Highly Stable Phase Change Material Emulsions Fabricated by Interfacial Assembly of Amphiphilic Block Copolymers during Phase Inversion

This study introduced a robust and promising approach to fabricate highly stable phase change material (PCM) emulsions consisting of <i>n</i>-tetradecane as a dispersed phase and a mixture of meso-2,3-butanediol (m-BDO) and water as a continuous phase. We showed that amphiphilic poly­(ethylene oxide)-<i>b</i>-poly­(ε-caprolactone) block copolymers assembled to form a flexible but tough polymer membrane at the interface during phase inversion from water-in-oil emulsion to oil-in-water emulsion, thus remarkably improving the emulsion stability. Although the incorporation of m-BDO into the emulsion lowered the phase changing enthalpy, it provided a useful means to elevate the melting temperature of the emulsions near to 15 °C. Interestingly, supercooling was commonly observed in our PCM emulsions. We attributed this to the fact that the PCM molecules confined in submicron-scale droplets could not effectively nucleate to grow molecular crystals. Moreover, the presence of m-BDO in the continuous phase rather dominated the heat emission of the emulsion system during freezing, which made the supercooling more favorable

Magnetic-Patchy Janus Colloid Surfactants for Reversible Recovery of Pickering Emulsions

We present a straightforward and robust method for the synthesis of Janus colloid surfactants with distinct amphiphilicity and magnetic responsiveness. To this end, hydroxyl-functionalized amphiphilic Janus microparticles (JMPs) are synthesized by seeded monomer swelling and subsequent photopolymerization. By incorporating controlled amounts of hydroxyl groups on poly­(styrene-<i>co</i>-vinyl alcohol) seed particles, we adjust the interfacial tension between the seed polymer and the poly­(tetradecyl acrylate) secondary polymer (γ₁₃). From theoretical and experimental observations, we verify that when γ₁₃ is tuned to ∼8.5 mN/m in a medium with controlled solvency, which corresponds to a 0.6 volume fraction of ethanol in water, the particles bicompartmentalize to form oval or ellipsoidal JMPs with controllable bulb dimensions. We also show that bulb site-specific patching of magnetic nanoparticles (NPs) can be achieved using the electrostatic interaction between the polyethylenimine-coated bulb surface and the polyvinylpyrrolidone-stabilized Fe₂O₃ NPs. Finally, we demonstrate that our magnetic-patchy JMPs can assemble at the oil–water interface, enabling magnetic-responsive reversible recovery of Pickering emulsions

Study of the Air–Water Interfacial Properties of Biodegradable Polyesters and Their Block Copolymers with Poly(ethylene glycol)

It has been reported that the surface pressure–area isotherm of poly­(d,l-lactic acid-<i>ran</i>-glycolic acid) (PLGA) at the air–water interface exhibits several interesting features: (1) a plateau at intermediate compression levels, (2) a sharp rise in surface pressure upon further compression, and (3) marked surface pressure–area hysteresis during compression–expansion cycles. To investigate the molecular origin of this behavior, we conducted an extensive set of surface pressure and AFM imaging measurements with PLGA materials having several different molecular weights and also a poly­(d,l-lactic acid-<i>ran</i>-glycolic acid-<i>ran</i>-caprolactone) (PLGACL) material in which the caprolactone monomers were incorporated as a plasticizing component. The results suggest that (i) the plateau in the surface pressure–area isotherm of PLGA (or PLGACL) occurs because of the formation (and collapse) of a continuous monolayer of the polymer under continuous compression; (ii) the PLGA monolayer becomes significantly resistant to compression at high compression because under that condition the collapsed domains become large enough to become glassy (such behavior was not observed in the nonglassy PLGACL sample); and (iii) the isotherm hysteresis is due to a coarsening of the collapsed domains that occurs under high-compression conditions. We also investigated the monolayer properties of PEG-PLGA and PEG-PLGACL diblock copolymers. The results demonstrate that the tendency of PLGA (or PLGACL) to spread on water allows the polymer to be used as an anchoring block to form a smooth biodegradable monolayer of block copolymers at the air–water interface. These diblock copolymer monolayers exhibit protein resistance

