Patent Application
20240287329
The present disclosure generally relates to methods of additive manufacturing and articles made therefrom.
Additive manufacturing (AM) of soft materials has enabled the rapid design and fabrication of a wide range of materials and complex geometries. These advancements in manufacturing have led to an emergence of soft matter devices that have tunable physical and functional properties across various length scales, creating soft multifunctional materials including active shape morphing, soft pneumatic channels to create robots and electrically conductive materials. To push these devices towards all soft matter systems, an emerging architecture is to create solid-liquid composite materials with liquid-phase fillers dispersed in soft elastomers. Liquid metals (LMs) like eutectic gallium-indium (EGaIn) have been of particular interest due to their low viscosity, low toxicity, high electrical and thermal conductivity, and rapid formation of a surface oxide. This surface oxide forms nearly instantaneously at low oxygen concentration and allows for physical droplet manipulation and retention of metastable shapes. LM-based solid-liquid composites can be engineered to exhibit a wide range of material properties including extreme toughening, exceptional electrical and thermal properties; shape-morphing; stiffness tuning; and the ability to form electrically conductive pathways through controlled mechanical pressure, deformation, and laser patterning. Key to these composites is the ability of the LM droplets to reconfigure their shape, orientation, and connections. In particular, control over LM microstructure ranging from spherical to ellipsoidal droplet shapes to connected droplet networks is essential for achieving advanced functions and properties; including over 10× enhancements in electrical conductivity, material toughness, and thermal conductivity.
Despite advances in additive manufacturing research, there is still a scarcity of methods and materials that are customizable and tunable on a microstructure scale. These needs and other needs are satisfied by the present disclosure.
In accordance with the purpose(s) of the disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to methods of additive manufacture of emulsion compositions.
Disclosed are methods of additive manufacture of emulsion compositions. Also disclosed are methods of direct writing using emulsion compositions. Further disclosed are composite materials comprising emulsions of inclusive compositions. Further disclosed are composite materials comprising microstructures formed by inclusive compositions in prepolymer compositions.
Methods are provided for additive manufacturing of an article comprising a composite material; the method comprising: (a) extruding a first emulsion ink composition through a first nozzle to form a first layer of a composite material in a pattern that corresponds to a first layer of an article; wherein the first emulsion ink composition comprises a plurality of discrete droplets of a liquid inclusion composition dispersed within a prepolymer composition; wherein the composite material comprises a plurality of microstructures formed from the liquid inclusion composition embedded within a polymer matrix formed from the prepolymer composition; and wherein a first nozzle height and a first nozzle velocity at which the first emulsion ink composition is extruded from the first nozzle are chosen to control one or more of a shape of a microstructure, an aspect ratio of a microstructure, and a connectivity of microstructures in the plurality of microstructures in the first layer of the article. Articles made by the methods are also provided.
Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described aspects are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described aspects are combinable and interchangeable with one another.
Further aspects of the present disclosure will be readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings.
By reconfiguring isolated spherical LM droplets into a connected network, an initially insulating film can be transformed into electrically conductive traces, which are also self-healing by the subsequent reconfiguration of droplets from damage events. Strain-invariant electrical resistance, which goes against kinematic predictions from Pouillet's Law, can be achieved as droplet networks deform under strain. While isolated ellipsoidal and oriented LM droplets create thermally conductive pathways to increase thermal conductivity over spherical droplets and deect cracks to increase toughness. These results demonstrate that material properties and performance are strongly dependent upon droplet microstructure and connectivity, spatial placement and orientation, and volume loading. However, common fabrication approaches using bulk replica molding, soft lithography, or patterning techniques result in primarily spherical inclusions with little control of shape, orientation, or spatial placement. While, connected LM droplet networks are typically formed using secondary operations or through the addition of a rigid filler. New fabrication processes are needed to enable spatial control of inclusion morphology and connectivity during fabrication to achieve programmable LM microstructures for systematic control of material properties and device performance.
