Loss and recovery in hydrophobicity of silicone rubber exposed to corona discharge

This paper describes the loss and recovery in the hydrophobicity of unfilled high temperature vulcanized silicone rubber (HTV-SR) resulting from corona discharge. In this study, HTV-SR specimens were exposed to corona stress generated by a parallel needle-plane electrode system, and physicochemical analyses on the surface layer of SR before and after corona discharge treatment were carried out by using Fourier transform infra-red (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It is demonstrated that hydrophilic OH groups that are by-products of ageing can be formed instead of hydrophobic CH₃ groups on the surface of aged SR and the corona discharge plays an important role on the temporary loss of hydrophobicity. After a substantial period of ‘rest’, the hydrophobic recovery of SR results from the diffusion of low-molecular weight (LMW) silicone fluid from the bulk onto the aged layer.     

Development of A New Silicone Base Transdermal System: III. Study of thermal properties of silicone elastomers containing liquid ingredients

In present work we have investigated the commonly used base silicone elastomers namely cured poly-dimethyl-siloxanes and the change of the inner polarity of silicone elastomers containing various amounts of polar liquid ingredients and trifunctional silicone additives. It was shown that the polarity of the inside of the matrix is related to the diffusion properties of model substances and thermal properties of silicone elastomers. The ingredients used have changed the matrix framework, that was influenced by the type of trifunctional additive too. These properties show large dependence on the timing of the measurement. Measurements carried out after 48 hour of the production of the polymer showed reproducible properties, indicating that the final structure of the polymer has been formed.These results show that the ingredients influence the properties of the silicone matrices considerably, thus the characteristics of the drug release of pharmaceutical forms can be varied too.This revised version was published online in November 2005 with corrections to the Cover Date.     

Update on fluoroelastomers: from perfluoroelastomers to fluorosilicones and fluorophosphazenes

A survey of the synthesis, properties and applications of fluoroelastomers is reported falling into two main parts. After describing commercially available (per)fluorocarbon elastomers, fluoro-phosphazenes and silicones, recent data on hybrid fluorosilicones containing longer chains (often fluorinated) between silicon atoms are supplied. The second part deals with well-architectured fluoroelastomers. First, fluorinated thermoplastic elastomers obtained either by sequential iodine transfer polymerisation of fluoroalkenes (leading to triblock copolymers) or by a two-step procedure involving a monomer bearing peroxide that generated macroperoxides which thus produced graft copolymers. Then, multiblock copolymers were achieved either from telechelic perfluoropolyethers or from polyhydrosilylation of telechelic non-conjugated diene polyimides with fluorinated polyhybrid siloxane bearing Si-H end groups leading to exceptional materials.     

The swelling behaviour of siloxane elastomers in relation to their microscopic structure

Swelling experiments have been performed in order to characterize elastomer networks. The value of the interaction parameter χ of the Flory‐Rehner equation has been evaluated. We were particularly interested in equilibrium swelling and the kinetics of swelling when the solvent was of the same nature as the network polymer; a siloxane fluid in a siloxane elastomer. Now, the swelling capacity of elastomers can easily be predicted and this is of particular importance in relation to their formulation. The swelling experiments also revealed a more complex kinetics than expected. We relate this kinetics to the self‐bleeding process and give an interpretation based on the network microstructure. Finally, some data from electron microscopy in relation to light and neutron scattering and also results of a thermoporometry study of the elastomers are discussed.     

Wettability control and patterning of PDMS using UV-ozone and water immersion

We demonstrate a simple method to tune and pattern the wettability of polydimethylsiloxane (PDMS) to generate microfluidic mimics of heterogeneous porous media. This technique allows one to tailor the capillary forces at different regions within the PDMS channel to mimic multi-phase flow in oil reservoirs. In this method, UV-ozone treatment is utilized to oxidize and hydrophilize the surface of PDMS. To maintain a stable surface wettability, the oxidized surfaces are immersed in water. Additionally, the use of a photomask makes it convenient to pattern the wettability in the porous media. A one-dimensional diffusive reaction model is established to understand the UV-ozone oxidation as well as hydrophobic recovery of oxidized PDMS surfaces. The modeling results show that during UV-ozone, surface oxidation dominates over diffusion of low-molecular-weight (LMW) species. However, the diffusivity of LMW species plays an important role in wettability control of PDMS surfaces.     

