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WO2013023110A2 - Revêtements uniformes obtenus par des suspensions de particules anisotropes - Google Patents

Revêtements uniformes obtenus par des suspensions de particules anisotropes Download PDF

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Publication number
WO2013023110A2
WO2013023110A2 PCT/US2012/050223 US2012050223W WO2013023110A2 WO 2013023110 A2 WO2013023110 A2 WO 2013023110A2 US 2012050223 W US2012050223 W US 2012050223W WO 2013023110 A2 WO2013023110 A2 WO 2013023110A2
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WIPO (PCT)
Prior art keywords
bodies
composition
anisotropic
particles
ellipsoids
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PCT/US2012/050223
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English (en)
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WO2013023110A3 (fr
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Peter J. YUNKER
Arjun G. Yodh
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The Trustees Of The University Of Pennsylvania
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Publication of WO2013023110A2 publication Critical patent/WO2013023110A2/fr
Publication of WO2013023110A3 publication Critical patent/WO2013023110A3/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
    • B05D3/0254—After-treatment

Definitions

  • the present invention relates to the field of coating compositions, to the field of colloidal science, and to the field of soft condensed matter.
  • compositions suitably including a fluid medium; a plurality of anisotropic bodies disposed within the fluid medium, at least some of the anisotropic bodies having an aspect ratio of major axis to minor axis of between about 1.0 and about 10,000, and at least some of the anisotropic bodies having at least one cross-sectional dimension in the range of from about 1 nm to about 500 micrometers.
  • the present disclosure also provides methods, the methods including dispersing a plurality of anisotropic bodies into a fluid medium, at least some of the anisotropic bodies having an aspect ratio of major axis to minor axis of greater than about 1.0, and the anisotropic bodies having at least one cross-sectional dimension in the range of between about 1.0 and about 10,000.
  • Also provided are methods for making uniform coatings including applying a plurality of droplets of a composition to a substrate, the composition comprising a fluid medium having a plurality of anisotropic bodies disposed within, at least some of the anisotropic bodies having an aspect ratio of major axis to minor axis of between about 1.0 and about 10,000.
  • compositions including a fluid medium; a plurality of anisotropic bodies disposed within the fluid medium, and at least some of the anisotropic bodies having hydrophobicities that differ from one another.
  • Figure 1 illustrates deposition of spheres and ellipsoids a,b. Image of the final distributions of ellipsoids (a) and spheres (b) after evaporation, c. Schematic diagram of the evaporation process depicting capillary flow induced by pinned edges. If the contact line were free to recede, the drop profile would be preserved during evaporation (dashed line). However, the contact line remains pinned, so the contact angle decreases (solid line). Thus, a capillary flow, from the drop's center to its edges, is induced to replenish fluid at the contact line. d.
  • Droplet-normalized particle number density, p/N plotted as function of radial distance from center of drop for ellipsoids with various major-minor axis aspect ratios, e.
  • Figure 2 illustrates transportation of particles over time.
  • pR The areal particle density, located within 20 pm of the contact line (i.e., drop edge) as a function of time during evaporation, j-m.
  • the three phase contact line can be seen in the bottom left corner of these snapshots.
  • Figure 3 presents high magnification microscopy images of particles near the drop contact line.
  • SDS surfactant
  • Spheres pack closely at the contact line.
  • Ellipsoids form loosely packed structures.
  • Surfactant lowers the drop surface tension, making ellipsoids pack closely at the contact line.
  • Figure 4 illustrates behavior of spheres, ellipsoids, and mixtures of spheres and ellipsoids in drying liquid drops.
  • the left and right panels are side views at early and late times, respectively, and the center panel is a top view showing particle trajectories linking those times, a-f.
  • Spheres leave a ring-like formation, while ellipsoids form loosely- packed structures on the air-water interface, g.
  • Figure 5 presents the mass, m, of drops of different suspensions plotted versus time, t, for evaporating drops.
  • Figure 6 presents the radius, R, of drops of different suspensions plotted versus time, t, for evaporating drops.
  • the red line is the best exponential fit.
  • Figure 8 presents a. the final distribution of core-shell polystyrene-NIPA spheres. These hydrophilic particles exhibit the coffee ring effect, b. The final distribution of core-shell polystyrene-NIPA ellipsoids. These particles, which are both anisotropic and hydrophilic do not exhibit the coffee ring effect.
  • Figure 9 presents the three-phase contact angle, 6 C plotted versus aspect ratio, a.
