Series Of Polydimethylsiloxane Research Articles

Improved electro‐actuation property of dielectric elastomer composites regulated by one‐dimensional CaCu3Ti4O12@TiO2 core–shell construction

AbstractDielectric elastomers (DEs) are typical electro‐active polymers that can achieve an electro‐actuated deformation under an applied electric field. However, obtaining a large low‐field‐actuated strain of DEs is still a key challenge, which is critical to their practical application range. Herein, a typical CaCu3Ti4O12@TiO2 (CCTO@TiO2) core–shell‐structured nanowires were synthesized by the micro‐emulsion method. Additionally, a series of polydimethylsiloxane (PDMS)‐based DE composites combining variable proportions of CCTO@TiO2 were prepared. The CCTO@TiO2 nanowires with the design of both decreasing dielectric constant from core to shell and a high aspect ratio can provide larger heterogeneous interfaces for the DE composites, leading to a promoted interfacial polarization. The maximum electro‐actuated strain of 37.66% is achieved from the DE composite incorporated with 20 wt% CCTO@TiO2 when subjected to a relatively low electric field of 40 V/μm, which is 14 times higher than that of pure PDMS (strain ~2.5%). Moreover, the composite exhibits the largest electro‐actuated strain (45.83%) under the electric field approaching its breakdown strength of 43.57 V/μm. The results demonstrate that the one‐dimensional core–shell nanowires have a positive effect on improving the low‐field‐actuated strain of DE composites. This research reveals an effective and feasible method to prepare the DE composites exhibiting enhanced low‐field electro‐actuated characteristics.

The improved low‐field electro‐actuation of dielectric elastomer composites regulated by entirely‐inorganicBaTiO3@TiO2core‐shell construction

AbstractDielectric elastomer (DE) as an important electro‐active polymer (EAP), is capable of providing a large elastic deformation under an external electric field. However, the excellent electro‐actuated performance is usually obtained under high electric fields, which greatly limits the practical application range of DE, especially in the field of in vivo organisms. Thus, it is essential to make a reasonable structural regulation to achieve an effectively improved electro‐actuation of DE materials under low driving electric fields. Herein, a typical BaTiO3@TiO2entirely‐inorganic core‐shell construction was prepared through the micro‐emulsion method. Meanwhile, a series of polydimethylsiloxane (PDMS)‐based DE composites incorporated with different fractions of BaTiO3@TiO2were synthesized by solution blending and compression molding. The BaTiO3@TiO2core‐shell construction endows DE composites with an enlarged heterogeneous interface and enhanced interfacial polarization synchronously, which is also benefit to maintain the flexibility of DE materials. The buffer effect offered by TiO2shell is helpful to alleviate the local electric field concentration at the fillers‐matrix interface in DE when being withstood an exponentially‐growing electric field. Specifically, the maximum electro‐actuated strain of 21% under a low electric field (40 V·μm−1) is obtained from the DE composite filled with 4 wt% BaTiO3@TiO2, which is 290% higher than that of pristine PDMS (5.38% at 40 V·μm−1). It is shown that the well‐designed inorganic core‐shell construction can effectively improve the electromechanical conversion capability of DE composites. This study provides a promising approach to obtain an optimized electro‐actuation under low electric fields.

Highly selective PDMS-PVDF composite membrane with hydrophobic crosslinking series for isopropanol-1,5 pentanediol pervaporation

An energy-efficient pervaporation (PV) facile approach was designed to remove isopropanol during α, ω-diol production. Accordingly, a series of polydimethyl siloxane (PDMS) membranes were prepared by tuning their surface chemistry through trifunctional (PFTES and OTMS) and traditional tetrafunctional (TEOS) crosslinkers and casting on a polyvinylidene fluoride (PVDF) membrane. Additional hydrophobic tail enrichment on the membrane surface because of alkyl (OTMS) and fluoroalkyl (PFTES) groups from the tri-functional crosslinker was confirmed by FTIR, XPS, and DSC. TGA and XRD revealed that the tetra crosslinking site promoted a denser structure across the membrane than the trifunctional crosslinker. In the water contact angle measurements of the different series of membranes, the contact angle was proportional to the hydrophobic site. When a series of PDMS membranes were tested for PV of the novel feed PDO/IPA (90/10 w/w) system, the highest flux was delivered from the fluoroalkyl type crosslinked membrane, which was attributed to its superior hydrophobicity and amorphous nature, with excellent IPA selectivity from all the membranes. As a result, a stabilized flux of 235.8 g/m2h and excellent separation factor (IPA content in permeated >99.95%) in a 40 h continuous PV test was achieved using the PDMS PFTES membrane.

