Bicontinuous Intraphase Jammed Emulsion Gels ... - ACS Publications

Subscriber access provided by The Library | University of Bath

Article

Bicontinuous Intraphase Jammed Emulsion Gels: A New Soft Material Enabling Direct Isolation of Co-Continuous Hierarchial Porous Materials Brandy Kinkead, Rachel Malone, Geena Smith, Aseem Pandey, and Milana Trifkovic Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.9b02398 • Publication Date (Web): 23 Aug 2019 Downloaded from pubs.acs.org on August 24, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials

Bicontinuous Intraphase Jammed Emulsion Gels: A New Soft Material Enabling Direct Isolation of Co-Continuous Hierarchial Porous Materials ‡Brandy Kinkead, ‡Rachel Malone, Geena Smith, Aseem Pandey and Milana Trifkovic* University of Calgary, Department of Chemical and Petroleum Engineering, 2500 University Dr. NW, Calgary AB T2N 1N4

ABSTRACT: Materials with hierarchical, bicontinuous porosity are desirable for numerous applications, providing a continuous pathway for reactants and products and a large interfacial surface area for reaction/storage. Herein, we demonstrate a low-energy and flexible route to dual scale co-continuous materials via a new class of soft material first reported here - bicontinuous intraphase jammed emulsion gels, coined here bipjels. Alumina coated silica nanoparticles (AlO-SiO NPs) are shown to stabilize bicontinuous emulsion gels formed by spinodal decomposition of water/2,6-lutidine (W/L) via a percolating network of attractive NPs within the water-rich phase. The prepared bipjels are tunable depending on pre-mixing conditions and NP concentration. Following bipjel formation, a free-standing co-continuous monolith of AlO-SiO NPs with macro- and mesoporosity is directly extractable owing to the high mechanical strength of the percolating network of stabilizing NPs. Overall, this new class of soft materials is shown to overcome the inherent difficulty in creating thermodynamically instable bicontinuous morphologies via a scalable, template- and organic binder- free method, producing materials that are near-ideal for catalytic, storage or separation applications.

Porous scaffolds with consistent channel widths and full bicontinuity are desirable for a wide variety of applications, owing to their superior mass transport properties via reduced diffusion lengths.1 Hierarchial scaffolds, having both nano- and micro- porosity, are particularly valuable for their ability to maintain a high surface area for applications such as electrochemical energy storage (EES) and electrocatalysis. Inverse opaline structures (also known as 3D ordered macroporous, 3DOM, structures) have recently been highlighted in literature for use as cathodes for EES and electrocatalysis technologies, due to their near ideality in several design aspects;2–6 namely, the 3DOM structures are fully bicontinuous and may be hierarchical in nature, using a solid template to create the macropores and either nanoparticles (NPs) or porous infiltration of the solid template to generate nanoscale features.5,7 The main drawback of the 3DOM structures is their reliance on templating, and the existence of constrictions between pores, which may negatively impact effective mass transport and increases diffusion lengths. In order to improve on 3DOM structures, bicontinuous materials prepared via spinodal decomposition routes are desirable. A range of methods have been used to prepare bi-continuous porous scaffolds (also termed monoliths) via spinodal decomposition; polymerization-induced phase separation was first used to prepare monoliths with silica in 1997,8 and later used in 2006 to prepare titania monoliths.9 Further studies have exploited gelation of spherical species in suspension with shortrange attractions by spinodal decomposition to generate bicontinuous flocculants,10,11 but we were unable to find a report of isolation of a free-standing monolith via this route. A more recent class of soft materials that utilizes fluid spinodal

decomposition to generate bicontinuous materials is bicontinuous interfacially jammed emulsion gels (bijels), whereby fluid spinodal decomposition is arrested by NP interfacial jamming to preserve a bicontinuous morphology.12,13 The preparation of porous materials with uniform, cocontinuous channels using bijels (and similar techniques) has been demonstrated in a number of recent publications,14–16 often requiring careful tuning of the NP stabilizers,17 and always requiring incorporation of a polymeric material for structural support in order to isolate free-standing monoliths, typically via polymerization of a monomer contained in one of the bicontinuous fluid phases. Critical polymer solutions can also produce co-continuous morphologies via spinodal decomposition, though typically with larger domain sizes and at higher processing temperatures than for fluid or gelation spinodal decomposition.18 Nanoparticle stabilization of these co-continuous polymer morphologies has typically been achieved through interfacial jamming.18,19 More recently, Li et al. demonstrated that the formation of a percolating network of attractive NPs localized in a single phase of a polymer blend can also arrest spinodal decomposition and stabilize bicontinuous morphologies.20 Herein, we report for the first time the stabilization of small molecule fluid spinodal decomposition derived bi-continuous materials via a percolating, attractive NP network in one phase of the de-mixed fluids. The aforementioned bicontinuous intraphase jammed emulsion jels, coined her bipjels, are shown here to be advantageous for the preparation of bicontinous materials for a number of reasons: tunable morphology depending on both pre-mixing conditions and NP concentration; use of commercially available NPs in as-

