Ethylene Oxide Block Copolymer Research Articles

Nanocomposite gels of poloxamine and Laponite for β-Lapachone release in anticancer therapy

Nano-hybrid systems have been shown to be an attractive platform for drug delivery. Laponite® RD (LAP), a biocompatible synthetic clay, has been exploited for its ability to establish of strong secondary interactions with guest compounds and hybridization with polymers or small molecules that improves, for instance, cell adhesion, proliferation, and differentiation or facilitates drug attachment to their surfaces through charge interaction. In this work, LAP was combined with Tetronics, X-shaped amphiphilic PPO-PEO (poly (propylene oxide)–poly (ethylene oxide) block copolymers. β-Lapachone (BLPC) was selected for its anticancer activity and its limited bioavailability due to very low aqueous solubility, with the aim to improve this by using LAP/Tetronic nano-hybrid systems. The nanocarriers were prepared over a range of Tetronic 1304 concentrations (1 to 20% w/w) and LAP (0 to 3% w/w). A combination of physicochemical methods was employed to characterize the hybrid systems, including rheology, particle size and shape (DLS, TEM), thermal analysis (TG and DSC), FTIR, solubility studies and drug release experiments. In vitro cytotoxicity assays were performed with BALB/3T3 and MCF-7 cell lines. In hybrid systems, a sol-gel transition can occur below physiological temperature. BLPC exhibits the most significant increase in solubility in formulations with a high concentration of T1304 (over 10% w/w) and 1.5% w/w LAP, or systems with only LAP (1.5%), with a 50 and 100-fold increase in solubilisation, respectively. TEM images showed spherical micelles of T1304, which elongated into wormlike micelles with concentration (20%) and in the presence of LAP, a finding that has not been reported before. A sustained release of BLPC over 140 hours was achieved in one of the formulations (10% T1304 with 1.5% laponite), which also showed the best selectivity index towards cancer cells (MCF-7) over BALB/3T3 cell lines. In conclusion, BLPC-loaded T1304/LAP nano-hybrid systems proved safe and highly effective and are thus a promising formulation for anticancer therapy.

An expedient in to the phase behaviour and scattering profile in PEO-PPO-PEO block copolymer mixed systems in aqueous solution

The present study aims to develop copolymeric micelles giving an account on the clouding behavior of two series of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers with varying molecular weight of PPO: one with moderate hydrophilicity i.e., 40 % PEO (L64, P84, P104) blended with very hydrophobic copolymers i.e., 10 % PEO (L61, L81, L101, L121). Marked changes in the solution behavior in our mixed copolymeric solution systems depicted the micellization and micelle growth/ transition along with the phase separation (2ϕ) which is well explained from cloud Point (CP) and solution relative viscosity (ηrel) study. The CP analysis showed the lower cloud point (LCP) and the conventional upper cloud point (UCP) i.e., two marvelous CP in the aqueous mixed Pluronics® system which motivated to explore the hypothesis of double cloud point. Such shifting phenomenon from LCP towards UCP demonstrated an increment in dynamic light scattering (DLS) intensity resulting in the obvious increment in the micellar dimensions i.e., hydrodynamic diameter (Dh) for the examined mixed copolymeric system. In addition, the small-angle neutron scattering (SANS) data were fitted to obtain the predictable parameters such as, hard sphere radius (Rhs), aggregation number (Nagg) and micellar morphology. Our findings corroborated the micellar transition from spherical to elongated ellipsoidal micelles with temperature ageing depicting a strong dependence on the amphiphilicity and concentration of the two BCPs in the mixed solution environment.

X-Ray Microtomography Analysis of Li-Sulfur Batteries with a Block Copolymer Electrolyte

