Flow hydrodynamics-dependent assembly of polymer-tethered gold nanoparticles in microfluidic channels†
Abstract
Recently, self-assembly of polymer-tethered inorganic nanoparticles (NPs) in microfluidic chips has been employed as an effective approach to fabricate novel assemblies. Herein, we systematically studied the self-assembly of polystyrene-grafted gold NPs (AuNP@PS) in microfluidic chips into various structures by changing the organic/aqueous flow rate ratio (RQ), the total flow rate (Qtot), the molecular weight of PS ligands (Mn), and the radius of the AuNP core (r0). Morphological transitions of the assemblies were demostrated to be dependent on the hydrodynamic conditions, i.e., RQ and Qtot. We then employed the effective softness (λeff) to describe the structural features of AuNP@PS and the formation of assemblies. The results indicated that the morphology of the AuNP@PS assemblies was affected by λeff. When λeff ≤ 2.96, lamellar structures (e.g., nanosheets and bowl-like assemblies) were captured by varying RQ and Qtot. When λeff > 2.96, only spherical assemblies were obtained with the increase of RQ and Qtot. We further found that the AuNP@PS assemblies showed an excellent photothermal conversion performance. These findings not only demonstrate the kinetics dependent assembly behavior of polymer-tethered NPs in microfluidic chips, but also provide a convenient way to prepare NP assemblies with well-ordered structures, potentially useful in drug delivery, photothermal therapy, and others.
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