title: Controlling water evaporation through self-assembly.
abstract: Water evaporation concerns all land-living organisms, as ambient air is dryer than their corresponding equilibrium humidity. Contrarily to plants, mammals are covered with a skin that not only hinders evaporation but also maintains its rate at a nearly constant value, independently of air humidity. Here, we show that simple amphiphiles/water systems reproduce this behavior, which suggests a common underlying mechanism originating from responding self-assembly structures. The composition and structure gradients arising from the evaporation process were characterized using optical microscopy, infrared microscopy, and small-angle X-ray scattering. We observed a thin and dry outer phase that responds to changes in air humidity by increasing its thickness as the air becomes dryer, which decreases its permeability to water, thus counterbalancing the increase in the evaporation driving force. This thin and dry outer phase therefore shields the systems from humidity variations. Such a feedback loop achieves a homeostatic regulation of water evaporation.
authors: Laboratoire de Génie Chimique, Université de Toulouse, CNRS, Institut National Polytechnique de Toulouse, Université Paul Sabatier, 31030 Toulouse, France; Division of Physical Chemistry, Chemical Center, Lund University, SE-22100 Lund, Sweden; kevin.roger@ensiacet.fr.
authors: Kevin
authors: K
authors: Roger
authors: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland;
authors: Marianne
authors: M
authors: Liebi
authors: MAX-IV Laboratory, Lund University, SE-22100 Lund, Sweden.
authors: Jimmy
authors: J
authors: Heimdal
authors: Division of Physical Chemistry, Chemical Center, Lund University, SE-22100 Lund, Sweden;
authors: Quoc Dat
authors: QD
authors: Pham
authors: Division of Physical Chemistry, Chemical Center, Lund University, SE-22100 Lund, Sweden;
authors: Emma
authors: E
authors: Sparr
mesh_terms: D000388:Air; D006801:Humans; D006813:Humidity; D008853:Microscopy; D053838:Scattering, Small Angle; D012867:Skin / Q000737:chemistry* / Q000648:ultrastructure; D012879:Skin Physiological Phenomena; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water
keywords: evaporation; gradient; homeostatic; regulation; self-assembly