UV-induced Photopolymerization Research Articles

UV cross-linked highly stable polymer garnet composite electrolyte with improved interphase for lithium metal batteries

The next-generation electric vehicles heavily rely on high-energy–density lithium metal batteries with enhanced safety. Replacing liquid electrolytes with solid-state polymer electrolytes offers superior protection, high flexibility, and stability. However, inadequate ionic conductivity and poor compatibility at the interfaces with the electrodes hinder the practical application of solid-state electrolytes. In this work, we developed a polyethylene glycol-based, highly cross-linked polymer electrolyte with a garnet-type, fast Li+ conductive Li6.2Al0.24La3Zr2O12 (Al-LLZO) filler. The Al-LLZO filler was incorporated into a cross-linking functional polymeric matrix of polyethylene glycol diacrylate, pentaerythritol tetrakis (3-mercaptopropionate), and lithium perchlorate salt. The cross-linked polymer garnet composite electrolyte (CPGCE) was prepared via UV-induced photo-polymerization. The resulting CPGCE exhibits superior free-standing flexibility, a desired ionic conductivity of 4.4 × 10−4 S cm−1, and a wide potential window up to 4.2 V. The Li|CPGCE|Li symmetric cell underwent stripping and plating at varying current densities of 0.05 to 0.3 mA cm−2, displaying a low overpotential range from ±0.02 V to ±0.08 V over 500 cycles. Similarly, the as-cycled Li|CPGCE|Li showed excellent stripping and plating performance at 0.1 mA cm−2 for 500 cycles at 60 °C. The incorporation of the Al-LLZO nanofiller provided active sites with continuous Li+ conducting pathways, suppressing the growth of dead lithium dendrites. The Li|CPGCE|LiFePO₄ full cell exhibited a discharge capacity of 155 mAh g−1 at a rate of 0.1C, with a coulombic efficiency of 96 % over 50 cycles at 25 °C. This work offers a straightforward and convenient approach to creating highly durable polymer composite electrolytes with enhanced interfacial stability, advancing the implementation of all-solid-state lithium metal batteries.

Preparation and properties of broadband reflective cholesteric-phase liquid crystal films based on chiral and achiral bilayer structures

In this work, N* and N bilayer liquid crystal composite systems were constructed. With the synergistic effect of diffusion and UV-induced photopolymerization, CLC films reflecting over the wavelength range of 1500 nm were prepared.

An Overview on Polymer-Based Electrolytes with High Ionic Mobility for Safe Operation of Solid-State Batteries

Liquid electrolytes used in commercial Li-ion batteries are generally based on toxic volatile and flammable organic carbonate solvents, thus raising safety concerns in case of thermal runaway. The most striking solution at present is to switch on all solid-state designs exploiting polymer materials, films, ceramics, low-volatile, green additives, etc. The replacement of liquids component with low-flammable solids is expected to improve the safety level of the device intrinsically. Moreover, a solid-state configuration is expected to guarantee improved energy density systems. However, low ionic conductivity, low cation transport properties and issues in cell manufacturing processes must be overcome [1].Electrochemical performance in lab-scale devices can be readily improved using different RTILs or specific low-volatile additives. Here, an overview is offered of the recent developments in our labs on innovative polymer-based electrolytes allowing high ionic mobility, particularly attractive for safe, high-performing, solid-state Li-metal batteries, and obtained by different techniques, including solvent-free UV-induced photopolymerization. Cyclic voltammetry and galvanostatic charge/discharge cycling coupled with electrochemical impedance spectroscopy exploiting different electrode materials (e.g., LFP, Li-rich NMC, LNMO, Si/C) demonstrate specific capacities approaching theoretical values even at high C-rates and stable operation for hundreds of cycles at ambient temperature [2,3]. Direct polymerization procedures on top of the electrode films are also used to obtain an intimate electrode/electrolyte interface and full active material utilization in both half and full-cell architectures. In addition, results of composite hybrid polymer electrolytes [4] and new single-ion conducting polymers [5] are shown, specifically developed to attain improved ion transport and high oxidation stability for safe operation with high voltage electrodes even at ambient conditions.

