High;#8208;Sensitivity Acoustic Molecular Sensors Based on Large;#8208;Area, Spray;#8208;Coated 2D C
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Evans, Austin M.↗
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Results for “colloids”
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Ultrafast Symmetry Control in Photoexcited Quantum Dots
Symmetry control is essential for realizing unconventional properties, such as ferroelectricity, nonlinear optical responses, and complex topological order, thus it holds promise for the design of emerging quantum and photonic systems. Nevertheless, fast and reversible control of symmetry in materials remains a challenge, especially for nanoscale systems. Here, reversible symmetry changes are unveiled in colloidal lead chalcogenide quantum dots on picosecond timescales. Using a combination of ultrafast electron diffraction and total X-ray scattering, in conjunction with atomic-scale structural modeling and first-principles calculations, it is revealed that symmetry-broken lead sulfide quantum dots restore to a centrosymmetric phase upon photoexcitation. The symmetry restoration is driven by photoexcited electronic carriers, which suppress lead off-centering for about 100 ps. Furthermore, the change in symmetry is closely correlated with the electronic properties, and the bandgap transiently red-shifts in the symmetry-restored quantum dots. Overall, this study elucidates reversible symmetry changes in colloidal quantum dots, and more broadly defines a new methodology to optically control symmetry in nanoscale systems on ultrafast timescales.
36 MATERIALS SCIENCE↗
Harnessing Particle Size‐Control and DNA‐Oligo Functionalization in ZIF‐76 for Biological Applications
Abstract Advanced therapeutics require novel nanocarriers to ensure their functionality is preserved during transit. Zeolitic imidazolate frameworks (ZIFs) have emerged as promising materials in this field owing to their combined biocompatibility, high porosity, and tunable chemistry. While a diverse family of ZIFs has been reported, few have been explored beyond the prototypical ZIF‐8. Herein, the size‐controlled synthesis of three distinct ZIF‐76 analogs is demonstrated, overcoming the unique synthetic challenges intrinsic to the lta topology and complex crystallization kinetics associated with the mixed linker approach. This assesses the materials’ platform effectiveness for intracellular delivery first by exploring the structural and colloidal stability in biologically relevant media. To circumvent particle aggregation, fluorescently labeled DNA oligonucleotides are post‐synthetically attached to the ZIF surface. This modification significantly improves the colloidal stability in media and facilitates particle internalization tracking. Finally, the particle‐cell interactions are assessed, revealing rapid cell membrane association with macrophages, but not lung epithelial cells, and ZIF accumulation within macrophages which increased over time. Importantly, this study outlines a generalized approach toward expanding the available library of ZIFs for biological applications, enabling the potential for targeted therapeutic delivery for intracellular infections treatment.
Deneff, Jacob I.↗
3D Printed Optical Quality Silica and Silica-Titania Glasses from Sol-Gel Feedstocks
We report a method for fabricating optical quality silica and silica-titania glasses by additive manufacturing, or 3D printing. Key to this success was the combination of sol-gel derived silica and silica-titania colloidal feedstocks, 3D direct ink writing (DIW) technology, and conventional glass thermal processing methods. Printable silica and silica-titania sol inks were prepared directly from molecular precursors by a simple one-pot method, which was optimized to yield viscous, shear-thinning colloidal suspensions with tuned rheology ideal for DIW. After printing, the parts were dried and sintered under optimized thermal conditions to ensure complete organic removal and uniform densification without crystallization. Characterizations of the 3Dprinted pure silica and silica-titania glasses show that they are equivalent to commercial optical fused silica (Corning® 7980) and silica-titania glasses (Corning ULE® 7972). More specifically they exhibit comparable chemical composition, SiO2 network structure, refractive index, dispersion, optical transmission, and coefficient of thermal expansion. 3D printed silica and silica-titania glasses also exhibited comparable polished surface roughness and meet refractive index homogeneity standards within range of commercial optical grade glasses. This method establishes 3D printing as a viable tool to create optical glasses with compositional and geometric configurations that are inaccessible by conventional optical fabrication methods.
