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Purdue Professor Creates Whitest Paint to Combat Global Warming | Xiulin Ruan

This is a podcast episode titled, Purdue Professor Creates Whitest Paint to Combat Global Warming | Xiulin Ruan. The summary for this episode is: <p>In this episode of This Is Purdue, professor of mechanical engineering at Purdue University,&nbsp;Xiulin&nbsp;Ruan,&nbsp;discusses&nbsp;his newest invention –&nbsp;ultra-white paint.&nbsp;</p><p><br></p><p><span style="color: windowtext;">In an effort to&nbsp;curb global warming,&nbsp;Xiulin&nbsp;and his team created the&nbsp;whitest white acrylic paint, which reflects 98.1 percent of sunlight and deflects infrared heat, allowing buildings to cool below the surrounding air temperature.&nbsp;</span></p><p><br></p><p><span style="color: windowtext;">Listen in as&nbsp;Xiulin&nbsp;shares&nbsp;his surprise at the amount of attention the invention received,&nbsp;not only in the science and engineering world, but also in the art&nbsp;space. Plus,&nbsp;he breaks down how this paint can help people save money on&nbsp;their electric bills.&nbsp;&nbsp;</span></p><p><br></p><p><br></p>

Kate Young: Hi. I'm Kate Young, and you're listening to This is Purdue, the official podcast for Purdue University. As a Purdue alum and Indiana native, I know firsthand about the family of students and professors who are in it together, persistently pursuing and relentlessly rethinking. Who are the next game changers, difference makers, ceiling breakers, innovators? Who are these Boilermakers? Join me as we feature students, faculty, and alumni taking small steps toward their giant leaps and inspiring others to do the same.

Xiulin Ruan: We did some analysis on using our paint on the hot climates in Reno, Nevada or Phoenix, Arizona. Those are hot and dry climates and will be ideal location for using our paints. Our analysis shows that during the summer months, using the paints can save up to 70% of the air conditioning cost.

Kate Young: You may have heard about this latest guest on This is Purdue through national media outlets like CNN, BBC, Fast Company, Yahoo, and, oh yeah, The Tonight Show with Jimmy Fallon. Xiulin Ruan is a professor of mechanical engineering at Purdue University. His giant leap as a Boilermaker? Inventing the whitest paint on record in an effort to curb global warming. We'll get more into the paint's effect on climate, but one of the most interesting things Xiulin shared with me, when the team first started this project, they didn't actually set out to create the whitest white paint.

Xiulin Ruan: When we started the project about seven years ago, we had the energy savings and fighting climate change in mind.

Kate Young: That's right. This invention is seven years in the making. Xiulin explains.

Xiulin Ruan: We started working on this in 2014. We tested many different materials, concentrations, and the different particle sizes and so on. So it does take a lot of effort, and many students who graduated and then new student continued the effort to really make it happen. So using radiative cooling in paints really started in the 1960s. At that time, people were trying to create white paint that can reflect the sunlight as much as they can. At the same time, we know any surfaces, when you put on the roof, they're going to emit their own heat to the surrounding as well. So the problem was at that time the whitest paint the people created can reflect 80% to 90% of sunlight, which means they absorb 10% to 20% of the sunlight. So that's still too much heat absorbed from the sunlight, and that's more than the heat they lose. So although they are cooler than the other colored paints, they cannot be cooled below the ambient temperature. A few years back, we started on this, first inspired by a group at the Stanford University which created multilayered metal structures that can do below ambient cooling but was very expensive, not viable for buildings. So we went ahead and think about whether we can create the paints to be below the ambient temperature, because we had much better nanotechnology then a half a century ago. So we eventually came up with this new paint formula with a few innovations compared to the commercial white paints.

Kate Young: This new whitest white acrylic paint reflects 98.1% of sunlight, compared with the 95.5% of sunlight reflected by the team's previous ultra- white paint. It defects infrared heat, allowing buildings to cool below the surrounding air temperature. In fact, the team's tests have shown that the paint is able to keep a surface around eight degrees cooler than its ambient temperature in the afternoon and up to 19 degrees cooler at night. But what makes this paint the coolest? A very high concentration of a chemical compound called barium sulfate. It's also used to make photo paper and cosmetics white. Barium sulfate was used in the paint and pigment particles of various sizes, which allows the paint to scatter more of the light spectrum from the sun. But the barium sulfate used had to be just the right amount. If they used a higher concentration of this, it would likely cause the paint to break or peel off, according to the research team. Xiulin walks us through how this new paint differs from commercial paint you can go buy at a local hardware store. Tell us about what's in the paint. How is this different from if you go to the store and buy a regular can of paint?

