PDMS Blends Research Articles

Elastomeric Foam-Based Soft Capacitive Pressure Sensors Using Direct Ink Writing

Conformable and flexible tactile/pressure sensors are of interest in applications such as robotics, wearable and interactive systems to measure the contact forces. These applications require a large number of robust sensors, for which simple manufacturing routes such as additive manufacturing can be useful. Herein, we present the fully 3D printed capacitive touch sensors comprising of elastomeric foam-based soft dielectric layers (blends of PDMS and BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) and PEDOT: PSS and AgNWs composite-based electrodes. The devices were encapsulated with 3D printed PDMS and tested under dynamic and static stimuli. The sensor with 1% wt. of BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> exhibited the best performance with a sensitivity of 0.571 %kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and excellent linearity (99.32%). The observed capacitive behavior of the sensor is significantly higher than a similar sensor with bulk PDMS as the dielectric. The fabrication approach employed in this work has the untapped potential to develop soft and flexible electronic skin (e-skin) for wearables, health monitoring, and rehabilitation.

A molecular dynamics simulation study to investigate poly(vinyl acetate)-poly(dimethyl siloxane) based easy-clean coating: An insight into the surface behavior and substrate interaction

Easy-clean coatings have received overwhelming interest in outdoor and indoor surface applications nowadays. Poly (dimethylsiloxane) (PDMS), though a popular hydrophobic material, exhibits poor substrate adhesion which limits its use for aforementioned coating applications. To counter this drawback, blends of PDMS with poly (vinylacetate) (PVAc) of different commercially available hydrolysis grades (0%, 86%, and 100%) have been proposed. Coatings made from such blends shall be sufficiently hydrophobic on one side to exhibit easy-cleaning nature, and on another side, demonstrate sufficient adherence with substrate for durability. Molecular dynamics (MD) simulations have been employed to model such blends to understand their surface behavior, substrate adhesion and to evaluate bulk properties. In this work, blends of PDMS and PVAc with the latter present in varying weight fractions and hydrolysis content have been both simulated and experimentally formulated. Properties like substrate interaction energy (IE), surface energy, transparency, water/oil contact angles (WCA/OCA), solubility parameter and thermal stability (T20/T50) have been investigated. Simulation estimates of surface energy, water/oil contact angles and refractive indices compared well with previously reported results and those of water contact angle and transparency are in proximity to experimental outcomes of this work. The improved surface behavior (WCA∼ 97 ± 1°/OCA∼ 41.6 ± 2°), substrate adhesion (−0.725 mN/m against Al substrate), thermal stability (T20 ∼322 °C/T50 ∼500 °C) and transparency (>89%) estimates enable us to screen and propose a 20 wt% PVAc (0% hyd.) in PDMS as a potential easy-clean coating material.

Next-generation rooftop tribo–piezo electric energy harvesting from rain power

In the present paper, authors report on the fabrication and testing of an energy harvester using polymer blends of PVDF and PDMS from raindrops. The films were characterised using microscopy techniques for morphology and frictional properties. The piezo–ferro–triboelectric nature of the blends was analysed using electrostatic force microscopy (EFM). The infrared (IR) spectroscopy was used for phase enhancements in neat as well as blends of the polymer. Three different configurations of the devices were fabricated and tested with polymer blend metal contact yielding an output of 16 V and 15.4 nA for a piezo–tribo area of 2.25 cm2. The charging characteristics of the device yielded a power density of 0.177 µW/cm2, and the device was also tested for knock sensing applications. A prototype of tribo–ferro energy harvester installed on a modelled house rooftop yielded an output voltage of 0.795 V for 10 ml of water dropped from 8 cm.

Morphology‐induced physico‐mechanical and biological characteristics of TPU–PDMS blend scaffolds for skin tissue engineering applications

Composition and architecture of scaffolds are the most important factors determining the performance of skin substitutes. In this work, morphology induced unique physical and biological characteristics of compatibilized TPU-PDMS blend scaffolds at 90:10, 80:20, and 70:30 blend ratios of TPU and PDMS was studied. The fiber morphology, porosity, surface wettability, and mechanical properties of electrospun scaffolds were distinctly influenced by the presence of PDMS. Interestingly, the scaffold architecture varied from electrospun fibers to porous fibers and finally occurrence of unique porous beads noticed at 30% PDMS in the microstructure which was confirmed using FESEM. Micro-CT analysis revealed that the porosity of electrospun scaffolds was enhanced from 61% to 79% with 30 parts of PDMS addition. Moreover, MTT assay and cell proliferation were studied using human skin fibroblast cells and found to be significantly enhanced with the PDMS percentage. TPU-PDMS blends offer better overall performance at 70:30 blend ratio of TPU and PDMS (T70P30). Only 4% of hemolysis was observed for T70P30 blends, which establishes the hemocompatibility of the material. In comparison, the results reveal the potential of the cytocompatible T70P30 scaffold for the fabrication of skin substitutes for tissue engineering applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1634-1644, 2019.

