image: Liquid in foams drain downwards through Plateau borders under the action of gravity. This leads to accumulation of liquid at the bottom, which can either pinch-off or simply stay at the bottom as the foam slips down.
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Credit: Tokyo Metropolitan University

Tokyo, Japan – Researchers from Tokyo Metropolitan University have uncovered a unique mechanism by which foams on walls drain and slip over time. They showed how a foam can lose liquid via “pinch-off”, like droplets from a faucet, finding that the amount of liquid and the extent of the foam determine exactly how it drains. Importantly, they identified thresholds between draining regimes common to different foams that may apply to everyday foam materials.

As spring cleaning comes around, many will be faced with the task of spraying walls with various commercial foam products, for degreasing, cleaning, or polishing. Similar situations arise for shaving, applying sealants or protective layers, or disinfecting surfaces. For all these examples, the length of time the foam stays stable against gravity plays a crucial role in how they do their job. A shaving foam, for example, would be useless if it ran off before we finished shaving. A more serious implication would be for disinfecting foams which drained before dangerous pathogens were dealt with. That makes understanding the basic mechanisms behind how foams stay on surfaces a topic of interest for both scientists and industry.

Assistant Professor Marie Tani and Professor Rei Kurita of Tokyo Metropolitan University have been using simple foams to try to understand how exactly foams drain and evolve. Studying a two-dimensional foam trapped between two flat surfaces, they found that the foam didn’t always just slip down under gravity. Foams are made of junction lines between bubbles called Plateau borders, which also form a connected channel for liquid. Under gravity, the liquid in the foam tends to follow these channels and make its way to the lowest point, making the lower part wetter than the upper part. Sometimes, they found that this excess liquid could form a string which stretched down from the lowest bubble before breaking off. This is similar to a phenomenon called “pinch-off”, commonly seen for droplets hanging from faucets. The sudden, drastic loss of liquid can significantly destabilize foams. Though previous works had looked at the pinch-off of foamy liquids, this was the first study to highlight how pinch-off occurs specifically for the liquid inside foams.

Through extensive experiments, the team found that several key parameters determined whether foams fell down via gradual slippage or liquid pinch-off. One was the amount of liquid in the foam. With a wetter foam, more liquid would accumulate at the bottom, making larger foams more unstable. Drier foams would allow for bigger foam areas since less liquid is collected, with the added advantage of slower drainage, making pinch-off slower, even if it eventually happened. They confirmed their findings for three-dimensional foams on vertical walls as well, formulating simple thresholds for when pinch-off occurs.

The universal rules uncovered by the team promise clear design principles for new foam materials, particularly ones which need to stay stable under gravity for longer. Less frequent application means less waste, making for more efficient, sustainable application in both home and industrial settings.

This work was supported by JSPS KAKENHI Grant Numbers 20K14431, 17H02945 and 20H01874.

Article Title

Pinch-off from a foam droplet in a Hele-Shaw cell

Article Publication Date

22-Feb-2022

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When you think about improving your health, you tend to focus more on sleeping habits, diet, and exercise. However, since your home is where you spend most of your time, it’s equally important that you identify ways to improve your indoor space. From adding a green touch and cleaning the dirty carpets to filtering pollutants and cleaning the air, below are some of the simple steps you can take to make your home healthier.

Go green

According to the EPA, indoor air pollution can be five times higher than outdoor. This is very serious because you spend more than 80% of your time indoors. However, you can greatly reduce indoor air pollution by getting air purifying plants. Plants like Aloe Vera, English Ivy, and Peace Lilies, among others, can help to eliminate toxins from your indoor space. What’s more, these plants can also absorb C02 and release oxygen.

Clean your carpets regularly

Carpets help to keep your home warm. However, they can also harbor dust, bacteria, allergens, and other pollutants. Eventually, these pollutants can cause serious health issues for you and your loved ones. Therefore, you need to be diligent about changing your air filters, vacuuming your carpets regularly, and organic carpet cleaning. Keep in mind that regularly cleaning your carpets will help increase their lifespan.

Prevent mold growth

Although there isn’t any single method to eliminate the likelihood of mold growth, there are some tips you can follow to minimize it by controlling the level of indoor moisture. According to the EPA, you can easily reduce humidity in your home to 60% by venting all bathrooms in your home, using a dehumidifier and air conditioner, and using exhaust fans when cooking.

Clean your appliances regularly

Apart from your fridge, your dishwasher, oven, and washing machine also need a regular health check. You can use vinegar for descaling coffee machines and kettles or use baking soda to remove stains from your fridge. Remember to also regularly clean food debris from the dishwasher filter and clean the inside of the door using hot soapy water. This is essential to keep bugs away.

Declutter every season

There are only four seasons in a year, which makes it very easy to declutter. However, if you’re scared about decluttering your entire house, you can start by tackling one room at a time. Decluttering is therapeutic, and it gives you the peace of mind you need by knowing that you have only what you need in your home. This makes it easier to know where everything is placed.

Bottom Line

Leaving a healthy life entails much more than what’s on your plate. Similar to how your career, hobbies, relationships, and level of fitness contribute to your well-being, your indoor space is no exception. This is where you and your loved ones spend most of your time, and it should contribute to your health and happiness. Therefore, follow the above steps to work your way to a cleaner home and learn how to determine the air quality in your home.

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The final weeks of winter, and even the first few weeks of spring, are still chilly in many parts of the world. Despite those last vestiges of winter chills, late winter is a great time to begin preparing gardens for the coming planting season.

Gardens may have to withstand months of harsh weather each winter, and such conditions can take a toll. Gardeners can consider the following tips as they try to restore their gardens and get them ready for spring planting.

• Disinfect your tools. It’s common to clean tools in late fall or whenever they’re typically placed in storage for the winter. But cleaning and disinfecting are not necessarily the same thing. If tools were not disinfected at the end of the previous gardening season, disinfect them before doing any work on the garden. Doing so can ensure any lingering bacteria or fungi on tool surfaces are killed prior to the beginning of gardening season. According to the University of Minnesota Extension, plant pathogens, including bacteria and viruses, can be transferred to and infect plants through bits of soil and plant debris left on shovels and pruner blades. Thoroughly disinfecting such tools prior to using them in the spring is a great way to reduce the risk of disease in your garden.

• Clear debris from garden beds. Leaves, twigs, sticks, and other debris may have gathered in the garden over the winter. Such debris can inhibit the growth of plants and vegetables, so make sure all of it is removed prior to planting. Weeds might even begin to sprout up in late winter and early spring, so remove them before they go to seed.

• Test the soil. Testing the soil prior to planting can help gardeners determine what their gardens will need to thrive in the coming months. Garden centers and home improvement stores sell home testing kits that are effective and easy to use. Once the results are in, speak with a professional at your local garden center about the best time to amend the soil.

• Loosen compacted soil. Soil can become compacted over winter. If compacted soil is not loosened prior to planting, plants will have a hard time getting the water and nutrients they need to thrive. Loosening the soil also provides another opportunity to inspect the garden for any underlying issues, such as fungi or weed growth, that you may have missed when clearing debris or testing the soil.

Late winter is a good time to assess a garden and address any issues that developed over the winter so plants and vegetables can thrive come the spring planting season.

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