Types Of Polyhedral Oligomeric Silsesquioxane Research Articles

Effect of cage and ladder configuration of polyphenyl silsesquioxane on mechanical performance and flame retardancy of ethylene–vinyl acetate composites

Improving the flame retardancy of ethylene–vinyl acetate copolymer (EVA) while maintaining its mechanical properties is critical for EVA applications. Polyhedral oligomeric silsesquioxane (POSS) can be a molecular structure designed to improve the flame retardancy of polymers while minimizing damage to the mechanical properties of polymers. In this study, two types of POSS with the same chemical structure but different spatial structures, which are named cage octaphenyl POSS (OPS) and ladder polyphenyl silsesquioxane (PPSQ) are prepared. The miscibility and dispersibility of these two types of POSS in the EVA matrix and their effects on mechanical properties, dielectric properties, and fire behaviors are also investigated. Compared to OPS-based EVA composite, the PPSQ with ladder structure has good miscibility and dispersion state in EVA matrix, obtaining better toughness, dielectric properties, and flame retardancy under cone calorimeter test. However, OPS-based EVA composite obtains superior flame retardancy than that of PPSQ-based EVA composite under small fire test (limiting oxygen index and UL-94 vertical burning tests). The mechanism of these two separate flame-retardant performances under various scenarios is explored. A novel flame-retardant model is proposed, as well as a new understanding of the role of POSS in EVA combustion. This study provides powerful guidance for obtaining EVA composites with excellent flame retardant and mechanical properties.

Thermoplastic polyurethane/POSS nanohybrids: Synthesis, morphology, and biological properties.

Recent studies show good osteoinductive properties of polyurethanes modified with polyhedral oligomeric silsesquioxanes (POSS). In this work, three types of POSS; propanediolisobutyl-POSS (PHI-POSS), disilanolisobutyl-POSS (DSI-POSS), and octahydroxybutyl-POSS (OCTA-POSS) were chemically incorporated into linear polyurethane based on an aliphatic isocyanate, hexamethylene diisocyanate (HDI), to obtain new nanohybrid PU-POSS materials. The full conversion of POSS was confirmed by Fourier transform infrared spectroscopy (FTIR-ATR) spectra of the model reactions with pure HDI. The materials obtained were investigated by FTIR, SEM-EDS, and DSC. The DSC studies showed the thermoplasticity of the obtained materials and apparently good recovery. 30-day immersion in SBF (simulated body fluid) revealed an increase in the rate of deposition of hydroxyapatite (HAp) for the highest POSS loadings, resulting in thick layers of hydroxyapatite (~60-40 μm), and the Ca/P ratio 1.67 (even 1.785). The structure and properties of the inorganic layer depend on the type of POSS, the number of hard segments, and those containing POSS, which can be tailored by changing the HDI/poly(tetramethylene glycol) (PTMG) ratio. Furthermore, the obtained composites revealed good biocompatibility, as confirmed by cytotoxicity tests conducted on two cell lines; normal human dermal fibroblasts (NHDF) and primary human osteoblasts (HOB). Adherent cells seeded on the tested materials showed viability even after a 48-h incubation. After this time, the population of viable, and proliferating cells exceeded 90%. Bioimaging studies have shown the fibroblast and osteoblast cells were well attached to the surface of the tested materials.

Processing and Characterization of UV Irradiated HDPE/POSS Fibers.

