A Robust Oil-in-Oil Emulsion for the Nonaqueous Encapsulation of

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A Robust Oil-in-Oil Emulsion for the Nonaqueous Encapsulation of Hydrophilic Payloads Xiaocun Lu, Joshua S Katz, Adam Schmitt, and Jeffrey S. Moore J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b11847 • Publication Date (Web): 19 Feb 2018 Downloaded from http://pubs.acs.org on February 20, 2018

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Journal of the American Chemical Society

A Robust Oil-in-Oil Emulsion for the Nonaqueous Encapsulation of Hydrophilic Payloads Xiaocun Lu,†‡ Joshua S. Katz,# Adam K. Schmitt,⊥ and Jeffrey S. Moore†‡§∥* †

Beckman Institute for Advanced Science and Technology, ‡Department of Chemistry, §Department of Materials Science and Engineering, and ∥Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States # Formulation Science, Corporate Research & Development, The Dow Chemical Company, Collegeville, Pennsylvania 19426, United States ⊥Information Research, Corporate Research & Development, The Dow Chemical Company, Midland, Michigan, 48674, United States ABSTRACT: Compartmentalized structures widely exist in cellular systems (organelles) and perform essential functions in smart composite materials (microcapsules, vasculatures, and micelles) to provide localized functionality and enhance materials compatibility. An entirely water-free compartmentalization system is of significant value to the materials community as nonaqueous conditions are critical to packaging microcapsules with water-free hydrophilic payloads while avoiding energy-intensive drying steps. Few nonaqueous encapsulation techniques are known, especially when considering just the scalable processes that operate in batch mode. Herein, we report a robust oil-in-oil Pickering emulsion system that is compatible with nonaqueous interfacial reactions as required for encapsulation of hydrophilic payloads. A major conceptual advance of this work is the notion of the partitioning inhibitor – a chemical agent that greatly reduces the payload’s distribution between the emulsion’s two phases, thus providing appropriate conditions for emulsion-templated interfacial polymerization. As a specific example, an immiscible hydrocarbon-amine pair of liquids is emulsified by the incorporation of guanidinium chloride (GuHCl) as a partitioning inhibitor into the dispersed phase. Polyisobutylene (PIB) is added into the continuous phase as a viscosity modifier for suitable modification of interfacial polymerization kinetics. The combination of GuHCl and PIB is necessary to yield a robust emulsion with stable morphology for three weeks. Shell wall formation was accomplished by interfacial polymerization of isocyanates delivered through the continuous phase and polyamines from the droplet core. Diethylenetriamine (DETA)-loaded microcapsules were isolated in good yield, exhibiting high thermal and chemical stabilities with extended shelf-lives even when dispersed into a reactive epoxy resin. The polyamine phase is compatible with a variety of basic and hydrophilic actives, suggesting that this encapsulation technology is applicable to other hydrophilic payloads such as polyols, aromatic amines, and aromatic heterocyclic bases. Such payloads are important for the development of extended pot or shelf-life systems and responsive coatings that report, protect, modify and heal themselves without intervention.

INTRODUCTION Cellular compartments and extracellular vesicles widely exist in all eukaryotic cells of higher organisms, comprising membrane-enclosed structures (e.g., nuclei, lysosomes, and mitochondria) that perform vital functions in distinct regions within and outside of cells.1 Similar to biological systems, compartmentalized structures such as microcapsules, vasculatures, and micelles have also been extensively employed in the development of smart materials and biomaterials for incorporation of additional functionality and improvement of materials compatibility.2 Efficient encapsulation methods for hydrophilic payloads such as amines, acids, and alcohols are in high demand for many materials, biological and agriculture applications.2b,3 Specifically, amine4 microcapsules have generated considerable interest for the development of advanced smart materials, such as self-healing and damage-reporting applications.5 Encapsulation of amines is difficult to achieve by most conventional encapsulation techniques,2b,6 such as emulsiontemplated interfacial polymerization,7 vacuum infiltration,5a,5d solvent evaporation,8 and microfluidics,9 due to issues with substantial solvent residues,5e,10 poor barrier properties,11 and

