Cross-linked Polysiloxane Research Articles

New Fluorescent Materials Based on Polysiloxanes and Boron Bis(β-diketonates)

Crosslinked polysiloxanes with boron bis(dibenzoylmethanate) complexes used as crosslink junctions of polymer networks are first synthesized, and their physicochemical, mechanical, thermal, and fluorescent properties are studied. It is shown that the polymers under study feature the elastic behavior, possess high thermal and thermo-oxidative stability, and exhibit intense fluorescence in a wide wavelength range (400‒700 nm).

Polysiloxane Coatings Biodeterioration in Nature and Laboratory.

Objects and structures made of organic glass require protection from damage caused by external factors. Light, humidity, temperature, dust pollution and, undoubtedly, microorganisms lead to the deterioration of optical and mechanical properties. Polysiloxane-based protective coatings, consisting of silicon–oxygen backbones linked together with organic side groups attached to the silicon atoms, are widely used. However, the polysiloxane coatings themselves also cannot avoid deterioration during operation that implies the constant development of new protective materials. Here, we created a new cross-linked polysiloxane that covers organic glasses to enhance their resistance to aggressive external factors, and investigated its own resistance to damage induced by micromycetes in natural tropical conditions and in the laboratory. It has been established that the surface of coatings in the tropics is prone to fouling with micromycetes, mainly of the genera Aspergillus and Penicillium, which produce oxalic, malic, lactic, and citric acids contributing to the biodeterioration of polysiloxane. The testing of monolithic polycarbonate, polymethyl methacrylate, and triplex coated with polysiloxane showed that they retained significant resistance to abrasion and transparency at a level of more than 90% under aggressive natural conditions. Under artificial laboratory conditions, the infection of samples with micromycete spores also revealed their growth on surfaces and a similar trend of damage.

New cross-linked polysiloxanes prepared by UV-induced thiol-ene click-reaction

A series of new cross-linked polysiloxane polymers based on functionalized cyclo- and oligosiloxane precursors was prepared by UV-induced hydrothiolation “click”-reaction using DMPA as the initiator and their physico-mechanical properties were studied. The study of a morphology of prepared polymers by scanning electron microscopy (SEM) shows that the microstructure of all samples is homogenous. The mechanical properties of all the samples were studied by the tension and compression tests. It was shown that mechanical properties of studied materials, which significantly depends on precursors nature, can be fine-tuned by changing the structure of the initial vinyl precursor. The Young's modulus varies in the range of 4.5–117 MPa in the tension test and in the rage of 6.3–209 MPa in the compression test. The tensile strength varies in the range of 0.3–3.9 MPa in the tension test and in the rage of 2.3–28 MPa in the compression test. The thermal stability of the samples was evaluated by thermal gravimetric analysis (TGA). The weight loss was observed in the range of 275–333 °C in air and 322–370 °C in argon for prepared samples. All samples were characterized by DSC method. It was shown that only DSC curves for polymers 1 and 3 contain transitions related to glass formation (−78 and −35 °C, respectively). All polymer samples have a similar water contact angle in the range of 90–102°.

Control of Hot Carrier Relaxation in CsPbBr3 Nanocrystals Using Damping Ligands.

In photon-conversion processes, rapid cooling of photo-induced hot carriers is a dominant energy loss channel. We herein report a 3-fold reduced hot carrier cooling rate in CsPbBr3 nanocrystals capped with a cross-linked polysiloxane shell in comparison to single alkyl-chain oleylamine ligands. Relaxation of hot charge carriers depends on the carrier-phonon coupling (CPC) process as an important channel to dissipate energies in nanostructured perovskite materials. The CPC strengths in the two samples were measured through cryogenic photoluminescence spectroscopic measurements. The effect of organic ligands on the CPC in CsPbBr3 nanocrystals is elucidated based on a damped oscillation model. This supplements the conventional polaron-based CPC model, by involving a damping effect on the CPC from the resistance of the ligands against nanocrystal lattice vibrations. The model also accounts for the observed linear temperature-dependence of the CPC strength. Our work enables predictions about the effect of the ligands on the performance of perovskite nanocrystals in future applications.