Li-ion batteries are the dominant solution for many applications, from small electronic devices up to hybrid and fully electric vehicles.[1] However, this technology is now mature and new chemistries are needed to reach high specific energy while ensuring safety. Despite a relatively low operating voltage, sulfur (S8) is an attractive cathode active material due to its high theoretical specific capacity; a factor of six higher than traditional LiCoO2 cathodes.[2] To realize high energy density systems, the S8 cathode must be paired with a Li metal anode. Many challenges remain to be addressed to effectively couple a Li metal with a S8 cathode such as the low S8 utilization, the strong volume change of active material upon cycling, the insulating nature of S8 and of the final product Li2S, the solubility of polysulfides in the electrolyte.[3] This issues lead to poor capacity retention, limited cycle life, and low Coulombic efficiency. To address the polysulfide dissolution problem one approach consists in confining S8 within mesoporous and nanoporous carbon.[4] However, conventional liquid electrolytes are not stable against Li metal. A solution is then to use a solid polymer electrolytes, such as polystyrene-b-poly(ethylene oxide) (SEO) block copolymer doped with LiTFSI salt, known to stabilize Li metal.[5]The goal of this study is to understand the behavior of Li-S8 batteries comprising a SEO electrolyte. The cathode is a composite made of carbon, SEO electrolyte and sulfur-impregnated carbon nanospheres.[6] The cells were cycled and exhibited significant capacity fade. We thus used hard X-ray microtomography to determine the reason for this capacity fade. Figure 1 represents tomography images prior and after cycling. In addition to polysulfide dissolution, our observations indicate that the battery failure in our system is also due to strong changes at the Li/SEO interface.

Coalescence-Driven Verticality in Mesoporous TiO2 Thin Films with Long-Range Ordering.

Mesoporous semiconducting films with continuous interconnectivity and minimal tortuosity, such as densely ordered arrays of vertical channels, are ideal for ensuring a maximal surface area at the heterojunction to increase the density of charges or photons. While the design of these films with nanostructures below 50 nm using modern lithography is not feasible, continuously perpendicular pores can be obtained throughout a TiO2 film using a traditional soft-templating approach and lyotropic crystal engineering. We demonstrate here that a polystyrene-b-poly(ethylene oxide) block copolymer in a three-solvent system can self-assemble into a body-centered cubic Im3̅m template. The long-range three-dimensional periodicity of the template combined with a high degree of vertical contraction results in coalescence of the pores into orthogonal channels that are strongly interconnected with their nearest neighbors in the (011̅) plane. This work presents evidence of lateral long-range ordering with continuously transverse vertical porosity in a TiO2 material, which will enable functional applications, such as filtration, sensing, catalysis, and optoelectronics. To this end, we demonstrate the ability of the films to template and host methylammonium lead iodide perovskite nanocrystals.

Drug Delivery System Based on pH-Sensitive Biocompatible Poly(2-vinyl pyridine)-b-poly(ethylene oxide) Nanomicelles Loaded with Curcumin and 5-Fluorouracil.

Smart polymeric micelles (PMs) are of practical interest as nanocarriers for the encapsulation and controlled release of hydrophobic drugs. Two hydrophobic drugs, naturally-based curcumin (Cur) and synthetic 5-fluorouracil (5-FU), were loaded into the PMs formed by a well-defined pH-sensitive poly(2-vinyl pyridine)-b-poly(ethylene oxide) (P2VP90-b-PEO398) block copolymer. The influence of the drug loading on the micellar sizes was investigated by dynamic light scattering (DLS) and it appears that the size of the PMs increases from around 60 to 100 nm when Cur is loaded. On the contrary, the loading of the 5-FU has a smaller effect on the micellar sizes. This difference can be attributed to higher molar mass of Cur with respect to 5-FU but also to higher loading efficiency of Cur, 6.4%, compared to that of 5-FU, 5.8%. In vitro drug release was studied at pH 2, 6.8, and 7.4, and it was observed that the pH controls the release of both drugs. At pH 2, where the P2VP sequences from the “frozen-in” micellar core are protonated, the drug release efficiencies exceed 90%. Moreover, it was demonstrated, by in vitro assays, that these PMs are hemocompatible and biocompatible. Furthermore, the PMs protect the Cur against the photo-degradation, whereas the non-ionic PEO corona limits the adsorption of bovine serum albumin (BSA) protein on the surface. This study demonstrates that these pH-sensitive PMs are suitable for practical utilization as human-safe and smart, injectable drug delivery systems.

Porous Ultra-Thin Films from Photocleavable Block Copolymers: In-Situ Degradation Kinetics Study of Pore Material.