Xiulin Ruan: It has a few key innovations compared to the commercial white paints you can buy. I mean, that took us a long time to figure out, actually, each aspect, each innovation over the years. Now, first, the commercial white paints are based on titanium dioxide. So, titanium dioxide reflects very well in the visible portion and near- infrared portion of the sunlight, but it absorbs the UV. So we first went out to look for materials that would not absorb UV at all. Those included oxides, carbonates, and sulfates, so those were our candidates. But that's not sufficient. We came to realize that we need a much higher concentration in the commercial paints. So commercial paints, they usually have less than 10% of the particle loading, and that's not sufficient to reflect sunlight for the energy purpose. So we tested different particle loading and eventually landed at 60%, and it's appropriate number to sufficiently reflect and to scatter sunlight. At the same time, it still behaves like the paints. So, a third key innovation that really push our paint to the performance we see today is not using a uniform size. That's a little bit counterintuitive at the beginning, but our predictions showed us eventually if you use a single size, it only reflects one wavelength of the sunlight really well, not the other wavelengths. So once you have different particle size in your paint, each size will be responsible to reflect one wavelength in the sunlight, so eventually the whole spectrum of sunlight can be reflected effectively. So these are the three key differences from the commercial paints. I can summarize again. First is a material that does not absorb UV. Second, high particle concentration. Third, non- uniform particle sizes.

Kate Young: Throughout Xiulin's journey with creating this paint and pushing the limits on their previous white paint, of course, came with challenges and roadblocks. The team had considered over 100 different materials, narrowed them down to 10, and tested about 50 different formulations for each material.

Xiulin Ruan: To be honest, seven years ago, we didn't know that we would achieve such great reflectance today. So we did run into a lot of roadblocks, but we're really happy that working with our students, postdocs, we were able to overcome these challenges, and that led us to arrive where we are today. So, each innovation actually came out of the challenges that we were facing. For example, at the beginning, we were trying to push the titanium dioxide that is used in commercial paints to perform very well. So we made many different trials based on titanium dioxide, different particle loading, different substrate. At that time, we didn't believe we were able to achieve this single layer, so we tried putting these materials into a two- layer structure and so on. So, after many trials, we were not able to get fully below the ambient temperature, and then we came to realize it's the materials' problem. So that's how we set out to look for other materials, like barium sulfate, calcite, and so on. But even with that, we tested the many materials, maybe as many as a hundred materials. Some materials, we expected them to work, but it didn't work eventually. We also had a hard time on the matrix material, like polymer, to use. Some of the particle failures, they don't really like the polymer. I mean, we are not able to disperse them so well in the polymer matrix or binders, so we would explore that to find the good pair of the filler as well as the polymer to have a good dispersion. We came to realize the particle concentration was not high enough, so we tested many particle concentration. And the last maybe challenge I want to highlight is that after we'd done all these, we were trying to explain the performance, why it is 98.1%. So, using previous models, we are not able to match the prediction with our experiment data. To be more specific, the theory says that reflectance should be lower than the experimental measurements. And we spent time on that, eventually find out that that's because we have different particle size in it. Previously, people just inaudible the non- uniformity in the size. We found that it plays a very important role increasing your reflectance from just above 90% now to 98.1%. So, I have to say that the innovations were pushed by the challenges we were facing, and that's how the science and engineering works.

Kate Young: I love that quote."The innovations were pushed by the challenges we were facing, and that's how science and engineering works." As Boilermakers, Xiulin and his team continued in their persistent pursuit of making this paint a reality. Let's dig further into how this whitest white paint can help our planet. Xiulin's team calculated that if 0. 5% to 1% of the Earth's surface was covered in this paint, it would reverse the total effects of global warming to date. When applied to the roof and walls of a building, the paint can reduce the need for air conditioning and the associated carbon emissions.

Xiulin Ruan: First of all, if you compare our paints against commercial white paints, we can see that it reflects 8% more of the sunlight back to the deep space, and it provides cooling by its own emission. So that will translate to about 10 kilowatts more cooling power from our paint compared to commercial paints if you have 1, 000 square feet one- story story house. Okay? So what does that mean to the energy sector and the global warming? Now, on one hand, again, using the house as example, you can save about 10 kilowatt hour power every day, right? That power usually comes from burning fossil fuels, which involves carbon emissions. So without using any power, our paint cuts carbon emission, that aspect. The other very important aspect for the conventional air conditioners, they just move the heat from inside of your house to the outside ambient, but the heat still stays in the city. It still stays on the Earth. So that really contributes to the urban heat island effect in cities that create many issues in large cities, even pose some serious threats to health. On the other hand, the heat is on the Earth and contributes to warming the Earth up. So total different from that, our paint on the roof, it sends off all the heat from the sun and from its own emission directly through the atmosphere and lost to the deep space, so the heat totally goes off the Earth.