ACS Paragon Plus Environment

Chemistry of Materials 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. (a) Storage modulus evolution of 5 and 10 NP-wt% AlO-SiO NP stabilized W/L bipjels pre-mixed via either vortexing or rotor stator homogenizing probed via small angle oscillatory shear at a frequency of 1 Hz. The temperature profile of the sample is shown on the right y-axis in black. (b, c, d, e) 3D renderings of LCSM images of the 5 NP-wt% vortexed AlO-SiO NP stabilized W/L at various stages in the experiment. Reflection of a 552 nm laser from the AlO-SiO NPs is shown in green, while fluorescence from Nile Red indicates the lutidine phase and is shown in red. Prior to heating and after re-mixing, W/L form a single phase over which Nile red uniformly fluoresces (shown as insets) and the reflection channel is shown separately to demonstrate the initial colloidal gel and final, spinodal decomposition templated, NP network.

received condition; and ability to directly extract a free-standing co-continuous monolith of AlO-SiO NPs with macro- and mesoporosity upon solvent removal due to the exceptional mechanical strength of the emulsion gel’s percolating colloidal network. This work provides a full characterization of the newly discovered soft material via confocal rheological analysis, and demonstrates the ability of this new material to produce free-standing, hierarchical structures by simply removing the solvent from the bipjels (isolating the freestanding, NP-only, co-continuous monolith). Results and Discussion The formation of W/L bipjels is performed as per a typical W/L bijel procedure, whereby a critical W/L (~72 wt% water) mixture is prepared with a defined concentration of NPs and subject to a temperature ramp as to induce W/L de-mixing via spinodal decomposition.12 The W/L mixtures begin in the onephase region at 30°C and are rapidly quenched into the 2-phase region (lower critical solution temperature/LCST, 34.1°C)21 by heating to 55°C at a rate of 25°C per minute. The bipjels are prepared with commercially available AlO-SiO NPs used asreceived (Nissan Chemicals, Table S1, Figure S1), with NP concentrations of either 5 or 10 NP-wt%, (volume fraction, φ, of 1.7% and 3.3% respectively). The W/L colloidal suspension is mixed with either a low-energy vortex mixer or high-energy

rotor stator homogenizer. The influence of NP concentration and premixing condition on local bipjel dynamics was evaluated by acquiring and analyzing time-resolved threedimensional reflectance and fluorescence confocal images, with simultaneous rheological analysis (Figure 1). As opposed to previous work, which studied emulsion gel rheology and morphology separately or only in two dimensions,15,19,22 the utilized confocal rheology method enables a more complete understanding of the synergy between a material’s evolving structure and properties under the influence of the external force (e.g. temperature, shear). Above the LCST, a lutidine-rich phase, tagged with Nile red, is seen by laser scanning confocal microscopy (LSCM) to separate into bicontinuous domains with a water-rich phase. Reflectance imaging (shown in green) indicates that a percolating AlO-SiO NP network within the water-rich phase is stabilizing the bicontinuous domains. Separate reflectance and fluorescence images, prior to overlay, can be seen in Figure S2, while evolution of the loss moduli for all samples is plotted in Figure S3.Prior to phase separation, the first important feature of this system emerges - the formation of an initial viscous colloidal gel of AlO-SiO NPs. This gelation is suggested here to occur for the AlO-SiO NPs due to the relatively large alumina-alumina Hamaker constant (~ 4 in water),23 and the near neutral surface charge of the AlO-SiO NPs at the pH of the W/L


