Polymerization-induced Phase Separation Research Articles

It's not just a phase: shaping the future of 3D photoprinted polymers with polymerization‐induced phase separation

AbstractAdditive manufacturing is a technology that promises to disrupt the conventional manufacturing industry due to its ability to create complex structures with improved macroscopic control not available with existing techniques like molding or milling. In addition to superior macroscopic structural control, photoprinting methods such as digital light projection can enable molecular‐scale control over the fabrication process by taking advantage of the self‐sorting or assembly properties of the monomers themselves. Polymerization‐induced phase separation (PIPS) allows for the remarkable introduction of microscopic control into additive manufacturing, using polymer‐rich and polymer‐poor regions that rely on incompatibilities to phase separate during polymerization creating new complex materials not achieved by traditional methods. With the incorporation of porogens or filler materials, microporosity and/or surface functionalization can be introduced in a facile one‐step printing process. This expands the potential applications of 3D printed materials, to include micro‐ and macroscale structural control. Using PIPS as a design strategy, polymeric materials with previously unprecedented capabilities can be produced with ease enabling 3D printing to grow into its full potential as a manufacturing tool. © 2024 Society of Chemical Industry.

Mechanical and Dimensional Stability of Gelatin-Based Hydrogels Through 3D Printing-Facilitated Confined Space Assembly.

Hydrogels have emerged as promising biomaterials for tissue regeneration; yet, their inherent swelling can cause deformation and reduced mechanical properties, posing challenges for practical applications in biomedical engineering. Traditional methods to reduce hydrogel swelling often involve complex synthesis procedures with limited flexibility. Inspired by nature's efficient designs, we present here the approach to improve hydrogel performance using 3D printing-assisted microstructure engineering. By utilizing polymerization-induced phase separation of hydrogel from copolymerization of gelatin methacrylate and hydroxyethyl methacrylate (poly(GelMA-co-HEMA)) in the confined space during vat photopolymerization (VPP) 3D printing, we replicate the cuttlebone-like microstructure of hydrogels with enhanced mechanical properties and swelling resistance. We demonstrate here a 4-fold increase in elastic modulus compared to bulk polymerization of poly(GelMA-co-HEMA), together with improved mechanical and dimensional stability. This method offers promising opportunities for practical biomedical and tissue engineering applications, overcoming previous limitations in the design and performance.

Polymerization-induced highly brilliant and color-recordable mechanochromic photonic gels for ink-free patterning

Mechanochromic photonic crystals (MPCs) are extremely attractive since they can adjust their structural color by forces. However, the poor color saturation and color-recordability of conventional MPCs significantly limit their practical applications. Herein, a highly brilliant and color-recordable MPC gel (MPCG) has been fabricated by photopolymerizing the liquid photonic crystals with silica particles non-closely packed in acrylate, dichlorobenzene, and oleylamine. Photopolymerization induces elastic gradient non-close-packing structures and thus broad photonic bandgaps (>100 nm), resulting in 1) high color saturation despite possessing a small refractive index contrast (0.06), 2) remarkable mechanochromic properties, including a large wavelength tuning range (228 nm), fast responsiveness (8.8–10.3 nm/ms), and high sensitivity (4.4 nm/kPa), and 3) unconventional color-recordable properties. MPCGs were experimentally proved to be ideal rewritable papers for constructing multicolor and high-resolution patterns in an ink-free way, difficult for traditional MPC-based units. The unique working mechanism of polymerization-induced phase separation and thus continuous swelling and gelation, and precise design of materials and structures are the keys to MPCGs’ characteristics. This study paves a new way for constructing advanced stimulus-responsive photonic structures and will promote their applications in printing, display, anti-counterfeiting, etc.

Designing a Refined Multi-Structural Polymer Electrolyte Framework for Highly Stable Lithium-Metal Batteries.

