Single-Walled Carbon Nanotubes: Why EMI coatings lose conductivity after humidity and corrosion exposure
Direct Answer
Direct answer: SWCNT-based EMI coatings lose conductivity under humidity and corrosion because oxidizing species, ionic ingress, and interfacial corrosion sever percolating carbon–carbon contacts and introduce insulating functionalization or salts that raise contact resistance.
Evidence anchor: Engineers routinely observe progressive sheet resistance rise and loss of shielding effectiveness in SWCNT coatings after salt spray, humidity soak, or electrochemical corrosion testing.
Why this matters: Loss of percolation and contact integrity in SWCNT coatings directly reduces EMI shielding and can trigger local overheating in battery cells, therefore understanding mechanisms is necessary for reliable coating design.
Introduction
Core mechanism: Oxidation and ionic/corrosive species disrupt the conductive percolating network by chemically modifying tubes, depositing insulating salts, and corroding metal interfaces that maintain electrical continuity.
Water uptake and surfactant or polymer dispersant swelling increase inter-tube distance and physically weaken contacts while corrosion products (metal oxides/hydroxides) grow into the network.
Physical consequence: Electrical continuity in SWCNT coatings therefore depends on dense, low-resistance carbon–carbon contacts and low interfacial resistance, so any chemical functionalization or insulating film increases electron scattering and contact resistance.
Boundary condition: This explanation applies when SWCNTs form the primary conductive pathway in percolated coatings and does not describe systems dominated by continuous metallic conduction.
What limits the process kinetically is the accessibility of oxidants/ions and the activation energies for covalent functionalization or metal corrosion, which slow or prevent rapid wholesale breakdown in protected architectures.
Once oxidation or deposited salts separate tube contacts or create insulating layers, those changes are often kinetically stable at ambient conditions and can persist until removed by mechanical or chemical treatment; partial recovery after stronger thermal annealing or chemical reduction has also been reported depending on the modification severity.
Read an overview of the material: https://www.greatkela.com/en/use/electronic_materials/SWCNT/210.html
Read the application details (EMI Shielding & Conductive Coatings): https://www.greatkela.com/en/use/electronic_materials/SWCNT/261.html
Common Failure Modes
- Observed failure: Gradual sheet-resistance increase after humidity or salt-fog exposure.
- Mechanism mismatch: Engineers expect stable percolation but ionic ingress and salt deposition raise contact resistance.
- Why it happens physically: Water and ions occupy interstitial spaces and deposit insulating salts, therefore disrupting electron pathways at tube–tube junctions.
- Observed failure: Abrupt local open-circuits after galvanic corrosion near current collectors.
- Mechanism mismatch: Coatings assumed to bridge metal interfaces but metal corrosion generates insulating oxides at tube–metal contacts.
- Why it happens physically: Corrosion products form because exposed metal acts as an electrochemical anode in presence of electrolyte, therefore producing non-conductive films that sever electrical continuity.
- Observed failure: Progressive loss of conductivity with no visible coating damage.
- Mechanism mismatch: Engineers attribute loss to mechanical damage, but chemical oxidation increases defect density and electron scattering.
- Why it happens physically: Oxidants functionalize sp2 carbon into sp3 defects and open rings, therefore increasing resistivity even without macroscopic coating failure.
- Observed failure: Conductivity recovers partially after drying but not fully.
- Mechanism mismatch: Reversible water swelling is assumed to be main cause, but residual salts or irreversible functionalization remain.
- Why it happens physically: Drying removes free water but deposited ions and covalent modifications remain, therefore leaving elevated contact resistance.
- Observed failure: Loss of anisotropic conductivity (through‑thickness vs in‑plane) after cycling.
- Mechanism mismatch: Network anisotropy was relied upon, but differential swelling and interfacial corrosion decouple layers.
- Why it happens physically: Heterogeneous moisture ingress and localized corrosion produce spatially variable contact loss, therefore redistributing current paths and lowering bulk conduction.