Page 2 of 8

Page 3 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials

Figure 2. Comparison of the zero-shear storage modulus of previous bijel systems (closed symbols), monogel systems (either bipjel or bijel, open symbols) the bipjel systems prepared in this work at various volume fractions. Values for the previous works taken from references.15,19,24,25

mixture (Figure S4), enabling surface interactions without electrostatic repulsion. Moreover, the preferential wetting of the AlO-SiO NPs for the water phase is suggested to be largely governed by the strong adsorption of water to the NP surfaces, particularly when the NPs are at their isoelectric point in the W/L mixture, as indicated by FTIR spectroscopy (Figure S5). The viscous AlO-SiO gels (Figures S6/S7, Table S2) are further shown to impact the kinetics of phase separation. During heating and at the onset of phase separation, there is a drop in the storage moduli for all bipjels, followed by a swift recovery and subsequent increase in the moduli (Figure 1). This behavior has been previously seen in a non-polar bijel system of styrene trimer and polybutene studied by Bai et al. and there suggested to be due to the competition between the localization of NPs at the interface (increase in G’) and the shrinking interfacial area (reduction in G’).19 Here we suggest that this behavior results from disruption of the colloidal gel structure as W/L phases begin to separate and colloidal flocs are swept and sequestered into the water phase where they are then restricted. The compression of the AlO-SiO NP network as the bicontinuous NP domains evolve eventually results in a recovery in colloidal gel strength upon heating. As the viscosity of the original suspension increases with increasing NP concentration, this drop happens at later times showing that this behavior is dependent on the system’s NP concentration and floc formation. Importantly, this drop, recovery, and continual increase in storage moduli observed for bipjels is not seen in control samples of AlO-SiO NP suspensions prepared with either the addition of a simple base (NaOH) or the W/L gel mixture without heating above the LCST (Figure S8). As the bipjels are held above the LCST of the W/L mixture, the storage modulus continually increases in systems with stable bicontinuity, as observed in previous bijel systems due to NPs jamming and rearranging along the interface.19 Here, the overall upturn seen in G’ is believed to be from both the phase separation of W/L and from compression of the colloidal gel within the water-rich phase. The network formation and floc rearrangement within the water phase suggested by the initial

drop, recovery, and continual increase in storage moduli can be concluded to also contribute to the growth of the storage modulus during aging, allowing the bipjels to reach strengths significantly higher than those reported for bijels (Figure 2).15 Upon cooling below the LCST, the W/L phases remix, however, the strength of the resulting monogel remains, as seen in Figure 1. The implications of this moduli behavior, which suggests that the bicontinuous templated networks remain intact after W/L re-mixing, are discussed in detail below. The spatiotemporal image data show a clear dependence of bipjel structure on the initial concentration of AlO-SiO NPs and the energy input into mixing of the initial colloidal gel (Figure 3). The bicontinuous domains are seen to persist throughout the temperature hold period for all but the 5-NP wt% homogenized sample shown. For systems with a lower weight fraction of NPs (5 NP-wt%) mixed via vortexing, the bipjels have water domains with an average object thickness, LW, of 3.2 +/- 0.2 µm after 2000s held above the LCST. For systems with a lower weight fraction of NPs (5 NP-wt%) mixed via homogenization, bicontinuous domains with a smaller LW of 0.87 µm (+/-0.1 µm) (700 s of heating) are initially formed (Figure S9/S10), but these domains are not stable and eventually coarsen to droplets. Correspondingly, the storage modulus of the 5 NP-wt% homogenized sample increases quickly after phase separation but exhibits a significantly lower growth rate in G’ while held above the LCST beyond t~1000s (Figure S11). The inability of the 5 NP-wt% homogenized sample to stabilize the bicontinuous domains is suggested to result from differing NP floc formation

Figure 3. Laser scanning confocal microscopy (LSCM) images of the 5 and 10 NP-wt% samples, with different pre-mixing conditions, at late stages of phase separation (t ≈ 2000s). The scale bar is 25 microns except for the 10 NP-wt% homogenized sample, where it is 5 microns. Lutidine is shown in red, NPreflectance is shown in green. during mixing of the NP-W/L suspensions and subsequent differences in density of AlO-SiO NP agglomerates within the bipjel structures. Agglomerates formed during initial addition of lutidine to the water-NP suspension are loosely flocculated and highly non-uniform, owing to the short time-scale of their formation and the low energy convective mixing that occurs. Vortex mixing provides a relatively low shear environment for the breaking and reformation



Figure 4. Surface reconstruction showing the mean curvature (a, c) for a 10 NP-wt%, vortex-mixed W/L bipjel sample after coarsening and the corresponding (b) Gauss and (d) mean curvature evolution of the same sample during coarsening. The size of the volume in the rendering in (a) corresponds to 93x93x32 µm, while (c) is a close-up of the same surface showing the surface triangles with a scale bar of 2 µm. In this curvature analysis, the final flocs curvature is defined as positive if it curves towards the lutidinerich phase.

