Spray Retention Using Pre-Mixed Polyelectrolyte Solutions

Technology #17877

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(a) Schematic of experimental set-up for simultaneous spraying of opposite polyelectrolytes. (b) Expected behaviour for the impact of a droplet with one polyelectrolyte polarity on a droplet with an oppositely charged polyelectrolyte. The coalesced drop sticks to the surface(c,d) Snapshots of simultaneous spraying on a superhydrophobic surface. Sprays with very low droplet density were used to enhance visualization and slow down the process. In the first row, the two sprayers are spraying water and the surface remains dry. Almost all droplets bounce off. Some small droplets are deposited but they are cleared as soon as another droplet impacts them (see Supplementary Movie 1). In the second row, opposite polyelectrolytes are sprayed. Individual droplets hitting the surface still bounce off. After 120 ms of spraying, the first event of a droplet of one polyelectrolyte hitting a droplet containing the opposite polyelectrolyte occurs. The coalesced drop sticks to the surface. Subsequent drops that hit this droplet also coalesce on it. Similar events happen all over the surface. Many droplets can be seen on the surface after 3 s of spraying (see Supplementary Movie 2). Scale bar, 1 cm.
Professor Kripa Varanasi
Department of Mechanical Engineering, MIT
External Link (varanasi.mit.edu)
Seyed Mahmoudi
Department of Mechanical Engineering, MIT
Nasim Hyder
Department of Chemical Engineering, MIT
External Link (nasim.mit.edu)
Maher Damak
Department of Mechanical Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Systems and Methods for Surface Retention of Fluids

PCT Patent Application WO 2017-070375

Systems and Methods for Surface Retention of Fluids

US Patent Pending
Enhancing droplet deposition through in-situ precipitation
Nature Communications, Aug. 30, 2016


Efficient deposition of spray would be beneficial for a wide range of applications, including agriculture, paints, coatings, cosmetics and medical applications.

Problem Addressed

There are two challenges associated with sprays. The first is eliminating the sources of deposition inefficiencies in sprays by using the maximum amount of the sprayed liquid. The second is to have maximum coverage of the target. Conventional methods try to overcome these challenges by changing the composition of the spray to reduce bouncing and drift when the liquid is sprayed. However, this technology overcomes these challenges through in-situ deposition of sparse hydrophilic defects, formed by the precipitation of oppositely charged polyelectrolytes, which modifies the wetting properties of the target surface.


This technology consists of spraying two polyelectrolytes, one positive and one negative, onto the target surface to create hydrophilic defects, which will allow the target surface to retain more of the liquid of interest. The polyelectrolytes can either be sprayed prior to the liquid of interest or in conjunction. To test this approach, both pure water and positive (LPEI) with negative (PAA) polyelectrolyte aqueous solutions were sprayed on a super-hydrophobic OTS-coated silicon nanograss surface. For pure water, coverage did not exceed 7% after six 500µL steps, but coverage reached 80% when 3mL of the polyelectrolyte solution were used.


  • Increased spray retention on hydrophobic surfaces
  • Reduces amount of spray necessary