Canadian Finishing & Coatings Manufacturing Magazine January/February 2022 - 52

PLATING AND ANODIZING: SURFACE TENSION
Cleansing fluids with lower surface tension will outperform
cleaning fluids with higher surface tension when it comes to
precise cleaning, mainly when used in a vapour degreaser.
Because of the lower surface tension, the cleaning fluid may
more readily enter small crevices. It directly impacts the ability
of the cleaning solution to wet a surface, and one cannot clean if
one cannot wet a surface.
When it comes to metal plating, effective and consistent
surface contact between the plating bath and the material to be
plated is critical to the overall quality of the finished product.
Specific tools measure the surface tension of the plating bath and
the concentration of wetting agents in the plating bath.
Surfactants, which act as wetting agents in the plating solution
containing the metal ions, are present. These ingredients ensure
that the surface tension of the plating solution is low enough for
the plating solution to evenly spread across the surface and fill
tiny gaps without adhering to them. In addition, the formation of
pits in the coated metal due to hydrogen bubbles being generated
at the cathode may be prevented with the right use of a surfactant.
Precision measurements of liquid surface tension, the
most crucial indication of the liquid's wetting qualities, may
be made using tensiometers. The same approach may be used
to determine the critical micelle concentration (CMC), which
offers information on the efficiency of the surfactant in question.
It is preferable to monitor the amount of the wetting agent
by measuring the concentration dependant surface tension
to guarantee efficient yet cost-effective surfactant addition.
However, in the concentration above the critical concentration
(CMC), which is frequent in plating baths, the static surface
tension does not change further as the concentration of the
solution increases. In our case, fortunately, the dynamic
surface tension recorded with our bubble pressure sensors is
concentration dependent. Consequently, it serves as an excellent
indication of the loss of surfactant with time. While laboratory
equipment creates a reference curve, our portable instrument
approach allows rapid content testing immediately in the bath.
While it is desirable for surfactant addition to have a surface
tension-lowering impact, it is not desirable for foam formation
to occur.
Suppose one conducts an electroplating or anodizing
operation. In that case, gas bubbles formed during the process
rise to the surface of the liquid and burst, causing damage. Minute
droplets of chromic acid are released into the surrounding
atmosphere upon exploding. With the addition of a wetting agent
to the tank bath, you may lessen the surface tension of the liquid,
which will minimize the production of the droplets.
A stalagmometer or a tensiometer is used in this procedure to
measure the surface tension of the bath to ensure that there is
enough wetting agent present in the bath.
In 2021, researchers from the University of Toronto reportedly
developed a new coating that allows certain liquids to move
across surfaces without experiencing fluid loss. The coating was
created in the Durable Repellent Engineered Advanced Materials
(DREAM) Laboratory and led by Professor Kevin Golovin. The
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coating can aid in advances in various fields, including medical
testing and cleaning surfaces. A paper on the study has since
been published in Advanced Functional Materials.
According to the university, current microfluidic devices are
limited. They can only effectively handle liquids with high surface
tension or cohesion, such as water. Microfluidics is defined as a
field in which small quantities of liquids are transported within
tiny channels, often less than a millimetre wide.
In contrast to low surface tension liquids such as alcohols
and other solvents, these high surface tension liquids tend to
adhere to themselves rather than being entangled on the sides
of the channel through which they are transporting themselves.
In contrast to raindrops on window glass, low surface tension
liquids adhere to the sides of a channel rather than flowing
independently of one another. It has been observed that
they barely travel around 10 centimetres before the droplet
disintegrates completely.
Because the capillary action does not operate on these
materials, an additional force, such as magnetism or heat,
is required to move the droplets for them to be transported.
Research into the development of a coating solution, on the other
hand, took inspiration from the natural world while considering
other methods of moving materials.
To build the material with microfluidics in mind, the team of
researchers at the University of Toronto employed two recently
developed polymer coatings, both of which were made of liquidlike
polymer brushes to create it. One of them was more liquidresistant
than the other. Because of the strategic combination of
these polymers, the more repellent coating served as a backdrop,
encircling the less repellent coating and forming microscopic
channels along the surface of the object being treated. Liquids
could be transported along this channel in a particular pattern or
direction without losing any liquid or extra energy input during
transit.
The scientists found that the new coating could be transferred
across lengths of more than 150 mm without losing any liquid,
almost 15 times longer than the current maximum distance
allowed.
In light of these results, liquids might potentially be carried
over a greater distance or moved in combination with other
liquids along a specific course in the future, and even merge
and split droplets-all without losing any volume or exposing
themselves to cross-contamination. The coating would identify
various ailments in minutes with only a drop or two of blood
in an ideal world. In addition, the solution will pave the way
for developments in lab-on-a-chip devices and other related
technologies. Despite this, the coating can be used in various
additional applications, such as miniaturizing conventional
analytical procedures often done in chemical labs.
In addition, the new technology will aid in the reduction of
waste in research laboratories. Due to the lack of residue left on
the device's surface and, therefore, the absence of the possibility
of cross-contamination, researchers may utilize the same devices
over and over again without concern.
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Canadian Finishing & Coatings Manufacturing Magazine January/February 2022

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