of flocs, while rotor-stator homogenization enables more rearrangement and more compact through higher shear.26 As such, small domains with a correspondingly high surface area initially formed in the homogenized 5 NP-wt% sample, which become unstable due to the inability of the dense NP flocs to percolate the entire water phase. For 10 NP-wt% homogenized samples, the smaller agglomerates again form smaller cocontinuous domains (LW of 0.55 +/- 0.03 µm at t = 2000 s), now with the concentration being sufficient to percolate the entire water phase and prevent coarsening to droplets during the temperature hold. Meanwhile, the 10 NP-wt% vortexed samples have the largest water domains of 5.6 +/- 1 µm at 2000 s, due to the combination of large floc size and high concentration which limits compaction of the water phase. In general, the average object thickness of the W/L domains and NP packing density is governed by both the initial floc size in the W/L suspension and (as the mixtures are held above their LCST for a period of time) the fluid spinodal decomposition. Time-dependent analysis of the characteristic length (Figure S12), storage modulus and curvature (Figure 4) provides further insight into the progression of spinodal decomposition templating as the bipjels are held above the LCST. Figure S12 shows that as the samples are held above LCST, the characteristic length scale (channel width) generally decreases, while G’ increases, suggesting compaction induced strengthening of the structure with time as spinodal decomposition drives templating of the NPs. Analysis of both the Guassian and mean curvature with time validates this evolution of the bicontinuous structures (Figure 4, Figure S13 and ESI further discussion);27 narrowing of the curvature with time indicates the progression of the spinodal decomposition and structure formation. The initial negative skew of the mean curvature is towards the water phase, suggesting that the NP network is imposing preferential curvature on the early bipjel structures. As the sample is aged further, the mean curvature distribution shifts positive (towards the lutidine phase) as expected for the minor (lutidine) phase.21 Additionally, Gaussian curvature analysis (Figure 4b) is seen to follow similar trends to that shown bijel literature,27 with narrowing of the normalized Gaussian distribution during aging, indicating increased hyperbolic character. The evolution of the bipjel curvature towards the ideal hyperbolic shape (as goverened by the minor lutidine phase) demonstrates that while the initial bipjel structure may be biased, spinodal decomposition is able to eventually dominate the final curvature to produce welltemplated bicontinuous structures. Overall, rheological,

curvature and characteristic length scale analysis all validate the mechanism of spinodal decomposition templating of the AlOSiO colloidal gel into a percolating bicontinuous network. A final and key observation for this new class of soft materials is that both the morphology and strength of the bipjel-templated AlO-SiO colloidal gel persists upon cooling and remixing of the W/L phases. As shown in Figure 2, the bipjel system studied in this work has a significantly higher storage moduli at lower volume loadings of stabilizing NPs than any other bijel system rheologically studied to date.15,19,24,25 This enhanced mechanical strength enables the isolation from the liquid phase as a freestanding bimodally porous material, that is porosity resulting from nanoparticle derived surfaces (nanoporosity) with micronsize channels derived from spinodal decomposition templating, directly from the bipjel stabilizing attractive NP network via quenching of the W/L bipjel in liquid nitrogen and subsequent drying at room temperature under vacuum (Figure 5). The 10 NP-wt% samples were chosen for drying due to their higher strength and because both mixing methods led to successful bipjel creation, enabling comparison. The porous structure ob served under SEM is shown to differ from that of a dried AlOSiO gel (not subjected to bicontinuous domain formation, Figure S14). The average object thickness of the dried 10 NPwt% homogenized samples observed with SEM are also shown to be comparable to LSCM images of the bipjel, with average domain sizes of 0.57 and 0.55 µm, respectively. The isolated structures

Figure 5. SEM images of dried co-continuous materials formed through bipjel templating for (a) 10 NP-wt% vortex mixed W/L bipjels and (b) 10 NP-wt% rotor stator homogenizer mixed W/L bipjels. The inset in (b) has a scale bar of 200 nm, demonstrating the mesoporosity at the surface of the NP-formed materials. Inset 3D reconstructions of LSCM images are both 18 µm in x/y and 2.5 μm in z, with red representing Nile red tagged lutidine and green


Page 4 of 8

Page 5 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials representing

reflection

from

the

AlO-SiO

NPs.

