Polyhedral Oligomeric Silsesquioxane Content Research Articles

Thermal stability and decomposition kinetics of polybenzoxazine and oligomeric polyhedral octaphenyl silsesquioxane nanocomposites

AbstractIn this study, the impact of octaphenyl polyhedral oligomeric silsesquioxane (POSS) on the thermal stability of polybenzoxazine resin at 1, 3, and 5 wt% POSS loading through dynamic thermogravimetric analysis (TGA) at heating rates of 10, 20, 30 and 40°C min−1 was investigated. Besides, the decomposition kinetics of polybenzoxazine resin (PBZ) and various nanocomposites were studied using Kissinger, Friedman, Flynn‐Wall‐Ozawa (FWO) and Coats‐Redfern (CR) models and also, the activation energies of samples were calculated. At first, benzoxazine monomer was synthesized and then nanocomposites were prepared via solution mixing method. The qualitative dispersion of nanoparticles in benzoxazine resin was examined through the utilization of scanning electron microscopy and x‐ray diffraction experiments. The results showed that the addition of nanoparticles improved the thermal stability of PBZ resin specially at 1 wt% POSS loading and at higher POSS content the thermal stability of the resin decreased. As determined by TGA, the char yield of resin was enhanced by 2.6% upon the addition of 1 wt% nanoparticles. In addition, in 1 weight percent of nanoparticles, as the heating rate rose from 10 to 40°C min−1, the Integral Program Decomposition Temperature (IPDT) has increased by about 260°C, and this increase is about 183°C compared to the resin, and also elevating the heating rate, Td (5%) and Td (10%) weight loss of samples shifted to higher temperatures. The degradation mechanism of the resin and nanocomposites was evaluated through Kissinger, Friedman, FWO and CR models. The results displayed that the addition of 1 wt% nanoparticles increased the activation energy (Ea) values of the nanocomposites compared to that of neat resin and above this filler content, the Ea values decreased. The findings derived from the FWO model indicated that the inclusion of a 1 wt% filler raised the Ea values of the first and second stages of PBZ resin decomposition from 136–200 and 151–214 kJ mol−1 to 148–210 and 180–228 kJ mol−1, respectively.

Construction of an Interfacial Layer of Aramid Fibers Grafted with Glycidyl POSS Assisted by Heat Treatment and Evaluation of Interfacial Adhesion Properties with Epoxy Resin.

The surface of para-aramid fibers (AFs) was modified via air-assisted heat pretreatment and solution impregnation by varying the glycidyl polyhedral oligomeric silsesquioxane (POSS) content. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed an ester group, confirming the graft reaction between glycidyl POSS and oxidized AFs. The mechanical properties of AFs could be altered by varying the glycidyl POSS content. The modified AFs exhibited an optimal tensile strength after embedding 5 wt % glycidyl POSS on the fiber surface. The thermal stability of the modified fibers decreased; however, no obvious changes in crystallinity were observed by varying the glycidyl POSS content. Moreover, the tensile strength of monofilament increased from 23.8 to 25.8 cN·dtex-1, the thickness of the grafted layer on the fiber surface was above 30-40 nm after the graft modification with 5 wt % glycidyl POSS, and the interfacial shear strength (IFSS) increased by 62.55% to 26.22 MPa. Thus, the modified glycidyl AFs can be used for the reinforcement of composite materials.

Photocured Zwitterionic Coatings Containing POSS for Antifogging Applications

The conventional fabrication of antifogging polymer coatings such as zwitterionic or amphiphilic copolymers typically require multiple processes. In this work, a simple photocuring method was used to create a series of zwitterionic coatings containing polyhedral oligomeric silsesquioxane (POSS) without the need to prepare copolymer. Surface analysis demonstrated that the coating thickness was typically about 6 μm, and the surface POSS content showed a tendency of increasing with POSS. A wettability analysis demonstrated that zwitterionic coating with high POSS content held better water absorbing capability than that with low POSS content and without POSS. Furthermore, it was found that a high proportion of POSS contributed towards the enhancement of transmittance. The excellent antifogging properties of coatings with a high mass fraction of POSS can be ascribed to the aforementioned good wettability and transmittance. It is expected that zwitterionic coating via the simple incorporation of POSS can be utilized for practical application.

