Programmable two-dimensional nanocrystals assembled from POSS-containing peptoids as efficient artificial light-harvesting systems

Inspired by the formation of hierarchically structured natural biominerals (e.g., bone and tooth), various sequence-defined polymers have been synthesized and exploited for design and synthesis of functional hybrid materials. Here, we synthesized a series of organic-inorganic hybrid peptoids by using polyhedral oligomeric silsesquioxane (POSS) nanoclusters as side chains at a variety of backbone locations. We further demonstrated the use of these hybrid peptoids as sequence-defined building blocks to assemble a new class of programmable two-dimensional (2D) nanocrystals. They are highly stable and exhibit an enhanced mechanical property and electron scattering due to the incorporated POSS nanoclusters. By varying peptoid side-chain chemistry, we further demonstrated the precise displacement of a large variety of function groups within these 2D nanocrystals and developed a highly efficient aqueous light-harvesting system for live cell imaging. Because these 2D nanocrystals are biocompatible and highly programmable, we expect that they offer unique opportunities for applications.

Vinyl-Functionalized Janus Ring Siloxane: Potential Precursors to Hybrid Functional Materials

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe2H)O]4 (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [-SiMe2H] via the Piers-Rubinsztajn reaction to obtain a family of new tetravinyl-substituted Janus rings [ViSi(OR')O]4 containing various functional groups in moderate yields. Remarkably, the tetravinyl groups on the structure remained intact after modification by the Piers-Rubinsztajn reaction. Since these synthesized compounds possess multiple functional groups (up to eight per molecule), they are potential precursors for advanced hybrid organic-inorganic functional materials.

POSS-Functionalized Graphene Oxide/PVDF Electrospun Membranes for Complete Arsenic Removal Using Membrane Distillation

This work demonstrates very high removal rates (below the detection limit of 0.045 ppb) of inorganic arsenic from water using electrospun polyvinylidene difluoride (PVDF) membranes enhanced by the addition of functionalized graphene oxide in membrane distillation. This shows potential for applications in the many parts of the world suffering from arsenic-contaminated groundwater. These membranes were enhanced by the addition of reduced graphene oxide functionalized with superhydrophobic polyhedral oligomeric silsesquioxane molecules (POSS-rGO) into the spinning solutions. The flux of the best-performing rGO-enhanced membrane (containing 2 wt % POSS-rGO) was 21.5% higher than that of the pure PVDF membrane and almost double that of a commercial polytetrafluoroethylene (PTFE) membrane after 24 h of testing, with rejection values exceeding 99.9%. Furthermore, the flux of this membrane was stable over 5 days (∼28 L m^-2 h^-1) of continuous testing and was more stable than those of the PTFE and control membranes when treating a concentrated fouling solution of calcium carbonate and iron(III) sulfate heptahydrate. It also achieved higher permeate quality in these conditions. The Young's modulus and ultimate tensile strength of the best-performing membrane increased by 38 and 271%, respectively, compared to the pure polymer membrane, while both had similar porosities of ∼91%.

Treating octasilanol [Si8O12][OH]8 with tetramethoxysilane and trimethoxyvinylsilane: a halogen-free synthetic route to alkoxysilyl-substituted double-four-ring siloxanes

The synthesis of methoxysilyl-substituted siloxanes with a double-four-ring (D4R) framework [Si8O12][OSiR(OMe)2]8 (R = OMe or vinyl) via the dealcoholative coupling between silanol [Si8O12][OH]8 and alkoxysilane was accomplished and achieved a halogen-free synthetic process. The solid-state structure of [Si8O12][OSi(OMe)3]8 was determined via a single-crystal X-ray diffraction analysis.

The synthesis of thermoresponsive POSS-based eight-arm star poly(N-isopropylacrylamide): A comparison between Z-RAFT and R-RAFT strategies

Z-Type POSS-based eight-arm star poly(N-isopropylacrylamide), POSS-(PNIPAM)₈-Z, is synthesized and demonstrated to be a thermoresponsive switchable emulsifier.