Ionic conductivity enhancement in solid polymer electrolytes by electrochemical in situ formation of an interpenetrating network.

Various overoxidized poly(1H-pyrrole) (PPy), poly(N-methylpyrrole) (PMePy) or poly(3,4-ethylenedioxythiophene) (PEDOT) membranes incorporated into an acrylate-based solid polymer electrolyte matrix (SPE) were directly electrosynthesized by a two-step in situ procedure. The aim was to extend and improve fundamental properties of pure SPE materials. The polymer matrix is based on the cross-linking of glycerol propoxylate (1PO/OH) triacrylate (GPTA) with poly(ethylene glycol) diacrylate (PEGDA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a conducting salt. A self-standing and flexible polymer electrolyte film is formed during the UV-induced photopolymerization of the acrylate precursors, followed by an electrochemical polymerization of the conducting polymers to form a 3D-IPN. The electrical conductivity of the conducting polymer is destroyed by electrochemical overoxidation in order to convert the conducting polymer into an ion-exchange membrane by introduction of electron-rich groups onto polymer units. The resulting polymer films were characterized by scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, differential scanning calorimetry, thermal analysis and infrared spectroscopy. The results of this study show that the combination of a polyacrylate-matrix with ion selective properties of overoxidized CPs leads to new 3D materials with higher ionic conductivity than SPEs and separator or selective ion-exchange membrane properties with good stability by facile fabrication.

Hydrogel Functionalized Polyester Fabrics by UV-Induced Photopolymerization.

We address a strategy to graft hydrogels onto polyethylene terephthalate (PET) fabrics using different acrylate-based monomers. The hydrogel-modified fabrics were prepared by a two-step modification. To this end, double functional groups were firstly introduced onto the PET surface via an aminolysis reaction involving allylamine. The final grafted polymer networks were then obtained after UV-induced radical photopolymerization by varying acrylate monomer types in the presence of a cross-linker. After characterization, the resulting hydrogels showed different morphologies and abrasion resistance performances depending on their chemical nature. UV-photopolymerization is a fast and low-cost method to achieve technical fabrics with specific desired properties.

Enhancing gas permeation and separation performance of polymeric membrane by incorporating hollow polyamide nanoparticles with dense shell

Many inorganic nanofillers including porous nanoparticles and nonporous nanoparticles, are incorporated into the polymer matrices to exceed the trade-off relationship between the gas permeability and the permselectivity of the polymeric membrane materials. However, the organic-inorganic combination often suffers from the undesirable interface between the organic matrices and the inorganic fillers. In this study, we fabricated the hollow polyamide nanoparticles with dense shell via the interfacial polymerization in the surfactant-free microemulsion. And then the hollow nanoparticles combined with liquid acrylate monomers to form the mixed matrix membranes (MMMs) via the UV-induced photo-polymerization. The nanoparticles with an average diameter of 42 nm dispersed uniformly in the membranes. The resulting membranes showed no obvious defect. Compared with those of the pure polymer membrane, the CO2 permeability and CO2/N2 permselectivity of the MMMs both increased as the nanofiller loading increased. And the gas permeation and separation performance exceeded the Robeson upper bound line with a maximum CO2 permeability of 1898 Barrer and a maximum CO2/N2 permselectivity of 43.9 at 1 wt% nanofiller loading. The improvement mainly arose from the increase in the CO2 solubility, the N2 diffusivity and the CO2/N2 solubility selectivity. This combination of the hollow polymer nanoparticle with the dense shell and the polymeric membrane is also promising for fabricating ultra-thin and defect-free membranes for gas separation.

Opto-Thermophoretic Manipulation and Construction of Colloidal Superstructures in Photocurable Hydrogels

Light-based manipulation of colloidal particles holds great promise in fabrication of functional devices. Construction of complex colloidal superstructures using traditional optical tweezers is limited by high operation power and strong heating effect. Herein, we demonstrate low-power opto-thermophoretic manipulation and construction of colloidal superstructures in photocurable hydrogels. By introducing cationic surfactants into a hydrogel solution under a light-directed temperature field, we create both thermoelectric fields and depletion attraction forces to control the suspended colloidal particles. The particles of various sizes and compositions are thus trapped and organized into various superstructures. Furthermore, the colloidal superstructures are immobilized and patterned onto solid-state substrates through UV-induced photopolymerization of the hydrogel. Our opto-thermophoretic technique will open up avenues for bottom-up assembly of colloidal materials and devices.

