Viscosity Of Polydimethylsiloxane Research Articles

Enhance the viscosity of polydimethylsiloxane by controlling the volume ratio of monomer and chain terminator

The production of polydimethylsiloxane (PDMS) as a vitreous substitute in Indonesia has been carried out. In our previous study, a good quality of low viscosity PDMS was well provided using a low-grade octamethylcyclotetrasiloxane (D4) monomer. We also reported that a new type of PDMS with medium viscosity had been produced. In vitreoretinal surgery, medium-viscosity PDMS has advantages over the other types of PDMS due to its injectability and lower propensity to emulsify. However, to produce a high-quality medium viscosity PDMS and fulfill stringent requirements, the conditions affecting the synthesis results need to be explored. Here, we reported the effect of changing one of the PDMS synthesis parameters, namely, the volume ratio composition of low-grade D4 monomer and chain terminator of hexamethyldisiloxane (MM) in producing medium viscosity PDMS. PDMS with low viscosity was successfully synthesized with a ratio of D4:MM = 26:10. However, only by changing the ratio of D4:MM from 26:10 to 46:10, the resulting PDMS increased in viscosity from low- to medium-viscosity PDMS of 1.81 Pa s. Quality improvement was also indicated by high surface tension and higher yield values. The medium viscosity PDMS had a refractive index and functional group values similar to the PDMS produced in previous studies.

Tailored nano-pillar structures on surfaces: facile formation and multifunctional properties

Nano-pillar structured surfaces have prized for exceptional optoelectronic properties and biocompatibility but commonly complex, expensive, and inflexible in production. A systematic investigation of the formation, mechanisms, and properties of nanostructures induced by nano-capillaries remains unexplored. Through this study, the facile formation of nano-pillared surfaces induced by designable nano-capillaries on AAO template demonstrated significant improvements in antibacterial effect, spectral structural color and anti-reflection characteristics. Reverse molding of nano-pillar arrays with aspect ratios of up to 1.2 on polydimethylsiloxane (PDMS) films yielded a super-hydrophobic surface of 150° contact angle (CA). Through the utilization of computational fluid mechanics model, a direct correlation was demonstrated between the aspect ratio of nano-pillars and the viscosity of PDMS. The nano-pillared surfaces had remarkable antibacterial rates of 91% for Escherichia coli and 89% for Staphylococcus aureus. In addition, the structured surfaces exhibited color spanning from light blue to light red by tuning nano-pillars dimensions, incident light angle, and/or adding reflective metallic coating, which offered unique visualization effects for anti-counterfeiting. Moreover, the superior light-trapping and anti-reflection of the nano-pillared surface significantly increased the power conversion efficiency (PCE) 19% from the base performance of the polysilicon solar cells.

Geopolymer-based radiative cooling coating: Tailoring surface hydrophobic properties while retaining optical characteristics

The longevity of geopolymer-based radiative cooling coatings is questionable due to their hydrophilic nature. This study used four hydrophobic agents - sodium methyl silicate (SMS), polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), and triethoxyoctylsilane (TEOS) - to modify the surface hydrophobicity of geopolymer while maintaining its optical properties. The optimal agent contents were determined by optical performance and water contact angle: 5 % for SMS, 10 % for 50 cP viscosity PDMS, and a single-layer thickness for PTFE and TEOS (60 °C). The agents' working mechanisms were analyzed using FTIR and XRD characterization: SMS forms a hydrophobic alkylsilanol layer by reacting with the geopolymer's silanol group; PDMS lowers the geopolymer's surface energy with its hydrophobic methyl groups; PTFE's low electric polarizability is due to its fluorine content; and TEOS replaces the geopolymer surface's hydroxyl groups with hydrophobic octyl groups. The long-term durability of these modified coatings was evaluated through outdoor exposure tests, resulting in total solar reflectance losses of 0.74 %, 1.9 %, 3.9 %, and 0.05 % respectively. A slight reduction in the water contact angle confirmed their enduring hydrophobic characteristics. These modification methods open up possibilities for the practical use of hydrophobic geopolymer radiative cooling coatings.

