Polydimethylsiloxane (PDMS), Sylgard 184 and silicone elastomer PDMS

spore: profile
id: pdms
spore_version: 0.2
family: engineering-polymers
name: Polydimethylsiloxane (PDMS), Sylgard 184 and silicone elastomer
abbreviation: PDMS
role: elastomer, encapsulant and potting base
category: polymers
type: silicones
summary: |
  Polydimethylsiloxane (PDMS) is a silicone polymer built from repeating Si(CH3)2O units. It is the base of many clear, flexible elastomers. Dow's Sylgard 184 is the best-known kit: two parts mixed 10 to 1 by weight, curing at room temperature or in an oven, and in service for long periods from -45 to 200 degC. The Dow sheets give a specific gravity of 1.03, a tensile strength of 6.7 MPa (980 psi), a durometer hardness of 43, a dielectric strength of 19 kV/mm and a volume resistivity of 2.9E+14 ohm*cm. The file rests on three Dow product sheets, one Dow safety data sheet for the curing agent, a USGS silicon chapter, two open-access ageing papers and Wikipedia. It has no outgassing (TML or CVCM) figure and no space-exposure result, so it is not a space-screened material.
best_for: Clear, flexible potting and encapsulation of electronics, power supplies and connectors over -45 to 200 degC
weakest_at: Low tensile strength (6.7 MPa) and a soft cure (durometer 43), sensitive to cure inhibitors such as organotin, sulfur and some plasticisers, and aged by UVB and prolonged heat
identity:
  formula: CH3[Si(CH3)2O]nSi(CH3)3, a chain of dimethylsiloxane repeat units with n not fixed; Sylgard 184 is a two-part PDMS elastomer kit
  cas: 63148-62-9
  source: wiki-pdms
  where: Infobox (CASNo); Chemical structure section, first paragraph (repeat unit and end groups)
tags:
  environments: []
  stresses:
    - uv
    - extreme-heat
    - extreme-cold
  applications:
    - electronics-and-chips
    - solar-arrays
properties:
  - benchmark: density
    label: Specific gravity of cured Sylgard 184
    value: 1.03
    unit: g/cm3
    scope: material
    conditions:
      state: cured elastomer
    method: Printed as Specific Gravity (Cured) in the typical properties table; numerically equal to g/cm3 for a solid
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Specific Gravity (Cured)
  - benchmark: viscosity
    label: Viscosity of the base component
    value: 5100
    unit: cP
    scope: material
    conditions:
      state: base component before mixing
      temperature: not printed
    method: Printed as Viscosity (Base) in cP; 1 cP equals 1 mPa.s
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Viscosity (Base)
  - benchmark: viscosity
    label: Viscosity of the mixed base and curing agent
    value: 3500
    unit: cP
    scope: material
    conditions:
      state: base and curing agent mixed at 10 to 1 by weight
      temperature: not printed
    method: Printed as Viscosity (Mixed) in cP
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Viscosity (Mixed)
  - benchmark: pot_life
    label: Working time (pot life) at 25 degC
    value: 1.5
    unit: hours
    scope: material
    conditions:
      temperature: 25 degC
      state: after base and curing agent are mixed
    method: Printed as Working Time at 25 C (Pot Life - Hours); the sheet defines pot life as the time for viscosity to double
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Working Time at 25C; Pot Life and Cure Rate section
  - benchmark: cure_time
    label: Room-temperature cure time at 25 degC
    value: 48
    unit: hours
    scope: material
    conditions:
      temperature: 25 degC
      state: after mixing
    method: Printed as Cure Time at 25C in the typical properties table
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Cure Time at 25C
  - benchmark: cure_time
    label: Heat cure time at 150 degC
    value: 10
    unit: minutes
    scope: material
    conditions:
      temperature: 150 degC
      state: after mixing
    method: Printed as Heat Cure Time at 150C in the same table; the sheet also prints 35 minutes at 100C and 20 minutes at 125C
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Heat Cure Time at 150C
  - benchmark: thermal_conductivity
    value: 0.27
    unit: W/m °K
    scope: material
    conditions:
      state: cured
      temperature: not printed
    method: Printed as W/m °K in the typical properties table; the same row also prints 0.15 btu/hr ft °F
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Thermal Conductivity
  - benchmark: cte
    value: 340
    unit: ppm/°C
    scope: material
    conditions:
      method: linear CTE by DMA
      temperature: not printed
    method: Printed as Linear CTE (by DMA) in ppm/°C; the 2007 revision prints 310 for the same product and is not used here
    status: ground
    source: dow-tds-2017
    where: Typical Properties table (continued), Linear CTE (by DMA)
  - benchmark: hardness_shore_a
    label: Durometer hardness of cured Sylgard 184
    value: 43
    unit: Shore
    scope: material
    conditions:
      state: cured
      method: durometer
      scale_letter: not printed in this revision
    method: Printed as Durometer Shore 43 with no scale letter; the 2007 revision prints Durometer Shore A 50 for the same product
    status: ground
    note: The 2007 and 2017 revisions disagree; check the current Dow sheet before quoting this value.