Preparation of chemically uniform and monodisperse microparticles as highly efficient solid acid catalysts for aldol condensation

Highly active heterogeneous catalysts are in high demand, but realizing an efficient heterogeneous catalyst with uniform active sites remains challenging. In this study, we present a facile preparation of carboxylic acid-incorporated monodisperse microparticles (COOH-MPs) with uniform active sites and their successful application as an efficient solid acid catalyst for aldol condensation. The micromolding integrated with UV-induced photopolymerization enables one-step preparation of COOH-MPs without any further purification or treatment. The successful fluorescent labeling of the COOH-MPs achieved by EDC/NHS (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/n-hydroxysuccinimide (NHS)) chemistry proves that carboxylic acids are uniformly incorporated throughout the COOH-MPs. The microparticle as a solid acid catalyst is applied for aldol condensation and the catalytic performance is compared with that of conventional inorganic solid acid catalysts. The selectivity for jasminaldehyde over the COOH-MPs is higher than that of conventional catalysts, zeolite H-beta (HBEA with different SiO2/Al2O3 ratios). Overall, the results clearly indicate the potential of this new class of chemically uniform and monodisperse microparticle-based solid acid catalysts for aldol condensation. This approach is highly promising for the application to preparations of various solid catalysts due to its reproducibility, tunability and simplicity.

Polymer brushes on hydrogen-terminated silicon substrates via stable Si[sbnd]C bond

We demonstrate a straightforward and efficient method for the creation of polymer brushes on hydrogen-terminated silicon substrates through the UV-induced photopolymerization. The surface grafting polymerization is applicable to a series of monomers, allowing the direct formation of homogeneous polymer coatings ranging from hydrophilic poly(2-isopropenyl-2-oxazoline) (PIPOx), amphiphilic poly(N-isopropyl acrylamide) (PNIPAM), to hydrophobic polystyrene (PS) and poly(4-(1H,1H,2H,2H-perfluorohexyl)oxymethylstyrene) (PPHMS) on Si(100) and Si(111) surfaces via stable SiC bonds. Polymerization kinetic investigation indicates a linear increase of polymer layer thickness with the polymerization time. Moreover, the as-prepared polymer brushes exhibit superior stability against basic conditions in contrast to those that were formed on silicon substrates via conventional SiOC bond.

Functionalized graphene oxide-reinforced electrospun carbon nanofibers as ultrathin supercapacitor electrode

Graphene oxide has been used widely as a starting precursor for applications that cater to the needs of tunable graphene. However, the hydrophilic characteristic limits their application, especially in a hydrophobic condition. Herein, a novel non-covalent surface modification approach towards graphene oxide was conducted via a UV-induced photo-polymerization technique that involves two major routes; a UV-sensitive initiator embedded via pi-pi interactions on the graphene planar rings, and the polymerization of hydrophobic polymeric chains along the surface. The functionalized graphene oxide successfully achieved the desired hydrophobicity as it displayed the characteristic of being readily dissolved in organic solvent. Upon its addition into a polymeric solution and subjected to an electrospinning process, non-woven random nanofibers embedded with graphene oxide sheets were obtained. The prepared polymeric nanofibers were subjected to two-step thermal treatments that eventually converted the polymeric chains into a carbon-rich conductive structure. A unique morphology was observed upon the addition of the functionalized graphene oxide, whereby the sheets were embedded and intercalated within the carbon nanofibers and formed a continuous structure. This reinforcement effectively enhanced the electrochemical performance of the carbon nanofibers by recording a specific capacitance of up to 140.10F/g at the current density of 1A/g, which was approximately three folds more than that of pristine nanofibers. It also retained the capacitance up to 96.2% after 1000 vigorous charge/discharge cycles. This functionalization technique opens up a new pathway in tuning the solubility nature of graphene oxide towards the synthesis of a graphene oxide-reinforced polymeric structure.

