Scattering from colloidal cubic silica shells: Part I, particle form factors and optical contrast variation

F Dekker,B.W.M Kuipers,A.V Petukhov,R Tuinier,A.P Philipse

doi:10.1016/j.jcis.2019.11.002

F Dekker, B.W.M Kuipers + Show 3 more

Open Access

https://doi.org/10.1016/j.jcis.2019.11.002

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Abstract

HypothesisColloidal cubic silica shells, prepared from cuprous oxide cubes, with a typical size of 100 nm are promising model particles for scattering studies on dilute, as well as concentrated fluids, of non-spherical colloids. ExperimentsSmall angle X-ray scattering, and static light scattering are employed to determine form factors of cubic silica shells and silica covered cuprous oxide cubes. Contrast variation experiments are performed to assess the refractive index and optical homogeneity of the cubic silica shells, which is important for the extension of the scattering study to concentrated dispersions of cubic shells in Part II (Dekker, submitted for publication). ResultsThe experimental form factors, which compare well to theoretical form factors, manifest cubic silica shells that are dispersed as single stable colloids with a shape intermediate between a sphere and a perfect cube. Contrast variation demonstrates that the silica shells are optically homogeneous, with a refractive index that is independent of the shell thickness. The results presented here open up the possibility to extract structure factors from light scattering measurements on concentrated cube dispersions in Part II.

Highlights

At high K-values, additional oscillations become visible at K 1⁄4 0:51 nmÀ1, which correspond to a length of 13 nm
The small angle X-ray scattering (SAXS) data indicate that the cuboid shape is in between that of a cube and a sphere, which corresponds to superballs with an m-value of 4
It is visible that for both models, the minima arising from the shell thickness are at slightly lower K values than for to the SAXS data (K 1⁄4 0:42 nmÀ1, vs K 1⁄4 0:50 nmÀ1). This discrepancy can be attributed to polydispersity in the silica shell thickness, which is not accounted for in the models

Summary

Introduction

We developed a preparation method for CSS with average sizes between 100 and 150 nm [5] These shells are expected to be suitable model particles to study the thermodynamic properties of concentrated cube fluids. Scattering measurements on concentrated dispersions of cubes, requires knowledge of single particles properties, such as the internal refractive index profile, details on the particle shape, and their corresponding form factor. Well defined colloidal cubes can be prepared in different sizes and in various materials [7,8,9,10,11,12,13] These cubic particles are of interest since they form different crystal structures compared to spherical particles [14,15,16]. Detailed characterisation of cubic silica shells is required to evaluate the applicability of silica shells in optical films

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