Kate Young: To put it in perspective, 10 kilowatts is more powerful than the central air conditioners used by most houses. New York recently coated more than 10 million square feet of rooftops white, and California has updated building codes to promote cool roofs. And painted on top of your average 1, 000 square foot ranch house, the team estimated that a coat of the super white paint alone could save an estimated$ 1 per day on your electric bill during the summer months. I'll let the expert break it all down for us.

Xiulin Ruan: Now we can use that 1, 000 square feet single- story house as an example. Our paint compared to the commercial white paint can provide 10 kilowatt additional cooling power if we use typical air conditioner efficiency numbers, so that translate to save about 10 kilowatt hour electricity per day for this house. If we use that 10 cents per kilowatt hour price, that's about one hour per day saving for the house. So I can give you another example. We did some analysis on using our paint on the hot climates in Reno, Nevada or Phoenix, Arizona. Those are hot and dry climates and will be ideal location for using our paints. Our analysis shows that during the summer months, using the paints can save up to 70% of the air conditioning cost. In other words, in certain days when it's not too hot, you do not need to turn on your air conditioners at all. The paint will just provide enough cooling for the temperature indoor to be comfortable for human beings. Now, if the outside becomes very, very hot, you need to turn on your air conditioner still, but the paints can offset a lot of heating and can reduce that amount for the air conditioner. So, overall, it saves up to 70% of the power, considering typical weather over a few months in the summer.

Kate Young: So what if people don't necessarily want a white roof? Do you have plans for the future of taking this formula and creating different colors with it?

Xiulin Ruan: Sure. Yeah. That's a great question. First of all, I want to highlight that many locations, people do like white color. For example, we got a lot of the inquiries from the Middle East, Africa, Central America, South America, or even the southern part of the United States. It's good to know that many locations, like Greece, they were painting their house already white. They were asking us whether they can get our white, which is whiter than the commercial white available these days. In New York, they were painting like a million square feet of roof area to be white to mitigate the urban heat island effect, so people are already using white. But, of course, other people may not like white. They want other color. So, that's definitely on our mind. Our white paint provides a great platform, actually, to develop color paints that are cooler than the other commercial color paints. Because our white, the barium sulfate base, can be a base pigment. Just like the other colored commercial paints, they are based on TiO2, or titanium dioxide, so we can modify the paints to be based on barium sulfate, and we are optimistic that the color paints created this way should be cooler than the color paints on the commercial market. It may not necessarily to cool below the ambient temperature anymore, because color paints means you got to absorb some portion of the sunlight to show the color. Yeah, that's something we're working on right now and that we hope to report some results in the future, that we have cooler color paints then the color paints you can get on the market today.

Kate Young: If you're ready to run out to the store and grab a can of this paint, it's not on the shelves just yet. The good news, though? This paint isn't going to be crazy expensive. It'll be comparable to a normal can of paint.

Xiulin Ruan: Our lab can only produce small amounts for painting samples or like a inaudible or so, but we are working with a large corporation towards commercializing our technology. So we need to do more testing and optimization of the paints to make sure it has a long- term reliability, it can anti- dust and last for many years. Yeah, we are working hard on that, and hopefully we will see this eventually on the market. If we do everything quick, a year or two or so. Yeah. I mean, we do get a lot of inquiries from people, especially from the hot climate. A large customer would be India. Very hot. If you use too many air conditioners, the heat island effect is very serious there. So pushing this into the market will really help a lot of people that really have the cooling needs. The cost is comparable to the commercial paints. So the barium sulfate pigment is actually slightly less expensive or maybe, at most, comparable to titanium dioxide. And, beyond that, the manufacturing process of our paint is compatible with the industry practice right now, so we expect that the final cost of our paint should be comparable or even slightly cheaper than the commercial paints on the market.

Kate Young: Xiulin realized this paint would make waves in the science and engineering industry, but what he didn't know was that artists and even art museums have reached out to the team about the ultra- white paint. Why? Artists have expressed interest in your work, as well as, obviously, all of the attention you're getting from the scientific and engineering world. But how does it feel to know that there may be art created with this paint someday?

