Seeded Growth Approach Research Articles

Spontaneous Emulsification of Organometallic Complexes Applied to the Synthesis of Nanocapsules Active for H2 Release from Ammonia-Borane.

Herein, we achieved spontaneous emulsification of organometallic precursors to elaborate subμm metal nanocapsules after interfacial reduction. Depending on the proportion of the three components, water, solvent, and the metal precursor, either thermodynamically stable "surfactant-free microemulsions" (SFME) or metastable Ouzo emulsions are formed. We investigated the catalytic transition metals Au, Pd, and Pt, individually or combined, and stabilized by various ligands. Upon reduction of the precursors, either shells of discrete nanoparticles (NPs) or continuous shells were obtained, for the SFME and Ouzo emulsions, respectively. The Au/Pd mixed emulsions lead to a unique structural morphology, in which the Au-Pd nanoparticles are embedded in a continuous submicronic metal shell. The AuNPs are available to grow larger particles within the NP shell using a seeded growth approach. The water-stable and surfactant-free nanocapsules are appealing as catalysts, and, as such, were evaluated for the hydrolysis of ammonia-borane as a promising catalytic strategy for H2 release from an H-high-content storage material. This work establishes for the first time a genuine activity of water-compatible gold colloids for this reaction.

Regulation of Two-Dimensional Platelet Micelles with Tunable Core Composition Distribution via Coassembly Seeded Growth Approach.

Seeded growth termed "living" crystallization-driven self-assembly (CDSA) has been identified as a powerful method to create one- or two-dimensional nanoparticles. Epitaxial crystallization is usually regarded as the growth mechanism for the formation of uniform micelles. From this perspective, the unimer depositing rate is largely related to the crystallization temperature, which is a key factor to determine the crystallization rate and regulate the core composition distribution among nanoparticles. In the present work, the coassembly of two distinct crystallizable polymers is explored in detail in a one-pot seeded growth protocol. Results have shown that polylactone containing a larger number of methylene groups (-CH2-) in their repeating units such as poly(η-octalactone) (POL) has a faster crystallization rate compared to poly(ε-caprolactone) (PCL) with a smaller number of -CH2- at ambient temperature (25 °C), thus a block or blocky platelet structure with heterogeneous composition distribution is formed. In contrast, when the crystallization temperature decreases to 4 °C, the difference of crystallization rate between both cores become negligible. Consequently, a completely random component distribution within 2D platelets is observed. Moreover, we also reveal that the core component of seed micelles is also paramount for the coassembly seeded growth, and a unique structure of flower-like platelet micelle is created from the coassembly of PCL/POL using POL core-forming seeds. This study on the formation of platelet micelles by one-pot seeded growth using two crystallizable components offers a considerable scope for the design of 2D polymer nanomaterials with a controlled core component distribution.

Precision control of one-/two-dimensional assemblies for Poly(hexamethylene carbonate) block copolymers

The precision control of monodisperse nanomaterials with spatially distinct functionalities and properties is of particular interest in materials science. Creating biocompatible/biodegradable nanoparticles that can be colloidally stable in aqueous solution further paves the way to a broad range of bio-related applications. In present work, we demonstrate the precise fabrication of aliphatic polycarbonate based one-dimensional (1D) cylinders and 2D platelet micelles using living crystallization-driven self-assembly (CDSA) by seeded growth method. By synthesizing aliphatic polycarbonate core-forming block copolymers with different corona-to-core ratios, excellent control over dimensions of 1D cylinders and 2D platelets with good uniformity is achieved through effectively epitaxial growth in ethanol based on the mass ratios of unimer-to-seed. Meanwhile, segmented nanoparticles with spatially-defined chemistries can further be prepared by sequential seeded growth approach. Moreover, these 1D/2D nanostructures are colloidally stable in water, and further show excellently biocompatible property towards L929 cells. These promising properties of polycarbonate-based micelles enable to a wide application as cargo vehicles in bio-related fields.

Increasing gold nanostars SERS response with silver shells: a surface-based seed-growth approach

A straightforward method to prepare surface enhanced Raman spectroscopy (SERS) chips containing a monolayer of silver coated gold nanostars (GNS@Ag) grafted on a glass surface is introduced. The synthetic approach is based on a seed growth method performed directly on surface, using GNS as seeds, and involving a green pathway, which only uses silver nitate, ascorbic acid and water, to grow the silver shell. The preparation was optimized to maximize signals obtaining a SERS response of one order of magnitude greater than that from the original GNS based chips, offering in the meantime good homogeneity and acceptable reproducibility. The proposed GNS@Ag SERS chips are able to detect pesticide thiram down to 20 ppb.