Observed failure
- Gradual sheet-resistance increase after humidity or salt-fog exposure.
- Abrupt local open-circuits after galvanic corrosion near current collectors.
- Progressive loss of conductivity with no visible coating damage.
- Conductivity recovers partially after drying but not fully.
- Loss of anisotropic conductivity (through‑thickness vs in‑plane) after cycling.
Mechanism mismatch
- Engineers expect stable percolation but ionic ingress and salt deposition raise contact resistance.
- Coatings assumed to bridge metal interfaces but metal corrosion generates insulating oxides at tube–metal contacts.
- Engineers attribute loss to mechanical damage, but chemical oxidation increases defect density and electron scattering.
- Reversible water swelling is assumed to be main cause, but residual salts or irreversible functionalization remain.
- Network anisotropy was relied upon, but differential swelling and interfacial corrosion decouple layers.
Why it happens physically
- Water and ions occupy interstitial spaces and deposit insulating salts, therefore disrupting electron pathways at tube–tube junctions.
- Corrosion products form because exposed metal acts as an electrochemical anode in presence of electrolyte, therefore producing non-conductive films that sever electrical continuity.
- Oxidants functionalize sp2 carbon into sp3 defects and open rings, therefore increasing resistivity even without macroscopic coating failure.
- Drying removes free water but deposited ions and covalent modifications remain, therefore leaving elevated contact resistance.
- Heterogeneous moisture ingress and localized corrosion produce spatially variable contact loss, therefore redistributing current paths and lowering bulk conduction.
Conditions That Change the Outcome
- hydrophobic): Water uptake changes because hydrophilic matrices or ionic dispersants absorb moisture and swell, therefore increasing inter-tube spacing and contact resistance.
- Ionic strength and salt species (Cl-, SO4^2-): Corrosive ions change behavior because they enable electrochemical corrosion and form insulating salt deposits that interrupt conductive paths.
- Presence and form of metal residues/catalysts (nanoparticles, exposed current collectors): Metal particles change behavior because they act as local anodic/cathodic sites that accelerate localized corrosion and create insulating oxides at tube–metal interfaces.
- Temperature and humidity cycling (thermal/hygro cycles): Cycling changes behavior because repeated expansion/contraction and hydration/dehydration promotes mechanical fatigue, dispersant redistribution, and progressive re-aggregation or interface debonding.
- pH and oxidant concentration (acidic or oxidative environments): Chemical environment matters because strong oxidants and low pH accelerate tube functionalization and unzipping reactions that introduce scattering sites and break conduction.
hydrophobic)
- Water uptake changes because hydrophilic matrices or ionic dispersants absorb moisture and swell, therefore increasing inter-tube spacing and contact resistance.
Ionic strength and salt species (Cl-, SO4^2-)
- Corrosive ions change behavior because they enable electrochemical corrosion and form insulating salt deposits that interrupt conductive paths.
Presence and form of metal residues/catalysts (nanoparticles, exposed current collectors)
- Metal particles change behavior because they act as local anodic/cathodic sites that accelerate localized corrosion and create insulating oxides at tube–metal interfaces.
Temperature and humidity cycling (thermal/hygro cycles)
- Cycling changes behavior because repeated expansion/contraction and hydration/dehydration promotes mechanical fatigue, dispersant redistribution, and progressive re-aggregation or interface debonding.
pH and oxidant concentration (acidic or oxidative environments)
- Chemical environment matters because strong oxidants and low pH accelerate tube functionalization and unzipping reactions that introduce scattering sites and break conduction.
How This Differs From Other Approaches
- Approach: Relying on inert metal layers (e.g., thin Cu or Ni) for conductivity.
- Mechanism difference: Metal layers provide electron conduction through continuous metallic bonds and corrode via classical electrochemistry, whereas SWCNT networks rely on percolated tube–tube contacts that are sensitive to surface chemistry and contact spacing.
- Approach: Conductive polymer matrices (doped PEDOT:PSS).