Exploring the influence of co-monomer content in the dry crosslinked ethylene octene copolymer based blends

This article illustrates the influence of co-monomer content in the ethylene octene copolymer (EOC) on the dry curing process of EOC:PDMS rubber blends. The EOC:PDMS blends were prepared by melt mixing in an internal mixer and crosslinked through electron beam radiation method. During electron beam irradiation both the EOC and PDMS phase gets crosslinked; which is evident from the gel content study. From the rheology analysis, it is understood that the EOC with high octene (co-monomer) content has better radiation crosslinkability as compared with the EOC with low co-monomer content. Through radiation crosslinking, the physico-mechanical properties of the EOC:PDMS system was improved significantly. The tensile strength of high co-monomer content EOC:PDMS 70:30 blends were drastically improved by 49.5% on irradiation with a dosage of 75 kGy. Morphology study of the EOC:PDMS system were carried out by scanning electron microscopy (SEM) and correlated with the physico-mechanical properties. The radiation crosslinked blends shows higher volume resistivity, lower dielectric constant, and loss as compared with the uncrosslinked counterparts. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

A microfabricated platform with hydrogel arrays and on-chip strain sensing for mechanical stimulation of 3D cell-seeded hydrogels

Event Abstract Back to Event A microfabricated platform with hydrogel arrays and on-chip strain sensing for mechanical stimulation of 3D cell-seeded hydrogels Haijiao Liu1, 2*, Yu Sun1, 2 and Craig A. Simmons1, 2* 1 University of Toronto, Mechanical and Industrial Engineering, Canada 2 University of Toronto, Institute of Biomaterials and Biomedical Engineering, Canada Introduction: Cellular microenvironments present cells with multiple stimuli, including not only biochemical and matrix cues but also mechanical factors[1]. Biomaterial arrays enable systematic screening of the combined effects of microenvironmental cues on cell function[2], but these array platforms typically fail to include the effects of dynamic mechanical stimulation, which is relevant to native and engineered connective and cardiovascular tissues. To address this need, we present a deformable membrane array that enables complex mechanical loading to cells embedded in 3D hydrogel constructs and has on-chip strain sensors for continuously monitoring of the samples’ stiffness. Materials and Methods: Stretching soft hydrogels is a challenge addressed by using off-stoichiometry thiol-ene based polydimethylsiloxane (OSTE-PDMS)[3] membranes to covalently bond polyethylene glycol norbornene (PEG-NB) hydrogels, a clinically-relevant model biomaterial with tunable properties[4], via a thiol-ene reaction (Fig.1A-C). Blends of carbon nanotube (CNT) and PDMS exhibit strain-dependent resistivity[5] and are patterned as strain sensors to monitor the membrane deflection. Sensors were preconditioned to ensure reliable strain signals, then calibrated with experimentally measured membrane deflection (Fig.1D-E). Mesenchymal stromal cells (MSCs) embedded in PEG-NB were cultured and stimulated (17% max strain, 0.1 Hz, 10 hrs/day) for 11 days. The resistive strain amplitude |ΔR/R0| was used to calculate sample elastic modulus by inverse finite element analysis (Fig. 1F). To assess the 3D mechanical stimulation effect, MSCs were stained for α-smooth muscle actin (αSMA) for myofibroblast differentiation and collagen type I (Col I) for collagen production. Results and Discussion: PEG-NB gels remained firmly attached to and deformed elastically with the OSTE-PDMS membranes up to at least 40% strain under tensile stretching (Fig. 1C). The CNT sensors were able to measure the elastic modulus of non-degradable PEGNB gels with stiffnesses up to 30 kPa. Mechanically-stimulated cell-seeded PEG-NB gels stiffened during culture, as evidenced by a 20% decrease in the time-dependent |ΔR/R0| (Fig. 2A top), in comparison with less than 10% reduction in |ΔR/R0| for the control sensors without gels. This corresponded to a ~2-fold increase in the elastic modulus of the stimulated gels from ~15 to ~30 kPa (Fig. 2A bottom). Cells within the mechanically-stimulated gels were spread throughout the gel volumes and expressed αSMA with visible stress fibers, indicating myofibroblastic differentiation (Fig.2B). Abundant collagen was evident in the gel peripheries (Fig. 2C). Conclusion: MSCs embedded in PEG-NB gels and subjected to dynamic mechanical stimulation undergo myofibroblast differentiation and synthesize collagen, leading to gel stiffening. This system can be scaled up to larger arrays to enable systematic screening of 3D microenvironmental cues on cell function and tissue formation in vitro.