Preparation and anti-icing performance of cross-linked polysiloxane coatings containing silicone oil

In this work, a cross-linked polysiloxane coating containing silicone oil was prepared via a simple two-component mixing method and the anti-icing performance of the coating was investigated by detecting the ice adhesion force (τice) on the coating. The results of infrared spectroscopy and solvent swelling show that the polysiloxane coating with a certain cross-link density can be prepared by the reaction of methylhydrosiloxane and dimethylsiloxane copolymer and divinyl-terminated polysiloxane, and the cross-link density of the coating can be adjusted by the proportion of polymethylhydrosiloxane (PMHS) and vinyltrimethylsilane (VTMS). The results of ice adhesion force test show that the ice adhesion force on the coating is related to the cross-link density of the coating. With the increase of the cross-link density from 234 ± 43 mol/m3 to 1358 ± 31 mol/m3, the ice adhesion force decreases from 51.15 ± 4.7 kPa to 27.8 ± 3.9 kPa. The lower ice adhesion force corresponds to a higher anti-icing performance. With the addition of silicone oil, the ice adhesion force on the coating can be further reduced to 9.2 ± 1.2 kPa, indicating a further enhancement in the anti-icing performance. The results of icing/deicing cycle test show that, after icing/deicing for 30 cycles, the coating still exhibits efficient anti-icing performance.

Facile Fluorine-free Finishing for Excellent Water Repellency of Cotton Fabric and Optimization Using Response Surface Methodology

ABSTRACT Cotton fabrics are popular for their excellent properties, but their wider application is always limited due to their disadvantages including lack of water repellency and easy pollution. In this paper, based on improving environmental protection and the durability of water repellent, an organic-inorganic nano-hybrid cross-linked polysiloxane was prepared by chemical compounding method and emulsified to get water repellent. The water repellent finishing of cotton fabrics was carried out using the pad-dry-cure process, and the effect of finishing conditions on the water contact angle (WCA) of fabrics was investigated. Furthermore, the finishing process was optimized by the central composite design (CCD)-response surface method (RSM). The results show that the significant order of factors affecting the WCA of cotton fabric finished is successively finishing agent concentration > curing temperature > curing time. The established model has high prediction accuracy and the best finishing conditions are finishing concentration 89 g/L, curing temperature 162°C, curing time 130 s, response prediction value Y = 149.5°, which is very close to the experimental value of 149.7 ± 0.5°.

Porous Materials Based on Poly(methylvinylsiloxane) Cross-Linked with 1,3,5,7-Tetramethylcyclotetrasiloxane in High Internal Phase Emulsion as Precursors to Si-C-O and Si-C-O/Pd Ceramics

Polysiloxane networks were prepared by hydrosilylation of poly(methylvinylsiloxane) (V3 polymer) with 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) at various Si-Vinyl: Si-H groups molar ratios in water-in-oil high internal phase emulsion (HIPE). Curing the emulsions followed by removal of water led to foamed cross-linked polysiloxane systems differing in the cross-linking degrees, as well as residual Si-H and Si-Vinyl group concentrations. Treatment of thus obtained materials in Pd(OAc)2 solution in tetrahydrofuran resulted in the formation of porous palladium/polymer nanocomposites with different Pd contents (1.09–1.70 wt %). Conducted investigations showed that pyrolysis of the studied materials at 1000 °C in argon atmosphere leads to porous Si-C-O and Si-C-O/Pd ceramics containing amorphous carbon and graphitic phases. Thermogravimetric (TG) analysis of the starting cross-linked polymer materials and those containing Pd nanoparticles revealed that the presence of palladium deteriorates thermal stability and decreases ceramic yields of preceramic networks. The extent of this effect depends on polymer cross-linking density in the system.

Swollen-induced in-situ encapsulation of chiral silver catalysts in cross-linked polysiloxane elastomers: Homogeneous reaction and heterogeneous separation

The immobilization of molecular catalysts to fabricate heterogeneous catalysts for catalytic asymmetric transformations is extremely important and has attracted great attentions. Herein we developed a simple and new strategy for the heterogenization of homogeneous molecular complexes into the cross-linked polymer. It is demonstrated for the first time that the cross-linked polysiloxane elastomers can be applied for the swollen-induced in-situ encapsulation of homogeneous catalysts with or without chiral ligands. The swollen-induced in-situ encapsulation of silver catalyst system in the cross-linked polysiloxane elastomers led to the formation of silicone rubber-based hierarchically porous that could be used in asymmetric [3+2] cycloaddition, asymmetric tandem conjugate addition−elimination reaction and oxidation of hydrosilanes to silanols. The swollen-induced in-situ encapsulation of chiral silver complex in the cross-linked polysiloxane elastomers was proved to be easily recycled by filtration or pick-up and reused by several times. The simplest heterogeneous catalysis by the strategy of swollen-induced in-situ encapsulation can be extended to the encapsulation of chiral metal catalysts into different polymeric materials for the heterogenization of homogeneous catalysis.