Synthesis and characterization of liquid crystalline elastomers bearing fluorinated mesogenic units and crosslinking mesogens

Several new side‐chain liquid crystalline (LC) polysiloxanes and elastomers ( IP ‐ VIP ) bearing fluorinated mesogenic units and crosslinking mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a fluorine‐containing LC monomer 4′‐undec‐10‐enoyloxy‐biphenyl‐4‐yl 4‐fluoro‐benzoate and a crosslinking LC monomer 4′‐(4‐allyloxy‐benzoxy)‐biphenyl‐4‐yl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, ¹H‐NMR, EA, TGA, DSC, POM and XRD. The effect of crosslinking mesogens on mesomorphic properties of the fluorinated LC polymers was studied as well. The obtained polymers and elastomers were soluble in many solvents such as toluene, tetrahydrofuran, chloroform, and so forth. The temperatures at which 5% weight loss occurred (T_d) were greater than 250°C for all the polymers, and the weight of residue near 600°C increased slightly with increase of the crosslinking mesogens in the fluorinated polymer systems. The samples IP , IIP , IIIP and IVP showed both smectic A and nematic phases when they were heated and cooled, but VP and VIP exhibited only a nematic mesophase. The glass transition temperature (T_g) of polymers increased slightly with increase of crosslinking mesogens in the polymer systems, but the mesophase–isotropic phase transition temperature (T_i) and smectic A–nematic mesophase transition temperature (T_S‐N) decreased slightly. It suggests that the temperature range of the mesophase became narrow with the increase of crosslinking mesogens for all the fluorinated polymers and elastomers. In XRD curves, the intensity of sharp reflections at low angle decreased with increase of crosslinking mesogens in the fluorinated polymers systems, indicating that the smectic order derived from fluorinated mesogenic units should be destroyed by introduction of more crosslinking mesogens. Copyright © 2008 John Wiley & Sons, Ltd.     

Reactive blends derived from modified soybean oil and silicone

Reactive blends prepared from methoxysilane terminated silicone polymers and silylated soybean oil are described and characterized. Although simple mixing of soy and silicones results in gross phase separation, homogeneous polymeric products are obtained by introducing reactive sites. These products can be used as protective coatings, additives to adhesives and new sealants. Exposure of the mixtures to moisture leads to hydrolysis of the methoxysilanes and subsequent condensation of the resulting silanols that yields stable siloxane linkages between the two immiscible phases. FTIR, TGA, and swell‐gel analyses indicate effective formation of these siloxane crosslinks. Reactive blends containing less than 20% silylated oil appeared completely transparent but increasing the soy content decreased the optical transparency. SEM micrographs reveal the silicone polymer as the continuous phase with individual spherical silylated soy oil particles distributed in it. The properties of these reactive blends vary from high elongation elastomers to high modulus resins depending on the composition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3086–3093     

Investigations on the Stability of Plasma Modified Silicone Surfaces

In this work it was investigated the effect of the exposure to different plasmas on the wettability of silicone samples. We have observed that oxygen. argon, and hydrogen glow discharges are quite effective in reducing the water contact angle of such polymer. However, indifferently to efficiency of the treatment, practically all the modified surfaces recovered great part of their original hydrophobicity. We have investigated this hydrophobic recovery using surface energy measurements and theoretical simulations based on the exponential decay of the population of polar groups on the surface. According to our results such recovery can be attributed to the decrease of polar species at the interface water–polymer surface.     

