[ R. COHEN, et al. ]
May 30, 2008
Beetle-Based Water Harvesting
By 2025, the United Nations forecasts that 1.8 billion people
will be living in countries or regions with water scarcity
and two thirds of the world’s population could be under
conditions of water stress.
Climate change is expected to aggravate water problems via more
extreme weather events. Many intelligent and improved management
options can overcome these challenges and one may rest on the
extraordinary ability of the Namib Desert beetle.
The beetle lives in a location that receives a mere half an
inch of rain a year yet can harvest water from fogs that blow in
gales across the land several mornings each month.
Enter a team from the University of Oxford and the UK defense
research firm QinetiQ. They have designed a surface that mimics
the water-attracting bumps and water-shedding valleys on the
beetle’s wing scales that allows the insect to collect and
funnel droplets thinner than a human hair.
The patchwork surface hinges on small, poppy-seed sized glass
spheres in a layer of warm wax that tests show work like the
beetle’s wing scales.
Trials have now been carried out to use the beetle film to
capture water vapour from cooling towers. Initial tests
have shown that the invention can return 10 per cent of lost
water and lead to cuts in energy bills for nearby buildings by
reducing a city’s heat sink effect.
An estimated 50,000 new water-cooling towers are erected
annually and each large system evaporates and loses over 500
Other researchers, some with funding from the US Defense
Advanced Research Agency, are mimicking the beetle water
collection system to develop tents that collect their own water
up to surfaces that will “mix” reagents for “lab-on-a-chip”
Namib Desert Beetle-based Dune Dew
The Namib Desert beetle lives in one of the driest places on
earth - just one half of an inch of rain per year. When early
morning fog offers the hint of moisture, the beetle is ready to
take a drink - from the amazing surface on its back. MIT
researchers, inspired by the beetle, have created a material
that can capture and control tiny amounts of water.
(The Namib Desert beetle - photo by Andrew Parker)
When the slightest fog blows horizontally across the beetle's
back, water droplets just 15-20 microns in diameter start to
accumulate on the bumps on its back. The bumps are surrounded by
waxy water-repelling channels. When a bump collects enough water
to form a big droplet, it rolls down a channel right into the
MIT researchers Robert Cohen and Michael Rubner
were inspired by a 2001 article in the journal Nature describing
the beetle, and thought it would be a good candidate for
biomimicry - the imitation of a natural-world solution to a
(MIT researchers Cohen and Rubner in situ in their lab)
Their newly designed material combines a superhydrophilic
(water-attracting) surface with superhydrophobic
(water-repelling) surface. A Teflon-like substance is applied to
a surface (for water-repulsion); silica nanoparticles and
charged polymers help create a rough texture to attract
droplets. The research was funded by our good friends at DARPA.
Science fiction writer Frank Herbert wrote about this same idea
in his remarkable 1965 novel Dune. Most of the novel takes place
on the planet Dune, which has no liquid surface water at all. In
order to plant vegetation, special materials are used to create
dew collectors, to gather even the tiniest amount of moisture.
"Each bush, each weed you see out there in the erg," she said,
"how do you suppose it lives when we leave it? Each is planted
most tenderly in its own little pit. The pits are filled with
smooth ovals of chromoplastic. Light turns them white. You can
see them glistening in the dawn if you look down from a high
place. White reflects. But when Old Father Sun departs, the
chromoplastic reverts to transparency in the dark. It cools with
extreme rapidity. The surface condenses moisture out of the air.
That moisture trickles down to keep our plants alive."
In the dew collectors of Herbert's imagination, a special
material changes from light to dark in order to pull moisture
out of the air. Cohen and Rubner's new material should be able
to do the same trick using a different technology.
NANOPARTICLE COATINGS AND METHODS OF MAKING
Inventor(s): GEMICI ZEKERIYYA [US]; RUBNER MICHAEL F [US];
COHEN ROBERT E
Applicant(s): MASSACHUSETTS INST TECHNOLOGY [US]; GEMICI
ZEKERIYYA [US]; RUBNER MICHAEL F [US]; COHEN ROBERT E [US]
Classification: - international: B05D1/12; B05D1/36;
B05D3/02; B05D1/12; B05D1/36; B05D3/02- European:
G02B1/11; G02B27/00C; Y01N6/00; Y01N10/00
Also published as: WO2008069848 (A3) //
Abstract -- A superhydrophilic coating on a substrate can
be antireflective and antifogging. The coating can remain
antireflective and antifogging for extended periods. The coating
can include oppositely charge inorganic nanoparticles, and can
be substantially free of an organic polymer. The coating can be
made mechanically robust by a hydrothermal calcination.