Rational structural designs of solid polymer electrolytes featuring rich interface-phase morphologies can improve electrolyte connection and rapid ion transport. However, these rigid interfacial structures commonly result in diminished or entirely inert ionic conductivity within their bulk phase, compromising overall electrolyte performance. Herein, a multi-component ion-conductive electrolyte was successfully designed based on a refined multi-structural polymer electrolyte (RMSPE) framework with uniform Li+ solvation chemistry and rapid Li+ transporting kinetics. The RMSPEis constructed via polymerization-induced phase separation based on a rational combination of lithiophilic components and rigid/flexible chain units with significant hydrophobic/hydrophilic contrasts. Further refined by coating a robust polymer network, this all-organic design endows a homogenous micro-nano porous structure, providing a novel framework favorable for rapid ion transport in both its soft interfacial and bulk phases. The RMSPE exhibited excellent ion conductivity of 1.91 mS cm-1 at room temperature and a high Li+ transference number of 0.7. Assembled symmetrical Li cells realized stable cycling for over 2400 h at 3.0 mA cm-2. LiFePO4 full batteries demonstrated a long lifespan of 3300 cycles with a capacity retention of 93.5% and stable cycling performance at -35 °C. This innovative design concept offers a promising perspective for achieving high-performance polymer-based Li metal batteries.

Omniphobic Photoresist‐Assisted Patterning of Porous Polymethacrylate Films

AbstractPatterning of various surface properties, including roughness, wettability, adhesiveness, and mechanical properties, can markedly enhance the functionality of test systems. Thus, porous polymethacrylates prepared by polymerization‐induced phase separation (PIPS) represent a promising class of functional materials for the construction of miniaturized test systems. Different porosity, surface chemistry, and wettability are achieved in porous polymethacrylates with different precursor compositions. Nevertheless, only wettability microstructuring has been highlighted for these materials thus far. Here, the study presents a novel method for the direct and selective deposition of porous polymethacrylate films with different surface chemistry and porosity. The selective adhesion of omniphobic–omniphilic wettability patterns is used to facilitate the polymer pattern formation. The feasibility of patterning with different monomers and porogenic solvents is demonstrated. The topological study confirms the selective application of polymer structures with different thickness and roughness. The wettability characterization of the omniphobic material shows no significant changes caused by the operations performed. Thus, a new pattern with a greater difference in the wettability of the areas is produced in the process. Discontinuous dewetting of different liquids is performed. The use of poly(2‐hydroxyethyl methacrylate‐co‐ethylene dimethacrylate) (HEMA‐EDMA) modified patterns for precise living cell patterning is also demonstrated.

Thickness regulation of electric double layer via electronegative separator to realize High-Performance Lithium-Metal batteries

Lithium metal anode is considered as a promising electrode material for next-generation energy storage systems due to their high theoretical capacity and a low redox potential. However, the uncontrollable growth of Li dendrites severely hindered its practical application. Separators, a vital component in batteries, offer a promising solution to this issue, which can regulate the transport of lithium ions (Li+) and guide the homogenous deposition of Li+. In this study, a three-dimensional porous structure coating layer is constructed on the surface of the commercial polyethylene separator by polymer-induced phase separation (PIPS) and UV-induced cross-linking reactions. The incorporation of synthetized sulfonated SiO2 particles (S-SiO2) enable the successful construction of a negatively charged separator (PE@S-SiO2) based on negatively charged moieties on the surface, which compresses the thickness of the electric double layer (EDL) to optimize the Li+ transport dynamics and suppress dendritic growth. The resulting PE@S-SiO2 separator displays superior electrolyte wettability, much higher thermal resistance, high lithium transference number (0.86), and ionic conductivity (1.15 mS/cm). Consequently, when assembled into lithium metal batteries, the negatively charged separator endows stable cycling over 800 h at a current density of 1 mA cm−2.