were further observed by SEM to exhibit both macroporosity in the main voids, as well as mesoporosity at the surfaces of the NP-based structure. The colloidal gel mixing technique is again seen to influence the resulting bimodally porous structures isolated from the 10 NP-wt% bipjels. The vortexed sample is shown to have less uniform domain sizes and page higher apparent surface roughness, resulting from non-uniformity and loose packing of the flocculants formed with low energy mixing when compared with the homogenized samples. Conclusions We demonstrate here a new class of materials, bipjels, that provide a tunable, template-free method for the preparation of hierarchical porous materials with consistent width, cocontinuous macroporous channels. Alumina coated silica nanoparticles are shown to form a percolating network with sufficient mechanical strength to prevent the phase separation of a water-lutidine mixture above the lower critical solution temperature, rather arresting the thermodynamically instable bicontinuous morphology. The morphology and strength of these materials are shown to be impacted by pre-mixing conditions; sensitivity to other factors such as heating rate are also anticipated but deemed to be beyond the scope of this manuscript. The isolation of free-standing bimodal, cocontinuous porous materials composed entirely of the alumina coated silica nanoparticles is readily achieved by direct isolation via solvent removal from the bipjels. These solid porous materials are highly desired for a number of applications requiring strict porous material morphologies, ranging from biomedical tissue scaffolding to separations and electrocatalysis. The present study lays the ground work for the functionalization, optimization and isolation of functional porous materials with continuous porosity and high internal surface area. Materials and Methods Bipjel Formation: Bipjels were prepared at the critical composition of 2,6-lutidine and water with AlO-SiO nanoparticle suspensions. The original suspension was diluted into the water phase at 5, 10 wt% silica content (φ = 1.7% and 3.3% respectively, herein denoted as 5 or 10 NP-wt%) with Millipore water. 2,6-Lutidine, tagged with Nile Red for imaging, was added after the dilution to bring the mixture to the critical composition (volume ratio L:W=30:70). Samples were then mixed one of two ways: “low-energy” vortex mixing (Fisher Mini Vortexer, 120 V), or with a “high-energy” rotor stabilized homogenizer (PRO Scientific Bio-Gen Series PRO200). For vortexed samples, 1.5 mL of bipjel solutions were vortexed on the highest setting for approximately 30 seconds; for homogenized samples, 2.5 mL of bipjel solutions were alternatively vortexed and homogenized for approximately 30 seconds of total mixing time (the vortex steps were required to bring the sample to the bottom of the centrifuge tube throughout the homogenization). Mixed samples were then heated as described below for the various experiments. Confocal-Rheology: Bipjels were imaged using a 25x water immersion objective or a 63x oil immersion objective and 552 nm laser on a Leica SP8 laser scanning confocal microscope (LSCM) equipped with a periscope arm (LSM Tech) and piezo stage (Piezosystem Jena). The 552 nm laser was also used to capture reflectance of the AlO-SiO NP throughout imaging. To prevent immersion liquid evaporation a gel solution with

