Cross-linked Polysiloxane Research Articles

Cross-link network of polydimethylsiloxane via addition and condensation (RTV) mechanisms. Part I: Synthesis and thermal properties

A series of highly cross-linked polysiloxane was synthesised via hydrosilylation and condensation reaction. Structural identification using Fourier Transform Infrared (FTIR) and 1H-NMR confirmed their chemical structures. Their thermal and, mechanical properties, and crystallinity, were analysed and related to the level of cross-link density. These systems displayed elevated thermal and hardness properties at an increased cross-link density. Furthermore, the level of crystallinity was reduced as displayed by XRD analysis. Along with this observation, the calculated fractional free volume (FFV) showed a decreasing trend leading to the ‘ densification’ effect. It was envisaged that the linear polysiloxane chain segments aligned parallel to each other in a triclinic crystal system to generate a crystalline domain. The spacing between these stacking chains was found to be about 7.2 Å as measured from simulated XRD pattern.

Nano-colloidal functionalization of textiles based on polysiloxane as a novel photo-catalyst assistant: Processing design

Due to the opposite surface charge of TiO(2) and silver nano-particles, at around neutral pH, it is expected that the interaction between these particles and cross-linkable polysiloxane (XPs) resin and thus their final properties would be affected by their processing technique. This paper has focused on the effect of processing design on the interaction, surface orientation and final properties of surface nano-colloidal functionalization. The results disclosed the key role of the applied process on the properties of the treated fabrics which have been well discussed through the modeling of this effect on orientations of nanoparticles on the surface. The developed models are interestingly verified by various characterizations. Applying a premixed TiO(2)/XPs colloid as an after treatment on Ag treated samples caused more enhanced stain photo-degradability and UV protection properties, while the reduction of enhanced hydrophobicity, washing durability, and stain-repellency were observed as compared to applying Ag/XPs premixed colloid on TiO(2). The role of processing on XPs stabilizing efficiency and its co-photo-catalytic function on TiO(2) nanoparticles has been concluded and deeply discussed. The appropriate processing design can be tailored in order to accomplish desirable hydrophilicity/hydrophobicity with a granted bioactivity. The results reveal that ideal bioactivity, stain photo-degradability, self-cleaning, UV protection, anti-staining properties, and washing durability can be achieved by applying a mixture of silver and XPs as an after-treatment on TiO(2) treated fabrics.

Hybrid proton conducting membranes based on sulfonated cross-linked polysiloxane network for direct methanol fuel cell

A series of novel hybrid membranes based on sulfonated poly(arylene ether ketone)s (SNPAEKs), polysiloxane (KH-560) and sulfonated curing agent (BDSA) has been prepared by sol–gel and cross-linking reaction for direct methanol fuel cells (DMFCs). All the hybrid membranes (SKB- xx) show high thermal properties and improved oxidative stability compared with the pristine SNPAEK membrane. The sulfonated cross-linked polysiloxanes networks in the hybrid membranes enhance the mechanical properties and reduce the swelling ratio. The swelling ratio of SKB-20 is 22%, which is much lower than that of the pristine SNPAEK (37%) at 80 °C. Meanwhile, SKB- xx membranes with greatly reduced methanol permeabilities show comparative proton conductivities to pristine SNPAEK membranes. Notably, the proton conductivities of SKB-5 and SKB-10 reach to 0.192 S cm −1 and 0.179 S cm −1 at 80 °C, respectively, which are even higher than the 0.175 S cm −1 of SNPAEK.

