to international efforts to develop RMs, for example as an active participant in international certification campaigns for a range of size-based (nano)particle reference materials. A comprehensive list of RMs for nanotechnologies that have been developed to date can be found here: http://www.nano-refmat.bam.de/en/

Documentary standards specify ways to comparably name and describe things, measure and test things, manage and test potential impacts, and to report findings. NMI Nanometrology is working to ensure that best practice in measurement translates to relevant documentary standards through active participation in Standards Australia’s Technical Committee NT-001 on Nanotechnologies, which also represents Australia at the international level through the International Organization for Standardization (ISO). The committee comprises four working groups, including one focussing on Measurement and Characterisation. Development of many documentary standards is driven by industry needs, and the committee is very keen to increase industry participation. It’s activities mirror those of the ISO Technical Committees on Nanotechnologies (ISO/TC 229) and Particle Characterisation (ISO/TC 24/SC 4), and NMI Nanometrology technical experts contribute to the work of these committees as well as to relevant pre-normative research.

The new training course
With its expertise in precision measurements, physical and documentary standard development, reference material use and certification, and a wide range of particle characterisation techniques covering the size range from one nanometre all the way to hundreds of microns, NMI’s Nanometrology team is well placed to advise, educate and train stakeholders on best practice in (nano)particle measurement. NMI recognises common concerns, assumptions and knowledge gaps in the field of particle characterisation and in response develops a training course to help stakeholders address some of these technical issues. We anticipate that the course will be offered in the first half of 2017. NMI conducted a web-based survey in March 2016 to determine the demand for such a course, and to identify the content that would be most useful for participants.  Taking this feedback into account, we are developing a full-day course designed to enable participants to be able to make critical assessments of particle size distribution data.  The proposed modules include:

  • interpreting a particle size distribution, and understanding the difference between distributions produced from different instrumentation;
  • an overview of the size information you can obtain from microscopy techniques;
  • an overview of the size information you can obtain from light scattering techniques;
  • other measurement techniques and relevant information;
  • guidance on deciding which measurement technique is most suitable for a specific application.

The modules will be delivered together with case studies derived from real-world examples, and there may also be the opportunity for participants to visit NMI Nanometrology’s comprehensive particle characterisation laboratory.
In order to maximise the benefit and relevance of such a course, NMI would welcome further input from interested stakeholders. In addition, we would like to call for expressions of interest from industry who might wish to help us optimise the course by participating in a pilot.  

 

Figure 1: Illustration of the principle of measurement used in a differential centrifugal sedimentation instrument.
 
Figure 2: Transmission electron micrograph of a sample of zinc oxide nanoparticles showing a wide variety of shapes and sizes.
 
Figure 3: Particle size distribution of a mix of six different sizes of gold nanoparticles measured using differential centrifugal sedimentation.
The inset shows a transmission electron micrograph of the same sample, with a scale bar of 50 nm.
 
Figure 4: Dr Bakir Babic with NMI’s metrological scanning probe microscope; Australia's primary standard for dimensional measurement at the nanoscale.


Upcoming NMI Training Courses

The following NMI courses are offered during October – December 2016.

Chemical Metrology Training City Date Price
Analytical Method Validation Perth 8-9 November 2016 $2,171.95
Estimating Measurement Uncertainty for Chemists Perth 10-11 November 2016 $2,171.95
Estimating Measurement Uncertainty for Biologists Brisbane 13 October 2016 $1,191.85
Physical Metrology Training City Date Price
Introduction to Estimating Measurement Uncertainty Adelaide
Perth
Melbourne
Sydney
6 October 2016
2 November 2016
1 December 2016
14 December 2016
$1,083.50
Time and Frequency Measurement Sydney 19 October 2016 $2,171.95
Calibration of Liquid Hydrocarbon Flow Meters Sydney 25 October 2016 $1,945.50
Testing Temperature Controlled Enclosures Sydney 28 October 2016 $1,083.50
Radiometry Measurement Sydney 29 November 2016 $2,171.95

For further information please visit the training page on our website.
Alternatively, please call us on +61 2 8467 3796 or email us at This email address is being protected from spambots. You need JavaScript enabled to view it.