Interparticle Distance Research Articles

Silica‐Coated Gold Nanorod Supraparticles: A Tunable Platform for Surface Enhanced Raman Spectroscopy

AbstractPlasmonic nanoparticle assemblies are promising functional materials for surface‐enhanced Raman spectroscopy (SERS). Gold nanorod (AuNR) assemblies are of particular interest due to the large, shape‐induced local field enhancement and the tunable surface plasmon resonance of the AuNRs. Designing the optimal assembly structure for SERS, however, is challenging and requires a delicate balance between the interparticle distance, porosity, and wetting of the assembly. Here, a new type of functional assemblies–called supraparticles–fabricated through the solvent‐evaporation driven assembly of silica‐coated gold nanorods into spherical ensembles, in which the plasmonic coupling and the mass transport is tuned through the thickness and porosity of the silica shells are introduced. Etching of the AuNRs allowed fine‐tuning of the plasmonic response to the laser excitation wavelength. Using a correlative SERS‐electron microscopy approach, it is shown that all supraparticles successfully amplified the Raman signal of the crystal violet probe molecules, and that the Raman signal strongly increased when decreasing the silica shell thickness from 35 to 3 nm, provided that the supraparticles have a sufficiently high porosity. The supraparticles introduced in this study present a novel class of materials for sensing, and open up a wide parameter space to optimize their performance.

Hydrogen sensing by plasmon decoupling effect in nanostructured Pd/Au films

Plasmon coupling effect occurs in plasmonic nanostructures when interparticle distances are in the order of particle size leading to spectral shifts in the plasmonic band. This effect has been recently highlighted for measurement of fluctuations in the interparticle distance at nanoscale level. In this study, nanostructured thin Au films were deposited on quartz substrates by pulsed laser deposition (PLD) for sensing of hydrogen gas. A blue shift from 730 to 560 nm in LSPR of Au films was observed when substrate temperatures rises from 25 to 600 °C due to variation in morphology of films from a continuous surface composed of tiny agglomerates to granular surface composed of bigger particles with increased interparticle spacing. For plasmon coupling sensing of hydrogen, a thin Pd film was deposited on top of nanostructured Au films. Upon hydrogen exposure, up to12 nm blue shift within few seconds was observed depending on hydrogen concentration. Based on field emission scanning electron microscope (FESEM) images and finite-difference time-domain (FDTD) simulations, this plasmon sensing is explained by hydrogen-induced decoupling due to the formation of surface stresses in Pd, which can affect the LSPR via an increase in interparticle spacing of Au nanoislands. • Nanostructured Au/quartz films were deposited prepared by pulsed laser deposition at different substrate temperatures. • The interparticle distance of Au films increases with temperature, leading to blue shift in the gold plasmonic absorption. • A thin Pd layer as hydrogen catalyst was deposited on Au/quartz samples by DC magnetron sputtering. • Hydrogen interaction led to a further blue shift, which was greater for films with smaller interparticle distance. • Using finite difference time domain (FDTD) simulation, this effect was attributed to a plasmon decoupling effect.

Gold and silver plasmonic nanoprobes trace the positions of histone codes

We visualized the distribution of heterochromatin in a single nucleus using plasmonic nanoparticle-conjugated H3K9me3 and H3K27me3 antibodies. Due to distance-dependent plasmonic coupling effects between nanoprobes, their scattering spectra shift to longer wavelengths as the distance between heterochromatin histone markers reduced during oncogene-induced senescence (OIS). These observations were supported by simulating scattering profiles based on considerations of particle numbers, interparticle distances, and the spatial arrangements of plasmonic nanoprobes. Using this plasmon-based colourimetric imaging, we estimated changes in distances between H3K9me3 and H3K27me3 during the formation of senescence-associated heterochromatin foci in OIS cells. We anticipate that the devised analytical technique combined with high-spatial imaging and spectral simulation will eventually lead to a new means of diagnosing and monitoring disease progression and cellular senescence.

