Sodium silicate particle size measurements using time-resolved fluorescence anisotropy

Doveiko, Daniel and Stebbing, Simon and Chen, Yu and Birch, David and Vyshemirsky, Vladislav and Rolinski, Olaf; Keršys, Martynas and Mickus, Šarūnas, eds. (2023) Sodium silicate particle size measurements using time-resolved fluorescence anisotropy. In: 66th International Open Readings Conference for students of Physics and Natural Sciences. Vilnius University Press, LTU, p. 88. ISBN 9786090708835 (

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Sodium silicates are versatile inorganic chemicals produced by combining silica sand and soda ash (sodium carbonate) under high temperature. When in aqueous solution, they are often used in coating and bonding applications. Additionally, they exhibit a range of attractive characteristics, such as being odorless and non-toxic, high strength and rigidity, resistance to high temperatures and low-cost [1].The important characteristics of silicates are the correlation between the ratio of silica to soda concentrations and the size of the species. Traditionally, the particle sizes of nanoparticles are determined using methods such as Dynamic Light Scattering (DLS) [2], Small-Angle X-Ray Scattering (SAXS) [3], Small Angle Neutron Scattering (SANS) [4] and Transmission Electron Microscopy (TEM) [5]. All these methods are far from ideal and have significant drawbacks: DLS becomes difficult for particles below 10 nm, SAXS and SANS are expensive and complex, and TEM requires complex sample preparations which can lead to alterations of particle sizes [6-8].Here, we present a new way of determining the particle sizes of sodium silicate liquors at high pH using time-resolved fluorescence anisotropy. Different from previous approach of using a single dye label, two fluorescent labels were used in this work [9,10]. Rotational times of the non-binding rhodamine B and electrostatically binding rhodamine 6G were used to determine the medium microviscosity and the silicate particle radius, respectively. This approach of using two dyes ensures that the microviscosity stays accurate in time, unlike in the case when a single dye was used. Applying this method to samples of various pH (prepared by diluting the stock solution of silicate to the concentrations of NaOH ranging from 0.2M to 2M) and different temperatures (10°C to 55°C), therecovered average particle size was found to have an upper limit of 7.0±1.2Å