On the basis of the major application for block copolymers to use them as separation membranes, lithographic mask, and as templates, the preparation of highly oriented nanoporous thin films requires the selective removal of the minor phase from the pores. In the scope of this study, thin film of polystyrene-block-poly(ethylene oxide) block copolymer with a photocleavable junction groups based on ortho-nitrobenzylester (ONB) (PS-hν-PEO) was papered via the spin coating technique followed by solvent annealing to obtain highly-ordered cylindrical domains. The polymer blocks are cleaved by means of a mild UV exposure and then the pore material is washed out of the polymer film by ultra-pure water resulting in arrays of nanoporous thin films to remove one block. The removal of the PEO materials from the pores was proven using the grazing-incidence small-angle X-ray scattering (GISAXS) technique. The treatment of the polymer film during the washing process was observed in real time after two different UV exposure time (1 and 4 h) in order to draw conclusions regarding the dynamics of the removal process. In-situ X-ray reflectivity measurements provide statistically significant information about the change in the layer thickness as well as the roughness and electron density of the polymer film during pore formation. 4 H UV exposure was found to be more efficient for PEO cleavage. By in-situ SFM measurements, the structure of the ultra-thin block copolymer films was also analysed and, thus, the kinetics of the washing process was elaborated. The results from both measurements confirmed that the washing procedure induces irreversible change in morphology to the surface of the thin film.

Polyarylate–Poly(ethylene oxide) Block Copolymers for Membrane Separation of Carbon Dioxide from Gas Mixtures

Polyarylate–Poly(ethylene oxide) Block Copolymers for Membrane Separation of Carbon Dioxide from Gas Mixtures

Simultaneous Improvement of Ionic Conductivity and Mechanical Strength in Block Copolymer Electrolytes with Double Conductive Nanophases.

The most daunting challenge of solid polymer electrolytes (SPEs) is the development of materials with simultaneously high ionic conductivity and mechanical strength. Herein, SPEs of lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI)-doped poly(propylene monothiocarbonate)-b-poly(ethylene oxide) (PPMTC-b-PEO) block copolymers (BCPs) with both blocks associating with Li+ ions are prepared. It is found that the PPMTC-b-PEO/LiTFSI electrolytes with double conductive phases exhibit much higher ionic conductivity (2 × 10-4 S cm-1 at r.t.) than the BCP electrolytes with a single conductive phase. Concurrently, the storage moduli of PPMTCn -b-PEO44 /LiTFSI electrolytes are ≈1-4 orders of magnitude higher than that of the neat PEO/LiTFSI electrolytes. Therefore, simultaneous improvement of ionic conductivity and mechanical properties is achieved by construction of a microphase-separated and disordered structure with double conductive phases.

Status and Targets for Polymer-Based Solid-State Batteries for Electric Vehicle Applications

There is growing interest in the development of Li-metal-based solid state batteries, driven by their promise in improving the energy density to satisfy electric vehicle requirements. In this contribution, we examine the status of Solid polymer electrolytes (SPEs) based solid state batteries for electric vehicle applications using a continuum scale mathematical model. We examine LiFePO4 (LFP) cathode/lithium metal anode batteries containing three different electrolytes, namely (1) a liquid electrolyte, (2) the polystyrene-b-poly(ethylene oxide) (SEO) block copolymer electrolyte, and (3) a single-ion conducting (SIC) block copolymer electrolyte, with the liquid electrolyte serving as the baseline for the comparison. By using an optimization procedure, we assemble “virtual” batteries to identify the optimal design that maximizes energy density while allowing the power requirements of electric vehicles (EVs) to be satisfied. Results show the present status of different SPEs are still below what is considered acceptable and further improvements are needed to achieve electric vehicle targets. The optimization studies conducted here show that for low transference number electrolytes (∼0.2) the conductivity target is 5 × 10−3 S cm−1, while for a unity transference number electrolyte this target decreases to 4 × 10−4 S cm−1. These targets provide guidance for polymer synthesis researchers to develop better polymers for use in EVs.

Adhesion Strength of Block Copolymer Toughened Epoxy on Aluminum

The effect of poly(ethylene-alt-propylene)-b-poly(ethylene oxide) block copolymer modifiers on the adhesion strength of epoxies was evaluated. Three block copolymer modifiers of varying block weigh...

Nanoscale Mapping of Thermal and Mechanical Properties of Bare and Metal-Covered Self-Assembled Block Copolymer Thin Films

We report on the structural, mechanical, and thermal analysis of 40 nm thick polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) films coated with evaporated chromium layers of ...