Inventor(s): ZHAI LEI [US]; COHEN ROBERT E [US]; RUBNER
MICHAEL F [US]; CEBECI FEVZI C [US]
Applicant(s): MASSACHUSETTS INST TECHNOLOGY [US]
Classification: - international: G11B5/64; G11B5/64 -
European: B05D5/04; C03C17/34B
Also published as: US2007104922 (A1)
WO2007056427 (A2) WO2007056427 (A3)
Abstract -- A superhydrophilic coating can be
antireflective and antifogging. The coating can remain
antireflective and antifogging for extended periods.
Inventor(s): LEE DAEYEON [US]; COHEN ROBERT E [US]; RUBNER
MICHAEL F [US]
Classification: - international: B32B5/16; B05D1/36;
B32B5/16; B05D1/36- European: C04B35/14; C03C17/00B;
C03C17/00D2; C03C17/23; C04B35/46
Also published as: WO2008021817 (A2) //
WO2008021817 (A8) // WO2008021817 (A3)
Abstract -- A superhydrophilic coating on a
substrate can be antireflective and antifogging. The coating can
remain antireflective and antifogging for extended periods. The
coating can include oppositely charge inorganic nanoparticles,
and can be substantially free of an organic polymer.
Hydrophobic and Hydrophilic Surface,
for Promoting Droplet Formation
LAWRENCE, Christopher; PARKER, Andrew
Classification: - international: B01D1/30;
B01D53/26; C02F1/18; E03B3/28; B01D1/00; B01D53/26; C02F1/18;
E03B3/00; (IPC1-7): B05D5/00; B01D5/00; B41M5/00 -
European: B01D1/30B; B01D53/26B; C02F1/18; E03B3/28
Also published as: GB2374818 (B)
WO02085484 (A1) US2004109981 (A1)
US2004109981 (A1) US7402195 (B2)
Cited documents: JP9131914 (A) JP10249977 (A)
US5145758 (A) WO9923437 (A1) WO9957185 (A1)
Abstract -- The surface comprises alternating liquid
attracting 13, 51 and liquid repelling 12, 52 materials. The
diameter of the droplets is controlled by the size of the
smallest dimension of the liquid attracting material. The
surface may be textured and/or form a pattern. The surface is
used for collecting and purifying water. It is also used in a
This invention relates to a surface suitable for promoting the
formation of droplets of a liquid on said surface in such a
manner as to control the droplet dimensions. The invention is in
particular suitable for enabling collection of that liquid from
a wind-blown fog or mist.
It is well-known that certain materials exhibit surfaces that
attract water whilst others actively repel it, such materials
being described as hydrophilic and hydrophobic respectively. It
is also still known that water is attracted or repelled due to
the fact that it is a polar liquid, and that any similar polar
liquid will be influenced in the same manner by such surfaces.
It should also be noted that non-polar liquids such as oils will
be attracted to a hydrophobic surface and repelled by a
There are a number of situations where the collection and
storage of liquids is of importance. One such situation is where
the environment is arid and there is no easily accessible source
of water. Another situation could be when chemicals are in
vapour form during distillation.
It is an object of the present invention to provide a surface
suitable for promoting the formation of liquid droplets of a
tailored size. It is a further object to collect said droplets.
According to a first aspect of the present invention a surface
suitable for promoting the formation of droplets of a liquid
comprises regions of liquid repelling and liquid attracting
material alternating in at least one direction across the
surface whereby the diameter of the droplets is controlled by
the size of the smallest dimension of the liquid attracting
If the liquid is polar, hydrophilic regions of the surface
attract the polar liquid and the hydrophobic regions repel the
polar liquid. If the liquid is an oil, the hydrophobic regions
attract the liquid and the hydrophilic regions repel the liquid.
The smallest dimension (the width) of the liquid attracting
regions determines the size of the droplet to be formed. There
is a maximum diameter that a stable droplet can attain which is
related to the width of the liquid attracting regions. The
liquid repelling regions separating the liquid attracting
regions are preferably of at least the same width, so as to
prevent overlap of droplets on neighbouring liquid attracting
Preferably, the liquid attracting regions take the form of
discrete regions on a liquid repelling substrate i.e. each
liquid attracting region is isolated from other liquid
attracting regions. This enables the droplets to form in
isolation, constraining them in two dimensions and limiting
their surface contact area with the liquid attracting substrate
(and hence their adhesion to the surface).