Hydrophobic solution functions as a multifaceted mosquito repellent by enhancing chemical transfer, altering object tracking, and forming aversive memory

Developing a safe and potent repellent of mosquitoes applicable to human skins is an effective measure against the spread of mosquito-borne diseases. Recently, we have identified that hydrophobic solutions such as low viscosity polydimethylsiloxane (L-PDMS) spread on a human skin prevent mosquitoes from staying on and biting it. This is likely due to the ability of L-PDMS in wetting mosquito legs and exerting a capillary force from which the mosquitoes attempt to escape. Here we show three additional functions of L-PDMS that can contribute to repel Aedes albopictus, by combining physicochemical analysis and behavioral assays in both an arm cage and a virtual flight arena. First, L-PDMS, when mixed with topical repellents and applied on a human skin, enhances the effect of topical repellents in reducing mosquito bites by efficiently transferring them to mosquito legs upon contact. Second, L-PDMS applied to mosquito tarsi compromises visual object tracking during flight, exerting an influence outlasting the contact. Finally, L-PDMS applied to mosquito tarsi acts as an aversive reinforcer in associative learning, making mosquitoes avoid the conditioned odor. These results uncover a multifaceted potential of L-PDMS in altering a sequence of mosquito behaviors from biting a human skin, visual object tracking following takeoff, to the response to an odor linked with L-PDMS.

Preparing hydrophobic alkali-activated slag mortar with lotus-leaf-like microstructure by adding polydimethylsiloxane (PDMS)

In this study, polydimethylsiloxane (PDMS) was applied for overall hydrophobic modification of alkali-activated slag (AAS) mortars aiming to reduce its high water sorptivity. The effects of the amount and viscosity of PDMS on the water absorption characteristics and mechanical properties of AAS mortars were investigated. Meanwhile, MIP, the surface contact angle of AAS mortars and SEM-EDS, Inverse gas chromatography (IGC), FT-IR, XRD of hardened AAS pastes were performed for analyzing the modification mechanisms. The results indicated that the water sorptivity of PDMS-modified AAS mortar decreased by 90 %, and the contact angle of the inner surface increased from 14° to 128° when the dosage of PDMS reached 8 % (by weight of binder). The main modification mechanisms of PDMS in AAS system can be summarized as: Firstly, the formation of hydrophobic coatings on the surface due to the cross-linking reaction between C-S-H gel and PDMS reduces the surface energy and the hydrophilicity of hardened AAS pastes, achieving chemical modification; Secondly, the hierarchical structures formed by micro papillary increases the surface roughness, thus enhancing the hydrophobic effect further through physical modification. Moreover, the coarsening of capillary pores also reduces the capillary force during water absorption process. Meanwhile, the addition of PMDS maintains comparable strength development of AAS mortars, which is beneficial for the practical application.

Investigation on the Rheological Properties of Polydimethylsiloxane

This paper focuses on studying the rheological properties of polydimethylsiloxane (PDMS). This polymer has been used to fabricate membranes and filters in engineering. The analysis of the rheological properties of this polymer is required for a further investigation of its mechanical behavior. In this study, the rheological behavior of PDMS is reported at different temperatures. This polymer showed steady shear viscosity during a short duration. However, this behavior changed with time and increased more with increasing temperature. The impact of the temperature increase was also observed when the shear viscosity of PDMS increased with shear strain. The increase of torque with shear strain and time was observed at different temperatures. Shear stress increased linearly with the shear rate at 20 °C and 40 °C. As expected, the deformation of the polymer required less shear stress with the increase of temperature. However, the change of shear stress with the shear rate at 60 °C was not linear, and the slope of the curve increased more at high shear rates. The results of this investigation can provide the required information for a better fabrication of membranes and filters with this polymer.

In-Line Rheo-Optical Investigation of the Dispersion of Organoclay in a Polymer Matrix during Twin-Screw Compounding.