Electrochemical Kinetics in Solid Battery Electrolytes

Solid electrolytes are of interest for improved battery safety and compatibility with advanced electrodes (such as lithium metal). They could potentially enable flexible, efficient batteries with the use of single-ion conducting polymer or composite electrolytes. However, the rate capability of solid-state batteries is problematic, as is long-term stability with certain electrode chemistries. In order to better understand these limitations, we have developed a pulsed voltammetry method to study electrode reaction kinetics in cells with solid polymer electrolytes. Traditionally, a rotating disk electrode has been used to study reaction kinetics in liquid electrolytes. This method minimizes mass transfer limitations by rotating the working electrode so that reaction kinetics can be accurately measured. Since electrode rotation is not possible in solid electrolytes, we use short, constant-voltage pulses and collect a current measurement. Then the cell is left at open circuit for an extended period of time to dissipate any concentration gradients that developed during the measurement. After sufficient relaxation, another pulse to a different voltage is made. Measurement at early time minimizes mass-transfer contribution to the measurement. We have validated this technique against rotating disk electrode measurements in a liquid electrolyte. It has also been applied to study oxidative degradation of polymer electrolyte and lithium and plating kinetics. The latter study is of particular interest due to the fact that a connection between reaction kinetics and lithium dendrite morphology has been observed in some systems. The solid polymer electrolyte used in this work consists of lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) dissolved in polystyrene-b-poly(ethylene oxide) block copolymers. The kinetic measurements from pulsed voltammetry will be compared to electrochemical impedance spectroscopy measurements and lithium surface morphology analysis. Interesting effect of salt concentration will also be presented.

Status and Targets for Polymer-Based Solid-State Batteries for Electric Vehicle Applications

As the market of electric vehicles (EVs) expands, numerous researchers and companies are focusing on the use of lithium metal anodes, which can enable higher energy densities required to extend the driving range of EVs and allow for lower cost [1]. However, the implementation of these metal anode batteries has several safety issues that emerge from dendrite growth in flammable liquid electrolytes. Solid polymer electrolyte has been studied as one of the promising candidates for lithium metal batteries because of the advantages of the non-flammability and relatively higher mechanical properties than liquid electrolytes [2, 3]. Compared to existing batteries based on liquid electrolytes, solid polymer electrolytes still have limitations, such as low ionic conductivity under room temperature conditions, which can significantly hinder its application in EVs. Hence, research on next-generation solid polymer electrolyte is being conducted to improve its transport properties. In this work, by using a model-based approach, the status of the present-day solid polymer electrolyte battery is examined, and compared with the traditional batteries with liquid electrolyte, with a focus on EVs. Using a mathematical model developed based on the macro-homogeneous approach pioneered by Newman and coworkers [4], we investigated Li-metal/LiFePO4 (LFP) batteries containing three different electrolytes, namely (i) liquid electrolyte (ii) polystyrene-b-poly(ethylene oxide) (SEO) block copolymer electrolyte and (iii) a single-ion conducting block copolymer electrolyte. Concentrated solution theory and modified Ohm’s law are used to calculate the mass transport and potential gradient inside the electrolyte. In addition, the mass balance of lithium, potential drop in the active material, and the charge-transfer reactions are considered for a composite positive electrode that consists of LFP active particles. More detailed information about the continuum model is available in the literatures [4, 5]. All the transport parameters for the solid polymers, which include SEO and single-ion block copolymer, are adopted from the previously-published experimental results [3, 6-8]. For validation, model predicted results of the three Li/LFP batteries are compared with experimental data. Next, we compared the performance of the three different electrolytes operating at the same specified electrode thickness and weight percent of electrolyte. Optimal design points of each cell that provides the highest specific energy and power are determined. Finally, the results demonstrate how the specific energy and power of a solid polymer cell should be improved to achieve similar performance as that of a liquid electrolyte cell. This work provides directions for improvements in present-day solid polymer electrolytes for usage in electric vehicle. References Gallagher, K.G., et al., Quantifying the promise of lithium-air batteries for electric vehicles. Energy & Environmental Science, 2014. 7(5): p. 1555-1563.Armand, M. and J.M. Tarascon, Building better batteries. Nature, 2008. 451(7179): p. 652-657.Bouchet, R., et al., Single-ion BAB triblock copolymers as highly efficient electrolytes for lithium-metal batteries. Nature Materials, 2013. 12(5): p. 452-457.Doyle, M., T.F. Fuller, and J. Newman, Modeling of Galvanostatic Charge and Discharge of the Lithium Polymer Insertion Cell. Journal of the Electrochemical Society, 1993. 140(6): p. 1526-1533.Fuller, T.F., M. Doyle, and J. Newman, Simulation and Optimization of the Dual Lithium Ion Insertion Cell. Journal of the Electrochemical Society, 1994. 141(1): p. 1-10.Bruce, P.G., et al., Li-O-2 and Li-S batteries with high energy storage. Nature Materials, 2012. 11(1): p. 19-29.Devaux, D., et al., Failure Mode of Lithium Metal Batteries with a Block Copolymer Electrolyte Analyzed by X-Ray Microtomography. Journal of the Electrochemical Society, 2015. 162(7): p. A1301-A1309.Pesko, D.M., et al., Comparing Two Electrochemical Approaches for Measuring Transference Numbers in Concentrated Electrolytes. Journal of the Electrochemical Society, 2018. 165(13): p. A3014-A3021.