Supramolecular organogel formation behaviors of beads-on-string shaped poly(azomethine)s dependent on POSS structures in the main chains

Organogel formation was observed for isobutyl-substituted cage octasilsesquioxane (T₈) in the main-chain type polyazomethines, while precipitates instead of gel formation were observed for phenyl-substituted double-decker-shaped silsesquioxanes (DDSQ)-poly(azomethine)s.

Assembly of discrete and oligomeric structures of organotin double-decker silsesquioxanes: inherent stability studies

Discrete and oligomeric organotin DDSQs have been synthesized and characterized, both experimentally and through computational study. The stability of these compounds remains intrigued with the organization of their structure in the crystal lattice.

Reduced graphene oxide-silsesquioxane hybrid as a novel supercapacitor electrode

Supercapacitor energy storage devices recently garnered considerable attention due to their cost-effectiveness, eco-friendly nature, high power density, moderate energy density, and long-term cycling stability. Such figures of merit render supercapacitors unique energy sources to power portable electronic devices. Among various energy storage materials, graphene-related materials have established themselves as ideal electrodes for the development of elite supercapacitors because of their excellent electrical conductivity, high surface area, outstanding mechanical properties combined with the possibility to tailor various physical and chemical properties via chemical functionalization. Increasing the surface area is a powerful strategy to improve the performance of supercapacitors. Here, modified polyhedral oligosilsesquioxane (POSS) is used to improve the electrochemical performance of reduced graphene oxide (rGO) through the enhancement of porosity and the extension of interlayer space between the sheets allowing efficient electrolyte transport. rGO-POSS hybrids exhibited a high specific capacitance of 174 F g^-1, power density reaching 2.25 W cm^-3, and high energy density of 41.4 mW h cm^-3 endowed by the introduction of POSS spacers. Moreover, these electrode materials display excellent durability reaching >98% retention after 5000 cycles.

SiO2/Ladder-Like Polysilsesquioxanes Nanocomposite Coatings: Playing with the Hybrid Interface for Tuning Thermal Properties and Wettability

The present study explores the exploitation of ladder-like polysilsesquioxanes (PSQs) bearing reactive functional groups in conjunction with SiO2 nanoparticles (NPs) to produce UV-curable nanocomposite coatings with increased hydrophobicity and good thermal resistance. In detail, a medium degree regular ladder-like structured poly (methacryloxypropyl) silsesquioxane (LPMASQ) and silica NPs, either naked or functionalized with a methacrylsilane (SiO2@TMMS), were blended and then irradiated in the form of a film. Material characterization evidenced significant modifications of the structural organization of the LPMASQ backbone and, in particular, a rearrangement of the silsesquioxane chains at the interface upon introduction of the functionalized silica NPs. This leads to remarkable thermal resistance and enhanced hydrophobic features in the final nanocomposite. The results suggest that the adopted strategy, in comparison with mostly difficult and expensive surface modification and structuring protocols, may provide tailored functional properties without modifying the surface roughness or the functionalities of silsesquioxanes, but simply tuning their interactions at the hybrid interface with silica fillers.

Surface Segregation of a Star-Shaped Polyhedral Oligomeric Silsesquioxane in a Polymer Matrix

A simple way to control only the surface properties of polymer materials, without changing the bulk properties, has long been desired. The segregation behavior when a component with a tiny amount fed into the matrix is thermodynamically enriched at the surface is one of the candidate methods. This capability was examined herein by focusing on a star-shaped polyhedral oligomeric silsesquioxane (s-POSS), where the central POSS unit is tethered to eight isobutyl-substituted POSS cages as a surface modifier. X-ray photoelectron spectroscopy revealed that the surface of a film of poly(methyl methacrylate) (PMMA) was almost completely covered with POSS units by adding just 5 wt % s-POSS to it. The segregated POSS dramatically altered the physical properties such as molecular motion and the mechanical and dielectric responses at the surface of the PMMA film. These findings make it clear that s-POSS is an excellent surface modifier for glassy polymers.

