A novel theoretical method to determine the effective optical properties of high refractive index nanocomposites

The continuous development of advanced optical devices towards high performance, miniaturization and integration has led to an increasing demand for high refractive index optical materials. Nanocomposites - made from high refractive index inorganic nanoparticles and good processability polymers - combine the advantages of both materials to create a synergistic effect. However, the diversity and complexity of the composites make laboratory preparation less efficient. Therefore, to prepare composites that meet the refractive index requirements, it is essential to predict the effective optical properties at different wavelengths. This study proposes a finite element parametric retrieval (FEPR) method to calculate the effective complex refractive index of nanocomposites (meff). The effects of the ratio of film thickness to particle diameter, particle arrangement, particle volume fraction (fv) and particle diameter (d) on meff are considered. The results demonstrate that changing the spatial arrangement, volume fraction and diameter of the particles can cause changes in the scattering effect of particles or the interaction between the electromagnetic waves and the particles, resulting in changes in the meff. Compared with effective medium theory (EMT), the FEPR method can be used to characterise the meff values in complex cases through finite element parametric modelling. The FEPR method is an efficient and accurate method for predicting the effective optical properties of nanocomposites, and can also be applied to the design and development of materials to discover the factors influencing the properties and variation patterns from large amounts of data, and to obtain predictive models that can guide the design of new materials.

NMR Characterization of Nanoscale Surface Patterning in Mixed Ligand Nanoparticles

Spontaneous phase separation in binary mixed ligand shells is a proposed strategy to create patchy nanoparticles. The surface anisotropy, providing directionality along with interfacial properties emerging from both ligands, is highly desirable for targeted drug delivery, catalysis, and other applications. However, characterization of phase separation on the nanoscale remains quite challenging. Here we have adapted solid-state ¹H spin diffusion NMR experiments designed to detect and quantify spatial heterogeneity in polymeric materials to nanoparticles (NPs) functionalized with mixed short ligands. Janus NPs and physical mixtures of homoligand 3.5 nm diameter ZrO₂ NPs, with aromatic (phenylphosphonic acid, PPA) and aliphatic (oleic acid, OA) ligands, were used to calibrate the ¹H spin diffusion experiments. The Janus NPs, prepared by a facile wax/water Pickering emulsion method, and mixed ligand NPs, produced by ligand exchange, both with 1:1 PPA:OA ligand compositions, display strikingly different solvent and particle-particle interactions. ¹H spin diffusion NMR experiments are most consistent with a lamellar surface pattern for the mixed ligand ZrO₂ NPs. Solid-state ¹H spin diffusion NMR is shown to be a valuable additional characterization tool for mixed ligand NPs, as it not only detects the presence of nanoscale phase separation but also allows measurement of the domain sizes and geometries of the surface phase separation.

Mesoporous Silica Nanoparticles: Properties and Strategies for Enhancing Clinical Effect

Due to the theragnostic potential of mesoporous silica nanoparticles (MSNs), these were extensively investigated as a novel approach to improve clinical outcomes. Boasting an impressive array of formulations and modifications, MSNs demonstrate significant in vivo efficacy when used to identify or treat myriad malignant diseases in preclinical models. As MSNs continue transitioning into clinical trials, a thorough understanding of the characteristics of effective MSNs is necessary. This review highlights recent discoveries and advances in MSN understanding and technology. Specific focus is given to cancer theragnostic approaches using MSNs. Characteristics of MSNs such as size, shape, and surface properties are discussed in relation to effective nanomedicine practice and projected clinical efficacy. Additionally, tumor-targeting options used with MSNs are presented with extensive discussion on active-targeting molecules. Methods for decreasing MSN toxicity, improving site-specific delivery, and controlling release of loaded molecules are further explained. Challenges facing the field and translation to clinical environments are presented alongside potential avenues for continuing investigations.

Bimodal Polymer End-Linked Nanoparticle Network Design Strategy to Manipulate the Structure-Mechanics Relation

