Triblock Copolymer Solutions Research Articles

Superior single-atom Pt/TiO2 mesoporous microspheres via microdrops-confined pyrolysis/deposition for low-temperature CO oxidation

This work demonstrate a polymer micelle-induced mesoporous single-atom Pt1/TiO2 microspheres with a mixed mother solution of triblock copolymer (Pluronic F127), H2PtCl6 and tetrabutyl titanate (TBT). The specific surface area and pore volume of mesoporous single-atom Pt1/TiO2 microspheres reach 179 m2/g and 0.39 cm3/g, respectively. The synthesis reaction is spatially confined in microdrops via aerosol spray. The obtained catalysts present superior activity for CO oxidation at low temperature. Typically, T100 (Temperature required to reach 100% conversion) of CO conversion (1.0% CO + 1.0% O2) is achieved at 120 °C with 0.5 at% Pt1/TiO2 catalysts, 50–60 °C lower than that with the same Pt loaded non-mesoporous catalysts from conventional photo-deposition and immersion-deposition of Pt on commercial TiO2 nanoparticles. Thus, this work paves a way to access efficient single-atom catalysts for CO oxidation.

Dynamic Light Scattering Based Microrheology of End-Functionalised Triblock Copolymer Solutions.

Nano-sized particles functionalised with short single-stranded (ss)DNAs can act as detectors of complementary DNA strands. Here we consider tri-block-copolymer-based, self-assembling DNA-coated nanoparticles. The copolymers are chemically linked to the DNA strands via azide (N3) groups. The micelles aggregate when they are linked with complementary ssDNA. The advantage of such block-copolymer-based systems is that they are easy to make. Here we show that DNA functionalisation results in inter-micellar attraction, but that N3-groups that have not reacted with the DNA detector strands also change the phase behaviour of the tri-block polymer solution. We studied the triblock copolymer, Pluronic® F108, which forms spherical micelles in aqueous solutions upon heating. We find that the triblock chains ending with either an N3 or N3-DNA complex show a dramatic change in phase behaviour. In particular, the N3-functionalisation causes the chain ends to cluster below the critical micelle temperature (CMT) of pure F108, forming flower-micelles with the N3-groups at the core, while the PPO groups are exposed to the solvent. Above the CMT, we see an inversion with the PPO chains forming the micellar core, while the N3-groups are now aggregating on the periphery, inducing an attraction between the micelles. Our results demonstrate that, due to the two competing self-assembling mechanisms, the system can form transient hydrogels.

Aggregate behavior in amphiphilic coil/rod block copolymer solutions

The self-assembly in coil/rod/coil BAB amphiphilic symmetric triblock copolymer solutions was investigated using lattice self-consistent field theory. At low concentrations, some peaks emerge on the heat capacity curve, i.e., multiple rearrangements (MRs) of micelles. For short hydrophobic rod blocks (HRBs), MRs are concerned with the emergences of vesicles, stellate, rod, and lamellar micelles (LMs), and the breakup and formation of LMs. At high concentrations with HRBs of intermediate length HRBs, MRs are associated to a few (quasi-)order/disorder transitions of micelles. For long HRBs, although only one quasi-order/disorder transition emerges, MRs do occur. It is found that the aggregation behavior of high concentrations with HRBs of intermediate length is similar to that of low concentrations compared with high concentrations with long HRBs. These results are explained by the reappearing behavior and dissolution, and the cooperative growth of micelles, where the micellar cores and coronas are rearranged alternately with temperature. This work is helpful for further interpreting the cooperativity and dynamics of self-assembly.

