Self-assembly Of Diblock Copolymers Research Articles

Investigation of off-chip and on-chip self-assembly of amphiphilic diblock copolymers based on poly(dimethylsiloxane) and poly(oligo(ethylene glycol)methacrylate)

This study aims to optimize the molecular architecture of poly(dimethylsiloxane)-b-poly(oligo (ethylene glycol) methacrylate) (PDMS-b-POEGMA) amphiphilic copolymers and investigate the phase behavior in solutions via alteration of chemical composition, initial concentrations of copolymers, none-solvent entry rates in the dialysis method, and also alterations in the micelle preparation methodology. To this end, PDMS-b-POEGMA copolymers are synthesized with different compositions and sequence lengths. Careful monitoring of the morphological permutations of polymeric nanoparticles in aqueous solution is performed through the dialysis method as an off-chip approach. Spherical and rod morphologies with different sizes are acquired due to variations in the properties of copolymer solutions such as chemical composition, concentration and the rate of water as non-solvent. For the on-chip process, a suitable microfluidic reactor is designed via a Shrinky-Dink method to produce micelles and compare them with micelles prepared by the dialysis method. Applying the on-chip method decreases the particle size from 500 to 50 nm, and reduces the particle size distribution from about 0.8 to 0.4. Hence, the particles reached from the microfluidic technique are smaller with a narrower particle size distribution, compared to those obtained from the off-chip method.

3D Micromachined Polyimide Mixing Devices for in Situ X-ray Imaging of Solution-Based Block Copolymer Phase Transitions.

Advances in modern interface- and material sciences often rely on the understanding of a system's structure-function relationship. Designing reproducible experiments that yield in situ time-resolved structural information at fast time scales is therefore of great interest, e.g., for better understanding the early stages of self-assembly or other phase transitions. However, it can be challenging to accurately control experimental conditions, especially when samples are only available in small amounts, prone to agglomeration, or if X-ray compatibility is required. We address these challenges by presenting a microfluidic chip for triggering dynamics via rapid diffusive mixing for in situ time-resolved X-ray investigations. This polyimide/Kapton-only-based device can be used to study the structural dynamics and phase transitions of a wide range of colloidal and soft matter samples down to millisecond time scales. The novel multiangle laser ablation three-dimensional (3D) microstructuring approach combines, for the first time, the highly desirable characteristics of Kapton (high X-ray stability with low background, organic solvent compatibility) with a 3D flow-focusing geometry that minimizes mixing dispersion and wall agglomeration. As a model system, to demonstrate the performance of these 3D Kapton microfluidic devices, we selected the non-solvent-induced self-assembly of biocompatible and amphiphilic diblock copolymers. We then followed their structural evolution in situ at millisecond time scales using on-the-chip time-resolved small-angle X-ray scattering under continuous-flow conditions. Combined with complementary results from 3D finite-element method computational fluid dynamics simulations, we find that the nonsolvent mixing is mostly complete within a few tens of milliseconds, which triggers initial spherical micelle formation, while structural transitions into micelle lattices and their deswelling only occur on the hundreds of milliseconds to second time scale. These results could have an important implication for the design and formulation of amphiphilic polymer nanoparticles for industrial applications and their use as drug-delivery systems in medicine.