non-scalable production.9b A nonaqueous system is crucial to many microcapsules’ performance because premature payload release is potentially promoted by aqueous residues7a and many systems react with water, leading to undesired byproducts.12 Designing an entirely water-free system avoids the need for energy-intensive drying steps.13 Thus, a facile, general and scalable technique for the encapsulation of hydrophilic actives with a water-free core, high payload, and excellent barrier properties is of significant value to the materials community. Oil-in-oil (o/o) emulsion-templated encapsulation is a promising approach to produce microcapsules in a nonaqueous environment. However, there is a dearth of nonaqueous emulsion systems available because identifying appropriate solvent pairs that drive phase separation into an emulsion is challenging.14 Liquid pairs employed in conventional nonaqueous emulsions include the combination of nonpolar solvents (e.g., hydrocarbons15 and polymers16) and highly polar solvents (e.g., methanol,17 formamide,18 polyols,19 and dichloromethane20). Amphiphilic block-polymers21 and Pickering particles19a,22 are typical stabilizers23 for o/o emulsions. Most research relating to reactions in o/o emulsions has focused on bulk polymerization within emulsion droplets to yield polymer nanoparticles,24

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with only a few examples of interfacial polymerization to form the shell materials,15,25 leaving a wide range of uncultivated research to pursue if the above-mentioned challenges are circumvented. Two specific challenges that hinder o/o emulsions for encapsulation of hydrophilic payloads are minimizing distribution of the payload into the continuous phase and tuning the interfacial polymerization kinetics. In an o/o emulsion, reactive polar payloads such as amines and alcohols tend to distribute into both emulsion phases, potentially interfering with the subsequent interfacial polymerization26 and promoting Ostwald ripening which significantly reduces emulsion stability.27 In this work we envisioned that there might exist chemical entities that function as partitioning inhibitors; that is, chemical agents that promote the redistribution of active core materials predominately to the interior of the emulsion droplets. Reaction kinetics of interfacial polymerization is the second challenge. Shell thickness and barrier properties are significantly influenced by the diffusion and reaction rates of reactants continuously delivered to the interface. Unfavorable reactant delivery generates local kinetic turbulence,28 leading to interrupted shell growth and yielding low-quality shell materials with poor barrier properties. We hypothesize that viscosity of the continuous phase is an efficient way to modify the diffusion rates of reactants to diminish undesired kinetic turbulence on the interface. Scheme 1. Development of an efficient o/o emulsion employing the concept of a partitioning inhibitor that promotes the redistribution of the payload to the droplet interior along with a viscosity modifier to enhance the emulsion stability and modulate the dispersion kinetics of reactants during the interfacial polymerization.

Herein we report an easily scalable (batch mode) nonaqueous emulsion system suitable for encapsulating hydrophilic payloads within a robust polyurea shell wall that provides good barrier properties and long shelf-life. We introduce the concept of partitioning inhibitors, which are species that greatly reduce payload mixing between the nonaqueous phases, thus providing appropriate conditions for emulsion-templated interfacial polymerization. We demonstrate these ideas with a stable polyamine-in-hydrocarbon o/o emulsion using guanidinium chloride (GuHCl) as a partitioning inhibitor and polyisobutylene (PIB) as a viscosity modifier to control the diffusion kinetics of reactants and enhance the emulsion stability (Scheme 1). This versatile nonaqueous emulsion has both technical and scientific merit; not only does it result in a stable, microcapsule storage and delivery system for water-free hydrophilic payloads such as polyamines, polyols, aromatic amines, and aromatic heterocyclic bases, but it also features a robust heterophase system for fundamental studies of nonaqueous interfacial properties and reactions. The waterfree emulsification and encapsulation techniques reported here

provide opportunities for many applications that impact a broad range of disciplines, exhibiting considerable promise to improve traditional industrial applications of coatings, printings, and composites, as well as advanced smart materials for self-healing and damage-reporting applications.

RESULTS AND DISCUSSION A pair of two immiscible organic solvents is essential for the development of o/o emulsions. Diethylenetriamine (DETA), a typical multifunctional amine, was used as the polar payload for the initial investigation. A comprehensive literature search14b,29 followed by screening experiments on solvent miscibility led us to conclude that many hydrocarbons are immiscible with DETA and therefore worthy of further consideration in pursuit of suitable o/o emulsions. Compared to other hydrocarbons, decalin has a relatively high density (0.9 g·mL-1),30 viscosity (2.7 cP),31 and surface tension (30.5 mN·m-1),30 which all facilitate the formation of a stable emulsion. However, the solubility of DETA (determined by GCMS) in decalin is higher (21 mg·mL-1) than in hexadecane (7 mg·mL-1). In order to balance the desirable with the undesirable characteristics of each of these hydrocarbons, we chose to use a 1:1 (wt:wt) mixture of decalin and hexadecane (DH).