The dispersion mechanisms in a clay-based polymer nanocomposite (CPNC) during twin-screw extrusion are studied by in-situ rheo-optical techniques, which relate the CPNC morphology with its viscosity. This methodology avoids the problems associated with post extrusion structural rearrangement. The polydimethylsiloxane (PDMS) matrix, which can be processed at ambient and low temperatures, is used to bypass any issues associated with thermal degradation. Local heating in the first part of the extruder allows testing of the usefulness of low matrix viscosity to enhance polymer intercalation before applying larger stresses for clay dispersion. The comparison of clay particle sizes measured in line with models for the kinetics of particle dispersion indicates that larger screw speeds promote the break-up of clay particles, whereas smaller screw speeds favor the erosion of the clay tactoids. Thus, different levels of clay dispersion are generated, which do not simply relate to a progressively better PDMS intercalation and higher clay exfoliation as screw speed is increased. Reducing the PDMS viscosity in the first mixing zone of the screw facilitates dispersion at lower screw speeds, but a complex interplay between stresses and residence times at larger screw speeds is observed. More importantly, the results underline that the use of larger stresses is inefficient per se in dispersing clay if sufficient time is not given for PDMS to intercalate the clay galleries and thus facilitate tactoid disruption or erosion.

Synthesis and Characterization of Polydimethylsiloxane (PDMS) with Medium Viscosity via Ring-Opening Polymerization

Duration of use and injectability are external factors for Polydimethylsiloxane (PDMS) that needs to be considered when PDMS utilized as a vitreous substituted liquid in vitreoretinal surgery. In general, PDMS which has been used as a substitute for vitreous humour is PDMS with a low viscosity in the value about 1000 cSt and a high viscosity at a value of about 5000 cSt. Various deficiencies have been encountered from low and high viscosity of PDMS, causing research to be continued to obtain PDMS which has suitable properties as a substitute for vitreous humour. One of them is research to obtain medium viscosity of PDMS with a viscosity value of about 2000 cSt. Here, we reported synthesis and characterization of PDMS with medium viscosity in ranges from 1800 to 2600 mPas. PDMS was synthesized through Ring-Opening Polymerization (ROP) pathway using the monomer of Octamethylcyclotetrasiloxane (D4) and the chain terminator of Hexamethyldisiloxane (MM). Various concentrations of potassium hydroxide (KOH) of 3, 4, 6 and 8 %(w/v) were applied as initiator to form gel of PDMS. All synthesized PDMS samples were identified to have viscosity values of 1800-2600 mPas, refractive index values of 1.4042-1.4044 and surface tension values of 22-23 mN/m. Meanwhile, the results of Fourier-Transform Infrared (FTIR) measurement showed that the absorption peaks were similar to that of our previous report.

Effect of polydimethylsiloxane viscosity on silica fume-based geopolymer hybrid coating for flame-retarding plywood

Hydroxyl-terminated polydimethylsiloxane (PDMS) modified silica fume-based geopolymer explores a novel challenging and interesting flame-retardant hybrid coating, and the effect of PDMS viscosity on the flame resistance and microstructure is investigated firstly. The optimum kinetic viscosity of PDMS is estimated as 350 cps according to the results of cone calorimeter (CC), which imparts a 50% decreased fire growth index (FGI) with the fire performance index (FPI) of 3.80 s·m2·kW−1 to the hybrid coating. The incorporation of PDMS renders the decreases in the weight loss percent (52.51%) and the average combustion velocity Vac (6.74 × 10−2%·s−1), as well as excellent smoke suppression. The doped PDMS (350 cps) facilitates the transformation from Q40 (no aluminum ion in Si-O-Si chains) to Q41 or Q42 groups (one or two aluminum ions Al3+ replace the pristine Si4+) involved in geopolymer coating, evidenced by the results of 29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) spectra, leading to a continuous, compact, and intact barrier layer from microstructure analysis. Moreover, the retarding mechanism of PDMS in the hybrid coating is elucidated including physical filling, heat sink effect of Si-O- chains, hydrogen bonding, and crosslinking. However, excessive PDMS viscosity exerts adverse flame resistance to the silica fume-based geopolymer hybrid coating.

