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DOE OSTI2023

Impact of temperature on light yield and pulse shape discrimination of polysiloxane-based organic scintillators formulated with commercial resins

This work investigates how increased temperature affects neutron/ discrimination and light yield (LY) in several different polysiloxane-based scintillators doped with either 9,9-dimethyl-2-phenylflourene (PhF) or 2,5-diphenyloxazole (PPO) as a primary fluorophore and 9,9-dimethyl-2,7-di((E)-styryl) fluorene (SFS) as the secondary fluorophore. The polysiloxane matrices were prepared from the commercial resins Wacker Lumisil 579 or Shin-Etsu KER-6000. Control scintillators were prepared from poly(vinyltoluene) (PVT), the industry standard matrix, as a reference point for LY and pulse shape discrimination (PSD) measurements. Samples with PhF and PPO dopant concentrations of 1 wt% and 5 wt% in the polysiloxanes and 3 wt% and 5 wt% in the PVT samples were tested at 20 °C, 35 °C, and 50 °C. In the polysiloxane samples, the KER-6000 resin outperformed the Wacker 579 and PhF proved to be a better dopant than PPO in both LY and PSD capabilities. Polysiloxane scintillators showed slight decreases in LY and increases in neutron/discrimination at increased temperatures, while PVT scintillators showed a similar LY decrease with little to no improvement in neutron/discrimination at increased temperatures. Altogether, polysiloxane scintillators may not require recalibration in applications where temperatures increase up to 50 °C.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Polysiloxane Scintillators for Efficient Neutron and Gamma-Ray Pulse Shape Discrimination

Plastic scintillators based on thermoplastics, such as polystyrene and poly(vinyl toluene) (PVT), are capable of neutron and γ radiation detection via pulse shape discrimination (PSD) when overdoped with select fluorescent molecules. This class of plastic scintillator has been extensively studied but is limited to applications suitable for thermoplastics. For applications requiring flexibility, scintillators composed of elastomers, such as polysiloxanes, offer an alternative to PVT scintillators. Polysiloxane scintillators are inherently flexible and have a short processing time on the order of 3 h in air and equivalent or better detection capability at reduced doping concentration (<5 wt %). This work presents polysiloxane-based scintillators, containing only 1–5 wt % of 2,5 diphenyl-oxazole (PPO) or 9,9-dimethyl-2-phenyl-9H-fluorene (PhF) as primary dopants and 9,9-dimethyl-2,7-distyryl-9H-fluorene (SFS) as a wavelength shifter. A 5 wt % PPO polysiloxane sample had improved neutron and gamma ray PSD and comparable light yield than EJ-299-33 tested under the same conditions, i.e., figure of merit (FoM) of 1.33 ± 0.03 at 450 keV ee and light yield of 94% relative to EJ-299-33. The 5 wt % PhF-polysiloxane sample had a higher light yield, 144% of EJ-299-33 but lower FoM under the same conditions (FoM of 1.09 ± 0.03). Furthermore, this work highlights the potential of polysiloxanes as a matrix for PSD capable plastic scintillators.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Development of new Polysiloxane Based Liquid Scintillators