Assembly of Colloidal Silica Crystals Inside Double Emulsion Drops

We investigated the assembly of colloidal silica crystals inside double emulsion drops generated in microcapillary microfluidic devices. The double emulsions are composed of an aqueous suspension of monodisperse silica particles in the inner drop surrounded by a PDMS oil drop that acts as a semipermeable membrane for the diffusion of water into or out of the inner drop in the presence of an osmotic gradient. Imposing a high osmotic pressure in the continuous phase induces water diffusion out of the inner drop, increasing the silica volume fraction (ϕ_silica) and leading to the formation of a spherical colloidal silica crystal. Silica suspensions with no salt or low salt concentration (<10^–3 M) formed colloidal crystals with ϕ_silica up to 0.68. Monodisperse spherical colloidal silica crystals with sizes ranging from 16 to 133 μm were generated by varying the device geometry, flow-rate ratios, and initial silica fraction. At salt concentrations > 10^–3 M, the electrostatic repulsion is reduced, and crystallization is suppressed. Crystals were preserved in a hydrogel matrix or inside a silicone rubber shell. This study demonstrates a robust path for controlled colloidal assembly inside double emulsion drops

Affinity Partitioning-Induced Self-Assembly in Aqueous Two-Phase Systems: Templating for Polyelectrolyte Microcapsules

Affinity partitioning refers to the preferential dissolution of solute molecules in a particular liquid phase of an immiscible liquid–liquid mixture, such as an aqueous two-phase system (ATPS). Affinity partitioning in ATPS is widely used to achieve extraction and purification of biomolecules. However, the potential of applying it to direct the self-assembly of solutes into controlled structures has been largely overlooked. Here we introduce the affinity partitioning of polyelectrolytes in ATPS to induce their self-assembly into polyelectrolyte microcapsules. The approach is purely based on the preferential solubility of different polyelectrolytes in different aqueous phases; therefore it has wide applicability and exhibits excellent compatibility with bioactives. The release of encapsulated components can be triggered by changing the pH value or ionic strength of the surrounding environment. The proposed method represents an important advance in fabricating multifunctional materials and inspires new ways to engineer sophisticated structures with hydrophilic macromolecules

Ultralight, Robust, Thermal Insulating Silica Nanolace Aerogels Derived from Pickering Emulsion Templates

Synthesis of silica aerogel insulators with ultralight weight and strong mechanical properties using a simplified technique remains challenging for functional soft materials. This study introduces a promising method for the fabrication of mechanically reinforced ultralight silica aerogels by employing attractive silica nanolace (ASNLs)-armored Pickering emulsion templates. For this, silica nanolaces (SiNLs) are fabricated by surrounding a cellulose nanofiber with necklace-shaped silica nanospheres. In order to achieve amphiphilicity, which is crucial for the stabilization of oil-in-water Pickering emulsions, hydrophobic alkyl chains and hydrophilic amine groups are grafted onto the surface of SiNLs by silica coupling reactions. Freeze-drying of ASNLs-armored Pickering emulsions has established a new type of aerogel system. The ASNLs-supported mesoporous aerogel shows 3-fold greater compressive strength, 4-fold reduced heat transfer, and a swift heat dissipation profile compared to that of the bare ASNL aerogel. Additionally, the ASNL aerogel achieves an ultralow density of 8 mg cm–3, attributed to the pore architecture generated from closely jammed emulsion drops. These results show the potential of the ASNL aerogel system, which is ultralight, mechanically stable, and thermally insulating and could be used in building services, energy-saving technologies, and the aerospace industry

Template-Free Uniform-Sized Hollow Hydrogel Capsules with Controlled Shell Permeation and Optical Responsiveness