Polar groups promoting in-situ polymerization phase separation for solid electrolytes enabling solid-state lithium batteries

Plastic-crystal-embedded elastomer electrolytes (PCEEs), produced through polymerization-induced phase separation (PIPS), are gaining popularity as solid polymer electrolytes (SPEs). However, it remains to be investigated whether all monomer molecules can achieve polymerization-induced phase separation and the corresponding differences in lithium metal battery performance. Herein, we prepared PCEEs with different functional groups (OH, CN, F) through in situ polymerization. Research findings show that PCEE containing – CN or – F achieves the separation of the plastic crystalline phase and succinonitrile (SN) phase, whereas PCEE containing OH cannot due to hydrogen bonding with the SN phase. Notably, the PCEE synthesized with the F monomer (FBA-PCEE) exhibited exceptional interfacial stability with lithium metal anodes and lithium iron phosphate (LFP) cathodes, due to its unique coordination mechanism with lithium ions. The FBA-PCEE demonstrated a high ionic conductivity (2.02 × 10−3 S cm−1) and lithium-ion migration number (tLi+ = 0.75). Moreover, lithium symmetric cells incorporating FBA-PCEE demonstrated stable cycling performance for more than 1000 h at a current density of 0.1 mA cm−2, resulting in the development of a solid electrolyte interphase (SEI) rich in LiF, Li3N, and Li2CO3 over time. Additionally, incorporating FBA-PCEE facilitated the stable cycling of LPF over 1000 cycles at 0.5C, maintaining a capacity retention of 77.38 % after 500 cycles. When coupled with high-voltage Nickel Cobalt Manganese Oxide (NCM-622) cathodes and lithium metal anodes, a discharge capacity of 119.70 mAh g−1 at 0.1C was sustained after 100 cycles, exhibiting a capacity retention of 78.95 %. This study elucidates the critical role of monomer design in achieving PIPS, offering valuable insights into developing high-performance polymer composite electrolytes for advanced lithium metal batteries.

3D Printed Nanoporous Separators Based on Polymerization-Induced Phase Separation for Fast-Charging, High Cycling Stability Li-Ion Batteries

3D Printed Nanoporous Separators Based on Polymerization-Induced Phase Separation for Fast-Charging, High Cycling Stability Li-Ion Batteries

A recyclable, interchangeable optical switch with a PDLC-PVA-PSCLC structure and a low-voltage drive system

ABSTRACT Polymer dispersed liquid crystals (PDLC) and polymer stabilised cholesteric liquid crystals (PSCLC) are an indispensable class of electrically switchable materials, which have been widely applied in the fabrication of efficient and systematic smart windows. And doping nanoparticles in PDLC films can greatly improve their properties. In this study, PDLC films doped with zirconia nanoparticles were prepared by polymerisation-induced phase separation (PIPS) method, PSCLC films with nematic liquid crystals as the main part (reflecting wavelengths in the range of 400–600 nm) were prepared by UV curing method, and a novel optical switch was developed by combining these two liquid crystal films. The optimal bilayer sample was developed through a comparative analysis of properties among samples with varying formulations for each liquid crystal layer. This study represents a novel advancement in PSCLC and nanoparticle-doped PDLC bilayer structures, showcasing fully actuatable properties in the visible wavelength range. These structures exhibit excellent electro-optical properties and demonstrate stable, sustainable performance that can be regenerated. The findings underscore the potential of PDLC and PSCLC for applications in smart curtains and flexible materials, opening up new avenues for innovative technological applications.

New graphene oxide doped polymer dispersed liquid crystal nanocomposites targeted to eco-friendly and energy-efficient smart windows

Graphene oxide-polymer dispersed liquid crystal (GO-PDLC) composites are proposed as a solution for energy-efficient switchable windows. These composites were prepared by incorporating varying concentrations of graphene oxide (GO) into a mixture of nematic liquid crystal (E7) and a UV–Vis curable resin using the polymerization-induced phase separation technique. The results indicate that the dispersion of GO at an optimum concentration of 0.005 wt% significantly affects the morphology, phase transition temperatures, and electro-optic properties of polymer dispersed liquid crystal (PDLC). In particular, the GO-PDLC composites exhibit a transition from an opaque to a transparent state at a remarkably low voltage (∼11.5 V) compared to pure PDLC cell. Dielectric analysis reveals that adding GO increases the permittivity, conductivity, and dielectric strength of PDLC composites. Moreover, the Cole-Cole plot indicates a non-Debye type relaxation in a higher frequency region. Furthermore, a blue shift in emission wavelength and enhanced photoluminescence intensity suggest alterations in electronic transitions within the composites. This comprehensive study provides valuable insights into optimizing the properties of PDLCs through the dispersion of GO, thereby offering promising prospects for their utilization in various optoelectronic applications.

