The mass of the shell is the volume of the shell multiplied by the density of the shell. For a spherical core particle the mass is given by The mass of the core is the volume multiplied by the density of the core. M total = m core + m shell = V coreρ core + V shellρ shell In this example, the total particle mass is calculated by For example, gold nanoshells consist of a silica core surrounded by a thin gold shell, and the mass of the core and the mass of the shell must be calculated separately to determine the total mass of the particle. When a nanoparticle is made from more than one material, separate calculations must be made to determine the particle mass. We use an effective density of 2.05 g/cm 3 for our silica nanoparticles, which is similar to other reported values in the literature measured by other techniques such as an aerosol particle mass analyzer ( Kimoto 2014, Kimoto 2017) How to Calculate the Mass of a Core-Shell Nanoparticle This condensation process leads to the silica becoming less porous and more dense, but is still typically a lower density than bulk silica prepared at high temperatures. Initially, there will be many -OH groups within the silica particle the number of hydroxyl groups can be reduced by heating, which converts two -OH bonds into a Si-O-Si bond while releasing a water molecule. Depending on the fabrication, environment and storage conditions, the degree to which the silica is condensed varies. Silica nanoparticles are typically prepared using the Stober method, in which silane precursors are condensed in the presence of a base. MaterialĮffective Density of Silica Nanoparticles ![]() The mass calculation is also adjusted for nanoparticles made of multiple materials, such as core/shell nanoparticles. In most cases the density of nanomaterials is the same as the bulk density, but for some materials the atomic structure is different than the bulk and a corrected density must be used. ![]() Once the nanoparticle volume has been calculated the mass can be determined simply by multiplying the volume by the material density (ρ): m=Vρ. How to Calculate the Mass of a Nanoparticle For example, when silica shelled, the nanoplates will often be rotated on edge when dried onto a TEM grid and a direct TEM measurement of the thickness can be made. Another method of measuring plate thickness is to measure the plate in composite particles. For example, nanoplates typically sit flat on the TEM grid so it is not possible to measure the thickness directly with TEM, and complimentary measurement techniques, such as atomic force microscopy (AFM) or high-resolution scanning electron microscopy (SEM) may be needed to measure the plate thickness. ![]() Sometimes, all of the needed dimensions cannot be obtained with TEM alone. The measurements are averaged and substituted in the formulas above. To obtain these dimensions, TEM images are analyzed with a program such as ImageJ/Fiji to measure many particles from multiple TEM grids. At nanoComposix we primarily use a transmission electron microscope (TEM) to measure particle dimensions, allowing the volume to be calculated.įor spherical nanoparticles, the volume is: V=4/3□ r 3, where r is the radius of the sphereįor rod shaped nanoparticles, the volume is: V=□ r 2l, where r is the radius of the rod and l is the lengthįor plate shaped nanoparticles, the volume is V=□ r 2h , where r is the radius of the nanoplate and h is the thickness.įor cube shaped nanoparticles, the volume is : V=d 3, where d is the diameter of the cube. The volume of a nanoparticle is determined by first measuring its dimensions. How to Calculate the Volume of a Nanoparticle In this module, we describe how we calculate these parameters for both solid particles and core/shell particle geometries. Nanoparticle volume, mass and concentration are fundamental nanoparticle characteristics.
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