matching refractive index was used in place of water for the 25x objective. Samples were imaged from below the coverslip on a Peltier stage on an Anton Paar MCR 302 WESP rheometer. Samples were loaded onto the coverslip at room temperature. Rheological testing included a 60 second pre-shear step (𝛾 = 5 s-1) at 30°C with a 25 mm parallel plate geometry. Samples were then probed with a frequency sweep, from 𝑓 = 100 to 0.1 Hz at a strain of 𝛾 = 0.5%. The sample was then pre-sheared again for 60 second (𝛾 = 5 s-1) at 30°C. Following this the sample was quenched into the 2-phase region by heating at 25°C minute-1 to 55°C where it was aged for 30 minutes. Samples were then probed again with a frequency sweep, from 𝑓 = 100 to 0.1 Hz at a strain of  = 0.5%. The sample was then cooled at 5°C minute-1 to 20°C to observe monogel formation and stability for 15 minutes. Samples were then probed a final time with a frequency sweep, from 𝑓 = 100 to 0.1 Hz at a strain of  = 0.5%. These frequency sweeps were used to probe the solid-like properties of the bipjels at various stages. Throughout the time sweep processes, the storage and loss moduli were monitored every 1 s with a constant oscillatory strain,  = 0.5% at a frequency, 𝑓 = 1 Hz, to perform a time sweep test to see structure evolution as the sample was taken to important temperatures for the critical W/L system. Confocal imaging occurred throughout this test. Stacks of 2D images, covering ~30 microns in the z-direction, took 1-2 minutes to acquire, depending on the averaging used to improve the signal to noise ratio, and a step size of 400 nm (25x) or 255 nm (63x) was used. Particle Characterization: A Malvern Zetasizer with Autotitration unit was used to perform a zeta-titration of the original AlO-SiO (SnowtexAK) nanoparticle suspensions provided by Nissan Chemicals (see Table S1 for properties). The suspension was diluted down to 0.5 wt% SiO2 content, and was titrated from the original pH to a pH of 10. The pH was adjusted with a 0.1 M NaOH solution - 4 different pH values were measured and 3 measurements of the zeta potential were taken at each point for standard deviation calculations. Fourier transform infrared spectroscopy was performed using an Agilent MicroLab spectrometer on AlO-SiO NPs which had been dried for ~ 2 hours at 50°C. Cryogenic transmission electron microscopy imaging was used to verify manufacturer specifications (Figure S1, experimental in ESI). Image Processing: Post-processing and image quantification was done using Avizo 9.3 software (CMC Microsystems). The fluorescent channels were deconvoluted and then a 3D median filter was applied to reduce noise. Images acquired with the 63x objective were additionally processed with a Gaussian filter prior to median filtering to further reduce noise from the higher magnification. Following this, each image’s histogram was normalized to minimize brightness variation as the lasers penetrated deeper into the samples. This step also helps correct for possible photo-bleaching that may occur during confocalrheology imaging as the same region is scanned many times. Following this, the samples were thresholded at similar values (possible due to the normalized brightness), a filter was applied to remove small spots contributing to noise, the inverse of the image was taken, and the cylinder-rod model (see Equation 1) was applied to calculate the average object thickness of the water-rich domains. 4 Equation 1: Average Object Thickness = LW = Obj.S Obj.V



Where Obj.S/Obj.V is the surface to volume ratio. For the SEM image samples, distance mapping through Avizo’s AutoSkeleton module was used to calculate the domain sizes from the 2D image. The generated value corresponded to a radius measurement and so was doubled for the total channel width. To calculate the errors, images were divided into quadrants and the surface area to volume ratio was calculated for each time step. The percent error found from the standard deviation of the four quadrants was applied to the average object size calculation for the reported times. Curvature Analysis: To analyze the curvature of the structures, a different image processing pathway was used to extract the surfaces. Image stacks were divided into 4 quadrants after the thresholding and filtering steps mentioned above. An isosurface was then created. During this step, it is possible to down sample the image for ease of computation, however, for all but the 10 NP-wt% vortexed samples, we were able to avoid this step through dividing the stacks into equally sized quadrants. Dividing into quadrants also allowed to calculate the standard deviation of the distributions within the individual images. The surface was extracted and remeshed for best isotropic vertex placement. Then the surface was smoothed by shifting the vertices to the average position of its neighbors. The mean (H) and Gaussian (K) curvatures were then calculated (see equations 2-3) from the triangles’ principle orthogonal curvatures (κ 1 and κ 2), and the area probability distributions were calculated using Equations 4-5. Equation 2: H =

κ1 + κ2

Equation 3: K = κ1 * κ2 Equation 4: PH(H) = Equation 5: PK(K) =

AUTHOR INFORMATION Corresponding Author * Milana Trifkovic, University of Calgary, Department of Chemical and Petroleum Engineering, Calgary, AB T2N 1N4, T (403) 220-8779, E - [email protected].

Author Contributions The manuscript was written through contributions of all authors. / All authors have given approval to the final version of the manuscript. / ‡These authors contributed equally.

ACKNOWLEDGMENT The authors would like to thank Olga Kleinerman and Tamar Segal-Peretz of Technion Israel Institute of Technology for cryoTEM micrographs and CMC Microsystems for access to Avizo software. This work was supported by the Natural Sciences and Engineering Research Council of Canada (Discovery Grant), the Canada Foundation for Innovation and Alberta Innovates – Technology Futures.

ABBREVIATIONS LSCM, laser scanning confocal microscopy; LCST, lower critical solution tempersture; W/L, water/2-6 lutidine; NP, nanoparticle; AlO-SiO, alumina coated silica; EES, electrochemical energy storage; 3DOM, three dimensional ordered porous.

REFERENCES

2

∑N A t=1

further discussion of curvature evolution. This material is available free of charge via the Internet at http://pubs.acs.org.