Enhancing Temperature Responsiveness of PNIPAM Through 3D‐Printed Hierarchical Porosity

AbstractMaterials with ultra‐fast responsive properties are essential for various applications. Among the responsive materials, poly(N‐isopropylacrylamide) (PNIPAM) stands out due to its well‐studied temperature‐responsive properties. Improving the kinetics of the responsive properties of PNIPAM is, however, still essential for advancing its practical use. Here, the responsive rate of PNIPAM hydrogels is enhanced by first incorporating sub‐micrometer porosity into the material through polymerization‐induced phase separation (PIPS), followed by introducing millimeter scale pores via 3D printing, thereby rendering the material with hierarchical porosity. The 3D‐printed porous PNIPAM structures show accelerated swelling and deswelling, when compared to non‐porous PNIPAM structures, due to enhanced water permeability associated with the continuous network of micrometer to millimeter‐sized pores. Additionally, thinner polymer structures result in faster temperature response rates. At the same time, the mechanical strength of PNIPAM hydrogels with high porosity and thinner polymer walls is not compromised, overcoming the common trade‐off between swelling and mechanical properties.

Macroporous hydrogel prepared via aqueous polymerization induced phase separation toward in situ immobilization of yeast

AbstractYeast‐loaded open‐cell macroporous poly(acrylamide) (PAM) hydrogels are prepared by polymerization induced phase separation (PIPS) with potassium persulfate (KPS)‐yeast as a redox initiator in a polyethylene glycol (PEG) aqueous solution. The presence of PEG not only allows the sizes of both void and interconnected pores of the hydrogels controllable, but also enlarges the void. Which makes it possible to embed cells in situ and efficiently transport nutrients inside the hydrogels. Yeasts are herein used to form a redox pair with KPS to run the polymerization of acrylamide (AM) at a mild temperature (less than 31°C), avoiding the cell inactivation during the polymerization. The in situ immobilization causes a uniformly distribution and high immobilization rate (~100%) of yeasts in the hydrogels. The hydrogels are then used to ferment glucose to produce ethanol, exhibiting high fermentation efficiency of 68%. After 10 cycles, the yeast can still maintain 86% of the initial fermentation efficiency. The yeasts maintain 87% and 93% of the initial cell activity after 1 week store at 4°C in dry state and in yeast extract peptone dextrose (YPD) medium, respectively. This study demonstrates that an aqueous PIPS initiated by peroxide‐target cells is an effective platform to efficiently in situ immobilize cells in a hydrogel for high performance fermentation.

Micron-Sized Thiol-Functional Polysilsesquioxane Microspheres with Open and Interconnected Macropores: Effects of the System Composition on the Porous Structure and Particle Size of the Microspheres.

Control of the porous structure and particle size is essential for improving the properties of polysilsesquioxane (PSQ) microspheres. Herein, using the strategy combining inverse suspension polymerization, two-step sol-gel- and polymerization-induced phase separation processes, micron-sized thiol-containing macroporous PSQ (TMPSQ) microspheres with controllable morphologies, adjustable particle diameters (4.9-17.3 μm), and pore sizes (40-3774 nm) were prepared. The morphology and size of the TMPSQ microspheres were characterized by SEM. The mercury intrusion method was employed to analyze the porous structure of the microspheres. The effects of the composition of the sol-gel disperse phase, the mass ratio of the sol-gel disperse phase to the oil continuous phase (WRW/O), and the Span 80 mass content in the oil continuous phase on the morphology, particle diameter and pore size of the TMPSQ microspheres were investigated. Results indicated that the composition of the sol-gel disperse phase determines the morphology and porous structure of the microspheres, and WRW/O and Span 80 content have remarkable impacts on the morphology and particle size of the microspheres. This study is beneficial to the design and fabrication of functional PSQ microspheres with desired properties and promising application prospects.