In a preferred embodiment, the surface is textured such that
the regions of liquid attracting material protrude in relation
to the regions of liquid repelling material. This allows for the
droplets, when formed, to sit proud in relation to the liquid
repelling regions, and encourages detachment of the droplets
from the liquid attracting material when a specified droplet
size is attained i.e. when the diameter of the droplet has
reached its maximum stable size.
Preferably the said smallest dimension of the liquid attracting
material regions is more than 150 .mu.m, more preferably more
than 200 .mu.m, and for certain applications is preferably more
than 300 .mu.m, 400 .mu.m, 500 .mu.m, or even at least 600
.mu.m. Preferably the said smallest dimension is in the said one
direction of the surface. If the said smallest direction is in
another direction from the said one direction, then in the said
one direction the smallest dimension of the liquid attracting
material region in the said one direction preferably also has
the stated preferred minimum sizes (more than 150, 200, 300,
400, 500, or at least 600 .mu.m).
The said surface is preferably substantially planar. It is also
envisaged that the surface may be curved, e.g. concave or
convex, or be a combination of curved and substantially planar
parts. Where we say that a surface is substantially planar, this
specifically includes substantially planar surfaces with regions
projecting or protruding from the surface, e.g. protruding above
The surface is preferably designed in use to be inclined to the
horizontal plane. This is described in more detail below with
reference to other categories of the invention. It is mentioned
here because, especially where the surface is substantially
planar, the said one direction of the said surface is preferably
the direction of the surface that defines the incline. More
specifically, when the surface is inclined the angle of
inclination is preferably defined as the angle between the
horizontal and any line drawn along the surface in the said one
Preferably the said smallest dimension of the liquid attracting
region is at most 5 mm, more preferably at most 4 mm, and for
certain applications is preferably at most 3 mm, 2 mm, 1 mm, or
0.8 mm (800 .mu.m).
Where we talk about the smallest dimension of the liquid
attracting region this will typically be the width, depending on
the shape of the region. Thus, for example if the liquid
attracting regions are in the shape of stripes, it will be the
width of the stripes. Similarly if the liquid attracting regions
are in the shape of discrete dots, it will be the width or
diameter of the dots. For other less regular shapes it will be
whatever is the smallest dimension in any direction. Preferably
where there are a plurality of liquid attracting regions these
will all be of similar shape and size. However it is envisaged
that combinations of shapes and sizes of liquid attracting
regions could also be used.
The liquid repelling regions are preferably at least as wide as
the liquid attracting regions, and possibly twice as wide.
Preferably the width or distance of liquid repelling region
separating adjacent liquid attracting regions is at least 400
.mu.m, more preferably at least 600 .mu.m, especially at least
800 .mu.m, or even at least 1 or 2 mm.
As mentioned above the smallest dimension of the liquid
attracting regions control the diameter of the droplets formed
on the surface. This can best be explained by considering a
preferred substantially planar surface in its preferred use
position in which it is inclined to the horizontal. In this
orientation, when small liquid droplets from a vapour adjacent
the surface strike the inclined surface, if they strike a liquid
attracting region then they may form a droplet attached to the
liquid attracting region, but if they strike a liquid repelling
region they will roll down the inclined surface to the nearest
liquid attracting region. The droplets grow, by joining with
other droplets that attach to the same liquid attracting region,
until they reach a point at which their surface contact area
covers the liquid attracting region. Beyond this size the
droplets are gaining in mass without any increase in contact
area, so that the droplet has to move into the liquid repelling
regions. As this happens the force of gravity increases without
any increase in surface adhesion, causing the droplet to move
down the inclined slope. If the surface is in a calm environment
the droplets will fall directly down the slope, but if the
surface is facing into a headwind the droplets may be blown
randomly across the surface by the wind. Preferably the surface
spacing and the size of the liquid attracting regions is
sufficiently large that the droplets will roll down the slope
only once they are sufficiently heavy to roll directly downwards
even against a headwind.
According to a second aspect of the present invention a method
of collecting a liquid carried by or condensed out of a vapour
comprises passing a vapour across a surface; and collecting
droplets of liquid formed on the surface in collecting means;
wherein the surface comprises alternating regions of liquid
repelling and liquid attracting material in at least one
direction across the surface and the collecting means is
disposed so as to collect drops formed on the surface.