In the last decade, attention toward neutron detection has been growing in the scientific community, driven by new requirements in different fields of application ranging from homeland security to medical and material analysis, from research physics, to nuclear energy production. So far neutron detection, with particular attention to fast neutrons, has been mainly based on organic liquid scintillators, owing to their good efficiency and pulse shape discrimination (PSD) capability. Most of these liquids have however some main drawbacks given by toxicity, flammability, volatility and sensitivity to dissolved oxygen that limits the duration and the quality of their performances with worse handiness and increased costs. Phenyl-substituted polysiloxanes could address most of these issues, being characterized by low toxicity, low volatility and low flammability. Their optical properties can be tailored by changing the phenyl distribution and concentration thus allowing to increase the solubility of organic dyes, to modify the fluorescence spectra and to vary the refractive index of the medium. Furthermore, polysiloxanes have been recently exploited for the production of plastic scintillators with very good chemical and thermal stability and very good radiation hardness and the development of polysiloxane liquid scintillators could allow to combine these interesting properties with the supremacy of liquid scintillators as regarding PSD over plastics. For these reasons, the properties of several phenyl-substituted polysiloxane with different phenyl amounts and different viscosities have been investigated, with particular attention to the scintillation response and the pulse shape discrimination capability, and the results of the investigation are reported in this work. More in details, the scintillation light yield towards gamma rays ({sup 60}Co and {sup 137}Cs) of several polysiloxane liquids has been analyzed and compared with the light yield of a commercial non-toxic liquid scintillator (EJ309). The results have been related to the optical characterization of these materials, especially as regarding the fluorescence response, and the best performing material (1,1,5,5-Tetraphenyl 1,3,3,5-Tetramethyl Trisiloxane) showed a scintillation light-yield only slightly lower than EJ309, proving to be a promising candidate for the production of an efficient polysiloxane based liquid scintillator. The results as regarding the neutron-gamma pulse shape discrimination capability of the best performing materials are also reported in this work and the scintillation decay time of these materials are compared to the results of fluorescence lifetime analysis. PSD tests have been performed at CN accelerator in Legnaro National Laboratories with a 2.2 MeV pulsed neutron beam using TOF procedure and the pulses have been analyzed in order to evidence the PSD capability of every sample. The reported results pave the way to the development of a new promising class of non-toxic liquid scintillating materials for neutron detection, with good light output and interesting PSD characteristics. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2020

Easy-Processable and Aging-Free All-Polymer Polysiloxane Composites

In this work, we report all-polymer polysiloxane composites that overcome the long-standing processing problems of silica-reinforced silicone rubbers. Polystyrene fillers are dispersed with styrene/dimethylsiloxane symmetric diblock and triblock copolymers that control the filler morphology, filler–matrix interactions, and filler–filler interactions. Surprisingly, the composites not only rival the traditional silica-reinforced polysiloxane in mechanical properties of cured materials but also have better processability and stability than the silica-filled compound before curing. Large amplitude oscillatory shear experiments demonstrate that the triblock copolymer addition strongly affects the rheological properties. We hypothesize that the bridges and entangled loops that were formed by the triblock copolymer can connect different PS domains to provide additional reinforcement. The aging effect that originates from PDMS chain adsorption on the filler particle surface is also avoided because of the thermodynamic repulsion between PS and PDMS phases.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Boron-10 Doped Polysiloxanes as Matrix Materials for Application in the Simultaneous Detection and Discrimination of Gamma Rays and Fast and Thermal Neutrons

Three boron-10 enriched aromatic molecules have been synthesized and incorporated into two different commercial polysiloxane resins, Shin Etsu KER-6000 and Wacker SilRes H62-C. Scintillating fluorophores, 9,9-dimethyl-2-phenylfluorene (PhF) and 2,5-diphenyloxazole (PPO), were tested in combination with each resin and boron-10 molecule for the simultaneous detection of gamma rays, fast neutrons, and thermal neutrons. Here, the H62-C resin was able to solubilize a large amount of PhF, in excess of 20 wt%. Cure kinetics were controlled through the addition of divinylbenzene and phenyl tris(dimethylsiloxy)silane cross-linker solution to the H62-C resin, with rheology experiments demonstrating a large reduction in time to gelation when 20 wt% cross-linker solution was added, from more than 4 hours to less than 1 hour. These polysiloxane resins can be cured in 3 hours under air, while common poly(vinyltoluene) scintillators require at least 4 days of heating and oxygen-free conditions. PhF-doped KER-6000 with tolyl boronate pinacol ester exhibited the best overall performance with a light yield of 62% relative to EJ-200 and thermal neutron capture at energies up to 103 keVee (84 keVee for EJ254B-5). Additionally, four samples exhibited light yields surpassing an industry-standard boron-doped plastic scintillator, Eljen’s EJ254B-5. Over the course of ten months, the KER-6000 samples showed precipitation of dopant molecules, which reduced their light yield by 15% on average, while H62-C proved to be more stable with only a 6% reduction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