Multifunctional coatings based on GNP/epoxy systems: Strain sensing mechanisms and Joule's heating capabilities for de-icing applications

Multifunctional coatings based on a GNP/epoxy system have been manufactured and their strain sensing and Joule's heating capabilities for anti-icing and de-icing applications have been explored. It has been observed that an increase in the GNP content induces a detriment on the gauge factor (from 5.75 at 8% to 2.49 at 12%) due to a lower interparticle distance between nanoparticles, being less sensitive. However, in any case, the GF values at bending conditions are significantly above conventional metallic gauges (which is around 2). On the other hand, the resistive heating is more efficient when increasing the GNP content, as expected, due to a higher number of conducting pathways that allows a more efficient Joule's heating effect. However, and due to the heterogeneity present at 12% GNP samples due to the much higher viscosity of the mixture during the dispersion process, the 10% ones were selected for a de-icing proof of concept, proving that the ice completely melts after 5 min of applying 200 V. Therefore, the proposed GNP coatings show an outstanding capability for both strain sensing and de-icing purposes by resistive heating, being useful for a wide range of applications.

Harmonic acoustics for dynamic and selective particle manipulation.

Precise and selective manipulation of colloids and biological cells has long been motivated by applications in materials science, physics and the life sciences. Here we introduce our harmonic acoustics for a non-contact, dynamic, selective (HANDS) particle manipulation platform, which enables the reversible assembly of colloidal crystals or cells via the modulation of acoustic trapping positions with subwavelength resolution. We compose Fourier-synthesized harmonic waves to create soft acoustic lattices and colloidal crystals without using surface treatment or modifying their material properties. We have achieved active control of the lattice constant to dynamically modulate the interparticle distance in a high-throughput (>100 pairs), precise, selective and reversible manner. Furthermore, we apply this HANDS platform to quantify the intercellular adhesion forces among various cancer cell lines. Our biocompatible HANDS platform provides a highly versatile particle manipulation method that can handle soft matter and measure the interaction forces between living cells with high sensitivity.

Cellulose nanocrystals to modulate the self-assembly of graphene oxide in suspension

Controlling the self-assembly(SA) of cellulose nanocrystals(CNC) and graphene-oxide(GO) sheets at nanoscale is crucial for exploiting properties of both CNC and GO. The SA mechanism of GO, CNC and CNC/GO in suspension is evaluated at different concentrations and mixing ratios. SAXS determine the interparticle distance, interaction and distribution of CNC and GO to resolve the self-assembling mechanism. At lower concentrations, the GO sheets are distributed randomly and separated by a large inter-sheet distance of 83 nm with poor inter-sheet interaction. As increases the GO concentration, the inter-sheet repulsion results in a nematic arrangement with the inter-sheet distance decreasing from 83 to 52 nm. Mixing isotropic and nematic phase of CNC with GO at different CNC/GO ratio from 2 to 50 shows transitions from isotropic, to biphasic and nematic state. In isotropic state, at low CNC/GO ratio, the GO sheets are randomly distributed between the CNC rods which increases the CNC inter-rod distance from 22 to 51 nm. However, at higher CNC/GO ratios, steric repulsion from the large amount of CNC forces the GO sheets to align following the direction of CNC nematic assembly. Understanding SA mechanisms of nanostructures in CNC-GO hybrid will enable to engineer applications for sensor, electronics and diagnostics.

Jamming of Nano-Ellipsoids in a Microsphere: A Quantitative Analysis of Packing Fraction by Small-Angle Scattering

The packing of particles is ubiquitous, and it is of fundamental importance, particularly in materials science in the nanometric length scale. It becomes more intriguing when constituent particles deviate from spherical symmetry owing to the inherent complexity in quantifying their positional and rotational correlation. For quantitative estimation of packing fraction, it requires a thorough analysis of the positional correlation of jammed particles. This article adopts a novel approach for determination of the packing fraction of strongly correlated nano-ellipsoids in a microsphere using small-angle scattering. The method has been elucidated through a quantitative analysis of structural correlation of nano-hematite ellipsoids in 3D micrometric granules, which are realized using rapid evaporative assembly. Owing to the deviation from spherical symmetry, the conventional analysis of scattering data fails to interpret the actual packing fraction of the anisotropic particles. The structural correlation gets smeared out because of orientation distribution among the packed anisotropic particles, which leads to an anomaly in the estimation of packing fraction using the conventional analysis approach. It is illustrated that consideration of an interparticle distance distribution function of the correlated nano-ellipsoids becomes indispensable in determining their packing fraction.