Factors Influencing the Rheological Properties of MRSP Based on the Orthogonal Experimental Design and the Impact Energy Test

In the preparation process of magnetorheological silly putty (MRSP), the influence factors of the relative shear thickening effect (RSE) and relative magnetorheological effect (RME) were studied by orthogonal experiments as well as range and variance analyses. The influence degree of each factor was also evaluated. The results showed that the viscosity of polydimethylsiloxane (PDMS) and the mass fraction of carbonyl iron powder (CIP) had a significant influence on the RSE and RME, respectively. With an increasing PDMS viscosity, the RSE of the silicon-boron copolymer matrix first increased and then decreased, while the RME of MRSP decreased gradually. In addition, the shear thickening mechanism of MRSP was explored by the molecular chain motion. Finally, the impact energy with different samples was tested, and it is demonstrated that with the increasing cross section, the impact energy of the sample increases gradually, but the rate of increase becomes smaller.

An Optimized PDMS Thin Film Immersed Fabry-Perot Fiber Optic Pressure Sensor for Sensitivity Enhancement

To effectively control the critical thickness of a polydimethylsiloxane (PDMS) film and enhance the sensitivity characteristics of the fiber pressure sensor, we propose a new method to optimize the thickness of the PDMS film in a fiber tube. It is characterized by analyzing the relationship between the diffusion rate of the PDMS and its viscosity, and using an oven to solidify the PDMS to a certain extent to accurately control the diffusion rate and diffusion length of the PDMS in the fiber tube. We also used multiple transfer methods to control the volume of the PDMS in the fiber tube to minimize the thickness of the formed PDMS film. Fabry-Perot interference occurs when the surface of the PDMS film layer filled into the fiber tube and the adjacent single mode fiber/fiber tube form a joint surface. This method forms a new fiber-optic Fabry-Perot pressure sensor that is very sensitive to external pressure parameters. The experimental results show that the optimized film thickness will be reduced to an order of 20 μm. Correspondingly, the fiber-optic pressure sensor has a sensitivity of up to 100 pm/kPa, which is about 100 times that reported in the literature. The structure also has better resistance to temperature interference. To our knowledge, this is the first in-depth study of the effects of the PDMS viscosity coefficient, diffusion rate, and fiber pressure sensitivity in fiber. The film thickness optimization method has some advantages, including a low cost, good controllability, and good application value in high sensitivity pressure and sound wave detection.

Deformable liquid metal polymer composites with tunable electronic and mechanical properties

Abstract

Microencapsulation of 2,2′-Azobis(2-methylpropionamide) dihydrochloride initiator using acrylonitrile butadiene styrene as shell for application in lost-circulation control

Gel sealants are often used to recover lost circulation, a problem that plagues drilling engineers throughout many oil and gas development project. Organic cross-linked polymer gel such as cross-linked polyacrylamide gel is one of the most popular and available gel sealant materials. It is of strong sealing ability, but the gelation time is too short to control and ensure safe drilling operation. Initiator used to supply free radical can prolong polyacrylamide gelation time, but the gelation time will dramatically decline with the increase of temperature. Microencapsulation of initiator can increase the gelation time because the concentration of initiator is controlled effectively by microcapsules. This paper proposes microcapsules of an initiator, 2,2′-Azobis(2-methylpropionamide) dihydrochloride (AIBA) encapsulated by Acrylonitrile Butadiene Styrene, prolonging the gelation time of cross-linked polyacrylamide gel. It was prepared via coacervation induced by polydimethylsiloxane (PDMS). The gelation time was prolonged to be eight times greater than that initiated by free AIBA initiator. Fourier transform infrared spectroscopy, thermogravimetric analysis, Ultraviolet-visible spectroscopy, specific surface area analysis, and scanning electron microscopy were used to observe the properties of microcapsules. The results indicated that AIBA was successfully microencapsulated and there were nano-sized pores in the outer surfaces of the microcapsules which serve to control the release of AIBA, and viscosity of PDMS and core/shell ration affected the content of AIBA loaded in the microcapsules. Moreover, it is microencapsulation that makes the concentration of AIBA in water increase stable as a function of time for prolonging the gelation time of sealant system. Computerized tomography (CT) scans revealed that the cross-linked polymer gel system significantly reduces the number of pores inside the cores and enhances pressure-bearing ability. Cross-linked polyacrylamide gel initiated by encapsulated AIBA shows notable potential for recovering lost circulation.

