Deep dive into the fundamental physics and chemistry that make smart textiles possible
At the most fundamental level, electrical conductivity in smart textiles follows the same physical principles as conventional electronics, but with unique challenges posed by the textile environment.
The relationship between current flow and material properties is described by:
Think of electricity in textiles like water flowing through a pipe:
In smart textiles, our "pipes" (conductive threads) are often fuzzy, stretchy, or uneven, which makes predicting the flow more challenging than in rigid wires.
Unlike rigid conductors, textile-based conductors show significant temperature sensitivity:
Metals like silver and copper conduct worse when they get hot. This means your heated glove might draw slightly less power as it warms up.
For carbon-filled polymers, α < 0. Resistance decreases with temperature as more charge carriers are activated.
Body heat (37°C) allows us to use temperature as a sensor input, but it also means we need to calibrate our sensors to ignore normal body warmth.
The piezoresistive effect describes how mechanical strain affects electrical resistance:
When you stretch a conductive fabric, you physically pull the conductive fibers apart.
Understanding the chemical processes that affect smart textile performance is crucial for designing durable systems.
Silver-plated conductive threads are susceptible to tarnishing:
Silver + Sulfur = Tarnish. Just like silverware, conductive thread turns black over time because of sulfur in the air (or rubber bands!). This black layer doesn't conduct electricity well, making your sensors drift or fail. Store your materials in sealed bags to keep them fresh.
UV radiation breaks polymer chains through free radical formation:
UV rays from the sun act like tiny scissors, cutting the microscopic chains that make plastic and rubber stretchy. Over time, this makes conductive fabrics brittle and prone to cracking.
Water molecules attack polymer backbones, particularly in polyesters:
Water doesn't just cause short circuits; it can actually break down some synthetic fibers over time, especially in hot, soapy washes. Always check if your conductive material is rated for washing.
When different metals are present with moisture, electrochemical reactions occur:
If you connect a Copper snap to a Silver thread and add sweat (salt water), you've accidentally made a tiny battery! This eats away at the metal (corrosion) much faster than normal.
Try to use the same metal throughout your circuit (Silver to Silver, Copper to Copper) or protect connections with waterproof glue or nail polish.
Avoid mixing dissimilar metals in humid conditions to prevent preferential dissolution.
Repeated thermal expansion and contraction creates mechanical stress:
-20°C to +60°C at 1°C/min maximum rate to avoid thermal shock
Resistance drift, mechanical stress from thermal expansion, phase transitions
Use flexible interfaces and account for differential expansion between materials
Moisture absorption changes both electrical and mechanical properties:
Hygroscopic materials absorb water, changing dielectric properties and creating unwanted conductive paths.
Fiber swelling can change fabric dimensions by 2-5%, affecting circuit geometry and component alignment.
10% to 95% RH at 25°C ± 2°C, measuring property changes every 10% increment.
Repeated loading leads to cumulative damage and eventual failure:
Where N = cycles to failure, Δσ = stress range, A & m = material constants
Explains conductivity in carbon-filled polymers:
In materials like Velostat (the black plastic bags sensitive to pressure), carbon particles are floating in plastic. At a certain point—the "Percolation Threshold"—there are just enough carbon particles touching each other to let electricity zip through. This is why they are so sensitive to pressure: squeezing them forces just a few more particles to touch, drastically changing the resistance.
Current flows between nanoparticles through quantum tunneling:
In some advanced sensors, particles don't even need to touch! If they get close enough, electrons can "jump" or "tunnel" through the gap. This effect is incredibly sensitive to tiny movements, making it perfect for detecting small gestures or breathing.
Polymer behavior depends on loading history:
Stretch sensors often have "memory." When you stretch them and let go, they take a moment to settle back to their original resistance. This lag is called hysteresis. It's like a memory foam mattress—it doesn't snap back instantly.
The Butler-Volmer equation describes electrode reactions:
Batteries are chemical reactors. Factors like temperature and how fast you draw power affect how long they last. In wearables, flexible batteries face extra challenges because bending them can disrupt their internal chemical layers.
Performance data for common smart textile materials:
Resistivity: 0.001-0.01 Ω·cm | Gauge Factor: 2-3 | Max Strain: 5-10% | Fatigue Life: 10³-10⁴ cycles
Resistivity: 0.01-0.1 Ω·cm | Gauge Factor: 2-4 | Max Strain: 2-5% | Fatigue Life: 10⁵-10⁶ cycles
Resistivity: 1-100 Ω·cm | Gauge Factor: 10-50 | Max Strain: 50-200% | Fatigue Life: 10⁴-10⁵ cycles
Resistivity: 0.0001-0.001 Ω·cm | Gauge Factor: 1-2 | Max Strain: 10-30% | Fatigue Life: 10⁶+ cycles
Following the systematic approach developed by Hannah Perner-Wilson and Mika Satomi:
Map all forces: tension, compression, shear, torsion. Consider how each affects electrical properties.
Account for body heat, ambient temperature, component heating, and thermal expansion effects.
Consider exposure to sweat (pH 4-6.8), detergents (pH 9-12), and environmental pollutants.
Source, batch numbers, and storage conditions for all materials used
Techniques, thread tensions, and environmental conditions during assembly
Document failure modes and their physical causes for future design improvement
Long-term monitoring of key metrics under realistic use conditions