36 MATERIALS SCIENCE↗
Linking Semiconductor Nanocrystals into Gel Networks through All‐Inorganic Bridges
Abstract For colloidal semiconductor nanocrystals (NCs), replacement of insulating organic capping ligands with chemically diverse inorganic clusters enables the development of functional solids in which adjacent NCs are strongly coupled. Yet controlled assembly methods are lacking to direct the arrangement of charged, inorganic cluster‐capped NCs into open networks. Herein, we introduce coordination bonds between the clusters capping the NCs thus linking the NCs into highly open gel networks. As linking cations (Pt 2+ ) are added to dilute (under 1 vol %) chalcogenidometallate‐capped CdSe NC dispersions, the NCs first form clusters, then gels with viscoelastic properties. The phase behavior of the gels for variable [Pt 2+ ] suggests they may represent nanoscale analogues of bridged particle gels, which have been observed to form in certain polymer colloidal suspensions.
Singh, Amita↗
Self‐Standing Chiral Covalent Organic Framework Thin Films with Full‐Color Tunable Guest‐Induced Circularly Polarized Luminescence
Abstract Exploring self‐standing chiral covalent organic framework (COF) thin films with controllable circularly polarized luminescence (CPL) is of paramount significance but remains a challenging task. Herein, we demonstrate the first example of self‐standing chiral COF films employing a polymerization‐dispersion‐filtration strategy. Pristine, low‐quality chiral COF films were produced by interfacial polymerization and then re‐dispersed into COF colloidal solutions. Via vacuum assisted assembly, these COF colloids were densely stacked and assembled into self‐standing, pure chiral COF films ( L‐ / D‐ CCOF‐F) that were transparent, smooth, crack‐free and highly crystalline. These films were tunable in thicknesses, areas, and roughness, along with strong diffuse reflectance circular dichroism (DRCD) and cyan CPL signals, showing an intrinsic luminescence asymmetric factor ( g lum ) of ~4.3×10 −3 . Furthermore, these COF films served as host adsorbents to load various achiral organic dye guests through adsorption. The effective chiral transfer and energy transfer between CCOF‐F and achiral fluorescent dyes endowed the dyes with strong chirality and tunable DRCD, resulting in intense, full‐color‐tunable solid‐state CPL. Notably, the ordered arrangement of dye guest molecules within the preferentially oriented chiral pores of CCOF‐F contributed to an amplified | g lum | factor of up to 7.2×10 −2 , which is state‐of‐the‐art for COF‐based CPL materials. This work provides new insights into the design and fabrication of self‐standing chiral COF films, demonstrating their great potential for chiroptical applications.
Tang, Xihao↗
Linking Semiconductor Nanocrystals into Gel Networks through All‐Inorganic Bridges
Abstract For colloidal semiconductor nanocrystals (NCs), replacement of insulating organic capping ligands with chemically diverse inorganic clusters enables the development of functional solids in which adjacent NCs are strongly coupled. Yet controlled assembly methods are lacking to direct the arrangement of charged, inorganic cluster‐capped NCs into open networks. Herein, we introduce coordination bonds between the clusters capping the NCs thus linking the NCs into highly open gel networks. As linking cations (Pt 2+ ) are added to dilute (under 1 vol %) chalcogenidometallate‐capped CdSe NC dispersions, the NCs first form clusters, then gels with viscoelastic properties. The phase behavior of the gels for variable [Pt 2+ ] suggests they may represent nanoscale analogues of bridged particle gels, which have been observed to form in certain polymer colloidal suspensions.