High Refractive-Index Hybrids Consisting of Water-Soluble Matrices with Bipyridine-Modified Polyhedral Oligomeric Silsesquioxane and Lanthanoid Cations

We report high refractive-index (RI) films composed of polyhedral oligomeric silsesquioxane (SSQ) matrices and various lanthanoid cations. The SSQ matrices were constructed from octaammonium SSQ by connecting with bipyridine dicarboxylic acid, which is expected to capture cations. By modulating the feed ratio between SSQ and dicarboxylic acid, the series of the SSQ matrices were obtained with variable cross-linking ratios among the SSQ units. Thin transparent films were able to be prepared through the drop-casting method with the aqueous mixtures containing SSQ matrices and various kinds of lanthanoid salts up to 40 wt %. From RI measurements, it was revealed that the increase of the amount of the metal ion can significantly lift up the RI values. In particular, critical losses of Abbe numbers, which theoretically have the trade-off relationship toward increases in RI values, were hardly detected. This effect could be obtained by cation assembly in local spots that are assisted by SSQ.

Integrated POSS-dendrimer nanohybrid materials: current status and future perspective

Polyhedral oligomeric silsesquioxane (POSS)-dendrimer hybrid materials have attracted great interest in the past ten years. The integration of inorganic POSS and organic dendrimer blocks in a single-phase material offers numerous possibilities to access desirable mechanical, optical, and biomedical properties for various applications. In this review article, we describe several kinds of POSS-dendrimer hybrid materials (POSS as the core, surface functionality, repeating unit of dendrimers and the POSS-dendron conjugates) with an emphasis on their synthetic strategies, tunable macroscopic properties, and potential applications. Moreover, the current trends, challenges and future directions of POSS-dendrimer hybrid materials are elaborated.

Ferroelectric P(VDF-TrFE)/POSS nanocomposite films: compatibility, piezoelectricity, energy harvesting performance, and mechanical and atomic oxygen erosion

Poly(vinylidene difluoride) (PVDF) and its copolymers as the polymers with the highest piezoelectric coefficient have been widely used as sensors and generators. However, their relatively low performances limit their applications in some harsh environments. In this work, piezoelectric poly(vinylidene-trifluoroethylene) P(VDF-TrFE) matrices with different amounts of polyhedral oligomeric silsesquioxane (POSS) were prepared by a low temperature solvent evaporation method and thermal poling. The morphology, surface performance, crystalline phase, and piezoelectric and ferroelectric properties of the nanocomposites were investigated and the influence of POSS on these performances was studied. POSS had good compatibility with P(VDF-TrFE) and did not affect the crystalline phase formation of the matrix. The composites presented good piezoelectric properties. Piezo- and triboelectric nanogenerators were designed and fabricated. The voltage and current outputs were analyzed and the polarization effect was evaluated. The average output voltage and the current density of the matrix were 3 V and 0.5 μA cm-2 when subjected to a force of 38 N on an area of 1 cm2. The mechanical properties of P(VDF-TrFE)/POSS nanocomposites were also studied by the nanoindentation test. The hardness and modulus of samples increased 20% and 17% with a low addition of POSS. Atomic oxygen erosion properties of the composites were numerically simulated by the Monte Carlo method. The erosion cavity shape and depth were compared and studied. The influence of POSS addition on the P(VDF-TrFE) matrix and the associated reinforcing mechanism were analyzed.

