etergent is needed during the entire cleaning process. Conventional liquid–liquid separation technologies require more than one separation units and consume a lot of external energy.27,28 However, waste oil–water mixtures can be further separated readily only by a solely gravity-driven separation unit, in which the as-prepared smart fabric is tightly sandwiched between two glass tubes (see Figures 3A–D). Pure water is collected as permeate as the fabric cleverly allows water to pass through and retains oil above it as retentate (see Figures 3A–C). A possible highly energy efficient way of industrial waste separation is demonstrated by feeding a complicated four component oil–water mixture (including free oil and water, oil-in-water emulsions, water-in-oil emulsions) into the single separation unit (see Figure 3D). Very high purity of permeate and retentate is revealed by thermogravimetric analysis (see Figure 3E). The effective solely gravity-driven oil– water separations are also demonstrated in Supporting Information Movie S2. Water flux29 during separation and a quasiempirical rating respect to surface self-cleaning and oil–water separation is discussed in Supporting Information Section 6