The surface will usually be a man-made surface, and the method
may comprise an initial step of selecting the smallest dimension
of the liquid attracting regions so as to determine the droplet
size having regard to the prevailing environmental conditions.
Throughout this specification, the term vapour is used to
embrace media both in an entirely gaseous state and also in
which liquid droplets are suspended in the gas forming for
example a fog or a mist.
Preferably the surface is inclined to the horizontal plane.
This enables the droplets to flow under the influence of gravity
towards the collecting means which is a container of some
According to a third aspect of the present invention a system
for collecting a liquid comprises a surface having alternating
regions of liquid repelling and liquid attracting material in at
least one direction across the surface; and collection means,
whereby on the movement of a vapour across the surface, droplets
within the vapour collect into larger droplets on the surface
and are collected by the collection means.
In a preferred method and system according to the invention for
collecting a liquid, the surface is preferably inclined to the
horizontal plane by an angle of at least 5.degree., more
preferably at least 10.degree.. For certain applications the
surface is preferably inclined by at least
20.degree.,30.degree., or even 40.degree.. Preferably the
surface is inclined at most 90.degree., especially at most
80.degree., or sometimes at most 70.degree.. The angle of
incline, like the width of the liquid attracting regions, is one
of the factors determining when a droplet forming on the surface
will roll down the slope for collection.
The surface, and the method and system for collecting a liquid
are particularly applicable for collecting liquid from a vapour
that is moving across the surface. This will be the case, for
example in a headwind.
The behaviour of droplets of liquid falling on various
surfaces, particularly where inclined into the headwind may be
described as follows. For a vapour carrying headwind striking an
entirely liquid attracting surface or an entirely liquid
repelling surface, the liquid droplets would form on the surface
in various sizes but would not amalgamate. These would therefore
be blown in random directions across the surface by the
headwind. For the surface of the present invention alternate
regions of liquid attracting and repelling regions are provided.
Droplets will either strike the liquid attracting regions and
stay there, or roll to the nearest liquid attracting region if
they initially land on a liquid repelling region. These droplets
amalgamate until they are so large that no further purchase on
the liquid attracting region is possible. At this time they will
roll away (if the surface is inclined).
Where the surface is inclined it is preferably inclined to face
any headwind. Typical preferred headwinds according to the
invention may be at most, or of the order of 5 ms.sup.-1, 10
ms.sup.-1, 15 ms.sup.-1or 20 ms.sup.-1. The headwind is another
factor that affects when droplet forming on the surface will
roll down the slope for collection too large a headwind (for the
size of drop and angle of surface incline) will cause a drop to
be randomly blown across the surface, rather than rolling
directly down for collection.
Where reference is made to "headwind" this may be in a natural
environment, or in a controlled environment such as a
distillation or a dehumidifier unit.
Preferably the smallest dimension of the liquid attracting
regions is selected so that it can be used in a variety of
headwinds, by appropriate variation of slope, such that in this
controlled manner the droplets always grow to a sufficiently
large size before rolling down the slope to be heavy enough to
roll directly down the slope even against the headwind.
Preferably the arrangement of liquid attracting and repelling
regions on the surface is such that along any line drawn along
the surface in the said one direction there will be alternating
liquid attracting and liquid repelling regions. The said one
direction is preferably the direction which together with the
horizontal defines the angle of tilt, so that with this
arrangement any drop rolling down the slope in the said one
direction will always meet a liquid attracting region as it
rolls. This arrangement can be for example provided by stripes
of liquid attracting and repelling regions crossing, preferably
perpendicular to the said one direction. As another example
there may be mentioned discrete portions, e.g. dots, of liquid
attracting regions in a surround of liquid repelling material,
the liquid attracting discrete portions being off set laterally
to each other relative to the said one direction. Thus, dots in
adjacent rows may be staggered with respect to each other so as
to prevent there being a clear "uphill" path of liquid repelling
regions along which droplets could be blown away.
In the method of collecting a liquid according to the present
invention, and in the system for collecting a liquid according
to the present invention the path into the collecting means of
substantially all the liquid is preferably across both liquid
attracting and liquid repelling regions.
The aforementioned method and/or system for collecting a liquid
may be a water collection method or system being used or
intended for use in an arid/desert environment and adapted to
collect at least 100 ml, preferably at least 0.5 l and ideally
at least 1 l per week.