Direct ink writing (DIW) is a filament-based AM method that allows printing of high-viscosity fluids, concentrated polymer solutions, and high-volume percent fillers at ambient conditions. A variety of DIW methods and inks have been developed to achieve alignment of fillers such as magnetic particles, liquid crystal molecules, high-aspect ratio fibers, and cellulose fibrils. While the orientation of fillers can be controlled, the aspect ratio remains fixed during printing due to the relatively rigid, non-deformable properties of the filler. Recently, the ability to DIW emulsions with LM inclusions was demonstrated, however the combination of printing process conditions and LM droplet size resulted in primarily spherical inclusions. Liquid inclusions can be elongated under mechanical deformation by inducing unrecoverable plastic strain or thermal annealing of composites after stretching, however these approaches require specific materials, lack spatial control, and only allow for elongation of inclusions along a single axis. While significant progress has been made towards achieving spatial control of composition, structure, and properties during DIW, emulsion-based inks offer new opportunities to not only control orientation but the shape and connectivity of LM fillers during the fabrication process.
Herein, a new DIW 3D printing strategy is introduced to achieve on demand programming of LM composite microstructures throughout a printed part. The functional emulsion ink consists of spherical LM microdroplets dispersed in a prepolymer matrix that can be printed and then cured into a soft and highly extensible elastomeric composite. By systematically controlling the printing process conditions and LM droplet size, we were able to transform the initially spherical LM droplets into highly elongated and orientated ellipsoids on demand at any location with very high aspect ratios (AR; major/minor ellipsoid axis). The rapid formation of the surface oxide locks these droplets into the programmed shape and allows for systematic control of the LM droplet microstructure throughout a printed part. In addition to shape and orientation, we can also transform the initially isolated LM droplets into a connected network using the same ink and manufacturing system. This on demand spatial control of LM microstructure (i.e., shape, orientation, and connectivity) has not been demonstrated with currently available casting, stretching, or patterning approaches. To rationally guide the DIW printing process, we created a quantitative design map as a function of the printing parameters, which shows that the LM microdroplet AR increases with nondimensionalized nozzle velocity and decreasing nozzle height. Utilizing the quantitative design map, we printed elastomer composites with unique LM microdroplet patterns such as smooth and discrete transitions from spherical to needle-like microstructures, curvilinear microstructures, geometrically complex thermal patterns, and embedded heat spreaders. We also create 3D structures that contain spatial variations in droplet shape in 3D configurations. These capabilities not only advance the manufacturing of LM-composites, but demonstrate new capabilities in DIW to tune inclusion shape, orientation, and connectivity on demand in composite materials, which is achieved through the use of liquid-phase fillers and is uniquely enabled by LM inclusions rapidly forming a surface oxide shell to lock in the programmed microstructure. The systematic integration of DIW 3D printing with advanced multifunctional materials provides opportunities to create composite architectures for emerging technologies such as soft robotics, human-machine interaction, and wearable electronics that demand mechanical compliance with a highly tunable functional response.
Many modifications and other aspects disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific aspects disclosed and that modifications and other aspects are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.
Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
As will be apparent to those of skill in the art upon reading this disclosure, each of the individual aspects described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several aspects without departing from the scope or spirit of the present disclosure.
Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.
All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.
While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.
It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.
Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.
As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.” Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.
As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.
As used herein, nomenclature for compounds, including organic compounds, can be given using common names, IUPAC, IUBMB, or CAS recommendations for nomenclature. When one or more stereochemical features are present, Cahn-Ingold-Prelog rules for stereochemistry can be employed to designate stereochemical priority, E/Z specification, and the like. One of skill in the art can readily ascertain the structure of a compound if given a name, either by systemic reduction of the compound structure using naming conventions, or by commercially available software, such as CHEMDRAW™ (Cambridgesoft Corporation, U.S.A.).
Reference to “a” chemical compound refers to one or more molecules of the chemical compound rather than being limited to a single molecule of the chemical compound. Furthermore, the one or more molecules may or may not be identical, so long as they fall under the category of the chemical compound. Thus, for example, “a” chemical compound is interpreted to include one or more molecules of the chemical, where the molecules may or may not be identical (e.g., different isotopic ratios, enantiomers, and the like).
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a metal oxide,” “an inert gas,” or “a catalyst,” includes, but is not limited to, two or more such articles, and the like.
It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.