Molecular Dynamics Simulation of Polyhedral Silsesquioxane Nanoparticles on Cathodes of Polymer Electrolyte Membrane Fuel Cells

The effect of octahedral cage-structured polyhedral oligomeric silsesquioxane (POSS) on the cathode catalyst layer (CCL) for polymer electrolyte membrane fuel cells (PEMFCs) is investigated via molecular dynamics simulations. A model of CCL is constructed consisting of Pt/C substrate/ionomer–POSS/water–gas. The pair correlation function analysis shows that the dense cover of ionomer chains on the Pt surface and the interaction between sulfonate groups and water molecules are weakened by POSS. At high hydration, the effective water content in the ionomer–POSS phase is drastically reduced with increasing POSS content. Interestingly, at low hydration, the effective water content is slightly improved as the POSS content increases. This water retention effect is probably due to the trapping of water molecules in the POSS cage. The diffusion coefficients of O2 and H3O+ are effectively increased. The method of inserting nanocages into ionomer can avoid the formation of a high-density ionomer film at the Pt/ionomer interface. Moreover, POSS-modified CCLs possess a self-balance of water content, thus achieving enhanced multicomponent transport involving proton, water, and oxygen transfer. It provides a strategy for designing high-performance PEMFC, particularly for fuel cell vehicles due to the self-balance property under changing humidity.

High‐Performance Low‐k Poly(dicyclopentadiene) Nanocomposites as Achieved via Reactive Blending with Norbornene‐Functionalized Larger POSS

AbstractLow dielectric constant (k) polymers with excellent comprehensive properties are useful materials in the microelectronics industry as matrix resins or encapsulation layers. With the inherent low polarization, high reactivity, good processability, and low cost, poly(dicyclopentadiene) (PDCPD) has received considerable attention as low‐k materials. However, its practical application is limited by the relatively high thermal expansion and k value. Herein, three norbornene‐functionalized polyhedral oligomeric silsesquioxanes (POSSs) with T8, T10, and T12 polyhedral cores are synthesized and employed for enhancing the dielectric and comprehensive properties of PDCPD via reactive blending. The results show that these POSSs have good compatibility with PDCPD matrix and nano‐dispersed POSSs particles could be obtained. As a result, the materials’ properties can be largely enhanced by varying the POSS content and POSS size. Especially, PT12N12‐40 (40 wt% of T12N12) shows the lowest k value (2.1) and coefficient of thermal expansion (63.4 ppm°C−1), highest glass transition temperature (202.5 °C), yield strength (78.0 MPa), and elastic modulus (2.36 GPa), along with excellent hydrophobicity. This study highlights a useful strategy to fabricate high‐performance low‐k polymer nanocomposites by using larger POSS and reactive blending, which provides useful materials for the future microelectronic industry and high frequency communication.

Synthesis of tetra(epoxy)-terminated open-cage POSS and its particle thermo-crosslinking with diphenols for fabricating high performance low-k composites adopted in electronic packaging

Polyhedral oligomeric silsesquioxanes (POSSs) are ideal particles to reduce the dielectric constant (k) and loss (tan δ) values of resin matrixes for electronic packaging, but greatly limited by its finite addition due to phase-separation. Herein, tetra(epoxy)-terminated open-cage TG-POSS was synthesized and utilized as a unique building block to crosslink with bisphenol A or hexafluoro-bisphenol A, respectively, for the preparation of novel high performance low-k composites (POSS/BPA or POSS/FBPA). Results reveal that such rational design endows these two materials with homogeneous hybridization even at high POSS loading (>72.0 wt%), which is the main reason for superior dielectric, thermal and hydrophobic properties as compared with counterparts reported previously. Especially, fluorinated POSS/FBPA shows the lowest k value of 2.38, lowest tan δ value of 0.008, highest initial decomposition temperature of 396.1 °C and largest water contact angle of 117.0°, under the extra-contribution of trifluoromethyl units. In addition, its well-dispersed, moderate-crosslinked and rigid-flexible polymer network also leads to outstanding mechanical properties (elongation at break of 3.50% and modulus of 2.75 GPa) for practical applications. Summarily, this work highlights a useful strategy to fabricate high performance low-k composites with high POSS content, which is not only potential for advanced microelectronic industry but also instructive for academic fields.

DC Surface Flashover Characteristics of Polyimide Containing Polyhedral Oligomeric Silsesquioxane (POSS) in the Main Chains under Vacuum.