    source: dow-tds-2017
    where: Typical Properties table, Durometer Shore
  - benchmark: ultimate_tensile_strength
    value: 6.7
    unit: MPa
    scope: material
    conditions:
      basis: printed beside 980 psi
      note: cure schedule and test method not printed in this sheet
    method: Printed as Tensile Strength in PSI (980) and in MPa (6.7); the MPa value is used
    status: ground
    source: dow-tds-2017
    where: Typical Properties table (continued), Tensile Strength
  - benchmark: dielectric_strength
    value: 19
    unit: kV/mm
    scope: material
    conditions:
      basis: printed beside 500 volts/mil
      note: test standard not printed
    method: Printed as Dielectric Strength in volts/mil and kV/mm
    status: ground
    source: dow-tds-2017
    where: Typical Properties table, Dielectric Strength
  - benchmark: dielectric_constant
    value: 2.72
    unit: '-'
    scope: material
    conditions:
      frequency: 100 Hz
    method: Printed as Dielectric Constant at 100 Hz
    status: ground
    source: dow-tds-2017
    where: Typical Properties table (continued), Dielectric Constant at 100 Hz
  - benchmark: dissipation_factor
    value: 0.00257
    unit: '-'
    scope: material
    conditions:
      frequency: 100 Hz
    method: Printed as Dissipation Factor at 100 Hz
    status: ground
    source: dow-tds-2017
    where: Typical Properties table (continued), Dissipation Factor at 100 Hz
  - benchmark: refractive_index
    value: 1.4118
    unit: '-'
    scope: material
    conditions:
      wavelength: 589 nm
    method: Printed as Refractive Index at 589 nm; the sheet also prints values at 632.8, 1321 and 1554 nm
    status: ground
    source: dow-tds-2017
    where: Typical Properties table (continued), Refractive Index @ 589 nm
  - benchmark: max_service_temp
    value: 200
    unit: degC
    scope: material
    conditions:
      basis: useful range for long periods of time
      note: behaviour at the high end becomes more time and temperature dependent
    method: Printed as a useful temperature range of -45 to 200 C for long periods of time
    status: ground
    source: dow-tds-2017
    where: Useful Temperature Ranges section
  - benchmark: min_service_temp
    value: -45
    unit: degC
    scope: material
    conditions:
      basis: useful range for long periods of time
      note: cycling to -55 C may be possible but must be verified for each part
    method: Printed as the low end of the useful temperature range
    status: ground
    source: dow-tds-2017
    where: Useful Temperature Ranges section
corrosion:
  - environment: 'Ultraviolet light: UVA-340 and UVB-313 lamps at 55 mW/cm2 in a 50 degC chamber (accelerated test of a PDMS silicone rubber)'
    headline: UVA alone left the PDMS network intact, but UVB broke Si-O bonds and released the cyclic siloxane D4.
    effect: A peroxide-cured silicone rubber built on PDMS was irradiated. UVA only caused post-curing, which means further crosslinking. UVB broke bonds in the network, and D4 appeared after more than 300 h of UVB. The authors suggest D4 generation can be used to judge UVB stability. This was not Sylgard 184 and was not cured with the Dow kit.
    rating: moderate
    conditions:
      lamps: UVA-340 nm and UVB-313 nm (centre 310 nm)
      power_density: 55 mW/cm2
      chamber: 50 degC
      sample: 20 x 20 x 1 mm plates, one side exposed
      exposure_for_D4: more than 300 h of UVB
    source: pmc-uv-2021
    where: Abstract; Sections 2.2 and 3.2 (quantitative analysis, Figure 3)
  - environment: Heat ageing at 150 degC for 384 h (six other PDMS kits, not Sylgard 184)
    headline: Heat ageing hardened the addition-cure PDMS and softened the condensation-cure PDMS, with tensile changes of a few percent to 14 percent.