High-performance polyethylene fibers, renowned for their superior attributes encompassing a high strength, modulus, and lightness, are conventionally manufactured through the gel spinning method. However, this method is encumbered by several drawbacks, including the requisite application of a separate process to eliminate solvents from the fibers and the utilization of chemicals deleterious to both the environment and human health. Alternatively, the adoption of the melt spinning method presents a cleaner and environmentally friendly approach to attain high-performance fibers. In the present investigation, high-density polyethylene (HDPE) fibers were produced employing the melt spinning method. After the spinning process, strategic orientation procedures were implemented to enhance the crystallinity of the spun fibers. As a concluding step, seeking to elevate the overall performance of the oriented spun HDPE fibers, a cross-linking treatment was applied via UV irradiation. Notably, this study pioneers the incorporation of polyhedral oligomeric silsesquioxane (POSS) hybrid nanoparticles into HDPE during melt spinning, presenting a novel advancement aimed at further enhancing the mechanical properties of oriented HDPE fibers during UV irradiation. For this purpose, two distinct types of POSS, namely octavinyl POSS (OVPOSS) and methacryl POSS (MACPOSS), both having unsaturated double bonds capable of participating in the network structure of oriented HDPE spun during UV cross-linking, were used. The thermal, morphological, and mechanical properties, as well as the crystal structure of samples with and without POSS molecules, were investigated. The mechanical properties of the fibers exhibited higher values in the presence of OVPOSS. The incorporation of OVPOSS and MACPOSS resulted in a noteworthy improvement in the material's tensile strength, exhibiting a marked increase of 12.5 and 70.8%, respectively. This improvement can be attributed to the more homogeneous dispersion of OVPOSS in HDPE, actively participating in the three-dimensional network structure. After orientation and UV irradiation, the tensile strength of HDPE fibers incorporating OVPOSS increased to 293 MPa, accompanied by a concurrent increase in the modulus to 2.8 GPa. The addition of POSS nanoparticles thus yielded a substantial improvement in the overall performance of HDPE fibers.

Fabrication of Liquid Crystalline Polyurethane/Polyhedral Oligomeric Silsesquioxane Nanofibers via Electrospinning

A series of fibrous meshes based on liquid crystalline polyurethane/POSS composites were prepared. Two types of polyhedral oligomeric silsesquioxanes (POSSs) of different structures were chosen to show their influence on electrospun fibers: aromatic-substituted Trisilanolphenyl POSS (TSP-POSS) and isobutyl-substituted Trisilanolisobutyl POSS (TSI-POSS) in amounts of 2 and 6 wt%. The process parameters were selected so that the obtained materials showed the highest possible fiber integrity. Moreover, 20 wt% solutions of LCPU/POSS composites in hexafluoroisopropanol (HFIP) were found to give the best processability. The morphology of the obtained meshes showed significant dependencies between the type and amount of silsesquioxane nanoparticles and fiber morphology, as well as thermal and mechanical properties. In total, 2 wt%. POSS was found to enhance the mechanical properties of produced mesh without disrupting the fiber morphology. Higher concentrations of silsesquioxanes significantly increased the fibers’ diameters and their inhomogeneity, resulting in a lower mechanical response. A calorimetric study confirmed the existence of liquid crystalline phase formation.

Multifunctional Properties of Polyhedral Oligomeric Silsesquioxanes (POSS)-Based Epoxy Nanocomposites.

In this study, a tetrafunctional epoxy resin was loaded with 5 wt% of three different types of polyhedral oligomeric silsesquioxane (POSS) compounds, namely, DodecaPhenyl POSS (DPHPOSS), Epoxycyclohexyl POSS (ECPOSS), Glycidyl POSS (GPOSS), and 0.5 wt% of multi-walled carbon nanotubes (CNTs) in order to formulate multifunctional structural nanocomposites tailored for aeronautic and aerospace applications. This work aims to demonstrate how the skillful combination of desired properties, such as good electrical, flame-retardant, mechanical, and thermal properties, is obtainable thanks to the advantages connected with nanoscale incorporations of nanosized CNTs with POSS. The special hydrogen bonding-based intermolecular interactions between the nanofillers have proved to be strategic in imparting multifunctionality to the nanohybrids. All multifunctional formulations are characterized by a Tg centered at values close to 260 °C, fully satisfying structural requirements. Infrared spectroscopy and thermal analysis confirm the presence of a cross-linked structure characterized by a high curing degree of up to 94% and high thermal stability. Tunneling atomic force microscopy (TUNA) allows to detect the map of the electrical pathways at the nanoscale of the multifunctional samples, highlighting a good dispersion of the carbon nanotubes within the epoxy resin. The combined action of POSS with CNTs has allowed to obtain the highest values of self-healing efficiency if compared to those measured for samples containing only POSS in the absence of CNTs.