Preparation and Application of Fluorine-Free Finishing Agent with Excellent Water Repellency for Cotton Fabric.

Water repellent is an important functional finish for cotton fabric. However, cotton fabrics often have poor washing resistance and other performances after actual finishing. In this study, based on the structural characteristics of cotton fiber and durability of water repellent, a cross-linked amino long-chain alkyl polysiloxane (CAHPS) was first prepared, and then reacted with modified silica. Finally, a chemically bonded organic–inorganic nanohybrid cross-linked polysiloxane (rSiO2–CAHPS) was fabricated. Furthermore, the rSiO2–CAHPS was emulsified to obtain a durable fluorine-free water repellent. The water repellent finishing for cotton fabric was carried out by the pad–dry–cure process. After finishing, the cotton fabric had good resistance to conventional liquids and excellent washing resistance, and still maintained good water repellency after 30 rounds of soaping. Moreover, properties including air permeability, mechanical property and whiteness are hardly affected after finishing. SEM and XPS characterization show that a layer of dense silicon film is formed on the surface of cotton fabric by rSiO2–CAHPS water repellent. The existence of nanosilica can improve the surface roughness of cotton fibers. The synergistic effect of fiber matrix, nanoparticles and CAHPS endows the fabric with a micro/nano-multi-scale micro-rough structure, which improves the water repellency of cotton fabric after water repellent finishing.

Synthesis of Polysiloxanes with Functional Groups by Using Organometallic Carboxylate Catalysts

Abstract Linear polysiloxanes were synthesized by using organometallic carboxylic acid catalysts containing tin, zinc, or iron. By optimizing the amount of catalyst and the reaction temperature, polysiloxanes could be synthesized from dialkoxysilanes linked with vinyl monomers by the thiol–ene reaction. Furthermore, cross-linked polysiloxanes could be formed through interactions between the catalyst and the carboxylic acid in the monomer side chain.

A Fluorinated Thermocrosslinkable Organosiloxane: A New Low-k Material at High Frequency with Low Water Uptake.

In order to obtain low-k material with good comprehensive properties, a trifluoromethyl-containing organosiloxane with thermocrosslinkable vinyl and benzocyclobutene groups is designed and synthesized through the Piers-Rubinsztajn reaction. After treating at high temperature, the organosiloxane changed to form a cross-linked polysiloxane (called as c-FSi-BCB). c-FSi-BCB exhibits good dielectric properties with dielectric constant (Dk ) of 2.60 and dielectric loss (Df ) of 1.49 × 10-3 at a high frequency of 5GHz. Importantly, c-FSi-BCB maintains such good dielectric properties and exhibits low water uptake of below 0.076%, even after immersing it in boiling water for 96 h. c-FSi-BCB also displays good thermostability with a 5% weight loss temperature (T5d ) of 453 °C. These data indicate that this fluorinated organosiloxane is suitable as the matrix resin for the fabrication of devices used in 5G communication.

One-component waterborne in vivo cross-linkable polysiloxane coatings for artificial skin.

Polysiloxane-based artificial skins are able to emulate the mechanical and barrier performance of human skin. However, they are usually fabricated in vitro, restricting their diverse applications on human body. Herein, we presented one-component waterborne cross-linkable polysiloxane coatings prepared from emulsified vinyl dimethicone, emulsified hydrogen dimethicone, and Karstedt catalyst capsules that were first synthesized by solvent evaporation method. The coating had good storage stability and meanwhile could form an elastic film quickly through merging of silicone oil droplets and subsequent hydrosilylation reaction. It was found that the mass ratio of vinyl dimethicone emulsion/hydrogen dimethicone emulsion (V/H), and the dosage of Karstedt catalyst capsules (K/(V + H)) were critical to the curing time, morphology, and mechanical properties of the coatings. With appropriate values of V/H and K/(V + H), the polysiloxane film had the mechanical performance comparable to that from solvent-based one. The coating could be topically applied to human skin in vivo and in situ turned into an elastic, invisible thin film with good water resistance. In contrast to those reported polysiloxane materials, the one-component waterborne polysiloxane coating was nontoxic and convenient for in vivo application on human body, making it be a promising candidate as artificial skin in the fields of cosmetics, medical treatment, and E-skin.