Synthetic biodegradable microporous hydrogels for in vitro 3D culture of functional human bone cell networks

Generating 3D bone cell networks in vitro that mimic the dynamic process during early bone formation remains challenging. Here, we report a synthetic biodegradable microporous hydrogel for efficient formation of 3D networks from human primary cells, analysis of cell-secreted extracellular matrix (ECM) and microfluidic integration. Using polymerization-induced phase separation, we demonstrate dynamic in situ formation of microporosity (5–20 µm) within matrix metalloproteinase-degradable polyethylene glycol hydrogels in the presence of living cells. Pore formation is triggered by thiol-Michael-addition crosslinking of a viscous precursor solution supplemented with hyaluronic acid and dextran. The resulting microporous architecture can be fine-tuned by adjusting the concentration and molecular weight of dextran. After encapsulation in microporous hydrogels, human mesenchymal stromal cells and osteoblasts spread rapidly and form 3D networks within 24 hours. We demonstrate that matrix degradability controls cell-matrix remodeling, osteogenic differentiation, and deposition of ECM proteins such as collagen. Finally, we report microfluidic integration and proof-of-concept osteogenic differentiation of 3D cell networks under perfusion on chip. Altogether, this work introduces a synthetic microporous hydrogel to efficiently differentiate 3D human bone cell networks, facilitating future in vitro studies on early bone development.

Low-Temperature Structural Battery Electrolytes Produced by Polymerization-Induced Phase Separation

Low-Temperature Structural Battery Electrolytes Produced by Polymerization-Induced Phase Separation

Robust Photocatalytic MICROSCAFS® with Interconnected Macropores for Sustainable Solar-Driven Water Purification.

Advanced oxidation processes, including photocatalysis, have been proven effective at organic dye degradation. Tailored porous materials with regulated pore size, shape, and morphology offer a sustainable solution to the water pollution problem by acting as support materials to grafted photocatalytic nanoparticles (NPs). This research investigated the influence of pore and particle sizes of photocatalytic MICROSCAFS® on the degradation of methyl orange (MO) in aqueous solution (10 mg/L). Photocatalytic MICROSCAFS® are made of binder-less supported P25 TiO2 NPs within MICROSCAFS®, which are silica-titania microspheres with a controlled size and interconnected macroporosity, synthesized by an adapted sol-gel method that involves a polymerization-induced phase separation process. Photocatalytic experiments were performed both in batch and flow reactors, with this latter one targeting a proof of concept for continuous transformation processes and real-life conditions. Photocatalytic degradation of 87% in 2 h (batch) was achieved, using a calibrated solar light simulator (1 sun) and a photocatalyst/pollutant mass ratio of 23. This study introduces a novel flow kinetic model which provides the modeling and simulation of the photocatalytic MICROSCAFS® performance. A scavenger study was performed, enabling an in-depth mechanistic understanding. Finally, the transformation products resulting from the MO photocatalytic degradation were elucidated by high-resolution mass spectrometry experiments and subjected to an in silico toxicity assessment.

Design of Fluorinated Elastomeric Electrolyte for Solid-State Lithium Metal Batteries Operating at Low Temperature and High Voltage.

This work demonstrates the low-temperature operation of solid-state lithium metal batteries (LMBs) through the development of a fluorinated and plastic-crystal-embedded elastomeric electrolyte (F-PCEE). The F-PCEE is formed via polymerization-induced phase separation between the polymer matrix and plastic crystal phase, offering a high mechanical strain (≈300%) and ionic conductivity (≈0.23 mS cm-1) at -10°C. Notably, strong phase separation between two phases leads to the selective distribution of lithium (Li) salts within the plastic crystal phase, enabling superior elasticity and high ionic conductivity at low temperatures. The F-PCEE in a Li/LiNi0.8Co0.1Mn0.1O2 full cell maintains 74.4% and 42.5% of discharge capacity at -10°C and -20°C, respectively, compared to that at 25°C. Furthermore, the full cell exhibits 85.3% capacity retention after 150 cycles at -10°C and a high cut-off voltage of 4.5V, representing one of the highest cycling performances among the reported solid polymer electrolytes for low-temperature LMBs. This work attributes the prolonged cycling lifetime of F-PCEE at -10°C to the great mechanical robustness to suppress the Li-dendrite growth and ability to form superior LiF-rich interphases. This study establishes the design strategies of elastomeric electrolytes for developing solid-state LMBs operating at low temperatures and high voltages.