When a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g. ‘about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y′, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’ as well as the ranges of ‘greater than x’, greater than y′, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.
It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.
As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.
As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere).
In various aspects, emulsion inks are provided that can be used for carrying out the methods and making the articles described herein. Emulsion ink compositions include a plurality of discrete droplets of a liquid inclusion composition dispersed within a prepolymer composition. A variety of liquid inclusion compositions can be controllably formatted in a variety of different prepolymer compositions to form emulsion inks having various particle sizes, volume loadings, and rheological properties such as the modulus and shear rate dependent viscosity.
In some aspects, the particle sizes include mean particle diameters from about 0.5 micron, 1 micron, 5 micron, 10 micron, 15 micron and up to about 200 micron, 250 micron, 300 micron, 400 micron, 500 micron, or more. The volume loading of the liquid inclusion composition can be from about 10% and up to about 80% e.g., from about 10 vol %, 20 vol %, 30 vol %, 40 vol % and up to about 50 vol %, 60 vol %, 70 vol %, 80 vol %, or more. The particle diameters and the loading volume can be controllably altered using techniques such as shear mixing, sonication, the use of surfactants, the use of solvent to lower viscosity where the solvents can be subsequently evaporated or removed, and other techniques that will become apparent to those skilled in the art.
The liquid inclusion composition can in principal include any liquid having suitable rheological properties and be chosen to provide valuable functional aspects to the articles made from the emulsion inks. In some aspects, the liquid inclusion composition is or includes a liquid metal. A liquid metal is a metal or a metal alloy which is liquid at or near room temperature. In some aspects, the liquid metal is mercury (Hg), cesium (Cs), gallium (Ga), rubidium (Rb), francium (Fr), indium (In), bismuth (Bi), tin (Sn), cadmium (Cd), thallium (TI), antimony (Sb), or alloys thereof and alloys including one or more other metals. In some aspects, the liquid metal includes GaIn or other Ga alloys.
The emulsion ink includes one or more prepolymers forming the prepolymer composition. The prepolymer composition can include an elastomer, a thermoset, a thermoplastic, and/or photocurable resin, For example, the prepolymer may be selected from the group consisting of acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), poly(methyl methacrylate) (PMMA), epoxy, polydimethylsiloxane (PDMS), polyamide (Nylon), polyimide (PI), polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluorethylene (PTFE), polyvinylchloride (PVC), polyurethane (PU), polycarbonate (PC), photocurable resins, epoxies, and hydrogels. The prepolymer can include various silicone resins. Suitable elastomers can include silicone, polyurethane, thermoplastic elastomers, or a combination thereof. Suitable thermosets can include epoxies, polyesters, polyurethanes, polyimides, acrylonitriles, copolymers thereof, and blends thereof. Suitable thermoplastics can include polyolefins, polystyrenes, polyesters, polycarbonates, nylons, acrylics, polyacrylates, butyl, polybutenes, polyisobutylenes, liquid crystal polymers (LCP), ethylene copolymers, vinyl chloride, polyvinyl chloride (PVC), ionomers, ketones, polyamides, polyether block amide (PBA), polyphenylene oxide (PPO), polyphenylene sulphide (PPS), acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyethylene terephthalate glycol-modified (PETG), nylon, copolymers thereof, and blends thereof.
The loading volume, particle size, and rheological properties of the emulsion ink can be controllably altered with various additional additives or components. For example, surfactants can be used to stabilize various emulsions having specific matrices and/or particle size and loading. Solvents can be used to assist in the mixing to achieve targeted volume loading, which can be later removed by evaporation or otherwise. Blends of polymers can also be used to achieve the targeted rheological properties. Tuning the modulus and shear rate dependent viscosity can be achieved through additives. Blends can further include rheology modifying agents such as fumed silica or silver flakes.
In various aspects, methods of additive manufacturing of an article using emulsion inks. The methods can include extruding a first emulsion ink composition through a first nozzle to form a first layer of a composite material in a pattern that corresponds to a first layer of an article. A single layer can include one or multiple different inks. In some aspects, there are two, three, four, or more inks used to spatially vary the properties of the printed articles. In other aspects, the properties are varied using a single ink but by controlling an aspect ratio of the liquid inclusion complexes in the emulsion ink as it is extruded. In instances where the method includes using multiple inks, some of the inks can lack the liquid inclusion complex. For example, by additive manufacturing with conventional polymers in a second ink along with emulsion inks, complex architectures can be created while only depositing the liquid inclusion complexes where needed.