  • Figure 11 depicts the dispersion of particles in a standard droplet (left) and in a droplet according to the present disclosure (right);
  • Figure 12 depicts an exemplary coffee ring effect from droplet drying in a standard suspension without anisotropic particles
  • Figure 13 depicts a cutaway view of the evaporation process in a coffee ring system
  • Figure 14 depicts a cutaway view of the evaporation process in a coffee ring system
  • Figure 15 depicts spheres deposited in a ring arrangement from evaporating a solution free of anisotropic particles
  • Figure 16 depicts an exemplary method for fabricating ellipsoids from polystyrene microspheres
  • Figure 17 depicts the effect of an ellipsoid particle on a fluid interface
  • Figure 18 depicts ellipsoids residing at an air/fluid interface
  • Figure 19 illustrates that adding surfactant to an exemplary composition according to the present disclosure can restore the so-called coffee ring effect
  • Figure 20 illustrates the situation of confined evaporation of a droplet containing anisotropic particles of various aspect ratios (a);
  • Figure 21 illustrates the effect of anisotropic particles (ellipsoids) on the coffee ring effect in a sessile drop - the left-hand of the figure illustrates evaporation behavior of a droplet that contains spheres, and the right-hand of the figure illustrates evaporation behavior of a droplet that contains ellipsoidal anisotropic particles;
  • anisotropic particles ellipsoids
  • Figure 22 depicts the physical configuration of a droplet confined between two opposing plates (right-hand side of figure), where confinement acts to impair the ability of ellipsoids (or other particles) from reaching the air- fluid interface;
  • Figure 23 illustrates that in the evaporative drying of a sessile drop, ellipsoids are distributed more evenly than spheres;
  • Figure 24 illustrates that in a droplet that contains spherical particles and ellipsoids (anisotropic particles), the spheres distribute more evenly upon evaporation than they do in a droplet that contains only spherical particles.
  • a cartoon below shows a side view of the experimental image, e.
  • Figure 26 illustrates the bending rigidity, ⁇ , of the particle coated air-water interface plotted as a function of particle aspect ratio, a
  • Figure 27 presents (a) Cartoon depicting droplet evaporating in a confined geometry.
  • the present disclosure provides methods of creating an essentially uniform particle deposition. These methods include applying, to a portion of a substrate, a composition that suitably includes a fluid medium and a plurality of anisotropic bodies disposed within the fluid medium. At least some of the anisotropic bodies suitably have an aspect ratio of major axis to minor axis of between about 1.0 and about 10,000. At least some of the anisotropic bodies also suitably have at least one cross-sectional dimension in the range of from about 1 nm to about 500 micrometers. The methods also include evaporating at least a portion of the fluid medium.
  • the anisotropic bodies suitably have at least one cross-sectional dimension (e.g., diameter, length) that is in the nanometer range, although a nanometer-scale cross-sectional dimension is not a requirement.
  • Cross-sectional dimensions in the range of from about 5 nm to about 100 micrometers, or from about 10 nm to about 50 micrometers, or even from about 100 nm to about 5 micrometers are all considered suitable.
  • Pfl viruses are considered suitable bodies. Such viruses may have a minor axis length of ⁇ 6 nm. Anisotropic particles of virtually any size may be used; suitable particles may be chosen such that gravity does not force them to sediment before they reach the air-water interface. Carbon nanotubes are considered suitable bodies, particularly where the carbon nanotubes are stabilized (e.g., with charge, or even sterically stabilized).
  • the anisotropic bodies prefferably be about as dense as the fluid medium (in this case the particles are about 5% more dense than the fluid). Less dense bodies are also suitable, as this will simply make the bodies reach the interface faster. If the anisotropic particles are denser than the fluid medium, this effect can still work. Even if the particles are pushed to the edge at the bottom of the drop, they will adsorb onto the interface and then become nearly evenly dispersed.
  • the bodies are suitably stabilized in some manner; charge stabilization and steric stabilization are both suitable ways to stabilize particles.
  • a user may also use a surfactant to stabilize particles; surfactants that do not greatly reduce surface tension are considered especially suitable.
  • the particles may begin as charge-stabilized spheres. These polystyrene spheres have charge groups (e.g., sulfate, carboxyl, amidine) on their surfaces. After the spherical particles are stretched (described elsewhere herein) to achieve an ellipsoidal shape, the groups remain on the particle surface, and the particles remain charge stabilized. Additional detail is shown in Figure 16.
  • charge groups e.g., sulfate, carboxyl, amidine
  • Actin filaments may be used as anisotropic bodies, and such filaments have aspect ratios in the range of from about 2000 to about 3000. At least some of the anisotropic bodies may have an aspect ratio of major axis to minor axis of between about 10 and about 10,000, 1,000, or even between from about 100 and about 500.
  • any anisotropic shape that creates an interparticle attraction at the air- fluid interface is suitable.
  • Some examples include ellipsoids, barbells, rods, doublets (two spheres that are connected), triplets (three connected spheres), branched particles (e.g., tripods), cubic particles, tetrahedra, as well as chemically heterogeneous particles (Janus particles).
  • the population of anisotropic bodies may be polydisperse in terms of size, aspect ratio, material composition, size, shape, or in some other aspect, such as hydrophobicity.
