Linear PDMS Research Articles

Association Constant of the Charge‐Transfer Complex Between Pyrene and Naphthalenediimide Derivatives in PDMS Elastomers

AbstractPolydimethylsiloxane (PDMS) elastomers with varying crosslink densities were synthesized using prepolymers with different molecular weights. The association constants (Ka) between a pyrene derivative (PySi) and naphthalenediimide derivative (NDISi) were measured in linear PDMS and PDMS elastomers. The shape of the absorption peak in the charge‐transfer (CT) band and the association constants were nearly independent of the crosslink density. Moreover, the temperature dependence of the association constants demonstrated consistent behavior across all PDMS media. This indicates that the structure of the CT complex and the Gibbs free energy of its formation in the PDMS are unaffected by the crosslink density, providing insights into the design of supramolecular architectures formed by the CT complex in a PDMS network.

In-situ cryogenic X-ray diffraction analysis of Poly(dimethylsiloxane) oil and film

Understanding the phase transitions and crystallographic characteristics of polysiloxane materials poses a significant challenge. To address this issue, a custom cryogenic chamber has been developed and integrated with a laboratory X-ray diffraction apparatus, enabling the execution of in-situ temperature-dependent X-ray diffraction (XRD) analyses across the cooling and heating cycles. Through the utilization of diverse sample holders, the real-time monitoring of crystallization and melting phenomena in both linear poly(dimethylsiloxane) (PDMS) oil and crosslinked PDMS film has been made feasible. Notably, high-quality X-ray diffraction data, encompassing 13 diffraction lines, are successfully acquired for the first time for linear PDMS oil at 153K. Subsequent crystallographic examination has revealed a tetragonal unit cell characterized by lattice parameters a = b = 8.3379 Å, c = 11.9284 Å, and space group I 41, suggesting the adoption of a fourfold helical conformation by two polymer chains, each comprising four monomer units, within the lattice structure. This improved and versatile X-ray instrumentation presents clear advantages over conventional commercial powder X-ray diffractometers, which is anticipated to provide a promising in-situ characterization approach for investigating the low-temperature behaviors of liquid or oil materials.

Triboelectric Nanogenerators: Enhancing Performance by Increasing the Charge-Generating Layer Compressibility.

Triboelectric nanogenerators (TENGs) have received significant attention for next-generation wearable electronics due to their simple device structure and low cost. Although the performance of TENGs is intimately tied to compressibility effects in the charge-generating layer, achieving high compressibility with conventional elastomers is challenging because molecular entanglements place a lower bound on the softness of cross-linked networks. Here, we demonstrate that bottlebrush elastomers are efficient charge-generating layers that improve the output performance of TENGs, including voltage, current, and surface potential, by minimizing entanglements and decreasing the compressive modulus (E). For example, a cross-linked bottlebrush with poly(dimethylsiloxane) side chains yielded TENGs with an output voltage (120 V) more than two times larger than a linear PDMS network (55 V). In conclusion, this study highlights the advantage of designing new charge-generating layers with improved compressibility to enhance TENG performance.

Magnetorheological Fluids Based on Star-Shaped and Linear Polydimethylsiloxanes

Magnetorheological fluids are obtained on the basis of star-shaped and linear PDMS containing 70, 75, and 80 wt % of carbonyl iron microparticles. While pure PDMS polymers are Newtonian fluids, composites exhibit pseudoplasticity. The viscoelastic properties of the obtained magnetorheological fluids of different composition are studied in magnetic fields up to 1 T. The viscosity and storage modulus of the magnetorheological fluids in the maximum magnetic field reach ~0.19–0.65 MPa s and 0.4 MPa, respectively. The relative increase in the viscosity and storage modulus of the magnetorheological fluids based on the star-shaped PDMS with a magnetic filler concentration of 70 wt % in a magnetic field exceeds four orders of magnitude. In the magnetic field, the yield stress of the magnetic composites is as high as 70 kPa at a magnetic field strength of 1 T.