In some aspects, a first nozzle height and a first nozzle velocity at which the first emulsion ink composition is extruded from the first nozzle are chosen to control one or more of a shape of a microstructure, an aspect ratio of a microstructure, and a connectivity of microstructures in the plurality of microstructures in the first layer of the article. Applicants have demonstrated that by controlling the nozzle height and the nozzle velocity (often referred to using the nondimensional velocity V* as described elsewhere herein), the aspect ratio of the liquid inclusion complex can be precisely controlled. In some aspects, controlling these parameters can control a shape of a microstructure, an aspect ratio of a microstructure, and a connectivity of microstructures in the plurality of microstructures in the article.
In some aspects, a method of additive manufacturing of an article is provided that includes extruding a first emulsion ink composition through a first nozzle to form a first layer of a composite material in a pattern that corresponds to a first layer of an article; wherein the first emulsion ink composition comprises a plurality of discrete droplets of a liquid inclusion composition dispersed within a prepolymer composition; wherein the composite material comprises a plurality of microstructures formed from the liquid inclusion composition embedded within a polymer matrix formed from the prepolymer composition; and wherein a first nozzle height and a first nozzle velocity at which the first emulsion ink composition is extruded from the first nozzle are chosen to control one or more of a shape of a microstructure, an aspect ratio of a microstructure, and a connectivity of microstructures in the plurality of microstructures in the first layer of the article.
In some aspects, the method can be completed multiple times to build an article in a layer by layer approach. By varying the nozzle height and nozzle velocity or the ink compositions for each layer, the properties can be controllably varied within layers and between layers. In some aspects, the method includes extruding a second emulsion ink composition through a second nozzle to form a subsequent layer of a composite material in a pattern that corresponds to a subsequent layer of the article; wherein the subsequent later is formed on either the first layer of the article or another subsequent layer of the article; wherein the second emulsion ink composition comprises a plurality of discrete droplets of a liquid inclusion composition dispersed within a prepolymer composition; wherein the subsequent layer of the composite material comprises a plurality of microstructures formed from the liquid inclusion composition embedded within a polymer matrix formed from the prepolymer composition; and wherein a second nozzle height and a second nozzle velocity at which the second emulsion ink composition is extruded from the nozzle are chosen to control one or more of a shape of a microstructure, an aspect ratio of a microstructure, and a connectivity of a microstructure in the plurality of microstructures in the second layer of the article.
In some aspects, the methods can include forming regions in the article wherein the liquid inclusion complex becomes interconnected upon printing. For example, the methods can include disturbing a layer of the composite material to interconnect one or more distinct microstructures of inclusion material. The interconnection can also be controlled through the printing process, whereby very high aspect ratios are achieved such that the inclusion compositions become interconnected. O or both of the first nozzle height and the first nozzle velocity can be chosen to interconnect two or more of the droplets to form interconnected microstructures. This can be particular advantageous, for instance, when the inclusion composition is electrically conductive. This can allow for the creation of electrically conductive and electrically insulating regions within the some article and using the same ink.
This disclosure will be better understood upon reading the following numbered aspects which should not be confused with the claims. Each of the aspects described below may, in other aspects, be combined with each other or be combined with aspects described elsewhere herein including aspects described above and any aspects demonstrated in the examples which follow.
Now having described the various aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of aspects of the present disclosure. In particular, while the examples provide one or more specific aspects, in other aspects the examples may be combined with aspects described elsewhere herein, including in the numbered aspects above.
