Solid Silicone Rubber Research Articles

Effect of fillers on the piezocapacitive behaviour of silicone rubber particulate composites

Robotics and fluid dynamics applications have created demand for development of electronic skins with embedded pressure sensors. These applications require simple and low-cost fabrication processes with large area deployment. Both structured and unstructured material approaches to sensor development have been followed. Among the various sensing mechanisms, piezo capacitive transduction is superior. This paper reports the influence of fillers on the piezo capacitive characteristics of unstructured solid silicone rubber composites. Dielectric, conductive and conductive-dielectric fillers were incorporated into solid silicone rubber and fabricated using high temperature compression moulding to form dielectric-dielectric, conductive-dielectric and conductive-dielectric dielectric composites. The results reveal that piezo capacitive sensitivity varies with filler type, filler loading, curing agent loading, mixing time and curing temperature. The experiments reveal improved normalized capacitance with pressure characteristics of linearity and sensitivity of 3.9 × 10−3 (kPa)−1 in the 0–20 kPa range of pressure. These composites are thus candidate materials for flexible pressure sensing applications.

A novel Foley catheter made of high-intensity near-infrared fluorescent silicone rubber for image-guided surgery of lower rectal cancer

BackgroundUrethral injury occurs in 1–6 % of male cases during minimally invasive surgery of lower rectal cancer. A Foley catheter emitting near-infrared (NIR) fluorescence of sufficient intensity has been expected to locate the urethra during image-guided surgery. Although it has been difficult to impart NIR fluorescent properties to biocompatible thermosetting polymers, we have recently succeeded in developing a NIR fluorescent compound for silicone rubber and a NIR fluorescent Foley catheter (HICARL). Here, we evaluated its NIR fluorescence properties and visibility performance using porcine anorectal isolation specimens. MethodsThe HICARL catheter was made of a mixture of solid silicone rubber and a NIR fluorescent compound that emits fluorescence with a wavelength of 820–880 nm, while a conventional transparent Foley catheter was made of solid silicone rubber only. As a standard for comparison of the intensity of NIR fluorescence, a transparent Foley catheter the lumen of which was filled with a mixture of indocyanine green (ICG) and human plasma was used. As a comparison to assess the visibility performance of the HICARL catheter, a transparent Foley catheter into which a commercially available NIR fluorescent polyurethane ureteral catheter (NIRC) was placed was used. ResultsA NIR fluorescence quantitative imaging analysis revealed that the Foley-NIRC catheter and the HICARL catheter emitted 3.42 ± 0.42 and 6.43 ± 0.07 times more fluorescence than the Foley-ICG catheter, respectively. The location of the HICARL catheter placed in the anorectum with a wall thickness of 3.8 ± 0.1 mm was clearly delineated in its entirety by NIR fluorescence, while that of the Foley-NIRC catheter was faintly or only partially visible. ConclusionsThe HICARL catheter emitting NIR fluorescence of sufficient intensity is a promising and easy-to-use tool for urethral visualization during image-guided surgery of lower rectal cancer.

Peroxide‐based crosslinking of solid silicone rubber, part II: The counter‐intuitive influence of dicumylperoxide concentration on crosslink effectiveness and related network structure

AbstractApplication of elastomers in general demands the conversion of their soluble networks into crosslinked structures. This abrupt change causes several modifications, both in the atomic/molecular level and at the macro‐scale. In this study, solid silicone rubber (high molecular weight poly(dimethylsiloxane)), was crosslinked with dicumylperoxide (DCP), a widely used crosslinking agent by the rubber industry. The changes caused by different DCP concentrations were investigated, aiming to bring attention to the molecular transformations, usually neglected when processing‐oriented studies are conducted. DCP concentration showed a limited contribution to the network's molecular dynamics, which was found to be mainly dominated by entanglements. The dominance of entanglements over other molecular constraints, like crosslink points, justifies the threshold and counter‐intuitive behavior of tensile and hardness properties. However, differences were found in the crystallization ability after crosslinking, when the more crosslink points were introduced, the lower the crystallinity was and the less stable the PDMS crystallites were. In addition to providing a deeper understanding of an industrially applied rubber system n terms of the effective concentration of DCP, and the reasoning behind such concentration, the findings of this study add to the state‐of‐the‐art comprehension of elastomeric networks, and how they behave on a molecular level.