Silicone Structurants for Soybean Oil: Foams, Elastomers, and Candles

Soybean oil-derived polyurethanes, while much greener than those derived from isocyanates, have a problematic combustion profile; concerns exist about the nitrogen-containing compounds found in the smoke. Silicones typically burn cleanly to form an insulating silica layer upon combustion. We have examined the ability of silicones to convey improved thermal stability to soybean oil. The oil was modified via an ene reaction to incorporate an alkoxysilane functionality that was used in a subsequent Piers–Rubinsztajn reaction with silicones to create foams and elastomers. Cross-linked materials with densities ranging from ∼0.6 to 0.9 g/mL and containing up 76% by weight soybean oil were prepared. The addition of varying amounts of a linear PDMS chain extender allowed for control of the modulus (0.04–0.32 MPa). Cross-linking rapidly occurred, <60 s for full cure. Foams were produced without the need for external blowing agents, due to the generation of methane as a byproduct of the Piers–Rubinsztajn reaction. ...

Effect of Chain Length and Topological Constraints on Segmental Relaxation in Cyclic PDMS

We present a detailed investigation of local dynamics of linear and cyclic poly(dimethylsiloxane) (PDMS) covering a wide range of molar masses. To aid interpretation of the experimental data, QENS measurements in the time scale from 2 to 200 ps and at Q = 0.3 to 1.8 A–1 are complemented by theoretical calculations. These make use of a methodology developed by us elsewhere applicable to both simple chain models and real chains and applied here, for the first time, to cyclic PDMS. Analysis of the incoherent dynamic structure factor at T < Tm shows that the rotational motion of the methyl groups is unaffected by polymer topology. At higher temperatures, the QENS data are described by a model that consists of two dynamic contributions: methyl group rotation and segmental motion, the latter described by a stretched exponential function. Relaxation times of both linear and cyclic PDMS increase with increasing molar mass. Several features predicted by theory are also reproduced by the experimental data. We show,...

シリコーンゴムにおけるメゾ相の形成と結晶化

Silicone rubber consists of cross-linked poly(dimethyl siloxane)(PDMS). Formation of the mesomorphic phase was found in silicone rubber that is highly stretched at room temperature. The mesomorphic phase is characterized by a pair of sharp equatorial reflections in the wide-angle X-ray diffraction (WAXD) pattern. At low temperature, the stretched silicone rubber crystallizes. The WAXD patterns from the crystallized silicone rubber exhibit totally different features depending on the draw ratio. The author successfully obtained single crystals of linear PDMS. Electron diffraction patterns of the single crystals indicate that at least four different crystal forms exist. The observed WAXD patterns and their peculiar transition scheme could be explained by the combination of the crystal forms.

Interfacial effects in PDMS/titania nanocomposites studied by thermal and dielectric techniques

Interfacial effects in polymer nanocomposites (PNCs) of poly(dimethylsiloxane) (PDMS) and titania, prepared by in-situ generation of titania nanoparticles in the presence of crosslinked PDMS (sol-gel PNCs) and by adsorption of linear PDMS on fumed crystalline titania nanoparticles (core-shell PNCs), were comparatively investigated by DSC and by two dielectric techniques, broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization currents (TSDC). The PNCs are characterized by the presence of hydrogen bonding interactions between the oxygens in the backbone of PDMS and the hydroxyls on the oxide surface. DSC results show that a fraction of polymer in an interfacial layer in the PNCs is immobilized making no contribution to the glass transition, whereas it shows reduced segmental mobility with respect to the bulk by dielectric techniques. The results are quantified in terms of the fraction of polymer with restricted mobility (the interfacial fraction), the thickness of the corresponding interfacial layer and the temperature dependence of restricted and bulk segmental mobility. The interfacial fraction is larger in the sol-gel PNCs, in agreement with a larger surface to volume ratio, whereas the interfacial dynamics is slower and less cooperative for the core-shell PNCs. Compared with similar PDMS/silica PNCs studied previously, interfacial effects are more pronounced in the titania based PNCs.

Unusual Morphologies of Poly(vinyl alcohol) Thin Films Adsorbed on Poly(dimethylsiloxane) Substrates.