Effects of Varying Composition and Kinetics on the Microstructural and Mechanical Properties of Polysiloxane Foams

Polysiloxane elastomers are used in a wide variety of applications including medicine, aerospace, and defense industries. Though these materials demonstrate many useful properties such as flexibility, resistance to chemical attack, electrical insulation, and biocompatibility, the mechanical properties and product integrity are sensitive and may degrade in harsh environments. Understanding the degradation mechanisms and their effects on the mechanical properties of foamed polysiloxanes has been the subject of many studies; however, current formulations still produce foams with poor mechanical and aging properties. The chemical complexity, environmental sensitivity, and multitude of synthesis and degradation reactions that continuously occur complicate predicting the physical and mechanical properties or aging behavior. These factors warrant continued investigations on the chemistry, microstructural characterizations, and aging behavior of these materials

36 MATERIALS SCIENCE↗

DOE OSTI2013

Electrochemical components employing polysiloxane-derived binders

A processed polysiloxane resin binder for use in electrochemical components and the method for fabricating components with the binder. The binder comprises processed polysiloxane resin that is partially oxidized and retains some of its methyl groups following partial oxidation. The binder is suitable for use in electrodes of various types, separators in electrochemical devices, primary lithium batteries, electrolytic capacitors, electrochemical capacitors, fuel cells and sensors.

25 ENERGY STORAGE↗

DOE OSTI2015

Polysiloxane binder for lithium ion battery electrodes

An electrode includes a binder and an electroactive material, wherein the binder includes a polymer including a linear polysiloxane or a cyclic polysiloxane. The polymer may be generally represented by Formula I: ##STR00001##

25 ENERGY STORAGE↗

DOE OSTI2019

Curable polysiloxane compositions and slippery materials and coatings and articles made therefrom

The present teachings generally provide curable polysiloxane compositions including a base resin including a MQ vinyl siloxane. Articles of manufacture including the curable polysiloxane compositions and slippery coatings and materials also are provided. The compositions may be used to provide slippery, lubricious, or repellent materials and coatings and may provide anti-fouling function. The compositions can provide anti-fouling or foul-release function on open surfaces, internal surfaces, membranes; to provide pinning free or low contact angle hysteresis surfaces; to provide homogeneous interface to suppress nucleation; to provide a barrier layer such as anti-corrosion; to provide anti-stain, anti-smudge, anti-fingerprint, anti-soil function.

Kim, Philseok↗

DOE OSTI2021

Curable polysiloxane compositions and slippery materials and coatings and articles made therefrom

The present teachings generally provide curable polysiloxane compositions including a base resin including a surface active polymer. Articles of manufacture including the curable polysiloxane compositions and slippery coatings and materials also are provided. The compositions may be used to provide slippery, lubricious, or repellent materials and coatings and may provide anti-fouling function. The compositions can provide anti-fouling or foul-release function on open surfaces, internal surfaces, membranes; to provide pinning free or low contact angle hysteresis surfaces; to provide homogeneous interface to suppress nucleation; to provide a barrier layer such as anti-corrosion; to provide anti-stain, anti-smudge, anti-fingerprint, anti-soil function.

Kim, Philseok↗

DOE OSTI2023

Curable polysiloxane compositions and slippery materials and coatings and articles made therefrom

Kim, Philseok↗

DOE OSTI2024

Polysiloxane-based objects and 3-dimensional printing method for making the same

Disclosed herein are embodiments of an additively manufactured polysiloxane-based object, as well as composition embodiments for making such object embodiments. Also disclosed are embodiments of a method for making the additively manufactured polysiloxane-based object using the composition embodiments described herein. The disclosed composition embodiments and method embodiments provide objects that are substantially free of contaminants that deleteriously affect structural integrity and that comprise a polymer skeleton consisting of oxygen-silicon bonds wherein the silicon component can further comprise one or more branching groups.