Nucleated nanocomposites of TPU–PDMS blends based on spherical nanohydroxyapatite

The present investigation gives a profound insight into the preparation of nucleated nanocomposites of TPU–PDMS blends based on uniquely synthesized PPG-wrapped spherical nanohydroxyapatite (nHap).

Investigation of sorption characteristics of polymeric membranes containing ionic liquids for n-butanol recovery from aqueous streams

Ionic liquid–polydimethylsiloxane (IL–PDMS) blending membranes were prepared to separate n-butanol from aqueous mixtures. The ionic liquids (ILs) used were [hmim][PF6] (1-hexyl-3-methylimidazolium hexafluorophosphate), [bmim][PF6] (1-butyl-3-methylimidazolium hexafluorophosphate), and [bmim][TF2N] (1-Butyl-3-methylimidazolium bistrifluoromethylsulfonylimide). Sorption experiments were carried out to define the sorption and separation capacity of the blending membranes using aqueous butanol solutions in the range of 1–5% (wt), and also sole solvents of butanol and water. The desorption experiments allowed to determine the selectivity of the membranes as the liquid composition inside the membrane could be obtained with the desorption step. The results obtained by IL–PDMS blends were compared with the results obtained by unblended PDMS membranes to show the effect of the IL in the PDMS matrix. [Hmim][PF6]–PDMS-blended membranes showed lower selectivity. The addition of [bmim][PF6] to PDMS enhanced the selectivity and sorption amounts mildly. [Bmim][TF2N]–PDMS-blended membranes presented the best sorption and selectivity results showing a great affinity to butanol and a reasonable rejection to water.

Highly conductive and stretchable poly(dimethylsiloxane):poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) blends for organic interconnects

Naturally immiscible PEDOT:PSS and PDMS, which are a typical conducting polymer and an transparent elastomer, respectively, were blended by the support of PDMS-b-PEO. A block copolymer, PDMS-b-PEO, consisting of hydrophobic PDMS backbones and hydrophilic PEO side chains, significantly improved the miscibility of PEDOT:PSS and PDMS. At an optimal PDMS-b-PEO concentration of 30%, a cured PEDOT:PSS:PDMS film was found to be comprised of three-dimensional PDMS networks and a PEDOT:PSS phase filling in between the networks. The optimal blend film exhibited a conductivity comparable to a pure PEDOT:PSS film and a maximum strain to rupture of about 75%. It was also demonstrated that interconnects made of this blend film functioned well irrespective of the substrate and the pattern size, and could reproducibly operate under strains up to 50%. These results indicate that the PEDOT:PSS:PDMS blends could be a practical choice for organic interconnects for future stretchable electronics.

Effects of Viscosity‐Controlled Interfacial Mobility on the Coalescence of Immiscible Polymer Blends

AbstractThe consequences of the interfacial mobility on the coalescence process in immiscible polymer blends was studied. Blends of PIB and PDMS with 10 vol.% PIB were subjected to shear‐flow step‐down experiments under controlled conditions. The blend was initially sheared at high shear rate to obtain a fine dispersion (small drop size). The shear rate was then stepped down and the coalescence process was monitored by performing repeated SAOS experiments. In the limit of high and low viscosity ratios, the experimental results were in excellent agreement with theory predictions for IMI and FMI conditions. In the intermediate range of viscosity ratio, corresponding to PMI conditions, a smooth transition between the limiting IMI and FMI states was found. magnified image

Selective polydimethylsiloxane/polyimide blended IPN pervaporation membrane for methanol/toluene azeotrope separation

The paper describes the preparation and investigation of membranes based on new interpenetrating polymer network (IPN) of vinyl terminated poly(dimethyl siloxane) (PDMS) and aromatic polyimide (PI) with respect to their thermal and pervaporation properties. The modified membranes were prepared using simultaneous IPN (SIPN) technique by variation of polyimide loading of 5, 10 and 15wt% respectively. These membranes were characterized by different thermal, mechanical, morphological, spectroscopic and pervaporative techniques and compared with those of neat PDMS membranes. The IPN membranes exhibited synergistic improvement in the thermal stability in the range of 445–490°C in air and 410–520°C in inert atmosphere for 10% loss. Activation energies for the decomposition of polymers and their IPN's were calculated using Coats and Redfern equation. Permeation properties of PDMS and IPN blends were evaluated by water diffusion, measured by Fourier transform-attenuated total reflectance (FT-ATR) method and moisture vapour transmission rate (MVTR) as per ASTM E 96. 15wt% polyimide content in PDMS membrane slows down the water diffusion and MVTR significantly. All the IPN's form mechanically strong membrane with tensile strength up to 15.5MPa and elongation at break up to 20%. IPN membranes prepared in this work were employed in pervaporation separation of azeotrope forming toluene/methanol mixtures. The pervaporation properties could be tuned by adjusting the blend composition. All the blend membranes tested showed a decrease in flux with increasing polyimide content for methanol/toluene liquid mixtures. Toluene permeated preferentially through all tested blend membranes, and the selectivity increased with increasing polyimide content. The pervaporation characteristics of the blend membranes were also strongly influenced by the feed mixture composition. The flux increased exponentially with increasing toluene concentration in the feed mixtures, whereas the selectivities decreased for liquid mixtures. This study demonstrates that polymer IPN blends is a simple way to modulate membrane's transport properties and can achieve higher performance than the pristine polymer materials.

