Intellectual merit

This collaborative award is focused on superbiphilic surfaces: these surfaces juxtapose regions that absorb water (superhydrophilic), and regions that have a strong tendency to remain dry (superhydrophobic and superrepellent). Such surfaces have demonstrated enhanced efficiency and thermal power removal in boiling and related heat management applications. The intellectual merit of this grant is to fabricate superbiphilic surfaces on metallic heaters to improve boiling performance and efficiency, experimentally characterize and model their performance in boiling.

The team at Iowa State University (ISU) explored a coating-less approach to manufacture superbiphilic surfaces. The coating-less method fabricates biphilic Copper surfaces, using a chemical treatment that modify the surface over multiple length scales, from mm to nanometer. Depending on process parameters, the process either remove Copper or add Copper oxides structures. Biphilic surfaces have been produced using a stamp or sacrificial material to selectively process different areas of the heater.

Using a mechanistic model, we have explained why metallic surfaces, which are typically hydrophilic, can be made superhydrophobic when roughened. The needed roughening involves the creation of multiple scales of roughness to minimize the contact between liquid and solid. Similar geometries are common to the leaves of plants such as rice and lotus.

The superbiphilic surfaces have been tested in commercial heat transfer devices called vapor chamber.

Other characterization experiments in a pool boiling have shown that Copper heaters with multiscale roughness could transition reversibly between a superhydrophobic and a superhydrophilic state, which is a new finding. Measurements show enhancement of boiling efficiency by 9 to 17 times.

A mechanistic model based on cellular and geometrical automata for pool boiling was developed with the group of Alejandro Clausse in Argentina.  Such model is faster and more suitable for modeling the complex physics of boiling on surfaces with complex wettability than computational methods based on continuum equations.

Broader impact

An underrepresented minority student has worked for six weeks on pool boiling measurements at Iowa State University. Her dream is to become an engineer. A graduate student was trained to manufacture biphilic surfaces on copper heater, and performed pool boiling experiments. A postdoc brought expertise on chemical surface modifications from his PhD and was trained on flow visualization and the design of a pool boiling cell. He is now a successful entrepreneur in an engineering startup that he leads.

The results and findings of the work were disseminated in one book chapter and seven peer-reviewed journal articles. I gave several invited talks in the following universities, Tsinghua and Peking University (China), Kyushu University and the University of Tokyo (Japan, as a fellow of the Japan Society for the Promotion of Science). Collaboration has continued with the Japanese team, using surfaces manufactured in this project.

A patent was granted and describes the manufacturing processes for wettability engineering developed in this research effort.

Wettability engineering findings of this project have been integrated in a graduate course developed and taught in 2017 ,?Microfluidics: Theory, Design and Devices?. Students in their comments appreciated the effectiveness of problem-based learning.

To encourage and explain the use of wettability engineering to enhance phase change heat transfer, the team has written with other colleagues a review article, already cited already 180 times.

Change/Problem

It is the duty of a primary investigator to report circumstances that negatively impact the performance of a Federal award. In an elected function in my academic department, I experienced a conflict with an administrator about the respect of academic freedom and governance rules. The administrator then interfered with my research team, harassed me in multiple ways, and projected similar accusations on me. Other administrators closed rank and disrupted further my ability to lead and perform research. These years of harassment brought unhealthy consequences for my mentees and our families. The dispute eventually was settled. The settlement grants me a new supervisor, ends most of the harassment, and reinstates some of my ability to lead a research team and pursue academic goals. I believe that the above episode illustrates how conflicts of interest and loyalty make it challenging for universities to investigate and prosecute issues of harassment. Maybe it is time to start a candid conversation on the goals, priorities and limits of the University as an institution.

Last Modified: 11/15/2019
Modified by: Daniel Attinger