According to a fourth aspect of the present invention a method
of spreading a liquid across a surface comprises providing a
surface having alternating regions of liquid repelling and
liquid attracting material in at least one direction across the
surface, placing a liquid on the surface; and spreading the
liquid across the surface using spreading means.
Preferably, the regions of liquid attracting material comprise
a pattern whereby on placing a sheet of printing material over
the surface, the pattern produced by the positioning of the
liquid attracting material is transferred to the sheet of
By tailoring the surface as described previously it is possible
to dictate the maximum size of the droplets held at the liquid
attracting regions when the surface is tilted, or otherwise
treated to remove excess liquid, and hence dictate the density
and distribution of liquid, for example in ink.
The patterned region may be made by a continuous liquid
attracting region, or more preferably by a plurality of discrete
liquid attracting regions, e.g. a plurality of liquid attracting
dots, surrounded by liquid repelling regions. The latter
configuration better controlling the density and distribution of
liquid, e.g. ink
A surface as hereinbefore described has the added advantage
that it may be self cleaning. The surface promotes droplet
formation and those droplets may be directed under the influence
of gravity. As the droplets move over the surface, small
particles will be picked up by the droplets and thus removed
from the surface.
In a further aspect the invention provides a water collection
kit that may be assembled to form a collection system as
described above, the kit comprising the surface, support means
for supporting the surface at a desired inclination, and
collection means. The kit may form part of a portable survival
A number of embodiments of the invention will now be described
by way of example only, with reference to the drawings, of
FIG. 1 is a schematic oblique illustration of a surface
according to the present invention.
FIG. 2 shows an alternative surface according to the
FIGS. 3a and 3d show a schematic sectional illustration
of a textured surface according to the present invention.
FIG. 4 shows a schematic sectional illustration of a
textured surface suitable for collecting a liquid according to
the present invention.
FIGS. 5a and 5b illustrates a surface suitable for a
method of printing according to the present invention.
FIG. 5c shows an alternative surface suitable for a
method of printing according to the present invention.
Fig 1 shows a surface 1 having hydrophobic 2 and
hydrophilic 3 regions.
The hydrophobic 2 and hydrophilic 3 regions alternate across
the surface 1 and form a striped pattern. An efficient surface
for the collection of water from wind-blown fogs consists of 600
to 800 micron width hydrophilic regions spaced a minimum of 800
microns apart on a hydrophobic substrate. This allows for the
formation of droplets of a size whereby, under the influence of
gravity on a tilted surface, the droplets flow downwards into a
FIG. 2 shows a surface 10 having hydrophobic 12 and
hydrophilic 13 regions.
The hydrophobic regions 12 form a grid structure across the
surface 10. The hydrophilic regions 13, are raised above the
hydrophobic regions 12 forming a textured surface. When a vapour
is passed over the surface 10, droplets within the vapour are
attracted to the hydrophilic regions 13. After a period of time,
larger droplets of liquid begin to form on the hydrophilic
regions 13 as the small droplets in the vapour combine on the
surface. When the droplets reach a certain size, they move from
one hydrophilic region 13a to another hydrophilic region 13b
under the influence of gravity.
FIGS. 3a to 3d show a textured surface 20 inclined to
the horizontal plane having hydrophobic 22 and hydrophilic 23
The hydrophilic regions 23 protrude in relation to the
hydrophobic regions 22. When small droplets from a wind-blown
vapour strike the tilted surface 20 then they may form a droplet
24 attached to a hydrophilic region 23. As such droplets grow
larger (by joining with other droplets that attach to the
surface or by getting larger), the drops will reach a point at
which their surface contact area covers the hydrophilic region
23, as is shown in FIG. 3b, 25. Beyond this size they are
gaining in mass without a corresponding increase in surface
contact area, as shown in FIG. 3c, 26, thereafter, the droplet
must now expand into the water-repelling hydrophobic regions of
the surface, shown in FIG. 3d, 27. As this happens the
gravitational forces on the droplet increase without a
corresponding increase in surface adhesion, and eventually the
droplet will move down the slope. By tailoring the slope of the
surface, the size and spacing of the hydrophilic regions, and
the exact hydrophobicity and hydrophilicity of the surface
regions, droplets of a tailored diameter can be formed that can
roll into the headwind of the wind-blown fog or mist and be
collected at the lowest point of the tilted surface. In certain
controlled environments, such as during distillation, the
windspeed may also be controlled and tailored.