Figure 1. (A) DETA partitioning concentrations in the nonpolar DH solvent mixture with various additives and concentrations. (B) Correlation of Dnp-p to GuHCl wt% in both decalin and the DH solvent mixture. (C) Correlation of the DETA partitioning concentration between experimental data and the simulated data by COSMOtherm.

It is common for polar organic payloads to partition in both phases of o/o emulsions, potentially interfering with the subsequent encapsulation chemistry. As expected, DETA is partially miscible with the DH solvent mixture. This amine has a partition coefficient Dnp-p (nonpolar:polar phase ratio) of 0.044 with a concentration of 11.3 mg·mL-1 detected in the continuous phase by GC-MS (Figure S1). Organic acids were first tested as partitioning inhibitors to prevent DETA from dispersing into the hydrocarbon phase. Weak organic acids (acetic, citric, and carboxylic acids) were not sufficient to reduce the DETA partitioning due to solubility and gelation issues. Strong organic acids (trifluoroacetic acid (TFA) and sulfonic acids (R-SO3H)) had a more significant effect in lowering the


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Journal of the American Chemical Society concentration of DETA in the continuous phase (Figure 1A). Addition of 65 wt% TFA completely inhibited DETA from dispersing into the nonpolar phase; but the strong organic acids reacted violently and exothermically with DETA, protonating about 30 mol% of the active amino groups in the payload. The introduction of ions into the polyamine phase is one approach to replace the acidic additives. However, most commonly used sodium, potassium and ammonium salts, as well as polymeric electrolytes based on sulfonic and acrylic acids, were insoluble in polyamines. Ammonium hexafluorophosphate (NH4PF6) and guanidinium chloride (GuHCl) were the only two salts tested that are soluble in DETA. Similar to the strong acid additives, Dnp-p was reduced from 0.044 to 0 (< 0.010, detection limit by GC-MS) with the addition of 65 wt% GuHCl (Figure 1B), indicating efficient inhibition of the DETA partitioning. Compared to NH4PF6, GuHCl is known to interact strongly with polyamines,32 and was the favored partitioning inhibitor, being economical and unreactive towards DETA as indicated by 1H-NMR (Figure S2). Phase separation of DETA from DH was theoretically evaluated using the Liquid Extraction module in COSMOtherm X33 with DETA as the first phase and DH as the second phase. This module performs iterative partitioning and solubility calculations to give the final concentrations of each compound in both phases. The final DETA concentration from the DH phase was taken as the theoretical prediction for partitioning of DETA into the continuous phase. The effects of various inhibitors on the partitioning of DETA were evaluated using the same process described above but incorporating the inhibitors in the DETA phase. While the experimental and theoretical results did not match exactly on an absolute basis, the theoretical prediction closely matched the observed experimental trend (Figure 1C) with a correlation coefficient, R2 = 0.75. This theoretical payload partitioning analysis is thus useful to assist in the identification of other suitable solvent systems and partitioning inhibitors for additional payloads of interest. The introduction of electrolytes into the amine phase significantly altered the phase separation behavior as revealed experimentally by the measurement of contact angles. The hydrophilicity of the polar phase was enhanced by the addition of GuHCl as indicated by an increased contact angle, θ, on a hydrophobic polystyrene surface (Figure 2). For example, when the ratio of GuHCl and DETA (RG-D, wt/wt) was increased from 0 to 0.65, θ changed from 48.7° to 71.9°.

Figure 2. Correlation of contact angle θ to GuHCl wt% on a nonpolar polyethylene substrate. As a benchmark, the contact angle of a pure water droplet on polyethylene is 87˚.

A ternary phase diagram of GuHCl-DETA-DH was constructed to get a complete overview of the strong polyamine/hydrocarbon phase separation system (Figure 3). GuHCl

reached its solubility limit when RG-D > 1 (Figure 3, red region). For RG-D < 1, there was always strong phase separation between the polar (DETA-GuHCl) and the nonpolar (DH) phases. Generally, more GuHCl (RG-D > 0.5) led to faster phase separation (Figure 3, green region). With a reduced GuHCl loading (RG-D < 0.5), the speed of phase separation was reduced and took more than 2 min (Figure 3, yellow region). The blue region summarizes the effective ratios of the partitioning inhibitor. The minimum RG-D to completely inhibit payload partitioning was ca. 0.6. Through extensive experimentation, the optimal composition of the polar phase was found at 43 wt% DETA, 20 wt% pentaethylenehexamine (PEHA), 10 wt% branched polyethyleneimine (PEI, MW ca. 20kDa), and 27 wt% GuHCl and in the following discussion will be referred to as DPPG-4213 (DETA-PEHA-PEI-GuHCl, ca. 4:2:1:3, weight ratios). PEHA and PEI are multifunctional polyamines, serving as crosslinkers in the subsequent interfacial polymerization to enhance barrier performance. They were essential to stabilize emulsion droplets and form robust shell materials because of their relatively large molecular weight, yielding robust shell materials during the interfacial polymerization.