  • the anisotropic bodies may represent represents a volume fraction of from about 0.0001 to about 0.2 of the composition, or even a volume fraction of from about 0.001 to about 0.02 of the composition.
  • a volume fraction of 0.3, 0.4, or 0.5 is also suitable.
  • any fluid medium may be used in the disclosed compositions.
  • Water, alcohol, and other fluids are all considered suitable.
  • Oils and hydrocarbons are also suitable fluids.
  • a user may select a fluid based on the fluid's non-reactivity with the anisotropic bodies or other components of the composition.
  • the disclosed compositions may also include a population of spherical or non- anisotropic bodies.
  • the anisotropic bodies may act to restrain the movement of the spherical bodies within the composition (e.g., during evaporation). In this way, the anisotropic bodies act to effect essentially even or even uniform dispersion of the spherical bodies within a quantity (e.g., a droplet) of the composition. At least some of the essentially spherical bodies suitably have a diameter that is greater than the minor axis of the plurality of anisotropic bodies.
  • a spherical body can be of virtually any material; it may be a polymer, a mineral, a metal, a biological entity (e.g., cell, tissue, organelle, organ, or any part thereof), and the like.
  • the spherical body may include a strand of DNA, or even comprise an individual molecule.
  • Exemplary molecules include biological molecules, chemical molecules and the like.
  • Anisotropic bodies can likewise be composed of virtually any material.
  • Bio- materials such as FD viruses, PF1 viruses, actin filaments, bacteria, and the like
  • core-shell particles e.g., core-shell polystyrene-PNIPAm particles
  • metal particles silicon particles, and the like are all suitable anisotropic bodies.
  • Bodies that are denser than the fluid medium are suitably of a comparatively small size so as to reduce or even avoid sedimentation.
  • Core-shell particles are considered especially suitable, as the core may be of a comparatively inexpensive material, and the shell may be used to carry some active material (e.g., DNA or other biologic).
  • the composition may include one or more pigments.
  • the pigment may be included in an anisotropic body, as a sphere, or even in the fluid itself.
  • Pigmented compositions are considered especially useful, as the composition enables uniform distribution of the pigment throughout a droplet during evaporation of the fluid medium.
  • the pigment may be present as a body or other particle. Such pigment bodies suitably have a major axis larger than the minor axis of the plurality of anisotropic bodies. In this way, the pigment bodies are restrained by the network of anisotropic bodies, and do not migrate to the edge of a drop of the composition. It should be understood that the compositions may include anisotropic and isotropic (e.g., spherical) bodies.
  • compositions may also contain a mono- or polydisperse mixture of anisotropic, spherical, or both bodies, as explained elsewhere herein.
  • a composition might include anisotropic bodies having a ratio of major to minor axis of 2: 1 as well as bodies having a majonminor axis ratio of 5: 1.
  • the composition may include bodies that are thermoplastic (e.g., polyethylene) in nature, which bodies in turn allow for uniform dispersion of the compositions bodies across a surface, after which the bodies may be thermally processed to form an essentially uniform coating.
  • compositions may also be formulated such that some of the bodies disposed within the composition are sacrificial, such that the composition may be disposed on a substrate so as to achieve a uniform disposition of the composition bodies, after which some of the bodies are eliminated (e.g., via chemical treatment, by heat, by application of radiation, or by other techniques known in the art). In this way, a user may achieve a final coating that include fewer than all of the bodies present in the composition initially.
  • the present disclosure also provides methods. These methods suitably include dispersing a plurality of anisotropic bodies into a fluid medium, at least some of the anisotropic bodies having an aspect ratio of major axis to minor axis of greater than about 1.0, and the bodies having at least one cross-sectional dimension in the range of between about 1.0 nm and about 500 micrometers.
  • Suitable fluids and bodies are described elsewhere herein.
  • the methods may also include dispersing spheres or other bodies having a major axis that is greater than the minor axis of the anisotropic bodies.
  • the user may also disperse a pigment into the composition;
  • compositions comprising a fluid medium having a plurality of anisotropic bodies disposed within, at least some of the anisotropic bodies having an aspect ratio of major axis to minor axis of between about 1.0 and about 10,000.
  • the methods may further include removing at least a portion of the fluid medium following application of the plurality of droplets. This may be effected, e.g., in printing applications, where the user (using, e.g., an inkjet or other printer) may apply droplets of the composition to a substrate and then evaporate the fluid medium so as to leave behind the bodies in the fluid.
  • the anisotropic bodies may be selectively removed (e.g., by application of heat, chemical reagent, or both) so as to leave behind the spheres, pigment, or other constituents in the composition.
  • a user may also apply thermal energy or a chemical reagent to one or more droplets so as to bond two or more anisotropic bodies.
  • the user may create a network of anisotropic bodies on a substrate after the fluid medium has been removed.