Reliable Condensation Curing Silicone Elastomers with Tailorable Properties

The long-term stability of condensation curing silicone elastomers can be affected by many factors such as curing environment, cross-linker type and concentration, and catalyst concentration. Mechanically unstable silicone elastomers may lead to undesirable application failure or reduced lifetime. This study investigates the stability of different condensation curing silicone elastomer compositions. Elastomers are prepared via the reaction of telechelic silanol-terminated polydimethylsiloxane (HO-PDMS-OH) with trimethoxysilane-terminated polysiloxane ((MeO)₃Si-PDMS-Si(OMe)₃) and ethoxy-terminated octakis(dimethylsiloxy)-T8-silsesquioxane ((QM^OEt)₈), respectively. Two post-curing reactions are found to significantly affect both the stability of mechanical properties over time and final properties of the resulting elastomers: Namely, the condensation of dangling and/or unreacted polymer chains, and the reaction between cross-linker molecules. Findings from the stability study are then used to prepare reliable silicone elastomer coatings. Coating properties are tailored by varying the cross-linker molecular weight, type, and concentration. Finally, it is shown that, by proper choice of all three parameters, a coating with excellent scratch resistance and electrical breakdown strength can be produced even without an addition of fillers.     

含有稠环侧链的聚硅氧烷的合成及其对加成型高温硫化硅橡胶性能的影响

将含有多乙烯基的聚硅氧烷与菲式环戊二烯酮和苊式环戊二烯酮分别在α-氯萘中进行Diels-Alder反应,生成含有稠环侧链的聚硅氧烷.该聚硅氧烷具有较好的耐热性.将其作为组分制成高温加成型硅橡胶,综合性能达到较高水平(高模量).随着其用量的增加,可使其耐热性能得到较大改善。     

Oligomeric carbon and siloxane series observed by matrix-assisted laser desorption/ionisation and laser desorption/ionisation mass spectrometry during the analysis of soot formed in fuel-rich flames

Oligomeric carbon and siloxane series have been observed by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS), during the analysis of the dichloromethane (DCM)-soluble fractions of condensable material recovered from fuel-rich flames. Laser desorption (LD) spectra showed a pattern of oligomeric dimethyl-siloxane structures with a spacing of 74 u. The siloxane series appears to have originated as contamination of samples by silicone oil used to lubricate connections of polymer tubing. This was confirmed by extracting silicone tubing and silicone grease with DCM followed by MALDI-MS analysis. A series of peaks with a mass spacing of 24 u was also observed, superimposed on the continuum of unresolved organic ions. This oligomeric series appears to correspond to polycyclic aromatics separated by (mainly) ethylene bridges. Thus LD-MS appears to have revealed a series of soot precursors, intermediate between polycyclic aromatics and particulate soot, which was not detected by MALDI-MS. More detailed work is necessary to define these species with precision.     

Antifoam effect of highly fluorinated polysiloxanes

Aqueous foaming solutions of permethylsiloxane surfactants and fluorocarbon surfactants are very resistant to antifoaming. Newly developed polysiloxane fluids having highly fluorinated chains showed very low surface tensions and were examined as antifoaming compounds to test against these two classes of surfactant systems. The fluorinated polysiloxanes evaluated were poly-[(3,3,4,4,5,5,6,6,6 - nonafluorohexyl)methylsiloxane] (PNFHMS), and 1H,1H,2H,2H-perfluorodecyl-terminated polydimethylsiloxane (Def-DMS). Poly(dimethylsiloxane) (PDMS) was also studied as a standard siloxane polymer fluid for comparison. The antifoams composed of PNFHMS and Def-DMS polymer fluids incorporated with silica showed effective antifoaming against the low surface tension aqueous solutions of representative permethylsiloxane and fluorocarbon surfactants.     

硅表面活性剂增强的双网络耐高温多孔有机硅弹性体

采用聚醚改性三硅氧烷表面活性剂、 丙烯酸酯改性硅油和水3种组分制备了稳定的油包水(W/O)乳液, 经酸碱催化水解、 紫外引发聚合和干燥除水过程得到了双网络多孔有机硅弹性体. 扫描电子显微镜(SEM)分析结果表明, 所制备的有机硅弹性体具有丰富的孔径结构分布. 压缩强度测试结果表明, 弹性体具备良好的耐压缩性能, 45%压缩应变下循环50次, 仍具备良好的回弹性能. 有机硅弹性体具有优异的耐高温性能, 分解温度为370 ℃, 高于绝大多数多孔有机硅弹性体材料的分解温度. 丙烯酸酯改性硅油的制备工艺成熟、 廉价易得, 显著降低了多孔有机硅弹性体的生产成本, 为规模性开发有机硅材料提供了新的思路和应用前景.     