Figure 3. Ternary phase diagram of GuHCl-DETA-DH. Compositions in the blue region have no detectable DETA in the nonpolar phase and promote fast separation of the immiscible phases.

The viscosity of a continuous phase significantly influences the stability of emulsion droplets.34 The polymeric hydrocarbon additive PIB (MW ca. 500kDa) was chosen as a viscosity modifier due to its compatibility and commercial availability. The viscosity, η, of the hydrocarbon phase increased from 3 cP (no PIB) to 4085 cP (12 wt% PIB), and a linear correlation between PIB wt% and log η was observed (Figure 4A). The enhanced viscosity led to improved emulsion stability as visualized by optical microscopy (Figure 4C). A stable emulsion was formed only when PIB was more than 4 wt% (η ca. 60 cP) and less PIB led to rapid coalescence of emulsion droplets. A PIB content in the continuous phase greater than 10 wt% (η ca. 2000 cP) maintains a robust emulsion template for the subsequent interfacial polymerization. PIB was in the semidilute-concentration regime of the solution assuming the estimated overlap concentration of 0.5 g·dL-1 (ca. 0.6 wt%). PIB did not have much effect on the surface tension of the continuous phase (Figure 4B, dashed line) or the interfacial tension, γ, between the two emulsion phases (Figure 4B, solid line), suggesting that PIB mainly served as a viscosity modifier without interfering with the interfacial energy. Increasing vis-



cosity extended the shelf-life of the emulsions from 5 min (4 wt% PIB) to 21 days (12 wt% PIB), maintaining intact emulsion droplets with similar morphologies and sizes (Figure 4D). The enhanced shelf-life was due in part to the reduced diffusion coefficient of the emulsion droplets. According to StokesEinstein equation, the diffusion coefficient was reduced by a factor of 103 with the addition of PIB from 0 to 12 wt%. Such a viscous solvent enhanced the emulsion stability by slowing down the droplet diffusion rate and diminishing the coalescence of the emulsion.

Figure 5. Relationship among Re, viscosity and stirring rate, based on Re = ρND2/µ (Ref. 36). A 100 × 100 matrix of data points was generated.

Figure 4. (A) Correlation between log η and PIB wt%. (B) Correlation between surface tension γ and PIB wt%. The dashed line is the surface tension of the DHP-012 phase with air; the solid line is the interfacial tension between the DPPG-4123 and DHP-012. (C) Optical microscope images of the emulsion droplets corresponding to PIB (a) 2 wt%, (b) 8 wt%, and (c) 12 wt%, respectively. (D) Size distribution vs. time with fluorescent images of the emulsion droplets with 12 wt% PIB after settling down for (a) 1h (red line) and (b) 21 days (blue line).

Increased viscosity also affected the transport characteristics and hence reaction kinetics of the subsequent interfacial polymerization. Generally, a steady and non-turbulent reactant delivery to the interface during a continuous dispersion is crucial for most interfacial polymerization to form shell materials with good barrier properties. Stable laminar flow with a low Reynolds number (Re < 200) is ideal for interfacial polymerization compared to transitional and turbulent flow (Re > 2000).35 Efficiency and kinetics of a dispersion process are determined by both convective methods (agitations such as stirring, mixing, and dispersion) and diffusion. Figure 5 shows how the Re changed as a function of viscosity and stirring rate in the polyamine/hydrocarbon emulsion. The blue region on the top left corner indicated Re < 10 and the green region reflected an increased Re range between 10 and 200. With a typical stirring rate of 300-750 rpm for the most commonly used stirring devices, a viscosity range of the continuous phase between 2000-4000 cP (10-12 wt% PIB) maintains Laminar flow (Figure 5, yellow triangle) and this viscosity range was also suitable to generate a stable emulsion as discussed previously. Overall, the optimized continuous phase contained 12 wt% PIB as the viscosity modifier and 88 wt% of the 1:1 wt/wt mixed DH solvent, which was referred to as DHP-012 (Decalin-Hexadecane-Polyisobutylene, 12 wt% of PIB) in the following discussion.