  • the user may also apply heat or a chemical reagent to bind spheres or pigment bodies to one another, or even to bind an anisotropic body to a sphere or pigment.
  • the heat or reagent may bond or fuse multiple particles to one another so as to leave behind a network of particles.
  • the heat or reagent may also be used to melt a previously-formed network so as to liberate a reagent that is disposed within some portion of the network particles.
  • a user may apply the disclosed compositions to achieve a uniform dispersion of particles, and then evaporate the fluid, which evaporation leaves behind an even dispersion of particles.
  • the user may then heat (or otherwise process) the particles so as to fuse the particles together (e.g., in the case of a thermoplastic particle) into a network.
  • the resultant network will itself be even.
  • compositions have many applications. For example, many coatings and paints contain two solvents, water and something that evaporates slower than water (e.g., an oil). After the water evaporates away, the coating particles are left in the slowly evaporating oil, where they form a film. If the slowly evaporating oil were removed, the coating would exhibit the coffee ring effect.
  • the disclosed compositions enable the user to eliminate the second solvent, making the process faster and more economical
  • the coatings created by the disclosed compositions are uniform and are also essentially monolayers in form. This is useful in the field of electronics for heat transfer, as thinner, nmore uniform coatings (e.g., conductive metals) allow electronics to dissipate heat more efficiently. Further, this can be useful in the miniaturization of technology, as a thin but effective coating allows more space for other components.
  • the uniformity of the resultant coating can be reduced, with only a small change to optical properties. This is in turn useful for windows or other applications where optical properties are a consideration.
  • compositions are also useful in packaging applications.
  • a monolayer of material may act to keep air-tight seals shut, but the monolayer also will not impair the user's ability to open a container.
  • compositions and methods are also useful in complex assembly.
  • Complicated materials can be assembled one monoloayer at a time.
  • One potential application of this type is photonics or creation of metamaterials.
  • Many such materials can be built out of thin uniform layers of different compositions.
  • a user may construct a device by depositing a quantity of material according to the present disclosure onto a substrate (or position a quantity of the material between two surfaces) and evaporating (or allowing to evaporate) the fluid medium.
  • the surfaces may be solid (e.g., substrates), but may also be fluids.
  • an amount of a composition may be positioned between layers of two other fluids. This will leave behind an essentially uniform dispersion of particles.
  • the user may then place a second quantity of material atop the same location and allow this second quantity to dry, so as to leave a second layer of uniformly-distributed particles atop the first layer.
  • the layers of material may be of the same particles or of different particles.
  • the user may select the particles of the composition to give rise to selective layers.
  • the user may employ a composition that includes anisotropic particles that may be chemically degraded and spherical particles that are chemically resistant.
  • the user may apply the composition and evaporate the fluid medium, leaving behind an essentially uniform distribution of anisotropic particles and spheres.
  • the user may then remove the anisotropic particles (e.g., by application of a suitable chemical agent that selectively removes the anisotropic particles but does not affect the spheres).
  • the user may then leave behind the uniform distribution of spheres or, depending on the user's needs and the characteristics of the spheres, apply heat (e.g., in the case of thermoplastic spheres) to bond the spheres to one another to create a network of fused particles.
  • a chemical agent e.g., a solvent or adhesive
  • a user may formulate compositions that result in a coating of fewer than all of the different kinds of particles or bodies in the fluid composition.
  • the user may, of course, build up structures or regions by depositing multiple particle populations atop one another.
  • a user may also add anisotropic particles (in a volume fraction of from 0.00001 to about 20, 30 or even 50%) to an existing suspension or colloid containing spherical particles.
  • anisotropic particles will confer on the composition the ability to produce essentially uniform (or at least more uniform) particle depositions upon evaporation of the fluid medium.
  • the user may modify or even improve the performance of existing compositions, such as paints, inks, and other coating compositions.
  • compositions and methods are also useful in biotechnology applications.
  • One such application is genotyping.
  • genotyping different complementary strands of DNA are attached to a substrate at known locations. The DNA being investigated is then washed over the substrate. The sequences present in the investigated DNA are then identified based on where it attaches to the substrate.
  • the present compositions may also be applied to liquid bandages. Wounds can be covered with a solution including anisotropic particles. After evaporation, the coating left behind will prevent contaminants from entering the wound, as the coating will be dense and uniformly distributed across the wound.
  • the coating may also be breathable, helping the wound to heal. The coating also would allow the patient to be more mobile, as a monolayer is not very restricting.
  • a user may use heat or reduced humidity to effect evaporation of the fluid medium.
  • Ambient conditions may also be useful to evaporating the fluid medium.
  • suspended particle shape may effect coatings and can be used to eliminate the coffee ring effect.
  • Ellipsoidal particles deposit uniformly during evaporation.
  • the anisotropic particles significantly deform interfaces, producing strong interparticle capillary interactions.