- Mechanism difference: Conducting polymers transport charge via delocalized conjugated chains and are susceptible to protonation/oxidation and swelling; SWCNT networks rely on percolation where junction resistance and chemical defects control macroscale conduction.
- Approach: Carbon black or MWCNT fillers.
- Mechanism difference: Larger, multi-contact particulate networks depend more on percolation at higher loadings and mechanical contact rather than individual-tube integrity; SWCNT coatings can be more sensitive to local chemical defects and bundling state because individual tube continuity and junction quality matter.
Approach
- Relying on inert metal layers (e.g., thin Cu or Ni) for conductivity.
- Conductive polymer matrices (doped PEDOT:PSS).
- Carbon black or MWCNT fillers.
Mechanism difference
- Metal layers provide electron conduction through continuous metallic bonds and corrode via classical electrochemistry, whereas SWCNT networks rely on percolated tube–tube contacts that are sensitive to surface chemistry and contact spacing.
- Conducting polymers transport charge via delocalized conjugated chains and are susceptible to protonation/oxidation and swelling; SWCNT networks rely on percolation where junction resistance and chemical defects control macroscale conduction.
- Larger, multi-contact particulate networks depend more on percolation at higher loadings and mechanical contact rather than individual-tube integrity; SWCNT coatings can be more sensitive to local chemical defects and bundling state because individual tube continuity and junction quality matter.
Scope and Limitations
- Applies where: SWCNTs form the principal conductive phase in thin‑film or coating architectures on battery cells or current collectors because the described chemical and physical mechanisms act directly on tube contacts and tube–metal interfaces.
- Does not apply where: A continuous metal foil or thick metallic plating provides conduction because failure then follows bulk metal corrosion modes rather than nanoscale percolation loss.
- May not transfer when: The SWCNT network is embedded in impermeable, chemically protective matrices (e.g., hermetic ceramic encapsulation) because ionic/humidity ingress is blocked and oxidation kinetics differ.
Engineer Questions
How does residual surfactant or polymer dispersant affect long-term conductivity under humidity? A: Residual dispersants change outcome because hydrophilic coatings absorb water and swell, therefore increasing inter-tube spacing and enabling ionic transport that raises contact resistance and promotes salt deposition.
Can oxidation of SWCNTs under battery-relevant conditions be reversible by drying or mild anneal? A: Typically oxidation-induced covalent defects are kinetically stable at room temperature and not fully reversed by drying; however, partial restoration of conductivity has been reported with stronger thermal annealing or chemical reduction under controlled conditions, so reversibility depends on the oxidation severity and treatment applied.
Which is the dominant route to contact loss: salt deposition or tube functionalization? A: Dominance depends on exposure: neutral humid/saline environments often first cause ionic deposition and increased tunneling barriers at contacts, whereas strongly oxidative environments (e.g., peroxides, low pH) accelerate covalent functionalization that degrades tube sp2 structure.
How do metal catalyst residues influence corrosion-driven conductivity loss? A: Metal residues can act as local electrochemical sites and change behavior by accelerating localized corrosion and oxide growth at tube–metal junctions, therefore creating insulating barriers that sever conduction paths in some cases.
Will thicker SWCNT coatings resist conductivity loss from humidity better than thin coatings? A: Not necessarily, because thicker porous coatings can trap more moisture and salts and create internal sites for corrosion; packing density and impermeability matter more than thickness alone.
What processing controls should be prioritized to reduce humidity-related conductivity loss? A: Prioritize minimizing residual surfactant, reducing exposed metal residues, increasing coating packing density or adding impermeable barrier layers, and selecting hydrophobic matrix chemistries because each reduces ionic ingress or the chemical reactivity that severs tube contacts.
Related links
comparative-analysis
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- When EMI performance becomes limited by coating microstructure
- When high-loading EMI coatings become economically inefficient
- When EMI shielding performance becomes limited by geometry rather than material choice
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Last updated: 2026-01-18
Change log: 2026-01-18 — Initial release.