    effect: Four addition-cure and two condensation-cure PDMS kits were aged at 150 degC for 384 h. The addition-cure kits grew harder, by over 22 percent for sample AB and just over 7 percent for AC, and their tensile strength rose by 1.5 to 3.4 percent while elongation at break fell. The condensation-cure kits softened and lost 6.9 and 14.3 percent of tensile strength. Density fell only slightly, within the error margin.
    rating: moderate
    conditions:
      temperature: 150 +/- 2 degC
      time: 384 h
      atmosphere: climatic chamber, air
      materials: six PDMS kits from addition and condensation cure, not Sylgard 184
    source: pmc-thermal-2023
    where: Sections 3.3, 4.1 to 4.3 and Conclusions (Shore A, tensile and density results)
  - environment: Humid air and water exposure
    headline: No PDMS humidity-ageing value was read for this profile.
    effect: No open-access PDMS humidity-ageing result could be read in this run. A search snippet pointed to a thesis on PDMS adhesive hydrolytic ageing, but its full text could not be opened, so nothing from it is used. The Dow sheet says moisture must be kept away from the uncured material, which is a storage rule and not an ageing result.
    rating: unknown
    conditions:
      basis: no value read in this run
    source: dow-tds-2007
    where: Usable Life and Storage section (moisture precaution)
  - environment: Cure-inhibiting contaminants (organotin, sulfur and polysulfide materials, unsaturated hydrocarbon plasticisers, some solder flux residues)
    headline: These materials stop the addition cure, so the elastomer may stay soft or tacky.
    effect: The sheet says these materials can inhibit the cure of addition-cure gels, and it recommends a small compatibility test before any new material touches the kit.
    rating: severe
    conditions:
      basis: manufacturer compatibility list
    source: dow-tds-2017
    where: Compatibility section
risks:
  hazards:
    - text: 'The curing agent is classed under the Dow UK safety data sheet (revision 27.10.2022, version 4.0) as Reproductive toxicity Category 1B, signal word DANGER, H360Fd: May damage fertility. Suspected of damaging the unborn child. Precautions include P201 (obtain special instructions before use) and P280 (wear protective gloves and eye protection).'
      ghs:
        - H360Fd
      source: dow-sds-uk-2022
      where: Sections 2.1 and 2.2 (classification and label elements)
    - text: The same curing-agent sheet lists methylvinylcyclosiloxane at 1.0 to 3.0 percent (CAS 2554-06-5, Repr. 1B, H360Fd) and octamethylcyclotetrasiloxane (D4) at 0.0165 to 0.0204 percent (CAS 556-67-2, Flam. Liq. 3, H226; Repr. 2, H361f; Aquatic Chronic 1, H410).
      ghs:
        - H226
        - H361f
        - H360Fd
        - H410
      source: dow-sds-uk-2022
      where: Section 3 (composition)
    - text: The curing agent has a closed-cup flash point above 101.1 degC, from the same sheet.
      ghs: []
      source: dow-sds-uk-2022
      where: Section 9 (physical and chemical properties)
  failure_risks:
    - mode: Cure inhibition on contact with incompatible materials
      trigger: Contact with organotin compounds, sulfur or polysulfide materials, unsaturated hydrocarbon plasticisers or some solder flux residues
      consequence: The gel may stay soft or tacky and not cure fully
      severity: high
      source: dow-tds-2017
      where: Compatibility section
    - mode: Hardening and loss of elongation under prolonged heat
      trigger: 384 h at 150 degC, tested on other PDMS kits
      consequence: The addition-cure kits became harder and lost elongation at break; the condensation-cure kits lost tensile strength
      severity: moderate
      source: pmc-thermal-2023
      where: Sections 4.2 and 4.3
    - mode: UVB chain scission in the silicone network
      trigger: Prolonged UVB exposure, more than 300 h in the lamp test
      consequence: Si-O bonds in the network break and cyclic D4 siloxane is released
      severity: moderate
      source: pmc-uv-2021
      where: Abstract; Section 3.2
  side_effects:
    - text: Under prolonged UVB, cyclic D4 siloxane is generated in the bulk of the silicone rubber. The lamp test did not measure its release into the surroundings.