Processing highly porous SiC ceramics using poly(ether-co-octene) and hollow microsphere templates

Ceramic components with high porosity, high strength, andgood permeability are especially required for hot-gas andmolten metal filters, catalyst supports, preforms for makingmetal matrix composites, gas burner media, and light-weight structural parts [1–8]. Silicon carbide (SiC) hasbeen considered a candidate material for hot-gas filters dueto its unique combination of such properties as high ther-mal conductivity, superior mechanical features, high ther-mal shock capacity, and corrosion resistance [9–13].Highly porous (porosity C 80%) SiC ceramics are pre-pared using the following processing methods: (1) immer-sion of the polyurethane (PU) foams in a ceramic slurry,and drying, burning out the PU, and then sintering [1, 5,14]; (2) freezing of gel containing SiC powders [4]orfreezing the polycarbosilane/camphene solution [15]; (3)gel-casting of SiC powder mixtures using agar as the gel-ling agent [16]; and (4) pyrolysis of a cross-linked bodyconsisting of a polycarbosilane precursor and polymermicrobead templates [17], or pyrolysis and carbothermalreduction of a cross-linked body consisting of a polysi-loxane precursor, polymer microbead templates, phenolresin, and optional sintering additives [18].The recent research studies indicate that highly porousceramic structures can be prepared by the compoundingand pyrolysis of polysiloxane and low density polyethelene(LDPE) blends [19, 20]. The processing temperature usingLDPE was 110–140 C. Polysiloxane is likely to cross-linkat such high temperatures [21], and the cross-linked poly-siloxane structure will in turn suppress the LDPE phasedispersion in the polysiloxane phase. Moreover, under highshear conditions, the dispersed polymer phase will tend toagglomerate again due to the rapid relaxation of thepolymer chain at high processing temperatures. Poly(ether-co-octene) (PEOc) is a type of thermoplastic elastomerwith a low melting point (melting peak around 60 C), highmolecular weight, and low crystallinity [22]. Thus, theconsequences of the high-temperature cross-linking ofpolysiloxane can be avoided during blending, and thedegree of co-continuous structure and mechanical proper-ties can be improved by using polysiloxane–PEOc polymerblends.This study describes a new method of preparing highlyporous SiC ceramics using polysiloxane, PEOc, and hollowmicrosphere templates. Commercially available polysilox-ane (YR3370, softening point: 109 C, melting point:*155 C GE Toshiba Silicones Co., Ltd, Tokyo, Japan), acarbon black (Corax MAF, Korea Carbon Black Co., Ltd.,Inchon, Korea), a-SiC (FCP15C, Norton AS, Lillesand,Norway), hollow poly(methyl methacrylate) microspheres(461DU40, Expancel, Sundsvall, Sweden), PEOc (metal-locene catalyzed copolymer of ethylene and 1-octene,Engage 8200, melting peak: 63.0 C, Dow Chemical Co.,Michigan, USA), AlN (Grade F, 1.3 lm, Tokuyama Soda.,Tokyo, Japan), and Y

A novel technique for producing durable multifunctional textiles using nanocomposite coating

The treatment of textiles with Ag/TiO 2 nanoparticles causes a brownish color that limits the application of this otherwise good composite. In this paper, a novel method is introduced to overcome this problem. To this end, the effect of various concentrations of cross-linkable polysiloxane (XPs) and Ag mixed with XPs on TiO 2 treated fabrics has been investigated. The results reveal the performance of the method in the application of Ag and TiO 2 nanoparticles separately. In addition to the major effect of XPs on durability, the synergistic effect of applying XPs, especially Ag mixed with XPs, on TiO 2 has been confirmed. Unexpectedly, increasing the concentration of XPs not only did not limit the TiO 2 activity but allowed light absorption by the TiO 2 particles due to the low refractive index of XPs. Therefore, XPs treatment can be helpful for increasing the bioactivity and the general photo-catalytic activity of TiO 2. The results also showed that the hydrophilicity–hydrophobicity of treated substrate can be adjusted over a broad range by controlling the concentrations of these two nanoparticles and the XPs ratio. Other characteristics of treated fabrics such as antibacterial, self-cleaning, stain photo-degradability, UV protection, air permeability and washing durability were also investigated.