Droplet phase in a nonlocal isoperimetric problem under confinement

<p style='text-indent:20px;'>We address small volume-fraction asymptotic properties of a nonlocal isoperimetric functional with a confinement term, derived as the sharp interface limit of a variational model for self-assembly of diblock copolymers under confinement by nanoparticle inclusion. We introduce a small parameter <inline-formula><tex-math id="M1">\begin{document}$ \eta $\end{document}</tex-math></inline-formula> to represent the size of the domains of the minority phase, and study the resulting droplet regime as <inline-formula><tex-math id="M2">\begin{document}$ \eta\to 0 $\end{document}</tex-math></inline-formula>. By considering confinement densities which are spatially variable and attain a unique nondegenerate maximum, we present a two-scale asymptotic analysis wherein a separation of length scales is captured due to competition between the nonlocal repulsive and confining attractive effects in the energy. A key role is played by a parameter <inline-formula><tex-math id="M3">\begin{document}$ M $\end{document}</tex-math></inline-formula> which gives the total volume of the droplets at order <inline-formula><tex-math id="M4">\begin{document}$ \eta^3 $\end{document}</tex-math></inline-formula> and its relation to existence and non-existence of Gamow's Liquid Drop model on <inline-formula><tex-math id="M5">\begin{document}$ \mathbb{R}^3 $\end{document}</tex-math></inline-formula>. For large values of <inline-formula><tex-math id="M6">\begin{document}$ M $\end{document}</tex-math></inline-formula>, the minority phase splits into several droplets at an intermediate scale <inline-formula><tex-math id="M7">\begin{document}$ \eta^{1/3} $\end{document}</tex-math></inline-formula>, while for small <inline-formula><tex-math id="M8">\begin{document}$ M $\end{document}</tex-math></inline-formula> minimizers form a single droplet converging to the maximum of the confinement density.

Tunable morphologies from solution self-assembly of diblock copolymers under nanoscale confinement

Tunable nanostructure self-assembled from diblock copolymers under nanoscale confinement are investigated by Monte Carlo simulation. In this study, a serial of nanostructures with controllable size or shape are fabricated from self-assembly of hydrophobic or amphiphilic diblock copolymers. The influences of plate surface property, confinement degree, block length ratio of copolymer and solvent property on self-assembled morphologies are systematically examined. The mean-square end-to-end distance and the orientation of polymer chains are calculated, and nanostructure phase diagrams for amphiphilic diblock copolymers are also constructed. This study provides guidance to fabricate tunable nanostructures by solution self-assembly under confinement or in channel.

Preparation of giant vesicles supporting hindered amine on their shells through photo living radical polymerization-induced self-assembly

Microsized giant vesicles supporting a hindered amine on their shells were obtained by the photopolymerization-induced self-assembly of amphiphilic diblock copolymers using the photo nitroxide mediated living radical polymerization (photo NMP) technique. The diblock copolymer consisting of hydrophilic poly(2,2,6,6-tetramethyl-4-piperidyl methacrylate) (PTPMA) and hydrophobic poly(methyl methacrylate-random-2,2,6,6-tetramethyl-4-piperidyl methacrylate), P(MMA-r-TPMA) produced various morphologies depending on the stirring speed during the photo NMP-induced self-assembly, block lengths of the copolymer, and hydrophobicity of the P(MMA-r-TPMA) block chain. A 300-rpm stirring speed during the polymerization provided worm-like vesicles with a long axis of over 100 μm along with small spherical vesicles with a 3-μm diameter. As the stirring speed increased to 600 rpm, the worm-like vesicles changed into spherical vesicles. A further increase in the stirring speed to 900 rpm produced much smaller spherical vesicles. The extension of the block chains also reduced the size of the vesicles. An increase in the hydrophobicity of the hydrophobic block chain varied the morphology of the vesicles. While PTPMA-b-P(MMA-r-TPMA) provided spherical vesicles, PTPMA-b-P(n-propyl methacrylate (PrMA)-r-TPMA) produced deformed vesicles accompanied by a size increase. On the other hand, PTPMA-b-P(n-butyl methacrylate (BuMA)-r-TPMA) produced much smaller vesicles. Furthermore, PTPMA-b-P(MMA-r-BuMA-r-TPMA) (MMA/BuMA = 0.487/0.513) provided a morphology similar to that formed by PTPMA-b-P(PrMA-r-TPMA) due to the negligible difference in the hydrophobic energy between Pr and Me0.487/Bu0.513. These observations indicated that the morphology of the vesicles was controlled by manipulating the hydrophobic energy of the hydrophobic block chain.

