Hydrophobes and Hydrophiles


Fluid Wettability

This week we learned about the wettability of different surfaces. The experiment we had in class dealt with various ways we changed the exterior of a copper plate to make it into a super hydrophobic or super hydrophilic surface.

While researching I came across an article that described a new material that switches from super hydrophobic to super hydrophilic in an instant.


Copper was deposited onto a surface by a process called electrodeposition which makes it grow like an array of Christmas trees. Electrodeposition i.e. electroplating is a process that uses electric current to reduce dissolved metal cations so that they form a coherent metal coating on a conductive material. The scientists used copper because it is cheap and abundant but the team believes that the electrochemical manipulation of other metals, metal oxides, and mixed oxides may yield similar results. 
They then ran a voltage through this new material and saw that water droplets that initially roll off stick to it more and more tightly. The voltage required to change the properties of the surface is as low as 1.5 volts which is lower than that found in a normal household battery. 
By changing the magnitude of the voltage and how long it is applied, they were able to easily control the angle that each water droplet forms with the surface. 
Running a current through the material changes the oxidation state of the copper surface because as copper loses electrons, it becomes less attracted to water and vice versa. 
The material should be able to manipulate any liquid as long as it is conductive. 


This new breakthrough in technology can open up a new world of possible applications such as cleaning up hazardous liquids such as contaminated blood more efficiently. Another use would be to use it as an electric sponge to “pick up” liquids from a drenched delicate object and place it elsewhere. Maybe we can even use it as a filtration system or use alternating currents in a pipe to be able to displace water uphill in a cost-efficient manner. 

On the other side of the coin, scientists at the University of Rochester were able to use lasers to carve out surfaces of metals to make intricate patterns of micro- and nanoscale structures to give the metals their new properties. Unlike spray-on chemical coatings that can wear out easily over time, these etchings are much more durable and are intrinsically part of the material surface.
The team first developed a super hydrophilic surface that made water run uphill against gravity using this method. Afterwards, they were able to develop a super hydrophobic surface that made water bounce off when applied. These new materials are much more effective than chemical coatings are. 

As the water droplet bounces off the hydrophobic surface, it also picks up dust particles while leaving the surface completely dry. This could open up a new range of self-cleaning materials. Shower screens and walls could be made to never be cleaned again. Or if water collection/storage units were etched with these patterns, they could be used as a more efficient rain water collector in developing countries.

Sources

Stapleton, Andrew. “This Crazy New Material Switches From Super Hydrophobic to Super Hydrophilic in an Instant.” ScienceAlert, www.sciencealert.com/this-crazy-new-material-switches-from-super-hydrophobic-to-super-hydrophilic-in-an-instant.

Zahiri, Beniamin, et al. “Active Control over the Wettability from Superhydrophobic to Superhydrophilic by Electrochemically Altering the Oxidation State in a Low Voltage Range.” Advanced Materials Interfaces, 26 Apr. 2017, onlinelibrary.wiley.com/doi/10.1002/admi.201700121/abstract;jsessionid=4883E86F4AD847DFE2580C92067798D9.f02t03.

“Laser-Generated surface structures create extremely water-Repellent metals.” Phys.org - News and Articles on Science and Technology, phys.org/news/2015-01-laser-generated-surface-extremely-water-repellent-metals.html.

UniversityRochester. YouTube, YouTube, 20 Jan. 2015, www.youtube.com/watch?time_continue=70&v=FLegmQ8_dHg.

David L. Chandler, MIT News Office. “Explained: Hydrophobic and hydrophilic.” MIT News, 16 July 2013, news.mit.edu/2013/hydrophobic-and-hydrophilic-explained-0716.

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