The exampled demonstrate a direct ink writing technique to program LM microstructure (i.e., shape, orientation, and connectivity) on demand throughout elastomer composites. In contrast to inks with rigid particles that have fixed shape and size, the example demonstrates that emulsion inks with LM fillers enable in-situ control of microstructure. This enables filaments, films, and 3D structures with unique LM microstructures that are generated on demand and locked in during printing. This includes smooth and discrete transitions from spherical to needle-like droplets, curvilinear microstructures, geometrically complex embedded inclusion patterns, and connected LM pathways. The printed materials are soft (modulus<200 kPa), highly deformable (>600% strain), and can be made locally insulating or electrically conductive using a single ink (in this case a gallium indium alloy) by controlling process conditions. This example demonstrates embedding elongated LM droplets in a soft heat sink, which rapidly dissipates heat from high power LEDs. These programmable microstructures enable new composite paradigms for emerging technologies that demand mechanical compliance with multifunctional response.
The LM emulsion inks were fabricated by dispersing microdroplets of eutectic gallium indium alloy (Ga:In in the ratio 3:1 by mass) in a two-component silicone elastomer (Ex-Sil™ 100; Gelest Inc.). First, the two-part silicone prepolymer was prepared by combining part A and part B at a 100:1 ratio by mass, then mixing and degassing in a planetary centrifugal mixer (Flaktek™ Speedmixer). The emulsion was formed by adding LM at 50% by volume to the silicone prepolymer and further mixing for 1 min at 2300 rpm for D=20 μm and 800 rpm for D=100, 200 μm. To obtain the D=200 μm size, hexane was added to the elastomer in a 1:8 ratio by weight before the addition of LM. The hexane was removed before printing by placing the ink in a vacuum chamber for 2.5 hours. To ensure a similar treatment before printing, the inks with D=20, 100 μm were also degassed to remove trapped air voids and allowed to sit for 2.5 hours after mixing. The ink was then loaded into a syringe for DIW, printed, and cured in a convection oven at 100° C. for 24 hours.
A Hyrel Engine SR 3D printer with SDS-10 head was modified to level the bed. A thin layer of Sylgard 184 (10:1 ratio) was cast on the aluminum bed and a 170×170 mm glass sheet was placed on the top. A thin layer of Ecoflex 00-30 was spin coated on a 70 mm diameter glass disk, which was attached to the glass sheet on the bed. Single-layer prints are printed on a 4-mil PET film (McMaster-Carr) adhered to the Ecoflex bed for convenience of removal and handling. Optimum® SmoothFlow™ nozzles (Nordson EFD) with 0.84 mm diameter were used to extrude the ink. An extrusion velocity of C=6.8 mm-s-1 was used for V*=1, 3, 6 filaments, and C=4.2 mm-s-1 was used for V*=12 filaments. Print head velocity was V=6.8, 20.4, 40.8, and 50.4 for V*=1, 3, 6, 12 filaments, respectively.
For multilayer prints, 5-mil polycarbonate film (McMaster-Carr) was used as the substrate. Each layer was partially cured before printing the next using a hot air gun set to 130° C. for 5 min, followed by cooling with a fan for 6 min. The hot air gun was attached as a print head to the H3D mounting system and controlled using an auxiliary output to provide directed heating and automate the partial curing process. The cooling fan was rigidly attached to the print bed and controlled using an auxiliary output to increase convection heat transfer. Before each layer, the syringe plunger was depressed at the desired velocity for 1 min to allow the extrusion velocity to reach equilibrium. Films containing both spherical and elongated droplets (
Before imaging, a layer of Sylgard 184 was deposited over each sample to reduce glare from the LM droplets. Optical micrographs were obtained using a Zeiss Axio Zoom v16 stereo microscope. Image analysis was performed using Fiji software. The LM droplets were manually outlined on the micrograph and a mask is created with dark regions for droplets and a bright background for the matrix. Gaussian fits were performed on inclusion histograms to obtain a mean and standard deviation for the distributions. Analysis for micrographs is presented in
Uniaxial tension tests were performed on an Instron 5944 mechanical testing machine. Printed single- and multi-filament samples were attached with tape on either end, and this section was inserted in the pneumatically controlled grips. The tested length of the filaments between the grips was approximately 40 mm. Samples were strained at an extension rate of 1 mm-s-1. The tensile modulus was calculated from the slope of the stress-strain curve up to 5% strain.