This study has established a robust and straightforward method for the fabrication of uniform poly­(vinylamine) hydrogel capsules without using templates that combines the dispersion polymerization and the sequential hydrolysis/cross-linking. The particle sizes are determined by the degree of cross-linking as well as by the cross-linking reaction time, while the shell thickness is independent of these variables. Diffusion-limited reactions occur at the periphery of the particles, leading to the formation of hydrogel shells with a constant thickness. The treatment of the surfaces of hollow hydrogel capsules with oppositely charged biopolymers limits the permeability through the shell of species even with low molecular weights less than 400 g/mol. Furthermore, we demonstrated that the hydrogel shell phase decorated with Au nanoparticles can be optically ruptured by exposure to laser pulse, a feature that has potential uses in optically responsive drug delivery

Monodisperse Microshell Structured Gelatin Microparticles for Temporary Chemoembolization

Embolization is a nonsurgical, minimally invasive procedure that deliberately blocks a blood vessel. Although several embolic particles have been commercialized, their much wider applications have been hampered owing mainly to particle size variation and uncontrollable degradation kinetics. Herein we introduce a microfluidic approach to fabricate highly monodisperse gelatin microparticles (GMPs) with a microshell structure. For this purpose, we fabricate uniform gelatin emulsion precursors using a microfluidic technique and consecutively cross-link them by inbound diffusion of glutaraldehyde from the oil continuous phase to the suspending gelatin precursor droplets. A model micromechanic study, carried out in an artificial blood vessel, demonstrates that the extraordinary degradation kinetics of the GMPs, which stems from the microshell structure, enables controlled rupturing while exhibiting drug release under temporary chemoembolic condition

Smart Cellulose Nanofluids Produced by Tunable Hydrophobic Association of Polymer-Grafted Cellulose Nanocrystals

Cellulose fibrils, unique plant-derived semicrystalline nanomaterials with exceptional mechanical properties, have significant potential for rheology modification of complex fluids due to their ability to form a physically associated semiflexible fibrillary network. Here, we report new associative cellulose nanocrystals (ACNCs) with stress-responsive rheological behaviors in an aqueous solution. The surface-mediated living radical polymerization was employed to graft poly­(stearyl methacrylate-<i>co</i>-2-methacryloxyethyl phosphorylcholine) brushes onto the nanofibrils, and then 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was conducted to produce nanoscale ACNCs in the aqueous solution. The ACNCs displayed interfibril association driven by the hydrophobic interaction that resulted in the formation of a nanofibrillar crystalline gel phase. We observed that the viscosity of the ACNC fluid showed reversible shear thinning and temperature-induced thickening in response to applied shear stress and thermal shock. Moreover, thanks to generation of a mechanically robust nanofibrillar crystalline gel network, the ACNC suspension showed extraordinary stability to changes in salinity and pH. These results highlighted that the interfibril hydrophobic association of ACNCs was vital and played an essential role in regulation of stimuli-responsive sol–gel transitions

Cell-Penetrating Peptide-Patchy Deformable Polymeric Nanovehicles with Enhanced Cellular Uptake and Transdermal Delivery

We herein propose a polymeric nanovehicle system that has the ability to remarkably improve cellular uptake and transdermal delivery. Cell-penetrating peptide-patchy deformable polymeric nanovehicles were fabricated by tailored coassembly of amphiphilic poly­(ethylene oxide)-<i>block</i>-poly­(ε-caprolactone) (PEO-<i>b</i>-PCL), mannosylerythritol lipid (MEL), and YGRK­KRRQ­RRR-cysteamine (TAT)-linked MEL. Using X-ray diffraction, differential scanning calorimetry, and nuclear magnetic resonance analyses, we revealed that the incorporation of MEL having an asymmetric alkyl chain configuration was responsible for the deformable phase property of the vehicles. We also discovered that the nanovehicles were mutually attracted, exhibiting a gel-like fluid characteristic due to the dipole–dipole interaction between the hydroxyl group of MEL and the methoxy group of PEO-<i>b</i>-PCL. Coassembly of TAT-linked MEL with the deformable nanovehicles significantly enhanced cellular uptake due to macropinocytosis and caveolae-/lipid raft-mediated endocytosis. Furthermore, the <i>in vivo</i> skin penetration test revealed that our TAT-patchy deformable nanovehicles remarkably improved transdermal delivery efficiency