Microphase separation of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) block copolymers induced by differential interactions with salt

This work describes the microphase separation behavior of poly(propylene monothiocarbonate)-b-poly(ethylene oxide) (PPMTC-b-PEO) block copolymers (BCPs), a type of new sulfur-containing block copolymer, induced by lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI). PPMTC-b-PEO BCPs with a fixed PEO block length but different PPMTC block lengths were synthesized and doped by LiTFSI. Temperature-variable small-angle X-ray scattering result indicates that microphase separation of the PPMTC-b-PEO BCPs can be induced by differential interactions with LiTFSI. However, the ability of LiTFSI to induce microphase separation in PPMTC-b-PEO BCPs does not monotonically increase with the doping ratio (r = [Li+]/([EO] + [PMTC])). It is observed that stronger microphase separation usually occurs at r = 1/12 and 1/6, but microphase separation is weaker at r = 1/24 and 1/3. In most cases, microphase-separated but disordered structures are obtained. Particularly, ordered lamellar structure is formed at suitable doping ratio and block composition. FTIR result confirms the differential complexation of LiTFSI with PEO and PPMTC. LiTFSI preferentially interacts with PEO at low rs, but also strongly interacts with PPMTC at high rs. This work provides a new method to prepare solid polymer electrolytes with double conductive nano-phases, which may be beneficial to both conducting and mechanical properties.

Structural hierarchy in blends of amphiphilic block copolymers self-assembled at the air-water interface

We present a concurrent self-assembly strategy for patterning hierarchical polymeric surface features by depositing variable-composition blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-block-poly(ethylene oxide) (PB-b-PEO) block copolymers at the air-water interface. Hierarchical strand networks of hydrophobic PS/PB blocks anchored via PEO blocks to the water surface, with an internal phase-separation structure consisting of periodic domains of PS blocks surrounded and connected by a matrix of PB blocks, are generated by the interplay of interfacial amphiphilic block copolymer aggregation and polymer/polymer phase separation. In contrast to the cylinder-in-strand structures previously formed by our group in which interfacial microphase separation between PS and PB blocks was constrained by chemical connectivity between the blocks, in the current system phase separation between PS and PB is not constrained by chemical connectivity and yet is confined laterally within surface features at the air-water interface. Investigations of multi-component polymer systems with different connectivities constraining repulsive and attractive interactions provides routes to new hierarchical surface patterns for a variety of applications, including photolithography masks, display technology, surface-guided cell growth and tissue engineering.

Temperature-dependent structure and compressive mechanical behavior of alginate/polyethylene oxide-poly(propylene oxide)-poly(ethylene oxide) hydrogels.

We report the structural and mechanical behavior of multicomponent hydrogels comprising the commercial poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in shear rheology. Here we explore the properties of these materials under compression and large deformations, relevant to applications such as wound dressings that require mechanical robustness. For gels with lower F127 concentration, we find that the stiffness of the gels can be ascribed to the alginate network, and that the Young's modulus and fracture stress do not strongly depend on temperatures. However, for gels with an F127 concentration of 30 wt %, the Young's modulus is enhanced at higher temperatures. Under large deformations, the fracture stress and fracture strain of the materials can be independently varied using the alginate and F127 concentrations, respectively; without the trade-off in these properties that is often observed in rigid polymer networks. Small-angle X-ray scattering shows a power-law dependence scattering intensity on q arising from the alginate network and scattering peaks consistent with rearranging micelles. For gels with lower F127 concentrations, we find a disordered-body-centered cubic (BCC)-face-centered cubic (FCC) progression of states with temperature, and a BCC/FCC mixture for gels with higher F127 concentrations.