Tailoring Mesoporous Silica Nanoparticles and Thin Films: Synthesis, Characterization and Electrochemical Applications

Mesoporous silica materials have played great roles in widespread application areas like adsorption, catalysis, and separation due to their high surface area, large pore volume and tunable pore size and structure. One of the approaches for extending the application of mesoporous silica materials is tailoring their wall with various functional groups. However, the conventional post-grafting method results in lightly dense, heterogeneously distributed and less accessible functional groups. In our work, a new method that leads to dense and uniform functionalization of the wall without clogging of the pores has been employed. The hybrid silica-based materials are fabricated either through diblock copolymer templated sol-gel method or through electro-assisted self-assembly method. In the former case, since the template is self-assembled functional amphiphilic diblock copolymer, the selective removing of the hydrophobic block results in porous and PEO functionalized silica materials. Textural and structural properties of the hybrid porous materials will be presented. Furthermore, their application in the area of Li-ion battery as solid composite polymer electrolytes will be discussed. In the later case, surfactant templated mesoporous silica films have been fabricated on conductive substrates via electro-assisted self-assembly method. Hexagonally well-ordered and vertically oriented mesochannels with a diameter of 3nm are obtained in a large domain across the resulted films. The permeability, morphology and nanostructure of the films will be presented. Figure 1

Large-Area Biomolecule Nanopatterns on Diblock Copolymer Surfaces for Cell Adhesion Studies.

Cell membrane receptors bind to extracellular ligands, triggering intracellular signal transduction pathways that result in specific cell function. Some receptors require to be associated forming clusters for effective signaling. Increasing evidences suggest that receptor clustering is subjected to spatially controlled ligand distribution at the nanoscale. Herein we present a method to produce in an easy, straightforward process, nanopatterns of biomolecular ligands to study ligand–receptor processes involving multivalent interactions. We based our platform in self-assembled diblock copolymers composed of poly(styrene) (PS) and poly(methyl methacrylate) (PMMA) that form PMMA nanodomains in a closed-packed hexagonal arrangement. Upon PMMA selective functionalization, biomolecular nanopatterns over large areas are produced. Nanopattern size and spacing can be controlled by the composition of the block-copolymer selected. Nanopatterns of cell adhesive peptides of different size and spacing were produced, and their impact in integrin receptor clustering and the formation of cell focal adhesions was studied. Cells on ligand nanopatterns showed an increased number of focal contacts, which were, in turn, more matured than those found in cells cultured on randomly presenting ligands. These findings suggest that our methodology is a suitable, versatile tool to study and control receptor clustering signaling and downstream cell behavior through a surface-based ligand patterning technique.

Formation Mechanisms of Porous Particles from Self-Assembly of Amphiphilic Diblock Copolymers inside an Oil-in-Water Emulsion Droplet upon Solvent Evaporation.

The formation mechanisms of porous particles from self-assembly of amphiphilic diblock copolymers inside an oil-in-water emulsion droplet upon evaporation of the organic solvent are investigated based on Monte Carlo simulations for the first time. A morphological diagram of particles is constructed as a function of the surfactant concentration (φ) and the copolymer composition characterized by the volume fraction of the hydrophilic B block ( fB). Particles with various morphologies are predicted. Morphological sequences from non-porosity to closed-porosity to capsules and finally to open-porosity particles are usually observed with increasing φ when fB ≤ 1/2, with the only exception that capsules do not occur when fB = 1/6. Furthermore, the critical φ value for a given morphological transition usually decreases with increasing fB. Micelles are always observed at higher φ regions when fB > 1/2. It is found that the specific surface area falls on almost the same regime for particles with the same kind of morphology, indicating that the morphology of a particle largely determines its specific surface area. The chain stretching varies with the particle morphology. It is the presence of the surfactant that makes the formation of porous particles possible, while when φ > 0, multiple morphological transitions can be induced by changing fB. In the process of organic solvent removal, the value of fB may affect the shape of pores inside the droplet and hence leads to the fB dependence of the morphological sequences. When the solvent evaporation is not too fast, the resulting morphological sequence does not depend on the evaporation rate. Our results are compared with related experiments.

Porous Surface Films With Tunable Morphologies and Hydrophobic Properties Based on Block Copolymer Under the Effects of Thermal Annealing.

