High Performance, 3D-Printable Dielectric ... - ACS Publications

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High Performance, 3D-Printable Dielectric Nanocomposites for Millimeter Wave Devices Michael Lis,† Maxwell Plaut, Andrew Zai, David Cipolle, John Russo, and Theodore Fedynyshyn* MIT Lincoln Laboratory, 244 Wood Street, Lexington, Massachusetts 02421, United States S Supporting Information *

ABSTRACT: The creation of millimeter wave, 3D-printable dielectric nanocomposite is demonstrated. Alumina nanoparticles were combined with styrenic block copolymers and solvent to create shear thinning, viscoelastic inks that are printable at room temperature. Particle loadings of up to 41 vol % were achieved. Upon being dried, the highest-performing of these materials has a permittivity of 4.61 and a loss tangent of 0.00298 in the Ka band (26.5−40 GHz), a combination not previously demonstrated for 3D printing. These nanocomposite materials were used to print a simple resonator device with predictable pass-band features.

KEYWORDS: 3D printing, nanocomposites, dielectrics, millimeter wave, Ka band, direct write

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INTRODUCTION As additive manufacturing has increased in precision and material palate, high frequency radio devices have become an important research goal. Additive manufacturing techniques allow for the creation of complex structures with minimal capital investment as well as the construction of devices not easily achievable by other means.1−3 Injection molding can create precision devices with much higher up-front cost and less flexibility for design changes. Machining can produce finely featured parts but at a much higher individual cost. Additive manufacturing can present a middle ground between these two, producing parts with the design flexibility of machining, with a per-unit cost closer to that of molded parts. Devices that operate at millimeter wave frequencies (30+ GHz) with high dielectric constants are particularly attractive, as they allow for the use of smaller devices that also avoid the crowded spectrum of lower frequency solutions. This paper presents the invention and use of 3D-printable, polymer-ceramic hybrid material for millimeter-wave radio frequency (RF) devices. There have been several previous accounts of dielectric materials in 3D-printed radio devices; however, nearly all of these focused on X-band (12−18 GHz) or lower frequency devices, and all of them were purely polymer-based.2−6 A previous report by the authors of this study1 demonstrates a low loss 3D-printable dielectric material based on styrenic block copolymers. There, a low loss block copolymer was combined with a volatile solvent (or curable monomer) to create roomtemperature extrudable materials that then dry or cure to form low loss, printed dielectrics. This material was successfully used to create functional RF devices with low loss in the Ka band (26.5−40 GHz), but the dielectric constant of the printed © XXXX American Chemical Society

material is low (less than 2.5). There are multiple reports of 3D-printed alumina materials, but these require high temperature thermal treatment7−10 to create the final usable form. The use of ceramic-polymer composites for RF is, however, a well-documented and rich field. Dispersions of spherical particles in a continuous matrix are known as 0-3 composites, where the first digit represents the degree of connectivity of the inclusion material and the second digit is the connectivity of the matrix. Previous work on the radio wave dielectric properties of 0-3 ceramic-polymer composites has already been welldocumented by Sebastian and Jantunen11 and will be only partially documented here. A wide variety of different polymer matrixes have been used, including epoxies,12−18 polytetrafluoroethylene (PTFE),19,19−26 polystyrene,27−29 and polyethylene.28−30 PTFE has exceptionally low loss but is difficult to solvate and impregnate with ceramic particles. Epoxies are very easy to process but have the penalty of increased dielectric loss at high frequencies. Polystyrene and polyethylene provide a balance of low loss tangent with more facile particle integration and solvation. To the authors’ knowledge, there are no accounts of the use of styrenic block copolymers as matrix materials for radio device dielectrics, but these materials were expected to have similar advantages to polystyrene and polyethylene given their chemical similarities. A wide variety of ceramic particles have also been used in these composites, including silica,19 alumina,25 barium titanate,18 strontium titanate,12,26 and more exotic ceramics such as Sr2Ce2Ti5O15.27 Received: September 14, 2016 Accepted: November 21, 2016