Xiulin Ruan: Yeah, that's a pleasant surprise. Again, as we publish our work, we didn't really emphasize the color aspect, but it's great to know that the artists got interested in this and they have the need to push the whitest white to create unique artwork. Actually, I have quite a few museums who contacted me, asking for samples to donate it to their collection, the whitest that they can have. So I already agreed to send them samples, including the US as well as from overseas, such as Singapore. Some of those museums, they have the blackest black, the Vantablack, if you know that. Yeah, they want to put the white as a counterpart in their collection. So that's really interesting. Other artists already emailed me, asking about where they can get the paint, or their interest of creating this paint. Definitely something interesting we are thinking about, and it's good to know there is a market on the art side, aside from the energy and the climate aspects. I didn't expect people who are interest in in so white, because white is, to me, before all these, a boring color, right? That you like blue or red or so. I mean, it's quite educational to me to see there is so much interest just into white and the black.

Kate Young: And what about all of the attention Xiulin and his team has received in the past few months? It's not everyday you get mentioned on an Emmy- winning late night show. At this point, you've been featured in hundreds of articles. You've been on CNN. You've been on the BBC, Fast Company, and Jimmy Fallon even mentioned this paint on The Tonight Show. That's crazy. So, what's your reaction to all of this response to this white paint?

Xiulin Ruan: Yeah, well, it definitely much exceeded what I expected. Every time we saw a big news outside of our expectation, we say," Wow, pretty good." The Tonight Show and so on, Jimmy Fallon. So it's great to get this level of publicity for paints, but we are really glad that our work together, the work in the field, now has contributed to raise awareness among the public about how important it is to save energy to help our environment and combat climate change. I think that that's the point that with all of this media reaches out to the corners over the globe, we contributed to that aspect. I mean, how the paints can help. Something as simple as paint can really help extremely important issue of the climate change.

Kate Young: Right. And you guys are certainly contributing to that conversation. So were you surprised by all of this media attention, too?

Xiulin Ruan: Yeah. Well, we were expecting coverage by a lot of media, but we were surprised by certain coverage, like the talk show, right?

Kate Young: Right.

Xiulin Ruan: Yeah. Then we got people from weather stations. They came to Purdue and shoot videos in our lab, too. So that really amazed us, on the climate side. Yeah. But these talk shows, we definitely helped spread the work and help. Also, maybe they didn't really focus on the energy/ climate side, but when people get more into either the news articles or even our paper, I realize that the paints can help. So, using white paints to help our climate has been there for some time, but people were resistant to that, if you don't like the white color. So I hope our work can contribute a little bit to the people's willingness to think about using paints to help our environment and the Earth's sustainability. Yeah, I think that would be great if our work made a tiny contribution towards that.

Kate Young: As for the Purdue University community, Xiulin shares this invention would not have happened without the resources and talent Purdue has at its fingertips.

Xiulin Ruan: Purdue definitely played a critical role for all this that we have achieved. Just a few aspects. Purdue has very strong academic reputation that help our lab and others' lab to attract the best students and postdoc fellows and the researchers all over the world. So I will say that without the high quality of our students and scholars, this work wouldn't have been possible. Lots of my students who worked on this project, they team up with solutions to the challenges we were facing, so that's really, really important. I feel the support from students, from colleagues, from administration and from industry members, so Purdue really provided the right and all the necessary resources, including human resources and the facilities.

Kate Young: In the meantime, what's Xiulin thinking about next? Well, naturally, he's already contemplating what he and his team can achieve in the future.

Xiulin Ruan: Thank you for the great questions that really inspired me to think about our journey over the many years and how the students contributed. And then many graduated or completing their postdoc experience and have their own successful either academic journey or are in the industry. It's a great moment also to reflect all those and to look forward what we are going to achieve in the future.

Kate Young: If you'd like to learn more about Xiulin and his team's research on this ultra- white paint, please visit purdue. university/ whitepaint. Thanks for listening to This is Purdue. For more information on this episode, visit our website at purdue. edu/ podcast. There, you can head over to your favorite podcast app to subscribe and leave us a review. And, as always, Boiler Up.

Today's Host

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Kate Young

|Digital Content Strategist + Host, This is Purdue Podcast

Today's Guest

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Xiulin Ruan

|Professor of Mechanical Engineering, Purdue University

In this episode of This Is Purdue, professor of mechanical engineering at Purdue University, Xiulin Ruan, discusses his newest invention – ultra-white paint. 


In an effort to curb global warming, Xiulin and his team created the whitest white acrylic paint, which reflects 98.1 percent of sunlight and deflects infrared heat, allowing buildings to cool below the surrounding air temperature. 


Listen in as Xiulin shares his surprise at the amount of attention the invention received, not only in the science and engineering world, but also in the art space. Plus, he breaks down how this paint can help people save money on their electric bills.