Adsorption of poly(vinyl alcohol) (PVOH), 99% and 88% hydrolyzed poly(vinyl acetate), to poly(dimethylsiloxane) (PDMS) substrates was studied. The substrates were prepared by covalently attaching linear PDMS polymers of 2, 9, 17, 49, and 116 kDa onto silicon wafers. As the PDMS molecular weight/thickness increases, the adsorbed PVOH thin films progressively transition from continuous to discontinuous morphologies, including honeycomb and fractal/droplet. The structures are the result of thin film dewetting that occurs upon exposure to air. The PVOH film thickness does not vary significantly on these PDMS substrates, implicating the PDMS thickness as the cause for the morphology differences. The adsorbed PVOH thin films are less stable and have a stronger tendency to dewet on thicker, more liquid-like PDMS layers. When PVOH(99%) and PVOH(88%) thin films are compared, fractal and droplet morphologies are observed on high molecular weight PDMS substrates, respectively. The formation of the unique fractal features in the PVOH(99%) thin films as well as other crystalline and semicrystalline thin films is most likely driven by crystallization during the dehydration process in a diffusion-limited aggregation fashion. The only significant enhancement in hydrophilicity via PVOH adsorption was obtained on PDMS(2k), which is completely covered with a PVOH thin film. To mimic the lower receding contact angle and less liquid-like character of the PDMS(2k) substrate, light plasma treatment of the higher molecular weight PDMS substrates was carried out. On the treated PDMS substrates, the adsorbed PVOH thin films are in the more continuous honeycomb morphology, giving rise to significantly enhanced wettability. Furthermore, hydrophobic recovery of the hydrophilized PDMS substrates was not observed during a 1 week period. Thus, light plasma oxidation and subsequent PVOH adsorption can be utilized as a means to effectively hydrophilize conventional PDMS substrates. This study illustrates that the stability and morphology of adsorbed polymer thin films depend on polymer crystallinity as well as substrate physical properties.

Organic/inorganic hybrids by linear PDMS and caged MA-POSS for coating

Novel organic/inorganic hybrids of PDMS-b-PMMAm-b-P(MA-POSS)n are synthesized by linear poly(dimethylsiloxane) (PDMS) macroinitiator initiating methyl methacrylate (MMA) and caged methacrylisobutyl-polyhedral oligomeric silsesquioxane (MA-POSS) via a two-step ATRP technique. The chemical structures of obtained hybrids are proved to be PDMS-b-PMMA408-b-P(MA-POSS)4.5, 8.2, 13.6 with molecular weight of 50,090–58,650 g mol−1 (PDI = 1.215–1.391). With the increase of P(MA-POSS)n content from 0%wt to 23.93%wt, the glass transition temperature of PDMS-b-PMMA408-b-P(MA-POSS)n is enhanced from 95 °C to 137 °C, and the corresponding storage modulus of mechanical property is increased from 579 ± 3 MPa to 902 ± 5 MPa. The surface of PDMS-b-PMMA408-b-P(MA-POSS)8.2 film casting from CHCl3 solution obtains higher water contact angle (120°) and higher water adsorption (Δf = −2300 Hz), but lower viscoelasticity (ΔD = 26 × 10−6) than the film casting from tetrahydrofuran (THF) solution (114°, Δf = −1540 Hz, ΔD = 52 × 10−6). This is because that 200–500 nm core/shell micelles of PMMA core and PDMS/P(MA-POSS) shell formed in CHCl3 solution are favor of the migration of PDMS and P(MA-POSS) onto film surface to improve the surface roughness (2.480 nm) and to get silicon-rich surface (14.62%) than 220 nm P(MA-POSS) core/PMMA shell/PDMS-corona micelles formed in THF solution (0.906 nm, 7.86%). Therefore, the accumulated P(MA-POSS) cages on the film surface are able to store absorbed water but do not increase the viscoelasticity of film. The results indicate that PDMS-b-PMMA408-b-P(MA-POSS)n are promising to be the solvent-dependent coating materials.

