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In Chapter 1, we developed the following lists of key properties and behaviors of nanomaterials:
- Critical Nanomaterial Properties
- Size (e.g., diameter for spherical nanoparticles; length and diameter for nanorods; length, width, and thickness for nanosheets)
- Shape or morphology (e.g., nanosphere, nanorod, nanosheet)
- Structure (e.g., homogeneous vs. core-shell)
- Composition — including the core material forming the nanomaterial, surface composition (adsorbates), and species carried by or embedded within the nanomaterial
- Surface charge
- Important Nanomaterial Behaviors
- Interactions with light, i.e., optical or electronic properties
- Colloidal stability, i.e., the tendency of the nanomaterials to remain separated in suspension or to form agglomerates or aggregates
- Chemical reactivity
Chapter 2 introduced standards related to nanotechnology, and Chapter 3 included an exercise in applying terminology standards to define nanomaterials. From Activities 1 and 2 and the theory chapters (Chapters 3 to 7), we observed how properties such as particle size and surface charge impact the behaviors of the nanomaterials, e.g., their color and agglomeration state.
This chapter presents two exercises in which we will explore other general standards that relate to overall characterization and reporting on the properties of nanomaterials, along with standard for the evaluation of specific products that contain nanomaterials.
8.1 General characterization and reporting standards
General characterization and reporting standards provide lists of properties that can be important to characterize or report for a type of material or sample, along with descriptions of those properties. As an example, you might consider what properties would be important to measure and report if you synthesized a new chemical in the laboratory, for example, a pesticide. Some important chemical properties would include the chemical formula of the pesticide compound, its chemical structure, and its melting and boiling points. In the following exercise, you will walk through a reporting standard to identify the uses of the standard and review the nanomaterial characteristics featured in the standard.
Exercise 8.1: General characterization and reporting standards for nanotechnology
Review the following standard:
This standard is structured with the following sections:
- Scope
- Referenced Documents
- Terminology
- Summary of Guide
- Significance and Use
- Information Categories and Descriptors
The following questions are intended to guide you through the standard.
1. You may not be familiar yet with the term “nano-objects” in the title of the standard. Review Section 3 (Terminology) to identify the definition of “nano-object” being utilized in the standard.
2. Each standard will include introductory information related to the goals of the standard, its intended uses and limitations, as well as the expected audience and how the standard can be beneficial for readers. Review Sections 1, 4, and 5 for this information, and compare to the list of nanomaterial properties/behaviors that we developed at the top of this chapter. Which items from the list do you expect will be covered in the standard, and are any items outside the scope of the standard?
3. Section 6 contains the bulk of the technical information from the standard, specifically, an outline of key characteristics of nanomaterial (e.g., size) and their applicable descriptors (e.g., radius). Review Sections 6.2 (Shape), 6.3 (Size), 6.4 (Physical Structure), 6.5 (Chemical Composition), 6.6 (Crystallographic Structure), and 6.7 (Surface Description). Which characteristics align with the list that we developed at the top of this chapter? Are there any nuances of these characteristics that were detailed in the standard that you might not have considered before?
After reviewing ASTM E3144-19, you may also review the following standard, which covers characteristics of “collections” of nano-objects:
The following questions relate to ASTM E3206-19:
1. Review Section 3 (Terminology) ahd Section 6 (Collections of Nano-Objects) to identify the definition of a “collection of nano-objects” being utilized in the standard and distinguish how these “collections” are different from the individual “nano-objects” covered in ASTM E3144-19. You should observe some key terms such as “aggregate” and “agglomerate” discussed in the prior chapters of this course book!
2. Review Section 7 (Information Categories and Descriptors) to identify characteristics that overlap those covered in ASTM E3206-19. These include Composition, Size, and Structure. How should these elaborated upon when characterizing a collection of nano-objects, rather than an individual nano-object?
3. Similarly, identify new categories of characteristics in Section 7 that were not listed in ASTM E3206-19. These include the the different modes of Association.
Interactive Question 8.1: Quiz on characterization and reporting standards
The original version of this chapter contained H5P content. You may want to remove or replace this element.
8.2 Product standards
Manufacturers of commercial products often rely on product standards that provide guidance on evaluating the properties or performance of their products, as well as reporting or labeling these properties. If you inpect household items around you, you may find standard designations on the product packaging. For example, one student in this course found that the Sharpie® markers and highlighters being used to mark up the standards documents being reviewed in class are labeled with “Conforms to ASTM D-4236” (a product standard for labeling any health hazards associated with art materials)!
Before we move to a nanomaterial standard, let’s first consider a product that may be more familiar to you — peanut butter. What properties would you deem important to evaluate or report on the product label? In addition, consider how the properties of the peanut butter may affect the ease of measuring those characteristics.
Common responses (click to reveal):
- Properties to characterize
- Weight of product in the container
- Chemical composition — e.g., amounts of major nutrients and presence of possible toxins or contaminants
- Physical properties — e.g., viscosity or type of peanut butter (smooth or chunky)
- Product stability — e.g., recommended storage conditions and expiration date
- Challenges for product characterization
- For samples with inhomogeneities (e.g., in chunky peanut butter), sample homogenization or digestion may be required to analyze the overall composition.
- Chemicals such as toxins may be present in trace concentrations, requiring extraction methods.
- Product storage and stability is important to consider, as the properties of the product may change over time.
In the following exercise, we will now consider a standard for evaluating nanomaterials in a product, specfically silver nanomaterials in textiles. Silver nanomaterials can be intentionally added into products such as textiles for their antimicrobial properties.
Exercise 8.2: Product standard for silver nanomaterials in textiles
Review the following standard:
Considering the list of important product characteristics above, we can develop an analogous list below related to properties that may be , identify if and where (i.e., which section of the standard) the item is discussed in the ASTM E3025‑22 product standard, and briefly summarize the relevant guidance provided in the standard.
Properties to characterize
1. Does the product contain silver (in any form – nanoscale or bulk silver)?
2. What is the overall concentration of silver?
3. What species of silver are present, and at what quantities? (e.g., Ag ions, Ag oxides, Ag salts, pure Ag metal, etc.)
4. Is any of the silver present in the form of a nanoscale material?
5. Where is the silver located, and how is it incorporated into the product? (e.g., on the outside of the textile fibers, embedded in the fibers, embedded in some other material coating the textile)
6. Is there any toxicity and/or antimicrobial property?
Challenges for product characterization
7. Should the product usage (e.g., aging, washing, etc.) be considered when characterizing the silver in the product?
8. If the silver is embedded within the product, what approaches can be taken to detect or characterize it?
Expected outcomes of this exercise (click to reveal):
You should be able to find all of the items above discussed in detail throughout the standard, including the following sections:
- Figure 1: Distinguishing different forms of silver
- Sections 4 and X1: Discussions of silver nanomaterial stability and tranformations
- Sections 8, 9, and X2: Methods for characterizing and quantifying silver in different forms, including considerations for extraction or detection of silver nanomaterials embedded in textiles
Notably, you should also find that the toxicity or antimicrobial properties are only briefly noted to describe the significance of the standard, but are otherwise outside the scope of testing discussed in the standard.
Overall, the standard provides valuable guidance for product testing specifically related to silver nanomaterials in textiles.
