Ionic liquids have transformative potential across industries, particularly in green solvents and liquid electrolytes development. Our advances in polymer composites and ionic liquids have been lately focused on developing sustainable polymer recycling solutions.
First, ionic liquids are not liquids in the traditional sense. Yes, they flow, but something that flows doesn’t make it a liquid. The name ionic liquids has caught on, so we will stick with it. However, I want to clarify that they should not be considered, treated or thought of as liquids. Ionic liquids are highly ordered, flowing solids. I want to clarify this before jumping into applications. They are just the coolest class of materials there are.
Figure: 1: As the chain length of the ionic liquid increases specific structures are formed mainly due to segregation.
Di Cola’s work on 1-alkyl-3-methyl imidazolium Cl salts shows nanometer-scale structures, as observed using X-ray diffraction. The size of these structures depends on the length of the alkyl chains. This supports molecular simulations that suggest alkyl chains tend to group and then likely form clusters of ionic moieties, resulting in nanostructures. The size of these structures changes with temperature. However, above its glass transition temperature Tg , the behavior becomes very complex. These findings offer insights into room-temperature ionic liquids’ unique physical and chemical properties.
It is well known that ionic interactions are orders of magnitude stronger than Van der Waals interactions and it gives insight into the very low vapor pressure of these materials. That said as these are very strong interactions, we can design systems that improve materials’ properties overall and open a new frontier in material science. At RoCo, we enjoy working with ionic liquids; the structural flexibility of these materials excites us.
Indeed, ionic liquids reshape industrial processes by offering non-toxic, sustainable, and highly effective solutions for persistent corrosion prevention and polymer recycling challenges. Dr. Hunaid Nulwala and Ms. Nulwala recently shared their technical work about RoCo® and LumiShield at the Rochester Institute of Technology. The polymer work was carried out in collaboration with Prof. Carlos Diaz, with funding from the US Department of Energy, to create the next generation of compatibilizers. These ionic liquid solvents have transformative potential across industries, particularly in green solvents and liquid electrolytes development.
Our advances in polymer composites and ionic liquids structure support sustainable polymer recycling solutions.
Collaboration with the Rochester Institute of Technology has been pivotal for our entrepreneurship initiatives to commercialize sustainable solutions. Lets now look at the problem of polymeric blends.
The Problem: Polymers Don’t Mix — An Entropy and Enthalpy Perspective
The immiscibility of most polymers is a balance play between entropy and enthalpy contributions, as described by the Gibbs free energy of mixing:
∆𝐺𝑚𝑖𝑥 = ∆𝐻𝑚𝑖𝑥 − 𝑇∆𝑆𝑚𝑖𝑥
Where:
∆𝐺𝑚𝑖𝑥: Gibbs free energy of mixing
∆𝐻𝑚𝑖𝑥 : Enthalpy of mixing
∆𝑆𝑚𝑖𝑥: Entropy of mixing
𝑇: Temperature
For polymers to mix, they must be negative. However, in most cases, this condition is not met due to the following factors:
1. Low Entropy of Mixing ∆𝑆𝑚𝑖𝑥:
Entropy is the measure of randomness or disorder in a system. For small
molecules, mixing significantly increases entropy because the molecules can distribute freely among one another. This is not the case with polymers. Polymers are bound together so they are difficult to mix. Couple that with the size and the volume they occupy. What this means is that they have few configurations to mix. Hence, there is a very low Entropy of mixing.
Basically, the entropy gained from mixing polymers is negligible due to their size and restricted configurational freedom.
2. Positive Enthalpy of Mixing ∆𝐻𝑚𝑖𝑥
Interactions between polymer molecules when they mix. For most polymers ∆𝐻𝑚𝑖𝑥 The enthalpy of mixing represents the energy change associated with the is positive due to Incompatible Intermolecular Interactions, as most polymers have weak interactions (Van der Waals forces) between their chains. These weaker interactions do not compensate for the energy required to break the stronger self- interactions and the solvent bonds within each polymer type. The bottom line is that both Entropy and Enthalpy favor phase separation.
The combination of a negligible entropy gains and a positive enthalpy of mixing leads to a situation where is positive. This makes the mixing of polymers thermodynamically unfavorable, and they remain immiscible.
Even when we look at similar molecules, such as High-Density Polyethylene (HDPE) and Polypropylene (PP), they are not miscible with each other. Overcoming immiscibility is a multi-billion-dollar opportunity.
Implications in Industry
The immiscibility of polymers is a critical challenge in composites, recycling and materials science. In recycling, it limits the ability to reuse mixed polymer waste. One way is to make the interfaces ionic, thus improving the use of ionic bonds and phase segregation to make polymeric blends that provide significant value.
Polymer Recycling with Reactive Ionic Liquids: The ionic liquids developed at RoCo have improved mixed PP/HDPE systems, overcoming both tensile and impact properties. These ionic liquids have transformative potential across industries, particularly in green solvents and liquid electrolytes development. Our advances in polymer composites and ionic liquid’s structure support sustainable polymer recycling solutions.
To build on the theme of ionic liquid as a compatibilizer, RoCo technology works by introducing ionic interaction at the interface of the phase separation and also modifies the polymers.
Figure 2: Introducing Ionic moieties at the interface significantly improves the phase separation strength.
Our initial results show that using reactive ionic liquid improves both tensile strength and properties. Our study used 0.5 wt.% ionic liquid, which improved the impact and tensile properties.
Figure 3: We see improvement in both impact and tensile properties.
Conclusion:
Ionic liquids offer significant advantages as a compatibilizer. However, this technology is nascent, and RoCo will keep working on this to take it to the market. These ionic liquid solvents have transformative potential across industries, particularly in green solvents and liquid electrolytes development.