A new type of smart composite microgels, which are able to control the catalytic activity of their loaded silver nanoparticles by light, was designed and fabricated based on the idea of function transfer between their constituent components. First, the surfaces of monodisperse gold nanorods (AuNRs) with strong photothermal effect were coated with poly(N-isopropylacrylamide) (PNIPAM) hydrogel by seed precipitation polymerization to prepare the two-component composite microgels with core–shell structure (AuNR@PNIPAM microgels). Then, Ag+ ions coordinated into the shell of AuNR@PNIPAM microgels were in situ reduced by sodium borohydride to produce silver nanoparticles (AgNPs) loaded three-component composite microgels (AuNR@(AgNPs/PNIPAM) microgels). The characterization results obtained by transmission electron microscopy show that the gold nanorod is located at the center of the three-component composite microgels and AgNPs with the average particle diameters of 6–10 nm are evenly distributed within its shell. The hydrodynamic diameters of the composite microgels, measured by dynamic light scattering before or after exposure of their aqueous dispersion to near-infrared (NIR) laser of 808 nm wavelength, indicate that they have photoresponsive property. The AgNPs and AuNR inside AuNR@(AgNPs/PNIPAM) microgels hold their respective localized surface plasmon resonance (LSPR) optical property, and the longitudinal LSPR wavelength of the latter is blue-shifted with increasing content of the former. Moreover, the LSPR efficiency of the AgNPs and the longitudinal LSPR wavelength of the AuNR are capable of being changed in response to the NIR illumination, and the stimulus-responsive behavior is reversible. AuNR@(AgNPs/PNIPAM) microgels are able to be used as the smart microreactor for reducing 4-nitrophenol by NaBH4, and the reaction rate can be modulated by power density of the NIR light, demonstrating that the three-component composite microgels have light-controllable catalytic activity.

Combining atom transfer radical polymerization (ATRP) and “click” chemistry, a set of well-defined amphiphilic block copolymers poly(n-butyl acrylate)-b-poly(acrylic acid) (PnBA20-PAA85) with a similar chemical component, but different topological structures, i.e., linear-, cyclic-, and multiblock structures, were successfully prepared, characterized (size exclusion chromatography (SEC), FT-IR and 1H NMR), and used as surfactants in emulsion polymerization. Our further transmission electron microscopy (TEM) and laser light scattering (LLS) characterization of the resultant latex particles demonstrates all the surfactants with different topologies can effectively stabilize the latex particles but no significant difference among the solids contents was observed. Moreover, we have, for the first time, experimentally established the quantitative relation between the final number of latex particles (Np) and the concentration of polymeric surfactant with different topologies (C), i.e., Np = kCα, and the order of our measured exponent α is as follows: αmulti(1.10) > αlinear(0.81) ≥ αcyclic(0.73), indicating cyclic surfactant molecules behave more like small-molecule surfactants attributed to its strongest unimers extraction and diffusion ability; in contrast, multiblock surfactant molecules can act as seeds to directly nucleate to create latex particles. In addition, Np,multi > Np,linear ≥ Np,cyclic at higher concentration, and Np,linear > Np,cyclic ≥ Np,multi at lower concentration was observed. Similar results (αmulti(1.02) > αlinear(0.65) ≥ αcyclic(0.58)) were also observed when polystyrene-b-poly(acrylic acid) (PS9–PAA60) copolymers were used as surfactants. Further aqueous SEC characterization shows the broad size distribution of our micellar solution has no effect on obtaining narrowly distributed latex particles. Finally, interfacial tension measurement of the micellar solution indicates, compared to multiblock structure, the rate of adsorption at a hydrophobic interface is much faster for linear and cyclic-block structures, agreeing with our observed order of exponent α.