Rheological signatures of gel–glass transition and a revised phase diagram of an aqueous triblock copolymer solution of Pluronic F127

In this work, we study temperature-induced state change of an aqueous solution of triblock copolymer composed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO (Pluronic F127), at different concentrations using rheology. While this temperature-dependent state change visually appears like a liquid–soft solid transition, and the soft solid state has been termed as a gel in the literature, there is a debate regarding the precise microstructure of the soft solid state. We observe that over a concentration domain of interest, an aqueous solution of F127 overwhelmingly demonstrates all the characteristic rheological features of not just a sol–gel–glass transition at low temperatures and glass–liquid transition at high temperatures, but also that associated with the individual states, such as sol, post-gel, and glass. The temperature at which the gel–glass transition is observed decreases while the temperature associated with glass–liquid transition increases with an increase in the concentration of F127. Based on the observed behavior, we propose a mechanism that considers the change in micelle volume fraction and alteration of the hydrophilicity of PEO corona as a function of temperature. Finally, we construct a phase diagram and discuss the similarities and differences with respect to various phase diagrams of F127 solution available in the literature.

Thermoresponsive and Injectable Composite Hydrogels of Cellulose Nanocrystals and Pluronic F127.

Thermoresponsive amphiphilic Pluronic F127 triblock copolymer solutions have been widely investigated in smart biomaterial applications due to the proximity of its critical gel temperature to human body temperature. Meanwhile, cellulose nanocrystals (CNCs) have quickly become the focus of many drug delivery and tissue engineering applications due to their biocompatibility, abundance, ability to conjugate with drug molecules, and superior rheological properties. Herein, we investigate the phase behavior and thermo-rheological properties of the composite hydrogels containing cellulose nanocrystals (up to 5% by weight) and the temperature responsive Pluronic F127. Our results revealed an unprecedented role of CNC network formation on micellization and gelation behavior of the triblock copolymer. Linear and nonlinear rheological analysis suggest that at low and moderate nanocrystal loadings (1-3% by weight), the composite gel remarkably becomes softer and deformable compared to the neat Pluronic F127 gels. The softening effect results from the disruption of the close packed micelles by the rodlike CNCs. At high concentrations, however, the nanocrystals form their own network and the micelles are trapped within the CNC meshes. As a result, the original (neat F127) hard-gel modulus is recovered at 4 to 5% nanocrystal loading, yet the composite gel is much more deformable (and tougher) in the presence of the CNC network. Our temperature sweep experiments show that the CNC addition up to 3% does not change the rapid thermal gelation of the F127 solutions; therefore, these composites are suitable for smart drug delivery systems. On the other hand, at higher CNC concentrations, abrupt viscosity transition is not observed, rather the composite gels smoothly thicken with temperature in contrast to thermal thinning of the aqueous neat CNC. Thus, they can be used as smartly adaptive biolubricants and bioviscostatic materials.

Direct measurement of interaction force between hydrophilic silica surfaces in triblock copolymer solutions with salt by atomic force microscopy

Triblock copolymers composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) are used in various fields as nonionic surfactants. In this study, we measured interaction forces between untreated hydrophilic silica surfaces in solutions with two typical triblock copolymers, Pluronic P123 (PEO20PPO70PEO20) and F127 (PEO99PPO65PEO99), in the presence of 1 mM and 500 mM NaCl using atomic force microscopy (AFM). In solutions at the copolymer concentration of 1 µM, which is below the critical micelle concentration (CMC), the measured interaction forces were monotonically repulsive in the presence of 1 mM NaCl, which suggested the brush-like conformation of copolymers on the surfaces. When the concentration of NaCl was increased to 500 mM, interaction forces became attractive, which indicated the bridging of adsorbed polymers onto surfaces, the strength of which varied depending on the affinity and adsorption density of copolymers. The interactions at the copolymer concentration of 1 mM, which were above the CMC of both copolymers, were steric repulsions between adsorbed micelles on the surfaces with 1 mM of NaCl. For 500 mM of NaCl, an attractive jump after a steric repulsion was observed only in the force curve for P123, which inferred that the displacement of micelles from the surfaces was presumably due to a decrease in the strength of adsorption caused by the dehydration of EO groups. These results indicated that the length of the EO group considerably affected the interactions.