(i│H -

∆H 2

H

≤ Hi < H + ∆ 2

(│

∆K 2

≤ Ki < K +

Lee, M. N.; Mohraz, A. Hierarchically Porous Silver Monoliths from Colloidal Bicontinuous Interfacially Jammed Emulsion Gels. J. Am. Chem. Soc. 2011, 133 (18), 6945–6947.

(2)

Yue, Y.; Liang, H. 3D Current Collectors for Lithium-Ion Batteries: A Topical Review. Small Methods 2018, 2 (8), 1800056.

(3)

Trogadas, P.; Ramani, V.; Strasser, P.; Fuller, T. F.; Coppens, M.O. Hierarchically Structured Nanomaterials for Electrochemical Energy Conversion. Angew. Chemie Int. Ed. 2016, 55 (1), 122– 148.

(4)

Chabi, S.; Peng, C.; Hu, D.; Zhu, Y. Ideal Three-Dimensional Electrode Structures for Electrochemical Energy Storage. Adv. Mater. 2014, 26 (15), 2440–2445.

(5)

Pilapil, B. K.; van Drunen, J.; Makonnen, Y.; Beauchemin, D.; Jerkiewicz, G.; Gates, B. D. Ordered Porous Electrodes by Design: Toward Enhancing the Effective Utilization of Platinum in Electrocatalysis. Adv. Funct. Mater. 2017, 27 (36), 1703171.

(6)

Kim, O.-H.; Cho, Y.-H.; Kang, S. H.; Park, H.-Y.; Kim, M.; Lim, J. W.; Chung, D. Y.; Lee, M. J.; Choe, H.; Sung, Y.-E. Ordered Macroporous Platinum Electrode and Enhanced Mass Transfer in Fuel Cells Using Inverse Opal Structure. Nat. Commun. 2013, 4, 2473.

(7)

Fischer, A.; Jun, Y.-S.; Thomas, A.; Antonietti, M. Synthesis of High-Surface-Area TiN/Carbon Composite Materials with Hierarchical Porosity via Reactive Templating. Chem. Mater. 2008, 20, 7383–7389.

(8)

Nakanishi, K. Pore Structure Control of Silica Gels Based on Phase Separation. J. Porous Mater. 1997, 4 (2), 67–112.

(9)

Junko Konishi, †; Koji Fujita, *; Kazuki Nakanishi, ‡ and; Hirao†, K. Phase-Separation-Induced Titania Monoliths with Well-Defined Macropores and Mesostructured Framework from Colloid-Derived Sol−Gel Systems. Chem. o 2006, 18, 864–866.

(10)

Gao, Y.; Kim, J.; Helgeson, M. E. Microdynamics and Arrest of Coarsening during Spinodal Decomposition in Thermoreversible Colloidal Gels. Soft Matter 2015, 11 (32), 6360–6370.

)

N ∆H∑t = iAi

∑N A i K t=1

(1)

)

∆K 2

N ∆K∑t = iAi

Where A refers to the area of a triangle on the surface. These distributions were normalized to the interfacial area per unit volume ratio, Q, for the mean, and Q2, for the Gaussian curvatures. Monolith Creation: Porous monoliths were created directly from the networked AlO-SiO bijels. 2.5 mL of the initial 10wt% vortexed and homogenized bijel mixtures were prepared as described and then placed into 4 mL glass vials. This vial was then quenched into the two-phase region by placing it in a 55°C oil bath (the approximate heating rate was measured to be 12°C min-1). It was kept in the oil bath for 20 minutes, before the networked bipjel was rapidly frozen by submerging the vial in a liquid nitrogen bath. The vial was readily placed into a vacuum chamber, and the water and lutidine were removed over 18 hours. The sample was then removed and imaged in a Zeiss Sigma VP scanning electron microscope. For the 10 NP-wt% vortexed control test, the sample was prepared the exact same way only it was not subjected to heating in the oil bath.

ASSOCIATED CONTENT Supporting Information. Additional experimental details, additional rheological, LSCM, and confocal rheology data, and


Page 6 of 8

Page 7 of 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chemistry of Materials (11)

Lu, P. J.; Zaccarelli, E.; Ciulla, F.; Schofield, A. B.; Sciortino, F.; Weitz, D. A. Gelation of Particles with Short-Range Attraction. Nature 2008, 453 (7194), 499–503.

(12)

Herzig, E. M.; White, K. A.; Schofield, A. B.; Poon, W. C. K.; Clegg, P. S. Bicontinuous Emulsions Stabilized Solely by Colloidal Particles. Nat. Mater. 2007, 6 (12), 966–971.

