Investigating the block copolymer deposition on Au nanoparticle surface via graphene liquid cell

The realm of block copolymer (BCP) micelles is a playground of structural diversity, showcasing an array of forms including spherical, cylindrical, lamellar, and vesicular micelles [1], [2]. Over the past decade, an intriguing convergence has emerged within this domain, as researchers have increasingly sought to integrate nanoparticles (NPs) into these micellar architectures [3], [4], [5]. This integration promises a plethora of functionalities ranging from plasmonic to fluorescent, magnetic, and photothermal properties [6], [7], [8].

The aspiration is clear: to precisely position a defined number of NPs within morphologically controlled micelles, thereby optimizing synergistic effects and enabling site-specific functionalization [9], [10], [11], [12], [13]. However, achieving such nanoscale structural order necessitates mastery over bottom-up self-assembly processes, a stark departure from the top-down manipulation of macroscopic entities [14], [15]. Consequently, unraveling the intricacies of NP-polymer co-assembly becomes imperative for the rational design and synthesis of novel hybrid micelles.

Central to this pursuit is the challenge of controlling the NP-polymer interface and comprehending micelle assembly and structural evolution. Fundamental principles underscore this endeavor, emphasizing the need to modulate the bonding interactions between the NP core and the polymer shell to minimize interfacial energy [16], [17]. Full encapsulation of NPs within the hydrophobic domains of amphiphilic polymer micelles represents an ideal scenario, necessitating surface modifications to enhance hydrophobic interactions. For example, one method encapsulated a single Au NP into the PS core of each PS-b-PAA micelle by adding deionized (DI) water into dimethylformamide (DMF) solutions of citrate-capped Au NPs, dodecanethiol, and PS-b-PAA copolymers [18]. Polymer cross-linking then topologically fixed the composite nanostructure. Another method was recently developed to incorporate preformed NPs into only the center of spherical/cylindrical micelles and the central portion of vesicle walls [19], [20]. The method involves stabilizing the NPs with diblock copolymers of a similar composition to that of the micelle-forming diblock, followed by preparing the micelles in the presence of the copolymer-coated NPs in solution [21], [22]. Besides, there are several examples of how many NPs randomly are distributed in the micelles [23], [24], [25]. However, the mechanism study is limited to simulations and intermediates trapping which is far from the deep learning of the polymer deposition dynamics.

In this context, surface modifications through appropriate ligands emerge as pivotal strategies, facilitating robust bonding with NPs while fostering compatibility with hydrophobic copolymer blocks. Conversely, achieving partial encapsulation of NPs at the interface and corona of polymers requires judicious manipulation of binding competitions between hydrophobic and hydrophilic ligands [9], [26], [27], [28]. For example, a simple thermal treatment of a mixture of Au NPs and thiol-terminated block-random copolymers in selected solvents produced a variety of patchy NPs with controlled morphology and number of polymeric patches [9], [29]. As reported, polymers can be designed to selectively adsorb onto NP surfaces already partially coated by other chains to drive the formation of patchy NPs with broken symmetry [30], [31].

As researchers delve deeper into the realms of NP-polymer interactions and micelle assembly dynamics, a vista of possibilities unfolds [32], [33], [34]. By harnessing these insights, revealing the dynamics of polymer deposition on NPs will help unlock novel properties and applications, thus charting new frontiers in materials science and nanotechnology.

In this study, two types of Au NPs were prepared: the hydrophobic surface of the Au NP was used to obtain complete encapsulation of Au NP in BCP micelles, while the hydrophilic one was used in the formation of BCP micelles with partially embedded Au NP. In-situ liquid-phase transmission electron microscopy (TEM) was applied using a graphene liquid cell to capture the polymer deposition dynamics on the Au NP surface. The deposition mechanism was developed based on the in situ imaging at the nanoscale. Additionally, three-dimensional (3D) electron tomography was introduced to quantify the surface area and volume of the core-shell nanoparticles. The insights gleaned from this study lay the groundwork for the precise manipulation and design of solid surfaces utilizing functional polymers across a spectrum of applications [35], [36], [37].