Nanostructured thermoset epoxy resin templated by an amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) diblock copolymer

AbstractAn amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006

Determination of Polymer Compatibility by Viscometric Measurements on Ternary Solutions of the Two Polymers

Results on the intrinsic viscosity [η] are reported for the system solvent(1)/polymer(2)/polymer(3) in which the solvent was benzene, polymer(2) was polystyrene (PS), and polymer(3) was poly(dimethylsiloxane) PDMS. The values of [η] were then used to determine the likely compatibility of polymer blends of PS and PDMS. Initial focus was on the traditional interaction parameter b 23 (1) used by several authors to predict compatibilities, it but depends on the molar mass, weight fractions, and concentrations of each polymer. A new interaction parameter b 23 (2) that is independent of polymer(3) concentration and molar mass was evaluated for determinations of polymer compatibility.

Onset and End of Transitions in PDMS/5CB Blends as Revealed by Static Light Scattering

The phase diagram of poly(siloxanes) and low molecular weight liquid crystals as obtained by polarized optical microscopy have shown a peculiar behavior : Transitions from a nematic to an isotropic and from an isotropic miscibility gap to a single isotropic phase take place in two steps interpreted as onset and end of transitions. This behavior has been observed in various systems and particular in those involving poly(dimethylsiloxane) (PDMS) and 4-cyano-4′- n -pentyl-biphenyl (5CB). In order to confirm this behavior we performed static light scattering on blends of PDMS ( M w =45000g/mol) and 5CB at different compositions. These experiments covered a temperature range from 20 to 115°C and several scattering angles.

Thermal degradation of blends of PVAC with polysiloxane — II

Thermal degradation of blends of poly(vinyl acetate) (PVAC) with polysiloxane; poly(dimethyl siloxane) (PDMS), poly(diphenyl siloxane) (PDPS), and poly(dimethyldiphenyl siloxane) (PDMDPS) has been investigated for comparison with the behaviour already reported for PVC–polysiloxane blends, using thermogravimetry (TG), differential thermogravimetry (DTG) and differential thermal analysis (DTA). The presence of PVAC has an effect very similar to that of PVC on the degradation of polysiloxane. Acetic acid/acetate radical production is accelerated in the blends compared to PVAC alone at the low loading of polysiloxane, which causes some destabilisation. However in blends containing 50% and more siloxane, both polymers are stabilized, particularly the PDMS blends which show much slower weight loss.

An investigation of the thermodynamic interactions of oligomeric cyclic methylphenylsiloxanes in siloxane melts and blends

The miscibility of cyclic poly(methylphenylsiloxanes) (PMPS) with molar masses less than 1000 g mol −1 have been studied in mixtures with either cyclic or linear poly(dimethylsiloxane) (PDMS). In all cases, an upper critical solution temperature (UCST) was observed and interaction parameters were determined from the phase boundaries. The results were compared with those from our previous studies of linear–linear PDMS–PMPS and cyclic–linear PDMS–PMPS polymer blends. The cyclic–linear PMPS–PDMS and cyclic–cyclic PMPS–PDMS blends in this investigation were found to have higher interaction energy density parameters than the corresponding linear–linear PDMS–PMPS homopolymer blends that we have reported elsewhere. An isomer effect upon the phase separation behavior was also seen for the isolated pure stereoisomers of cyclic PMPS in mixtures with linear PDMS.

Surface segregation of components in poly(vinyl chloride)-polydimethylsiloxane and polystyrene-poly(propylene oxide) solvent-cast blends

X-ray photoelectron spectroscopy and scanning electron microscopy are used to study the surface composition and morphology of poly(vinyl chloride)–polydimethylsiloxane (PVC–PDMS) and polystyrene–poly(propylene oxide) (PS–PPO) solvent-cast blends as a function of the blend composition and constituent molecular weights. The PVC–PDMS blends show a pronounced surface enrichment of PDMS, which is higher the lower the molecular weight of PDMS. The surface behavior ofthe PPO–PS blends is strongly dependent on the solvent used. Despite the much lower surface tension of PPO compared to that of PS, no surface segregation of PPO isobserved in the PPO–PS blends cast from tetrahydrofuran, while the blends cast from chloroform exhibit a high surface enrichment of PPO. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 517–522, 1998