  • strong long-ranged interfacial attractions towards other ellipsoids lead to the formation of loosely -packed quasi- static or arrested structures on the air-water interface. These structures prevent the suspended particles from reaching the drop edge and ensure uniform deposition. Under appropriate conditions, suspensions of spheres mixed with a small number of ellipsoids also produce uniform deposition.
  • a drop of evaporating water is a complex, difficult-to-control, non-equilibrium system.
  • the evaporating drop features a spherical-cap-shaped air- water interface and Marangoni flows induced by small temperature differences between the top of the drop and the contact line. Attempts to reverse or ameliorate the coffee ring effect have thus far focused on manipulating capillary flows.
  • uniform coatings during drying can be obtained by changing particle shape.
  • the uniform deposition of ellipsoids after evaporation (Fig. la) is readily apparent, and it stands in stark contrast to the uneven "coffee ring" deposition of spheres (Fig. lb) in the same solvent, with the same chemical composition, and experiencing the same capillary flows (Fig. lc).
  • the droplet contact line remains pinned in all suspensions, and fluid (carrying particles) flows outward from drop center to replenish the edges.
  • Spherical articles are efficiently transported to the edge, either in the bulk or along the air-water interface, leaving a ring after evaporation is complete.
  • Anisotropic particles (a > 1.0), however, are only transported toward the edge until they reach the air-water interface. For example, once at the air-water interface, ellipsoids experience strong long-ranged attractions to other ellipsoids, leading to the formation of loosely -packed quasi-static or arrested structures at the interface. On the interface, the interparticle attraction between anisotropic particles is more than two orders of magnitude stronger than the attraction between spheres.
  • anisotropic particles in these "open" structures are comparatively strongly bound to each other and to the interface, so the energy cost of deforming, moving, or breaking up these clusters is large.
  • ellipsoid mobility is markedly reduced, and they resist the radially outward flow.
  • anisotropic particles are much more uniformly deposited on the glass surface than spheres. While spheres also adsorb onto the interface during evaporation, they do not significantly deform the interface. Therefore, the radially outward fluid flow continues to push them to the drop's edge.
  • Spherical particles are primarily deposited at the original perimeter of the droplet (Fig. 1 b).
  • Ellipsoidal particles are distributed much more uniformly (Fig. 1 a).
  • This behavior is summarized by calculating pMAX/pMID (Fig- l e ) > where p MAX is me maximum value of (typically located at r/R ⁇ 1) and pMID is me average value oip in the middle of the drop (r/R ⁇ 0.25).
  • Quantification of the spatio-temporal evaporation profile of the suspensions provides a first step toward understanding why ellipsoids are deposited uniformly.
  • Spheres also adsorb onto the interface during evaporation. However, spheres do not strongly deform the interface and they experience a much weaker interparticle attraction than ellipsoids; thus, radially outward fluid flows push spheres to the drop's edge.
  • the calculated Boussinesq number is greater than 1, and grows exponentially with time (see Fig. 7). Shear stress grows linearly with particle velocity, but elastic modulus grows exponentially with ellipsoid area fraction; and dominates the ratio.
  • the Boussinesq number for spheres was much smaller than for ellipsoids, i.e., it is less than 1.
  • a small amount of surfactant e.g., sodium dodecyl sulfate, SDS, 0.2% by weight
  • SDS sodium dodecyl sulfate
  • a 3.5
  • surfactant lowers the surface tension of the drop, thus making interfacial deformations less energetically costly and shorter- range. This restores the coffee ring effect; ellipsoids pack closely at the contact line (Fig. 3c), in a manner similar to spheres.
  • the addition of ellipsoids or other anisotropic particles to a confined solution will produce a uniform deposit when the ellipsoids (or other anisotropic particles) can adsorb on the air-water interface.
  • This technique is effective for micron sized colloids, nanometer sized colloids and macromolecules, and also for individual molecules. It should be understood that the presence of anisotropic (e.g., ellipsoid) particles is effective in forming uniform deposits in sessile (open) and in confined drops (confined drops may be confined between surfaces that are fluid or solid).
  • Figure 26 shows the bending rigidity, ⁇ , of the particle coated air-water interface plotted as a function of particle aspect ratio, a.
  • ⁇ increases by almost two orders of magnitude. Without being bound to any single theory, it is more energetically costly to bend an interface covered with ellipsoids than to bend an interface covered with spheres.
  • the uniform deposition of ellipsoids in confined drops can be explained by measuring the bending rigidity of the particle laden air- water interface as a function of particle shape. Ellipsoids produce a large bending modulus, while spheres produce a small bending modulus. Both spheres and ellipsoids attach to the air-water interface.
  • Ellipsoids deform the air- water interface, creating an effective elastic membrane with a high bending rigidity. When enough ellipsoids are present, pinning and bending the interface becomes energetically costly and the spheres (and ellipsoids) are deposited as the interface recedes.