The fabrication of porous-structured polymer films with patterned surface structures has recently attracted increased interest within the material science field. In this work, a series of microstructure scale patterned polymer films were obtained via breath figure methods (BF) with hydrophobic surface films based on self-assembled diblock copolymers by atom-transfer radical polymerization (ATRP). The surface characteristics and morphological properties, pore size, roughness, thickness, and wettability of the block copolymer films was studied in response to variation of the hydrophilic co-monomer structures. A significant improvement of the quality and order of the hydrophobic films was observed in response to thermal annealing and a consequent optimization of the assembly process.

Ion-Implantation-Induced Disorder in FePt-C Thin Films

The effects of ion implantation through a mask on the structural and magnetic properties of FePt-C films were investigated. The mask pattern was fabricated using self-assembly of di-block copolymers. For implantation, high- (40 keV for 14N+ and 100 keV for 40Ar+) and low- (7.5 keV for 14N+ and 4.5 keV for 40Ar+) energy 14N+ and 40Ar+ ions were used to modify the structural and magnetic properties of these films. The X-ray diffraction and transport of ions in matter simulations were performed for understanding the structural changes due to the ion implantations. These results revealed the conversion of face-centered tetragonal phase to face-centered cubic (FCC) phase for 40Ar+ ion implantations and increase in inter-planar spacing of FCC FePt (111) planes for 14N+ ion implantations. Magnetic properties were then probed by using a vibrating sample magnetometer (VSM), torque magnetometer, and magnetic force microscopy (MFM). The results from VSM and torque magnetometer showed a change in anisotropy from out-of-plane to in-plane directions for all the implantation cases except for low-energy 40Ar+ ion implantations. The MFM images also showed an absence of stripe domains confirming the above-mentioned effects.

Single gyroid-structured metallic nanoporous spheres fabricated from double gyroid-forming block copolymers via templated electroless plating

Herein, we suggest a methodology for the fabrication of well-defined metallic nanoporous spheres with single gyroid (SG) structure by simply using self-assembled diblock copolymer with double gyroid (DG) structure as a template for electroless plating. Note that owing to the consideration of thermodynamic stability, the self-assembly of diblock copolymers gives rise to a DG phase instead of an SG phase. By controlling the nucleus density for the reduction of Pd ions within the diblock copolymer template, SG-structured Ni can be easily fabricated through the nucleation and growth processes. Consequently, nanoporous Ni spheres with uniform pore sizes and high specific surface areas can be fabricated. Moreover, nanoporous Ni spheres with controlled microscale particle sizes can thus be obtained by controlling the reduction time for the growth of Ni, which enables the feasibility of recyclability via magnetic fields. The combination of structural and morphological characteristics of the fabricated nanoporous Ni spheres make them appealing for use in a wide variety of applications, such as high-efficiency and well selectivity hydrogenation catalysts with recyclability due to their narrow pore size distributions, high specific surface areas, 3D curved surfaces, and controlled microscale particle sizes.

Controllable Self-Assembly of Amphiphilic Tadpole-Shaped Polymer Single-Chain Nanoparticles Prepared through Intrachain Photo-cross-linking.

We report the use of intramolecular cross-linking chemistry as a tool to control the self-assembly of amphiphilic diblock copolymers (di-BCPs). Two amphiphilic di-BCPs of poly( N, N'-dimethylacrylamide)- block-polystyrene (PDMA- b-PS) with photo-cross-linkable cinnamoyl groups in either hydrophobic or hydrophilic blocks were prepared using reversible addition-fragmentation chain transfer polymerization. Intramolecular photo-cross-linking of cinnamoyl groups led to the formation of tadpole-shaped polymer single-chain nanoparticles (SCNPs) consisting of a self-collapsed block as the "head" and an un-cross-linked block as the "tail". When intramolecular photo-cross-linking was carried out in hydrophobic PS blocks, a clear morphological transition from branched cylindrical micelles (for the linear di-BCP) to completely spherical micelles at a dimerization degree of ∼63% was observed. A pattern of morphological transitions from cylindrical micelles to spherical micelles is observed through stepwise downsizing the length of cylindrical micelles when increasing the self-collapse degree of PS blocks, whereas, in case of photo-cross-linking carried out in hydrophilic PDMA blocks, the size of micelles showed a dramatic increase due to the shift of hydrophobic-to-hydrophilic balance. When the cross-linking degree of PDMA blocks reached >60%, tadpole-shaped SCNPs assembled into nonconventional aggregates with a nonsmooth surface. Our results illustrate the impact of chain topologies on the self-assembly outcomes of amphiphilic di-BCPs, which likely opens a door to control the micellar morphologies from just one parent linear di-BCP, rather than resynthesizing BPCs with different volume fractions of the two blocks.