Dilution-Induced Physico-Chemical Changes of Metal Oxide Nanoparticles Due to Homeopathic Preparation Steps of Trituration and Succussion.

Although the presence of starting materials in extreme dilutions of homeopathic medicines has been established, the physico-chemical changes of these materials induced by the manufacturing steps-that is, solid-solid mixing involving grinding (trituration) and slurry mixing involving impact (succussion), followed by dilution-are still unknown. We subjected cupric oxide and zinc oxide nanoparticles (NPs) to the homeopathic processes of trituration and succussion, followed by dilution up to 6 cH. Particle image velocimetry was employed to analyze the fluid motion during succussion and its effect on the NPs. The resulting microstructural and chemical changes at different dilution steps were determined by X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and transmission electron microscopy. The succussion triggered multi-sized bubble generation and turbulent fluid motion up to a duration of 400 ms, with maximum average velocity of 0.23 m/s. Due to 1% transfer of kinetic energy from a moving eddy with this velocity, upon collision, the rate of temperature change in a particle of size 1 µm and 1 nm was predicted to rise by approximately 102 K/s and 106 K/s respectively. During trituration, the oxide NPs reduced to metals and did not aggregate by remaining within lactose, but they converted to oxidized finer NPs after impact. Silicate chains leached from the vial cross-linked after third dilution, forming large macro-particles and encapsulating the NPs that were retained and carried at higher dilution steps. The results showed that the NPs sustained significant rate of temperature change due to energy transfer from moving eddies during succussion. Different physico-chemical changes, such as size reduction, successive reduction and oxidation of NPs, and morphological changes, were achieved through trituration and succussion. The retention of NPs within cross-linked poly-siloxane chains reveals the importance of both the borosilicate glass vial and the ethanol solution during preparation of homeopathic medicines.

Silicon oxycarbide (SiOC) ceramic microspheres – Structure and mechanical properties by nanoindentation studies

Abstract The mechanical properties of silicon oxycarbide (SiOC) microspheres were studied using the nanoindentation technique. The nanoindentation process was also simulated by the finite element modeling (FEM) method. The microspheres were prepared by the ceramization of polysiloxane microspheres obtained by processing the aqueous emulsion of polyhydromethylsiloxane (PHMS). The preceramic microspheres consisted of cross-linked polysiloxane. Their flexible structure enabled obtaining fracture-free solid SiOC microspheres from the pyrolysis process carried out at temperatures up to 1400 °C. The hardness and elastic modulus of the microspheres are high, reaching up to 15.9 GPa and 144.9 GPa, respectively. Using 1,3-divinyltetramethyldisiloxane (DVTMDS), divinylbenzene (DVB) and 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane (V4) as cross-linkers in the preparation of the preceramic microspheres yields ceramic particles with an enhanced content of carbon-silicon bonds, as well as particles with an increased amount of segregated free carbon. The particles possessing an enhanced content of silicon-bonded carbon exhibit the largest hardness and elastic modulus. The microspheres were also characterized by 29Si MAS NMR and Raman spectroscopies, XRD, SEM and elemental analysis.

Densely cross-linked polysiloxane dielectric for organic thin-film transistors with enhanced electrical stability

A solution-processable organic–inorganic hybrid material composed of a polysiloxane urethane acrylate composite (PSUAC) was developed through a dual cross-linking mechanism and satisfies all the requirements for use as a gate dielectric for flexible organic thin-film transistors (OTFTs).

Bulk Polymer-Derived Ceramic Composites of Graphene Oxide.

Bulk polymer-derived ceramic (PDC) composites of SiCO with an embedded graphene network were produced using graphene-coated poly(vinyl alcohol) (PVA) foams as templates. The pyrolysis of green bodies containing cross-linked polysiloxane, PVA foams, and graphene oxide (GO) resulted in the decomposition of PVA foams, compression of GO layers, and formation of graphitic domains adjacent to GO within the SiCO composite, leading to SiCO composites with an embedded graphene network. The SiCO/GO composite, with about 1.5% GO in the ceramic matrix, offered an increase in the electrical conductivity by more than 4 orders of magnitude compared to that of pure SiCO ceramics. Additionally, the unique graphene network in the SiCO demonstrated a drop in the observed thermal conductivity of the composite (∼0.8 W m–1 K–1). Young’s modulus of the as-fabricated SiCO/GO composites was found to be around 210 MPa, which is notably higher than the reported values for similar composites fabricated from only ceramic precursors and PVA foams. The present approach demonstrates a facile and cost-effective method of producing bulk PDC composites with high electrical conductivity, good thermal stability, and low thermal conductivity.

