Mohamed S. El-Aasser, a renowned expert in emulsion polymerization and polymer colloids, has served Lehigh as university provost since 2004 and was recently named vice president for international affairs. In 37 years with Lehigh, El-Aasser has earned numerous honors for his research and has advised 64 Ph.D. students, 53 M.S. students and 31 postdoctoral fellows. El-Aasser also directs Lehigh’s Emulsion Polymers Institute. Under his leadership, EPI’s annual short courses have attracted more than 5,000 scientists to Lehigh and to Davos, Switzerland, in the last three decades. El-Aasser and his students have published almost 400 technical articles.
Q: Give a general overview of emulsion polymerization and its history and impact on society.
A: During World War II, when the West was cut off from its supply of natural rubber, the U.S. launched a national project to seek a way to synthesize rubber. Emulsion polymerization emerged as a way of doing this. The process takes a monomer derived from petroleum products and converts it to a polymer. The polymerization yields a colloidal dispersion of the polymer suspended in water.
The original intent was to synthesize tires, conveyor belts and other products previously made from natural rubber. But because you can make polymers from different types of monomers, the process has evolved into a means of making plastics, paper and textile coatings, paints, adhesives and many other products.
Meanwhile, we’ve learned to control the size of the colloidal particles and make different kinds of polymers. We’ve come up with new processes, materials and approaches to create new products.
These polymer particles, because they are monodispersed, with each particle having the same size, are useful in applications requiring uniform metrics, such as calibration of instruments and microfilters. They are also useful in medical diagnostics and drug delivery, which is where the field is moving.
Q: What role did you and your colleagues play in the invention of miniemulsion polymerization in the early 1970s?
A: In classic emulsion polymerization, the first step is to make the nuclei. These nuclei, which are suspended in water, grow when the monomer, which exists in large droplets, diffuses through the water to the polymerization site. In a material with little or no water solubility this diffusion will occur slowly and it will limit or inhibit the transport of water-insoluble materials to the site of polymerization.
We took the monomer, the water and the emulsifier and subjected them to the right agitation. We ended up with monomer droplets suspended in water that were 50 to 500 nm in size, much smaller than we’d seen before. This allowed us to carry out polymerization inside the monomer droplets.
Q: How has the field of miniemulsion polymerization evolved?
A: We can now take tiny metal particles — gold, titanium dioxide — suspend them in the monomer phase, do miniemulsification and end up with gold or titanium dioxide particles embedded in particles 0.2 micron across. The encapsulated gold particles have found therapeutic and medical diagnostic applications. Because they are inert as well as tiny, they can be targeted to any part of the body.
The field is also giving us tools to do things with particles ranging down to 10 nm in diameter. This is helping us make small-volume, high-value-added materials in areas like biotechnology and drug-delivery systems, therapeutics and diagnostics, which require uniform-sized particles.
Q: In 1984, NASA named you and two colleagues Inventors of the Year for designing a device that synthesized the first products made in space. What products were fabricated, and what were the challenges of making them in zero gravity?
A: NASA wanted to do a scientific experiment to examine the influence of lack of gravity on the rate of a chemical process. Every theoretical treatise said there should be no influence. We proposed to determine if the lack of gravity influenced the rate of emulsion polymerization.
When you do polymerization, you end up with sub-micron-sized polymer particles. At that time, we could make monodispersed particles only as large as 1 micron. But some applications require larger particles. To obtain a larger particle, we suggested taking a sub-micron particle, swelling it with monomer and restarting polymerization. To do this, you need to maintain each particle’s individuality by using surfactants whose positive or negative charges create a repulsion between the particles.
As your particles increase in size and change from a monomer to a polymer, the density of the material also changes. Polystyrene is heavier than water, but the monomer from which you make polystyrene is lighter than water. At the same time, you have a faster rate of sedimentation or creaming, respectively. On earth you offset this by increasing the agitation to keep the particles in suspension. But this causes the particles to collide more frequently. When that happens they collapse and are no longer separate.
We told NASA that if we carried out polymerization in the absence of gravity, we could maintain the individuality of the particles while increasing their size with a surfactant and with the addition of more monomer. We were able to make 10-micron particles which under earth’s gravitational effect would sediment in a short period of time, but which in the microgravity of space remained suspended throughout polymerization.
Our size – 10 microns – turned out to have a useful medical application. Blood cells are 7 microns across. The 10-micron polystyrene particles we made have been used in hospitals for calibrating blood counters.
We ran five experiments in the space shuttles. We ended up making 30-micron particles. Since then, using our process, engineers have succeeded in making polymer particles as large as 215 microns that are very uniform in size. You learn through the process of making.
Q: The last quarter-century has seen a huge increase in papers and patents resulting from advances in miniemulsion polymerization. How does it feel to be one of the founders of this field?
A: It shows that science is not the property of any one human being. You take a good idea and develop it. Your idea becomes more mature because of the ingenuity of other scientists who expand on your work and make something even better out of it.
Q: You have served as department chair, dean and provost while teaching, mentoring graduate students and directing research centers. What is the secret of your organizational abilities?
A: All of us know we have to budget our time, set priorities and be focused. Also, it’s important to have a good team. I have been blessed with the students, faculty and staff whom I’ve worked with.
Q: What are the qualities a person needs to be a good researcher?
A: You start with good ideas and an interest in exploring them. You come up with the right scientific methodologies to explain the phenomena you see. You must be open to criticism because that’s what pushes you to find the answers. You should also be interested in disseminating your outcomes. It’s also important to reach out to your counterparts and to develop a team whose members complement each other. This pushes your research at a faster rate and helps your ideas mature.
Q: How do you come up with ideas for projects?
A: Some of them you dream up, but most come from listening to other people at conferences. You bounce an idea off your colleagues, they poke holes in it and that pushes you to refine your original idea.
Q: What do you consider your greatest achievement?
A: What’s most gratifying for me are the people. My graduate students and postdocs have helped me build my career and have become extremely successful. Many of them are now independent researchers. This human aspect of research is much more rewarding to me than anything else.