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DOI: 10.1021/acsami.6b11643 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

mixer (Thinky USA, Laguna Hills, CA). The polymer and nanoparticle were combined in a 20 mL glass vial. Solvent was then added, and the inks were loaded into the mixer and spun at 2200 rpm for 20 min. If a homogeneous ink was not obtained, the ink was hand mixed to disperse inhomogeneities followed by an additional cycle in the planetary centrifugal mixer at 2200 rpm for 20 min. This mixing cycle was repeated until homogeneous ink was obtained. Ink Rheology. Inks were characterized as before1 by a DHR-2 Rheometer (TA Instruments, New Castle, DE) using a 20 mm coneand-plate geometry. 3D Printing. Inks were loaded into 3 mL luer-lock polypropylene syringes by methods previously reported.1 The loaded syringes were mounted to the head of a modified Hyrel System 30 3D printer (Hyrel3D, Norcross, GA). Tapered, luer-lock polypropylene syringe tips were used to deposit the materials onto the printing substrate. Air pressure to the HP7x was supplied by house air through a manual regulator and valve. Differential Scanning Calorimetry. Printable ink was smeared in a film on a glass slide and allowed to dry for 48 h. Films were then removed from the slide and placed in an aluminum pan and loaded into a TA Instruments 2920 differential scanning calorimeter. The sample was then heated at 20 °C/min to 200 °C, held for 10 min, cooled at 10 °C/min to −50 °C, and heated again at 20 °C/min to 200 °C. This final heating curve was used for glass transition temperature measurements. The glass transition was measured as the inflection point of the change in heat capacity of the sample during heating. Data points are the average of three independent experiments, and the error bars are the standard error. Scanning Electron Microscopy. Images were taken using a Zeiss LEO 1525 field emission scanning electron microscope. Samples were coated in chromium before loading to reduce charging. The electron beam was created at 1 kV, and a secondary electron detector was used to construct the image. Dielectric Property Measurement. Complex dielectric permittivity was measured using previously reported methods in a WR-28 waveguide across the Ka band (26.5−40 GHz).1 Dielectric constant and loss values were taken as the median value across the Ka band. Rexolite 1422 (C-Lec Plastics, Philadelphia, PA) was used as a reference for a commercial low loss material. Waveguide Filter Device Measurement. Filter devices were measured on identical equipment as before.1 Three block resonator filter devices were printed and placed inside a split WR-28 waveguide, and signal transmission through the waveguide was measured from 26.5 to 40 GHz.

There is one recent account of the use of a 3D-printed polymer/ceramic nanocomposite dielectric. Castles et al.35 report the creation of a printable ABS/BaTiO3 composite. The material was tested for dielectric properties at 15 GHz. While the permittivity of the nanoparticle-loaded material was high (8.7), the loss tangent (0.027) was an order of magnitude greater than that of the best-in-class materials.11 At millimeter wave frequencies (30+ GHz), loss in polymer systems is usually worse. There are several approaches to modeling the predicted permittivity of these materials, including the Lichtenecker equation,31 the Maxwell−Wagner mixing rules,32 and the core− shell model by Tanaka.33,34 Each of these models has their own specific strengths and limitations, and which model is best can depend on the features such as difference between the two dielectric constants and the quality of the interface between the matrix and ceramic. As one of the simplest models, corresponding to a random dispersion of spheres in a matrix, the Lichtenecker model is used as the standard of comparison for the permittivity values collected in this study. Low-loss composite materials provide a route to both increasing and varying the permittivity value. Increasing the permittivity value gives more degrees of freedom when designing filters, which are essentially resonators with the resonant mode formed inside the discontinuity between two different materials, for example, air and a polymer or a polymer and a composite. Having a suite of 3D-printable materials with differing dielectric values gives more flexibility in designing resonators as well allowing for smaller resonators due to the higher dielectric constant of the composites. This paper presents the first report of 3D-printed ceramicpolymer composites for use in millimeter wave radio devices. Alumina, while not the highest dielectric ceramic available, possesses the advantage of extremely low loss, ready availability, and low cost. It would be of strong interest to see if the combination of two low loss materials (alumina and the styrenic block copolymers) would result in a low loss composite with a dielectric value that could be set by the polymer/alumina ratio. Alumina nanoparticles are combined with solvent and the styrenic block copolymers styrene− butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), and styrene-ethylene/butylene-styrene (SEBS) to create printable ceramic nanocomposites. These materials are characterized by their morphology and rheological properties. This material is printed into solid blocks, and their dielectric properties are measured and compared to the expected results as given by the Lichtenecker equation. Finally, simple filter devices are printed, and their frequency response is characterized.