Peroxide-Based Crosslinking of Solid Silicone Rubber, Part I: Insights into the Influence of Dicumylperoxide Concentration on the Curing Kinetics and Thermodynamics Determined by a Rheological Approach.

Predicting the curing behaviour of industrially employed elastomeric compounds under typical processing conditions in a reliable and scientifically driven way is important for rubber processing simulation routines, such as injection moulding. Herein, a rubber process analyser was employed to study the crosslinking kinetics of solid silicone rubber based on the concentration of dicumylperoxide. A model was proposed to describe the optimal cure time variation with peroxide concentration and temperature, based on the analysis of processing parameters applying kinetic and thermodynamic judgments. Additionally, the conversion rate was described with the aid of a phenomenological model, and the effect of dicumylperoxide concentration on the final crosslink state was investigated using kinetic and thermodynamic explanations. Optimal curing time was affected both by temperature and dicumylperoxide concentration. However, the effects were less pronounced for high temperatures (>170 C) and high concentrations (>0.70 phr). A limit on the crosslink state was detected, meaning that the dicumylperoxide capacity to crosslink the silicone network is restricted by the curing mechanism. Curing restrictions were presumed to be primarily thermodynamic, based on the proton abstraction mechanism that drives the crosslinking reaction. In addition to providing more realistic crosslinking models for rubber injection moulding simulation routines, the results of this study may also explain the chemical behaviour of organic peroxides widely used for silicone crosslinking.

Synergistic Enhancement Properties of a Flexible Integrated PAN/PVDF Piezoelectric Sensor for Human Posture Recognition.

The flexible pressure sensor has attracted much attention due to its wearable and conformal advantage. All the same, enhancing its electrical and structural properties is still a huge challenge. Herein, a flexible integrated pressure sensor (FIPS) composed of a solid silicone rubber matrix, composited with piezoelectric powers of polyacrylonitrile/Polyvinylidene fluoride (PAN/PVDF) and conductive silver-coated glass microspheres is first proposed. Specifically, the mass ratio of the PAN/PVDF and the rubber is up to 4:5 after mechanical mixing. The output voltage of the sensor with composite PAN/PVDF reaches 49 V, which is 2.57 and 3.06 times that with the single components, PAN and PVDF, respectively. In the range from 0 to 800 kPa, its linearity of voltage and current are all close to 0.986. Meanwhile, the sensor retains high voltage and current sensitivities of 42 mV/kPa and 0.174 nA/kPa, respectively. Furthermore, the minimum response time is 43 ms at a frequency range of 1–2.5 Hz in different postures, and the stability is verified over 10,000 cycles. In practical measurements, the designed FIPS showed excellent recognition abilities for various gaits and different bending degrees of fingers. This work provides a novel strategy to improve the flexible pressure sensor, and demonstrates an attractive potential in terms of human health and motion monitoring.

Incidence of Clinically Significant Aniseikonia Following Encircling Scleral Buckle Surgery: An Evaluation of Refractive and Axial Length Changes Requiring Intervention