Singh, Amita↗
Shape-Shifting Patchy Particles
In this work, a facile method to synthesize shape-shifting patchy particles on the colloidal scale is described. The design is based on the solvent-induced shifting of the patch shape between concave and convex features. The initial concave patchy particles were synthesized in a water suspension by a swelling-induced buckling process. Upon exposure to different solvents, the patches were tuned reversibly to be either concave or convex. These particles can be assembled into chained, branched, zigzag, and cyclic colloidal superstructures in a highly site-specific manner by surface–liquid capillary bridging. The biphasic nature of the particles also enables site-selective surface functionalization.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Alkene Hydrosilylation on Oxide-Supported Pt-Ligand Single–Site Catalysts
Heterogeneous single-site catalysts (SSCs), widely regarded as promising next-generation catalysts, blend the easy recovery of traditional heterogeneous catalysts with desired features of homogeneous catalysts: high fraction of active sites and uniform metal centers. We previously reported the synthesis of Pt-ligand SSCs through a novel metal-ligand self-assembly method on MgO, CeO 2 , and Al 2 O 3 . Here, we present their applications in the industrially-relevant alkene hydrosilylation reaction, with 95 % yield achieved under mild conditions. As expected, they exhibit better metal utilization efficiency than traditional heterogeneous Pt catalysts. The comparison with commercial catalysts (Karstedt and Speier) reveals several advantages of these SSCs: higher selectivity, less colloidal Pt formation, less alkene isomerization/hydrogenation, and better tolerance towards functional groups in substrates. Despite some leaching, our catalysts exhibit satisfactory recyclability and the single-site structure remains intact on oxide supports after reaction. Pt single-sites were proved to be the main active sites rather than colloidal Pt formed during the reaction. An induction period is observed in which Pt sites are activated by Cl detachment and replacement by reactant alkenes. The most active species likely involves temporary detachment of Pt from ligand or support. Catalytic performance of Pt SSCs is sensitive to the ligand and support choices, enabling fine tuning of Pt sites. This work highlights the application of heterogeneous SSCs created by the novel metal-ligand self-assembly strategy in an industrially-relevant reaction. It also offers a potential catalyst for future industrial hydrosilylation applications with several improvements over current commercial catalysts.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Expanding the Schulze-Hardy Rule and the Hofmeister Series to Nanometer-Scaled Hydrophilic Macroions
The Schulze-Hardy Rule is a well-established observation in colloid science (can be derived from the DLVO theory) that demonstrates the relationship between the critical coagulation concentration (CCC) of colloids and the valence of extra counterionic electrolytes (z), with a simple mathematical relationship of CCC ~ z -6 . Here the Schulze-Hardy Rule is expanded to much smaller, nanoscaled soluble macroions in aqueous solution, by examining the stability of the macroions in the presence of additional electrolytes. The CCC values of the macroions follow the general trend of CCC~z -n but the n value is significantly dependent on the surface charge density of the macroions, ranging from n=2 at very low surface charge density to n=6 at a high surface charge density. In addition, different cations with the same valence showed obvious different impacts on the CCC values, with an interesting trend being connected to the Hofmeister Series originally discovered in protein solutions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Lines of Bound States in the Continuum in Monodisperse Microsphere Structures
Incorporating epitaxially grown active semiconductor media into self-assembled microsphere crystals has remained a major challenge as the curved geometry of the spheres is incompatible with conventional planar growth and patterning techniques. As a result, active photonic devices based on such self-assembled structures, which have other desirable properties such as enabling the rapid assembly of large area systems, have been elusive. Here, we numerically demonstrate an alternative route to creating high-Q resonances in microsphere-based nanophotonic assemblies compatible with standard optical gain materials. We show that close-packed layers of monodisperse microspheres can exhibit symmetry bandgaps, regardless of their layer stacking order. Thus, this microsphere environment can be used to create lines of bound states in the continuum (BICs) of an embedded slab made of active material. Using a realistic ZnS@SiO 2 (core-shell) architecture and sphere diameters compatible with scalable colloidal assembly, we predict sharp spectral features in angle-resolved transmission that trace these lines of BICs and persist in the presence of some fabrication disorder. Altogether, in enabling the integration of unpatterned epitaxial gain slabs with large-area colloidal microsphere assemblies, this approach opens a practical path toward active, dynamically reconfigurable photonic devices that leverage BIC physics for narrow-linewidth lasing and enhanced light–matter interactions.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Laponite® and Laponite®‐PEO hydrogels with enhanced elasticity in phosphate‐buffered saline
Hydrogels of the synthetic clay Laponite® and Laponite®‐poly (ethylene oxide) (PEO) have long been studied as model systems to understand fundamental aspects of colloidal disks and colloid‐polymer systems. More recently, these systems have been explored for a variety of biomedical applications. However, there is limited information in the literature on the fundamental properties of Laponite and Laponite‐polymer gels at pH < 9. Here, we report the rheological behavior of Laponite and Laponite‐PEO systems at biologically relevant conditions (e.g. physiological pH and ionic strength) and examine the effect of phosphate‐buffered saline on the properties of the gel. Our results show that the elastic modulus of both Laponite and Laponite‐PEO gels increases dramatically, in some cases by one order of magnitude or more, after immersing gels in phosphate‐buffered saline. This may be due to an enhanced edge–face interaction between particles in buffered solutions, which would promote a long‐lasting network structure of clay particles. These results are relevant to the design of clay‐polymer gels and nanocomposites hydrogels for biomaterials applications. Copyright © 2015 John Wiley & Sons, Ltd.