Thermosensitive Hybrid Elastin-like Polypeptide-Based ABC Triblock Hydrogel

We report the synthesis of a well-defined hybrid ABC triblock terpolymer containing a synthetic poly(trimethylene carbonate) (PTMC) block A and a thermosensitive BC diblock of recombinant elastin-like polypeptides (ELPs). The triblock in diluted solution (0.1–0.3% w/v), at low temperatures in ultrapure water, forms micellar structures of 10–60 nm sizes in diameter as characterized by dynamic light scattering (DLS) and liquid atomic force microscopy (AFM). While heated above its transition temperature (Tt), larger particles of 200–300 nm sizes are obtained, consistent with the formation of coacervates. When concentrated, the viscosity of the triblock copolymer solution progressively increases, giving a free-standing gel at 4% w/v formed by a network of micron-sized particles. The formed hydrogels are thermally reversible, and their sol–gel transitions are fast and sharp. The gel formation mechanism appears to interestingly biomimic tropoelastin, the native monomeric form of natural elastin, as demonstrated by optical and cryogenic-scanning electron microscopy (cryo-SEM) imaging.

Improved Effect of Fe on the Stable NiFe/Al2O3 Catalyst in Low-Temperature Dry Reforming of Methane

Bimetallic catalysts with alloy structure have been extensively explored to tailor and boost the catalytic performance of the dry reforming of methane. Herein, NiFe/Al2O3 catalyst was designed from an aluminum gel with metal nitrate in a triblock copolymer solution by an evaporation-induced self-assembly process and calcination for the low-temperature dry reforming of methane (LT-DRM). The resultant NiFe/Al2O3 exhibited a large surface area of 203 m2 g–1 and porosity of 0.8 cm3 g–1. Bimetallic NiFe/Al2O3 promoted CH4 and CO2 conversion as well as the H2/CO ratio relative to monometallic Ni/Al2O3. CH4 and CO2 conversion on the NiFe/Al2O3 was 26.6 and 37.8% with a H2/CO ratio of 0.67 at 550 °C. Furthermore, NiFe/Al2O3 possessed good stability at 450 °C during LT-DRM reaction for 20 h. The Ni3Fe alloy structure is favorable for the resistance of oxidation and coke deposition. This work sheds light on the sophisticated design of the alloy structure of the bimetallic catalyst for efficient and stable catalytic performances.

Lubrication performance of aqueous copolymer lubricants with phosphate ester additive at different temperature on the Si surface

AbstractThe lubrication performance of adsorbed triblock copolymers polypropylene oxide‐polyethylene oxide‐polypropylene oxide (PPO–PEO–PPO) with phosphate ester films at different temperature on the Si surface was investigated using a pin‐on‐disc tribometer. The results revealed that the molecular architecture of the triblock copolymer and the temperature had a significant influence on the tribological behaviour. The triblock copolymer with a higher weight percentage of PPO exhibited a better lubrication performance both below and above the cloud point. However, when the temperature is above the cloud point, the adsorbed PPO–PEO–PPO film showed worse lubricity than that below the cloud point. The addition of phosphate ester to the triblock copolymer solution resulted in the decrease of the coefficient of friction and the improvement of the anti‐wear property. Moreover, with the added phosphate ester, the tribological performance became insensitive to the temperature.

Aqueous solutions of triblock copolymers used as the media affecting the magnetic relaxation properties of gadolinium ions trapped by metal-oxide nanostructures