Thermal Switching of Near-Field Radiative Heat Transfer Between Nanoparticles via Multilayered Surface Modes

We theoretically demonstrate near-field radiative thermal switching between two nanoparticles located above a multilayered slab. We propose a multilayered structure composed of $\mathrm{Si}\mathrm{C}$ and the phase transition material ${\mathrm{VO}}_{2}$. The high tunability of the multilayered structure enables the active modulation of surface polaritons when combined with the phase transition feature of ${\mathrm{VO}}_{2}$, overcoming the intrinsic resonance of the thermal radiation of ${\mathrm{VO}}_{2}$. Utilizing this feature, the surface polaritons enormously excited at the particle's resonant frequency above the multilayer can be switched on or off, resulting in the efficient modulation of heat flux between nanoparticles. The effects of interparticle distance and multilayer parameters on thermal switching ratios are investigated. We demonstrate that the multilayer with metallic ${\mathrm{VO}}_{2}$ can significantly inhibit the heat flux between particles as a result of the destructive interference between direct and reflected waves. The excited surface modes above the multilayer with insulating ${\mathrm{VO}}_{2}$ can still improve the heat flux between nanoparticles, resulting in a thermal switching ratio of ${10}^{\ensuremath{-}5}$ at the particle resonant frequency at a large interparticle distance.

High enhancement of near-field radiative heat transfer between nanoparticles via the surface modes of the dielectric thin film

We study the radiative heat transfer between two nanoparticles placed above the thin film under the framework of the dipole approximation and reflection Green's function. We show a high enhancement of heat transfer between particles, owing to the antisymmetric and symmetric surface modes excited at a wide band. The presence of the SiC thin film produces four orders of magnitude of amplification for the case of SiC particles which support the localized surface phonon polaritons (SPhPs). Enhancement is caused by the intense surface modes excited at the particle resonance and further proved through spectral analysis. The thin film can also provide an enhancement at a considerable distance, different from the huge inhibitory effect exhibited in the semi-infinite slab case. We address the role of the interparticle distance in the enhancement of heat flux by analyzing the SPhPs propagation length above the thin film. Finally, we show the thin film can intensify the coupling between SiC and doped Si particles, bringing out a high enhancement of radiative heat transfer between two particles with dissimilar materials. This enhancement is also attributed to the strong antisymmetric modes that amplify the emitted electric field energy density in the half-space from the SiC particle. This type of strong amplification can play an essential role in thermal tuning in the nanoparticle system.

Effective viscosity of random suspensions without uniform separation

This work is devoted to the definition and the analysis of the effective viscosity associated with a random suspension of small rigid particles in a steady Stokes fluid. While previous works on the topic have conveniently assumed that particles are uniformly separated, we relax this restrictive assumption in the form of mild moment bounds on interparticle distances.

Effect of size and interparticle distance of nanoparticles on the formation of bubbles induced by nanosecond laser

When a laser beam is irradiated on nanoparticles (optical absorbers) in a liquid, massive heat is generated, which causes vaporization of a nearby liquid, followed by the formation of bubbles. Despite the potential application of these bubbles for cancer diagnosis and therapy, solar energy harvesting, and local chemical reaction enhancement, little is known on how the size and interparticle distance of optical absorbers affect laser-induced bubble formation. Additionally, observing the bubble dynamics near nanomaterials is challenging due to their fast growth and immediate collapse. In this study, we trapped bubbles using hydrogels and investigated how their diameter changed with the size and interparticle distance of nanoparticles or their agglomerates and the energy level of laser irradiation. We found that the size of trapped bubbles increased with softer hydrogels, higher laser energy level, larger agglomerate size, and smaller interparticle distance among agglomerates. Based on these observations, we suggest that nanobubbles initially formed on nanoparticles merged to become microbubbles.