Two different patterns were analyzed with elongated droplets as the letters ‘N’ and ‘VT’ and spherical droplets at other regions. The samples were kept on the 5-mil polycarbonate film and placed on a hot plate set to 50° C. IR images were captured with a FLIR A655sc IR
LM traces were spray coated using a nitrogen-assisted masking deposition technique to form interconnects on top of the composite. Then 4 LEDs (Cree® XLamp® XHP50) were placed on the surface of the composite in contact with the LM trace. The composite was placed on an aluminum block and a current of 0.5 A was applied to the 4-LED circuit in series for 40 seconds and then switched off. An IR camera (FLIR E54sc) was used to capture the thermal distribution.
Electrical measurements were performed using a Fluke 117 True RMS multimeter. Stainless steel needles (25 gauge) were attached to the multimeter probes for measuring resistance of a single droplet and regions around it.
For DIW of functional emulsion inks, the ink is loaded into a syringe and the material is extruded from the nozzle at a desired flow rate using a mechanically driven syringe pump, while the nozzle is moved laterally along a substrate. The functional emulsion ink consists of LM microdroplets dispersed in a silicone prepolymer, which has been previously demonstrated.27, 33 The emulsion ink is fabricated with three different LM microdroplet diameters (D=20, 100, 200 μm; see Experimental Section for more details). We can spatially control the orientation and AR of the LM microdroplets in the extruded filament by controlling printing parameters including the i) nondimensionalized nozzle velocity (V*=V/C) that represents the ratio of the nozzle velocity (V) to extrusion velocity (C) and ii) nozzle height (H) along a straight motion path. Systematically controlling the printing parameters V* and H results in a gradual and controlled change in the AR of the LM microdroplets with high AR fillers aligning along the printing direction (
A cross section of the printing nozzle is illustrated in
To systematically study the influence of printing parameters on the programmed LM microstructure, we independently investigated three parameters: i) the diameter (D) of the LM microdroplets in the emulsion ink, ii) the nondimensionalized nozzle velocity (V*), and iii) the height of the nozzle from the printing bed (H). The influence of LM microdroplet diameter on LM microstructure for a given printing velocity and nozzle height (V*=12, and H=20 μm) is shown in
To guide the programming of LM microstructures and the selection of printing parameters for the new DIW strategy, we examined AR as a function of printing conditions. We performed particle analysis for the filaments printed with D=200 μm droplets, shown in
The DIW of LM-composites results in materials that are soft and highly deformable due to the combination of a soft elastomer with liquid-phase inclusions. This is demonstrated by the printed filaments capable of being stretched and easily wrapped around a human finger. To quantify their mechanical properties, the filaments were stretched in uniaxial tension until they failed and the stress-strain curves were analyzed.
The printed composite filaments can also be stretched over multiple loading cycles. This was evaluated by stretching a filament printed with V*=1, H=100 μm, and D=200 μm up to 500% strain in 100% increments with 3 cycles at each increment (
The DIW strategy for controlling LM microstructure throughout a printed part enables us to create single layer films and multilayer structures with varying inclusion morphology using a single ink and AM system. By following a curve instead of a straight motion path, we could create nonlinear, high AR LM microstructures with shapes that mimic the print path. Here, we demonstrated this ability by printing a spiral pattern. The optical micrograph of the printed film is shown in
To further demonstrate the ability to spatially control the LM microstructure, microstructural patterns can be embedded in the printed structure. This allows for the embedding of different functional properties throughout a part. We demonstrated spatial control of LM microstructure by printing the letter ‘N’ with high AR (V*=12, H=70 μm, and D=200 μm) LM droplets, with spherical (V*=2, H=210 μm, and D=200 μm) LM droplets surrounding the letter.
To further demonstrate the versatility of the DIW strategy to program LM-composite microstructures, we printed a multilayer, multimaterial soft heat sink. We utilized two extrusion-based print heads to create a 15-layer part with two regions of pure silicone elastomer (E1, E2) and two regions of LM-composite containing oriented LM droplets (LM1, LM2) using the following printing parameters V*=12, H=70 μm, and D=200 μm. A schematic illustration of the programmed LM microstructure is shown in
The DIW strategy for programming LM-composite microstructures enables the fabrication of 3D multilayered structures consisting of isolated LM droplets with controllable shape and orientation. These microstructures are important for applications that require electrical insulation. To enable applications where electrical conductivity is needed, the formation of LM networks is essential. Therefore, the ability to control LM microstructures form spherical to ellipsoidal to connected networks can open possibilities system to print composites with diverse functionalities. Here, using the same emulsion ink and manufacturing, we demonstrate that the initially isolated LM droplets could be printed and then reconfigured into a connected network of LM droplets to form electrically conductive traces.