Polymer brushes on metal–organic frameworks by UV-induced photopolymerization

A general strategy for creating polymer brushes on the surface of MOF nanoparticles and membranes is described.

Additive manufacturing of 3D gelatin scaffolds: direct versus indirect printing

Event Abstract Back to Event Additive manufacturing of 3D gelatin scaffolds: direct versus indirect printing Jasper Van Hoorick1, 2, Aleksandr Ovsianikov3, Heidi Declerq4, Maria Cornelissen4, Jürgen Van Erps2, Hugo Thienpont1, 2, Peter Dubruel1 and Sandra Van Vlierberghe1, 2 1 Ghent University, Polymer Chemistry & Biomaterials Group, Belgium 2 Vrije Universiteit Brussel, Brussels Photonics Team, Belgium 3 Vienna University of Technology, Institute of Materials Science and Technology, Austria 4 Ghent University, Tissue Engineering Group, Belgium Introduction: To date, gelatin is one of the most frequently applied materials in the biomaterials field. It contains tripeptide Arg-Gly-Asp sequences which are known to interact with the cell’s integrins. In the present work, we evaluate and compare the potential of direct and indirect additive manufacturing for the development of porous gelatin scaffolds for soft tissue engineering. Materials and Methods: Methacrylic anhydride was applied to modify gelatin type B resulting in photo-crosslinkable gelatin derivatives (gel-MOD) [1]. Physical gelation properties were assessed using DSC. Crosslinking was performed using 2 mol% Irgacure 2959 and UV-A light (365 nm). Mechanical properties of hydrogel films were monitored using rheology. The hydrogels were subjected to swelling and degradation studies [2],[3]. The direct additive manufacturing approach was performed using an in-house developed polymer processing device ( figure 1). In short, the device enables the combination of 3D printing and electrospinning of (bio)polymers into one single scaffold. Moreover, it also integrates UV-induced photopolymerization capabilities. Figure 1: In-house developed processing apparatus. For indirect additive manufacturing, PLLA (Mw = 16 kDa) scaffolds were developed via FDM. After curing 5 and 10 w/v% gel-MOD solutions (t = 120 mins), the sacrificial scaffolds were dissolved using chloroform followed by extensive washing with acetone and water. The gelatin scaffolds were characterized using SEM, µCT, optical microscopy and texturometry. Biocompatibility tests using human foreskin fibroblast (HFF) cells were performed on both types of scaffolds (i.e. live/dead staining and histology). Results and Discussion: DSC measurements indicated that the physical gelation of gel-MOD depends on the degree of methacrylation and the concentration. Rheology indicated that cross-linked 5 w/v% gel-MOD (97% methacrylated) exhibits sufficient mechanical properties (G’= 3600 Pa ) for the production of 3D scaffolds. As the direct additive manufacturing approach only enabled the fabrication of 10 w/v% scaffolds [4], we compared this approach with an indirect approach. It was shown that a proper design transfer was realized from PLLA scaffold to gelatin hydrogel, with the latter being self-supporting [3]. Physico-chemical testing revealed scaffold properties (mechanical, degradation, swelling) to depend on the applied gelatin concentration and the methacrylamide content. The scaffolds obtained using both approaches were suitable to support the adhesion and proliferation of HFFs. After 5 days the scaffolds (V = 5*5*5 cm3) were nearly completely covered with viable cells indicating a nice cell proliferation onto the scaffolds (see figure 2). Figure 2: Live/dead fluorescence image obtained of the 5 w/v% scaffold seeded with HFF after 5 days of cell culture (left). Histological evaluation of the 5 w/v% scaffold after 21 days of cell culture (right). Conclusion: Scaffold structural analysis indicated the success of the selected indirect additive manufacturing approach for the production of cell-interactive, low-density (5 w/v %) gelatin scaffolds. Furthermore, the first steps have been realized to develop combination scaffolds containing both 3D printed and electrospun polymer layers in one single 3D construct using the novel in-house developed polymer processing device. Research Foundation Flanders; Ghent University; Vrije Universiteit Brussel