Hydration and glass transition of hybrid non-isocyanate polyurethanes with POSS inclusions

A non-isocyanate poly (hydroxyurethane) network was synthesized by reaction of a tricyclic carbonate compound with diamines. The system was modified by two types of Polyhedral Oligomeric Silsesquioxane (POSS) molecules, one retaining the crosslinked nature of the system, and another effectively loosening it. We studied water absorption as a function of environmental humidity and observed that all systems are extremely hydrophilic, absorbing up to 65% of water when exposed to 97% environmental humidity. In parallel, using differential scanning calorimetry and dielectric spectroscopy, we studied the effects of POSS and the significant plasticization caused by absorbed water on the glass transition and charge mobility. In dry materials, crosslinking POSS seems to reinforce the matrix and at least initially slow down mobility while the opposite effect is observed for the moiety that loosens the network. Both POSS inhibit plasticization, both indirectly by inhibiting water absorption, and directly, by stiffening the network, especially in the case of crosslinking POSS.

Influence of POSS Type on the Space Environment Durability of Epoxy-POSS Nanocomposites.

In order to use polymers at low Earth orbit (LEO) environment, they must be protected against atomic oxygen (AO) erosion. A promising protection strategy is to incorporate polyhedral oligomeric silsesquioxane (POSS) molecules into the polymer backbone. In this study, the space durability of epoxy-POSS (EPOSS) nanocomposites was investigated. Two types of POSS molecules were incorporated separately—amine-based and epoxy-based. The outgassing properties of the EPOSS, in terms of total mass loss, collected volatile condensable material, and water vapor regain were measured as a function of POSS type and content. The AO durability was studied using a ground-based AO simulation system. Surface compositions of EPOSS were studied using high-resolution scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that with respect to the outgassing properties, only some of the EPOSS compositions were suitable for the ultrahigh vacuum space environment, and that the POSS type and content had a strong effect on their outgassing properties. Regardless of the POSS type being used, the AO durability improved significantly. This improvement is attributed to the formation of a self-passivated AO durable SiO2 layer, and demonstrates the potential use of EPOSS as a qualified nanocomposite for space applications.

Improvement of DC Breakdown Strength of the Epoxy/POSS Nanocomposite by Tailoring Interfacial Electron Trap Characteristics.

To date, breakdown voltage is an underlying risk to the epoxy-based electrical high voltage (HV) equipment. To improve the breakdown strength of epoxy resin and to explore the formation of charge traps, in this study, two types of polyhedral oligomeric silsesquioxane (POSS) fillers are doped into epoxy resin. The breakdown voltage test is performed to investigate the breakdown strength of neat epoxy and epoxy/POSS composites. Electron traps that play an important role in breakdown strength are characterized by thermally stimulated depolarized current (TSDC) measurement. A quantum chemical calculation tool identifies the source of traps. It is found that adding octa-glycidyl POSS (OG-POSS) to epoxy enhances the breakdown strength than that of neat epoxy and epoxycyclohexyl POSS (ECH-POSS) incorporated epoxy. Moreover, side groups of OG-POSS possess higher electron affinity (EA) and large electronegativity that introduces deep-level traps into epoxy resin and restrain the electron transport. In this work, the origin of traps has been investigated by the simulation method. It is revealed that the functional properties of POSS side group can tailor an extensive network of deep traps in the interfacial region with epoxy and enhance the breakdown strength of the epoxy/POSS nanocomposite.

The Effect of POSS Type on the Shape Memory Properties of Epoxy-Based Nanocomposites.