  • polystyrene particles 1 .3 ⁇ diameter polystyrene particles are suspended in a polyvinyl alcohol (PVA) gel and are heated above the polystyrene melting point (100° C), but below the PVA melting point (180°C). Polystyrene melts in the process, but the PVA gel only softens. The PVA gel is then pulled so that the spherical cavities containing liquid polystyrene are stretched into ellipsoidal cavities. When the PVA gel cools, polystyrene solidifies in the distorted cavities and becomes frozen into an ellipsoidal shape. The hardened gel dissolves in water, and the PVA is removed via centrifugation (see Supplementary Information).
  • PVA polyvinyl alcohol
  • Fig. la and b To quantify the behavior shown qualitatively in Fig. la and b, one may determine the areal number fraction of particles deposited as a function of radial distance from the drop center (Fig. Id). Specifically, image analysis enables counting of the number of particles, N r , in an area set by the annulus bounded by radial distances r and r + Sr from the original drop center; here 5r is ⁇ 8 ⁇ .
  • p(r)/N a function oi r/R, where R is the drop radius.
  • p/N ⁇ 70 times larger at r/R ⁇ 1 than in the middle of the drop.
  • the density profile of ellipsoidal particles is fairly uniform as a function of r/R, though there is a slight increase at large r/R. As aspect ratio is increased in between these extremes, the peak at large r/R decreases.
  • P MAXJ P MID (Fig. le)
  • P MAX is the maximum value of p (typically located at r/R ⁇ 7)
  • P MID is the average value of p in the middle of the drop (r/R ⁇ 0.25).
  • P MAXJ P MID ⁇ V0.
  • P MAXJ P MID decreases to -38 and 13, respectively.
  • P MAX/ P MID is more than ten times smaller.
  • the deposition of spheres and ellipsoids differs significantly.
  • r shear stress from bulk flow
  • G' the elastic modulus of the interfacial layer
  • L the probed lengthscale.
  • Bo will vary spatially with the local number of ellipsoids on the air-water interface, so one may focus here on a region within 40 ⁇ of the contact line.
  • One may first calculate Bo at an early time (t 0.1 tp).
  • the shear stress, calculated from the particle velocity and drop height is r ⁇ 3 10 " 4 Pa.
  • About 40% of the surface is covered with ellipsoids.
  • the probed length scale, L is at most 0.01 m.
  • t O. ltp, B 0 -300. This calculation is performed at different times during evaporation, until the aggregate of ellipsoids begins flowing towards the drop center (Fig. 7).
  • the Boussinesq number grows
  • spherical and ellipsoidal polystyrene-PNIPAm core-shell particles i.e., polystyrene particles coated with PNIPAm. These suspensions were evaporated at 23 °C; at this temperature, PNIPAm is hydrophilic.
  • the core-shell spheres exhibit the coffee ring effect (Fig. 8).
  • the core-shell ellipsoids are deposited evenly. In fact, they form the same aggregates on the drop surface that polystyrene ellipsoids that are not coated with PNIPAm do (Fig. 8).
  • the three-phase contact angle, ⁇ was measured by placing a large drop (100 ⁇ ) on a glass slide. Then, a side-view picture was taken, allowing the contact angle to be measured (Fig. 9). Spheres do not modify the contact angle. However, as a increases, Qc increases as well.
  • the contact line remains pinned, and the spheres exhibit the coffee ring effect.
  • the PVA weight percent is decreased by a factor of 100 (to an absolute maximum of 0.05%), the deposition of the spatially uniform deposition of ellipsoids persists.
  • Figure 1 1 illustrates (left-hand side) a traditional coffee ring pattern that results from evaporation of a fluid droplet that contains some particulates.
  • the right side of Figure 1 1 illustrates a uniform distribution of particles that results from evaporation of a droplet according to the present disclosure, which droplet includes anisotropic particles.
  • Figure 12 provides a more detailed representation of the so-called coffee ring effect.
  • a droplet of a liquid containing particulates e.g., coffee
  • a ring-shaped deposit of particulate is left behind. This may be explained as set forth in Figure 13, which depicts the evaporation of a droplet; while evaporation occurs across the surface of the drop, the edges of the droplet will evaporate first.
  • the contact line ( Figure 14) is pinned, so fluid flows to the contact line to replenish the fluid. Colloids (or other particles) are carried with the fluid to the edge of the droplet.
  • Figure 15 shows the characteristic ring-link deposition of spheres that present in a fluid droplet that has evaporated.
  • the inclusion of anisotropic particles in such a fluid droplet can prevent the formation of such a coffee ring pattern and instead promote uniform or even distribution of particles when the fluid evaporates, as shown in the right-side of Figure 1.
  • Figure 16 depicts an exemplary method of forming anisotropic (ellipsoidal) particles from spheres.