Cluff, Kyle↗

DOE OSTI2026

Temperature-dependent changes in gas chromatographic separation metrics for trihexyl(tetradecyl)phosphonium-based ionic liquid stationary phases and comparison to conventional polysiloxane stationary phases

Here, to assess whether the trihexyl(tetradecyl)phosphonium chloride ([P 66614 + ][Cl - ]) ionic liquid (IL), employed as a gas chromatographic stationary phase, exhibits temperature-dependent phase transitions or structural heterogeneity, retention thermodynamics for probe molecules of varied chemical structure were investigated by gas chromatography (GC) over the temperature range of 25 to 64 °C using van’t Hoff analysis. All van’t Hoff plots for n-alkanes (C8–C12) and other probe analytes were linear, indicating the absence of detectable phase-transition behavior. The [P 66614 + ][Cl - ] IL was further compared with the [P 66614 + ] bis[(trifluoromethyl)sulfonyl]imide ([P 66614 + ][NTf 2 - ]) IL and commercial polysiloxane stationary phases in terms of temperature-dependent resolution behavior and chromatographic selectivity over the temperature range of 28–52 °C. The resolution factors of analytes in mixtures obtained using gas chromatography–mass spectrometry (GC–MS) and the summation of resolution values decreased smoothly with temperature on both IL stationary phases and on the dimethylphenylcyano-substituted polymeric stationary phase (OV-1701), whereas the poly(50% diphenyl/50% dimethyl siloxane) stationary phase (SPB-50) exhibited irregularities in its temperature-dependent summation of resolution profile, showing a distinct maximum in the temperature range of 34–40 °C. Selectivity values for the IL stationary phases were largely determined by the anion, with the [P 66614 + ][Cl - ] IL providing enhanced separation between polar and aromatic analytes, while the [P 66614 + ][NTf 2 - ] IL favored dispersive and π-π interactions that resulted in a reversal of elution order for some aliphatic–aromatic and alkyne-containing analyte pairs. Capillary columns prepared using different surface activation methods and coated with identical [P 66614 + ][Cl - ] IL stationary phase showed indistinguishable temperature-dependent trends in summation of resolution value and selectivity. An evaluation of analyte-specific selectivity provides insight into the characteristic separation behavior of the stationary phases and enables identification of analyte classes that are more efficiently separated on the [P 66614 + ]-based IL stationary phases compared to conventional stationary phase materials.

Chromatographic selectivity↗

DOE OSTI2023

Ultrathin polyorganosilica membranes synthesized by oxygen-plasma treatment of polysiloxanes for H 2 /CO 2 separation

Oxygen plasma treatment of polydimethylsiloxane (PDMS) induces an ultrathin polyorganosilica (POSi) layer (<10 nm) on top of a PDMS membrane, leading to excellent H 2 /gas separation properties and providing a rapid and scalable way to fabricate robust silica membranes compared with conventional high-temperature and time-consuming sol-gel methods. Here, we thoroughly investigate POSi membranes derived from poly (dimethylsiloxane-co-methylhydroxidesiloxane) (poly (DMS-co-MHOS)) containing -SiOH groups that can be more easily converted to silica networks than the -SiCH 3 in PDMS. Further, the effect of the polysiloxane structure and plasma treatment conditions (including plasma generating powers, oxygen flowrate, chamber pressure, and treatment time) on the silica chemistry, structure, and H 2 /CO 2 separation properties are systematically determined to derive structure/property relationships. An optimized membrane exhibits H 2 permeance of 880 GPU and H 2 /CO 2 selectivity of 67 at 150 °C, superior to state-of-the-art polymeric membranes. The membrane retains H 2 /CO 2 selectivity as high as 46 when challenged with simulated syngas containing 2.8 mol% water vapor at 150 °C, demonstrating the potential of these POSi membranes for practical applications.