Degradable photopolymerized thiol-based solid polymer electrolytes towards greener Li-ion batteries

Thermoset initiator-free membranes are prepared by the UV-induced photopolymerization of thiol and (meth)acrylic monomers having polyethylene oxide chains, being known that the use of such monomers can lead to the formation of readily degradable membranes. The photopolymerization of different formulations is studied and the influence of the addition of a monofunctional methacrylate is investigated. By incorporation of lithium bis(oxalate)borate salt, solid polymer electrolytes are prepared and used as electrolyte membranes in Li-ion batteries. The ionic conductivity of the samples is measured and correlated to their thermal characteristics. The best performing sample shows encouraging cycling behaviour when tested in a truly-solid state lab-scale lithium test cell, thus enlightening the promising prospects of the newly designed polymer electrolytes. Furthermore, a preliminary degradation study is performed demonstrating the possibility to hydrolytically degrade the proposed UV cured networks making them extremely appealing for the development of sustainable and easily recyclable, thus greener, energy power sources.

Design and characterization of a conductive nanostructured polypyrrole-polycaprolactone coated magnesium/PLGA composite for tissue engineering scaffolds.

A novel biodegradable and conductive composite consisting of magnesium (Mg), polypyrrole-block-ploycaprolactone (PPy-PCL), and poly(lactic-co-glycolic acid) (PLGA) is synthesized in a core-shell-skeleton manner for tissue engineering applications. Mg particles in the composite are first coated with a conductive nanostructured PPy-PCL layer for corrosion resistance via the UV-induced photopolymerization method. PLGA matrix is then added to tailor the biodegradability of the resultant composite. Composites with different composition ratios are examined through experiments, and their material properties are characterized. The in vitro experiments on culture of 293FT-GFP cells show that the composites are suitable for cell growth and culture. Biodegradability of the composite is also evaluated. By adding PLGA matrix to the composite, the degrading time of the composite can last for more than eight weeks, hence providing a longer period for tissue formation as compared to Mg composites or alloys. The findings of this research will offer a new opportunity to utilize a conductive, nanostructured-coated Mg/PLGA composite as the scaffold material for implants and tissue regeneration.

Polymer Brushes on Planar TiO2 Substrates

A facile and universal method is presented for the preparation of polymer brushes on amorphous TiO2 film. Homogeneous and stable poly(methyl methacrylate), polystyrene, poly(4-vinylpyridine), and poly(N-vinyl imidazole) (PNVI) brushes up to 550 nm are directly created onto TiO2 via UV-induced photopolymerization of corresponding monomers. Kinetic studies reveal a linear increase in thickness with the polymerization time. Characterization of the resulting polymer brushes by FTIR spectroscopy, X-ray photoelectron spectroscopy, contact angle, and atomic force microscopy (AFM) indicates an efficient UV-grafting reaction. Finally, we have demonstrated the possibility in converting the PNVI brushes to poly(vinyl imidazolium bromide), i.e., poly(ionic liquid) brushes by polymer-analogous reactions.

In-situ graphene oxide reduction during UV-photopolymerization of graphene oxide/acrylic resins mixtures

The preparation of electrically conductive acrylic resins containing reduced graphene oxide (rGO) by photopolymerization is presented. The synthesis consists of a single-step procedure starting from a homogeneous water dispersion of GO, which undergoes reduction induced by the UV radiation during the photopolymerization of an acrylic resin. The role played by the amount of radical photoinitiator added to the resin has been evaluated in relation to the in-situ reduction of GO, that was monitored by X-ray photoelectron spectroscopy. Results show that the UV-induced photopolymerization of acrylic resins with added GO gives rise to conductive acrylic composites thanks to the simultaneous reduction of GO to rGO and crosslinking of the resin. On this basis UV-induced photopolymerization is proposed as a sustainable strategy for the production of conductive graphene/polymer composites.