Block and Graft Copolymers of Poly(ethylene glycol) and Poly(dimethylsiloxane) for Blood Contacting Biomedical Materials Applications

The incorporation of both hydrophobic and hydrophilic groups into a synthetic polymer is a potent way of controlling its surface and interfacial properties. With this end result in mind, we describe herein the synthesis and characterization of poly(dimethylsiloxane-b-ethyleneoxide) block copolymers (PDMS-b-PEO) and poly(dimethylsiloxane-g-ethyleneoxide) grafted copolymers (PDMS-g-PEO). These amphiphillic copolymers were also investigated as surface modifying agents for passifying hydrophobic polymer surfaces in blood contacting applications. Specifically, the various (PDMS-b-PEO) and (PDMS-g-PEO) copolymers were coated onto poly(styrene-divinylbenzene) microspheres by their physical adsorption from solution. These surfaces were then evaluated for blood contacting applications utilizing a fibrinogen and thrombin protocol. In particular, the binding of fibrinogen and the functionality of the surface bound fibrinogen on an otherwise hydrophobic surface (polystyrene) was investigated. As the conversion of fibrinogen to fibrin is facilitated by thrombin, the aggregation of the copolymer-coated hydrophobic microspheres was followed using an optical method after the sequential exposure of the microspheres to fibrinogen and then to thrombin. We were able to determine how the adsorbed copolymers affected the functionality of the bound fibrinogen at an interface. Our hypothesis is that the hydrophobic siloxane units of the copolymers will be in close proximity to the polystyrene surface and that the PEO will extend out from the surface and therefore render the synthetic polymer system hemocompatible. Following the fibrinogen and thrombin protocol and determining the fibrinogen-dependent aggregation, the results show that the PDMS-b-PEO copolymers (having a PEO content from 4.6 to 11.5 weight %) were similar in terms of particle aggregation when compared to the pure polystyrene microspheres (blank) or to the microspheres that were coated with a linear PDMS homopolymer. By comparison, the PDMS-g-PEO copolymers (having a PEO content from 58 to 80 weight %) were seen to reduce the fibrinogen functionality on the microsphere system surface. Thus the data indicate that the PDMS-g-PEO copolymers can behave like molecular brushes that are able to pacify the surface of the hydrophobic polystyrene microspheres. A somewhat unexpected observation was that for the copolymer system having a low PEO content the fibrinogen-dependent aggregation of the otherwise hydrophobic microspheres was observed to increase relative to the pure microspheres (blank). It is clear from the findings of this investigation that the surface packing and molecular orientation of both the adsorbed copolymer and also of the fibrinogen are important factors that govern the properties and applications of blood contacting biomaterials.

Optimization of PDMS network for a fast response and sensitive actuation material applied in a MEMS spatial light modulator

The cross-linked networks of linear vinyl-terminated poly(dimethylsiloxane) (PDMS) with trimethylsiloxy-terminated methyhydrosiloxane–dimethylsiloxane copolymer (cross-linker) were investigated by tuning the cross-linker concentration, the chain length of linear PDMS and the functionality of the cross-linker. Response time and elastic modulus of the cross-linked PDMS elastomer were characterized by home-made measurement systems and analyzed based on their network topologies. An optimized PDMS elastomer, which has response time of 9 μs and elastic modulus of 601 kPa, was utilized as the actuation material in a MEMS spatial light modulator (SLM). The fabrication processes were described. This polymer based SLM has shown fast response time (9 μs) and successfully diffracted light into higher orders with 84% first-order diffraction efficiency.

Antimicrobial properties of Ag + loaded zeolite polyester polyurethane and silicone rubber and long-term properties after exposure to in- vitro ageing