Thermally activated shape memory polymers (SMPs) can memorize a temporary shape at low temperature and return to their permanent shape at higher temperature. These materials can be used for light and compact space deployment mechanisms. The control of transition temperature and thermomechanical properties of epoxy-based SMPs can be done using functionalized polyhedral oligomeric silsesquioxane (POSS) additives, which are also known to improve the durability to atomic oxygen in the space environment. In this study, the influence of varying amounts of two types of POSS added to epoxy-based SMPs on the shape memory effect (SME) were studied. The first type contained amine groups, whereas the second type contained epoxide groups. The curing conditions were defined using differential scanning calorimetry and glass transition temperature (Tg) measurements. Thermomechanical and SME properties were characterized using dynamic mechanical analysis. It was found that SMPs containing amine-based POSS show higher Tg, better shape fixity and faster recovery speed, while SMPs containing epoxide-based POSS have higher crosslinking density and show superior thermomechanical properties above Tg. This work demonstrates how the Tg and SME of SMPs can be controlled by the type and amount of POSS in an epoxy-based SMP nanocomposite for future space applications.

Fire protection of ultraviolet-aged intumescent coatings containing polyhedral oligomeric silsesquioxanes

Intumescent coatings are alternatives for protecting substrates against fire and can be applied externally, being exposed to inclement weather, such as solar radiation, making it necessary to know the effect of this exposure on their protective properties. This study developed benzoxazine- and epoxy-based intumescent coatings containing different types of polyhedral oligomeric silsesquioxanes (POSS), to evaluate the influence of UV aging on fire resistance properties. The coatings were formulated, applied on metallic substrates, and exposed to UV aging. Coatings without exposure to aging were also evaluated. The coatings were characterized using burning tests, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, combustion microcalorimetry and visual analysis. The char layers were characterized using optical microscopy and scanning electron microscopy. FTIR results indicated absorption bands related to functional groups typical of degradation for each resin. The burning test revealed that aging exposure decreased the fire protection of all coatings. Coatings containing POSS with nonreactive groups showed better protective properties after UV aging when compared with the ones containing reactive groups.

The Role of POSS Functionality on Induced Deviation of Nano and Micromechanical Properties of UV Curable Urethane Acrylate Nanocomposite Coatings

The inorganic-organic hybrid coatings based on UV curable urethane acrylate contained two types of polyhedral oligomeric silsesquioxane (POSS) were prepared. The hydroxyl functionalized POSS nanoparticles, pristine POSS, and the one modified by acrylic acid utilized to study the effect of nanoparticle content and its functionality on ultimate mechanical properties of the hybrid coatings. The nanomechanical properties and scratch resistance of nanocomposite coatings were evaluated with nanoindentation and nanoscratch techniques, respectively. Consequently, the results compared with previously obtained DMTA data. The results revealed that by embedding acrylic acid modified POSS, the surface hardness and elastic modulus improved. Further increasing acrylic acid modified POSS content to 5%, the surface elastic modulus and hardness improved to 37% and 35%, respectively, relative to neat coating and also the enhanced scratch resistance was observed. Furthermore, the discrepancy between the surface elastic modulus and bulk elastic modulus was rationalized and the contributed parameters that led to this deviation such as pile-up area, holding time and hydrostatic stress was investigated. The results showed that apart from the inefficiency of Oliver and Pharr method to precisely evaluate the nanomechanical properties of hybrid coatings, the targeted placement of POSS nanoparticle is responsible for this disparity between surface mechanical properties and its bulk values.

POSS Compounds as Modifiers for Rigid Polyurethane Foams (Composites).

Three types of polyhedral oligomeric silsesquioxanes (POSSs) with different functional active groups were used to modify rigid polyurethane foams (RPUFs). Aminopropylisobutyl-POSS (AP-POSS), trisilanoisobutyl-POSS (TS-POSS) and octa(3-hydroxy-3-methylbutyldimethylsiloxy-POSS (OH-POSS) were added in an amount of 0.5 wt.% of the polyol weight. The characteristics of fillers including the size of particles, evaluation of the dispersion of particles and their effect on the viscosity of the polyol premixes were performed. Next, the obtained foams were evaluated by their processing parameters, morphology (Scanning Electron Microscopy analysis, SEM), mechanical properties (compressive test, three-point bending test, impact strength), viscoelastic behavior (Dynamic Mechanical Analysis, DMA), thermal properties (Thermogravimetric Analysis, TGA, thermal conductivity) and application properties (contact angle, water absorption). The results showed that the morphology of modified foams is significantly affected by the fillers typology, which resulted in inhomogeneous, irregular, large cell shapes and further affected the physical and mechanical properties of the resulting materials. RPUFs modified with AP-POSS represent better mechanical properties compared to the RPUFs modified with other POSS.