The present work introduces the optimization of the oxidative degradation, complex formation and aggregation of the water-soluble metal oxide nanostructures (the so-called keplerates) [{W6O21(H2O)5(OAc)0.5}12{Mo2O4(OAc)}30]48− (W72Mo60), [{Mo6O21(H2O)3(SO4)}12(VO)30(H2O)20]26− (Mo72V30), and [{Mo6O21}12Fe30(OAc)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91] (Mo72Fe30) in aqueous solutions containing Gd3+ ions and triblock copolymers, which can be used as a tool to enhance magnetic relaxivity of the gadolinium-bound nanostructures. The particularly significant enhancement in the magnetic relaxivity of the Gd3+ ions bound with W72Mo60 versus Mo72Fe30/V30 is due to the more convenient size of the external pores in the keplerate framework, which are the binding sites for Gd3+ aqua ions. The structure of the W72Mo60 keplerate is also responsible for the high stabilities of its gadolinium complexes against oxidative degradation in the solutions. The aggregation of the gadolinium-bound W72Mo60 keplerates controlled by the Gd:keplerate molar ratio is a factor in addition to the structure affecting the relaxivity. The assembly of the gadolinium-bound keplerates with the triblock copolymers enhances the relaxivity values by limiting the size of the aggregates, while the relaxivity of the molecular complexes is insignificantly affected by the assembly with the triblock copolymers. The gadolinium complexes exhibiting competitively high magnetic relaxivity values, coupled with their high chemical stability and low cytotoxicity, are introduced herein as the result of the structural optimization, both on molecular and supramolecular levels.

ROS‐Sensitive Degradable PEG–PCL–PEG Micellar Thermogel

A reactive oxygen species (ROS)-sensitive degradable polymer would be a promising material in designing a disease-responsive system or accelerating degradation of polymers with slow hydrolysis kinetics. Here, a thermogelling poly(ethylene glycol)-polycaprolactone-poly(ethylene glycol) (PEG-PCL-PEG or EG12 -CL20 -EG12 ) triblock copolymer with an oxalate group at the middle of the polymer is reported. The polymers form micelles with an average size of 100 nm in water. Thermogelation is observed in a concentration range of 8.0-37.0 wt%. In particular, the aqueous PEG-PCL-PEG triblock copolymer solutions are in a gel state at 37 °C in a concentration range of 25.0-37.0 wt%, whereas the aqueous PEG-PCL diblock copolymer solutions are in a sol state in the same concentration range at 37 °C. Thus, the gel depot could dissolve out once degradation of the triblock copolymers occurs at the oxalate group as confirmed by the in vitro experiment. In vivo gel formation is confirmed by injecting an aqueous PEG-PCL-PEG solution (36.0 wt%) into the subcutaneous layer of rats. The gel completely disappears in 21 d. A model polypeptide drug (cyclosporine A) is released over 21 d from the in situ formed gel. The micelle-based thermogel of PEG-PCL-PEG with ROS-triggering degradability is a promising injectable material for biomedical applications.

Surface excess at water/air interface and micellization in solutions of an amphiphilic triblock copolymer

PEO-PPO-PEO triblock copolymers (usually referred as EPE) have been employed in different fields, with a remarkable emphasis in biomedical-related applications. They are amphiphilic macromolecules, in which PEO segments are soluble in the aqueous phase, while PPO blocks have hydrophobic character. In this work we carried out experiments with surface tensiometry of aqueous solutions of an EPE copolymer, well-known as Kolliphor P188, as a function of temperature and concentration. From the resultant data, thermodynamic relationships were related to adsorption at non-saturated liquid/air interface (low copolymer concentrations). Surface excess curves were calculated from Kohlrausch-William-Watts (KWW) functions fitted to experimental data and critical micellar concentration, was determined. The relationship of and temperature was similar to the observed for the adsorption of EPE copolymer at non-saturated liquid/air interface: there was a drastic change in enthalpy and entropy of adsorption/micellization at which was correlated to the critical micellar temperature, for this copolymer.

Unveiling the interaction between carbon nanodot and IR light emitting fluorescent dyes inside the confined micellar environment