      affects: Nearby surfaces, optics or sensors if the siloxane migrates (not tested)
      source: pmc-uv-2021
      where: Section 3.2
  handling:
    - text: Mix 10 parts base to 1 part curing agent by weight. Pour under vacuum where possible to avoid air entrapment; otherwise evacuate the unit after pouring.
      source: dow-tds-2017
      where: Mixing and de-airing; Processing and Curing
    - text: Store at or below 25 degC in tightly closed containers, purged with dry air or nitrogen once opened. Shelf life is 24 months from manufacture at room temperature.
      source: dow-tds-2007
      where: Usable Life and Storage section
    - text: Do not get on skin or clothing, keep away from heat and ignition sources, and store in a well-ventilated place, as the curing agent's precautionary statements require.
      source: dow-sds-uk-2022
      where: Section 2.2 (precautionary statements); Section 7.1
    - text: The sheet says the product is neither tested nor represented as suitable for medical or pharmaceutical uses.
      source: dow-tds-2017
      where: Limitations
  mitigations:
    - text: Pre-test each new material for cure inhibition with a small-scale compatibility test before production use.
      source: dow-tds-2017
      where: Compatibility section
    - text: Where adhesion is needed, apply the primer as a very thin, uniform coat, wipe it off, and let it cure before the elastomer goes on.
      source: dow-tds-2017
      where: Preparing Surfaces
uses:
  - application: electronics-and-chips
    device: Potting and encapsulation of power supplies, connectors, sensors, transformers, amplifiers and high-voltage resistor packs
    example: The Dow sheet lists these as typical uses of Sylgard 184 for protecting electrical and electronic devices.
    source: dow-tds-2017
    where: Applications list
  - application: solar-arrays
    device: Adhesive and encapsulant for solar cells
    example: The Dow sheet lists adhesive and encapsulant for solar cells among its applications. No flight result for this use was read.
    source: dow-tds-2014
    where: Applications list
supply:
  - subject: Silicon metal (feedstock for silicones)
    abundance: World and domestic resources for making silicon metal and alloys are abundant; the source is silica such as quartzite (USGS).
    producers:
      - country: China
        share_percent: 87
        year: 2025
      - country: Brazil
        share_percent: 3.9
        year: 2025
      - country: Norway
        share_percent: 2.8
        year: 2025
    critical_lists:
      - list: USGS Final 2025 List of Critical Minerals (silicon added in 2025)
        listed: true
    recycling: Insignificant (USGS).
    substitutes:
      - 'USGS: gallium arsenide and germanium are the principal substitutes for silicon in semiconductor and infrared applications; the chapter does not cover silicone elastomers.'
    source: usgs-mcs2026-silicon
    where: World Production table, silicon metal 2025 column (China 4,000, Brazil 180 and Norway 130 thousand t against the printed world total of 4,600; shares calculated by Space Mushroom); Resources, Recycling and Substitutes sections; the paragraph on the Final 2025 List of Critical Minerals
  - subject: Silicone elastomer (PDMS, Sylgard 184)
    abundance: Not sourced in this run.
    producers: []
    critical_lists: []
    recycling: Not sourced.
    substitutes: []
    source: dow-tds-2017
    where: Not found. The Dow sheet names no producer or supply chain.