Liu, Xiao↗
Zinc Thiolate Enables Bright Cu‐Deficient Cu‐In‐S/ZnS Quantum Dots
Abstract Copper indium sulfide (CIS) colloidal quantum dots (QDs) are a promising candidate for commercially viable QD‐based optical applications, for example as colloidal photocatalysts or in luminescent solar concentrators (LSCs). CIS QDs with good photoluminescence quantum yields (PLQYs) and tunable emission wavelength via size and composition control are previously reported. However, developing an understanding and control over the growth of electronically passivating inorganic shells would enable further improvements of the photophysical properties of CIS QDs. To improve the optical properties of CIS QDs, the focus is on the growth of inorganic shells via the popular metal‐carboxylate/alkane thiol decomposition reaction. 1) The role of Zn‐carboxylate and Zn‐thiolate on the formation of ZnS shells on Cu‐deficient CIS (CDCIS) QDs is studied, 2) this knowledge is leveraged to yield >90% PLQY CDCIS/ZnS core/shell QDs, and 3) a mechanism for ZnS shells grown from zinc‐carboxylate/alkane thiol decomposition is proposed.
Hansen, Eric C.↗
Ligand synthesis and passivation for silver and large gold nanoparticles for single-particle-based sensing and spectroscopy
Here, silver and large gold nanoparticles are more efficient scatterers than smaller particles, which can be advantageous for a variety of single-particle-based sensing and spectroscopic applications. The increased susceptibility to surface oxidation and the larger surface area of these particles, however, present challenges to colloid stability and controllable bio-conjugation strategies. In this chapter, ligand syntheses and particle passivation procedures for yielding stable and bio-conjugatable colloids of silver and large gold nanoparticles are described.
36 MATERIALS SCIENCE↗
Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20
This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. Here, the results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas in the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 μm filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites.
54 ENVIRONMENTAL SCIENCES↗
Use of diffusive gradients in thin films (DGT) to measure potentially bioavailable metals in southeastern USA blackwater streams
Here, we used diffusive gradients in thin films (DGT) to measure potentially bioavailable metals in coastal plain streams in the southeastern USA that exhibited strong to moderate blackwater characteristics. Metals were partitioned into particulate metals, DGT-inert metals (i.e., colloidal and refractory organic complexes not accumulated by DGT), and DGT-labile metals (i.e., free metal ions, small inorganic complexes, and labile organic complexes). We also examined the influence of different DGT deployment times using data collected from the field and a follow-up laboratory study. The DGT-measured fraction of dissolved metals in the streams was 15% for Cd, 21% for Zn, 33% for Cu, 37% for Pb, and 98% for Mn. Metals bound to particulates predominated only for Pb. Most of the Cd, Pb, Zn, and Cu were associated with colloids, refractory organic complexes, or particles. Relatively small amounts were in free ion or labile complexes likely to be bioavailable through respiratory surfaces. Modeled concentrations of free and inorganically bound Cu and Pb were lower than the DGT fraction indicating that DGT accumulated some organically bound Cu and Pb that might not have been bioavailable. DGT-exposure times in excess of 5 days may have contributed to the accumulation of partly labile organic–metal complexes and were associated with substantial biofouling that caused metal uptake by DGT to depart from linearity.
54 ENVIRONMENTAL SCIENCES↗
Formulation and Evaluation of Matrix Type Transdermal Patch Containing Silver Nanoparticles
This research aimed to prepare the silver nanoparticles (AgNPs)-loaded antimicrobial wound dressing patch using ethyl cellulose as a matrix membrane and diethyl phthalate as a plasticizer. The polymer suspension was homogeneously mixed with plasticizer, and then added to the colloidal AgNPs suspension. This mixture was poured into Petri dish and subsequently dried in a hot air oven at 80 ± 2 °C for 10 h. The minimum inhibition concentration of the colloidal AgNPs suspension was 2.5 µg/ml. The AgNPs-loaded antimicrobial wound dressing patch was evaluated for physical properties by differential scanning calorimeter, X-ray diffraction, scanning electron microscope, and in vitro study. The antimicrobial wound dressing patch did not exhibit any interaction between the matrix membrane and AgNPs. The AgNPs were evenly dispersed in the patch. The patch could control the release of silver at 102.98 ± 4.11% over 12 h. Although the AgNPs-loaded antimicrobial wound dressing patches can be easily prepared by the simple method, in future studies antimicrobial wound dressing patch will be developed by employing different types of film forming agents.
77 NANOSCIENCE AND NANOTECHNOLOGY↗