Fabrication of a micro through-hole array by gas-blowing a PDMS-treated polyamide screen for a flexible drag-reducing skin-like device

We propose a method for fabricating a flexible skin-like device for generating and trapping micro bubbles with the aim of reducing underwater drag. This low-cost, efficient, high-pressure gas-blow method is used to fabricate a micro through-hole array in a flexible polydimethylsiloxane (PDMS) gel-based skin. The key parameters in the gas-blowing method are investigated, such as the viscosity of PDMS and the blowing pressure in order to optimize the quality of through-hole layer. Deviation of the linear dimensions of the obtained micro holes was less than 4.5%. In addition, multiphase computational fluid dynamics models were built to analyze the drag-reduction performance of bell-shaped holes made by this method. Compared with cylindrical through holes produced by molding, the drag-reduction effect of bell-shaped holes increased as much as 34%.

Polydimethylsiloxane assisted supercritical CO2 foaming behavior of high melt strength polypropylene grafted with styrene

Foamable high melt strength polypropylene (HMSPP) was prepared by grafting styrene (St) onto polypropylene (PP) and simultaneously introducing polydimethylsiloxane (PDMS) through a one-step melt extrusion process. The effect of PDMS viscosity on the foaming behavior of HMSPP was systematically investigated using supercritical CO2 as the foaming agent. The results show that the addition of PDMS has little effect on the grafting reaction of St and HMSPP exhibits enhanced elastic response and obvious strain hardening effect. Though the CO2 solubility of HMSPP with PDMS (PDMS-HMSPP) is lower than that of HMSPP without PDMS, especially for PDMS with low viscosity, the PDMS-HMSPP foams exhibit narrow cell size distribution and high cell density. The fracture morphology of PDMS-HMSPP shows that PDMS with low viscosity disperses more easily and uniformly in HMSPP matrix, leading to form small domains during the extrusion process. These small domains act as bubble nucleation sites and thus may be responsible for the improved foaming performance of HMSPP.

Flexible dry electrode based on carbon nanotube/polymer hybrid micropillars for biopotential recording

A novel flexible dry electrode based on carbon nanotube (CNT) and polydimethylsiloxane (PDMS) is proposed for recording biopotentials. Because the homogeneous dispersion of CNTs in PDMS is challenge due to the high viscosity of PDMS and aggregation of CNTs, a novel process is developed through addition of an organic solvent to disentangle CNTs and reduce the viscosity of PDMS. The electrical performance of the composite of CNTs and PDMS as the function of CNT concentration was characterized. The optimized 10wt% MWCNTs is dispersed in PDMS as the material of flexible dry electrode. In order to apply for long-term, wearable biopotential recording devices, the flexible dry electrode with micropillar array is designed and fabricated by MEMS process. The testing result shows that the skin-electrode contact impedance of the flexible mciropillar electrode is lower an order magnitude than that of the flexible flat electrode without micropillar array structures. Moreover, the contact impedance of this fabricated electrode was stable during two-day continuous testing, which indicates the flexible dry electrode is suitable for long-term measurement. In order to investigate the effect of motion artifact on the ECG signal, ECG signals are recording under two statuses of resting and walking. The ECG signals measured by the fabricated micropillar electrode were good fidelity, and did not degrade because of the motion.

Collision of atoms with porous polymer surface: evidence of influence of bulk diffusion on anomalously long dwell time of Rb atoms

We present the results of a systematic study of Knudsen’s flow of Rb atoms in cylindrical capillary cells coated with a polydimethylsiloxane (PDMS) compound. The purpose of the investigation is to measure the adsorption energy and dwell time of Rb atom on the two types of coating of high and median viscosities. We report the measurement of the adsorption energy which yields E = 0.026 eV. This parameter is the same for the two kinds of PDMS used. We find that at room temperature the dwell times for high viscosity and median viscosity PDMS are 22 ± 3 μs and 49 ± 6 μs, respectively. These dwell times are many orders of magnitude longer than the dwell time derived from the measured adsorption energy of Rb atom and temperature of the coating. A tentative explanation of this surprising result, based on the bulk diffusion of the atoms that collide with the surface and penetrate inside of the coating, is proposed.