Influence of the polymer architecture on the high temperature behavior of SiCO glasses: A comparison between linear- and cyclic-derived precursors

Two series of cross-linked polysiloxanes, precursors for silicon oxycarbide glasses, have been synthesized from a linear and a cyclic Si–H-containing siloxane having the same chemical formula (SiCOH 4). The crosslinking has been achieved by hydrosilylation reaction with various amounts of divinylbenzene (DVB). A detailed structural characterization has been performed by 29Si and 13C MAS NMR, FT-IR and chemical analysis. As a result, two different structural models have been proposed for the two series of resins. The two resins have been pyrolyzed at 1400 °C and the resulting SiCO ceramics characterized by X-ray diffraction. It has been shown that the stability of the amorphous silica phase present in the SiCO ceramics is strongly influenced by the molecular organization of the starting precursors. The presence of siloxane rings in the cyclic-derived polysiloxane decreases the stability of the amorphous SiO 2 and promotes the crystallization of cristobalite.

Effect of UV-Ozone Treatment on Poly(dimethylsiloxane) Membranes: Surface Characterization and Gas Separation Performance

A thin SiO(x) selective surface layer was formed on a series of cross-linked poly(dimethylsiloxane) (PDMS) membranes by exposure to ultraviolet light at room temperature in the presence of ozone. The conversion of the cross-linked polysiloxane to SiO(x) was monitored by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX) microanalysis, contact angle analysis, and atomic force microscopy (AFM). The conversion of the cross-linked polysiloxane to SiO(x) increased with UV-ozone exposure time and cross-linking agent content, and the surface possesses highest conversion. The formation of a SiO(x) layer increased surface roughness, but it decreased water contact angle. Gas permeation measurements on the UV-ozone exposure PDMS membranes documented interesting gas separation properties: the O(2) permeability of the cross-linked PDMS membrane before UV-ozone exposure was 777 barrer, and the O(2)/N(2) selectivity was 1.9; after UV-ozone exposure, the permeability decreased to 127 barrer while the selectivity increased to 5.4. The free volume depth profile of the SiO(x) layer was investigated by novel slow positron beam. The results show that free volume size increased with the depth, yet the degree of siloxane conversion to SiO(x) does not affect the amount of free volume.

Synthesis and Modeling of Polysiloxane-Based Salt-in-Polymer Electrolytes with Various Additives

The effect of both nanoparticles and low molecular weight borate esters on the ionic conductivity of cross-linked polysiloxanes was systematically investigated by means of measuring conductivity spectra in the impedance regime at temperatures between -30 and 90 degrees C. Salt-in-polymer electrolytes were prepared by dissolving lithium triflate (LiSO(3)CF(3)) in comblike polysiloxanes bearing one methyl and one oligoether side group per silicon. An amount of 10 mol % of the oligoether side groups exhibited a terminal allytrimethoxysilane serving as a cross-linker moiety (T(0.1)OPS). Thus prepared polymer electrolyte membranes were completely amorphous and mechanically stable with an optimum conductivity value of 5.7 x 10(-5) S x cm(-1) at 15 wt % of lithium triflate (LiSO(3)CF(3)) at room temperature (T(0.1)OPS + 15 wt % LiSO(3)CF(3)). Further investigations concerned the influence of additives, i.e., nanosized ceramic fillers (alpha-Al(2)O(3) and SiO(2), up to 10 wt %) as well as two low molecular weight borate esters (tris(2-(2-methoxyethoxy)ethyl) borate (B2) and tris(2-(2-(2-methoxyethoxy)ethoxy)ethyl) borate (B3)) with maximum concentrations of 40 wt % as referred to polysiloxane T(0.1)OPS. The addition of borate esters resulted in a considerable increase of the conductivity, while still maintaining the mechanical stability. Optimum conductivities of 3.7 x 10(-5) and 1.6 x 10(-4) S x cm(-1) were measured for B2 and B3, respectively, at room temperature. A fit of the temperature-dependent DC conductivity by the empirical Vogel-Tammann-Fulcher (VTF) equation showed that there was an increased number density of mobile charge carriers in the case of borate esters as additives. However, the shape of the conductivity spectra in the dispersive regime changed considerably in going from nanoparticles as additives to borate esters. A careful and consistent modeling of the conductivity spectra and of the temperature dependence of the DC conductivity was done within the framework of the MIGRATION concept. The result was that the addition of borate esters to the polymer host most probably increased both number density of mobile charge carriers as well as their mobility.