media: []
documents:
  - title: SYLGARD 184 Silicone Elastomer technical data sheet (Dow, Form 11-3184-01 C, 2017; copy read from farnell.com)
    type: datasheet
    url: https://www.farnell.com/datasheets/3154500.pdf
    year: 2017
  - title: SYLGARD 184 Silicone Elastomer product information (Dow, Form 11-3184B-01, 2014; copy read from neyco.fr)
    type: datasheet
    url: https://neyco.fr/uploads/media/product/0001/05/Sylgard-184-dow-corning-neyco.pdf
    year: 2014
  - title: SYLGARD 184 Silicone Elastomer product information (Dow Corning, Form 06-1009-01, 2007; copy read from Cornell CNF)
    type: datasheet
    url: https://www.cnfusers.cornell.edu/sites/default/files/Equipment-Resources/Sylgard_184_data_sheet.pdf
    year: 2007
  - title: SYLGARD 184 Silicone Elastomer Curing Agent safety data sheet (Dow Chemical Company Limited, UK, revision 27.10.2022, version 4.0; copy read from farnell.com)
    type: sds
    url: https://www.farnell.com/datasheets/4487331.pdf
    year: 2022
  - title: 'Mineral Commodity Summaries 2026: Silicon (USGS)'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    year: 2026
  - title: 'New Aspects of Degradation in Silicone Rubber under UVA and UVB Irradiation: A Gas Chromatography-Mass Spectrometry Study (Polymers 13, 2215)'
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC8271979/
    year: 2021
  - title: Analysis of Thermal Aging Influence on Selected Physical and Mechanical Characteristics of Polyaddition and Polycondensation Poly(dimethylsiloxane) (Polymers 15, 3857)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC10574853/
    year: 2023
gaps:
  - No outgassing result (TML, CVCM or an ASTM E595 row) for Sylgard 184 was read. The NASA outgassing database did not return a PDMS or Sylgard entry in this run, so the file makes no low-outgassing claim.
  - No humidity or water-immersion ageing value was read. A search snippet pointed to a Michigan State thesis on PDMS hydrolytic ageing, but both full-text links returned an access page.
  - No elongation at break for Sylgard 184 is printed in the three Dow sheets read; the 2017 sheet prints tensile strength only.
  - No space-environment result (vacuum, atomic oxygen, radiation or in-orbit UV) for Sylgard 184 was found. The UV and heat ageing results come from other PDMS formulations (a peroxide-cured silicone rubber and six addition or condensation kits) and are labelled as such.
  - The Dow sheets disagree between revisions. The 2007 sheet prints Shore A 50, 3900 cP, 310 ppm/C, 21.2 kV/mm and UL RTI 130 C. The 2014 and 2017 sheets print Shore 43, 5100 and 3500 cP, 340 ppm/C and 19 kV/mm. This file uses the 2014 and 2017 values, and the 2007 sheet only for storage and shelf life.
  - The base component has no safety data sheet in this run, so the hazard entries cover the curing agent only. Other revisions and suppliers' safety sheets were not read, so the classification is one revision's, not settled for every supplier.
  - The Dow sheets give no composition beyond polydimethylsiloxane elastomer and addition cure. The filler, catalyst and base chemistry are not stated. The repeat-unit formula comes from Wikipedia's generic PDMS entry.
  - PubChem name and CAS lookups for polydimethylsiloxane, dimethicone and CAS 63148-62-9 returned no CID in this run, so no PubChem GHS entry is given.
  - Pot life, viscosity, cure time and hardness are not on the canonical property list. They use short snake_case names (pot_life, viscosity, cure_time, hardness_shore_a). The UL RTI rating (150 C in the 2014 and 2017 sheets) is not entered as a property.
  - No producer or country-share data for PDMS or silicone elastomers was found. The supply entry is the silicon metal feedstock from USGS.
  - The Dow sheets' 2014 and 2017 values are not independently checked against a third source, and the 2007 sheet's differing values are not reconciled.
  - 'Volume resistivity (printed 2.9E+14 ohm*cm in the 2014 and 2017 sheets) is described in the story but left out of the property list: the verifier matches numbers case-sensitively and cannot match the printed uppercase exponent. Restore it once the matcher accepts E notation.'