Bacterial cell killing properties of silver-loaded polysiloxane microspheres

Cross-linked polysiloxane microspheres containing a large number of SiOH groups were modified by introduction of organic thiol groups, which were further used for the functionalization of the microspheres with silver thiolate groups. The microspheres were characterized by 29Si MAS NMR, 13C MAS NMR, SEM, XPS and elemental analysis. They were tested as biocides against selected Gram-positive and Gram-negative bacteria strains and exhibited high bactericidal activity. Separately, linear polysiloxane polymers equipped with organothiol groups and loaded with silver were synthesized. Their antibacterial activity was compared with that of silver thiolate-functionalized microspheres. Different shape of particles and a different form of silver explained somewhat lower activity of polymers.

A New Fluorinated Polysiloxane with Good Optical Properties and Low Dielectric Constant at High Frequency Based on Easily Available Tetraethoxysilane (TEOS)

A novel fluorinated macromonomer (TFVE-Si) with four functional groups derived from easily available tetraethoxysilane (TEOS) has been successfully synthesized through the Piers–Rubinsztajn reaction using B(C6F5)3 as a catalyst. This procedure efficiently avoids the generation of Si–OH and −Si–CH2–CH2– groups, which greatly affect the properties of the organosiloxanes. Prepolymerizing the macromonomer in mesitylene solution gives an oligomer which can form a flexible and highly transparent free-standing cross-linked polysiloxane film followed by a postpolymerization procedure at high temperature. The cross-linked polysiloxane (thickness = 2 mm) shows a transmittance of higher than 91% in the visible region and an absorbance of near 100% in the UV region (<350 nm), exhibiting its potential application as a transparent coating for blocking ultraviolet rays in both household and industrial uses. In particular, the cross-linked film shows low dielectric constant (Dk) of 2.50 and low dissipation factor (Df) of...

Breath figures decorated silica-based ceramic surfaces with tunable geometry from UV cross-linkable polysiloxane precursor

Little has been published so far on the fabrication of porous ceramic films by using the Breath Figure method. In this work we explored the Breath Figure method to obtain ceramics with patterned surfaces. A UV cross-linkable polysiloxane was used to produce Breath Figures with tunable pore size. Pores formation, in terms of size and distribution on the polysiloxane films, were studied as a function of the concentration of the starting solution and time before UV irradiation. The polymeric breath figures were then pyrolyzed in controlled atmosphere to obtain, through the polymer-derived ceramic, PDCs, route the corresponding ceramic preserving the original porous surface. Pyrolysis under different gases, in particular air, nitrogen and ammonia, allows obtaining films of three different ceramic materials: silicon dioxide, SiO2, silicon oxycarbide, SiOC and silicon oxynitride, SiON respectively.

Wafer Scale Fabrication of Dense and High Aspect Ratio Sub-50 nm Nanopillars from Phase Separation of Cross-Linkable Polysiloxane/Polystyrene Blend.

We demonstrated a simple and effective approach to fabricate dense and high aspect ratio sub-50 nm pillars based on phase separation of a polymer blend composed of a cross-linkable polysiloxane and polystyrene (PS). In order to obtain the phase-separated domains with nanoscale size, a liquid prepolymer of cross-linkable polysiloxane was employed as one moiety for increasing the miscibility of the polymer blend. After phase separation via spin-coating, the dispersed domains of liquid polysiloxane with sub-50 nm size could be solidified by UV exposure. The solidified polysiloxane domains took the role of etching mask for formation of high aspect ratio nanopillars by O2 reactive ion etching (RIE). The aspect ratio of the nanopillars could be further amplified by introduction of a polymer transfer layer underneath the polymer blend film. The effects of spin speeds, the weight ratio of the polysiloxane/PS blend, and the concentration of polysiloxane/PS blend in toluene on the characters of the nanopillars were investigated. The gold-coated nanopillar arrays exhibited a high Raman scattering enhancement factor in the range of 108-109 with high uniformity across over the wafer scale sample. A superhydrophobic surface could be realized by coating a self-assembled monolayers (SAM) of fluoroalkyltrichlorosilane on the nanopillar arrays. Sub-50 nm silicon nanowires (SiNWs) with high aspect ratio of about 1000 were achieved by using the nanopillars as etching mask through a metal-assisted chemical etching process. They showed an ultralow reflectance of approximately 0.1% for wavelengths ranging from 200 to 800 nm.