With the optimized polyamine/hydrocarbon liquid pair, a survey of emulsion stabilizers was undertaken. Commonly used polymeric surfactants Brij® 93, Span® 80, Span® 85, and Tween® 20 were not able to facilitate generation or stabilization of the o/o emulsions under various agitation methods including ultra-sonication, homogenization, and vigorous stirring (see SI). This is consistent with the literature that has shown that conventional surfactants are not efficient stabilizers of systems that deviate from oil and water.7b,21,37 Hydrophobically functionalized clay (Closite® #20) as a Pickering particle enabled generation of a stable o/o emulsion due to its relatively large size.37-38 More clay produced smaller-sized emulsion droplets with enhanced stability. With the addition of 2 wt% or more Closite® #20, droplet sizes were maintained around 6 µm and did not further decrease. Thus, 2 wt% loading of Closite® #20 was used as an optimized emulsifier. Less loading of the Pickering particles provided less stable emulsion templates with reduced polymerization efficiency and lower isolation yields. With a stable emulsion system in hand, next, the encapsulation of active amines was probed. Polyurea shell walls were formed through interfacial polycondensation of isocyanates (added to the continuous phase) and payload amines on the surface of the emulsion droplets. A screening of the commercially available polyisocyanate crosslinkers has been performed. Most of the aromatic isocyanates such as naphthalene 1,5-diisocyanate (NDI), 4,4'-diphenylmethane diisocyanate (MDI) and polymethylene polyphenyl isocyanate (PMPPI) were not miscible with the continuous phase DHP-012, except for toluene 1,4-diisocyanate (TDI). Most of the aliphatic isocyanates such as hexamethylene diisocyanate (HDI), 4,4'methylene dicyclohexyl diisocyanate (H12MDI), and tetramethylxylene diisocyanate (TMXDI) were miscible with the non-polar phase DHP-012, except for HDI-oligomers and isophorone diisocyanate (IPDI). Among the only four commercial available polyisocyanates that were miscible with DHP-012 (TDI, HDI, H12MDI, and TMXDI, see SI), only H12MDI (secondary isocyanate) and TMXDI (tertiary isocyanate) yielded stable microcapsules with good isolation yield. The other two isocyanates, TDI (aromatic isocyanate) and HDI (primary aliphatic isocyanate), produced unstable microcapsules. Aromatic isocyanates usually react faster than aliphatic isocyanates.39 The sterically hindered secondary/tertiary isocyanates exhibit lower reactivities compared to the less-hindered primary NCO group.40 Our working hypothesis is that isocyanates with appropriate reactivities maintain moderate polycondensation kinetics and is a critical aspect to


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Journal of the American Chemical Society achieve good barrier properties of the microcapsules. Highly reactive isocyanates trigger fast interfacial polymerization, disrupt the shell formation/growth process due to unfavorable reaction kinetics. The exact mechanism on how the isocyanate reactivity affects barrier property is not understood at this time because of the limited commercial availability of more secondary/tertiary polyisocyanates. Future work will be conducted to include other synthetic polyisocyanates with various secondary and tertiary structures. The morphology of the encapsulation process was monitored by optical microscopy (Figure 6). The size distribution of initial emulsion droplets averaged 6.0 ± 1.5 µm. The robust emulsion droplets maintained their morphologies through the interfacial polymerization. Isolated DETA-loaded microcapsules exhibited an increased size distribution averaging 10.2 ± 2.6 µm and their morphology showed a slight shape deformation following washing with neat hexanes.

and the core materials. The normalized viscosity of the epoxy resin increased only about four-fold over 40 days’ storage compared to the 2h curing time between the pure payload and the epoxy resin, indicating the significantly enhanced stability of the DETA-loaded microcapsules in the epoxy resin (Figure 7C, red line). The microcapsules maintained their morphologies when they were dispersed and stored in the liquid epoxy resin (Figure 7C, bottom SEM). High shear forces were applied to microcapsule suspensions after storage of the microcapsules in the epoxy for 40 days. The rapid sharp viscosity increase indicated that the amine payloads were still chemically active and that the system is triggered to cure by shear. The epoxy resin became completely cured after homogenization of the amine microcapsules (Figure 7C, top SEM). The stability of the nonaqueous amine capsules reported here is much improved over what had previously been recognized as the best system – the water-based TEPA capsule (Figure 7C, green line).7a Compared to the water-based TEPA encapsulation system, the nonaqueous encapsulation system reported here produced water-free microcapsules, higher loading, improved barrier properties, and enhanced survivability under high vacuum conditions.