To evaluate the incidence of symptomatic anisometropia and aniseikonia requiring intervention following surgery with combined pars plana vitrectomy (PPV) and broad 276 style encircling scleral buckle (ESB) for the repair of rhegmatogenous retinal detachments (RRD) and to report axial length (AL) and keratometry changes, a retrospective review of consecutive RRD patients treated with combined PPV and ESB between June 2016 until September 2019 was performed. All patients with symptomatic optically induced aniseikonia requiring additional interventions or surgical procedures including clear lens exchanges, secondary intraocular lens implants or contact lenses were documented. Keratometry and AL measurements were recorded for each eye and changes calculated. In total, 100 patients underwent combined PPV, ESB and endotamponade with mean age of 59.47 years (SD 11.49). AL was significantly increased (25.39 mm [SD 1.27] to 26.54 mm [SD 1.16], p = 0.0001), with a mean change of 1.15 mm (SD 0.67). Mean corneal astigmatism increased by –0.95 D (SD 0.51) in control eyes preoperatively and –1.33 (SD 0.87) postoperatively (p = 0.03). Over half of phakic patients (39/61; 64%) developed a visually significant cataract, subsequently undergoing surgery. Six of 100 patients developed symptomatic anisometropia with aniseikonia postoperatively (6%). Four proceeded with clear lens exchange despite absence of visually significant cataract (4%). Two of these initially trialled contact lenses (2%). One was intolerant, while the other decided to proceed with clear lens exchange for convenience. Only one patient (1%), being pseudophakic in both eyes, had persistent anisometropia/aniseikonia. AL and keratometry changes induced by encirclement with broad solid silicone rubber buckles are acceptable and similar to those reported previously using narrow encircling components, being unlikely to induce troublesome symptomatic anisometropia/aniseikonia. Many patients are phakic and develop visually significant cataracts, allowing correction of changes induced with the aim of visual restoration. A minority require more prolonged methods of visual rehabilitation, such as contact lens wear or clear lens exchanges. Caution and appropriate consent should be made in patients that are pseudophakic in both eyes at presentation.

Influence of conductive and dielectric fillers on the relaxation of solid silicone rubber composites

Flexible dielectrics possessing high permittivity and low loss are desirable for many electromechanical transduction applications. Solid silicone rubber composites are promising materials for electromechanical applications. These composites are fabricated using high-temperature vulcanization process, with various amounts of conductive, dielectric and conductor-dielectric filler and processing parameters. Dielectric and conductivity relaxations of these composites are investigated using dielectric spectroscopy in the 20 Hz–2 MHz frequency range at room temperature. Dielectric relaxations of dielectric filler composites show different behaviour compared to conductive and conductive—dielectric filler composites even with the same filler loading. All composites show increased permittivity at lower frequencies. The maximum permittivity of 46, 5.8 and 46 at 20 Hz was attained for the conductive, dielectric and conductive-dielectric composites respectively at similar filler loadings. The composites follow the AC universality law with exponents in the range of 0.82 to 1.02. The conductive filler is more reinforcing than dielectric filler as seen from the variation of Young’s modulus with filler type. Uniform dispersion of fillers is observed for all the three composites.

Influence of filler and processing parameters on the mechanical properties of dielectric elastomer composites

Dielectric elastomer composites are used as actuators and sensors. They convert electrical energy directly into mechanical energy and vice versa. Conductive and dielectric fillers are added to elastomers in order to improve its permittivity, thereby altering its mechanical properties. This study investigates the effect of conductive filler and processing parameters on the mechanical properties of dielectric elastomer composites fabricated using solid silicone rubber as matrix and ketjenblack as conductive filler using compression moulding process. The processing parameters such as amount of curing agent, mixing time and curing temperature also influence the mechanical properties. Maximum values of Young’s modulus, density and shore A hardness recorded were 25.2 MPa, 1210 kg/m3 and 86 for the present study.

Investigation on Electromechanical Properties of Solid Silicone Rubber Composites with Conductive Carbon Filler

Dielectric elastomers belonging to the class of electroactive polymers are promising materials for electromechanical transduction. They are used as actuators, capacitive sensors and energy harvesters. In the present study solid silicone rubber-super conducting carbon black composites are prepared through compression moulding process and evaluated for their mechanical and dielectric properties. Electromechanical sensitivity is estimated and discussed using Taguchi orthogonal arrays for the factors, such as content of active filler and curing agent, mixing time in roll mill, curing temperature. Permittivity of the composites increased 6 times when compared with the sample without active filler. Electromechanical sensitivity of the composite improved 2 times, thus highlighting that this approach could lead to development of newer dielectric elastomer transducer materials.