Preparation and micro-mechanical studies of polysiloxane-containing dual-layer film on Au surface

A novel polysiloxane-containing self-assembled dual-layer film was grafted onto Au surface with a simple three-step method. Firstly, (3-mercaptopropyl)trimethoxysilane (MPTMS) molecules were self-assembled on Au surfaces through S–Au bond followed by hydrolysis and condensation, then the octadecyltrichlorosilane molecules were attached to the resultant hydroxyl terminated surface via the Si–O–Si bonds. The structure and morphology of the film were characterized by means of contact angle measurement, ellipsometry, attenuated total reflectance Fourier transformed infrared spectra, and atomic force microscopy. The resistant ability of charge transfer in the film forming process was detected by electrochemical techniques. Using force–volume technique, we investigated how the different surface chemical groups influence the surface adhesion properties. The nano-friction properties of the as-prepared films were investigated by frictional force microscopy. The results indicated that the dual-layer film fabricated via the hydrolyzation of MPTMS underlayer had significantly less friction. Moreover, compared to the self-assembled monolayer of octadecane thiol, the resultant dual-layer film showed much less wear. This improvement was mainly ascribed to the existence of the network of lateral cross-linked polysiloxane layer within the film which can enhance the stability of the film.

A new method to stabilize nanoparticles on textile surfaces

This paper presents a novel idea to achieve permanent antibacterial activity with no negative effect on other properties such as comfort and strength. To this end, PET fabric samples were treated with crosslinkable polysiloxane via different methods, simultaneous or after treatment with various concentrations of nanosized colloidal silver. Furthermore, this research has investigated and compared the effect of presence or absence of the spin finish on fabric surfaces in the same treatment condition to indicate the possibility of applying this method without spin finish elimination. Finally, the antibacterial efficiency of modified fabrics was quantitatively evaluated and compared against Klebsiella pneumoniae and Staphylococcus aureus according to AATCC 100. Very good biostatic efficacy against S. aureus appeared even by applying a low nanosilver content. However, a higher nanosilver content was necessary to attain such antibacterial effects against K. pneumoniae. Crosslinked polysiloxane resulted in a remarkable control in the release of silver from the coating and can improve the long-term microbiological activity, especially against home laundering. Increasing nanosilver mass fraction resulted in bioactivity enhancement against both kinds of tested bacteria. Simultaneous application of nanosized silver solution and polysiloxane emulsion on the fabric surfaces showed improved antibacterial efficiency as compared to separate application. The presence of spin finish declined bioactivity because of providing an enrichment culture for fast thriving of microorganisms. The polysiloxane treatment has compensated for this difference to some extent. The experiment results revealed that polysiloxane also compensated for some adverse effects of nanosilver treatment such as decreasing conductivity and softness.

Preparation and tribological studies of self-assembled triple-layer films

A self-assembled triple-layer film was grafted onto a silicon surface with a simple three-step method. Firstly, 3-glycidoxypropyltrimethoxysilane molecules were self-assembled on silicon surfaces, then coupled to 3-aminopropyltriethoxysilane through a surface ring-opening reaction, and finally octadecyltrichlorosilane (OTS) molecules were attached to the resultant alkoxysilane-terminated surface via Si–O–Si bonds. The structure and morphology of this triple-layer film were characterized with various techniques, such as contact angle measurement, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). The influence of different surface chemical groups on surface adhesion properties was identified using the AFM force-volume technique. The micro- and macro-tribological properties of the triple-layer film were evaluated by friction force microscopy and a ball-on-plate tribometer. The triple-layer film shows good adhesive resistance and can greatly reduce the micro- and macro-friction force. Moreover, compared to self-assembled monolayer of OTS, this triple-layer film exhibited much better wear-resistance. This improvement was mainly ascribed to the network structure of a lateral cross-linked polysiloxane layer formed within the film which can enhance the stability of the film.