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RESULTS AND DISCUSSION

To increase the dielectric permittivity of the block copolymerbased inks previously reported,1 hydrophobically coated alumina nanoparticles with an average diameter of 60 nm were added as a filler material. A list of prepared formulations is shown in Table 1. After several cycles of mixing, the ink becomes a qualitatively homogeneous, white material. To measure the integration between the nanoparticles and the polymer-based ink, samples were dried, and their glass transition temperatures (Tg) were measured by differential scanning calorimetry (DSC). Earlier work integrating silica nanoparticles into polystyrene demonstrated that changes in Tg correlated with particle dispersion into the polymer matrix.36 Increasing Tg values meant strongly favorable surface energy interactions between the nanoparticles and the polymer matrix, while decreasing Tg values indicated phase segregation and agglomeration of the nanoparticles. Figure 1 shows the results of the DSC experiments. Note that the x-axis shows the final volume percent concentration of nanoparticles in the final material remaining after the ink has dried. The SIS series consists of formulations 1a, 1c, 1e, and 1f; the SBS series consists of formulations 2a, 2c, 2e, and 2f, and

EXPERIMENTAL SECTION

Materials. Polystyrene-block-polybutadiene-block-polystyrene (SBS, 432490), polystyrene-block-polyisoprene-block-polystyrene (SIS, 432415), polystyrene-block-polyethylene-ran-polybutylene-blockpolystyrene (SEBS, 200565), toluene, and xylenes were all acquired from Sigma-Aldrich, Milwaukee, WI. Hydrophobized alumina nanoparticles (60 nm, US3005) were purchased from US Nano, Inc. All materials were used as purchased without further modification. Three milliliter polypropylene luer-lock syringes, 200 and 400 μm polypropylene, luer-lock, tapered syringe tips, and an HP7x high pressure adapter were all purchased from Nordson EFD, Westlake, OH. Ink Formulation. Printable inks were created by combining polymer, hydrophobized alumina nanoparticles coated with an aluminic ester, and aromatic solvent in an AR-100 planetary centrifugal B


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the SEBS series consists of formulations 3a, 3b, and 3c. For the SIS and SBS series of polymers, there is little change to the Tg values with the addition of nanoparticles with the SIS series holding steady at 87−94 °C and the SBS series holding steady at 90−95 °C. This suggests neither ideal nor catastrophic interactions between polymer and nanoparticle. By contrast, the Tg values for the SEBS series drop precipitously from 85 to 70 °C, suggesting poor dispersion of the nanoparticles within the SEBS polymer. Indeed, the authors were unable to adequately mix a SEBS-based ink with a nanoparticle loading higher than that of formulation 3c. To confirm these results, samples from the SIS and SEBS series were examined using scanning electron microscopy (SEM). Printed samples using ink formulations 1a, 1c, 1e, 3a, 3b, and 3c were made, and cross sections were imaged. Figures 2a−c show the results for the SIS series. Figure 2a, with no particle loading, gives a smooth surface without any defects. The increasing particle loadings in Figures 2b and c continue to show dispersion of the nanoparticles into the polymer matrix. The sample in Figure 2b contains 12 vol % alumina, and the sample in Figure 2c contains 23 vol % alumina. Polydispersity among the nanoparticles is evident but with very little aggregation. Figures 2d−f show the SEBS series. Figure 2e, with only 13 vol % nanoparticle loading, already displays significant particle aggregation. Figure 2f, with 26 vol % loading, shows intense phase formation and aggregation, in line with the predicted results from the DSC measurements. It is clearly evident, then, that homogenization and printability of these inks are limited by the dispersion of the coated nanoparticles into the polymer/solvent matrix. The likely culprit for the difference in dispersion behavior is that both SBS and SIS have unsaturated midblocks with one vinyl group per repeat unit, while the SEBS is hydrogenated. It is likely that the additional π-electron content of the polymer improves the surface compatibility between the polymer and the aluminic ester coating of the nanoparticles. With an understanding of the mixing behavior of the inks, the next requirement is that these inks have the prerequisite rheological properties for 3D printing. Solvent-cast, direct-write