Seeded growth synthesis, reshaping, and damping of the localized surface plasmon resonance in Au@Fe2O3 nanoparticles

Core@shell Au@Fe2O3 nanoparticles with different iron oxide content were synthesized by a seeded-growth approach. The morphology and structural analysis were carried out by transmission electron microscopy (TEM and HR-TEM) and X-ray diffraction (XRD). The oxidation state of the iron was determined through cyclic voltammetry measurements. The plasmonic resonance modes were investigated by Infrared (IR) and UV–vis spectroscopy. The morphology analysis of Au nanowires (AuNW’s) shows a modification from NW’s (seeds) to faceted nanoparticles, while spectroscopic studies show a disappearance of the Propagation Surface Plasmon Resonance (PSPR) due to this change. Localized Surface Plasmon Resonance (LSPR) is damped due to the aggregation of the iron oxide layer.

Understanding the Seeded Heteroepitaxial Growth of Crystallizable Polymers: The Role of Crystallization Thermodynamics.

Seeded heteroepitaxial growth is a "living" crystallization-driven self-assembly (CDSA) method that has emerged as a promising route to create uniform segmented nanoparticles with diverse core chemistries by using chemically distinct core-forming polymers. Our previous results have demonstrated that crystallization kinetics is a key factor that determines the occurrence of heteroepitaxial growth, but an in-depth understanding of controlling heteroepitaxy from the perspective of crystallization thermodynamics is yet unknown. Herein, we select crystallizable aliphatic polycarbonates (PxCs) with a different number of methylene groups (xCH2, x = 4, 6, 7, 12) in their repeating units as model polymers to explore the effect of lattice match and core compatibility on the seeded growth behavior. Seeded growth of PxCs-containing homopolymer/block copolymer blend unimers from poly(ε-caprolactone) (PCL) core-forming seed platelet micelles exhibits distinct crystal growth behavior at subambient temperatures, which is governed by the lattice match and core compatibility. A case of seeded growth with better core compatibility and a smaller lattice mismatch follows epitaxial growth, where the newly created crystal domain has the same structural orientation as the original platelet substrate. In contrast, a case of seeded growth with better core compatibility but a larger lattice mismatch shows nonepitaxial growth with less-defined crystal orientations in the platelet plane. Additionally, a case of seeded growth with poor core compatibility and larger lattice mismatch results in polydisperse platelet micelles, whereby crystal formation is not nucleated from the crystalline substrate. These findings reveal important factors that govern the specific crystal growth during a seeded growth approach by using compositionally distinct cores, which would further guide researchers in designing 2D segmented materials via polymer crystallization approaches.

Ligand Induced Morphology Change and Enhancement of Luminescence Emission in CaF2:Eu(III) Nanoparticles: The Role of Ethylene Glycol, Trisodium Citrate and EDTA in Tuning the Particle Size in Seeded-Growth Approach

Ligand Induced Morphology Change and Enhancement of Luminescence Emission in CaF2:Eu(III) Nanoparticles: The Role of Ethylene Glycol, Trisodium Citrate and EDTA in Tuning the Particle Size in Seeded-Growth Approach

Uniform segmented platelet micelles with compositionally distinct and selectively degradable cores

The creation of nanoparticles with controlled and uniform dimensions and spatially defined functionality is a key challenge. The recently developed living crystallization-driven self-assembly (CDSA) method has emerged as a promising route to one-dimensional (1D) and 2D core–shell micellar assemblies by seeded growth of polymeric and molecular amphiphiles. However, the general limitation of the epitaxial growth process to a single core-forming chemistry is an important obstacle to the creation of complex nanoparticles with segmented cores of spatially varied composition that can be subsequently exploited in selective transformations or responses to external stimuli. Here we report the successful use of a seeded growth approach that operates for a variety of different crystallizable polylactone homopolymer/block copolymer blend combinations to access 2D platelet micelles with compositionally distinct segmented cores. To illustrate the utility of controlling internal core chemistry, we demonstrate spatially selective hydrolytic degradation of the 2D platelets—a result that may be of interest for the design of complex stimuli-responsive particles for programmed-release and cargo-delivery applications.