Holographic polymer nanocomposites with ordered structures and improved electro-optical performance by doping POSS

Holographic polymer nanocomposites containing the liquid crystal (LC) have garnered a great deal of attention primarily because of their unique electric-switchable optical properties. Herein, three types of polyhedral oligomeric silsesquioxane (POSS) are doped into the holographic polymer nanocomposites to tune their ordered structure and electro-optical performance. These POSS dopants are methacryl POSS with eight reactive double bonds, methacrylisobutyl POSS with one reactive double bond, and aminopropylisobutyl POSS with nonreactive groups. Interestingly, methacryl POSS is primarily chemically bonded to the polymer network within the constructive regions, which deteriorates the diffraction efficiency and electro-optical performance due to the depressed ordered structures. In contrast, methacrylisobutyl POSS displays a negligible effect on the diffraction efficiency and electro-optical performance while significantly improving the thermostability of holographic polymer nanocomposites, although it is also chemically linked to the polymer network within the constructive regions. Distinctively, aminopropylisobutyl POSS mainly locates in the destructive regions and clearly improves the electro-optical performance and thermostability of holographic polymer nanocomposites.

The wetting properties of Langmuir-Blodgett and Langmuir-Schaefer films formed by DPPC and POSS compounds.

The possibility of modification of surface wettability is especially desirable in implantology. This effect is achieved by coating a given material with thin films containing nanoparticles of different chemical properties. In recent years, much interest has been paid to supported phospholipid bilayers (SPBs), because they can be exploited in novel biotechnological devices such as biosensors and mimetic membrane-coated implants. In view of the above, we decided to study the modification of wetting properties of phospholipid layer by two types of polyhedral oligomeric silsesquioxanes (POSS) with different functional groups attached to the silica open-cage. The POSS and phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) were vertically (Langmuir-Blodgett; LB) and horizontally (Langmuir-Schaefer; LS) deposited on quartz substrates to form a thin layer structure. The advancing contact angles on the modified surface coated with thin films were measured. The surface free energy (SFE) of DPPC, POSS and their mixed DPPC/POSS films was estimated by using Owens-Wendt-Rabel-Käelbe (OWRK) method. It was shown that the chemical structure of POSS used as a modifier influence the wetting properties of modified quartz surface. Incorporation fluoroalkyl-POSS into DPPC monolayer leads to obtaining a more hydrophobic film, while the addition of polyethylene glycol-POSS creates a more hydrophilic film. The transfer of the film with a more condensed structure led to a more hydrophobic material. The deposition technique (horizontal or vertical) had a particular impact on the modification of wettability of quartz surface coated with monocomponent fluoroalkyl-POSS film, whereas for the modification with mixed DPPC/POSS systems the choice of transfer method was not so significant.

Tailoring the molecular sieving properties and thermal stability of carbonized membranes containing polyhedral oligomeric silsesquioxane (POSS)-polyimide via the introduction of norbornene