Figure 6. General encapsulation procedures with representative micrographs during each key step: optical micrographs (a)(c) and corresponding fluorescent images (b)(d) on the identical viewing areas. An SEM micrograph (e) and a fluorescent image (f) of dried microcapsules.

Thermal stability of the DETA-loaded microcapsules was evaluated by dynamic thermal gravimetric analysis (TGA). The dried microcapsules were heated to 100 ºC and held at this temperature for 3 h to examine their thermal stability. The microcapsules maintained a stable weight at 100 ºC with only a slight weight loss attributed to solvent residues with high boiling points, indicating good thermal stability and limited permeability. The temperature was then ramped to 650 ºC at a heating rate of 10 ºC / min (Figure 7A, blue line). A sharp weight loss appeared around 150 ºC because of the thermal degradation of polyurea shell walls7a which led to the immediate release of the polyamine payload (Figure 7A, red line). The DETA-loaded microcapsules also exhibited long-term chemical stability in a liquid epoxy resin. The reactivity of DPPG-4213 was maintained after encapsulation as demonstrated by the fast reaction between salicylaldehyde and the payload from the ruptured microcapsules. (Figure 7B). A mixture of the unencapsulated liquid core materials DPPG-4123 and epoxy resin (DER-331) solidifies within 2h at room temperature, exhibiting a 30× viscosity increase (Figure 7C, blue line). When the DPPG-4213-loaded microcapsules were suspended in the epoxy resin, the polyurea shell walls served as barriers to prevent direct contact between the epoxy resin

Figure 7. (A) TGA traces of the pure payload and the DETAloaded microcapsules: the weight loss curves of DPPG-4213 (green line) and microcapsules (red line) as well as the temperature ramping curve (blue line). (B) Payload reactivity confirmation: 1H NMR of salicylaldehyde (top) and the reaction between the ruptured capsules and salicylaldehyde (bottom). (C) Normalized viscosity of DER-331 epoxy resin formulations containing DPPG-4123 (blue) or DPPG-4123 capsules (red). Waterbased amine capsules from Ref. 7a (green) was included for comparison. The jumps in viscosity in both the red curve at 40 days and green curve at 31 days follow from exposure of the formulation to homogenization for 120 s at 160 Hz. SEM images revealed morphologies of the microcapsules dispersed in the liquid epoxy (top) and the completely cured epoxy resin after homogenization (bottom).

CONCLUSION An efficient polyamine/hydrocarbon-based anhydrous emulsion system suitable for the nonaqueous encapsulation of hydrophilic payloads has been developed. Issues that prevent encapsulation in conventional nonaqueous emulsions were overcome by adding a partitioning inhibitor to the polar phase.



A nonpolar polymer PIB was incorporated into the continuous phase as a viscosity modifier which was used to enhance the emulsion stability and tune the diffusion kinetics during the interfacial polymerization. The system is generalizable through computational prediction of partitioning. Morphology monitoring of the entire encapsulation process showcased the high efficiency and feasibility of this nonaqueous encapsulation technique. DETA-loaded microcapsules exhibited thermal stability at temperatures as high as 100 °C and chemical stability in epoxy resins with extended shelf-life up to forty days. The immiscible polyamine/hydrocarbon solvent pair provides an initial foray into the uncultivated research area of nonaqueous emulsions, generating a heterophase system for the study of interfacial properties and reactions. This o/o solvent pair also exemplifies a platform for anhydrous emulsification, useful for hydrophilic payload encapsulation. The resulting microcapsules have potential to significantly advance the development of industrial formulations and smart compartmentalized materials.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website. General methods, experiment procedures, emulsifier and isocyanate screenings are included.

AUTHOR INFORMATION Corresponding Author * [email protected].

Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT This work was supported by a grant from The Dow Chemical Company to the University of Illinois (226772AA). We thank Drs. Dan Dermody, Andy Li, Tom Kalantar, Keith Harris and Prof. Randy H. Ewoldt for informative discussions.

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A Robust Oil-in-Oil Emulsion for the Nonaqueous Encapsulation of

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