Efficient use of (nano)particle self-assembly for creating nanostructured materials requires sensitive control over the interactions between building blocks. Here, a very simple method for rendering the interactions between almost any hydrophobic nano- and microparticles thermoswitchable is described and this attraction is characterized using colloid probe atomic force microscopy (CP-AFM). In a single-step synthesis, a thermoresponsive surfactant is prepared that through physical adsorption generates a thermosensitive brush on hydrophobic surfaces. These surface layers can reversibly trigger gelation and crystallization of nano- and microparticles, and at the same time can be used to destabilize emulsions on demand. The method requires no chemical surface modification yet is universal, reproducible, and fully reversible.