Correction to: Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites

The article listed above was initially published with incorrect Table 1 and Table 2 values.

Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites

Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation.

High-Performance PZT-Based Stretchable Piezoelectric Nanogenerator

Stretchable piezoelectric nanogenerators are highly desirable for power supply of flexible electronics. Piezoelectric composite material is the most effective strategy to render piezoelectric nanogenerators stretchable. However, the generated output performance is unsatisfactory due to the low piezoelectric phase proportion. Here we demonstrate a high-performance Pb(Zr0.52Ti0.48)O3 (PZT)-based stretchable piezoelectric nanogenerator (HSPG). The proposed HSPG exhibits excellent output performance with a power density of ∼81.25 μW/cm3, dozens of times higher than previously reported results. Mixing technique, instead of conventional stirring technology, is used to incorporate PZT particles into solid silicone rubber. The filler distribution homogeneity in matrix is thus remarkably improved, allowing higher filler composition. The PZT proportion in composite can be increased to 92 wt % with satisfactory stretchability of 30%. On the basis of the excellent electrical and mechanical properties, the proposed HS...

All-in-one filler-elastomer-based high-performance stretchable piezoelectric nanogenerator for kinetic energy harvesting and self-powered motion monitoring

Flexible nanogenerators with advantages of conformal structure and easy assembly have become an appealing research field for wearable electronics recently. Here, an all-in-one filler-elastomer-based high-performance stretchable piezoelectric nanogenerator (SPENG) is reported. By mechanically shearing and uniformly dispersing high weight compositions of PZT particles and Ag-coated glass microspheres fillers into the identical solid state silicone rubber matrixes, the piezoelectric layer and electrode layers are prepared, respectively, and the SPENG can be fabricated in an all-in-one structure with tight adhesion and reliable durability, which is very important to the tension sensing and energy harvesting for the limb motion with large strain and variable degree of freedom. The stretchable energy harvester exhibits excellent output performances (Voc≈20 V, Isc≈0.55μA, 3.93μW/cm3) and can respond to different external stimulations (such as stretched, clustered, folded, twisted, etc.). The SPENG can be not only mounted on a joint to efficiently capture and convert random body kinetic energy into electricity as a power supply for portable electronics, but also used as the self-powered tension and gesture sensors to monitor dynamic motions. This work has demonstrated a great progress in stretchable electronics and energy harvesting technology, which may have important prospects in artificial intelligence and individualized medical care.

Effects of Tail Prosthesis Mass and Length on the Kinematics and Activity of an American Alligator