Charge Transfer Metal-Organic Framework Containing Redox-Active TTF/NDI Units for Highly Efficient Near-Infrared Photothermal Conversion.

Metal-organic frameworks (MOFs), as a class of new inorganic-organic hybrid crystal materials, could have important applications in near-infrared (NIR) photothermal conversion. Herein, a new charge-transfer MOF (Co-MOF) with mixed ligands of H4 TTFTB and bpmNDI incorporating redox-active tetrathiafulvalene/naphthalene diimide (TTF/NDI) units into one system is reported. Due to the presence of TTF/NDI oxidative and reductive couples, stable radicals can be observed in the MOF. In addition, charge transfer from the electron donor (TTF) to the acceptor (NDI) results in a broad absorption in the NIR region. The Co-MOF exhibited an efficient photothermal effect induced by irradiation with a NIR laser. Under the 808 nm laser (0.7 W cm-2 ) illumination, the temperature of the Co-MOF increased from room temperature to 201 °C in only 10 s. Furthermore, a series of polydimethylsiloxane (PDMS) films doped with trace amounts of Co-MOF showed efficient NIR photothermal conversion. When a Co-MOF@PDMS (0.6 wt %) film is irradiated by 808 nm laser with power of 0.5 W cm-2 , it's temperature can reach a plateau at 62 °C from 20 °C within 100 s. Our experimental results from the Co-MOF@PDMS film demonstrate that the effectiveness and feasibility of the material is promising for photothermal applications.

Dimensional effect of SrTiO3 particles on functional performance optimization of polydimethylsiloxane-based composites for dielectric elastomer actuators

Dielectric elastomer materials have a great application potential in electromechanical sensing and energy-harvesting fields. However, the realization of high electro-actuation properties under a relatively low electric field is still a critical challenge. Herein two series of polydimethylsiloxane (PDMS)-based dielectric elastomer composites incorporated SrTiO3 (STO) with distinguishing diameters were prepared through solution-blending and compression moulding methods. The resultant STO/PDMS composites showed significantly enhanced dielectric permittivity and Young’s modulus. Moreover, the PDMS-based composite filled with 4 vol.% nano-scaled STO exhibited an improved electro-actuation strain of 3.3% at a very low electric field of 24 V μm−1, which was 30% larger than that of the neat PDMS. The experimental results revealed that the electro-active performance of dielectric elastomer composite under low electric fields can be influenced by the size of incorporating functional units, and be also successfully optimized by regulating the fillers-matrix interfacial interaction. This study provides a promising strategy to design and fabricate novel dielectric elastomers with advanced low-field driving electro-active properties.

Measurement of nanoindentation properties of polymers considering adhesion effects between AFM sharp indenter and material

Nanomechanical properties of polymer samples were calculated using an adhesive contact model appropriate for AFM indentation problems. A series of Polydimethylsiloxane (PDMS) samples were indented by the sharp indenter in the air by using an AFM, and dozens of the force–displacement curves of each sample were obtained. An adhesive contact model suitable for sharp indentation with adhesion was established based on the same assumptions of the JKR model which is only suitable for spherical indentation at small penetration depth. Differences between sharp indentation problems with and without adhesion were discussed, and the limitations of the traditional adhesion model were given. The elastic modulus was obtained by fitting experimental force–displacement curves with theoretical ones, and results were compared to those macroscopic values in literature. The adhesion energy between the indenter and the sample surface was accurately calculated using the adhesion model based on the calculated elastic modulus. The influence of the indenter tip angle on the calculation results of the elastic modulus was also discussed theoretically. In this study, the mechanical properties of polymer samples were calculated at the nanoscale considering the adhesion effect.

One-Step Fabrication of Bioinspired Lubricant-Regenerable Icephobic Slippery Liquid-Infused Porous Surfaces.

Icephobic coating and surfaces are essential for protecting infrastructures such as transmission lines, transportation vehicles, and many others from severe damages of excessive icing. The slippery liquid-infused porous surfaces (SLIPS) are attracting escalating attention because of their low-ice adhesion strength. Despite all of the encouraging laboratory scale results, the SLIPS are still far from being applicable in real environments owing to the key unsolved problem, namely anti-icing durability. Inspired by the functionality of the amphibians’ skin, lubricant regenerability was introduced to conventional SLIPS and realized by a facile and scalable fabrication route. A series of polydimethylsiloxane (PDMS)-based skinlike SLIPS were designed and fabricated by using a one-step method, the solvent evaporation-induced phase separation technique. The obtained skinlike SLIPS were able to regenerate surface lubricant constantly by internal residual stress because of phase separation and survive more than 15 cycles of wiping/regenerating tests. Thanks to the regenerability of the surface lubricant, the new SLIPS demonstrated durable icephobicity, showing a long-term low-ice adhesion strength below 70 kPa, which was only 43% of 160 kPa that for the pristine PDMS (Sylgard 184), even after 15 icing/deicing cycles. This work paves a new and facile way for achieving icephobic durability of SLIPS.

