Glue is a ubiquitous substance found in homes, schools, offices, and industrial settings around the world. From gluing paper together to assembling furniture to securing electronics, glue serves an important adhesive function across countless applications. But one thing that most glues lack is the ability to conduct electricity.
The Composition of Common Glues
To understand why glues are not conductive, we first need to consider their composition. Many common glues are formulated using polymers such as polyvinyl acetate, epoxy resin, cyanoacrylate, and polyurethane. When in liquid form, these polymer molecules slide past each other freely. But when the glue dries, these polymers form long, tangled chains that bind surfaces together with strong adhesive forces.
The important thing to note is that these polymer molecules do not readily allow the flow of electrical charge. So when the glue hardens, it creates an insulating barrier between the glued surfaces rather than a conductive bridge. This is the primary reason standard glues do not transmit electricity.
Some examples of non-conductive glues include:
- White glue – Made from polyvinyl acetate emulsion. Used widely in school, office, and home settings for paper crafts and light duty bonding.
- Super glue – Cyanoacrylate formulations that cure rapidly when pressed between surfaces. Bonds tight but allows flexibility. Popular for assembling electronics, ceramics, plastics, etc.
- Epoxy – Created by mixing resin and hardener components. Produces rigid, heat-resistant bonds. Used for high-strength structural and industrial applications.
- Hot glue – Thermoplastic adhesives applied molten then hardened upon cooling. Allow quick, temporary bonding of materials.
- Wood glue – Utilizes polyvinyl acetate or polyurethane. Designed specifically for bonding wood while allowing some flexibility.
So whether it’s the PVA in white glue, the cyanoacrylate in super glues, or the epoxy resins, the polymers in these common glues simply do not support electrical conductivity. But why is this the case on a chemical level?
The Role of Water and Solvents
Another factor influencing the non-conductive properties of most glues is whether they are water-based or solvent-based formulations.
Water-based glues like white glue and wood glue use water as the carrier fluid to disperse the polymer resin molecules. Once the water evaporates as the glue dries, the resin remains as a solid adhesive. But water itself does not conduct electricity well, so these water-based glues are naturally insulating.
Solvent-based glues like super glue and epoxy use volatile organic compounds (VOCs) as the carrier fluid instead of water. Though some solvents can conduct, they eventually evaporate as the glue hardens leaving only the insulating polymer chains behind. This prevents electricity from flowing through the dried glue.
So in summary, the water or solvent carrier fluids used in most glues are not inherently conductive. Once they dissipate, the remaining polymers certainly do not help conduct current either. This combination results in a thoroughly non-conductive dried glue material.
When Are Glues Conductive?
While standard glues do not conduct electricity, there are some specialized conductive adhesives formulated to transmit electrical currents or signals. These glues contain conductive filler materials such as silver, copper, carbon, or nickel particles blended with the adhesive resin.
When the glue hardens, these conductive particles provide pathways for electrons to flow across the adhesive gap. Applications of conductive glue include:
- Bonding electrical components – In electronics assembly, conductive glue can mechanically attach and electrically connect circuit elements like chips, capacitors, or sensors.
- Printed circuit boards – Conductive traces printed from silver or copper particle-filled glue replace traditional etched metal PCB circuitry.
- Electromagnetic shielding – A conductive glue barrier can block electromagnetic interference between sensitive electronic devices.
- Flexible electronics – Conductive glues allow electricity transmission across flexible circuits that experience bending, folding, or vibration.
- Wearable technology – Adhesives with conductive nanoparticles are ideal for smart watch or fitness tracker applications where flexibility is required.
- Photovoltaics – Conductive glues can electrically interconnect the cells in solar panel arrays.
So conductive adhesives provide electrical functionality exceeding that of standard glues. But they represent specialty formulations that contain highly engineered conductive fillers. Their development came specifically in response to unique electronics assembly and flexible printed circuit demands that emerged relatively recently.
Glue Conductivity Considerations
When assessing the conductivity potential of any glue, here are some key considerations:
- Filler material – Does the glue contain metallic or carbon particles for conduction? Standard glues do not, while conductive adhesives do.
- Carrier fluid – Is the glue water-based or solvent-based? Both options generally evaporate to leave an insulating polymer.
- Polymer composition – Epoxy, polyurethane, cyanoacrylate, etc. do not conduct electricity well when hardened.
- Drying/Curing – Does the drying or curing process leave conductive particles suspended in a polymer matrix? Or does it produce an insulating barrier?