Table 1. Formulations Used in This Study formulation

polymer

solvent

polymer (wt %)

1a 1b 1c 1d 1e 1f 2a 2b 2c 2d 2e 2f 3a 3b 3c

SIS SIS SIS SIS SIS SIS SBS SBS SBS SBS SBS SBS SEBS SEBS SEBS

toluene toluene toluene toluene toluene toluene toluene toluene toluene toluene toluene toluene xylenes xylenes xylenes

50 55 40 44 30 20 50 55 40 44 30 20 45 36 27

solvent (wt %)

Al2O3 (wt %)

dry Al2O3 (vol %)a

50 45 40 36 30 20 50 45 40 36 30 20 55 44 33

0 0 20 20 40 60 0 0 20 20 40 60 0 20 40

0 0 12 11 23 41 0 0 12 11 23 41 0 13 26

a

Vol % of alumina nanoparticles after total solvent evaporation, calculated.

Figure 1. Glass transition temperature of the styrenic phase of dried ink samples. A drop in glass transition temperature with added particle content indicates poor particle dispersion.

Figure 2. (a−c) Cross-sectional samples of printed material containing SIS polymer and (a) 0, (b) 12, and (c) 23 vol % nanoparticles. Note that particles remain well-dispersed even at very high particle concentrations. (d−f) Cross-sectional samples of printed material containing SEBS polymer and (a) 0, (b) 13, and (c) 26 vol % nanoparticles. Particles show significant agglomeration and segregation in the material. C


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ACS Applied Materials & Interfaces inks must have sufficiently shear thinning to allow for dispensing through a nozzle and a sufficiently high yield stress to support their own weight.8 In a previous study, it was shown that styrenic block copolymers provided superior shear thinning and yield stress properties compared to similar mixtures of homopolymer polystyrene.1 This is similar to an effect shown in other triblock copolymer systems such as pluronics at concentrations above their critical micellar concentration.37 Under these conditions, interactions between block copolymer chains in the solvent lead to the formation of a weak gel that breaks down under shear. Figures 3 and 4

Figure 4. (a) Elastic and loss moduli and (b) shear viscosity across nanoparticle loadings ranging from 0 to 60% with SIS polymer and toluene.

(combined with elasticity) allows the printed ink to support its own weight after extrusion. There is some variation in elasticity ratios. 1e has a ratio of 1.02, while 2e has a ratio of 1.65. This holds consistent across the SBS series, where the nanoparticleloaded inks have elasticities higher than those of both the SIS and SEBS series, suggesting that this trait is specific to the interaction of the hydrophobized alumina nanoparticles with the SBS-solvent mixture. Figures 4a and b give the rheological properties of the SIS series (formulations 1a, 1c, 1e, and 1f). All of these samples have identical polymer/solvent ratios with increasing alumina particle loading from 0 to 60% (see Table 1). In Figure 4a, the slope of shear thinning response is largely identical across nanoparticle loading. Formulations 1a, 1c, 1e, and 1f all have shear thinning slopes in the range of −0.520 to −0.650. Samples 1e and 1f do, however, show substantially higher viscosity values from the additional nanoparticle content. The lower viscosity of formulations 1a and 1c allows for a decrease in solvent content (formulations 1b and 1d, respectively). While these samples still have a volume fraction of solvent (and thus higher volume loss upon drying) higher than those of formulations 1e and 1f, 1b and 1d are an improvement in this regard over 1a and 1c. The yield stress values do not change consistently with nanoparticle loading; there is no clear trend matching them. In some previous polymer-ceramic hybrid systems,8,38 the interactions between the polymer and nanoparticles are critical in imparting both the shear-thinning and yield stress behavior. This is because the particles and polymer combine to form a network, and the breakdown of that network under shear is responsible for the printable nature of the ink. In this system, that is not the case. The block copolymers provide the shear thinning and yield stress behaviors, and while the addition of the nanoparticles increases viscosity, the inks do not become noticeably more shear thinning, nor do their yield stress values increase. That indicates that the nanoparticles are acting more as a passive solvent and do not contribute to