Impact of surface topography on biofilm formation by Candida albicans.

Candida albicans is a fungal pathogen that causes serious biofilm-based infections. Here we have asked whether surface topography may affect C. albicans biofilm formation. We tested biofilm growth of the prototypical wild-type strain SC5314 on a series of polydimethylsiloxane (PDMS) solids. The surfaces were prepared with monolayer coatings of monodisperse spherical silica particles that were fused together into a film using silica menisci. The surface topography was varied by varying the diameter of the silica particles that were used to form the film. Biofilm formation was observed to be a strong function of particle size. In the particle size range 4.0–8.0 μm, there was much more biofilm than in the size range 0.5–2.0 μm. The behavior of a clinical isolate from a clade separate from SC5314, strain p76067, showed results similar to that of SC5314. Our results suggest that topographic coatings may be a promising approach to reduce C. albicans biofilm infections.

The effects of counter anions on the dynamic mechanical response in polymer networks crosslinked by metal–ligand coordination

ABSTRACTMetal–ligand coordination has been proven to be an attractive strategy to tune a polymer network's dynamic mechanical properties, such as self‐healing ability. Nonetheless, the role of counter anions is often overlooked. To address this, a series of polydimethylsiloxane (PDMS) films crosslinked through lanthanide metal cations (Eu3+, Tb3+)–bipyridine interactions have been prepared and studied. Neutral 2,2'‐bipyridine ligands were embedded into the linear polydimethylsiloxane (PDMS) chain through polycondensation. With nitrate ( ) as the coordinating anions, metal salts Eu(NO3)3 and Tb(NO3)3 were found to be ineffective crosslinkers. With noncoordinating anions, such as triflate (OTf‐: CF3 ), metal salts Eu(OTf)3 and Tb(OTf)3 showed improved interaction strength with bipyridine ligands. Surprisingly, the addition of Eu(OTf)3 and Tb(OTf)3 salts also increased the d‐spacing distances of the phase‐segregated domains between metal–ligand complexes and the PDMS polymer backbone. For the Eu(OTf)3‐, Tb(OTf)3‐PDMS films, the much‐improved self‐healing abilities are attributed to the crosslinker dynamics and the enhanced chain mobility. This work underlines the importance of counter anions on the mechanical properties, and provides further guidance on the future design of self‐healing metal−ligand crosslinked polymers.) © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3110–3116

Polydimethylsiloxane and Castor Oil Comodified Waterborne Polyurethane

In view of both improving properties of waterborne polyurethane (WPU) and sufficient utilization of renewable resources, a series of polydimethylsiloxane (PDMS) and castor oil (C.O.) comodified anionic WPUs with internal cross-linking was prepared through a prepolymer mixing process. The chemical structure of synthesized polymers was characterized by Fourier transforms infrared spectroscopy (FT-IR). In comparison with traditional linear WPU synthesized from petroleum-based polyols, these novel WPU films exhibited superior properties in solvent and water resistance, thermal stability, and mechanical strength, which suggest promising applications of these new environmentally friendly materials, particularly in the area of decorative and protective coatings. In addition, the results showed that with the increase in PDMS content in these co-modified WPUs the average particle size, the water resistance, and the thermal stability increased accordingly while the solvent resistance and the mechanical properties decreased.

Spatially monitoring oxygen level in 3D microfabricated cell culture systems using optical oxygen sensing beads