Hybrid line-dot nanopatterns from directed self-assembly of diblock copolymers by trenches.

We demonstrate that the directed self-assembly of AB diblock copolymers by periodic trenches can be used to fabricate large-scale ordered hybrid line-dot nanopatterns in addition to a defect-free dot nanopattern. The formation of line or dot nanopatterns in thin films with proper surface affinities is controlled by the film thickness, which is modulated by a topographic pattern consisting of steps and trenches. Two kinds of line-dot nanopatterns are achieved with cylinder-forming and sphere-forming copolymers, respectively. One kind of hybrid nanopatterns is composed of perpendicularly standing cylinders (dots) on the steps and parallel monolayer cylinders (lines) within the trenches, while the dots of the other kind are replaced by monolayer spheres on the steps. The thermodynamic stability region of target hybrid nanopatterns is identified by constructing two-dimensional phase diagrams with respect to two control parameters of step height and film thickness using self-consistent field theory. Furthermore, a process window of the line-dot nanopatterns is estimated using cell dynamics simulations based on time-dependent Ginzburg-Landau theory, confirming their feasibility in kinetics.

Self-assembly of polyelectrolyte diblock copolymers at monovalent and multivalent counterions.

In this work, the self-assembly behaviors of diblock copolymers consisting of one hydrophobic block and one ionizable polyelectrolyte (PE) block in the presence of monovalent and multivalent counterions are systematically discussed through molecular dynamics simulation. Copolymers are molded as bead-spring chains and the ions are explicitly considered. First, the self-assembled structures of symmetrical block copolymers at different charge fractions are analyzed in detail. Spherical hydrophobic cores are favored by all of the micelles. The effect of counterion valence is much more noticeable at high values of charge fraction. When the PE blocks are fully charged, the presence of multivalent counterions preferably provokes the formation of macroscopic structures. A precipitant spherical micelle is generated in the presence of divalent counterions. Special shapes of coronas are created in the presence of trivalent ions, and a remarkable one dimensional macroscopic cylindrical aggregation of micelles forms; the whole assembly is not typical core-shell micelles, but rather a cylinder with alternating spherical micelles arranged perpendicular to the cylinder axis. The self-assemblies with different lengths of fully charged PE blocks are also discussed. Surprisingly, in the presence of divalent counterions, two dimensional in-plane macroscopic aggregation of micelles is realized when the proportion of PE blocks is larger than 1/2; the self-assembled spherical micelles locate approximately in the same plane to form an inter-linked network. One dimensional aggregation of micelles in the presence of trivalent counterions is maintained with an increased proportion of the PE block. Owing to the dominant intra- and inter-condensation of divalent and trivalent counterions, respectively, two and one dimensional macroscopic aggregation of the micelles is achieved. Our findings indicate that varying the counterion valence is a powerful mechanism to tune the properties of self-assemblies, and the bridging effect introduced by multivalent counterions is the key parameter for the aggregation of the micelles.

Hybrid patterns from directed self-assembly of diblock copolymers by chemical patterns.

The surface affinity is a critical factor for controlling the formation of monolayer nanostructures in block copolymer thin films. In general, strong surface affinity tends to induce the formation of domains with low spontaneous curvature. Abiding by this principle, we propose a facile chemoepitaxial scheme for producing large-scale ordered hybrid patterns by the directed self-assembly of diblock copolymers. The guiding chemical pattern is designed as periodic stripes with alternately changing surface affinities. As a consequence, two different geometries of domains are formed on the stripes with different affinities. The self-assembly process of block copolymers guided by the stripe patterns is investigated using cell dynamics simulations based on time-dependent Ginzburg-Landau theory, and the kinetic stability diagram is estimated. Hybrid patterns are successfully achieved with both cylinder-forming and sphere-forming diblock copolymers. In the cylinder-forming system, the major hybrid pattern exhibiting a considerable stability window is composed of parallel cylinders and perforated lamellae, while it is composed of monolayer spheres and parallel cylinders in the other system. Encouragingly, the chemoepitaxial method is valid till the period of the guiding pattern is a large multiple of the domain spacing. The chemoepitaxial scheme demonstrated in this work serves as a nice supplement to the graphoepitaxial one proposed in our previous work.