  • polystyrene spheres PS
  • PVA polyvinyl alcohol
  • Heat is applied to the composition, which heat liquefies the PS spheres while leaving the PVA solid.
  • the composition is stretched, which stretching elongates the cavities in which the PS spheres resided, and the liquid PS conforms to the newly- stretched cavities.
  • the composition is then cooled, and the PS solidifies into ellipsoidal bodies.
  • the ellipsoidal bodies may have an aspect ratio of greater than 1 ; as shown in the figure, the process may be used to form bodies having an aspect ratio of about 3.
  • Figure 18 illustrates a comparison between the positions of spheres (top) and ellipsoids (bottom) in a drop, as shown in cross- section. As shown in the figure, the ellipsoids form a loosely-packed structure at the fluid-air interface, whereas the spheres are (top) essentially concentrated at the edge of the drop.
  • Figures 20-24 further illustrate the effect of the presence of anisotropic particles in a droplet.
  • Figure 20 illustrates the evaporation of a confined droplet containing anisotropic particles of various aspect ratios (a). As shown in Figure 20, the greater the aspect ratio of the anisotropic particles, the more even the distribution of particles following evaporation. This demonstrates that the advantages of the present disclosure are not confined to standard droplets having an upper surface open to the environment.
  • FIG. 21 Further illustration of this effect is shown in Figure 21.
  • the left- hand of the figure illustrates evaporation behavior of a droplet that contains spheres
  • the right-hand of the figure illustrates evaporation behavior of a droplet that contains ellipsoidal anisotropic particles.
  • the presence of the anisotropic ellipsoids effects a uniform distribution of particles within the evaporated droplet.
  • Figure 22 illustrates the physical configuration of a droplet that is confined between two opposing plates.
  • a standard droplet placed on a substrate, the droplet having an upper surface that is exposed to the environment exterior to the droplet.
  • the right-hand side of figure illustrates a confined droplet, where the droplet is confined between upper and lower substrates. The confinement may act to impair the ability of ellipsoids (or other particles) from reaching the air- fluid interface.
  • Figure 24 illustrates that in a droplet that contains spherical particles and ellipsoids (anisotropic particles), the spheres distribute more evenly upon evaporation than they do in a droplet that contains only spherical particles.
  • anisotropic particles effects an essentially uniform distribution of spheres in a droplet following evaporation.
  • the volume fraction of spheres to ellipsoids was approximately 10. It should be understood that this exemplary volume: volume ratio is not a minimum or maximum, as post-evaporation uniform particle distribution may be achieved by other ratios of anisotropic particles to spheres.
  • colloidal particles When colloidal particles adsorb onto air-water, oil-water, and other such interfaces, novel elastic membranes are created.
  • the mechanical properties of these colloidal monolayer membranes (CMMs) may depend on many factors, including surface tension, capillary forces, particle size, shape, hydrophobicity, packing, and interaction potential.
  • the resulting interface phenomenology is rich with physics that influences a wide range of applications from film drying to Pickering emulsion stabilization.
  • Bending rigidity is of interest because the buckling behavior of membranes is controlled by the ratio of bending rigidity ( ⁇ ) to Young's modulus (E), and the buckling behavior of membranes can substantially affect phenomena such as particle deposition during droplet evaporation.
  • CMM bending rigidity increases with increasing adsorbed-particle shape anisotropy.
  • bending rigidity increases with increasing adsorbed-particle shape anisotropy.
  • Increased interfacial bending rigidity dramatically changes particle deposition during evaporation.
  • Spheres can locally pin the three-phase contact line, which then bends around the pinning site and produces an uneven deposition.
  • the large bending rigidity induced by adsorbed ellipsoids makes deformation of the contact line energetically costly and ultimately induces uniform deposition.
  • drops of spheres doped with small numbers of ellipsoids are also deposited relatively uniformly in these confined geometries.
  • the exemplary experiments presented here utilize micron-sized polystyrene particles with modified shape, stretched asymmetrically to different major-minor diameter aspect ratio, a.
  • the spheres are 1.3 ⁇ in diameter; all ellipsoids are stretched from these same 1.3 ⁇ spheres.
  • the colloidal drops are confined between two glass slides separated by 38.1 ⁇ spacers (Fisher Scientific); qualitatively similar results are found for chambers made from slightly hydrophobic cover slips.
  • the air-water interface deforms and crumples [Figs. 27(b) and 27(c)].
  • the buckling behaviors exhibited by the ribbonlike CMMs in confined geometries may depend on the shape of the adsorbed particles, and the buckling events appear similar to those observed in spherical-shell elastic membranes. Before buckling events occur, particles are maximally packed near the three-phase contact line, regardless of particle shape. Further, because the volume fraction is relatively low, membranes may contain a monolayer of particles; i.e., buckling events occur before multilayerparticle membranes form. These buckling events occur in-plane; i.e., the curvature in the i direction does not change after the membrane buckles .