Biosensors utilizing monolayers on electrode surfaces

Abstract The applications of monolayer technologies to the fabrication and use of biosensors are described. The introduction of accessible cysteine residues and that of lipid tags by genetic engineering techniques were demonstrated to be viable methods to immobilize protein molecules in controlled manner using the self-assembly and Langmuir–Blodgett (LB) methods, respectively. A self-assembled monolayer of a thiol-derivatized adenine on a gold electrode could recognize thymidine, a complementary base derivative, in an aqueous solution via the hydrogen bond pairing at the monolayer/solution interface. Monolayers of redox-active species, such as hydroquinone and ferrocene derivatives, were used for transducing the signal of enzyme-catalyzed reactions. For example, the pH-dependent benzoquinone/hydroquinone-redox system was applied to detect the pH change at the immobilized urease surface with the enzymatic hydrolysis of urea. A two-dimensional cross-linked polysiloxane LB film has been proved to be useful as a permselective layers in amperometric hydrogen peroxide detecting biosensors. The formation/desorption process of thiol monolayers could be applied to the construction of a high-sensitive immunoassay system for a cardiac marker, BNP. Thus, the monolayer-based systems are of interest not only from the fundamental aspect as shown in the bottom-up approach to the construction of protein or nucleic acid base-based sensors but also from the viewpoint of possible practical use as shown in the immunosensor for BNP.

Covalently Cross-Linked Perfluorosulfonated Membranes with Polysiloxane Framework

Proton exchange membranes with low methanol permeability are constructed by incorporating Nafion into a covalently cross-linked network composed of 4,4‘-methylenedianiline (MDA) and 3-glycidoxypropyltrimethoxysilane (GPTMS) by ionical cross-linking. The robust framework is full of covalently bonded polysiloxane. The association of Nafion with the cross-linked polysiloxane network results from the ionic interaction between the sulfonic acid groups on Nafion and the amine groups next to polysiloxane. Evidence of the interaction is the shift of the XPS spectra in the S 2p region and the -SO3 stretching band at 1057.8 cm-1 in ATR/FTIR which induced a change of the hydrophilic/hydrophobic microphase separation. The polysiloxane network contributed to the increase in bound water degree, higher proton conductivity at temperatures higher than 70 °C, and greatly decreased methanol permeability. The increasing polysiloxane concentration reduces the methanol permeability to 10-8 cm2/s. With a polysiloxane concentrat...

Electrochemical nitric oxide microsensors based on two-dimensional cross-linked polymeric LB films of oligo(dimethylsiloxane) copolymer

Two-dimensional cross-linked polysiloxane Langmuir–Blodgett (LB) films were prepared and applied to nitric oxide (NO)-permselective membranes in order to block other electroactive interfering species. The cross-linked siloxane LB films deposited on platinum micro-disc electrodes (10 μm in diameter) offered revealing high performances as a permselective membrane for NO sensor such as high sensitivity to NO (detection limit, 40 nM) and high selectivity (e.g., the ratio of current response for acetaminophen or uric acid on the modified electrode to that on the bare electrode, less than 10 −3). Furthermore, the permselective membrane could be easily deposited irrespective of the size and shape of electrode.

A novel and facile method for direct synthesis of cross-linked polysiloxanes by anionic ring-opening copolymerization with Ph 12-POSS/D 4/Ph 8D 4

The cross-linked polysiloxanes were directly synthesized by anionic ring-opening copolymerization of Ph 12-POSS as multifunctional monomer with D 4 and Ph 8D 4 under KOH or Me 4NOH siloxanolate. And the influences of the polar additive DMAc on gelation time were investigated. The results of gel content and swelling ratio, GPC, solid-state 29Si and 13C NMR, FT-IR, WAXD showed that Ph 12-POSS was reacted and most of the product was cross-linked. The DSC and TG results indicated that the cross-linked polysiloxanes exhibited distinct glass transition temperatures ( T g) and excellent thermal stability. Compared to that with KOH siloxanolate, the cross-linked polysiloxane synthesized with Me 4NOH siloxanolate has more preferable thermal stability.