In this contribution, using microwave heating of polyethylene glycol (PEG 200), we have prepared carbon nanodot (CND). It is found that in aqueous medium as well as in the micellar solutions of triblock copolymer, P123 and in anionic surface active ionic liquid (SAIL), 1-butyl-3-methylimidazolium n-octylsulfate ([C4mim][C8SO4]) the fluorescence intensity of CND gets quenched in the presence of cationic cyanine dye HITCP and cationic phenoxazine dye Nile blue (NB). Stern-Volmer constant indicates that the quenching of fluorescence intensity is more in the aqueous medium compared to P123 and [C4mim][C8SO4] i.e., (BmimOs) micelles. Time-correlated single photon counting (TCSPC) measurement reveals that the fluorescence quenching is static in nature and the quenching through Förster resonance energy transfer (FRET) process is not dominant here. Addition of both the cationic dye molecules (HITCP and NB) in CND solution generates new excited state absorption peaks in transient absorption measurement. This observation suggests that a transient species is generated through photoinduced electron transfer (PET) between the donor-acceptor pairs and this PET is responsible for the fluorescence quenching of CNDs by the dye molecules. Moreover, this electron transfer kinetics is relatively faster in bulk water compared to that inside P123 and BmimOs micelle due to the intervention of the surfactant molecules between CND and the dye molecules. Therefore, this study provides a new insight about the PET dynamics between CND and fluorescent dye molecules.

Chlorophylls B formulated in nanostructured colloidal solutions: Interaction, spectroscopic, and photophysical studies

Chlorophylls (Chls) are natural pigments essential to photosynthesis that have been shown to act as photosensitizers for Photodynamic Therapy (PDT). Many studies have used Chls A and its colloidal formulations in the PDT field but little is known about the potential of Chls B for this application. Here we have detailed the interaction, spectroscopic, and photophysical properties of Chlorophyll b (Mg-Chl b), Pheophytin b (Pheo b), and its formulations with nonionic surfactants aiming photodynamic applications. Both pigments were formulated in some suitably nanostructured drug delivery systems based on aqueous solutions of Pluronics triblock copolymers and Tweens surfactants. High binding constants have evidenced that Chls B interact strongly with these micelles, and the results are correlated with logP, zeta potential, and hydrodynamic diameter. Spectroscopic studies showed high molar absorption coefficients in the therapeutic window (600–800 nm), significant fluorescence quantum yields, and solubilization of Chls B as monomers, especially for Pluronics systems. Pheo b is completely photostable in all investigated micellar systems, whereas Mg-Chl b is photobleached with a rate constant correlated with the interaction and relative location in these micelles. High singlet oxygen quantum yields identify these chlorophylls B as possible Type II photosensitizers for PDT. Mg-Chl b in particular is almost twice as effective as Mg-Chl a, which makes it one of the most potent generators of singlet oxygen in nature.

Confined film structure and friction properties of triblock copolymer additives in oil-based lubrication

The friction properties of a dilute solution of block copolymer additives in poly-α-olefin (PAO) confined between mica surfaces were investigated using the surface forces apparatus. Friction measurements were made for poly(11-acrylamidoundecanoic acid)-block-poly(alkyl methacrylate)-block-poly(11-acrylamidoundecanoic acid) with an alkyl chain length of C12 (A5L946A5) in the poly(alkyl methacrylate) blocks. The results were compared to those for a PAO solution of a similar triblock copolymer with an alkyl chain length of C18 (A5S992A5) examined in our previous work (Yamada et al., Langmuir 2015). The friction coefficient μ for A5L946A5/PAO was approximately 0.5, which was one or two orders of magnitude larger than that for A5S992A5/PAO (μ of 0.002–0.039). Detailed analysis of the dynamic thickness and contact geometry enabled us to investigate the difference in the friction reduction abilities of the two additives. A5L946A5 has a high affinity to PAO and the molecules have expanded conformation in PAO; extensive chain entanglement effect results in the formation of a thick and viscous lubricant layer, which gives rise to high friction. On the other hand, A5S992A5 has low affinity to PAO, and the shrunken A5S992A5 molecules adsorbed on the surfaces form a rigid slip plane at the interface, which gives rise to low friction. Our results provide insights into the oil/additive combinations used for low friction in oil-based lubrication. The friction properties of a dilute solution of block copolymer additives in a base lubricant oil confined between mica surfaces were investigated using the surface forces apparatus. Friction force, sliding film thickness, and contact geometry were evaluated in detail, and the results were compared to those of the solutions of a different block copolymer additive having similar molecular structure. The relationship between the chemical structure of additives, confined structures between surfaces, and friction mechanisms were discussed, which shed new light of the design of low-friction surfaces in oil-based lubrication.

