Porous Elastic Teflon Composite

Stretch this material to change how water interacts with it.

This phase-changing composite is composed of Teflon adhered to an elastic PDMS film, and coated with a lubricating oil.  When the material is stretched, the liquid coating on the Teflon drops into its matrix of pores until it can balance the pressure difference. Unfilled open pores in the membrane result in transparency. Gradually increasing the strain results in an opaque material. The figure below illustrates the composition and the phase change of the material.

This phase-changing material responds to mechanical strain. Adapted from (Yao, et al., 2013).

 When the membrane is infused with lubricating oils such as DuPont Krytox 103, liquids that are introduced to the material can be distributed in controllable ways. For instance, 6 microlitres of silicon oil on the surface stops its sliding motion when exactly 6% of strain is applied by mechanically stretching the material. The phase change that occurs with applied strain is illustrated in the diagram below.

Figure 1: Porous Membrane. Adapted from (Yao, et al., 2013). Materials from top to bottom: Lubricating Oil, Porous Teflon, PDMS Adhesive and Elastic PDMS Film.

   


As seen above, the composition of the material layers allow it to control liquid flow by trapping the added liquid within the expanded pores (Wang, et al., 2018). The diagram demonstrates what occurs to the liquid drop at the nanoscale, but to the human eye, this appears as a normal liquid drop staying still on the membrane, held in place by surface tension.

Benefits and Drawbacks

 

The advantages of this substrate are that when it is stretched or bent, the pore sizes change. At rest, the material is smooth, transmits light and repels water. In tension, the material is rough, opaque and hydrophilic. This material presents the possibility of a responsive plumbing system or building envelope which can regulate liquid flow rates automatically.

 

The drawbacks are that this substrate is still in the experimental phases, and it needs to undergo extensive testing before it can be commercially viable for building purposes.

 

 

Commercial Readiness

 

The latest study of this material occurred in 2018. There is no recent news discussing the commercialization of this science or the creation of a product. The controllable properties of its interactions with liquid show that it could be applied to buildings in plumbing applications (Wang, et al., 2018).

 

 Cost Analysis

PDMS membranes can be purchased in bulk from suppliers at starting costs of $200 per roll.

Teflon sheets are readily available and can be purchased from various online retailers for prices ranging from $7 to $20 CAD for 15” x 15” sheets. The availability of the key materials of this composite mean that it has a large potential for scalability as a building material.

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