In biomedical applications, tubes (e.g. catheters etc.) are commonly produced from polyurethane (PU) and silicone rubber which are known to be biocompatible materials. Several studies have shown that tubes, which are connected to the body (invasive) (especially urinary, tracheotomy and central venous catheters) are associated with infections. The present study reports the development of a new method aiming at obtaining antibacterial properties for PU and silicone rubber by mixing respective material with a natural antibacterial agent (Ag+ loaded zeolite) in different weight fractions. The influence of the zeolite content on the antimicrobial properties were analysed by exposure to bacteria (ISO 22196) and mixtures of fungi (ISO 846). The materials were also subject to artificial body fluids (Artificial Lysosomal Fluid (ALF) and Gamble’s solution) for periods up to three months and the subsequent changes in the chemical properties after in-vitro exposure were determined by Matrix Assisted Laser Deposition/Ionization Time Of Flight Mass Spectrometry (MALDI-TOF MS) and Attenuated Total Reflection Fourier Transform Infra Red spectroscopy (ATR-FTIR). It was established that the antimicrobial effect of the materials increased with the increase of the zeolite content. The wettability of the materials was found to decrease significantly during the in-vitro exposure, but this could not be correlated to the zeolite content. In the PU samples, the formation of free carbonyl and –OH groups was observed, which corresponds to oxidative degradation. In case of the silicone rubber the ratio of cyclic PDMS to linear PDMS (H, CH3 and dimethyl terminated) decreased, which indicates a change in the concentration of the compounds. The formation and increase of the O–H bond during the exposure was also confirmed by the infrared spectra of the material which corresponds to hydrolysis of the silicone rubber.

Molecular dynamics in grafted polydimethylsiloxanes

Rheological and dielectric behavior of linear PDMS and alkyl-modified PDMS melts has been studied. Molecular dynamics of linear PDMS, being a model of grafted polydimethylsiloxanes studied, has been examined carefully with particular attention paid to its ability to form the semicrystalline phase. Random incorporation of alkyl groups into PDMS chain has been shown to prevent the polymer crystallization. The glass transition temperature of the grafted PDMS changes proportionally to the modifier content. Both techniques allow characterization of the main α-relaxation, which is related to the glass transition and exhibits similar behavior in all systems. This relaxation is discussed in terms of the Vogel–Fulcher–Tammann–Hesse (VFTH) approach. The fragility of grafted PDMS materials was found to be higher as compared to the linear polymer. The analysis of the rheological data shows the existence of additional slow relaxation, which has been interpreted as the polymer chain motion.

Particle-induced network formation in linear PDMS filled with silica

We study the formation of permanent elastomers from linear PDMS chains by solution blending with up to 25wt% fumed silica. The physical networks are characterized by time-domain multiple-quantum NMR. Based upon dynamic parameters measured for the linear precursor polymer, we develop a reliable strategy for component separation in this complex heterogeneous system, providing information on the amount of monomers involved in network-like material, in elastically inactive yet entangled linear chains, and isotropically mobile chain ends, as well as on the effective network chain length as measured via the average residual dipolar coupling constant. The use of untreated silica leads to permanent networks, for which the NMR results correlate well with macroscopic determinations of the relaxed Young modulus and the degree of swelling. Surface-modified silicas do not lead to percolated network structures, but still lead to the formation of 20–40% network-like material, with effective network chain lengths that depend on the surface functionalization and thus on the nanoparticle dispersion. Characteristic changes in the mobile chain end fraction with temperature, in particular its decrease with increasing degree of filling are interpreted as a consequence of altered contour-length fluctuations. An aging experiment conducted on a sample prepared by melt blending reveals the microscopic changes in the network structure occurring over many months.

Improved Hydrophilicity from Poly(ethylene glycol) in Amphiphilic Conetworks with Poly(dimethylsiloxane)

This paper focuses on the improvement of hydrophicility and water content of poly(dimethylsiloxane) (PDMS) by bonding a hydrophilic macromer, hydroxyl-terminated linear poly(ethylene glycol) (PEG), into a highly hydrophobic macromer, hydroxyl-terminated linear PDMS to prepare amphiphilic conetworks (APCNs) with the crosslinkers, tetraethoxysilane (TEOS) and bis[(3-methyldimethoxysilyl)propyl]-polypropylene oxide (BMPPO), which also functioned as a compatibilizer. Fourier transform infrared results clearly demonstrated the occurrence of the hydrolysis reactions between the terminal hydroxyl groups on the terminal of the two polymer chains and the alkoxy groups in TEOS and BMPPO. Differential scanning calorimetry results and X-ray diffraction obviously showed the presence of the two phases in the conetworks. The contact angle (CA) indicated the wettability of the conetworks increased in the surfaces, that is, CA values decreased significantly from 105° in PDMS to 55° in the PEG/PDMS APCN (10/1 mol ratio), and the swelling degrees of the APCNs increased from ca. 0 to 60 % when the PEG/PDMS mol ratio was larger than 4/1. The APCNs with such high hydrophilicity and the good mechanical properties should be useful as biomaterials.