Figure 3. (a) Elastic and loss moduli and (b) shear viscosity across polymer systems with similar nanoparticle loadings: 1e (30/30/40% SIS/toluene/Al2O3), 2e (30/30/40% SBS/toluene/Al2O3), and 3c (27/33/40% SEBS/toluene/Al2O3).

highlight the rheological properties of a subset of these inks (a summary of all rheological properties is given in Table S1). Figure 3 demonstrates the variation of rheological properties among formulations with similar nanoparticle loadings but different polymers, while Figure 4 shows the increase in viscosity associated with increased nanoparticle content in the SIS system. Figures 3a and b show the rheological properties of formulations of the three triblock copolymers with similar polymer/solvent/alumina ratios: 1e (30/30/40% SIS/toluene/ Al2O3), 2e (30/30/40% SBS/toluene/Al2O3), and 3c (27/33/ 40% SEBS/toluene/Al2O3). In each case, the samples are shear thinning across the measured shear stress range, showing that all three composite inks are capable of sheer thinning. Note that the SEBS requires a solvent loading higher than that of the other inks to achieve similar rheological behavior. This is due to the more aliphatic ethylene-butylene polymer midblock of the SEBS polymer.1 All three samples show nearly identical shear thinning slopes of −0.520 to −0.575, ensuring low enough viscosity at high shear to allow material to flow through the nozzle. As can be seen in Figure 3b and Table S1, all three ink formulations have similar yield stress (1390−1690 Pa), which D


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ACS Applied Materials & Interfaces network formation. This behavior allows for greater material flexibility, as the rheological behavior is independent of particle loading. Figure 5 demonstrates the ability to print detailed, high aspect ratio features using these inks. A triangle lattice pattern

Table 2. Dielectric Properties of the Printed Samples formulation

predicted permittivity

permittivity (ε′)

loss tangent (ε″/ε′ × 103)

Rexolite 1b 1d 1e 1f 2b 2d 2e 2f

2.50 2.91 3.42 4.38 2.50 2.91 3.42 4.38

2.50 2.22 2.87 3.34 4.30 2.57 2.75 3.85 4.50

0.52 1.62 2.99 3.11 1.89 2.58 1.67 4.17 2.30

permittivity of the alumina nanoparticles (assumed to be 9.8), and νc is the volume fraction of alumina nanoparticles. Using this method, predicted dielectric values are given in Table 2. Additionally, Figure 6 shows a plot of the volume

Figure 6. Dielectric constant vs alumina content for printed blocks fit into a WR-28 waveguide. The dotted line represents the expected permittivity given by the Lichtenecker equation.

fraction of nanoparticles against the measured dielectric constant. The dotted line shows the predicted values. The measured permittivities largely matched the trend of the predicted values, though there is some variation. The highest particle loadings for samples 1f and 2f contained 41 vol % ceramic particles and had measured permittivity values of 4.30 and 4.61, respectively. As a standard of comparison, dielectric loss values were compared to a sample of the commercial low loss dielectric Rexolite 1422, which had a measured permittivity of 2.50 and a loss tangent of 5.2 × 10−4. As had been previously demonstrated,1 the pure SEBS polymer had loss (4.5 × 10−4) comparable to that of the Rexolite, while the SIS (1.64 × 10−3) and SBS (2.28 × 10−3) both had higher losses but were still fairly low loss materials. In the case of these nanocomposites, then, both the polymer base and the alumina are low loss materials in the Ka band. Modeling of these behaviors is complex, and models often do not match well with reported data, as both microscopic and macroscopic materials defects strongly impact the loss tangent.11 As can be seen in Table 2, all three sets of samples show losses inconsistent but higher than those of the polymer bases alone. The increased loss may be due to particle scattering, resonance of the particles within the matrix, or scattering off of void defects within the sample. The latter seems unlikely, as any printed defects are much smaller than the size of the waves themselves. Overall, though, there is a maximum loss of about 2× or less for the nanoparticle-filled samples over their polymer-only counterparts.