(13)

Huang, C.; Forth, J.; Wang, W.; Hong, K.; Smith, G. S.; Helms, B. A.; Russell, T. P. Bicontinuous Structured Liquids with SubMicrometre Domains Using Nanoparticle Surfactants. Nat. Nanotechnol. 2017, 12 (11), 1060–1063.

(14)

Witt, J. A.; Mumm, D. R.; Mohraz, A. Microstructural Tunability of Co-Continuous Bijel-Derived Electrodes to Provide High Energy and Power Densities. J. Mater. Chem. A 2016, 4, 1000– 1007.

(15)

Lee, M. N.; Thijssen, J. H. J.; Witt, J. A.; Clegg, P. S.; Mohraz, A. Making a Robust Interfacial Scaffold: Bijel Rheology and Its Link to Processability. Adv. Funct. Mater. 2013, 23 (4), 417–423.

(16)

Haase, M. F.; Stebe, K. J.; Lee, D. Continuous Fabrication of Hierarchical and Asymmetric Bijel Microparticles, Fibers, and Membranes by Solvent Transfer-Induced Phase Separation (STRIPS). Adv. Mater. 2015, 27 (44), 7065–7071.

(17)

Cai, D.; Clegg, P. S. Stabilizing Bijels Using a Mixture of Fumed Silica Nanoparticles. Chem. Commun. 2015, 51 (95), 16984– 16987.

(18)

Huang, S.; Bai, L.; Trifkovic, M.; Cheng, X.; Macosko, C. W. Controlling the Morphology of Immiscible Cocontinuous Polymer Blends via Silica Nanoparticles Jammed at the Interface. Macromolecules 2016, 49 (10), 3911–3918.

(19)

Bai, L.; Fruehwirth, J. W.; Cheng, X.; Macosko, C. W. Dynamics and Rheology of Nonpolar Bijels. Soft Matter 2015, 11 (26), 5282–5293.

(20)

Li, L.; Miesch, C.; Sudeep, P. K.; Balazs, A. C.; Emrick, T.; Russell, T. P.; Hayward, R. C. Kinetically Trapped CoContinuous Polymer Morphologies through Intraphase Gelation of Nanoparticles. Nano Lett. 2011, 11 (5), 1997–2003.

(21)

Grattoni, C. a; Dawe, R. a; Seah, C. Y.; Gray, J. D. Lower Critical Solution Coexistence Curve and Physical Properties (Density, Viscosity, Surface Tension, and Interfacial Tension) of 2,6Lutidine + Water. J. Chem. Eng. Data 1993, 38 (4), 516–519.

(22)

Tavacoli, J. W.; Thijssen, J. H. J.; Schofield, A. B.; Clegg, P. S. Novel, Robust, and Versatile Bijels of Nitromethane, Ethanediol, and Colloidal Silica: Capsules, Sub-Ten-Micrometer Domains, and Mechanical Properties. Adv. Funct. Mater. 2011, 21 (11), 2020–2027.

(23)

Lu, S.; Pugh, R. J.; Forssberg, E. Particle-Particle Interactions. In Studies in Interface Science; Elsevier, 2005; pp 172–244.

(24)

Witt, J. a.; Mumm, D. R.; Mohraz, A. Bijel Reinforcement by Droplet Bridging: A Route to Bicontinuous Materials with Large Domains. Soft Matter 2013, 9 (29), 6773.

(25)

Imperiali, L.; Clasen, C.; Fransaer, J.; Macosko, C. W.; Vermant, J. A Simple Route towards Graphene Oxide Frameworks. Mater. Horiz. 2014, 1 (1), 139–145.

(26)

Oles, V. Shear-Induced Aggregation and Breakup of Polystyrene Latex Particles. J. Colloid Interface Sci. 1992, 154 (2), 351–358.

(27)

Reeves, M.; Stratford, K.; Thijssen, J. H. J. Quantitative Morphological Characterization of Bicontinuous Pickering Emulsions via Interfacial Curvatures. Soft Matter 2016, 12 (18), 4082–4092.



Page 8 of 8

A new class of soft material, bicontinous intraphase jammed emulsion gels (bipjels), is shown here for the first time formed via spinodal decomposition templating of colloidal gels. Direct isolation of hierarchial porosity, co-continuous materials is then achieved by solvent removal, generating ideal structures for a range of emerging technologies in catalysis and storage.


8

Bicontinuous Intraphase Jammed Emulsion Gels ... - ACS Publications

Recommend Documents