Near-Infrared Light-Induced Sequential Shape Recovery and Separation of Assembled Temperature Memory Polymer Microparticles.

Light-induced, shape-changing polymeric microparticles have many applications. Here, the near-infrared (NIR)-light-triggered sequential recovery and separation of assembled large and small polymer microparticles using cross-linked blends of poly(ethylene-vinyl acetate) and trans-polyisoprene as temperature memory polymers as well as two NaYF4 based up-conversion nanoparticles (UCPs) to provide luminescent and photothermal effects are reported. Under irradiation of NIR light with a low light power density, small particles assembled onto the compressed large one recover first due to the low switching temperature (T-sw) arising from the temperature-memory effect. The small particles can separate from the underlying large particle in flowing aqueous media. The recovery of the large particle occurs at a high power density. Two UCPs of NaYF4: 20Yb, 0.2Tm, 5Gd and NaYF4: 18Yb, 2Er, 5Gd facilitate the detection of small and large microparticles via providing blue and green light emissions, respectively. This work can expand the applications of light-induced shape-changing polymer microparticles in the biomedical field, controlled catalysis, microfluidic devices, and so on.