We have demonstrated spatial control of LM droplet microstructure in elastomer composites through a DIW 3D printing process. The interplay between the printing velocity, printing height, and the LM droplet size in the DIW setup leads to controllable droplet architectures (i.e., shape, orientation, and connectivity). The liquid nature of the gallium-indium LM alloy with rapidly forming surface oxide in combination with the DIW process enables programmable architectures in a rapid single step process without the need for post processing. This allows for highly tunable microstructures throughout a manufactured part that can enable spatial programming of material properties. The nearly instantaneous formation of the LM oxide shell is key to this printing process as it allows for on-demand formation of non-spherical droplets that are rapidly locked into shape during printing. We hypothesize that the oxide shell prevents surface tension from restoring the droplet to a spherical shape. The rapid oxide formation coupled with the droplet elongation generated during printing enables the on-demand creation of unique microstructures in the printed filament, including smooth and discrete transitions from spherical to needle-like droplets with ARs as high as 40, curvilinear microstructures, connected LM networks, and geometrically complex embedded inclusion patterns. We demonstrate the spatial LM microstructure control by creating films and 3D structures with unique LM microstructure gradients and patterns. Although we demonstrated the functionality of the printing process by creating a passive heat spreader for an LED circuit, the new DIW 3D printing process could be utilized to print parts with programmable and anisotropic properties for actuators, sensors, and circuits for soft robotics and electronics. The combination of the solid-liquid composites with our new DIW fabrication approach provides capabilities and insights to the AM and LM communities to develop advanced materials and devices with exceptional multifunctional capabilities.
Droplet aspects ratios were compared for varying print conditions including varying the droplet diameter (D), varying the print velocity (V*) and varying the height (H). For some of the larger droplets (e.g. the 200-micron GaIn droplets), hexane is mixed in the elastomer matrix to reduce viscosity for mixing and then evaporated prior to printing. The methods mirrored those for Example 1 unless indicated otherwise.
Elastomer matrices tested include the two-component silicone elastomer Ex-Sil™ 100; Gelest Inc from Example 1, as well as the platinum catalyzed silicone elastomer Ecoflex™ 00-30, the SYLGARD™ 184 Silicone Elastomer, and the DOWSIL™ SE 1700 polydimethylsiloxane matrix. LM concentrations ranged from 30 vol % to 50 vol %. As demonstrated in
It should be emphasized that the above-described aspects of the present disclosure are merely possible examples of implementations and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described aspects of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure.
The following references are provided to assist in better understanding the disclosure and technologies described therein. The citation of any publication is for disclosure purposes only and should not be construed as an admission that the publication is material in any way to patentability of the claims nor that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided could be different from the actual publication dates that may need to be independently confirmed. References are cited herein throughout using the format of reference number(s) in superscript corresponding to one or more of the following numbered references. For example, citation of references numbers 1 and 2 immediately herein below would be indicated in the disclosure as (Refs.1,2).
This application claims priority to, and the benefit of, co-pending U.S. provisional application entitled “METHODS OF ADDITIVE MANUFACTURING BY DIRECT INK WRITING OF EMULSION COMPOSITIONS” having Ser. No. 63/323,466, filed Mar. 24, 2022 and co-pending U.S. provisional application entitled “ADDITIVE MANUFACTURING OF FUNCTIONAL EMULSIONS” having Ser. No. 63/214,161, filed Jun. 23, 2021, the contents of both of which are incorporated by reference herein.
This invention was made with government support under contracts CMMI2054409 and CMMI2054411 awarded by the National Science Foundation, and D18AP00041 awarded by the Defense Advanced Research Projects Agency. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/034801 | 6/23/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63214161 | Jun 2021 | US | |
| 63323466 | Mar 2022 | US |