Photo-Healable Materials Based on Block Copolymers and Ionic Liquids

Ion gels are composed of ionic liquids (ILs) immobilized within a three-dimensional molecular network. Such gels preserve the attractive physicochemical properties of ILs, such as nonvolatility, thermal stability, electrochemical stability, and high ionic conductivity, while maintaining a soft solid consistency. Ion gels are a novel platform for many applications such as electrolyte membranes, actuators, gas-separation membranes, flexible electrochemiluminescent gels, and organic thin-film transistors. We present here the reversible micellization and sol-gel transition of block copolymer solutions in an IL triggered by a photostimulus. The ABA triblock copolymer employed consists of a random copolymer A block, including thermosensitive N-isopropylacrylamide (NIPAm) units and a methacrylate incorporating an azobenzene chromophore into the side chain (AzoMA); the B block is composed of an IL-soluble poly(ethylene oxide) (PEO) (P(AzoMA-r-NIPAm)-b-PEO-b-P(AzoMA-r-NIPAm)). We observed a reversible unimer-to-micelle transition of a dilute ABA triblock copolymer (1 wt%) in an IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6) induced by photostimuli at an intermediate, “bistable” temperature. We demonstrate a reversible sol-gel transition cycle of the ion gel at the bistable temperature, with reversible association and fragmentation of the polymer network structure consisting of the self-assembled ABA triblock copolymer (20 wt%) in [C4mim]PF6. Such sol-gel transition has been utilized to design photo-healable materials. Damaged part of materials is UV-irradiated to convert gel to sol, followed by irradiated by visible light in order to convert again sol to gel. By this procedure, the damaged part was demonstrated to be healed to the original state (Figure 1). Furthermore, we propose moving the azobenzene groups from the polymer chains to the IL structure as a molecular-level photoswitchable IL. Photoisomerization of an azobenzene IL at the molecular level can evoke a macroscopic response (light-controlled mechanical sol-gel transitions) for ABA triblock copolymer solutions. Therefore, an azobenzene IL as a molecular switch can tune the self-assembly of a thermoresponsive polymer, leading to macroscopic light-controlled sol-gel transitions. Surprisingly, a sight change in chemical structures of thermosensitive A segments induces opposite photo responsiveness, unimer/micelle transition and sol/gel transition, against UV/Vis-irradiation. Figure 1. Photographs showing photo-healing of a star shaped ABA ion gel (20 wt%) cut at the center: (Left) damage before applying light stimuli, (Right) completely repaired damaged part after 64 h UV-light exposure, followed by 30 min visible-light exposure. The cracked part is highlighted by white dotted square. Figure 1

Physicochemical study of the interactions between Econazole and DL-α-Tocopherol with triblock copolymer aggregates in PBS media

Solubilization enhancement of the pharmaceutical drug Econazole and vitamin E (DL-α-Tocopherol) in phosphate buffered saline aqueous media (PBS) at 298.15 K, due to the presence of aggregates of two triblock copolymers (F127 and P123), is reported. The increment in the solubility of the compounds as a function of the concentration of the triblock copolymer was determined by UV-Visible spectrophotometry. From these datum, the molar solubilization capacity, micelle–water partition coefficients and standard free energy of solubilization for each of the compounds in the different triblock copolymer solutions is reported. The effect on the thermodynamics of aggregate formation due to the incorporation of the solute into the aggregate arrangement of the triblock copolymers was investigated using differential scanning calorimetry (DSC). From our results it is evident that the presence of the solute in the triblock copolymer aggregates disrupts the original arrangement of the aggregates free of the solute, since the thermodynamic parameters associated with the aggregate formation are modified e.g. the presence of the solute lowers the enthalpy of aggregation as well as the onset temperature of aggregate formation and in general the profile of the calorimetric trace is modified. The size of the aggregates loaded with the solute was established through the determination of their hydrodynamic diameter, obtained from dynamic light scattering (DLS) measurements carried out at 283.15, 298.15 and 313.15 K. The hydrodynamic diameters of the aggregates of the triblock copolymers loaded with Econazole are very similar to the diameters obtained for the aggregates which are solute free. These results indicate that the solute most be completely engulfed by the aggregate. In the systems where the solute is DL-α-Tocopherol, the resulting hydrodynamic diameters are very different from the values obtained for the pure triblock copolymers which suggests that the solute does not sit inside the aggregate but it must be intercalated between the triblock copolymer molecules or in positions where the normal arrangement is disrupted significantly. From in vitro drug release studies of the two solutes encapsulated in the aggregates of the triblock copolymers in PBS buffer media to simulate physiological conditions we have determined that their liberation profiles can be described in terms of the Korsmeyer-Peppas and Peppas-Fassihi models.

