▲ Pak is leading the Soft Matter Physics Research Group of the CSLM, focusing on research on nonequilibrium fluctuations and solid-liquid interfaces.

"The term 'Soft Matter' started to be widely used from the early 1990s and research in this field is flourishing in the U.S., Japan and Europe."

At the CSLM, Pak assists Director Granick in managing research topics and administrative work, as well as helps foreign researchers adapt to a new environment. He also leads the Soft Matter Physics Research Team to develop nanoscale engines and to study interfaces between solids and liquids.

The New York Times covering his work

Pak has a long relationship with soft materials. He earned a Ph.D. in physics from the University of Pittsburgh with his research on turbulence in the energy transfer where large-scale eddies, which contain most of the kinetic energy, split into smaller ones until the eddies become so small that their kinetic energy is converted to the thermal energy.
As a postdoctoral research associate, he studied the 'chaos experiment' and granular systems at Duke University and liquid thin films at Kansas State University. His research encompasses various areas but they all boil down to one thing: Soft Matter.

▲ Experimental physicist Pak studies theoretical physics as well.

When he was at Duke University, his research was published in the journal Nature. It is possible to change properties of grain and powder by floating them using gas or wind and coating their particle surface. His study showed that vibrating granular materials with a force stronger than gravity can produce the same result.

After returning to Korea in 1995, Pak studied soft materials through optical methods and performed thermodynamic experiments, serving as a professor at PNU. In 2001, Pak and two colleagues published a paper on silo jamming in the journal Physical Review Letter and the New York Times covered the research. He also drew attention in 2013 by developing a method to generate electricity using water droplets. His team succeeded in generating electrical power by mechanically modulating the shape of distilled-water droplets for the first time in the world and coming up with a supporting theory. At the lab, the team was able to light up 6 LED lights with only 1g of distilled-water. The outcomes were published in the journal Nature Communications and now many scientists refer to this research for energy harvesting.

Stimulating global interdisciplinary research

Pak is an experimental physicist but he also is interested in theoretical physics. Free energy, which determines thermodynamic properties of materials, is not calculable in non-equilibrium processes such as chemical reactions. However, with his experiment, he has proved the theory that free energy change can be calculated by observing and analyzing fluctuations in physical quantities and published the results in Physical Review Letters. That explains how he became the first experimental physicist who served as chair of the Thermal & Statistical Physics Division of the Korean Physical Society for two years even though most of the division members are theoretical physicists.

Pak had been a physics professor at PNU for 19 years before he moved to UNIST and joined the CSLM within IBS in August 2014. He said, "The opportunity offered by the Center was very timely as I was feeling the need for change. IBS certainly provides a wonderful research environment but what's special about UNIST is that it differentiates itself from existing universities and colleges with its creative systems and passion." UNIST boasts of active interdisciplinary research by lowering barriers between different disciplines. Also, it is attractive for foreign researchers because all academic courses are conducted in English and most of faculty members are young and passionate. These merits can also be found at the CSLM. Dr. Bartosz GRZYBOWSKIi, Tsvi TLUSTY and other foreign researchers who have studied diverse fields are serving as group leaders. And it is easy to see researchers from various disciplines, including biology, physics and chemistry, passionately discussing their research at the lounge designed by Pak.

Recently, his team focuses on developing a 100nm engine and studying the charge distribution near the liquid-solid interfaces utilizing the method of electrical power generation by mechanically modulating liquids. Developing a nanoscale engine starts from an experiment to confine a colloidal particle in water in an optical trap, which was made through shooting ultra-fine laser lights. Colloidal particles continue their random motion in the optical trap, colliding with water molecules, but they cannot escape from the trap due to energy barriers. His group has succeeded in driving colloidal particles to a certain direction by delicately adjusting the position of the laser. This experiment can prove "Maxwell's Demon"* – a thought experiment designed to question the possibility of violating the Second Law of Thermodynamics and is expected to provide a basis for the development of technologies that can maximize energy efficiency in nanoscale systems.

* "Maxwell's Demon" is an imaginary creature that the scientist James Clerk Maxwell conceived to contradict the Second Law of Thermodynamics, which states: The entropy of an isolated system never decreases over time. Let's suppose a small door which divides two adjoining rooms, A and B, of different temperatures. If the door is kept open, fast-moving hot molecules get mixed up with slow-moving cold molecules and in the end, A and B reach the same final temperature. But if a demon, who can see individual molecules, guards the door, it can selectively open and close the door to allow only swifter molecules to pass from B to A and slower ones to pass from A to B. After a while, A will be filled with fast molecules, while B is left with the slow ones. Consequently, the demon will raise the temperature of A and lower that of B, without the expenditure of work, in violation of the Second Law.

▲ Pak enjoys interacting with fellow researchers at the lounge that he designed.

Pak concluded the interview saying, "I hope the CSLM becomes a globally-recognized research center in the field of soft materials. And my personal goal is that my research on fluctuations in nanoscale systems can contribute to a better understanding of the Second Law of Thermodynamics, which describes a non-equilibrium system - a system whose equilibrium is broken by external inputs. In addition, I would like come up with a new research method for solid-liquid interfaces."

Pak is now busy preparing for the IBS Soft Matter Summer School, an important event in the field even supported by the US National Science Foundation. Marking its fourth anniversary this year, this event will be held from July 4 to 14 at the CSLM in UNIST. The Summer School invites 10 world-famous scientists to deliver a lecture and serves as a forum for their lively discussions with 70-80 young researchers.