It should be noted that small droplets striking a hydrophobic
surface would immediately be free to roll across that surface,
but are likely to be blown away by the prevailing wind due to
their small size, and may simply bounce from the surface back
into the vapour. If the surface were entirely hydrophilic then
the droplets would form a film that would move in a more random
fashion, if at all, and limit the speed and efficiency of the
When droplets move on such a tailored surface, they may also be
guided by the hydrophilic regions, the surface attraction being
sufficient to influence their direction and speed of motion.
This would particularly be the case if the liquid attracting
regions formed channels or stripes on the hydrophobic surface.
A textured surface as described above can manufactured using a
variety of techniques. Clean (grease-free) glass surfaces are
hydrophilic, and hence glass can be combined with hydrophobic
materials such as waxes in order to produce appropriate
patterns. Glass beads of 800 micron diameter can be partially
embedded into a wax film to produce an array of hydrophilic
hemispheres on a hydrophobic substrate. A clean glass surface
can be made hydrophobic by exposure to materials such as
hexamethyldisilazane, and this may be used in combination with
contact masks to produce an appropriate pattern of hydrophilic
regions. Surface texturing can be achieved via techniques such
as the moulding and hot-pressing of plastics, which can
subsequently be treated with hydrophilic/hydrophobic surface
FIG. 4 shows a schematic sectional illustration of a
textured surface 30 suitable for collecting liquid 35 having a
surface 31 with hydrophobic 32 and hydrophilic 33 regions. A
collector 34 is positioned below the surface.
When a vapour is passed over the surface 30, droplets in the
vapour are attracted to the hydrophilic regions 33. After a
period of time, larger droplets of liquid begin to form on the
hydrophilic regions 33 as more and more small droplets from the
vapour are attracted to the surface. When the droplets reach a
certain size, they move under the influence of gravity. The
hydrophilic regions 33 are tapered towards the collector 34 and
the droplets tend to move from one hydrophilic region to another
so the liquid from a number of hydrophilic regions 33 is
collected in one collector 34.
An application of such a surface would be in distillation
processes, for example, to purify a liquid. If a vapour is to be
cooled and collected it is often passed through a tube that is
enclosed in a cooling system (e.g. a second tube through which
cold water flows). Vapour condenses on the walls of the inner
tube and runs down to a collector. Since any vapour that
condenses into a film on this inner wall insulates the remaining
vapour from the cold surface, the inner tube is sometimes coated
with a hydrophobic material to encourage condensed droplets to
quickly flow downwards. However, small vapour droplets are more
likely to be repelled from the hydrophobic walls, being
deflected back into the vapour and hence slowing the collection
process. Also, if the vapour is travelling in a specific
direction (e.g. rising up a vertical pipe via convection
currents) then small droplets are less likely to fall downwards
against the vapour flow. For such applications a textured
hydrophobic/liquid attracting surface such as those described
above would improve the efficiency of the distillation process.
FIG. 5a illustrates a surface 50 having ink attracting
51 and ink repelling 52 regions. The ink repelling regions 52
form or define a recognisable shape. Ink 54 (not shown) is
spread across the surface 50.
Ink 54 is attracted to the ink attracting 51 regions and
repelled from the ink repelling regions 52 shown in FIG. 5b.
This causes the ink 54 to only be present on the surface 50 in
the ink attracting regions 51. A sheet of paper (not shown)
placed over the surface 50 results in a transfer of ink from the
surface 50 to the paper and thus in production of a print of the
recognisable shape or negative thereof.
Whichever region is ink attracting and ink repelling depends on
whether the ink is oil or water based.
FIG. 5c shows an alternative surface 50' having a
plurality of densely distributed discrete dot shaped ink
attracting regions 51' in a surround or matrix of ink repelling
material 60. These ink attracting regions 51' in a surround or
matrix of ink repelling material 60 form a pattern (which is the
letter "A" in the Figure). The pattern region is in a background
of ink repelling material 52 as in the previous embodiment. Ink
54 (not shown) is spread across the surface 50'. As in the
previous embodiment, ink is attracted to the regions 51'. Ink is
repelled from regions 60 and 52. The discrete dot nature of the
liquid attracting regions 51' in the "A" pattern better controls
the density of the ink held on the pattern compared with the
continuous liquid attracting region 51 of the FIGS. 5a and 5b
embodiment. The pattern can then be printed by transfer to a
sheet of paper as in the FIGS. 5a/5b embodiment.
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