Figure 5. Triangle lattice printing demonstration showing (a) an angled view and (b) a top view. The demonstration was printed using formulation 1e and a 200 μm nozzle to give a 57% by weight alumina structure. Scale bar is 5 mm.

was printed on glass using a 200 μm nozzle as a demonstration of the printing capabilities of formulation 1e. The ink was thus clearly self-supporting and adequate for a wide range of applications. While there is some texturing as a result of the layered nature of the printing process, Figure 5b shows that the printed lines stack neatly on top of one another and hold their structure even after many layers and even with solvent loss. After establishing printability, the dielectric constants of several printed nanocomposite blocks were measured (Table 2). The simple Lichtenecker equation was used to predict the dielectric constant of the printed samples:11,18,31 ⎛ε ⎞ log εeff = log εp + υc log⎜⎜ c ⎟⎟ ⎝ εp ⎠

(1)

where εeff is the effective permittivity of the composite, εp is the permittivity of the polymer (assumed to be 2.5), εc is the E


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the minimum possible loss achievable in the pass band of the filter. As can be seen comparing the output of the two devices, changing the permittivity of the material while holding the design dimensions constant alters the frequency response. The out-of-band absorption, however, is largely determined by device design. As was demonstrated in our previous work,1 an 8 block filter (−36 dB) and a 3 block filter (−8 dB) have drastically different out-of-band absorbance values. The performance of the materials generated in this work suggests that they are suitable as a materials platform for 3D printing of complex antenna and filter devices in the Ka band that have features and geometries that cannot be easily fabricated by traditional fabrication techniques and opens up the possibility of printing devices employing multiple inks of differing dielectric values.

To demonstrate how this change in dielectric constant impacted filter performance, two identical resonator filters were created with formulations 1a and 1e, respectively. This dielectric filter was selected as a simple demonstration of the utility of printing RF devices that can function as predicted by RF simulation. The filter design is identical to that showcased in our earlier work.1 The device was printed using a 200 μm nozzle and contained 3 equally spaced resonator blocks to create a band-pass filter for the Ka frequency range. As shown in Figure 7a, the filters closely matched dimensionally. The

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CONCLUSIONS A new set of 3D-printing materials for use as millimeter wave dielectrics are presented. Previous accounts have demonstrated the creation of 3D-printable low loss polymer dielectrics as well as nonprintable polymer-ceramic nanocomposites. Presented here is a low loss, high permittivity 3D-printable dielectric nanocomposite for use at millimeter wave (30+ GHz) frequencies. Alumina nanoparticles are combined with styrenic block copolymers to create low loss, high K dielectric materials. The nanoparticles mixed well into the SBS and SIS block copolymers but less well into the SEBS block copolymer. The combination of block copolymer, nanoparticle, and solvent created a shear thinning, printable ink capable of creating freestanding structures. Dielectric permittivities of these materials were in line with predicted results with the best material (41 vol % alumina in SIS) having a measured dielectric constant of 4.61. A nanocomposite ink was used to create a simple filter resonator device, and the device output was compared to that from a pure polymer device. As expected, the nanocomposite had a narrower pass-band at a frequency slightly lower than that of the device made with polymer alone.