Edge fluctuations and third-order phase transition in harmonically confined long-range systems

We study the distribution of the position of the rightmost particle x max in a N-particle Riesz gas in one dimension confined in a harmonic trap. The particles interact via long-range repulsive potential, of the form r −k with −2 < k < ∞ where r is the inter-particle distance. In equilibrium at temperature O(1), the gas settles on a finite length scale L N that depends on N and k. We numerically observe that the typical fluctuation of y max = x max/L N around its mean is of . Over this length scale, the distribution of the typical fluctuations has a N independent scaling form. We show that the exponent η k obtained from the Hessian theory predicts the scale of typical fluctuations remarkably well. The distribution of atypical fluctuations to the left and right of the mean ⟨y max⟩ are governed by the left and right large deviation functions (LDFs), respectively. We compute these LDFs explicitly ∀ k > −2. We also find that these LDFs describe a pulled to pushed type phase transition as observed in Dyson’s log-gas (k → 0) and 1d one component plasma (k = −1). Remarkably, we find that the phase transition remains third order for the entire regime. Our results demonstrate the striking universality of the third order transition even in models that fall outside the paradigm of Coulomb systems and the random matrix theory. We numerically verify our analytical expressions of the LDFs via Monte Carlo simulation using an importance sampling algorithm.

The effect of sink strength on helium bubble formation at elevated temperatures

In present study, the model Fe–9Cr alloy and two nanostructured ferritic alloys (NFAs) CNA1 and 9YWTV with high application potential in advanced nuclear power systems were selected to systematically investigate the effect of sink strength on helium bubble behavior at elevated temperatures. Helium bubble formation for a constant implanted He concentration of ∼7500 atomic parts per million (appm) was characterized using transmission electron microscopy (TEM) at 500 and 700 °C. A quantitative research and comparison of the influence for a specific sink strength on bubble formation was illustrated. Results showed that the introduction of nanoparticles into NFAs can effectively reduce bubble coarsening by sequestering the implanted helium into dispersed small bubbles due to the sufficient He entrapment by interfaces between the nanoprecipitates and the surrounding matrix. In addition, the NFAs with higher sink strength (9YWTV) revealed a higher suppression effects on bubble growth compared to general particle-free Fe–9Cr alloy and CNA1 with lower sink strength. This can be attributed to the comparable mean free path of He diffusion with the inter-particle distance for high particle density in 9YWTV. Meanwhile, the suppression effects of sinks on bubble growth decreased with increasing temperature from 500 to 700 °C. The sink strength of the order of 1015 m−2 and 1016 m−2 showed favorable suppression effect on bubble coarsening at 500 °C and 700 °C, respectively.

Warm Dark Matter Galaxies with Central Supermassive Black Holes

We generalize the Thomas–Fermi approach to galaxy structure to include central supermassive black holes and find, self-consistently and non-linearly, the gravitational potential of the galaxy plus the central black hole (BH) system. This approach naturally incorporates the quantum pressure of the fermionic warm dark matter (WDM) particles and shows its full power and clearness in the presence of supermassive black holes. We find the main galaxy and central black hole magnitudes as the halo radius rh, halo mass Mh, black hole mass MBH, velocity dispersion σ, and phase space density, with their realistic astrophysical values, masses and sizes over a wide galaxy range. The supermassive black hole masses arise naturally in this framework. Our extensive numerical calculations and detailed analytic resolution of the Thomas–Fermi equations show that in the presence of the central BH, both DM regimes—classical (Boltzmann dilute) and quantum (compact)—do necessarily co-exist generically in any galaxy, from the smaller and compact galaxies to the largest ones. The ratio R(r) of the particle wavelength to the average interparticle distance shows consistently that the transition, R≃1, from the quantum to the classical region occurs precisely at the same point rA where the chemical potential vanishes. A novel halo structure with three regions shows up: in the vicinity of the BH, WDM is always quantum in a small compact core of radius rA and nearly constant density; in the region rA&lt;r&lt;ri until the BH influence radius ri, WDM is less compact and exhibits a clear classical Boltzmann-like behavior; for r&gt;ri, the WDM gravity potential dominates, and the known halo galaxy shows up with its astrophysical size. DM is a dilute classical gas in this region. As an illustration, three representative families of galaxy plus central BH solutions are found and analyzed: small, medium and large galaxies with realistic supermassive BH masses of 105M⊙, 107M⊙ and 109M⊙, respectively. In the presence of the central BH, we find a minimum galaxy size and mass Mhmin≃107M⊙, larger (2.2233×103 times) than the one without BH, and reached at a minimal non-zero temperature Tmin. The supermassive BH heats up the DM and prevents it from becoming an exactly degenerate gas at zero temperature. Colder galaxies are smaller, and warmer galaxies are larger. Galaxies with a central black hole have large masses Mh&gt;107M⊙&gt;Mhmin; compact or ultracompact dwarf galaxies in the range 104M⊙&lt;Mh&lt;107M⊙ cannot harbor central BHs. We find novel scaling relations MBH=DMh38 and rh=CMBH43, and show that the DM galaxy scaling relations Mh=bΣ0rh2 and Mh=aσh4/Σ0 hold too in the presence of the central BH, Σ0 being the constant surface density scale over a wide galaxy range. The galaxy equation of state is derived: pressure P(r) takes huge values in the BH vicinity region and then sharply decreases entering the classical region, following consistently a self-gravitating perfect gas P(r)=σ2ρ(r) behavior.

