Towards crack-resistant nanoparticle-based latex films
(Nanowerk News) Synthetic polymeric materials, such as plastic and rubber, have become commonplace in our daily life. Therefore, it is important to ensure that they are safe, durable and sustainable. This is especially true for synthetic latex films, which are widely used in packaging, biomedical and electronics.
But what exactly is a synthetic latex film? Simply put, they are a type of nanoparticle-based film that is produced by drying a mixture of polymer nanoparticles and water. As the solvent evaporates, the nanoparticles become denser until finally the interactions between the polymer chains at the nanoparticle boundaries produce a coherent film. Unfortunately, the latex films produced in this way are weak. In most cases, organic solvents and fillers must be added to the initial mixture to improve the mechanical properties of the final product. These additives are not only expensive but also harmful to the environment.
A research team from Japan, led by Associate Professor Daisuke Suzuki of Shinshu University, recently developed an innovative way to produce resilient and crack-resistant elastic nanoparticle-based latex films without the use of such additives. Their work is published in Langmuir (“Nanoparticle-Based Tough Polymer with Crack Propagation Resistance”), including contributions from Yuma Sasaki of Shinshu University and Professor Toshikazu Takata of Hiroshima University.
Key to their approach was a new molecular structure known as rotaxane, which consists of two main components—a ring-like molecule and a linear “axis” molecule. The ring-like molecules are threaded through the shaft molecules, which are then mechanically trapped due to the shape of the shaft terminations.
The researchers exploit this interlocking mechanism in rotaxane by creating ring-like molecules that chemically bond to one polymer chain and axle molecules to another. Next, they prepared a mixture of water and polymer nanoparticles via standard ultrasonication and subsequent polymerization which, in turn, was used to produce latex films. Stretching experiments performed on these films revealed that the rotaxane-based strategy produced some remarkable properties.
“In contrast to conventional nanoparticle-based elastic polymers, latex films composed of rotaxane-crosslinked nanoparticles exhibit unusual crack propagation behavior,” explained Dr. Suzuki. “The direction of crack propagation changed from parallel to the crack to perpendicular to the crack, resulting in increased tear resistance.”
This new approach to making latex films offers many advantages over conventional methods. Most importantly, no toxic additives are required to achieve reasonable film toughness. In addition, because only a small amount of rotaxane is required, the total film weight can be kept low while maintaining flexibility. The proposed latex film is also sustainable.
“They are degradable and can be easily disassembled into individual nanoparticles by simply immersing them in an environmentally friendly organic solvent, such as a dilute ethanol solution,” Dr. Suzuki highlighted. “These nanoparticles can then form films again after evaporation of the solution. In doing so, the findings of this study could help create materials that are highly durable and recyclable.”
Overall, the team expects their work to broaden the scope of new polymer film designs without additives. The material can thus be made biocompatible, with potential applications in biotechnology and medicine besides packaging, industrial coatings and adhesives.
