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Self-assembly of octapod-shaped colloidal nanocrystals into a hexagonal ballerina network embedded in a thin polymer film.

Arciniegas MP, Kim MR, De Graaf J, Brescia R, Marras S, Miszta K, Dijkstra M, van Roij R, Manna L - Nano Lett. (2014)

Bottom Line: In the resulting structure, each octapod is oriented like a "ballerina", that is, only one pod sticks out of the polymer film and is perpendicular to the polymer-air interface, while the opposite pod (with respect to the octapod's center) is fully immersed in the film and points toward the substrate, like a ballerina performing a grand battement.As the solvent evaporates, the octapods form a ballerina-rich octapod-polymer composite in which the octapods are in close contact with the substrate.Finally, we found that the resulting octapod-polymer composite is less hydrophilic than the polymer-only film.

View Article: PubMed Central - PubMed

Affiliation: Istituto Italiano di Tecnologia (IIT) , via Morego 30, IT-16163 Genova, Italy.

ABSTRACT
Nanoparticles with unconventional shapes may exhibit different types of assembly architectures that depend critically on the environmental conditions under which they are formed. Here, we demonstrate how the presence of polymer (polymethyl methacrylate, PMMA) molecules in a solution, in which CdSe(core)/CdS(pods) octapods are initially dispersed, affects the octapod-polymer organization upon solvent evaporation. We show that a fast drop-drying process can induce a remarkable two-dimensional (2D) self-assembly of octapods at the polymer/air interface. In the resulting structure, each octapod is oriented like a "ballerina", that is, only one pod sticks out of the polymer film and is perpendicular to the polymer-air interface, while the opposite pod (with respect to the octapod's center) is fully immersed in the film and points toward the substrate, like a ballerina performing a grand battement. In some areas, a hexagonal-like pattern is formed by the ballerinas in which the six nonvertical pods, which are all embedded in the film, maintain a pod-pod parallel configuration with respect to neighboring particles. We hypothesize that the mechanism responsible for such a self-assembly is based on a fast adsorption of the octapods from bulk solution to the droplet/air interface during the early stages of solvent evaporation. At this interface, the octapods maintain enough rotational freedom to organize mutually in a pod-pod parallel configuration between neighboring octapods. As the solvent evaporates, the octapods form a ballerina-rich octapod-polymer composite in which the octapods are in close contact with the substrate. Finally, we found that the resulting octapod-polymer composite is less hydrophilic than the polymer-only film.

No MeSH data available.


Related in: MedlinePlus

Arrangement of octapods after slow drying of a drop froman organic-richtoluene solution. (a) LABE-SEM top-view image revealing the self-assemblyof octapods into a hexagonal-like structure in the coffee-stain regionformed on the SiO2 substrate; the inset shows a close-upview of the same image. (b) A 45°-tilt-SEI-SEM image demonstratingthe presence of the organic residues (light gray); for each octapodonly the upper section of the pod pointing upward actually protrudesout of the organic film (see sketch in the inset). (c) A 45°-tilt-LEI-SEMimage of the same zone evidencing that the remaining seven pods areinside the organic layer (see sketch in the inset). (d) Sketches summarizingthe observed assembly in both top and side view.
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fig2: Arrangement of octapods after slow drying of a drop froman organic-richtoluene solution. (a) LABE-SEM top-view image revealing the self-assemblyof octapods into a hexagonal-like structure in the coffee-stain regionformed on the SiO2 substrate; the inset shows a close-upview of the same image. (b) A 45°-tilt-SEI-SEM image demonstratingthe presence of the organic residues (light gray); for each octapodonly the upper section of the pod pointing upward actually protrudesout of the organic film (see sketch in the inset). (c) A 45°-tilt-LEI-SEMimage of the same zone evidencing that the remaining seven pods areinside the organic layer (see sketch in the inset). (d) Sketches summarizingthe observed assembly in both top and side view.

Mentions: In thiswork, we demonstrate the formation of superstructures ofoctapods that fully exploit the parallel pod–pod configuration.Such an assembly was serendipitously discovered upon drying a solutionof octapods and excess unwashed organics on a SiO2 substrateat room temperature in a solvent-saturated atmosphere. Here, the excessorganics, which stem from the synthesis, are impurities mainly consistingof free unbound surfactants and Cd-phosphate complexes. Scanning electronmicroscopy (SEM) analysis of the sample after evaporation evidenceda ringlike deposit on the substrate with a primarily hexagonal-likestructure as discerned from the top view shown in Figure 2a.