Low molecular weight PEG-PLGA polymers provide a superior matrix for conjugated polymer nanoparticles in terms of physicochemical properties, biocompatibility and optical/photoacoustic performance.

The near-infrared absorbing conjugated polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) has been investigated as a contrast agent for optical and photoacoustic imaging. Lipophilic π-conjugated polymers can be efficiently encapsulated within self-assembling diblock copolymer poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG-PLGA) nanoparticles, although the effect of variations in PEG and PLGA chain lengths on nanoparticle properties, performance and biocompatibility have not yet been investigated. In this study, PEG-PLGA with different block lengths (PEG2kDa-PLGA4kDa, PEG2kDa-PLGA15kDa and PEG5kDa-PLGA55kDa) were used to encapsulate PCPDTBT. Nanoparticle sizes were smallest (<100 nm) when using PEG2kDa-PLGA4kDa, with <5% PCPDTBT content and a reduction in the total solids concentration of the organic phase. All PEG-PLGA nanoparticles were colloidally stable in water and serum-supplemented cell culture medium over 24 h at 37 °C, with slight evidence of protein surface adsorption. PEG2kDa-PLGA4kDa systems showed a threefold lower cytotoxicity (IC50 value) than the other two systems. Haemolytic activity was <2.5% for all systems and no platelet aggregation or inhibition of ADP-induced platelet aggregation was observed. Encapsulation of PCPDTBT within a PEG-PLGA matrix shifted fluorescence emission towards red wavelengths (760 nm in THF vs. 840 nm in nanoparticles) and reduced the quantum yield by 30-70-fold compared to THF. Nonetheless, PCPDTBT:PEG2kDa-PLGA4kDa systems had a marginally higher quantum yield and signal-to-background ratio in a phantom mouse compared with PEG2kDa-PLGA15kDa and PEG5kDa-PLGA55kDa systems. As a photoacoustic imaging probe, PCPDTBT:PEG2kDa-PLGA4kDa systems also showed a higher photoacoustic amplitude compared to higher molecular weight PEG-PLGA systems. Overall, the low molecular weight PEG2kDa-PLGA4kDa nanoparticle systems conferred the benefits of smaller sizes, reduced cytotoxicity and enhanced imaging performance compared to higher molecular weight matrix polymers.

Supramolecular Modification of ABC Triblock Terpolymers in Confinement Assembly.

The self-assembly of AB diblock copolymers in three-dimensional (3D) soft confinement of nanoemulsions has recently become an attractive bottom up route to prepare colloids with controlled inner morphologies. In that regard, ABC triblock terpolymers show a more complex morphological behavior and could thus give access to extensive libraries of multicompartment microparticles. However, knowledge about their self-assembly in confinement is very limited thus far. Here, we investigated the confinement assembly of polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT) triblock terpolymers in nanoemulsion droplets. Depending on the block weight fractions, we found spherical microparticles with concentric lamella–sphere (ls) morphology, i.e., PS/PT lamella intercalated with P4VP spheres, or unusual conic microparticles with concentric lamella–cylinder (lc) morphology. We further described how these morphologies can be modified through supramolecular additives, such as hydrogen bond (HB) and halogen bond (XB) donors. We bound donors to the 4VP units and analyzed changes in the morphology depending on the binding strength and the length of the alkyl tail. The interaction with the weaker donors resulted in an increase in volume of the P4VP domains, which depends upon the molar fraction of the added donor. For donors with a high tendency of intermolecular packing, a visible change in the morphology was observed. This ultimately caused a shape change in the microparticle. Knowledge about how to control inner morphologies of multicompartment microparticles could lead to novel carbon supports for catalysis, nanoparticles with unprecedented topologies, and potentially, reversible shape changes by light actuation.