Facile Fabrication of High-Performance Si/C Anode Materials via AlCl3-Assisted Magnesiothermic Reduction of Phenyl-Rich Polyhedral Silsesquioxanes

Si/C composites, combining the advantages of both carbon materials and Si materials, have been proposed as the promising material in lithium-ion storage. However, up to now, the most common fabrication methods of Si/C composites are too complicated for practical application. Here, we first use phenyl-substituted cagelike polyhedral silsesquioxane (T_n-Ph, n = 8, 12) as both carbon and silicon precursors to prepare the high-performance Si/C anode materials via a low-temperature and simple AlCl₃-assisted magnesiothermic reduction. AlCl₃ plays two roles in the reduction process, on the one hand, it acts as liquid medium to promote the reduction of siloxane core in such a mild condition (200 °C), and on the other hand, it act as catalyst for phenyl groups polycondensation into carbon materials, which makes the procedure of fabrication feasible and controllable. Impressively, T₁₂-Si/C exhibits an excellent lithium anodic performance with a reversible capacity of 1449.2 mA h g^-1 with a low volume expansion of 16.3% after 100 cycles. Such superior electrochemical performance makes the Si/C composites alternative anode materials for lithium-ion batteries.

Alkoxy- and Silanol-Functionalized Cage-Type Oligosiloxanes as Molecular Building Blocks to Construct Nanoporous Materials

Siloxane-based materials have a wide range of applications. Cage-type oligosiloxanes have attracted significant attention as molecular building blocks to construct novel siloxane-based nanoporous materials with promising applications such as in catalysis and adsorption. This paper reviews recent progress in the preparation of siloxane-based nanoporous materials using alkoxy- and silanol-functionalized cage siloxanes. The arrangement of cage siloxanes units is controlled by various methods, including amphiphilic self-assembly, hydrogen bonding of silanol groups, and regioselective functionalization, toward the preparation of ordered nanoporous siloxane-based materials.

Synthesis and properties of chromophore-functionalized monovinylsilsesquioxane derivatives

Herein, an effective and selective synthesis of chromophore-functionalized monovinylsilsesquioxane derivatives by a cross-metathesis reaction along with discussion of their photophysical and thermal resistance properties is disclosed.

POSS nanostructures in catalysis

In this review we highlight the use of appealing POSS-based nanostructures for both homogeneous and heterogeneous catalytic applications.

Simplistic one-pot synthesis of an inorganic–organic cubic caged material: a new interface for detecting toxic bisphenol-A electrochemically

Polyhedral oligomeric silsesquioxane (POSS) based hybrid nanomaterials have been terminally functionalised with three different functional groups and are newly explored for the electrochemical sensing of bisphenol A.

A Selenone-Functionalized Polyhedral Oligomeric Silsesquioxane for Selective Detection and Adsorption of Hg2+ ions in Aqueous Solutions

Developing novel functional polyhedral oligomeric silsesquioxane (POSS) for various applications is highly desirable. Herein we present the first example of a novel selenone-functionalized POSS (POSS-Se) by treating an imidazolium-containing POSS with selenium powder under mild condition. The structure of POSS-Se was characterized by FT-IR, ¹H NMR, ¹³C NMR, ²⁹Si NMR, and elemental analysis. Acid treatment of POSS-Se results in a hydrophilic red-orange colored solid, which is highly sensitive and selective for the detection of Hg²⁺ ions in aqueous solutions by visually observing the color change to pale yellow, and to white. Interestingly, POSS-Se has no activity on this detection. This finding is due to the Se-Se formation by acid-treatment and subsequent coordination-induced cleavage upon the addition of Hg²⁺ ions. The detection behavior can be precisely monitored by a "turn-on" fluorescence phenomenon with the limit of detection (LOD) of 8.48 ppb, comparable to or higher than many reported Hg²⁺ sensors. Moreover, POSS-Se demonstrates a selective and efficient adsorption of Hg²⁺ ions with a maximum capacity of 952 mg g^-1. The value is higher than most reported adsorbents for Hg²⁺ ions, typically thiol and/or thioether functional materials, indicating its promise as an efficient adsorbent for the selective removal of Hg²⁺ ions from industrial wastewater. This work may open up new horizons for the exploration of selenium-containing functional POSS.