Capability of measuring and monitoring local oxygen concentration at the single cell level (tens of microns scale) is often desirable but difficult to achieve in cell culture. In this study, biocompatible oxygen sensing beads were prepared and tested for their potential for real-time monitoring and mapping of local oxygen concentration in 3D micro-patterned cell culture systems. Each oxygen sensing bead is composed of a silica core loaded with both an oxygen sensitive Ru(Ph2phen3)Cl2 dye and oxygen insensitive Nile blue reference dye, and a poly-dimethylsiloxane (PDMS) shell rendering biocompatibility. Human intestinal epithelial Caco-2 cells were cultivated on a series of PDMS and type I collagen based substrates patterned with micro-well arrays for 3 or 7 days, and then brought into contact with oxygen sensing beads. Using an image analysis algorithm to convert florescence intensity of beads to partial oxygen pressure in the culture system, tens of microns-size oxygen sensing beads enabled the spatial measurement of local oxygen concentration in the microfabricated system. Results generally indicated lower oxygen level inside wells than on top of wells, and local oxygen level dependence on structural features of cell culture surfaces. Interestingly, chemical composition of cell culture substrates also appeared to affect oxygen level, with type-I collagen based cell culture systems having lower oxygen concentration compared to PDMS based cell culture systems. In general, results suggest that oxygen sensing beads can be utilized to achieve real-time and local monitoring of micro-environment oxygen level in 3D microfabricated cell culture systems.

Effect of structure and additives on thermal stability of silicone fluids

AbstractA series of polydimethylsiloxane (PDMS) polymers and poly(dimethyl‐diphenyl siloxane) (PDMS‐PMPS) copolymers were synthesized by the anionic ring‐opening polymerization method and then blended with titanium isooctoate as thermal additives. Their thermal stabilities have been investigated by TGA in an inert gas atmosphere. The temperature for 10% conversion, 50% conversion, and the temperature for the maximum rate of decomposition (MRDT) initiated from TGA curves recorded at a heating rate of 5, 10, 15, and 20°C min−1 and the apparent activation energy Ea using the FWO method as a function of conversion α indicated that the thermal stabilities of the polysiloxanes could be enhanced either by modifying the structure of the polymer or by introducing a certain amount of a thermal additive. PDMS‐PMPS copolymers with a MePhSiO segment content of 10.2 mol % and terminated by diphenylmethylsiloxyl groups exhibited optimal heat resistance. The thermal stabilities of the polysiloxanes could be further improved by introducing homogenous titanium additives and with the addition of 1550 ppm content of titanium additives, the temperature for 10% conversion, the temperature for 50% conversion, and MRDT have been found to be increased by 20.11, 71.28, and 98.67 K, respectively, relative to the unmodified PDMS‐PMPS copolymer. Fourier transform infrared (FTIR) analysis has proven the formation of a SiOTi bond in the titanium‐modified PDMS‐PMPS copolymer, which may be responsible for the efficient enhancement of its thermal stability. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Synthesis and characterization of α-butyl-ω-{3-[(2,2-dihydroxymethyl)-propionyloxy]}propylpolydimethylsiloxanes

A series of polydimethylsiloxanes containing two primary hydroxyl groups at one single chain end were synthesized by five-step reactions which included esterification, hydroxyl protection, anionic ring-opening polymerization, hydrosilylation and deprotection. The prepared compounds in each step were characterized. The results showed that each step synthesis was successfully carried out and objective products could be achieved.

EFFECT OF MOLECULAR WEIGHT OF PDMS ON MORPHOLOGY AND MECHANICAL PROPERTIES OF PP/PDMS BLENDS

A series of polydimethylsiloxane (PDMS) with varied molecular weights (Mw = 3 × 106, 1 × 106 and 0.5 × 106) were melt blended with PP to investigate the effect of PDMS molecular weight (MW) on the morphology and mechanical properties of PP/PDMS blends. Scanning electron microscopic (SEM) examination showed that the size of PDMS domains was dependent on the MW of PDMS. It was found that the lower the value of PDMS MW, the better dispersion of the PDMS domains in the PP matrix. Tensile and Izod impact tests revealed that the addition of PDMS with lower MW would lead to a more significant increase in impact strength of the blends compared with the blends with higher MW ones, while the influence of the molecular weight on tensile strengths of the blends was relatively small in the MW range studied. Differential scanning calorimetry (DSC) results also showed that the crystallization temperature of PP was increased with decreasing PDMS MW, indicating a better nucleation capability of lower MW of PDMS. Melting flow rate (MFR) measurements indicated that the processibility of PP could be enhanced by adding PDMS, and again the lower MW PDMS resulted in better data. Our work demonstrates that not only the processibility but also the mechanical properties of PP could be enhanced to a more significant degree by using low MW PDMS than the higher ones.