The tail has many functions for an American Alligator (Alligator mississippiensis). Previous research demonstrates that adding a prosthetic tail to a tailless alligator improves locomotor performance and restores posture. We experimented on the effects of prosthesis parameters on the kinematics and behavior of an American Alligator whose tail has been reduced to the proximal seven vertebrae. We tested three different prostheses to determine the effects of tail mass and length on behavior and restoration of proper locomotion and pelvic and spinal alignment. Prostheses effects were compared to a control alligator with a tail, and the previous results with a prosthesis.All three prostheses were solid silicone rubber, modeled from digital scans of an actual alligator tail. The first prosthesis tested was of a mass and length designed to restore center of mass to a normal position. This matched the expected 28% of the body mass that makes up the tail in alligators. In the second prosthesis, mass was the same as the first, but prosthesis length was increased 34%. For the third, length was the same as the first, but prosthesis mass was increased 34%.Behavioral data were collected over four different four‐week periods, period one with no tail, and each successive period for tails one, two and three. The alligators' number of occurrences for seven different behaviors were recorded using motion activated video cameras. Statistical behavioral differences between the alligator with the prosthesis and a normal control were noted within these categories: walking and getting into and out of the pond. Statistical differences between the periods for each tail were noted within these categories: tail whipping in period 1 was significantly different than period 4, swimming in period one compared to all other periods, and getting into and out of the pond in period 1 was significantly different than period 2.Locomotion was tested in a biomechanics lab using reflective markers and motion capture cameras. Stride parameters including stride length, stride duration, and duty factor were used to compare kinematic profiles between the control subject and the test subject. Marker position representing important skeletal landmarks were used to measure postural effects. Preliminary results from tail one show a relationship that most closely represents the high walk of the control alligator. Excessive length has a smaller effect on stride parameters. However, due to tail 3 having higher frictional braking forces relating to the higher mass, locomotion was more difficult for the subject and not enough locomotion data were captured to run statistical tests.The results suggest that mass is the more important factor for function than length. This raises questions about why tail length in alligators is fixed, and how abilities such as turning maneuverability with a shorter tail or better swimming with a longer tail may cause a certain tail length to be evolutionarily beneficial.Support or Funding InformationBiomedical Sciences Program at Midwestern University, Glendale, AZThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Circumferential silicone sponge scleral buckling induced axial length changes: case series and comparison to literature

BackgroundThis study compared axial length changes induced by circumferential scleral buckling using a silicone sponge with literature reports for solid silicone rubber.MethodsRecords of patients treated with scleral buckling in 2009–2013 using a silicone sponge, with preoperative axial length biometry measurements were reviewed. Additional information included age, type of surgery, additional surgeries, phakic status and anatomical success of reattachment. Patients underwent repeat biometry. The medical literature was reviewed for articles describing axial length changes induced by circumferential buckling using solid silicone rubber.ResultsTwenty-eight patients (mean age 49.7 years, range 16–72) met the inclusion criteria. Mean axial length was 25.38 mm preoperatively and 26.12 mm at least 6 months postoperatively (SD 0.50 ± 0.09, p < 0.001); a mean increase of 0.74 mm. Half the patients subsequently underwent cataract surgery. Post-operative changes were not significant compared to pre-surgical refraction and corneal astigmatism. Axial length change was not significant between sexes (9 women and 19 men).ConclusionsAxial length changes induced by circumferential scleral buckling using silicone sponge exclusively are similar to those reported in the literature for solid silicone rubber buckles. Scleral buckling using a silicone sponge, which may offer several surgical advantages, induces an acceptable axial length change similar to that seen with widely-used solid silicone rubber buckles.

Internet Access to Advanced 3-Dimensional Software for the Prototyping and Design of Complex and Precise Custom Mandibular Implants

A large percentage of patients with microgenia requesting chin augmentation also exhibit an associated component of micrognathia with either narrow or acutely angled mandibular bodies and/or hypoplasia of the gonial angles. Augmentation of the face and mandible should optimally address all regions of deficiency and can now be customized with a high degree of accuracy using software that can be accessed over the Internet. We discuss the advanced capabilities of merging a sophisticated software system (Geometric Freeform® software; Morrisville, North Carolina) and computed tomography (CT) imaging to design precise, total custom mandibular implants over the Internet without the need for physical modeling. In revision cases, this process also allowed for the implant to be removed and replaced within a single-stage procedure. We retrospectively reviewed 34 cases in an outpatient surgical center and described the preoperative evaluation, imaging protocol, customization process, and surgical procedure for custom mandibular and custom total mandibular augmentation. Between January 2004 and June 2015, 25 patients underwent total mandibular augmentation and 9 had custom extended mandibular angle and body augmentation. All patients received solid silicone rubber implants that were customized using virtual or acrylic prototypes digitally designed via real-time video conferencing. This custom process achieved an enhanced level of satisfaction with an improved ability to achieve symmetry based on quantitative measurements during the interactive design process, alloplastic facial implants can be customized with a high degree of accuracy, precision, and fit by combining the capabilities of 3-dimensional CT and advanced computer design software accessed via the Internet.