Chemical and Physical Properties of Photonic Noble-Metal Nanomaterials.

Colloidal noble metal nanoparticles (NPs) are composed of metal cores and organic or inorganic ligand shells. These NPs support size- and shape-dependent plasmonic resonances. They can be assembled from dispersions into artificial metamolecules which have collective plasmonic resonances originating from coupled bright and dark optical electric and magnetic modes that form depending on the size and shape of the constituent NPs and their number, arrangement, and interparticle distance. NPs can also be assembled into extended 2D and 3D metamaterials that are glassy thin films or ordered thin films or crystals, also known as superlattices and supercrystals. The metamaterials have tunable optical properties that depend on the size, shape, and composition of the NPs, and on the number of NP layers and their interparticle distance. Interestingly, strong light-matter interactions in superlattices form plasmon polaritons. Tunable interparticle distances allow designer materials with dielectric functions tailorable from that characteristic of an insulator to that of a metal, and serve as strong optical absorbers or scatterers, respectively. In combination with lithography techniques, these extended assemblies can be patterned to create subwavelength NP superstructures and form large-area 2D and 3D metamaterials that manipulate the amplitude, phase, and polarization of transmitted or reflected light.

Kinetic aspects of casein micelle cross-linking by transglutaminase at different volume fractions

Milk protein concentrates (MPC) are widespread food ingredients, due to their high protein-to-solids ratio, nutritional value, and technological properties, which can be tailored to various end uses. Interest has been given to modifying such ingredients through enzymatic cross-linking by microbial transglutaminase. However, no systematic studies on the cross-linking kinetics of casein micelles at different concentration factors are currently available, although the enzyme might act in a considerably different fashion at decreased inter-particle distances. In this study, cross-linking of casein micelles was studied in a 4x MPC obtained by ultrafiltration, and compared to that of the original skim milk. The cross-linking kinetics were evaluated by following the degree of casein polymerisation using size exclusion chromatography. The extent of polymerisation for both skim milk and 4x MPC could be scaled to a master curve by normalising the incubation time to concentration factor and enzyme level, indicating similar cross-linking kinetics. Likewise, the cross-linking of individual casein types followed the same trend regardless of treatment. However, the casein micelle size increased with cross-linking at 4x but decreased at 1x concentration, suggesting enhanced cross-linking on the surface of the casein micelles in MPC suspensions. These results are relevant for the design of novel milk protein ingredients.

A new mix design method for low-environmental-impact blended cementitious materials: Optimization of the physical characteristics of powders for better rheological and mechanical properties

The use of blended cements has attracted much interest in the quest to overcome the environmental challenges facing the concrete industry. However, partially replacing cement with supplementary cementitious materials (SCMs) can result in complex rheological behavior that is influenced by the type of SCM and the replacement percentage, as well as the physical characteristics of the particles. Adequate physical control of the blended cements is essential for improving the rheology of the suspensions. A new mix design methodology based on the physical optimization of SCMs is proposed and validated to ensure adequate rheology of the suspensions. The physical characteristics that influence the viscosity of the cement-based suspensions investigated in this study include particle-size distribution, surface roughness, maximum packing density of the powder, and interparticle distance. Based on the experimental results presented in this paper, ternary binders with optimized physical characteristics enhanced the 28-day compressive strength of mortar by 20% while decreasing the clinker content by 15% and maintaining constant fluidity.

