Polymer/layered silicate nanocomposites: a review from preparation to processing

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

https://cyberleninka.org/article/n/1018032.pdf

Polymer nanotechnology: Nanocomposites

Coinage metals, such as Au, Ag, and Cu, have been important materials throughout history.1 While in ancient cultures they were admired primarily for their ability to reflect light, their applications have become far more sophisticated with our increased understanding and control of the atomic world. Today, these metals are widely used in electronics, catalysis, and as structural materials, but when they are fashioned into structures with nanometer-sized dimensions, they also become enablers for a completely different set of applications that involve light. These new applications go far beyond merely reflecting light, and have renewed our interest in maneuvering the interactions between metals and light in a field known as plasmonics.2–6

In plasmonics, the metal nanostructures can serve as antennas to convert light into localized electric fields (E-fields) or as waveguides to route light to desired locations with nanometer precision. These applications are made possible through a strong interaction between incident light and free electrons in the nanostructures. With a tight control over the nanostructures in terms of size and shape, light can be effectively manipulated and controlled with unprecedented accuracy.3,7 While many new technologies stand to be realized from plasmonics, with notable examples including superlenses,8 invisible cloaks,9 and quantum computing,10,11 conventional technologies like microprocessors and photovoltaic devices could also be made significantly faster and more efficient with the integration of plasmonic nanostructures.12–15 Of the metals, Ag has probably played the most important role in the development of plasmonics, and its unique properties make it well-suited for most of the next-generation plasmonic technologies.16–18

1.1. What is Plasmonics?
Plasmonics is related to the localization, guiding, and manipulation of electromagnetic waves beyond the diffraction limit and down to the nanometer length scale.4,6 The key component of plasmonics is a metal, because it supports surface plasmon polariton modes (indicated as surface plasmons or SPs throughout this review), which are electromagnetic waves coupled to the collective oscillations of free electrons in the metal.

While there are a rich variety of plasmonic metal nanostructures, they can be differentiated based on the plasmonic modes they support: localized surface plasmons (LSPs) or propagating surface plasmons (PSPs).5,19 In LSPs, the time-varying electric field associated with the light (Eo) exerts a force on the gas of negatively charged electrons in the conduction band of the metal and drives them to oscillate collectively. At a certain excitation frequency (w), this oscillation will be in resonance with the incident light, resulting in a strong oscillation of the surface electrons, commonly known as a localized surface plasmon resonance (LSPR) mode.20 This phenomenon is illustrated in Figure 1A. Structures that support LSPRs experience a uniform Eo when excited by light as their dimensions are much smaller than the wavelength of the light.



Figure 1

Schematic illustration of the two types of plasmonic nanostructures discussed in this article as excited by the electric field (Eo) of incident light with wavevector (k). In (A) the nanostructure is smaller than the wavelength of light and the free electrons ...



In contrast, PSPs are supported by structures that have at least one dimension that approaches the excitation wavelength, as shown in Figure 1B.4 In this case, the Eo is not uniform across the structure and other effects must be considered. In such a structure, like a nanowire for example, SPs propagate back and forth between the ends of the structure. This can be described as a Fabry-Perot resonator with resonance condition l=nλsp, where l is the length of the nanowire, n is an integer, and λsp is the wavelength of the PSP mode.21,22 Reflection from the ends of the structure must also be considered, which can change the phase and resonant length. Propagation lengths can be in the tens of micrometers (for nanowires) and the PSP waves can be manipulated by controlling the geometrical parameters of the structure.23

/pdf/controlling-the-synthesis-and-assembly-of-silver-1ktlgomyt6.pdf

Controlling the synthesis and assembly of silver nanostructures for plasmonic applications

A review on polymer–layered silicate nanocomposites

We demonstrate a unique capability in partially oxidizing the oligoaniline shell on gold nanoparticles to polyaniline. Because of the solubility difference, the unreacted inner shell section can be selectively dissolved by 2-propanol, giving yolk-shell nanostructures and, thus, making it possible for assessing the oxidized section. The ionic diffusion through the polymer shell is found to be the rate-determining step in the overall process. Conservative estimates show that the diffusion coefficient of AuCl4– is at least 700 times slower than that of the typical rate values in traditional studies. It is most likely caused by the lack of micropores in the polymer structures. Such mircopores are hard to avoid in preparing polymer membranes by casting or drying of polymers dissolved in organic solvents. We can rule out the presence of irregular pores on the basis of the uniformly oxidized shell section. With the nanoscale shells, the system is sensitive enough to detect minute changes in the shell or small di...

Measuring the Unusually Slow Ionic Diffusion in Polyaniline via Study of Yolk-Shell Nanostructures

Understanding detailed electric near-field distributions around noble metal nanostructures is crucial to the rational design of metallic substrates for maximizing surface-enhanced Raman scattering (SERS) efficiency. We obtain SERS signals from specific regions such as the ends, the sides and the entire surfaces of gold nanorod by chemisorbing analytes on the respective areas. Different SERS intensities from designated surfaces reflect their electric near-field intensities and thus the distributions. Our experimental results show that approximately 65% of the SERS enhancement emanated from the ends of gold nanorods which occupies only 28% of the total surface area, quantitatively exhibiting the strongly localized electric field around the ends. The reliability and generality of the investigation is confirmed by employing analytes with different chemical characteristics: positively and negatively charged, neutral, hydrophobic and hydrophilic ligands, which are selectively adsorbed on the different sites. Numerical simulations of the electric near-field distributions around the nanorod are in well agreement with our experimental results. In addition, we observed that the SERS intensities of colloidal gold nanospheres are independent of surface areas being functionalized by analytes, indicating a homogenous electric near-field distribution around gold nanospheres.

/pdf/site-selective-localization-of-analytes-on-gold-nanorod-6wn6mh28wq.pdf

Site-selective localization of analytes on gold nanorod surface for investigating field enhancement distribution in surface-enhanced Raman scattering

We report a new approach to study the kinetics of ligand exchange on colloidal gold nanoparticles, where the coordination and dissociation of surface ligands could be monitored in situ by surface-enhanced Raman scattering.

/pdf/probing-the-kinetics-of-ligand-exchange-on-colloidal-gold-3mlx3384xp.pdf

Probing the kinetics of ligand exchange on colloidal gold nanoparticles by surface-enhanced Raman scattering.

Probing the Kinetics of Short‐Distance Drug Release from Nanocarriers to Nanoacceptors

Parallel-stacked gold nanowires (NWs) in a ring conformation are induced to coalesce, forming solid seamless rings. The axial lattice orientation of the original Au NWs is preserved in the coalesced rings (see picture; scale bars 2 nm, insets 50 nm). A zipper mechanism is proposed to reconcile the three major events in coalescing nanocrystals: ligand loss, lattice alignment, and coalescence.

Hongyu Chen

Papers

Measuring the Unusually Slow Ionic Diffusion in Polyaniline via Study of Yolk-Shell Nanostructures

Site-selective localization of analytes on gold nanorod surface for investigating field enhancement distribution in surface-enhanced Raman scattering

Probing the kinetics of ligand exchange on colloidal gold nanoparticles by surface-enhanced Raman scattering.

Probing the Kinetics of Short‐Distance Drug Release from Nanocarriers to Nanoacceptors

Preservation of lattice orientation in coalescing imperfectly aligned gold nanowires by a zipper mechanism.