A kind of bimodal polymer end-linked network employing nanoparticles (NPs) as net points has been designed and constructed through coarse-grained molecular dynamics simulation. We systematically explore the effects of the molecular weight (length of the long polymer chains), chain flexibility, and temperature on the accurate distribution of the spherical NPs and the resulting mechanical properties of the bimodal network. It is found that the NPs can be dispersed well, and a larger average distance between the NPs is realized with the increase of the length of the long polymer chains, the rigidity of short and long chains, and the temperature. There is a linear relationship between the average interparticle distance of NPs and the arithmetical average of the root-mean-square end-to-end distance of long and short chains. By adopting the uniaxial deformation, the stress-strain behavior and the bond orientation are examined. The results illustrate that introducing the short chains into the uniform long chains network can notably improve the tensile stress-strain performance. The bond orientation behaviors present that short chains are more prone to be oriented and stretched, contributing to more stress during the stretching process. Furthermore, enhanced stress-strain behaviors can be observed by manipulating the chain stiffness and temperature. Interestingly, the bimodal end-linked network reveals a distinctively enhanced stress-strain behavior versus the temperature, which is opposite to that of traditional physically mixed polymer nanocomposites (PNCs), attributed to a higher entropic elasticity and the uniform dispersion of NPs of the end-linked system at high temperatures. The network exhibits a linear relationship for the stress at a fixed strain versus the temperature. Notably, it is indicated that the contribution of entropy accounts for most of the total stress, while the change of internal energy only accounts for a small part, which is consistent with the experimental observation of the classic rubber elastic theory. In general, our study demonstrates a rational route to precisely control the spatial dispersion of the NPs and effectively tailor the mechanical properties of PNCs.

Zirconia/phenylsiloxane nano-composite for LED encapsulation with high and stable light extraction efficiency

To obtain a rapid processible LED encapsulant that leads to high and stable light extraction efficiency (LEE), UV curable ZrO₂/phenyl-siloxane nano-composite (ZSC) double-layer encapsulants were prepared and optimized. The highly crystalline ZrO₂ nanoparticles with a diameter of ∼14 nm were synthesized through a modified hydrothermal method at mild conditions, and a UV curable methacryl-diphenyl-polysiloxane (MDPS) with a refractive index (RI) of 1.54 (at 633 nm) was synthesized from self-condensation of diphenylsilanediol and an end-capping reaction. High refractive indexes (RIs) from 1.54–1.61 have been obtained for ZSC composites by adding 0–20 wt% ZrO₂. Before and after sulfur vapor erosion, the double-layer encapsulated sample (M-10/M) showed 11.2% and 64.8% higher LEE respectively than that of Dow Corning OE-7662. Meanwhile, the variation of LED light color temperature (T_c) was less than 1%. The effect of the ZrO₂ nanoparticle content on LEE of double-layer and single-layer encapsulation were compared and discussed based on Fresnel loss and Rayleigh scattering theories. The double-layered UV curing processing took only 1/6 of the time needed for common thermal curing.

The double-layer encapsulation by a highly crystalline ZrO₂/polydiphenylsiloxane composite affords 11.2% and 64.8% higher LEE respectively than that of OE-7662 before and after sulfur vapor erosion.

Reactions of Zirconium (IV) n-Propoxide with SiH-Functional Polysiloxanes as a Route to Siloxane-Zirconium Hybrid Materials with Enhanced Refractive Index

The reaction of poly(hydromethylsiloxane-co-methylphenylsiloxane) with zirconium (IV) n-propoxide in dry toluene leads to extensive scission of the siloxane chain and conversion of Si-H groups. These processes produce oligomeric siloxanes and organosilanes containing moisture sensitive propoxy and siloxy-zirconate groups. The obtained post-reaction solution of zirconium containing heterosiloxane oligomers is stable under anhydrous conditions for several weeks. However, its exposure to moisture initiates the hydrolytic condensation of the reactive groups leading to cross-linking and the formation of a siloxane-zirconium composite. Spin coating of the siloxane-zirconium prepolymer followed by exposure to moisture produces thin films with excellent light transparency and increased refractive index. The final coatings are characterized by ellipsometry, UV-Vis, IR, and ²⁹ Si MAS NMR spectroscopies.

Polymers on nanoparticles: structure & dynamics

Grafting polymers to nanoparticle surfaces influences properties from the conformation of the polymer chains to the dispersion and assembly of nanoparticles within a polymeric material. Recently, a small body of work has begun to address the question of how grafting polymers to a nanoparticle surface impacts chain dynamics, and the resulting physical properties of a material. This Review discusses recent work that characterizes the structure and dynamics of polymers that are grafted to nanoparticles and opportunities for future research. Starting from the case of a single polymer chain attached to a nanoparticle core, this Review follows the structure of the chains as grafting density increases, and how this structure slows relaxation of polymer chains and affects macroscopic material properties.

Thermomechanical Properties and Glass Dynamics of Polymer-Tethered Colloidal Particles and Films

Polymer-tethered colloidal particles (aka "particle brush materials") have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush-brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems.