Effect of Chain Architecture on Self-Assembled Aggregates from Cyclic AB Diblock and Linear ABA Triblock Copolymers in Solution.

The self-assembly behaviors of two block copolymers with the same chain length but different chain architectures (cyclic AB, linear ABA) in B-selective solvents are investigated using Monte Carlo simulations. A morphological transition sequence, from spherical micelles to cylindrical micelles, to vesicles and then to multicompartment vesicles, is observed for both copolymer systems when the interaction between the solvophobic A-block and the solvent is increased. In particular, toroidal micelles could be formed in triblock systems due to the presence of the bridging chains at the parameter region between cylindrical micelles and vesicles whereas disklike micelles are formed in cyclic systems. The simulation results demonstrated that the architecture of block copolymers could be used to regulate the structural characteristics and thermal stability of these self-assembled aggregates.

Self-Assembled CNT-Polymer Hybrids in Single-Walled Carbon Nanotubes Dispersed Aqueous Triblock Copolymer Solutions

We have carried out scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), electrical conductivity, and 1H NMR studies as a function of temperature on single-walled carbon nanotubes (SWCNTs) dispersed aqueous triblock copolymer (P123) solutions. The single-walled carbon nanotubes in this system aggregate to form bundles, and the bundles aggregate to form net-like structures. Depending on the temperature and phases of the polymer, this system exhibits three different self-assembled CNT-polymer hybrids. We find CNT-unimer hybrid at low temperatures, CNT-micelle hybrid at intermediate temperatures wherein the polymer micelles are adsorbed in the pores of the CNT nets, and another type of CNT-micelle hybrid at high temperatures wherein the polymer micelles are adsorbed on the surface of the CNT bundles. Our DSC thermogram showed two peaks related to these structural changes in the CNT-polymer hybrids. Temperature dependence of the 1H NMR chemical shifts of the molecular groups of the polymer and the AC electrical conductivity of the composite also showed discontinuous changes at the temperatures at which the CNT-polymer hybrid’s structural changes are seen. Interestingly, for a higher CNT concentration (0.5 wt.%) in the system, the aggregated polymer micelles adsorbed on the CNTs exhibit cone-like and cube-like morphologies at the intermediate and at high temperatures respectively.

UCST-Type Thermoresponsive Polymers in Synthetic Lubricating Oil Polyalphaolefin (PAO)

This Article reports a family of UCST-type thermoresponsive polymers, poly(alkyl methacrylate)s with an appropriate alkyl pendant length in an industrially important nonvolatile organic liquid polyalphaolefin (PAO). The cloud point (CP) can be readily tuned over a wide temperature range by changing the alkyl pendant length; at a concentration of 1 wt % and similar polymer molecular weights, the CP varies linearly with the (average) number of carbon atoms in the alkyl pendant. PAO solutions of ABA triblock copolymers, composed of a PAO-philic middle block and thermoresponsive outer blocks with appropriate block lengths, undergo thermoreversible sol–gel transitions at sufficiently high concentrations. The discovery of thermoresponsive polymers in PAO makes it possible to explore new applications by utilizing PAO’s unique characteristics such as thermal stability, nonvolatility, superior lubrication properties, and so on. Two examples are presented: thermoresponsive physical gels for control of optical trans...