Synthesis and properties of thermoplastic and dissolvable polysiloxanes containing polyhedral oligomeric silsesquioxane

There are many benefits associated with thermoplastic silicones, but very few examples exist: silicone resins or rubbers are normally thermosets. In this article, a facile and efficient approach was reported to prepare thermoplastic silicone by introducing a bulky side siloxane group. Monofunctional polyhedral oligomeric silsesquioxane (POSS), as the bulky siloxane group, was grafted onto the linear polysiloxane backbone via thiol–ene click reaction, endowing the liquid polysiloxane with thermoplastic nature. The POSS-grafted polysiloxane could be remolded by a hot-melting or solution casting process. It was worth noting that the novel thermoplastic silicone was composed of both linear siloxane main chains and siloxane side groups, which was distinctly different from previous researches on thermoplastic silicones consisted of siloxane main chains and organic side groups. Thermal analysis, rheological characterization and molecular dynamics simulation results revealed the thermoplastic properties of POSS-grafted polysiloxane depended on the bulky POSS's hindrance to the movement of the polymer backbone rather than the interaction between the organic side groups.     

On the feasibility of chemical reactions in the presence of siloxane-based surfactants

Siloxane-containing surfactants have been tested as stabilizers for the preparation of polymer nanoparticles by three types of chemical reactions. Two crosslinking reactions were used to obtain silicone elastomers particles: one involved HO-terminated polydimethylsiloxane and tetraethoxysilane, while the other one was a crosslinking via polyhydrosilylation. The third reaction was a linear polycondensation between a diamine and a siloxane dialdehyde. The monitoring of the reactions has been made by infrared spectroscopy and the resulting particles have been analyzed in dispersion by light scattering and in dry state by electron microscopy and atomic force microscopy. The particles size was of hundreds of nanometers and their spherical shape was generally maintained after drying. The spectral and microscopy data proved efficient stabilization, which allowed the reactions to evolve after the formation of the particles.     

Effects of filler–polymer interactions on cold‐crystallization kinetics in crosslinked,silica‐filled polydimethylsiloxane/polydiphenylsiloxane copolymer melts

Crystallization in a series of variable crosslink density poly(dimethyl‐diphenyl)siloxanes random block copolymers reinforced through a mixture of precipitated and fumed silica fillers has been studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), nuclear magnetic resonance (NMR), and X‐ray diffraction (XRD). The silicone composite studied was composed of 94.6 mol % dimethoylsiloxane, 5.1 mol % diphenylsiloxane, and 0.3 mol % methyl‐vinyl siloxane (which formed crosslinking after peroxide cure). The polymer was filled with a mixture of 21.6 wt % fumed silica and 4.0 wt % precipitated silica previously treated with 6.8 wt % ethoxy‐end‐blocked siloxane processing aid. Molecular weight between crosslinks and filler–polymer interaction strength were modified by exposure to γ‐irradiation in either air or in vacuo. Isothermal DMA experiments illustrated that crystallization at ?85 °C occurred over a 1.8 hour period in silica‐filled systems and 2.2–2.6 hours in unfilled systems. The crystallization kinetics for irradiated samples were found to be dependent on crosslink density. Irradiation in vacuo resulted in faster overall crystallization rates compared to air irradiation for the same crosslink density, likely due to a reduction in the interaction between the polymer chains and the silica filler surface for samples irradiated in air. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1898–1906, 2006     

Post-irradiation grafting of tetrafluoroethylene at low temperatures

Low-temperature postirradiation grafting of tetrafluoroethylene (TFE) to polyolefines and silicone elastomers was the subject of study. After preliminary dissolution of TFE in the polymer at 273°K the system was slowly cooled to 77°K. In this process a certain part of TFE in polyolefines (ethylene-propylene copolymer and polypropylene) is retained by the vitreous polymer matrix. When slowly heated after radiolysis at 77°K this system shows graft polymerization of dissolved TFE after T_g. The graft copolymer is soluble and its IR spectra contain absorption bands characteristic of polytetrafluoroethylene. In polydimethylsiloxane rubber (SKT) the dissolved TFE when frozen to 77°K remains sorbed between the SKT crystallites rather than in a separate phase. When these radiolyzed samples are heated the graft-polymerization occurs primarily over the temperature range between the TFE and SKT melting points. The technique provedes for 100–150% grafting of TFE. This method also permits grafting to silicone rubbers and to several other polymers and elastomers.     

