If only the minds of Natick could invent a fabric that didn’t need laundering. If everything splashed, smeared, or spilled on a uniform just beaded up and rolled off, if uniforms could be cleaned with a quick spray of water, think how much longer they’d last. And how much safer they’d be in the event chemical weapons rained down on them.
The minds of Natick are on it. Over in the liquid repellency evaluation lab, they’re putting to the test a new “super-shedding” fabric treatment technology. Escorting me to a demo will be Natick’s calm, likable public affairs officer, David Accetta. We meet up in his office, one side of which is piled with boxes from a recent move. A wall calendar features dog breeds. September is a large white poodle. Accetta was most recently deployed to Bagram Airfield in Afghanistan, where he spent his days writing press releases about the Army’s humanitarian efforts. His superiors would ask him why the stories rarely got any play. “They didn’t get it. It’s not news.” He relates this with no trace of anger. There are many irritating things about Accetta’s job, but he never sounds irritated. He takes everything in stride, which is a bad cliché to use for him, because he’s not a striding sort of guy. He’s more of a moseyer. He has long eyelashes and a slow way of blinking. I almost wrote doll-like there, but the adjective seems out of place with the rest of Accetta’s face, which is crossed by a thin, rakish scar that begins at one temple and curves down and around his cheek. I don’t ask about it, preferring to supply my own made-up narrative of flashing sabers and staircase choreography.
We are early, so we take a walk along Lake Cochituate, which forms a property line for part of the Natick grounds. Sunlight is scattered on a low chop. Water from the lake, a deep blue-green in today’s light, was at one time used to make Black Label lager. Natick activities pretty much put a stop to that. For a Superfund site, the grounds are quite pretty, with gazebos and meandering footpaths. Cylindrical gray-white Canada goose droppings add to the parklike atmosphere. It took a while to realize what these were, because I didn’t see any geese. It’s fall. Maybe they just flew south.
Accetta and I stop to watch an officer addressing a group of HRVs: human research volunteers—arms and feet and heads to go inside the parkas and boots and helmets. They are soldiers deployed to taste rations, sleep in new sleeping bags: test, report back, test something else. A temporary duty assignment at Natick is not necessarily a soft gig. I saw a photograph, from the sixties, of a group of soldiers in raincoats and waterproof pants, heads bent, hoods dripping, walking in circles under a simulated downpour. Apparently this went on for hours.
The volunteers, ten or so, stand in a row in the parking lot outside their barracks. A car backs out of a parking slot behind them. The soldiers take three steps forward, in formation, and one step up, onto the curb. When the car pulls away, they step backward and down. Anytime they walk someplace in a group of four or more, Accetta says, they have to be in formation. Like geese flying south.
THE DEMONSTRATION begins with the farting sound of a squeezable mustard bottle. A line of glistening yellow joins the duns and drab olives of a square of camouflage fabric. The cloth is clipped to a sloping board to foster roll-off. This being a roll-off test. As a cameraman and a small crowd look on, the line of mustard creeps down the cloth, holding its shape perfectly. A young chemical engineer, Natalie Pomerantz, directs onlookers’ attention to the terrain across which the condiment has just traveled. “No residue trail!”
Ketchup follows, then coffee, and milk, as though the owner of the uniform had engaged the enemy in a food fight. Everything rinses clean with water. Natalie invites me to feel the underside of the cloth, and I do. It is completely dry.
Natalie started with the easy ones. Liquids that are mostly water have high surface tension. That means that the molecules prefer to bond more strongly to each other than to most of the things you might spill them on. A liquid with lower surface tension, like alcohol, won’t bead up on a fabric the way water will; it soaks right in. A bead of water is a molecular huddle, a withdrawal inward, a refusal to join hands with strangers. Confronted with air, the surface of water pulls together powerfully enough to form a weak skin. The insect kingdom has water striders, but no gin striders. At the far high end of the surface-tension spectrum is mercury. Mercury beads up and rolls off pretty much any surface you drop it on without leaving a trace.§ One of mercury’s qualifications for old-timey thermometerdom—along with staying liquid in extremes of cold and heat—is that it doesn’t wet the inside of the glass. No residue trail! So you can clearly read the temperature.
Many of the things the military tends to spurt and dribble on itself—motor oil, aviation fuel, hexane—have far lower surface tension than water. Natalie drips motor oil on another square of cloth. She picks up a cup of water and launches the contents like an outraged dinner date. Again, the mess rinses away with no trace remaining. “That was the money shot,” a colleague says.
Natalie is nodding. Beaming, even. “This is like a day out in the sun for us.” She’s joking, but it’s true in a way, in a good way. The delight she takes from science is an effervescence, something sparkly and hard to hold back. We should all love our jobs this much.
The super-repellent coating takes its inspiration from the leaves of the water lily. The surface of a lily pad, viewed under an electron microscope, is a carpet of tiny nubs, each covered with yet-smaller nano-nubs of waxlike crystals. (Paraffin wax is itself an effective fabric waterproofer, but it’s too flammable for the military to use.) The tiny nubs and peaks reduce the contact and interaction between the cloth and whatever liquid spills on it. The coating also makes the surface more energetically stable, further discouraging interactions between the textile and the glop.