A Solid-Liquid Bicontinuous Fiber with Strain-Insensitive Ionic Conduction.

Stretchable ionic conductors are crucial for enabling advanced iontronic devices to operate under diverse deformation conditions. However, when employed as interconnects, existing ionic conductors struggle to maintain stable ionic conduction under strain, hindering high-fidelity signal transmission. Here, it is shown that strain-insensitive ionic conduction can be achieved by creating a solid-liquid bicontinuous microstructure. A bicontinuous fiber from polymerization-induced phase separation, which contains a solid elastomer phase interpenetrated by a liquid ion-conducting phase, is fabricated. The spontaneous partitioning of dissolved salts leads to the formation of a robust self-wrinkled interface, fostering the development of highly tortuous ionic channels. Upon stretch, these meandering ionic channels are straightened, effectively enhancing ionic conductivity to counteract the strain effect. Remarkably, the fiber retains highly stable ionic conduction till fracture, with only 7% resistance increase at 200% strain. This approach presents a promising avenue for designing durable ionic cables capable of signal transmission with minimal strain-induced distortion.

Facile Synthesis of Poly(methyl methacrylate) Silica Nanocomposite Monolith by In Situ Free Radical Polymerization of Methyl Methacrylate in the Presence of Functionalized Silica Nanoparticles.

Novel porous poly(methyl methacrylate) (PMMA) silica nanocomposites have been produced by utilization of polymerization-induced phase separation in a simple one-pot approach. A facile free radical polymerization of MMA in the presence of surface methacrylate-functionalized silica nanoparticles was carried out in ethanol-based solvents, successfully producing novel, morphologically designable porous nanocomposite monoliths. Differing from standard free radical polymerization in solution, a mixture of good and poor solvents (ethanol/N,N-dimethylformamide ratio) for the resulting polymer was used to trigger spinodal phase separation. The influence of monomer concentration, as well as solvent composition, on the morphology of the resulting porous polymers has been investigated. Porous monolith structures composed of connected particles and co-continuous morphologies were observed under a scanning electron microscope depending on the polymerization conditions. The resulting polymers were insoluble and showed swelling characteristics in some organic solvents that are capable of dissolving regular PMMA, indicating covalent bonds between the functionalized silica nanoparticles and the polymer chains. The presence of silica particles in the final polymer was proven via an ATR-IR analysis. The glass transition temperature of the present PMMA-silica nanocomposite was higher than that of the conventional PMMA. The porous polymer immersed in a mixed organic solvent showed coloration induced by the Christiansen effect.

Preparation of a double-layer liquid crystal optical shutter with fluorescent properties and its ultraviolet shielding screening properties

ABSTRACT Polymer dispersed liquid crystal (PDLC) films and polymer-stabilised cholesteric liquid crystals (PSCLC) films have been widely applied in smart optoelectronics due to electrical switching properties. In this study, fluorescent dyes were introduced into PDLC films and combined with PSCLC films to invent a new type of optical shutter, and the optimal formulations of each of liquid crystal structural layers were investigated. Then, PDLC anti-counterfeit optical device doped with fluorescent materials were fabricated by UV curing method using polymerisation-induced phase separation. The novel optical shutter could be driven layer by layer at room temperature according to different voltages to realise the switching of three states, namely, off state, PDLC layer-driven, and full-driven (open state). Samples under optimal conditions showed that the new optical shutter could achieve 96.5% UV shielding in the off state and had a long lifetime. The results demonstrate the attractive potential of the new optical shutter for optoelectronic devices and smart curtain applications.