Chemical shield effect of metal complexation on seeded growth of poly(ε-caprolactone) core-forming blends

Seeded growth approach is an ambient temperature, living crystallization-driven self-assembly (CDSA) process of crystallizable block copolymers (BCPs) in selective solvents, which enables to the formation of micelle particles in a controllable and designable way. However, the seeded growth of crystallizable BCPs under spatial restriction exerted by external interactions is rarely explored. In present work, the seeded growth of polymer blend involving homopolymer and BCP is extensively studied with the unique complexation interaction between metal ions and poly(4-vinylpyridine) (P4VP) corona segments. Incorporation of certain amount of metal ions with 1D PCL-b-P4VP (PCL = poly(ε-caprolactone)) seeds would result in the inactivity of crystalline seeds. This chemical shield effect is largely related to the binding strength and molar ratio of metal ion to 4VP groups. The metal complexation between Cu2+ and PCL/PCL-b-P4VP blend unimer that is for seeded growth would also lead to the failure of successful epitaxial growth, which is caused by the cross-linking effect of P4VP segments in the presence of metal ions. Nevertheless, this cross-linking effect could be efficiently removed by adding a ligand that has a much stronger binding strength with Cu2+. Our finding provides a deep understanding of metal complexation on the seeded growth of crystallizable BCPs, and also provides useful information about the chemical shield effect exerted by corona conformation that will guide future studies of living CDSA.

Synthesis of chorogi-like Au nanoparticles with chiral plasmonic response and enantioselective electrocatalytic activity

Shape control of Au nanoparticles is crucial for their optical and catalytic applications. Herein, we present a chiral cysteine-directed seeded-growth approach to synthesize chorogi-like Au nanoparticles. The formation of such unique structure is due to the selective adsorption of chiral cysteine molecules on high-Miller-index surfaces of Au nanoparticles during growth, which also result in the chirality transfer from molecule to nanoparticle. The obtained Au nanoparticles exhibit distinct chiral plasmonic response and excellent enantioselective electrocatalytic activity for tryptophan oxidation. Our work adds a new member to Au nanoparticle library and will offer new opportunities for broadening optical and catalytic applications of Au nanoparticles.

Scalable and Uniform Length-Tunable Biodegradable Block Copolymer Nanofibers with a Polycarbonate Core via Living Polymerization-Induced Crystallization-Driven Self-assembly.

Uniform 1D block copolymer (BCP) nanofibers prepared by the seeded-growth approach termed living crystallization-driven self-assembly (CDSA) offer promising potential for various applications due to their anisotropy, length tunability, and variable core and coronal chemistries. However, this procedure consists of a multi-step process involving independent BCP synthesis and self-assembly steps, where the latter is performed at low solution concentrations (<1 wt %), hindering scale-up. Here, we demonstrate the use of a one-pot BCP synthesis and self-assembly process, polymerization-induced CDSA (PI-CDSA), to access length-disperse nanofibers with a biodegradable crystalline poly(fluorenetrimethylenecarbonate) (PFTMC) core and a hydrophilic poly(ethylene glycol) (PEG) corona derived from PEG-b-PFTMC at concentrations up to 20 wt %, 400 times higher than those previously reported. Furthermore, living PI-CDSA could be used to access scalable, low dispersity, and length-tunable 1D PEG-b-PFTMC nanofibers at concentrations of up to 10 wt %. This provides the first example of living PI-CDSA involving an all-organic and biodegradable BCP that utilizes a conveniently implemented BCP synthesis protocol and does not involve living anionic polymerization. Significantly, samples of low-dispersity nanofibers of controlled lengths from 100 to 660 nm (Lw/Ln = 1.08-1.20) were prepared, allowing for upscaled access to well-defined biodegradable nanofibers at useful length-scales for applications in nanomedicine. Interestingly, detailed studies revealed a key role for PFTMC homopolymer impurities in the BCP prepared in situ in the formation of nanofibers under the reaction conditions used.

Precise Control of Two-Dimensional Platelet Micelles from Biodegradable Poly(p-dioxanone) Block Copolymers by Crystallization-Driven Self-Assembly

Two-dimensional (2D) core–shell nanoparticles have been attracting increasing interest due to their wide applications in materials science. Living crystallization-driven self-assembly (CDSA) is an ambient temperature, seeded growth method of crystallizable block copolymers (BCPs) in selective solvents, which has been demonstrated to be a powerful tool for the creation of one-dimensional (1D)/2D nanomaterials with precise control over size and compositions. Nevertheless, the development of an efficient living CDSA approach is a challenge for the case of semicrystalline poly(p-dioxanone) (PPDO) as a core-forming block, where the dimensional control is poor. Herein, we demonstrate that the insufficient size control of 2D PPDO platelets could be overcome through modulation of solvent compositions or elevating the crystallization temperatures for PPDO. The possible mechanism involves an improved unimer solubility that avoids fast unimer aggregation. As a result, uniform 2D platelet micelles with a controlled area over a substantial size range are created via epitaxial growth of the unimer. It is noteworthy that the shape control of 2D platelet micelles from quasi-square to elongated hexagon to lozenge shapes can be accessible by regulating the crystallization conditions such as adding different amounts of cosolvents or crystallization at an elevated temperature. Meanwhile, spatially defined block comicelles can be achieved via the seeded growth approach from PPDO core-forming BCPs with different corona functionalities at elevated temperatures. The excellent water stability and biocompatibility properties of 2D PPDO platelet micelles further enable them to have a potential application as cargo vehicles in the drug delivery field.