Polyimide, which is widely used to insulate power equipment operating in a vacuum environment, is prone to insulation failure due to surface flashover. Using POSS to modify it is an effective solution. This paper focuses on the study of DC surface flashover characteristics in vacuum of POSS/polyimide composite film, by introducing 1%, 3%, 5% equivalent mole content of POSS into polyimide, and conducting a surface flashover characteristics test in vacuum together with pure polyimide. The physical and chemical properties of the composite films were tested utilizing Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. Combined with resistivity, SEM, and other test techniques, the influence mechanism of POSS molecular modification on DC surface flashover characteristics of polyimide films in vacuum was initially revealed. The results showed that after the introduction of POSS, the overall functional group structure of polyimide remained unchanged, the intermolecular charge transfer complexation was inhibited, and the transmittance of the film increased. The thermal conductivity and thermogravimetric temperature of the film are improved to a certain extent, and the mechanical properties are slightly decreased. With the increase of the introduced POSS content, the dielectric strength of the composite film is also enhanced. The surface flashover voltage of the composite film with a POSS content of 5% is 17.5 kV in vacuum, which is 30.5% higher than that of the pure film. Further analysis shows that the introduction of POSS will reduce the resistivity of the composite film, accelerate the dissipation of surface charges, and increase the flashover voltage. In addition, POSS forms a uniformly distributed Si-O-Si cage-like structure through molecular modification. When the surface of the film is damaged, SiOx inorganic flocculent particles are generated, which can not only scatter electrons, but also shallow the depth of trap energy level and accelerate the dissipation rate of surface charge, thus increasing the flashover voltage.

Preparation of Low-k Poly(dicyclopentadiene) nanocomposites with excellent comprehensive properties by adding larger POSS

Low dielectric constant (low-k) polymer nanocomposites with good comprehensive properties are essential for microelectronics and wireless communication industry. Although extensive studies show that incorporation of polyhedral oligomeric silsesquioxane (POSS) is an effective strategy to realize this purpose, nearly all of them are based on T8 POSS and the influence of larger POSSs (i.e., T10 and T12 POSS) on polymer’s properties remains unclear. Herein three vinyl POSSs (T8V8, T10V10, and T12V12) with increased sizes were introduced into poly(dicyclopentadiene) (PDCPD) for preparation of high-performance low-k nanocomposites. Because these three POSSs are soluble in dicyclopentadiene monomer, a series of nanocomposites with molecular scale POSS dispersion were achieved after thermo-crosslinking. The results show that the k value of PDCPD can be decreased not only by increasing the content of these three POSSs but also by altering the POSS size. Consequently, the k value of PDCPD at 1 kHz was found to be reduced from 2.54 to 2.10 by adding high content of larger POSS (i.e., 7 wt% of T12V12) without damaging its inherent low dielectric loss. This result highlights the rule of POSS size and POSS content on the dielectric properties and could be used to predicate ultralow-k polymer nanocomposites by extrapolating to larger POSS and higher POSS content. Meanwhile, the comprehensive properties of PDCPD such as glass transition temperature, dimensional stability, mechanical properties, and hydrophobicity, are able to be enhanced by altering the POSS size and increasing the POSS content, making these resulting nanocomposites become useful materials for future microelectronic industry.

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.

The effect of polyhedral oligomeric silsesquioxanes (POSSs) incorporation in ethylene-propylene-diene-terpolymer (EPDM): a thermal study

A series of ethylene-propylene-diene-terpolymer (EPDM)/polyhedral oligomeric silsesquioxane (POSS) composites at different percentage of POSS were prepared and subjected to γ-irradiation. Both irradiated and non-irradiated EPDM and composites were investigated by the means of thermal analysis to verify if the presence of POSS molecules is able to reduce the oxidation level of free radicals generated during the degradation and to evaluate the effects of the irradiation. EPDM composites at 1, 3 and 5 mass% of POSS were thus degraded in a thermogravimetric (TG) balance in dynamic heating conditions (25–700 °C), in both inert and oxidative atmosphere by flowing nitrogen and air respectively. Thermal characterization was then completed by carrying out Differential Scanning Calorimetry (DSC) analysis from sub-ambient to better highlight the melting of the polymer and polymer composites occurring just above the room temperature. FTIR spectroscopy was also performed for the prepared samples to check the presence of the molecular filler in the composites and for the TG’s residue at 700 °C, in order to evaluate its nature. DSC and TGA parameters were detected and discussed to have information about the effect of the degradation’s environment, the effect of irradiation on polymer stabilization and the effect of POSS content in the polymer matrix.