36 MATERIALS SCIENCE↗

DOE OSTI2015

The effects of gamma irradiation on RTV polysiloxane foams

The present paper involves the investigation of ionizing radiation effects on silica filled poly (dimethyl siloxane) foam vulcanized at room temperature. In order to better predict aging effects in these materials, it is important to understand the influence of irradiation on structural-rheological property relationships. Polysiloxane foams were subjected to moderate doses of gamma irradiation in an inert atmosphere and characterized by thermal (DSC and TGA), chemical (FT-IR, NMR, Mössbauer, mass spectroscopy, EPR, solvent swelling), microscopy (SEM and AFM), and mechanical (uniaxial compressive load) techniques. Radiation exposure induced cross-linking reactions that predominated over chain scission reactions for the dose range investigated. No long-lived radiation-induced radicals were detected and the porous structure of the irradiated foam remained unchanged. Finally, radiation exposure resulted in gas evolution, decrease in crystallization levels, slight changes in chemistry, and decrease in the molecular weight between cross-links, thereby hardening the foam.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Aging mechanisms in RTV polysiloxane foams

The long-term use of polysiloxane foams requires a good understanding of the diverse factors that may influence their performance. The aim of the present work was to understand the interplay between in-service environments and reactive species that reside in the foams. Two foams (SX358 and S5370) were thermally aged under compressive strain to gauge the onset of compression set, an indicator of degradation. In this study, experiments were performed by either aging the foams in open air containers or in high humidity environments. Our results indicated that foams aged in open air environments exhibited less compression set than when aged in presence of moisture. These results were analyzed in terms of post-curing reactions, hydrolysis and rearrangement of the network, which are promoted by active residues that are left in the foam from the curing process. In particular, the residues from tin octoate, the catalyst used in the cure of the foams, were identified and their role in promoting aging was determined. Reactions were either catalyzed by tin(II) species or by a combination of trace amounts of water and octanoic acid, a product of the hydrolysis of tin octoate. More precisely, this work demonstrated that reactive residues promote chemical changes in the polymer, which resulted in compression set. On the other hand, the oxidized residues of the tin octoate show no catalytic activity towards promoting condensation reactions between silanol groups. In conclusion, our work established that, depending on service conditions, certain residues are more harmful to the foam's lifetime than others.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Thermophysical property and electrical conductivity of titanium isopropoxide – polysiloxane derived ceramics

In this work, high temperature resistant Si-O-C-Ti has been successfully prepared based on the pyrolysis of polysiloxane (PSO) and titanium (IV) isopropoxide (TTIP) at 1200–1400 °C. PSO can homogeneously mix with TTIP to enhance its conversion to TiC. The carbothermal reactions between TiO 2 (product of thermal decomposition of TTIP) and carbon result in the formation of TiC. All the Si-O-C-Ti composites pyrolyzed at 1200–1300 °C are stable up to 1000 °C in an oxidizing air atmosphere. TiC leads to high electrical conductivity at elevated temperatures; the maximum conductivity is 1176.55 S/m at 950 °C, which is the first reported value of >1000 S/m conductivity for Si-O-C-Ti ceramics. However, too high a pyrolysis temperature, such as 1400 °C, can potentially ‘destabilize’ the Si-O-C-Ti system by consuming the free carbon and result in lower conductivities.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Polysiloxane coatings on microspheres based on Multiphase Flow with Interface Exchange-Discrete Element Modelling

Polysiloxane coatings on yttria stabilized zirconia (YSZ) microspheres of 500 μm were simulated in a spout fluidized bed coater using Multiphase Flow with Interface Exchange-Discrete Element Modelling (MFiX-DEM). In this work, two different coater configurations were developed to study the influence of gas velocity and its distribution on particle dynamics. The presence of the Wurster tube not only enhances the distribution but also increases the overall residence time of the particles. Investigations were also carried out with different Wurster tube positions (normal, 10% and 20% lowered from its initial position). Among these, 20% lowered Wurster tube position demonstrated the most effective coating process. The effects of gas inlet pressure on the average gas velocity and the distribution of particles were analyzed. More than 97% of the particles can be retained. The derived results, including average gas velocity, particle retention percentage, and distribution of particles with gas velocity, are being used to guide the experimental work in obtaining defect-free coatings for YSZ microspheres.

36 MATERIALS SCIENCE↗