Control of Crystalline-Amorphous Structures of Polyhedral Oligomeric Silsesquioxanes Containing Two Types of Ammonium Side-Chain Groups and Their Properties as Protic Ionic Liquids

Polyhedral oligomeric silsesquioxanes (POSSs), Am-POSS(x,y), prepared by hydrolytic condensation, contains two types of ammonium side-chain groups, where the numbering of x and y represents the type of ammonium ions in the POSS structure, corresponding to primary (1), secondary (2), tertiary (3), and quaternary (4) ammonium ions. Mixtures of the two starting materials selected from organotrialkoxysilanes containing primary, secondary, and tertiary amines and a quaternary ammonium salt [(RO)₃Si(CH₂)₃R′, R = CH₃ or CH₂CH₃, R′ = NH₂, NHCH₃, N(CH₃)₂, and N(CH₃)₃Cl] were dissolved in dimethyl sulfoxide (DMSO). The hydrolytic condensation was performed in the presence of bis(trifluoromethansulfonyl)imide (HNTf₂) and water. All Am-POSS(x,y) structures consisted of a cage-type octamer (T₈-POSS), as confirmed by ²⁹Si NMR spectrometry and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses indicated that Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) had amorphous structures. These POSSs have two or three differences in the number of methyl groups between the two types of ammonium side-chains. Conversely, Am-POSS(1,2), Am-POSS(2,3), and Am-POSS(3,4) had crystalline structures. The difference in the number of methyl groups between the two types of ammonium side-chains in these POSSs is only one. Therefore, the crystalline-amorphous structure of Am-POSS(x,y) is controlled by the side-chain group combinations. Furthermore, Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) are protic ionic liquids with relatively low flow temperatures.

Langmuir-Blodgett films of membrane lipid in the presence of hybrid silsesquioxane, a promising component of biomaterials

Functionalized polyhedral oligomeric silsesquioxanes (POSS) derivatives have great potential in biomedical applications such as tissue engineering, drug delivery, biosensors, dental composites and biomedical devices. Having the above in mind, in this paper, the study of the surface characteristics of binary Langmuir-Blodgett films consisting of an open cage silsesquioxane POSS-poly (ethylene glycol) (POSS-PEG) and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), as a representative of phospholipid was conducted based on contact angle measurements of three liquids. The measured values of the contact angle (with water, formamide and diiodomethane as the wetting liquids) allowed to calculate surface free energy of the films from van Oss et al. approach. The film structure of the deposited layers was evaluated using an atomic force microscope. Analysis of the obtained results led to the conclusion, that the pure DMPE molecules create agglomerates onto a solid substrate, whereas the POSS-PEG molecules form a homogenous monolayer. After an addition of POSS-PEG to lipid film, changes in the surface properties are visible. The wettability as well as surface free energy depend on the molar ratio of both components. The AFM images shed more light on the changes of the DMPE monolayer topography caused by the POSS-PEG addition.

Synthetic Routes to Silsesquioxane-Based Systems as Photoactive Materials and Their Precursors

Over the past two decades, organic optoelectronic materials have been considered very promising. The attractiveness of this group of compounds, regardless of their undisputable application potential, lies in the possibility of their use in the construction of organic–inorganic hybrid materials. This class of frameworks also considers nanostructural polyhedral oligomeric silsesquioxanes (POSSs) with “organic coronae” and precisely defined organic architectures between dispersed rigid silica cores. A significant number of papers on the design and development of POSS-based organic optoelectronic as well as photoluminescent (PL) materials have been published recently. In view of the scientific literature abounding with numerous examples of their application (i.e., as OLEDs), the aim of this review is to present efficient synthetic pathways leading to the formation of nanocomposite materials based on silsesquioxane systems that contain organic chromophores of complex nature. A summary of stoichiometric and predominantly catalytic methods for these silsesquioxane-based systems to be applied in the construction of photoactive materials or their precursors is given.