Facile strategy for low dielectric constant polyimide/silsesquioxane composite films: structural design inspired from nature

It is important for the development of high-performance dielectric materials to reduce the dielectric constant and water uptake simultaneously, with the maintenance of mechanical properties. Herein, sandwich-type composite film was prepared through coating the both sides of flat polyimide (PI) film with polyhedral oligomeric silsesquioxanes (POSS) contained hierarchical porous structure using the microemulsion method, in which water droplets were used as the template for patterned pores. Due to the introduction of two layers of hierarchical porous structure with patterned pores and POSS, the dielectric constant of PI film was significantly reduced, accompanied by the low dielectric loss. In addition, the water uptake was also greatly reduced, thus contributing to its excellent durability under high humidity. More importantly, even with the introduction of porous structure, the mechanical properties of PI film can still be maintained, or even improved by optimizing POSS content. Through varying the POSS content from 10 to 50%, low dielectric constant of 2.28–2.42, dielectric loss of 0.005–0.009, water uptake of 0.56–0.62%, increment of dielectric constant under high humidity of 1.19–2.35%, with 26–32%, 43–69%, 77–80% and 31–37% of reduction, respectively, compare to flat PI film were achieved. These results indicate the potential of our sandwich-type composite film as low dielectric material in microelectronics.

Hierarchical porous structure contained composite polyimide film with enhanced dielectric and water resistance properties for dielectric material

Low-dielectric-constant materials are in great demands to satisfy the requirements in microelectronics. In this study, polyhedral oligomeric silsesquioxanes (POSS) contained hierarchical porous structure, which was prepared by the self-assembly of water droplets, was used as a coating for flat polyimide (PI) film. Evident declines were found in dielectric constant and water uptake upon the introduction of the hierarchical porous coating due to the existence of fluorine-containing groups, POSS and the hierarchical porous structure. In addition, almost undamaged mechanical properties were shown when the dielectric and water resistance properties were optimized because the hierarchical porous structure was used as a coating but not the bulk of the PI film. When the content of POSS varies from 10 % to 50 %, low dielectric constants of 2.42–2.75 and low water uptakes of 0.60 %– 0.67 %, with 22 %–27.63 % and 75.96 %–78.43 % of reductions were obtained, compared to 3.36 of dielectric constant and 2.80 % of water uptake for flat PI film. More importantly, the stability of dielectric properties in humid environment was verified by only 2.94 %–4.83 % of increase in dielectric constant after exposing to high humidity for more than 25 h, compared to 9.43 % of increase for flat PI film. The present study provides a versatile method for the preparation of low-dielectric-constant polymer materials with comprehansive properties.

Preparation and Properties of Intrinsically Atomic-Oxygen Resistant Polyimide Films Containing Polyhedral Oligomeric Silsesquioxane (POSS) in the Side Chains.

The relatively poor atomic-oxygen (AO) resistance of the standard polyimide (PI) films greatly limits the wide applications in low earth orbit (LEO) environments. The introduction of polyhedral oligomeric silsesquioxane (POSS) units into the molecular structures of the PI films has been proven to be an effective procedure for enhancing the AO resistance of the PI films. In the current work, a series of POSS-substituted poly (pyromellitic anhydride-4,4′-oxydianiline) (PMDA-ODA) films (POSS-PI) with different POSS contents were synthesized via a POSS-containing diamine, N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS). Subsequently, the effects of the molecular structures on the thermal, tensile, optical, and especially the AO-erosion behaviors of the POSS-PI films were investigated. The incorporation of the latent POSS substituents decreased the thermal stability and the high-temperature dimensional stability of the pristine PI-0 (PMDA-ODA) film. For instance, the PI-30 film with the DABA-POSS content of 30 wt% in the film exhibited a 5% weight loss temperature (T5%) of 512 °C and a coefficient of linear thermal expansion (CTE) of 54.6 × 10−6/K in the temperature range of 50–250 °C, respectively, which were all inferior to those of the PI-0 film (T5% = 574 °C; CTE = 28.9 × 10−6/K). In addition, the tensile properties of the POSS-containing PI films were also deteriorated, to some extent, due to the incorporation of the DABA-POSS components. The tensile strength (TS) of the POSS-PI films decreased with the order of PI-0 > PI-10 > PI-15 > PI-20 > PI-25 > PI-30, and so did the tensile modulus (TM) and the elongations at break (Eb). PI-30 showed the TS, TM, and Eb values of 75.0 MPa, 1.55 GPa, and 16.1%, respectively, which were all lower than those of the PI-0 film (TS = 131.0 MPa, TM = 1.88 GPa, Eb = 73.2%). Nevertheless, the incorporation of POSS components obviously increased the AO resistance of the PI films. All of the POSS-PI films survived from the AO exposure with the total fluence of 2.16 × 1021 atoms/cm2, while PI-0 was totally eroded under the same circumstance. The PI-30 film showed an AO erosion yield (Es) of 1.1 × 10−25 cm3/atom, which was approximately 3.67% of the PI-0 film (Es = 3.0 × 10−24 cm3/atom). Inert silica or silicate passivation layers were detected on the surface of the POSS-PI films after AO exposure, which efficiently prevented the further erosion of the under-layer materials.