A Direct Method for the Fabrication of Macro‐Porous SiOC Ceramics from Preceramic Polymers

Cellular SiOC ceramics having a complex morphology were produced using two silicone precursors. Linear PDMS and two different silsesquioxanes (containing either methyl or methyl-phenyl side groups) were mixed, crosslinked and pyrolyzed at 1200 °C, resulting in the formation of macroporous ceramic components. Pore formation was attributed to the different behavior of the precursors upon pyrolysis. The amount of porosity depended on the amount of PDMS, which acted as a sacrificial filler, leading to the formation of pores ranging from a few microns to a few hundred microns.

Mechanical characterization of anisotropic planar biological soft tissues using finite indentation: Experimental feasibility

Heart valve tissue engineering offers a promising alternative for current treatment and replacement strategies, e.g., synthetic or bioprosthetic heart valves. In vitro mechanical conditioning is an important tool for engineering strong, implantable heart valves. Detailed knowledge of the mechanical properties of the native tissue as well as the developing tissue construct is vital for a better understanding and control of the remodeling processes induced by mechanical conditioning. The nonlinear, anisotropic and inhomogeneous mechanical behavior of heart valve tissue necessitates a mechanical characterization method that is capable of dealing with these complexities. In a recent computational study we showed that one single indentation test, combining force and deformation gradient data, provides sufficient information for local characterization of nonlinear soft anisotropic tissue properties. In the current study this approach is validated in two steps. First, indentation tests with varying indenter sizes are performed on linear elastic PDMS rubbers and compared to tensile tests on the same specimen. For the second step, tissue constructs are engineered using uniaxial or equibiaxial static constrained culture conditions. Digital image correlation (DIC) is used to quantify the anisotropy in the tissue constructs. For both validation steps, material parameters are estimated by inverse fitting of a computational model to the experimental results.

N-Propylpyridinium chloride-modified poly(dimethylsiloxane) elastomeric networks: Preparation, characterization, and study of metal chloride adsorption from ethanol solutions

An n-propylpyridinium chloride-modified PDMS elastomeric network, PDMS/Py +Cl −, was prepared from linear PDMS chains containing Si(CH 3) 2 OH end-groups cross-linked by 3-chloropropyltrimethoxysilane and posterior reaction with pyridine. PDMS/Py +Cl − material was structurally characterized by infrared spectroscopy (IR) and solid state 13C and 29Si NMR. Thermogravimetric analysis of the product showed good thermal stability, with the initial temperature of weight loss at 450 K. The ion-exchange capacity of the PDMS/Py +Cl − was 0.65 mmol g −1. Metal halides, MCl z [M = Fe 3+, Cu 2+, and Co 2+], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes MCl z + n n − . The nature of the anionic complex structure was proposed by UV–vis diffuse reflectance spectra. The species adsorbed were FeCl − 4, CuCl 2− 4, and CoCl 2− 4. The specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures. The trend in affinities of PDMS/Py +Cl − for the metal halides were found to be FeCl 3 > CuCl 2 ∼ CoCl 2.

Cyclosiloxane‐based networks: Synthesis, thermal characterization, and microstructure

AbstractThis article mainly concerns the synthesis of novel PD5/PDMS conetworks by the copolymerization of cyclic D5H and linear HOPDMSOH units, and the characterization of the product by DMTA, DSC, and TGA. The ultimate properties of the conetworks may be controlled by varying the relative composition of D5H and PDMS components. DMTA and DSC thermograms indicate compatibility between the PD5 and PDMS domains. Understanding of the polymer chemical transformations involved in conetwork formation combined with an analysis of DMTA and DSC thermograms led to a proposition of the microarchitecture of PD5/PDMS conetworks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 630–637, 2005