Solvent mediated inclusion of metal oxide into block copolymer nanopatterns: Mechanism of oxide formation under UV-Ozone treatment

Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time.

Synthesis and Study of Gas Transport Properties of Polymers Based on Macroinitiators and 2,4-Toluene Diisocyanate.

Nowadays, block copolymers hold great promise for the design of novel membranes to be applied for the membrane gas separation. In this regard, microporous block copolymers based on a macroinitiator with an anionic nature, such as potassium-substituted block copolymers of propylene oxide and ethylene oxide (PPEG) and 2,4-toluene diisocyanate (TDI), were obtained and investigated as effective gas separation membranes. The key element of the macromolecular structure that determines the supramolecular organization of the studied polymers is the coplanar blocks of polyisocyanates with an acetal nature (O-polyisocyanate). In the present research, the influence of the content of peripheral polyoxyethylene (POE) blocks in PPEG on the supramolecular structure processes and gas transport characteristics of the obtained polymers based on PPEG and TDI was investigated. According to the study of polymers if the POE block content is 15 wt %, the polyoxypropylene segments are located in the internal cavity of voids formed by O-polyisocyanate blocks. When the POE block content is 30 wt %, the flexible chain component forms its own microphase outside the segregation zone of the rigid O-polyisocyanate blocks. The permeability for polar molecules, such as ammonia or hydrogen sulfide, significantly exceeds the permeability values obtained for non-polar molecules He, N2 and CH4. A relatively high permeability is also observed for carbon dioxide. At the same time, the content of POE blocks has a small effect on the permeability for all studied gases. The diffusion coefficient increases with an increase in the POE block content in PPEG for all studied gases.

Structure and thermodynamics of mixed polymeric micelles with crystalline cores: tuning properties via co-assembly.

We investigate micelles formed by mixtures of n-alkyl-poly(ethylene oxide) block copolymers, Cn-PEO, with different alkyl block lengths in aqueous solution. This model system has previously been used to shed light on the interplay between exchange kinetics and crystallinity in self-assembling systems [König et al., Phys. Rev. Lett., 2019, 122, 078001]. Now we report on the structure and thermodynamics of these micelles by combining results from small-angle X-ray scattering, differential scanning calorimetry and volumetric measurements. We show that mixed micelles are formed despite the fact that length-mismatched n-alkanes of similar weights in bulk tend to demix below the crystallization temperature. Instead, the system exhibits similar properties as single-component micelles but with a modulated melting region. Interestingly, the melting point depression due to self-confinement within the micellar core can be approximately described by a generalized Gibbs-Thomson equation, similar to single-component micelles [Zinn et al. Phys. Rev. Lett., 2014, 113, 238305]. Furthermore, we find a novel scaling law for these micelles where, at least for larger n, the aggregation number scales with the third power of the length of the hydrophobic block, Nagg ∝ n3. Possibly, there might be a cross-over from the conventional Nagg ∝ n2 behaviour around n ≈ 19. However, the reason for such a transition as well as the strong n dependence remains a challenge and requires more theoretical work.

Formation and Characteristics of Lipid-Blended Block Copolymer Bilayers on a Solid Support Investigated by Quartz Crystal Microbalance and Atomic Force Microscopy.

Liposomes grafted with polymer have long been used in drug delivery applications, and block copolymersomes have emerged as attractive and more robust alternatives for both drug delivery and artificial organelle applications. Hybrid membranes that could combine the respective advantages of fluid lipid and robust polymer bilayers are an attractive and enticing alternative. The properties of membranes in amphiphile vesicles are challenging to study and many applications benefit from surface-based access to the membrane. We therefore explore the self-assembly and mechanical properties of supported hybrid bilayers (SHBs) composed of polybutadiene- block-poly(ethylene oxide) block copolymers and zwitterionic phosphatidylcholine lipids on SiO2 supports. Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements show that formation of SHB on SiO2 by vesicle fusion depends on the mass fractions of lipids and block copolymers. Atomic force microscopy was used to study the microscopic mixing of lipids in the SHB to reveal that lipid-phase separation is not observed in SHBs. Force spectroscopy was performed to extract information about thickness and mechanical properties of the hybrid membranes. SHBs are shown to combine the properties of lipid membranes and polymer brushes, and the tip force required to rupture the membrane decreases and the bilayer thickness increases as the block copolymer fraction is increased.