# Investigation of the Degree of Functionalization and Colloidal Stability of Shell‐by‐Shell Functionalized TiO2 Nanoparticles as a Function of Different Phosphonic Acid Chain Lengths

## TL;DR

This study examines how different chain lengths of phosphonic acids affect the stability and agglomeration of titanium dioxide nanoparticles in water.

## Contribution

The work introduces a method to assess the efficiency of phosphonic acid and SDBS chain overlap in nanoparticle functionalization.

## Key findings

- Agglomerates formed depend on the length of the phosphonic acid chain used.
- Thermogravimetric analysis and analytical ultracentrifugation revealed insights into nanoparticle stability.
- The degree of functionalization and thermal stability varies with phosphonic acid chain length.

## Abstract

In this work, a series of Shell‐by‐Shell (SbS)‐functionalized colloidal systems consisting of 6 nm TiO2 anatase nanoparticles (NPs), one of the phosphonic acids (PAs) propylphosphonic acid (PAC3), hexylphosphonic acid (PAC6), dodecylphosphonic acid (PAC12), tetradecylphosphonic acid (PAC14), hexadecylphosphonic acid (PAC16), octadecylphosphonic acid (PAC18) and the amphiphile sodium dodecylbenzenesulfonate (SDBS) were prepared, resulting in TiO2‐PACX@SDBS (X = 3, 6, 12, 14, 16, or 18) NPs dispersed in deionized water (DIW). During the whole functionalization process, the NPs were subjected to thermogravimetric analysis (TGA) to gain insights into their degree of functionalization and respective thermal stability. In addition, the colloidal stability of the NPs as a function of PA chain length was analyzed by analytical ultracentrifugation (AUC). By combining both TGA and AUC, it was found that the resulting hierarchical NP architectures form agglomerates, with the degree of agglomeration depending on the length of the PA used for the first‐shell functionalization. This allows conclusions to be drawn about the efficiency of the overlap between the PA and the SDBS carbon chains.

The Shell‐by‐Shell structures of TiO2 nanoparticles, phosphonic acids (PAs) and sodium dodecylbenzenesulfonate (SDBS) in their solid and colloidal state were studied by thermogravimetric analysis and analytical ultracentrifugation. This combination showed that agglomerates were formed whose size depended on the PA chain length. This allowed conclusions to be drawn about the efficiency of the overlap between the PA and SDBS.