  • ⁇ is the radial displacement of the membrane from its initial configuration
  • h is the chamber height
  • r is the in-plane radius of the droplet.
  • d is the width of the rim formed by the bent air- water interface, where the deformation bending and stretching energy is concentrated.
  • d is independent of the depth of the invagination. Thus, measurements of d are unaffected by pinning events during buckling.
  • the ellipsoid- CMM contact line recedes radially, and the ellipsoids near the contact line are deposited on the substrate.
  • This behavior is similar to convective assembly techniques wherein a drying front is created by pulling the substrate away from the contact line or by heating a confined drop near the contact line; in each case a thin film is thus formed that leads to the creation of a monolayer.
  • the present system has neither moving nor mechanical parts. Uniform coatings are created essentially as a result of shape-induced capillary attractions which produce CMMs that are hard to bend.
  • the membrane still resists bending around pinning sites.
  • This behavior in confined geometries is different than that of sessile drops wherein it was discovered that if the spheres are larger than the ellipsoids, then the spheres are distributed uniformly after drying, but if the spheres are smaller than the ellipsoids, then they exhibit the coffee ring effect. It is thus surprising that small spheres are deposited uniformly from droplets doped with small numbers of ellipsoids and confined between glass plates.
  • ellipsoids adsorbed on the air-water interface create an effective elastic membrane, and, as particle anisotropy aspect ratio increases, the membrane's bending rigidity increases faster than its Young's modulus.
  • the different elastic properties produce particle depositions that are highly dependent on particle shape.
  • This observed increase in bending rigidity with particle shape aspect ratio holds consequences for applications of colloidal monolayer membranes as well.
  • increased bending rigidity may help stabilize interfaces (e.g., Pickering emulsions) and thus could be useful for industrial applications, e.g., food processing.
  • CMMs in confined geometries may be a convenient model system to study buckling processes that are relevant for other systems, e.g., polymeric membranes, biological membranes, and nanoparticle membranes.

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Abstract

L'invention concerne des compositions qui comprennent des particules anisotropes, lesquelles particules anisotropes permettent aux compositions de sécher et de laisser derrière elles une distribution uniforme de particules au lieu de ce que l'on appelle « rond de café » de particules qui caractérise typiquement des gouttelettes séchées. L'invention concerne également des procédés et des formulations de telles compositions.
PCT/US2012/050223 2011-08-11 2012-08-10 Revêtements uniformes obtenus par des suspensions de particules anisotropes WO2013023110A2 (fr)

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CN105154868A (zh) * 2015-08-28 2015-12-16 清华大学 一种基于抽气方法的纳米涂层沉积装置及方法
CN107379767A (zh) * 2017-07-31 2017-11-24 华南理工大学 一种均匀墨水打印线喷墨打印方法及装置
CN111398277A (zh) * 2020-04-03 2020-07-10 四川师范大学 一种面膜分析检测方法
WO2021109246A1 (fr) * 2019-12-06 2021-06-10 深圳市华星光电半导体显示技术有限公司 Encre à points quantiques, procédé de fabrication de panneau d'affichage et panneau d'affichage
CN118288684A (zh) * 2024-03-21 2024-07-05 中国科学院力学研究所 一种基于主动气流控制的咖啡环抑制方法

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US6951666B2 (en) * 2001-10-05 2005-10-04 Cabot Corporation Precursor compositions for the deposition of electrically conductive features
JP5570721B2 (ja) * 2005-06-17 2014-08-13 ザ ユニバーシティ オブ ノース カロライナ アット チャペル ヒル ナノ粒子の製造方法、システム、及び材料
EP2152788B1 (fr) * 2007-05-29 2019-08-21 Tpk Holding Co., Ltd Surfaces ayant des particules et procédés associés
JP2013514193A (ja) * 2009-12-17 2013-04-25 メルク パテント ゲゼルシャフト ミット ベシュレンクテル ハフツング ナノ粒子の堆積

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105154868A (zh) * 2015-08-28 2015-12-16 清华大学 一种基于抽气方法的纳米涂层沉积装置及方法
CN107379767A (zh) * 2017-07-31 2017-11-24 华南理工大学 一种均匀墨水打印线喷墨打印方法及装置
CN107379767B (zh) * 2017-07-31 2023-02-14 华南理工大学 一种均匀墨水打印线喷墨打印方法及装置
WO2021109246A1 (fr) * 2019-12-06 2021-06-10 深圳市华星光电半导体显示技术有限公司 Encre à points quantiques, procédé de fabrication de panneau d'affichage et panneau d'affichage
CN111398277A (zh) * 2020-04-03 2020-07-10 四川师范大学 一种面膜分析检测方法
CN118288684A (zh) * 2024-03-21 2024-07-05 中国科学院力学研究所 一种基于主动气流控制的咖啡环抑制方法

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