Nanoparticle Characterization: What to Measure?

Abstract

What to measure? is a key question in nanoscience, and it is not straightforward to address as different physicochemical properties define a nanoparticle sample. Most prominent among these properties are size, shape, surface charge, and porosity. Today researchers have an unprecedented variety of measurement techniques at their disposal to assign precise numerical values to those parameters. However, methods based on different physical principles probe different aspects, not only of the particles themselves, but also of their preparation history and their environment at the time of measurement. Understanding these connections can be of great value for interpreting characterization results and ultimately controlling the nanoparticle structure–function relationship. Here, the current techniques that enable the precise measurement of these fundamental nanoparticle properties are presented and their practical advantages and disadvantages are discussed. Some recommendations of how the physicochemical parameters of nanoparticles should be investigated and how to fully characterize these properties in different environments according to the intended nanoparticle use are proposed. The intention is to improve comparability of nanoparticle properties and performance to ensure the successful transfer of scientific knowledge to industrial real‐world applications.

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1901556 (1 of 26) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Nanoparticle Characterization: What to Measure?
Mario M. Modena,* Bastian Rühle, Thomas P. Burg, and Stefan Wuttke*
Dr. M. M. Modena
ETH Zurich
Department of Biosystems Science and Engineering
Mattenstrasse 26, 4058 Basel, BS, Switzerland
E-mail: mario.modena@bsse.ethz.ch
Dr. B. Rühle
Federal Institute for Materials Research and Testing (BAM)
Richard-Willstätter - Str 11, 12489 Berlin, Germany
Prof. T. P. Burg
Max Planck Institute for Biophysical Chemistry
Am Fassberg 11, 37077 Göttingen, Germany
Prof. T. P. Burg
Department of Electrical Engineering and Information Technology
Technische Universität Darmstadt
Merckstrasse 25, 64283 Darmstadt, Germany
Prof. S. Wuttke
Department of Chemistry
Center for NanoScience (CeNS)
University of Munich (LMU)
81377 Munich, Germany
E-mail: stefan.wuttke@cup.uni-muenchen.de
Prof. S. Wuttke
BCMaterials
Basque Center for Materials
UPV/EHU Science Park, 48940 Leioa, Spain
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.201901556.
DOI: 10.1002/adma.201901556
1. Introduction
Nanomaterials are defined as materials
that consist of nanoparticles of which
at least 50% have one or more external
dimensions between 1 and 100 nm.[1] Their
small dimensions do not only allow more
surface functionality in a given volume,
but also lead to physical properties that
often differ from their bulk counterparts
in many aspects, including electronic,
optical, and magnetic features.[2–7] Nano-
particles possess a much higher surface-
to-mass ratio than bulk materials and,
therefore, surface atoms and surface
energy strongly contribute to the material
properties, e.g., leading to reduced lattice
constants and lower melting points.[8–10]
Moreover, the high number of surface
atoms and the high surface energy of
nanoparticles can have a strong impact on
the catalytic performance. Thus, catalyti-
cally inactive bulk materials can become
very active catalysts when produced as
nanoparticles with high surface areas.[11]
If fewer atoms comprise a solid, a lower
number of orbitals contribute to the band
formation. This effect leads to changes in the band structure,
such as band gap variations in semiconductors, which depend
on the nanomaterial dimensions.[12,13] These unique properties
render nanoparticles extremely attractive for a large range of
applications, including catalysis, gas and energy storage, photo-
voltaic, electrical and optical devices, and biological and medical
technologies.[14–23] For this reason, nanoparticles are not only a
growing topic of interest in research settings, but they are also
already widely used in consumer products.[24]
Currently, a key issue hindering the utility of nanoparticles
in industry is reproducibility. This problem is, however, partially
intrinsic, as the product of synthesis is always prone to yield a
polydispersion of nanoparticles, sometimes with a broad dis-
tribution of sizes, shapes, and defects. Nanoparticle characteri-
zation is therefore a crucial step required to fully comprehend
the origin of nanoparticle behavior, and subsequently translate
their performance benefits from laboratories into specific real-
word applications.
Determining the physicochemical properties of nanoparti-
cles and exploring their structure–function relationships is a
critical challenge for scientists today. This endeavor is limited
by our ability to fully investigate the nanoscale realm: Different
characterization techniques are based on different physical
properties, therefore only providing a partial picture of the
nano particle characteristics. Making matters more challenging
What to measure? is a key question in nanoscience, and it is not
straightforward to address as different physicochemical properties
define a nanoparticle sample. Most prominent among these properties
are size, shape, surface charge, and porosity. Today researchers have an
unprecedented variety of measurement techniques at their disposal to
assign precise numerical values to those parameters. However, methods
based on different physical principles probe different aspects, not only
of the particles themselves, but also of their preparation history and
their environment at the time of measurement. Understanding these
connections can be of great value for interpreting characterization results
and ultimately controlling the nanoparticle structure–function relationship.
Here, the current techniques that enable the precise measurement of these
fundamental nanoparticle properties are presented and their practical
advantages and disadvantages are discussed. Some recommendations
of how the physicochemical parameters of nanoparticles should be
investigated and how to fully characterize these properties in different
environments according to the intended nanoparticle use are proposed.
The intention is to improve comparability of nanoparticle properties and
performance to ensure the successful transfer of scientific knowledge to
industrial real-world applications.
Nanoparticle Characterization
“Measure that which is measurable and make measurable that which is not”—Galileo Galilei
Adv. Mater. 2019, 31, 1901556