Control of the supercrystallinity, nanocrystallinity, morphology and magnetism of cobalt nanoparticle assemblies. Towards novel colloidal crystals with high magnetic anisotropy

Starting from a colloidal solution of dodecanoic acid-coated Co nanoparticles (NP) of 8.1 nm in size and of low anisotropy and using a solvent-mediated ligand-ligand interaction strategy, we obtain either colloidal crystals or supercrystalline films. The comparison between the structural and magnetic properties of these two different architectures of supercrystals evidences improved magnetic properties for the colloidal crystals. This is interpreted as a result of both an increase in the mesoscopic coherence length and a decrease in the interparticle distance. In this work we extend this comparative study between the two types of supercrystals after annealing treatment. A common batch of NP is used for the native and the annealed samples in order to optimize the accuracy of the comparison. A complete set of structural characterizations and magnetic measurements shows that upon annealing the NP evolve from soft to hard magnetic NP, with changes of both the anisotropy constant and saturation mangnetization, while the supercrystal structures remain unchanged. Both native and annealed colloidal crystals remain characterized by a smaller interparticle distance compared to the corresponding films, inducing higher dipolar interactions, which is evidenced by an increase in the blocking temperature. In this study, we highlight the first fcc colloidal crystals made of hcp-Co single crystals resulting from the annealing of their native counterparts made of fcc-Co polycrystals. In addition, the comparative magnetic study between both the annealed supercrystalline films and colloidal crystals evidences enhanced magnetic properties for the latter ones.

Systematical investigation of rheological performance regarding 3D printing process for alkali-activated materials: Effect of precursor nature

This research aims to illuminate the effect of precursor nature on the rheology of alkali-activated materials (AAM) for providing some understanding for the precursor selection and mixture design of 3D-printing AAM (3DPAAM). Binary AAM pastes were prepared with several precursors, including ground granulated blast-furnace slag (GGBFS), fly ash (FA) and silica fume (SF). Various 3D-printing-related rheological properties were characterized, including static yield stress, thixotropy and viscosity recovery evolutions. Results show that the replacements of GGBFS with FA or SF increase the static yield stress of AAM systems within 30 min after deposition. The FA or SF incorporation affects the structural build-up rates in the flocculation and polycondensation stages as well as their intersection times. The structure build-up rate in the flocculation stage is governed by the inter-particle distance of suspension, while the counterpart in the polycondensation stage depends on the reactivity of the precursor. The effects of FA or SF incorporation on the thixotropy and viscosity recovery are dependent not only on the adopted dosage but also on the rest time. 25 wt% FA or 10 wt% SF is the appropriate incorporated dosage in 3DPAAM to improve the 3D-printing-related rheology.

Lagrangian PAFs in multiple optical scattering by two absorptive dielectric parallel cylinders

The objective of this work is to derive semi-analytical integral expressions for the Lagrangian longitudinal (L) and transverse (T) photophoretic asymmetry factors (PAFs) for an aggregate pair of parallel absorptive dielectric cylinders of arbitrary radii in plane waves with arbitrary incidence angles and polarizations. Based on the multiple scattering theory of waves and its rigorous mathematical formalism, the components of the internal electric field vectors in cylindrical coordinates are determined and used subsequently to compute the PAFs. The L- and T-PAFs are directly proportional to the L and T components of the photophoretic (known also as radiometric) force vector, respectively, induced by light absorption inside each dielectric cylinder. The modal expansion method in cylindrical coordinates and adequate boundary matching at the surface of each particle are used to determine the internal coefficients to compute the PAFs. Subsequently, the integral expressions are derived and evaluated assuming TE- and TM-polarized plane waves with arbitrary angles in the polar plane. Additional computations for the dimensionless intensity function are performed, and the corresponding results provide quantitative assessment of the internal heated portions of the absorptive dielectric cylinders at different interparticle distances while illuminated by plane waves with variable incidence angles and polarizations. The results are of some importance in electromagnetic/optical multiple scattering theory and related applications in optical binding, optical tweezers, particle manipulation, and photophoresis.