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Figure 7. (a) Examples of printed resonators,: sample 1b (left) is a pure SIS polymer, while sample 1e (right) contains 23 vol % Al2O3 nanoparticles. (b) Output of the resonator filters.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b11643.

outputs of the filters, shown in Figure 7b, differed greatly, however. The filter printed with formulation 1b has pass band peaks at 30.1 and 35.3 GHz. A bandwidth of 3 dB can be calculated form the cutoffs on either side at 29.2 and 37.3 GHz. Maximum stop-band attenuation from 26.5 to 40 GHz is about 8 dB. As would be expected with a higher dielectric material, the filter printed with formulation 1e had its resonance peaks shifted to lower frequencies. The resonance peaks for this device are at 29.1 and 32.6 GHz, respectively. Because the resonance peaks are so much sharper, there is also a lowered signal output between them with a loss of about 3.0 dB at 31.3 GHz. Three dB drop-offs on either side of the pass band lie at 28.4 and 34.0 GHz. Beyond the pass-band region (35−39 GHz), there are also multiple interference anomalies due to resonances specific to the geometry of the chamber and reflections off of the ends of the device. Dimensions were maintained for the two samples to illustrate the differences in dielectric constant and loss, as opposed to redesigning the filter for the higher dielectric material. It is important to note that the performance of these devices is constrained both by design and by materials. On the materials side, the loss tangent determines

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Complete list of rheological properties (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address †

M.L.: Viridis3D, 10 Roessler Road, Woburn, MA 01801, United States. Funding

This material is based upon work supported by the Assistant Secretary of Defense for Research and Engineering under Air Force Contract FA8721-05-C-0002 and/or FA8702-15-D-0001. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Assistant Secretary of Defense for Research and Engineering. Notes