Continuous flow synthesis of plasmonic gold patches and nearly-complete nanoshells on polystyrene core particles

We describe the development of a T-mixer based continuous flow process for the coating of 86–500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth. After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters. This reveals a considerable tunability of the patch morphology and, by virtue of the localized surface plasmon resonance of gold, the optical properties of the product dispersions. In order to further widen the range of nanostructures accessible by our process, a second T-mixer was added. This introduced new gold precursor, leading to further growth of the patches that were formed after the first mixer. By this approach, nearly-complete gold nanoshells could be produced in high yield on both small and large core particles, without the unwanted production of free-standing gold nanoparticles. Due to the pronounced optical properties of nearly-complete gold nanoshells on small core particles, we could estimate from electrodynamic simulations the equivalent shell thickness to be as low as 8.6 nm. This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells. Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical properties.

Monodisperse CuInS2/CdS and CuInZnS2/CdS Core–Shell Nanorods with a Strong Near‐Infrared Emission

AbstractGiven the ubiquitous examples of semiconductor nanorods synthesis, CuInS2‐based anisotropic heterostructures still lag behind in terms of shape/optical properties control. Here, core/shell CuInS2/CdS dot‐in‐rod nanoheterostructures which exhibit high degree of the morphology control, and a strong emission in the near‐infrared range of 700–900 nm, are realized. The authors made use of the seeded growth approach utilizing wurtzite CuInS2 quantum dots as seeds, which allows for tuning the dimension of the resulting core/shell nanorods, including the core size and the shell thickness. Time‐dependent photoluminescence studies reveal slowing down of the recombination rate with increasing thickness of the shell, which is characteristic for the quasi‐type II heterostructure. Alloying of the CuInS2 cores with Zn does not perturb the shell growth process, but enables improvement of the photoluminescence quantum yield of the resulting core/shell CuInZnS2/CdS nanorods to 45%, as compared to ≈30% for CuInS2/CdS nanorods.

Supramolecular polymerization based on the metalation of porphyrin nanosheets in aqueous media

The metalation-dependent assembling behavior of porphyrin-based supramolecular aggregates with tunable areas and narrow dispersity is demonstrated via a seeded growth approach.

Polyallylamine assisted synthesis of 3D branched AuNPs with plasmon tunability in the vis-NIR region as refractive index sensitivity probes

This paper describes the synthesis of highly branched gold nanoparticles (AuNPs) through a facile seeded growth approach using poly(allylamine hydrochloride) (PAH) as shape inducing agent. The obtained branched AuNPs present highly tunable optical properties in the Vis-NIR region from ca. 560 nm to 1260 nm. We controlled the morphology, and therefore the optical response, of the NPs by either changing the gold salt to seeds ratio or by fine-tuning the solution pH. We proposed that the formation of size-dependent PAH-AuCl4- aggregates as demonstrated by dynamic light scattering measurements, together with pH-dependent gold salt speciation might be responsible for the branched morphology. Advanced electron microscopy techniques demonstrated the polycrystalline nature of the AuNPs and facilitated a better understanding of branched morphology. Additionally, the refractive index sensitivity estimated by the inflection point of the Localized Surface Plasmon Resonance (LSPR) band can be controlled by tuning the nanoparticle branching. Furthermore, the versatility of the PAH chemistry allowed the easy functionalization of the synthesized NPs.

Stable Iron Oxide Nanoflowers with Exceptional Magnetic Heating Efficiency: Simple and Fast Polyol Synthesis.

Magnetically induced hyperthermia has reached a milestone in medical nanoscience and in phase III clinical trials for cancer treatment. As it relies on the heat generated by magnetic nanoparticles (NPs) when exposed to an external alternating magnetic field, the heating ability of these NPs is of paramount importance, so is their synthesis. We present a simple and fast method to produce iron oxide nanostructures with excellent heating ability that are colloidally stable in water. A polyol process yielded biocompatible single core nanoparticles and nanoflowers. The effect of parameters such as the precursor concentration, polyol molecular weight as well as reaction time was studied, aiming to produce NPs with the highest possible heating rates. Polyacrylic acid facilitated the formation of excellent nanoheating agents iron oxide nanoflowers (IONFs) within 30 min. The progressive increase of the size of the NFs through applying a seeded growth approach resulted in outstanding enhancement of their heating efficiency with intrinsic loss parameter up to 8.49 nH m2 kgFe-1. The colloidal stability of the NFs was maintained when transferring to an aqueous solution via a simple ligand exchange protocol, replacing polyol ligands with biocompatible sodium tripolyphosphate to secure the IONPs long-term colloidal stabilization.

