A Simple Synthesis Towards Colloidal Particles with a Defined Size and Composition Gradient

Colloidal particles are essential in numerous applications, necessitating precise control over their size and size distribution.^[1] Seeded growth reactions are a well-established synthetic approach to achieve good structural control in combination with a wide choice of the material’s composition. However, traditional batch synthesis methods typically produce discrete particle sizes,^[2] which do not meet the requirements for tailored drug delivery system^[3] or advanced optical devices such as photonic displays or sensors.^[4] Therefore, innovative methods for producing colloidal particles with controlled and complex size distributions or compositions are in high demand.<br/>The controlled emulsion extraction process (CrEEP), introduced by Schöttle <i>et al.</i>,^[5] represents a notable advancement. It enables the production of polymer nanoparticle dispersions with defined, gradual size distributions via time-resolved extraction during the synthesis. In our study, we present significant improvements to this technique, enhancing both its reliability and versatility. Our refinements include achieving more complex size distributions by selectively omitting specific size ranges. Additionally, we demonstrate the ability to vary the monomer feed composition, resulting in a gradual change in both particle size and glass transition temperature.<br/>Moreover, the CrEEP method is not limited to polymer particle synthesis. It can be adapted to sol-gel processes, such as the established silica Stöber synthesis.^[6] This adaption, referred to as the controlled extraction Stöber process (CrESP), yields a similar size gradient, thereby expanding the applicability of this innovative technique. By improving and extending CrEEP and CrESP, we provide versatile tools for producing colloidal particles with tailored properties.<br/><br/>^[1] Y. Wang <i>et al.</i>, <i>Drug Deliv. Transl. Res.</i> <b>2024</b>; A. C. Arsenault <i>et al.</i>, <i>Nat. </i><i>Photonics</i> <b>2007</b>, <i>1</i>, 468-472; S. Y. Lee <i>et al.</i>, <i>Adv. Mater.</i> <b>2014</b>, <i>26</i>, 2391-2397.<br/>^[2] P. P. Ghimire, & M. Jaroniec, <i>J. Colloid. Interface Sci.</i> <b>2021</b>, <i>584</i>, 838-865; Li & Salovey, <i>J. Polym. Sci., Part A: Polym. Chem.</i> <b>2000</b>, <i>38</i>, 3181-3187.<br/>^[3] Y. Wang <i>et al.</i>, <i>Drug Deliv. Transl. Res.</i> <b>2024</b>, DOI 10.1007/s13346-023-01500-x.<br/>^[4] A. C. Arsenault <i>et al.</i>, <i>Nat. </i><i>Photonics</i> <b>2007</b>, <i>1</i>, 468–472; S. Y. Lee <i>et al.</i>, <i>Adv. Mater.</i> <b>2014</b>, <i>26</i>, 2391–2397.[5] M. Schöttle <i>et al.</i>, <i>Adv. Mater.</i> <b>2023</b>, e2208745.<br/>^[6] W. Stöber, A. Fink, E. Bohn, <i>J. Colloid Interface Sci.</i> <b>1968</b>, <i>26</i>, 62–69.