Fabrication of highly luminescent and concentrated quantum dot/poly(methyl methacrylate) nanocomposites by matrix-free methods

We present matrix-free methods for fabricating highly luminescent and transparent CdSe/ZnS quantum dot (QD)/polymer nanocomposites utilizing poly(methyl methacrylate) (PMMA)-grafted QDs with various molecular weights. We found that the QD-PMMA nanocomposites prepared by these matrix-free methods were superior to those prepared by a simple blending method in relation to their optical property, QD dispersion, and quantum efficiency (QE). In particular, a matrix-free nanocomposite containing PMMA with a molecular weight of 2000 had the highest QE (52.8%) and transmittance of all the samples studied even at a very high QD concentration (49 wt%). This finding was attributed to the enhanced passivation of the QD surface due to the higher grafting density of the PMMA ligands and reduced energy transfer due to more uniform dispersion of QDs. Finally, we applied the nanocomposites to LED devices, and found that the matrix-free nanocomposite exhibited a higher color conversion efficiency and smaller redshift in the peak emission wavelength than that prepared using a simple blending method.

pH and Thermal Dual-Responsive Nanoparticles for Controlled Drug Delivery with High Loading Content

A pH and thermal dual-responsive nanocarrier with silica as the core and block copolymer composed of poly(methacrylic acid) (PMAA) and poly(N-isopropylacrylamide) (PNIPAM) as the shell was prepared by surface-initiated reversible addition-fragmentation chain-transfer (SI-RAFT) polymerization. The resulting SiO2-PMAA-b-PNIPAM particles dispersed individually in an aqueous solution at a high pH and a low temperature but reversibly agglomerated under acidic conditions or at elevated temperatures. These dual-responsive nanoparticles were used as carriers to deliver the model drug doxorubicin (DOX) with unusually high entrapment efficiency and loading content, which is due to the small size (15 nm), light weight of the cores, and high graft density (0.619 chains/nm2) achieved by SI-RAFT polymerization. The release rate was controlled by both the pH and temperature of the surrounding medium. Moreover, these particles selectively precipitated at acidic conditions with increased temperature, which may enhance their ability to accumulate at tumor sites. Cytotoxicity studies demonstrated that DOX-loaded nanoparticles are highly active against Hela cells and more effective than free DOX of an equivalent dose. A cellular uptake study revealed that SiO2-PMAA-b-PNIPAM nanoparticles could successfully deliver DOX molecules into the nuclei of Hela cells. All these features indicated that SiO2-PMAA-b-PNIPAM nanoparticles are a promising candidate for therapeutic applications.

Transparent and High Refractive Index Thermoplastic Polymer Glasses Using Evaporative Ligand Exchange of Hybrid Particle Fillers

Development of high refractive index glasses on the basis of commodity polymer thermoplastics presents an important requisite to further advancement of technologies ranging from energy efficient lighting to cost efficient photonics. This contribution presents a novel particle dispersion strategy that enables uniform dispersion of zinc oxide (ZnO) particles in a poly(methyl methacrylate) (PMMA) matrix to facilitate hybrid glasses with inorganic content exceeding 25% by weight, optical transparency in excess of 0.8/mm, and a refractive index greater than 1.64 in the visible wavelength range. The method is based on the application of evaporative ligand exchange to synthesize poly(styrene-r-acrylonitrile) (PSAN)-tethered zinc oxide (ZnO) particle fillers. Favorable filler-matrix interactions are shown to enable the synthesis of isomorphous blends with high molecular PMMA that exhibit improved thermomechanical stability compared to that of the pristine PMMA matrix. The concurrent realization of high refractive index and optical transparency in polymer glasses by modification of a thermoplastic commodity polymer could present a viable alternative to expensive specialty polymers in applications where high costs or demands for thermomechanical stability and/or UV resistance prohibit the application of specialty polymer solutions.

Preparation and Evaluation of a Zirconia/Oligosiloxane Nanocomposite for LED Encapsulation

A zirconia/oligosiloxane nanocomposite encapsulant has been developed and tested in a high-power LED package against commercial silicone resins. The composite was a marriage of zirconia nanocrystals modified with butyric acid (BA) and 3-methacryloxy propyl trimethoxysilane (MPTMS) and a high-index methacryloxy-oligosiloxanes resin made from MPTMS plus dimethyl, diphenyl, and triphenyl silanes. The modified zirconia had an index of 1.762 (@589 nm) and was dispersible in many solvents. The oligosiloxane resin, however, had an index of 1.5413 with good encapsulation properties and low viscosity allowing the incorporation of more zirconia. The final nanocomposite showed a refractive index of 1.625 with high transparency and a wavelength-independent scattering, both desirable for the light extraction from LED. When tested in a high-power LED package, the composite encapsulant resulted in 13% more light output compared to the commercial encapsulant (OE-6630, Dow Corning Corp.) and showed longer than 1000 h of lifetime (L70) under the steady-state Temperature Humidity Bias (THB) test.

Inorganic nanoparticles engineered to attack bacteria

Antibiotics delivered to bacteria using engineered nanoparticles (NP), offer a powerful and efficient means to kill or control bacteria, especially those already resistant to antibiotics.