Rapid optical inspection of bubbles in the silicone rubber

Silicone rubber mold is frequently used in the indirect tooling of rapid tooling technology. Defect inspection of silicone rubber after degassing process using vacuum machine is usually evaluated by visual inspection. The drawbacks of this method include human error, time consuming and exhaustive. An optical inspection system for inspecting the bubbles in the silicone rubber is developed in this work. Bubbles in solid silicone rubber or liquid silicone rubber can be easily inspected with high accuracy in the millimeter range by studying the peak intensity distribution profile of He–Ne laser radiation passed through the silicone rubber.

Model for a solid‐liquid airlift two‐phase partitioning bioscrubber for the treatment of BTEX

AbstractBACKGROUND: Airlift solid–liquid two‐phase partitioning bioreactors (SL‐TPPBs) have been shown to be effective for the treatment of gas streams containing benzene, toluene, ethylbenzene and o‐xylene (BTEX). The airlift SL‐TPPB is a low‐energy system that utilizes a sequestering phase of solid silicone rubber beads (10%v/v) that will uptake and release large amounts of BTEX in order to maintain equilibrium conditions within the system. This increases mass transfer from the gas phase during dynamic loading periods and improves degradation performance. This study discusses the development and analysis of a steady‐state, tanks‐in‐series mathematical model, arising from mass balances on BTEX and oxygen in the gas, aqueous and polymer phases to predict the performance of the airlift SL‐TPPB over various gas flow rates and BTEX loadings.RESULTS: An estimability analysis on model parameters determined that the parameters to which model output is most sensitive are those that affect biological activity, which were targeted for estimation. The developed tanks‐in‐series model was able to predict the removal of BTEX components and dissolved oxygen concentrations over various inlet loadings (20, 60 and 100 mg L−1 h−1) and gas flow rates (2,3 and 4 L min−1) that resulted in a range of system performance from effective BTEX treatment to oxygen limiting conditions.CONCLUSIONS: The model developed, with estimated parameters, provides a valuable tool to determine operating conditions that will result in favourable performance of the airlift SL‐TPPB. Copyright © 2009 Society of Chemical Industry

Scleral buckle removal associated with pars plana vitrectomy for recurrent retinal detachment

Scleral buckle (SB) removal is rarely performed due to extrusion, infection, or diplopia. We report a series of patients with recurrent retinal detachment (RRD) after primary SB due to new breaks occurring at sites where the presence of a pre-existing SB was judged counterproductive. All patients were treated by means of pars plana vitrectomy (PPV) and SB removal with the sole purpose of achieving a more favorable retinal profile. We retrospectively reviewed all patients undergoing PPV and SB removal for RRD due to new breaks occurring at sites hidden by pre-existing exoplants. Mean age was 52 years and VA on presentation was 20/620 and 20/216 at latest visit (p<0.01), 23 months of follow-up. On presentation, 3/11 (27%) had a VA better than 20/400 and 1/11 (9%) better than 20/40. At the end of follow-up, 9/11 (81%) and 3/11 (27%) saw better than 20/400 and 20/40 (p<0.05). At the end of follow-up, 8/11 (72%) had an attached retina, 2/11 (18%) had a partially attached retina, and 1/11 (9%) had a total RD. Explanted buckles included 5 silicone sponges and 6 solid silicone rubber elements. Although occasionally cumbersome and time-consuming, SB removal may provide a more favorable retinal profile and improve retina-tamponade contact. Larger series are needed to assess if this translates into a significant benefit in the treatment of selected RRD.

The Comparison of Solid Silicone Rubber Types Manufactured by Diverse Technologies

The paper presents the current results of our ongoing research on the field of silicon rubber applications in precision engineering and in medical industry. We have demonstrated two technologies for the manufacturing of precision parts and devices for the medical industry. The mechanical properties of the silicone rubber materials manufactured by press vulcanisation and by moulding (diving) are compared.