- Hardness – Hard, rigid glues when dried may preclude electron mobility. Flexible or elastic glues may allow better conductivity.
- Bond line thickness – Thinner glue lines focus conductive particles into a tighter space for increased conductivity.
Evaluating these factors will provide insight into whether a specific glue formulation has been engineered to conduct electricity or not. Most common glues are designed for adhesion, not conduction. But specialty conductive adhesives are an exception where electron transfer is desired across a bonded joint.
Examples of Glue Conductivity
Let’s take a look at a few examples to showcase when standard glues do not conduct versus conductive adhesives that do:
White glue – This water-based school glue contains polyvinyl acetate emulsion polymers but no conductive fillers. Hardened white glue forms an insulating barrier that prevents electricity from transmitting across the bond line.
Epoxy – The resin and hardener in epoxy glue cure to create rigid, highly crosslinked polymer chains. This thermoset plastic matrix does not support electron flow. Epoxy provides excellent adhesion but no conduction.
Hot glue – While hot when initially applied, this thermoplastic glue quickly hardens into an insulating solid. No conductive particles are present. Hot glue bonds are temporary and electrically insulating.
Conductive silver epoxy – Adding microscopic silver flakes to epoxy resins produces a glue that conducts electricity via the silver particle network. It provides strong adhesive bonds with electrical conductivity.
Carbon-filled cyanoacrylate – Tiny carbon grains dispersed in cyanoacrylate glue create conduction pathways. Upon hardening, the carbon-loaded super glue retains flexibility and high conductivity.
Copper nanoparticle polyurethane – Conductive copper particles combined with stretchable polyurethane make this glue ideal for flexible printed circuit applications where electrical transmission and bendability are required.
So the examples clearly show the difference between non-conductive general purpose glues and those with specialized conductive formulations. This distinction arises due to differences in composition and filler materials between the two glue types.
Conduction Considerations for Electronics Applications
Electrically conductive adhesives offer unique benefits but also some limitations compared to soldering for electronics manufacturing. Here are some considerations when using conductive glue for bonding and circuit assembly:
Bonding strength – Conductive glue can provide firm mechanical attachment, but high-temperature solder often creates stronger joints. Glues may work loose over time.
Electrical conductivity – The conductivity through hardened conductive glue is generally lower than pure metallic solder. This may limit applications.
Corrosion resistance – Silver or copper particles can corrode over time, gradually increasing joint resistance. Less of an issue with solder.
Process control – Achieving consistent bond line thickness and uniform filler dispersion requires precise process control during conductive adhesive application.
Cost – Specialty conductive adhesives typically cost more than standard solders per volume used.
Repairability – Soldering allows easier repair by reheating and disassembly. Conductive glues form more permanent bonds.
Operating temperature – Glues may not withstand high temperatures like solder, imposing operating limits for electronics.
So while conductive adhesives provide unique assembly and flexibility benefits, soldering remains superior for high-temperature, high-reliability, or high-conductivity electronics connections. Conductive glues complement soldering but do not provide a complete replacement in all situations.
The Future of Conductive Adhesives
Conductive adhesives represent an area of rapid innovation and product development. Here are some emerging trends:
- Nanocomposite fillers – Using tiny conductive metal or carbon nanoparticles or nanotubes allows lower filler levels for improved performance.
- Anisotropic conductivity – Glues engineered to conduct along one axis but insulate perpendicular to it allow dense component spacing on circuits.
- Hybrid solders – Combining conductive adhesive with solder paste or flux improves solder joint strength and electrical performance.
- Silver nanowires – Aligned silver nanowire arrays embedded in glue produce conductivity rivaling metals at lower cost.
- Graphene – Graphene flakes offer high conductivity for flexible adhesives and lower processing temperatures.
- 3D printing – Printable conductive “inks” containing adhesive polymers and metallic nanoparticles enable printed electronics.
So continued materials advances will expand the functionality and applications for electrically conductive glues across diverse fields from electronics to energy to aerospace and beyond.
Conclusion
Most common glues do not conduct electricity well due to their non-conductive polymer composition and water or solvent carrier fluids that evaporate upon curing. But specialty conductive adhesives have been formulated to provide electrical conductivity in addition to adhesive bonding. These glues incorporate conductive fillers like silver, copper, or carbon that enable electron flow when hardened. Conductive adhesives are advancing rapidly, offering unique assembly solutions, though traditional solder maintains advantages in some electronics manufacturing situations. Nevertheless, conductive glues represent an emerging technology area that will continue expanding into new applications across multiple industries.