Science & Technology (Commonwealth Union) – When a carefully placed step has the ability to make a major hurdle easier to solve, it opens up new possibilities. Scientists from Cornell University have indicated a similar principle may apply to the way nanoparticles are changed into crystals.
People really like crystalline nanomaterials because their precise, orderly structures give them unique properties that are useful in technologies like data storage and optical systems. But making nanoparticles from these well-ordered crystals can be hard. Instead of forming neatly, the particles often get stuck in arrangements that don’t turn into the right crystal structure.
In a study published on Feb. 26 in the journal Proceedings of the National Academy of Sciences, scientists from the Cornell Engineering report that mesophases—states of matter that lie between fully disordered liquids and solid crystals—can serve as useful intermediate stages that help crystals form more quickly and consistently. Examples of mesophases include liquid crystals commonly used in electronic displays and sensors.
The senior author Fernando Escobedo, the Samuel W. and M. Diane Bodman Professor in the R.F. Smith School of Chemical and Biomolecular Engineering pointed out that it had long suspected that mesophases might be beneficial because they occur along the pathway to a crystalline state.
They further indicated that their findings show that mesophases truly function as stepping stones, offering what could be described as a ‘golden path’ toward successful crystallization.
Through sophisticated computer simulations, Escobedo and B. P. Prakash, Ph.D. ’24, analysed multiple nanoparticle systems to observe how they evolved from a disordered state into well-ordered crystalline structures. In every instance, systems that first passed through an intermediate mesophase formed crystals more rapidly than those attempting to crystallize in a single step. The study explains that crystallization is normally slowed by the need to overcome a free-energy barrier.
Escobedo compared the process to clearing a physical obstacle and indicated that it is like attempting to jump over a one-metre-high barrier. He further indicated that it is difficult, but if the jump is broken into two smaller steps of half a metre each, the task becomes far easier and more efficient, that is effectively what the mesophase does.
The team was also able to precisely measure the free-energy barriers involved as well as the rates at which crystallization occurred. Their findings showed that mesophases ease kinetic bottlenecks and, in some cases, accelerated crystallization by several orders of magnitude. In addition to speeding up the process, the presence of mesophases may also help improve the overall quality of the resulting crystals.
“It’s a lot easier to anneal defects in a mesophase because it’s a more mobile, more flexible phase,” explained Escobedo. “There are different ways you can ensure that it’s a more homogeneous state and then when that phase crystallizes, you end up with fewer defects.”
The results offer new guidelines for scientists and engineers working with nanomaterials, outlining how experimental conditions can be arranged so particles assemble in the correct order. By identifying which intermediate stages are most beneficial, the study highlights ways to construct material structures more dependably while reducing the risk of particles becoming trapped in unwanted crystal forms.
Escobedo indicated that even if a material has not previously been observed to form a mesophase, it can often be encouraged to do so by adjusting external conditions or modifying the design of the nanoparticles.
Although the research centred on nanoparticles, Escobedo noted that the same principles could apply to other systems, including polymers and proteins, where intermediate phases frequently emerge during the assembly process. By deliberately making use of these transitional states, scientists may be able to produce new materials with unique properties more efficiently.