Synthesis of a thermosensitive surface by construction of a thin layer of poly (N-isopropylacrylamide) on maleimide-immobilized polypropylene

Thermosensitive surfaces were developed by the grafting of a thin layer of PNIPAAm through an UV-induced photopolymerization reaction of vinyl monomers with a free radical-activated polypropylene (PP) surface. PNIPAAm layer covering the PP surface corrected, to some extension, both depressions and fissures of the previously modified PP surfaces. The layered surfaces have morphological characteristic different from those of the non-layered surfaces, and their thickness was dependent on irradiation time. Water contact angles of the layered surfaces revealed a transition at approximately 33.5–36.5°C as a result of a response to the variation of temperature. There was an increase in the values of the contact angles with an increase in temperature from 26°C to 44°C, revealing the nature both hydrophilic and hydrophobic of the surfaces due to a conformational rearrangement of PNIPAAm exposing its isopropyl groups to the liquid drop. This work offers a chemically stable thermosensitive surface (because it is covalently structured) with great potential for use as sensors and actuators.

Water uptake, transport and structure characterization in poly(ethylene glycol) diacrylate hydrogels

Crosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by UV-induced photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) crosslinker in the presence of varying amounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS) when the water content of the prepolymerization mixture was greater than 60 wt%. These phase separated films contain pores that scatter visible light, rendering them translucent or opaque. Visible light absorbance measurements, water uptake, water permeability, and salt kinetic desorption experiments were used to characterize the structure of these phase separated, crosslinked hydrogels. The films with PIPS exhibited a porous morphology in CryoSEM studies. Dead-end filtration experiments using deionized water and 1 g/l bovine serum albumin (BSA) solutions were performed to explore the fundamental transport and fouling properties of these materials. The total flux of pure water through the films after prior exposure to BSA solution was nearly equal to that measured for the as-prepared material, indicating that these PEGDA films resist fouling by BSA under the conditions studied.

Structure, water sorption, and transport properties of crosslinked N-vinyl-2-pyrrolidone/N,N′-methylenebisacrylamide films

Crosslinked N-vinyl-2-pyrrolidone (NVP) free-standing films were prepared by UV-induced photopolymerization in the presence of water using N,N′-methylenebisacrylamide (MBAA) as the crosslinker. A series of crosslinked films were prepared at various prepolymerization water contents and NVP/MBAA ratios. The films underwent phase separation during polymerization. Cryogenic scanning electron microscope (CryoSEM) was used to characterize the morphology of the films. The influence of monomer/crosslinker ratio and prepolymerization water content on morphology and water transport was characterized. Higher water content or higher monomer content in the prepolymerization mixture led to more open structures and, in turn, higher water permeability.

Preparation of monodisperse and size-controlled poly(ethylene glycol) hydrogel nanoparticles using liposome templates

Liposomes were used as templates to prepare size-controlled and monodisperse poly(ethylene glycol) (PEG) hydrogel nanoparticles. The procedure for the preparation of PEG nanoparticles using liposomes consists of encapsulation of photopolymerizable PEG hydrogel solution into the cavity of the liposomes, extrusion through a membrane with a specific pore size, and photopolymerization of the contents inside the liposomes by UV irradiation. The size distributions of the prepared particles were 1.32 ± 0.16 μm (12%), 450 ± 62 nm (14%), and 94 ± 12 nm (13%) after extrusion through membrane filters with pore sizes of 1 μm, 400 nm, and 100 nm, respectively. With this approach, it is also possible to modify the surface of the hydrogel nanoparticles with various functional groups in a one-step procedure. To functionalize the surface of a PEG nanoparticle, methoxy poly(ethylene glycol)–aldehyde was added as copolymer to the hydrogel-forming components and aldehyde-functionalized PEG nanoparticles could be obtained easily by UV-induced photopolymerization, following conjugation with poly- l-lysine-FITC through amine–aldehyde coupling. The prepared PEG particles showed strong fluorescence from FITC on the edge of the particles using confocal microscopy. The immobilization of biomaterials such as enzymes in hydrogel particles could be performed with loading β-galactosidases during the hydration step for liposome preparation without additional procedures. The resorufin produced by applying resorufin β- d-galactopyranoside as the substrate showed the fluorescence under the confocal microscopy.