Preparation and properties of polydimethylsiloxane-modified chitosan

Preparation and properties of polydimethylsiloxane (PDMS)-modified chitosan are discussed herein. A series of PDMS with systematically varied molecular weights were first prepared via acid-catalyzed ring opening polymerization of octamethylcyclotetrasiloxane (D 4) to obtain PDMS prepolymers. They were subsequently functionalized with allyl glycidyl ether to obtain epoxy functional groups at PDMS terminals. Their chemical structures and molecular weights were characterized using 1H NMR, 13C NMR and FTIR, and thermal properties were determined by DSC. The reaction of the epoxidized PDMS and chitosan was carried out in an acidic aqueous solution. Increasing the molecular weights of PDMS and/or its concentrations improved flexibility and water swellability due to the formation of PDMS microphase. Water contact angle and water vapor permeability measurements indicated that incorporation of the PDMS enhanced its hydrophobicity as compared to the unmodified one.

Nanoscopic properties of silica filled polydimethylsiloxane by means of positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) was performed on a series of polydimethylsiloxane (PDMS)/fumed silicon dioxide (SiO 2) composites at temperatures between −185 and 100 °C to study the effect of filler content and filler particle size on the free volume properties and the positron annihilation characteristics. The glass transition behavior of the PDMS/SiO 2 composites was determined with differential scanning calorimetry. A clear influence on the o-Ps lifetime ( τ 3) in the polymer upon addition of nano-sized fumed SiO 2 was observed at all temperatures. The observed o-Ps lifetime behavior was related to filler content and filler particle size. A transition in the temperature dependence of the o-Ps lifetime was observed close to −35 °C above which temperature PDMS exhibits long o-Ps lifetimes. A relationship between τ 3 and the surface tension, equivalent to the behavior of ordinary molecular liquids was observed in this temperature region. The o-Ps yield was strongly reduced in the crystallization region and by addition of SiO 2. The reduction due to filler addition did, however, in the case of nano-sized SiO 2 not follow a linear relationship with filler weight, which was observed for micron-sized fillers. The nonlinear relationship between filler weight and o-Ps yield could be due to out-diffusion of positrons and/or o-Ps from the filler particles to the matrix.

Evaluation of photocrosslinkable fluorinated polydimethylsiloxanes as gas permeation membranes

Dense permselective membranes were prepared from two series of polydimethylsiloxanes (PDMS) bearing fluorinated groups and acrylic or vinyl ether type photocrosslinkable groups linked to the polysiloxane chain through urethane bridges. These dense permselective membranes were evaluated for their application as gas permeation membrane for the purification of natural gas. Permeabilities and selectivities towards the CO 2/CH 4 gas pair were measured. This study showed that the selectivity increased with the introduction of C 8F 17 fluorinated groups and/or acrylic groups.

Synthesis and Characterization of Phenyl Modified PDMS/PHMS Copolymers

AbstractA series of polydimethylsiloxane (PDMS)/polyhydrogenmethylsiloxane (PHMS)/polymethylphenylsiloxane (PMPS) random copolymers with different phenyl contents were synthesized in one step through triflic acid‐catalyzed ring‐opening polymerization of cyclic comonomers and characterized by GPC, IR and NMR. Sequential structures of the random copolymers were determined by 29Si‐NMR spectroscopy. Thermal properties of these copolymers were studied by DSC and TGA. The effect of phenyl moiety on the thermal properties of the copolymers was discussed. The refractive index (nD) increased regularly with the introducing of phenyl‐functionality as expected.

Electrochemical preparation and characterization of carbon fiber reinforced poly(dimethylsiloxane)/polythiophene composites: electrical, thermal and mechanical properties

A series of polydimethylsiloxane (PDMS)/polythiophene (Pth)/carbon fiber (CF) composites was synthesized by electrochemical polymerization using tetrabutylammoniumtetrafluoroborate (TBAFB) as supporting electrolyte and acetonitrile as solvent. Composites were characterized by TGA, SEM, and mechanical tests and conductivity measurements. Conductivities of composites were in the range of 2–5 S/cm. SEM studies show that CF were coated by PDMS/Pth matrix and well oriented in the matrix. In mechanical tests it has been observed that higher percent elongation was obtained by increasing PDMS content whereas tensile strength and modulus of composites increases with increasing CF content.

Rheo-optical Fourier transform near-infrared spectroscopy of polydimethylsiloxane/polycarbonate block copolymers

A series of polydimethylsiloxane (PDMS)/polycarbonate (PC) block copolymers with varying compositions were investigated by simultaneous mechanical and Fourier transform near-infrared (FTNIR) spectroscopic (rheo-optical) measurements to study segmental orientation during elongation-to-break and cyclic elongation–recovery procedures. Depending on the composition and the block lengths of the copolymers, different orientational and recovery phenomena were observed for the hard (PC) and soft (PDMS) segments. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1349–1357, 1998