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Research Lab Profile: The Freedman Group

30 January 2023
miriam freedman
Freedman standing behind her lab's cavity ring-down spectrometer, the first instrument she built at Penn State.


Kathryn: You began your career at Penn State Chemistry in 2010, and work in the areas of analytical, physical, and environmental chemistry. Can you explain how these different areas overlap in your research?

Miriam: Most research performed by chemists today does not fit nicely within just one traditional discipline of chemistry. The applications of my research are generally to atmospheric chemistry, but individual projects may address the physical chemistry origins of a phenomenon we observe or be focused on the analytical chemistry of instrument/sensor design.


Freedman Lab
Freedman with postdoctoral researcher Lucy Nandy, who is building a microfluidic set up to measure the ice nucleation of solid particles within aqueous droplets.


Kathryn: What projects are your group currently working on?

Miriam: My research group is working on four major projects.  

1) We study liquid-liquid phase separation in atmospheric particles, which has potential impact on heterogeneous chemistry, cloud formation, and the growth of new particles. We study the fundamental physical chemistry of the liquid-liquid phase separation process as well as applications of liquid-liquid phase separation to haze and cloud droplet formation (with Prof. Akua Asa-Awuku at the University of Maryland and Profs. Dabrina Dutcher and Timothy Raymond at Bucknell University) and to the growth of new particles (with Prof. Murray Johnston at the University of Delaware and Prof. Nicole Riemer at the University of Illinois).  

2) My research group is interested in the surface chemistry of materials that promote ice nucleation in clouds in the atmosphere. Aerosol-cloud-light interactions are among the poorest understood aspects of our climate system. Currently we work with synthetic materials in which the surface chemistry can be tuned, to determine the relative importance of different surface properties on ice nucleation. We are also exploring a few new directions for this research.  

3) We have recently developed carbon quantum dots for the measurement of aerosol pH. Aerosol particles are generally thought to be very acidic (pH = 0-4), which has significant consequences for their reactive chemistry and health effects.  

4) We have had ongoing collaborations with a number of other Penn State faculty to investigate the health effects of aerosol particles (either environmental or human-produced).  


Freedman Lab
Postdoctoral researcher Lucy Nandy working with the microfluidic device.


Freedman Lab
The Freedman group's microfluidics set up for the measurement of ice nucleation of solid particles within aqueous droplets.


Kathryn: Why is your research important now more than ever?

Miriam: My research is important for three main reasons.

1) We are currently experiencing the consequences of a warming climate, and to predict the consequences of climate change, we need accurate climate models. Among the least understood aspects of our climate system are the interactions between aerosol particles, clouds, and radiation (e.g. light from the Sun). The role of chemists is to characterize these interactions, which can then be used in different scales of models to better model our climate system.  

2) Air pollution is considered by the World Health Organization (WHO) to be the most lethal environmental hazard. Studies of the growth of new particles and physical characterization that has an impact on heterogeneous chemistry are both relevant for understanding the severity of air pollution events.  

3) The recent pandemic has given additional significance to the study of the aerosol particles that we produce through breathing, speaking, coughing, etc.  Understanding the physical properties of respiratory aerosol and how long it stays suspended in the air in indoor environments has significant consequences for determining disease transmission potential of different viruses.


Freedman Lab
Graduate student Heidi Busse is studying the ice nucleation behavior of water soluble aqueous polymers.
Freedman Lab


Kathryn: Has the recent pandemic shifted your understanding of aerosol particles?

Miriam: I have been delighted to see the shift in the field of atmospheric chemistry towards applying techniques of aerosol science to develop a better understanding of respiratory aerosol. I’ve appreciated learning a lot about a system I rarely thought about previously, and I look forward to seeing future advances in this area. For example, aerosol scientists have modeled how long respiratory droplets of different sizes will remain airborne, and I feel these studies have called into question social distancing guidelines, as respiratory aerosol can remain in the air for very long timescales, dependent on their size. A number of aerosol scientists have developed a cheap indoor air filtration system, using 4 air filters and a fan, that can easily be installed in schools or other areas of need. Some atmospheric chemists continue to engage in studies of mask efficiency. Others are debating how the viscosity of respiratory aerosol may influence how long viruses can survive in the air.

Kathryn: With undergrads, grads, and postdocs coming and going, all bringing different skills and ideas, how has your group's research changed over the years?

Miriam: Over the past five years, I have been focusing on expanding my research group into new areas and pursuing more collaborations. I wanted to pursue a career at a research-intensive university to 1) continually keep learning new science through research and teaching, 2) keep working on my writing, and 3) to train personnel (undergraduate students, graduate students, postdocs) over longer periods of time than a single semester. My hope is that each graduate student and postdoc starts with a project in my lab while making it their own, and eventually pursues areas of their own interests. This approach allows us to be able over time to explore new areas. Collaborations can start this process even faster, as my colleagues and I try to figure out new goals to work towards. I often think of each discipline of science as having its own language, and there is much to be gained from having to translate between disciplines to be able to work together.


Freedman Lab
Freedman and graduate student Heidi Busse.


Kathryn: In your opinion, what are some of your lab’s biggest accomplishments? What are some of your proudest moments leading your group?

Miriam: The projects I started in my first several years on liquid-liquid phase separation and ice nucleation have proceeded in very different ways. For the project on liquid-liquid phase separation, I feel there have been points in time where we have reached significant breakthroughs – showing that this phase transition was absent in sufficiently small particles and being able to flash freeze samples to watch snap shots of the phase separation process. For the ice nucleation process, we have developed an incredible understanding of the relative importance of different surface features, but the work has been slow and steady, performed by many personnel over a long period of time.  In both of these projects, I am just so proud of my group and where we have gotten, though I continually see inspiring work in my field that makes me want to try even harder to reach new accomplishments.

Kathryn: You served as Associate Department Head for Climate and Diversity and you received the 2019 Dean’s Climate and Diversity Award. What sort of diversity, equity, and inclusion initiatives have you implemented over the course of your career? 

Miriam: There are many items I have worked on in the DEI space. Some of the ones that I have worked on in the department were: have graduate student advocates who are available for students to talk to if an issue arises and they do not want to talk with a department ombudsperson, and facilitating student initiatives in the departmental Climate & Diversity Committee. At the college level, I have served on the Next STEPS committee at the college level to develop and deliver workshops for faculty on best practices in faculty hiring, graduate admissions, and promotion and tenure.  Through Next STEPS, I have also helped to start and administer a Launch Program to help new tenure-track faculty become more easily acclimated to the university over the first year in their faculty position.


Freedman Lab
Graduate student Kiran Pitta explaining to Freedman his studies on the phase transitions of atmospherically relevant mixtures of organic compounds with salts. The screen image depicts droplets with atmospherically relevant compositions showing the beginnings of crystallization of the inorganic compounds.


Media Contacts
Kathryn Harlow
Chemistry Communications Coordinator
Miriam Freedman
Professor of Chemistry