Effect of Gold Nanoparticles on Transport Properties of the Protic Ionic Liquid Propylammonium Nitrate

Here, we analyze the effect of gold-nanoparticle (AuNPs)-doping of the protic ionic liquid (IL) propyl ammonium nitrate (PAN) on some physical properties, such as density, viscosity, and ionic conductivity, in a broad temperature range. This IL was lightly doped with four different AuNPs (concentration of gold lower than 0.2 mM): Au nanospheres of about 15, 60, and 80 nm diameter and Au nanorods of about 40 nm length and 12 nm width. AuNPs were synthesized following a seed growth approach and further functionalized with O-[2-(3-mercapto propionylamino)ethyl] O′-methyl-poly(ethylene glycol) (m-PEG-SH) in order to provide stability to the IL medium. The stability of the AuNPs in PAN was characterized by UV–vis spectroscopy. The results obtained here indicate that their presence produces a strong influence on the measured transport properties of PAN, decreasing viscosity up to 25% and increasing ionic conductivity up to 10% for the smallest AuNPs. Moreover, as temperature increases, the influence of AuNPs produces a decrease in the percentage deviations for viscosity and ionic conductivity. In the case of density, the AuNP-doping produces a mainly unexpected increase only for the sample with the smallest AuNPs, that is practically constant with temperature. When we equalize the AuNP concentration for all sizes and shapes, it is observed that the smallest AuNPs give higher variations in the studied properties than the bigger ones; also, the shape of the rod has an influence on the measured results. In addition, we have applied Walden’s rule to relate the three measured magnitudes, observing that AuNP addition decreases ionicity with respect to the reference sample, which is even more when we added smaller AuNPs. Finally, we explain all data assuming cation solvation of the AuNPs, which creates a local breaking of the pseudolattice structure of the PAN. Comparison with other published data is difficult because the behavior of a nanoparticle solution strongly depends on its particular composition and no data are available, in our knowledge, of any similar mixture to those studied here.

Ionic Liquid-Assisted MAPbI3 Nanoparticle-Seeded Growth for Efficient and Stable Perovskite Solar Cells.

With the rapid improvement of perovskite solar cells (PSCs), long-life operational stability has become a major requirement for their commercialization. In this work, we devised a pristine cesium-formamidinium-methylammonium (termed as CsFAMA) triple-cation-based perovskite precursor solution into the ionic liquid (IL)-assisted MAPbI3 nanoparticles (NPs) through a seeded growth approach in which the host IL-assisted MAPbI3 NPs remarkably promote high-quality perovskite films with large single-crystal domains, enhancing the device performance and stability. The power conversion efficiency (PCE) of the MAPbI3 NP-seeded growth of MAPbI3 NPs/CsFAMA-based PSCs is as high as 19.44%, which is superior to those of MAPbI3 NPs and pristine CsFAMA films as the photoactive layer (9.52 and 17.33%, respectively). The long-term light-soaking and moisture stability of IL-aided MAPbI3 NPs/CsFAMA-based devices (non-encapsulated) remain above 90 and 80%, respectively, of their initial output after 2 h of light illumination (1 sun) and 6000 h storage at ambient with a relative humidity range of 30-40%. The use of the IL-assisted MAPbI3 NP-seeded growth for PSCs is a significant step toward developing stable and reliable perovskite photovoltaic devices.

Dendritic Micelles with Controlled Branching and Sensor Applications.

Although micelles derived from the solution self-assembly of amphiphilic molecules and polymers have been prepared with a wide variety of shapes, examples with well-defined branched structures have remained elusive. We describe a divergent, directed self-assembly approach to low dispersity dendritic micelles with a high degree of structural perfection and tailorable branch numbers and generations. We use block copolymer amphiphiles as precursors and a crystallization-driven seeded growth approach whereby the termini of fiber-like micelles function as branching sites. Different dendrimeric generations are accessible by adjusting the ratio of added unimers to pre-existing seed micelles where the branch positions are determined by the reduced coronal chain grafting density on the surface of the micelle crystalline core. We demonstrate the spatially defined decoration of the assemblies with emissive nanoparticles and utility of the resulting hybrids as fluorescent sensors for anions where the dendritic architecture enables ultrahigh sensitivity.