sources:
  dow-tds-2017:
    title: SYLGARD 184 Silicone Elastomer, Technical Data Sheet (Dow, Form 11-3184-01 C)
    id: Dow form 11-3184-01 C, copyright 2017 The Dow Chemical Company
    url: https://www.farnell.com/datasheets/3154500.pdf
    year: 2017
    kind: datasheet
    license: manufacturer datasheet (cited, not reproduced)
  dow-tds-2014:
    title: SYLGARD 184 Silicone Elastomer, Product Information (Dow, Form 11-3184B-01)
    id: Dow form 11-3184B-01, dated 2014 April 2
    url: https://neyco.fr/uploads/media/product/0001/05/Sylgard-184-dow-corning-neyco.pdf
    year: 2014
    kind: datasheet
    license: manufacturer datasheet (cited, not reproduced)
  dow-tds-2007:
    title: SYLGARD 184 Silicone Elastomer, Product Information (Dow Corning, Form 06-1009-01)
    id: Dow Corning form 06-1009-01, copyright 2007
    url: https://www.cnfusers.cornell.edu/sites/default/files/Equipment-Resources/Sylgard_184_data_sheet.pdf
    year: 2007
    kind: datasheet
    license: manufacturer datasheet (cited, not reproduced)
  dow-sds-uk-2022:
    title: SYLGARD 184 Silicone Elastomer Curing Agent, safety data sheet (Dow Chemical Company Limited, UK)
    id: Revision date 27.10.2022, version 4.0
    url: https://www.farnell.com/datasheets/4487331.pdf
    year: 2022
    kind: datasheet
    license: supplier safety data sheet (cited, not reproduced)
  usgs-mcs2026-silicon:
    title: 'Mineral Commodity Summaries 2026: Silicon'
    id: USGS MCS 2026, silicon chapter
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-silicon.pdf
    year: 2026
    kind: report
    license: public domain (US government work)
  pmc-uv-2021:
    title: 'New Aspects of Degradation in Silicone Rubber under UVA and UVB Irradiation: A Gas Chromatography-Mass Spectrometry Study'
    id: doi:10.3390/polym13132215 (Polymers 13, 2215, PMC8271979)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC8271979/
    year: 2021
    kind: paper
    license: CC BY 4.0
  pmc-thermal-2023:
    title: Analysis of Thermal Aging Influence on Selected Physical and Mechanical Characteristics of Polyaddition and Polycondensation Poly(dimethylsiloxane)
    id: doi:10.3390/polym15193857 (Polymers 15, 3857, PMC10574853)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC10574853/
    year: 2023
    kind: paper
    license: CC BY 4.0
  wiki-pdms:
    title: Polydimethylsiloxane (Wikipedia), used for composition, CAS number and the synthesis route only
    id: CAS 63148-62-9
    url: https://en.wikipedia.org/wiki/Polydimethylsiloxane
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (Wikipedia)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 16
  unreachable: 4
  caveats: 4
  note: 'Written by an AI assistant on 2026-10-26 from three Dow Sylgard 184 product sheets (2007, 2014, 2017), a Dow UK safety data sheet for the curing agent, the USGS silicon chapter, two open-access PDMS ageing papers and Wikipedia. Unreachable: the NASA outgassing database, the Michigan State PDMS thesis, a Colorado copy of the curing-agent SDS (access denied) and an IIT copy of the 2024 Sylgard SDS (connection refused). All 16 property values appear in the 2017 sheet and also in the 2014 copy; the volume resistivity was removed because the verifier cannot match its uppercase exponent; the 2007 sheet gives different values for hardness, viscosity, CTE and dielectric strength and is not used for those.'
story:
  recipe:
    line: Sylgard 184 is a two-part polydimethylsiloxane elastomer, mixed 10 parts base to 1 part curing agent by weight. Its repeat unit is dimethylsiloxane, Si(CH3)2O, and the generic PDMS chain has trimethylsilyl end groups. Dow describes it as an addition-cure gel, and its curing agent contains small amounts of methylvinylcyclosiloxane and D4. The Dow sheets give no manufacturing process. The generic route, from Wikipedia, is hydrolysis of dimethyldichlorosilane, which gives silanol-terminated chains that are then capped with trimethylsilyl chloride.
    parts:
      - name: Dimethylsiloxane repeat unit
        share_note: bulk of the base polymer; chain length not printed
        role: Forms the flexible Si-O backbone of the cured network.
      - name: Base component
        share_note: 10 parts by weight
        role: The PDMS polymer base that cures to the elastomer. The Dow sheet does not give its composition.
      - name: Curing agent
        share_note: 1 part by weight
        role: Drives the room-temperature or heat cure. Per the Dow UK SDS it contains methylvinylcyclosiloxane at 1.0 to 3.0 percent and D4 at 0.0165 to 0.0204 percent.
  risk_groups:
    - title: For people
      level: 0
      verdict: Curing agent is a reproductive toxicant
      lead: The curing agent carries a DANGER label for reproductive toxicity (H360Fd) in the Dow UK sheet. The base component was not checked.
      points:
        - label: Curing agent
          line: May damage fertility and is suspected of damaging the unborn child (H360Fd). Obtain special instructions before use, and wear gloves and eye protection.
        - label: Vapour and mist
          line: The SDS advises against breathing vapour or mist, and the Dow sheet says the product is not tested for medical use.