PDMS, A Robust Casing for Flexible W-BAN Antennas [EurAAP Corner

This paper describes a new technology for the realization of soft, flexible, and robust antennas intended to operate in a harsh environment. One of the main characteristics of the proposed technology is the ease of fabricating antennas in a simple lab environment. The method is based on the use of a silicon-based elastomer, polydimethylsiloxane (PDMS), for the substrate material, and copper meshes or any kind of perforated metal plates as flexible conductive materials. The initial liquid state of the PDMS allows a lot of freedom in the fabrication process, both from the electrical and mechanical points of view. The electrical and mechanical properties of the substrate can be adjusted by loading the PDMS with inclusions having low or high permittivity and/or density, thus controlling the permittivity and the rigidity. Another good characteristic of the initial low viscosity of PDMS is the possibility of shaping the antennas and substrates in in-house fabricated moulds. Copper meshes or perforated metal structures enable good adhesion between the substrate and 288 IEEE Antennas and Propagation Magazine, Vol. 55, No. 5, October 2013 conductor, and improve the overall flexibility. Measured results showed good repeatability of the substrate samples, both with or without inclusions. To demonstrate the versatility of the proposed technique, several antenna prototypes were built and characterized. All the antennas were flexible and showed good radiation characteristics. The antennas were exposed to tests such as washing and bending, in order to assess their robustness to environmental changes.

Instantly switchable adhesion of bridged fibrillar adhesive via gecko-inspired detachment mechanism and its application to a transportation system

Inspired by the exceptional climbing ability of gecko lizards, artificial fibrillar adhesives have been extensively studied over the last decade both experimentally and theoretically. Therefore, a new leap towards practical uses beyond the academic horizon is timely and highly anticipated. To this end, we present a fibrillar adhesive in the form of bridged micropillars and its application to a transportation system with the detachment mechanism inspired by the climbing behaviour of gecko lizards. The adhesive shows strong normal attachment (~30 N cm(-2)) as well as easy and fast detachment within 0.5 s without involving complex dynamic mechanisms or specific stimulus-responsive materials. The fabrication of the bridged micropillars consists of replica moulding of polydimethylsiloxane (PDMS) micropillars, transfer of the PDMS precursor to the heads of the micropillars, and inverse placement on an inert Teflon-coated surface. Owing to the spontaneous interconnections of low viscosity PDMS precursor, bridged micropillars with a uniform capping nanomembrane (~800 nm thickness) are formed over a large area. Interestingly, macroscopic adhesion in the normal direction can be immediately switched between on and off states by changing the two detachment modes of pulling and peeling, respectively. To prove the potential of the fibrillar adhesive for practical use, an automated transportation system is demonstrated for lifting and releasing a mass of stacked glass slides over 1000 cycles of attachment and detachment.

The viscosity and density of 1-propene,1,1,2,3,3,3-hexafluoro- oxidized,polymd and polydimethylsiloxane at temperatures from (313 to 373) K and a pressure of 0.1 MPa

The viscosity of polydimethylsiloxane {(CH 3) 3SiO[SiO(CH 3) 2] n Si(CH 3) 3 with CAS# 63148-62-9} and 1-propene,1,1,2,3,3,3- hexafluoro-, oxidized,polymd {CF 3O[CF 2C(CF 3)FO] n (CF 2O) m CF 3 with CAS# 69991-67-9} has been measured with an oscillating sinker viscometer at temperatures between (313 and 373) K and a pressure of 0.1 MPa. The viscometer was calibrated with a reference fluid and found accurate to ±2%. The viscosity reported for 1-propene,1,1,2,3,3,3-hexafluoro-, oxidized,polymd at T = 373 K is 5% above the value reported by the supplier and these differences increase smoothly with decreasing temperature to be about 15% at T = 333 K. The density of both fluids has been determined with a vibrating tube densimeter at temperatures in the range (313 to 363) K at a pressure of 0.1 MPa with an uncertainty of ±0.03% and our results are less than 0.5% above the values reported by the suppliers in the overlapping temperature range.