Self-Assembled Micellar Nanosensor toward pH with high photo-stability and its application in living cells

Based on photo-induced electron transfer, 1,8-naphthalic anhydride-based organic molecular fluorescent pH-sensor (1) was designed and synthesized. Hydrophobic, fluorescent hybrid nanosensor (1-PS35-b-PAA30) encapsulated with the hydrophobic pH responsive fluorophore for sensing intracellular pH has been fabricated based on the self-assembly of amphiphilic diblock copolymer PS35-b-PAA30 and 1. The as-synthesized 1-PS35-b-PAA30 sensor exhibits excellent photo-stability, good anti-disturbance ability, and enhanced fluorescence intensity under acidic environment with respect to the corresponding free dye in highly polar aqueous system because of the encapsulation of 1 inside nanoparticle cores with weak polarity environment. The fluorescence intensity of 1-PS35-b-PAA30 is enhanced by 7.3-fold upon changing from base (pH = 9.0) to acid (pH = 4) in aqueous system, which can exactly meet the physiological pH range in cells. Moreover, its linear fluorescent response from pH 5.2 to 7.4 makes this sensor suitable for the practical tracking of pH fluctuation in live cells. The fluorescence imaging and TEM experiments indicated that the sensor permeated into cells and could not be observed because of aggregation in acidic condition.

Toward Uniform Nanofibers with a π-Conjugated Core: Optimizing the “Living” Crystallization-Driven Self-Assembly of Diblock Copolymers with a Poly(3-octylthiophene) Core-Forming Block

Crystalline poly(3-alkylthiophene) (P3AT) nanofibers are promising materials for a myriad of device applications, but nanofiber length control and colloidal stability are difficult to achieve. We report an in-depth study of the solution self-assembly of regioregular poly(3-octylthiophene)-b-poly(dimethylsiloxane) (P3OT-b-PDMS) diblock copolymers with a crystallizable π-conjugated core-forming block. Use of the “living” crystallization-driven self-assembly (CDSA) seeded-growth method in solvents selective for PDMS allowed access to relatively low length dispersity, colloidally stable P3OT-b-PDMS fiber-like micelles with a crystalline, tape-like P3OT core, a PDMS corona, and lengths up to ca. 600 nm under optimized conditions. Significantly, the presence of a small percentage of common solvent and the use of slightly elevated temperature (35 °C) were found to enhance the length control. Analogous studies for P3OT-b-PS (PS = polystyrene) suggest that solvent composition and temperature represent key paramete...

Synthesis of density-multiplied Pt-NP arrays and their application in fuel cell by self-assembly of di-block copolymer

Self-assembly of di-blcok copolymers (di-BCs) with precise control on morphologies and structures of nanomaterials makes it a promising technology for catalyst preparation. However, applications of the BC-synthesized Pt nanoparticles (NPs) on fuel cell have less been discussed. The major challenge may be the difficulty in achieving high-density nanopatterns which require a low degree of polymerization but a high effective segment-segment interaction parameter of the BC templates. As a resolution, sequentially double- or triple-layered BC route provides a new density-increased idea of harnessing these materials. In present work, monolayer of ordered and high-dispersed Pt-NP arrays with a density 27-folded has been achieved by the multiple di-BC routes consisted of identical self-assembly and plasma-cleaning processes. The multiplication has been proved to be equivalent to the duplication and oriented translation of the initial Pt-NP arrays, which provides not only a well-defined approach to control the spacing precisely, but also a bottom-up process to synthesize hexagonal-arranged arrays with predicable densities. Electrochemistry shows that the density multiplication has no negative effects on the Pt utilization of the monolayer arrays, and a remarkable ECSA value of ∼114.5 m2 g−1 is found. Further characterization of the monolayer arrays as cathodic catalysts for PEMFC reveals that, neither the ohmic losses nor the mass-transport losses are enhanced after the density multiplication, and the power density of the PEMFC assembled here is significantly higher than that using commercial Pt/C catalysts. All the results demonstrate that the multiple di-BC approach has great potential in preparation of BC-synthesized Pt-NP arrays for fuel cell applications.