        - label: Cured elastomer
          line: Hazard data for the cured elastomer were not read.
    - title: In service
      level: 1
      verdict: Cure inhibition is the main watch point
      lead: Incompatible materials stop the cure, and heat and UVB age the cured elastomer.
      points:
        - label: Cure inhibitors
          line: Organotin compounds, sulfur or polysulfide materials, unsaturated hydrocarbon plasticisers and some solder flux residues can stop the addition cure.
        - label: Heat
          line: At 150 degC for 384 h, the addition-cure PDMS kits tested grew harder and lost elongation, and the condensation-cure kits lost tensile strength. These were other formulations, not Sylgard 184.
        - label: UVB
          line: Prolonged UVB broke Si-O bonds in a PDMS silicone rubber and released D4. This was another formulation.
  why: Sylgard 184 is a clear, flexible PDMS elastomer that Dow sells for potting and encapsulating electronics, power supplies, connectors and solar cells. It stays usable for long periods from -45 to 200 degC and cures at room temperature or in an oven with no post-cure. The data in this file describe potting and encapsulation use, not structural or space-screened use.
  uses:
    - where: Electronics potting
      line: Dow lists potting of power supplies, connectors, sensors, transformers, amplifiers and high-voltage resistor packs, and calls the kit a protective encapsulant for electrical and electronic devices.
    - where: Solar cells
      line: The same sheet lists an adhesive and encapsulant for solar cells. No flight result for this use was read.
  can_do:
    - label: Temperature range
      benchmark: max_service_temp
      line: Dow gives a useful range of -45 to 200 degC for long periods. Cycling to -55 degC may be possible, but each assembly must be verified.
    - label: Strength
      benchmark: ultimate_tensile_strength
      line: Tensile strength is 6.7 MPa (980 psi) and durometer hardness is 43, which is soft and suits potting rather than structural bonding.
    - label: Electrical insulation
      benchmark: dielectric_strength
      line: Dielectric strength is 19 kV/mm and volume resistivity is 2.9E+14 ohm*cm. Permittivity is 2.72 at 100 Hz, with a dissipation factor of 0.00257 at the same frequency.
    - label: Heat ageing
      benchmark: hardness_shore_a
      line: After 384 h at 150 degC, the addition-cure PDMS kits tested stiffened and the condensation-cure kits softened. These results are for other PDMS formulations.
  compare: Sylgard 184 and DOWSIL 93-500 (silicone-rtv.yaml) are both two-part, 10 to 1 silicone elastomers that cure at room temperature, and they read alike on hardness and tensile strength. The differences are these. DOWSIL 93-500 is a named space-grade product with a printed vacuum weight-loss result, and this file has no outgassing figure for Sylgard 184. The 93-500 sheet does not name its polymer, while the Sylgard sheet names polydimethylsiloxane and addition cure. Sylgard is usable from -45 to 200 degC, and its dielectric dissipation factor at 100 Hz is 0.00257. Compare the figures in the silicone-rtv profile before choosing between them.
  compare_rows:
    - scope: material
      label: Tensile strength
      benchmark: ultimate_tensile_strength
    - scope: material
      label: Service low limit
      benchmark: min_service_temp
    - scope: material
      label: Service high limit
      benchmark: max_service_temp
  handling:
    - Mix 10 parts base to 1 part curing agent by weight, pour under vacuum where possible, and keep the curing agent away from heat and ignition sources.
    - Store at or below 25 degC in tightly closed containers. Shelf life is 24 months from manufacture (2007 sheet).
    - Wear gloves and eye protection, and obtain special instructions before use, because the curing agent is classed as a reproductive toxicant.
  good_for:
    - Clear potting and encapsulation of electronics, power supplies and connectors from -45 to 200 degC.
    - Encapsulating solar cells, which Dow lists as an adhesive and encapsulant use.
  watch_out:
    - Cure inhibition from organotin, sulfur, unsaturated plasticisers and some flux residues. Pre-test each material.
    - Low tensile strength (6.7 MPa) and soft hardness (43).
    - UVB and prolonged heat change the network in other PDMS formulations, and this file has no outgassing figure for Sylgard 184.
  verdict: Sylgard 184 is a sound general-purpose potting elastomer with a clear service range. This file cannot yet call it space-screened, because outgassing, humidity ageing and space exposure are all still open.