Two types of POSS (polyhedral oligomeric silsesquioxane)-polymers, (POSS-polyimide-phenyl (POSS-PI-Ph) and POSS-polyimide-phenyl-norbornene (POSS-PI-Ph-Norbornene)), were utilized for the fabrication of highly permeable gas-separation membranes. POSS-PI-Ph and POSS-PI-Ph-Norbornene separation layer for selective gas separation were successfully formed on porous intermediate layer. A POSS-derived membrane calcined at 250–350 °C under N2 showed approximately the same levels of selectivity for He/N2 and CO2/N2 as conventional polyimide membranes, which shows there was no formation of large pores that decreases gas selectivity. The introduction of norbornene, which forms a cross-linked structure by thermally inducing cross-linking at 500 °C under N2, improved gas permeance without decreasing the gas-permeance ratio. A POSS-PI-Ph-Norbornene membrane heat treated at 500 °C showed increases in He permeance that ranged from 1.2 × 10−7 to 4.6 × 10−7 mol m−2 s−1 Pa−1 with He/N2, CO2/N2, He/CF4, and He/SF6 permeance ratios of 38; 8; 2700; and 14000, respectively. The relationship between the activation energy of H2 permeation and the He/H2 permeance ratio in POSS-derived, organosilica, and polymer (polyimide, polyamide, polysulfone) membranes suggests that gas permeation properties depend on the concentration of organic groups (C/Si ratio) in networks, because networks become more flexible when carbon concentration increases and dominates the permeation properties, which corresponds to a solution-diffusion mechanism.

Effect of different POSS structures on the crystallization behavior and dynamic mechanical properties of biodegradable Poly(ethylene succinate)

The effect of different polyhedral oligomeric silsesquioxanes (POSS) structures on the crystallization behavior and dynamic mechanical properties of biodegradable poly(ethylene succinate) was investigated in this work. Two kinds of POSS molecules with different structures, i.e., trisilanolisobutyl-polyhedral oligomeric silsesquioxanes (tsib-POSS) with an open cage structure and octaisobutyl-polyhedral oligomeric silsesquioxanes (oib-POSS) with a close cage structure, were separately incorporated into PES matrix at the same low loading of 1 wt%. Both types of POSS dispersed finely in the matrix, with the size of tsib-POSS aggregates being smaller than that of oib-POSS aggregates, which was in agreement with the solubility parameter difference between the two types of POSS molecules and PES matrix. The crystallization processes of PES under different conditions were accelerated by both types of POSS; moreover, oib-POSS showed stronger acceleration effect than tsib-POSS probably due to the good lattice matching between PES and oib-POSS. The crystallization mechanism and crystal structure remained unchanged for PES in the composites, despite the type of POSS. Tsib-POSS remarkably increased the storage modulus of PES, while oib-POSS slightly decreased the storage modulus of PES.

Influence of POSS fillers on the transport properties of natural rubber nanocomposites

Three types of polyhedral oligomeric silsesquioxane (POSS)—octaphenyl (OP), POSS@TESPT (TT), and MWCNT@POSS (VC)—were incorporated into natural rubber (NR) to fabricate nanocomposites. The transport properties of POSS–NR nanocomposites were studied through solvent diffusion techniques. Diffusion studies were done with toluene (aromatic solvent) and the influence of nanofiller structure, concentration and compatibility with the NR matrix on various diffusion parameters were analyzed. The fillers that have good interaction with the polymer matrix showed the lowest solvent uptake. The network structure analysis revealed that the polymer chains deformed affinely. The effect of fillers on the chain flexibility was also discussed based on mechanical property studies. POLYM. COMPOS., 40:3020–3031, 2019. © 2018 Society of Plastics Engineers

Mammary fibroblasts remodel fibrillar collagen microstructure in a biomimetic nanocomposite hydrogel