Liquid crystallinity and thermal properties of polyhedral oligomeric silsesquioxane/side-chain azobenzene hybrid copolymer

Abstract Acrylic acid-modified polyhedral oligomeric silsesquioxane (AC-POSS) was synthesized by the reaction between the amine groups in polyhedral oligomeric silsesquioxane (POSS) and acrylic acid, which could dissolve in water and can be easily purified. Free-radical copolymerization was applied to synthesize azobenzene liquid crystalline polymer silsesquioxane (LCP-POSS) with different proportions of AC-POSS and liquid crystalline monomers. The trans-isomers of azobenzene moieties in LCP-POSS were gradually transformed to cis-isomers with increasing ultraviolet irradiation time. The photoisomerization reaction of liquid crystalline polymer (LCP) and LCP-POSS showed the first-order dynamic reaction. Compared with the LCP, the photoisomerization rate constant of LCP-POSS was decreased due to the space steric hindrance of the POSS as a rigid segment. The phase transition temperature of liquid crystalline in LCP-POSS increased with increasing POSS content, and the liquid crystalline texture in LCP-POSS became smaller under the polarized light. With further increasing the POSS content (>50 wt%) in LCP-POSS, the ordered structure of the liquid crystalline phase was gradually affected, resulting in one-way liquid crystal (LC) phase behavior. The synthesized LCP-POSS has LC properties, light-responsive properties, and thermal stability. When the POSS is introduced into the LC material, the phase state of the LC material will become more abundant and the LC phase will become more stable. The significance of this study is to develop and extend its applications as stimuli-responsive materials and devices.

Effect of different molecular architectured POSS-fluoropolymers on their self-assembled hydrophobic coatings

A total of 1/2/4/6-armed molecular architectured polyhedral oligomeric silsesquioxane (POSS) fluoropolymers were synthesized via atom transfer radical polymerization (ATRP) by linear (L), dicephalus (D), four-arm (T), and six-arm (S) initiators initiating same content of methyl methacrylate (MMA), methacrylate POSS (MA-POSS), and dodecafluoroheptyl methacrylate (DFHM). The obtained L/D/T/S-(PMMA-b-PMAPOSS-b-PDFHM)1/2/4/6 had increased molecular weight with arm increase. Driven by the stereo-hindrance and curvature effects of segments in tetrahydrofuran (THF), they assembled into the decreased spherical core-shell micelles (250–100 nm) with arm increase as PMA-POSS/PDFHM core and PMMA shell. Because of easy surface migration of fluorine-containing groups in small micelles, the casted film by S-(PMMA-b-PMAPOSS-b-PDFHM)6 performed the fluorine-rich (46.44%) and rough (5.41 nm) surface, and therefore with the hydrophobic (112°) and low water adsorption surface (1522 ng/cm2). Also, POSS-fluoropolymers obtained the enhanced thermostability with arm increase. It is believed that this research will provide a bright view for design and application of POSS-fluoropolymers.

Influence of trisilanol isooctyl POSS content on the structure, morphology and rheological properties of thermoplastic polyurethane (TPU)

Abstract In this study, thermoplastic polyurethanes (TPUs) containing trisilanol isooctyl polyhedral oligomeric silsesquioxane (POSS), a reactive nanofiller, were synthesized and characterized rheologically and morphologically, and the effects of POSS content on the melt thermal stability of the TPUs are investigated. Samples containing 0, 0.23, 0.57, 1.14, and 2.23% (w/w) POSS were synthesized by reactive extrusion and characterized by Fourier transform infrared spectroscopy (FTIR), oscillatory and extensional rheometry, atomic force microscopy (AFM), and small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). The rheological properties of molten TPU are time-dependent and the melt thermal stability of the TPU is maximal at 1.14% of POSS. The addition of 0.23 and 0.57% POSS promotes strain-hardening at low extensional strain rates (0.01 and 0.10 s−1), not affecting the extensional characteristics at higher strain rates. The addition of increasing amounts of POSS leads to the formation of POSS-rich clusters well dispersed in the TPU matrix. SAXS and WAXS results show that the POSS domains are amorphous and that POSS does not modify the crystalline structure of TPU. Therefore, this work indicates that synthesizing TPU in the presence of trisilanol isooctyl POSS can increase the melt thermal stability of the polymer, facilitating its processing.