The authors declare no competing financial interest. F


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(16) Bhalla, A. S.; Newnham, R. E.; Cross, L. E.; Schulze, W. A.; Dougherty, J. P.; Smith, W. A. Pyroelectric PZT-Polymer Composites. Ferroelectrics 1981, 33 (1), 139−146. (17) George, S.; Sebastian, M. T. Three-Phase Polymer−ceramic− metal Composite for Embedded Capacitor Applications. Compos. Sci. Technol. 2009, 69 (7−8), 1298−1302. (18) Cho, S.-D.; Lee, S.-Y.; Hyun, J.-G.; Paik, K.-W. Comparison of Theoretical Predictions and Experimental Values of the Dielectric Constant of Epoxy/BaTiO3 Composite Embedded Capacitor Films. J. Mater. Sci. 2005, 16 (2), 77−84. (19) Chen, Y.-C.; Lin, H.-C.; Lee, Y.-D. The Effects of Filler Content and Size on the Properties of PTFE/SiO2 Composites. J. Polym. Res. 2003, 10 (4), 247−258. (20) Deepa, K. S.; Sebastian, M. T.; James, J. Effect of Interparticle Distance and Interfacial Area on the Properties of Insulator-Conductor Composites. Appl. Phys. Lett. 2007, 91 (20), 202904. (21) Rajesh, S.; Murali, K. p.; Ratheesh, R. Preparation and Characterization of High Permittivity and Low Loss PTFE/ CaTiO3Microwave Laminates. Polym. Compos. 2009, 30 (10), 1480−1485. (22) Xiang, F.; Wang, H.; Yao, X. Preparation and Dielectric Properties of Bismuth-Based Dielectric/PTFE Microwave Composites. J. Eur. Ceram. Soc. 2006, 26 (10−11), 1999−2002. (23) Stanly Jacob, K.; Satheesh, R.; Ratheesh, R. Preparation and Microwave Characterization of BaNd2−xSmxTi4O12 (0 ≤ X ≤ 2) Ceramics and Their Effect on the Temperature Coefficient of Dielectric Constant in Polytetrafluoroethylene Composites. Mater. Res. Bull. 2009, 44 (10), 2022−2026. (24) Subodh, G.; Pavithran, C.; Mohanan, P.; Sebastian, M. T. PTFE/Sr2Ce2Ti5O16 Polymer Ceramic Composites for Electronic Packaging Applications. J. Eur. Ceram. Soc. 2007, 27 (8−9), 3039− 3044. (25) Rajesh, S.; Murali, K. P.; Priyadarsini, V.; Potty, S. N.; Ratheesh, R. Rutile Filled PTFE Composites for Flexible Microwave Substrate Applications. Mater. Sci. Eng., B 2009, 163 (1), 1−7. (26) Rajesh, S.; Murali, K. P.; Rajani, K. V.; Ratheesh, R. SrTiO3Filled PTFE Composite Laminates for Microwave Substrate Applications. Int. J. Appl. Ceram. Technol. 2009, 6 (5), 553−561. (27) Subodh, G.; Deepu, V.; Mohanan, P.; Sebastian, M. T. Dielectric Response of Sr 2 Ce 2 Ti 5 O 15 Ceramics Reinforced High Density Polyethylene. J. Phys. D: Appl. Phys. 2009, 42 (22), 225501. (28) George, S.; Deepu, V. N.; Mohanan, P.; Sebastian, M. T. Influence of Ca[(Li1/3Nb2/3)0.8Ti0.2]O3-δ Filler on the Microwave Dielectric Properties of Polyethylene and Polystyrene for Microelectronic Applications. Polym. Eng. Sci. 2010, 50 (3), 570−576. (29) Thomas, S.; Deepu, V.; Uma, S.; Mohanan, P.; Philip, J.; Sebastian, M. T. Preparation, Characterization and Properties of Sm2Si2O7 Loaded Polymer Composites for Microelectronic Applications. Mater. Sci. Eng., B 2009, 163 (2), 67−75. (30) Subodh, G.; Deepu, V.; Mohanan, P.; Sebastian, M. T. Dielectric Response of High Permittivity Polymer Ceramic Composite with Low Loss Tangent. Appl. Phys. Lett. 2009, 95 (6), 62903. (31) Goncharenko, A. V.; Lozovski, V. Z.; Venger, E. F. Lichtenecker’s Equation: Applicability and Limitations. Opt. Commun. 2000, 174 (1−4), 19−32. (32) Wagner, K. W. Erklärung der dielektrischen Nachwirkungsvorgänge auf Grund Maxwellscher Vorstellungen. Arch. Elektrotech. 1914, 2 (9), 371−387. (33) Tanaka, T. Dielectric Nanocomposites with Insulating Properties. IEEE Trans. Dielectr. Electr. Insul. 2005, 12 (5), 914−928. (34) Tanaka, T.; Montanari, G. C.; Mulhaupt, R. Polymer Nanocomposites as Dielectrics and Electrical Insulation-Perspectives for Processing Technologies, Material Characterization and Future Applications. IEEE Trans. Dielectr. Electr. Insul. 2004, 11 (5), 763−784. (35) Castles, F.; Isakov, D.; Lui, A.; Lei, Q.; Dancer, C. E. J.; Wang, Y.; Janurudin, J. M.; Speller, S. C.; Grovenor, C. R. M.; Grant, P. S. Microwave Dielectric Characterisation of 3D-Printed BaTiO3/ABS Polymer Composites. Sci. Rep. 2016, 6, 22714.

ACKNOWLEDGMENTS We wish to acknowledge the Technology Office of Lincoln Laboratory for funding this research through the Novel and Engineered Materials Novel and Engineered Materials Technology Category and Professor Jennifer A. Lewis of Harvard University for helpful discussions.

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ABBREVIATIONS

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REFERENCES

SBS, styrene-butadiene-styrene block copolymer SIS, styrene-isoprene-styrene block copolymer SEBS, styrene-ethylene/butylene-styrene block copolymer

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Research Article

ACS Applied Materials & Interfaces (36) Bansal, A.; Yang, H.; Li, C.; Benicewicz, B. C.; Kumar, S. K.; Schadler, L. S. Controlling the Thermomechanical Properties of Polymer Nanocomposites by Tailoring the Polymer−particle Interface. J. Polym. Sci., Part B: Polym. Phys. 2006, 44 (20), 2944−2950. (37) Wu, W.; DeConinck, A.; Lewis, J. A. Omnidirectional Printing of 3D Microvascular Networks. Adv. Mater. 2011, 23 (24), H178− H183. (38) Compton, B. G.; Lewis, J. A. 3D-Printing of Lightweight Cellular Composites. Adv. Mater. 2014, 26 (34), 5930−5935.

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High Performance, 3D-Printable Dielectric ... - ACS Publications

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