Architecture and microstructure of type I collagen fibers constitute central regulators of tumor invasion with aligned fibers providing a route for migration of stromal and cancer cells. Several different aspects of fibrillar collagen, such as stiffness, density, thickness, and pore size, may regulate migration of cancer cells, but determining effects of any one parameter requires clear decoupling of physical properties of collagen networks. The objective of this work is to develop and apply an in vitro three-dimensional (3D) tumor-extra cellular matrix (ECM) model with tunable physical parameters to define how stromal fibroblasts modulate collagen microstructure to control migration of breast cancer cells. We incorporated two different types of polyhedral oligomeric silsesquioxane (POSS) nano-molecules into a collagen/alginate matrix to induce different mechanisms of gelling. The resultant biomimetic, nanocomposite hydrogels show different collagen fibrillar microstructures while maintaining constant overall matrix stiffness, density, and porosimetry. Spheroids of human mammary fibroblasts embedded in these 3D matrices remodel the collagen network to varying extents based on differences in underlying matrix microstructures. The remodeled collagen matrix shows oriented, thicker fibrillar tracks, facilitating invasion of tumor cells. By decoupling effects of matrix stiffness and architecture, our nanocomposite hydrogels serve as robust platforms to investigate how biophysical properties of tumor environments control key processes regulating tumor progression in breast cancer and other malignancies. Statement of SignificanceOur manuscript demonstrates a new type of nanocomposite hydrogel with two different gelling mechanisms, produced by incorporating two types of polyhedral oligomeric silsesquioxane (POSS) nano-molecules into a collagen/alginate matrix. The resultant biomimetic hydrogels show different fibrillar collagen microstructures while maintaining constant overall matrix stiffness, density, and porosimetry. These gels allow us to uncouple effects of matrix stiffness versus architecture on migration and invasion of breast cancer cells and stromal fibroblasts. Upon embedding spheroids of human mammary fibroblasts (HMFs) and dissociated 231 breast cancer cells, we showed that HMFs remodeled the collagen network to differing extents dependent on starting matrix microstructures in each hydrogel. The remodeled collagen matrix showed aligned collagen fibers perpendicular to the surface of a spheroid with migrating HMFs following these fibers as occurs in tumors in vivo. To our knowledge, this is the first study showing significant different fibrillar collagen microstructures with constant collagen density and gel stiffness. This study establishes a new type of nanocomposite 3D hydrogels for studies of biophysical and cellular interactions in engineered tumor environments.

POSS Nanofiller-Induced Enhancement of the Thermomechanical Properties in a Fluoroelastomer Terpolymer

The present study reports on the use of three types of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles with various organic substituents as fillers in a fluoroelastomer (FKM). A series of/POSS elastomer composite thin films is prepared. Microstructural SEM/TEM (scanning electron microscopy/transmission electron microscopy) imaging reveals a dispersion state allowing the presence of micron-sized domains. The influence of POSS content is studied in order to optimize thermal stability and mechanical properties of the composite thin films. Both POSS-A (with an acryloyl functional group and seven isobutyl substituents) and POSS-P (with eight phenyl substituents) lead to higher thermal stability and modulus of the composites, with respect to the unfilled FKM terpolymer matrix. covalent grafting of POSS-A onto the FKM network is found to play a critical role. Enhanced storage modulus in the rubbery plateau region (+210% at 200 °C for 20 phr) suggests that POSS-A is particularly suitable for high temperature applications.

CO₂ Separation in Nanocomposite Membranes by the Addition of Amidine and Lactamide Functionalized POSS® Nanoparticles into a PVA Layer.

In this article, we studied two different types of polyhedral oligomeric silsesquioxanes (POSS®) functionalized nanoparticles as additives for nanocomposite membranes for CO2 separation. One with amidine functionalization (Amidino POSS®) and the second with amine and lactamide groups functionalization (Lactamide POSS®). Composite membranes were produced by casting a polyvinyl alcohol (PVA) layer, containing either amidine or lactamide functionalized POSS® nanoparticles, on a polysulfone (PSf) porous support. FTIR characterization shows a good compatibility between the nanoparticles and the polymer. Differential scanning calorimetry (DSC) and the dynamic mechanical analysis (DMA) show an increment of the crystalline regions. Both the degree of crystallinity () and the alpha star transition, associated with the slippage between crystallites, increase with the content of nanoparticles in the PVA selective layer. These crystalline regions were affected by the conformation of the polymer chains, decreasing the gas separation performance. Moreover, lactamide POSS® shows a higher interaction with PVA, inducing lower values in the CO2 flux. We have concluded that the interaction of the POSS® nanoparticles increased the crystallinity of the composite membranes, thereby playing an important role in the gas separation performance. Moreover, these nanocomposite membranes did not show separation according to a facilitated transport mechanism as expected, based on their functionalized amino-groups, thus, solution-diffusion was the main mechanism responsible for the transport phenomena.