Solid‐state bonding of silicone elastomer to glass by vacuum oxygen plasma,atmospheric plasma,and vacuum ultraviolet light treatment

We experimentally demonstrated that treating a silicone elastomer by a vacuum oxygen plasma, an atmospheric pressure plasma, and vacuum ultraviolet (VUV) radiation resulted in different surface modifications that gave different contact angles, contact angle aging, and bond strengths. The aim of this study was to assess whether high‐throughput surface modification techniques of atmospheric pressure plasma and VUV radiation have the potential to replace conventional oxygen plasma modification. Four silicone elastomers with different hardnesses were used as specimens. The surfaces of all four silicone elastomers were successfully modified from hydrophobic to hydrophilic and they were also bonded to glass surfaces by the three surface modification techniques, although considerable variations were observed in the surface hydrophobicity and the bonding properties. The results clearly reveal that atmospheric pressure plasma and VUV treatment have the potential to replace conventional oxygen plasma treatment. In particular, VUV irradiation produced the most hydrophilic surface that was preserved for a long time. Thus, VUV irradiation is the most promising technique for realizing high‐throughput surface modification and bonding of silicone elastomers. Copyright © 2012 John Wiley & Sons, Ltd.     

Solubility of carbon dioxide,methane, and propane in silicone polymers: Effect of polymer side chains

The solubility of methane, carbon dioxide, and propane in five silicone polymers was measured at 10.0, 35.0 and 55.0°C and at pressures up to 26 atm. The polymers were poly(dimethyl siloxane), poly(methyl propyl siloxane), poly(methyl octyl siloxane), poly(trifluoropropyl methyl siloxane), and poly(phenyl methyl siloxane). At a given temperature and pressure, the solubility of the penetrant gases decreases with increasing bulkiness of the polymer side chains, and with decreasing critical temperature of the penetrant. The solubility of carbon dioxide in poly(trifluoropropyl methyl siloxane) appears to be anomalously high, possibly because of specific penetrant/polymer interactions. The temperature and pressure dependence of the solubility coefficients for the penetrant/polymer systems studied are described, and different methods of correlating these coefficients are compared.     

Effect of Atomic Oxygen on the Surface Morphology of Polyethylene

The chemical species created in a low-pressure electrical discharge in oxygen attack the polymer at the surface, converting it to gaseous products. This process is interesting because: 1) the chemical changes on the resulting surface facilitate the formation of strong adhesive bonds and provide sites for the chemical attachment of other molecules, 2) significant morphological features lying below the surface may be revealed, 3) polymer can be cleanly removed from surfaces which are resistant to oxidation, and 4) dielectric breakdown frequently is preceded by the attack on the polymer of chemical species created in a corona discharge. Atomic oxygen is an important chemical species created in such a discharge. It reacts with organic substances rapidly at room temperature, but lives long enough in the low-pressure gas that it can be separated from many other reactive species created in the discharge. “Titration” with NO₂ provides a straightforward chemiluminescent means for determining the concentration of atomic oxygen to which the sample is exposed. This paper characterizes the attack of atomic oxygen, perhaps in the presence of long lived but less reactive species such as excited O₂molecules, on polymer surfaces, using electron microscopic observations of known morphological features of polyethylene to observe the changes produced by atomic oxygen. Lamellar polyethylene crystals were attacked both at the edges and the fold surfaces. Layers many microns thick were removed from spherulitic samples and replicas obtained from the surfaces thus exposed. Thick samples were thinned to the point at which they were transparent to an electron beam and interior morphological features were directly observed.