A survey of the rheological properties, phase morphology, and crystallization behavior of PP‐POSS materials with weak phase separation

AbstractPolypropylene (PP) compounds with varying amounts (0.4‐8.2 vol%) of tailored allyl‐isobutyl polyhedral oligomeric silsesquioxane (POSS) were prepared by melt‐blending. The dependence of the crystallization behavior and crystalline structure of PP on the melt‐state phase morphology of PP‐POSS materials is addressed. PP‐POSS systems were predicted to exhibit weak phase separation in both the molten and solid states based on Bagley plot using Hansen solubility parameters. Small‐amplitude shear rheometry analysis suggested that the highest loaded (8.2 vol%) PP‐POSS system behaves as a two‐liquid emulsion, whereas the low‐content POSS (0.4‐4.0 vol%) systems deviate from this model, resembling a polymer nanocomposite. Based on these findings we hypothesized the formation of a heterogeneous phase morphology in the molten state comprised of nano‐size “pseudo‐solid” POSS clusters and micrometer‐size “pseudo‐liquid” POSS droplets dispersed within the PP matrix, depending on the POSS content. Upon cooling, POSS droplets comingle, forming cube‐like micrometer‐sized crystal domains. The nonisothermal crystallization of PP is enhanced by the presence of POSS clusters. Small‐angle X‐ray scattering analysis revealed the formation of thinner and more heterogeneous folded chain PP lamellae in the PP‐POSS systems.

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.

Preparation and characterization of POSS-PEG high performance membranes for gas separation

The efficient CO2 separation process depends on the trade-off among permeability and selectivity requirements. In this work, copolymers of polyhedral oligomeric silsesquioxanes (POSS) with cage-like rigid structure and polyethylene glycol (PEG) with good CO2 affinity were synthesized by introducing allyl-POSS and allyl-EO into the side chain of polymethylhydrosiloxane (PMHS) in different proportions. The POSS80PEG20 copolymer fashioned into membrane showed good CO2 separation performance (permeability of 679 barrer and CO2/N2 selectivity of 38.1). The effect of POSS content on morphology, thermal stability and mechanical properties was also investigated. Multilayered composite membranes using POSS80PEG20 copolymer of different concentration as a selective layer, polyacrylonitrile (PAN) support layer and polydimethylsiloxane (PDMS) middle layer were also fabricated to achieve improved mechanical stability. The composite membrane with selective layer concentration of 0.25 wt% (POSS-PEG-0.25) offered optimum CO2/N2 and CO2/O2 selectivity performances. Moreover, the effect of feed pressure on mixed gas permeance was also reported.

Development of Cycloaliphatic Epoxy-POSS Nanocomposite Matrices with Lambas Enhanced Resistance to Atomic Oxygen.

The preparation of ultra-thin CFRP laminates, which incorporate a cycloaliphatic epoxy resin reinforced with polyhedral oligomeric silsesquioxane (POSS) reagent nanofiller, using out-of-autoclave procedure is reported. The influence of the amount of POSS within the laminate on the mechanical properties and surface roughness of the laminates is analysed before and after exposure to atomic oxygen (AO) to simulate the effects of low Earth orbit (LEO). The addition of 5 wt% POSS to the base epoxy leads to an increase in both flexural strength and modulus, but these values begin to fall as the POSS content rises, possibly due to issues with agglomeration. The addition of POSS offers improved resistance against AO degradation with the laminates containing 20 wt% POSS demonstrating the lowest erosion yield (1.67 × 10−24 cm2/atom) after the equivalent of a period of 12 months in a simulated LEO environment. Exposure to AO promotes the formation of a silicon-rich coating layer on the surface of the laminate, which in turn reduces roughness and increases stiffness, as evidenced by measurements of flexural properties and spectral data after exposure.