Polymerization in Surfactant Liquid Crystalline Phases

We report the formation of cross-linked polysiloxane particles having rodlike and sheetlike morphologies by condensation of monomers in organized liquid crystalline mesophases of nonionic surfactants. The characteristic diffraction pattern obtained from the liquid crystalline surfactant assembly is preserved during polymer synthesis. The polymer colloids are rodlike when synthesized in a hexagonal mesophase and are sheetlike when synthesized in a lamellar mesophase. Interestingly, the size of the polymer particles is on the order of micrometers, viz. 3 orders of magnitude larger than the characteristic size of the surfactant mesophase. Thus, the polymers phase separate from the liquid crystalline phase during polymerization, and organize to resemble the mesophase geometry. The polymer particles are organized so as to minimize the elastic distortion of the surfactant mesophase after they phase separate. We speculate that the observed particle morphologies are formed due to the slow kinetics of polycondensa...

Some Interesting Things about Polysiloxanes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Some Interesting Things about Polysiloxanes

Poly(dimethylsiloxane) [-Si(CH3)(2)O-] is by far the most studied of the polysiloxanes and is known to exhibit some intriguing physical properties, in particular very high permeability to gases. Simulations are underway in an attempt to understand some of these peculiarities. In addition, other symmetrically substituted polysiloxanes exhibit mesophases that are not understood at all. In the case of cross-linked polysiloxanes, there have been many important developments, including (i) elastomers undergoing strain-induced crystallization through control of chain stiffness or stereochemical structure, (ii) model elastomers (including dangling-chain networks), (iii) possible thermoplastic elastomers, (iv) bimodal network chain-length distributions, and (v) cross linking in solution. Interesting elastomeric composites include those with (i) in-situ-generated ceramiclike particles, (ii) ellipsoidal fillers, (iii) claylike-layered fillers, (iv) polyhedral oligomeric silsesquioxane (POSS) particles, (v) porous fillers, (vi) controlled particle-elastomer interfaces, and (vii) elastomeric domains generated within ceramic phases. Also of interest are some new techniques that have been used to characterize polysiloxane networks.

H 2O outgassing from silica-filled polysiloxane TR55

Temperature-programmed desorption/decomposition (TPD) was employed to obtain the moisture content and outgassing kinetics of TR55, a silica-filled cross-linked polysiloxane. The total moisture content of TR55 in the as-received state and after 20–30 min of vacuum pumping in the load-lock prior to TPD was measured to be on the order of 0.35 wt%. Physisorbed H 2O and chemisorbed H 2O account for about 13.2 and 86.8%, respectively, of the 0.35 wt% measured moisture content. H 2O outgassing models based on the kinetics measured from TPD experiments suggest that loosely bound chemisorbed water outgasses in a dry environment slowly but continuously over many decades at or a little above room temperature. However, physisorbed water can be easily pumped out in a matter of hours at around 400 K.

Solid polymer electrolytes based on cross-linked polysiloxane- g-oligo(ethylene oxide): ionic conductivity and electrochemical properties

Poly(siloxanes- g-oligo(ethylene oxide)) with acrylate groups at the terminal position were prepared and examined for the solid polymer electrolyte (SPE) by curing them. Poly(ethylene glycol) dimethyl ether (PEGDME) was added as a plasticizer. Conductivity of the resulting polymer electrolytes was greatly enhanced with increasing amounts of low molecular weight PEGDME. Maximum conductivity was found to be 8×10 −4 S/cm at 30 °C with an [EO]/[Li] ratio of about 8. These electrolytes showed oxidation stability up to 4.95 V against the lithium reference electrode. Reversible electrochemical plating/stripping of lithium was observed on the nickel electrode. The plating/stripping efficiency of lithium on nickel was measured to be about 53%.