Self-assembly of octapod-shaped colloidal nanocrystals into a hexagonal ballerina network embedded in a thin polymer film.

Arciniegas MP, Kim MR, De Graaf J, Brescia R, Marras S, Miszta K, Dijkstra M, van Roij R, Manna L - Nano Lett. (2014)

Arrangement of octapods after slow drying of a drop froman organic-richtoluene solution. (a) LABE-SEM top-view image revealing the self-assemblyof octapods into a hexagonal-like structure in the coffee-stain regionformed on the SiO2 substrate; the inset shows a close-upview of the same image. (b) A 45°-tilt-SEI-SEM image demonstratingthe presence of the organic residues (light gray); for each octapodonly the upper section of the pod pointing upward actually protrudesout of the organic film (see sketch in the inset). (c) A 45°-tilt-LEI-SEMimage of the same zone evidencing that the remaining seven pods areinside the organic layer (see sketch in the inset). (d) Sketches summarizingthe observed assembly in both top and side view.
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Related In: Results  -  Collection

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fig2: Arrangement of octapods after slow drying of a drop froman organic-richtoluene solution. (a) LABE-SEM top-view image revealing the self-assemblyof octapods into a hexagonal-like structure in the coffee-stain regionformed on the SiO2 substrate; the inset shows a close-upview of the same image. (b) A 45°-tilt-SEI-SEM image demonstratingthe presence of the organic residues (light gray); for each octapodonly the upper section of the pod pointing upward actually protrudesout of the organic film (see sketch in the inset). (c) A 45°-tilt-LEI-SEMimage of the same zone evidencing that the remaining seven pods areinside the organic layer (see sketch in the inset). (d) Sketches summarizingthe observed assembly in both top and side view.
Mentions: In thiswork, we demonstrate the formation of superstructures ofoctapods that fully exploit the parallel pod–pod configuration.Such an assembly was serendipitously discovered upon drying a solutionof octapods and excess unwashed organics on a SiO2 substrateat room temperature in a solvent-saturated atmosphere. Here, the excessorganics, which stem from the synthesis, are impurities mainly consistingof free unbound surfactants and Cd-phosphate complexes. Scanning electronmicroscopy (SEM) analysis of the sample after evaporation evidenceda ringlike deposit on the substrate with a primarily hexagonal-likestructure as discerned from the top view shown in Figure 2a.

Bottom Line: In the resulting structure, each octapod is oriented like a "ballerina", that is, only one pod sticks out of the polymer film and is perpendicular to the polymer-air interface, while the opposite pod (with respect to the octapod's center) is fully immersed in the film and points toward the substrate, like a ballerina performing a grand battement.As the solvent evaporates, the octapods form a ballerina-rich octapod-polymer composite in which the octapods are in close contact with the substrate.Finally, we found that the resulting octapod-polymer composite is less hydrophilic than the polymer-only film.

View Article: PubMed Central - PubMed

Affiliation: Istituto Italiano di Tecnologia (IIT) , via Morego 30, IT-16163 Genova, Italy.

ABSTRACT
Nanoparticles with unconventional shapes may exhibit different types of assembly architectures that depend critically on the environmental conditions under which they are formed. Here, we demonstrate how the presence of polymer (polymethyl methacrylate, PMMA) molecules in a solution, in which CdSe(core)/CdS(pods) octapods are initially dispersed, affects the octapod-polymer organization upon solvent evaporation. We show that a fast drop-drying process can induce a remarkable two-dimensional (2D) self-assembly of octapods at the polymer/air interface. In the resulting structure, each octapod is oriented like a "ballerina", that is, only one pod sticks out of the polymer film and is perpendicular to the polymer-air interface, while the opposite pod (with respect to the octapod's center) is fully immersed in the film and points toward the substrate, like a ballerina performing a grand battement. In some areas, a hexagonal-like pattern is formed by the ballerinas in which the six nonvertical pods, which are all embedded in the film, maintain a pod-pod parallel configuration with respect to neighboring particles. We hypothesize that the mechanism responsible for such a self-assembly is based on a fast adsorption of the octapods from bulk solution to the droplet/air interface during the early stages of solvent evaporation. At this interface, the octapods maintain enough rotational freedom to organize mutually in a pod-pod parallel configuration between neighboring octapods. As the solvent evaporates, the octapods form a ballerina-rich octapod-polymer composite in which the octapods are in close contact with the substrate. Finally, we found that the resulting octapod-polymer composite is less hydrophilic than the polymer-only film.

No MeSH data available.


Related in: MedlinePlus