Block copolymer strands with internal microphase separation structure via self-assembly at the air-water interface

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.

pH-Induced evolution of surface patterns in micelles assembled from dirhamnolipids: dissipative particle dynamics simulation

Dissipative particle dynamics (DPD) simulation is used to study the effect of pH on the morphological transition in micelles assembled from dirhamnolipids (diRLs), and analyze the pH-driven mechanism and influence factors of micellar surface patterns.

Evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer techniques

Polymeric biomaterials are of specific relevance in medical and pharmaceutical applications due to their wide range of tailorable properties and functionalities. The knowledge about interactions of biomaterials with their biological environment is of crucial importance for developing highly sophisticated medical devices. To achieve optimal in vivo performance, a description at the molecular level is required to gain better understanding about the surface of synthetic materials for tailoring their properties. This is still challenging and requires the comprehensive characterization of morphological structures, polymer chain arrangements and degradation behaviour. The review discusses selected aspects for evaluating polymeric biomaterial-environment interfaces by Langmuir monolayer methods as powerful techniques for studying interfacial properties, such as morphological and degradation processes. The combination of spectroscopic, microscopic and scattering methods with the Langmuir techniques adapted to polymers can substantially improve the understanding of their in vivo behaviour.

Redox-Responsive Multicompartment Vesicles of Ferrocene-Containing Triblock Terpolymer Exhibiting On-Off Switchable Pores

Multicompartment vesicles of ferrocene-containing triblock terpolymer containing on-off switchable pores in the vesicular membrane are prepared by seeded RAFT polymerization. In these multicompartment vesicles, the incompatible solvophobic poly(4-vinylbenzyl ferrocenecarboxylate) (PVFC) and poly(benzyl methacrylate) (PBzMA) blocks form the porous phase-segregated membrane and the solvophilic poly[2-(dimethylamino) ethyl methacrylate] block locates at the inner and outer sides of the membrane. These porous multicompartment vesicles are redox-responsive and the membrane pores can be on-off switched through redox triggering. These porous multicompartment vesicles are deemed to be new nanoassembly of ABC triblock terpolymer and are anticipated to be a smart host to load and release guests.

Multicompartment morphologies self-assembled from fluorinated ABC triblock terpolymers: the effects of flexible and rigid hydrophobic moieties

Two kinds of fluorinated ABC triblock terpolymers have been prepared by oxyanion-initiated polymerization, and the effects of flexible and rigid polyolefin moieties on their self-assembled multicompartment morphologies were investigated.

Influence of gold species (AuCl4−and AuCl2−) on self-assembly of PS-b-P2VP in solutions and morphology of composite thin films fabricated at the air/liquid interfaces

A new and facile approach was developed to fabricate functional composite films of block copolymers at the air/liquid interface through a self-emulsification, self-assembly and adsorption process.

Doubly thermo-responsive nanoparticles constructed with two diblock copolymers prepared through the two macro-RAFT agents co-mediated dispersion RAFT polymerization

Doubly thermo-responsive nanoparticles constructed with two diblock copolymers were prepared, and the nanoparticles exhibit a two-step phase-transition with increasing temperature.

Synthesis of multicompartment nanoparticles of a triblock terpolymer by seeded RAFT polymerization

Seeded RAFT polymerization based on AB diblock copolymer nanoparticles is performed, and multicompartment nanoparticles of ABC triblock terpolymer are prepared.

A new and facile way to fabricate catalytically active block copolymer/Au nanoparticle multilayer thin films at the air/liquid interface

A catalytically active multilayer film of PB-b-P2VP doped with Au nanoparticles was fabricated through liquid/liquid interfacial mass transfer, self-assembly in an aqueous phase and adsorption at the air/liquid interface.

Preparation of cylindrical multi-compartment micelles by the hierarchical self-assembly of ABC triblock polymer in solution

Amphiphilic linear ABC triblock copolymer PnBA₂₈-b-PS₃₇-b-P2VP₇₃ was prepared by the RAFT method. Spherical patchy micelles and cylindrical MCMs were formed in different steps of its two-step hierarchical self-assembly in selected solvents.

A new strategy to fabricate composite thin films with tunable micro- and nanostructures via self-assembly of block copolymers

A new and facile strategy to fabricate composite thin films with tunable morphologies at the air/liquid interface is first reported, paving a new way for the generation of composite films in nanotechnology applications.

Synthesis of Multicompartment Nanoparticles of Block Copolymer through Two Macro-RAFT Agents Co-Mediated Dispersion Polymerization

A new and efficient strategy to synthesize multicompartment block copolymer nanoparticles (MCBNs) by two macro-RAFT agents comediated dispersion polymerization is proposed. By simultaneously employing two macro-RAFT agents in dispersion RAFT polymerization, one-pot synthesis of well-defined MCBNs constructed with two diblock copolymers of poly(tert-butyl methyl acrylate)-block-polystyrene (PtBMA-b-PS) and poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-polystyrene (PVEA-b-PS) is achieved. These MCBNs contain a PS core and discrete PVEA and/or PtBMA nodules on the PS core. By changing the ratio of the two macro-RAFT agents or the polymerization degree of the solvophobic block in the two diblock copolymer mixture, the structure of MCBNs can be tuned. Our strategy overcomes the inconvenience and difficulty in synthesis of MCBNs, and it introduces a valid way to prepare well-defined MCBNs constructed with two or more diblock copolymers.

Aggregation behavior of the blends of PS-b-PEO-b-PS and PS-b-PMMA at the air/water interface

Upon compression, large close-packed aggregates in the mixed LB films split into small uniform ones. Hysteresis degree can be interpreted with chain entanglement and block mobility.

A new strategy to prepare thermo-responsive multicompartment nanoparticles constructed with two diblock copolymers

Thermo-responsive multicompartment nanoparticles containing a PS core, discrete PVEA nodules on the PS core and a PDMAEMA corona are prepared.

Effect of selective solvent on the aggregate behavior of the mixed Langmuir monolayers of PS-b-PEO and PS-b-PMMA

An interesting way to control morphology evolution in the mixed LB films was performed by mainly using a selective spreading solvent. Furthermore, a peculiar hysteresis phenomenon in the polymeric Langmuir monolayers is reported.

Polythiophene-gold nanoparticle hybrid systems: Langmuir-Blodgett assembly of nanostructured films

In this work, we demonstrate a simple method of synthesizing nanoscale polythiophene-gold nanoparticle (AuNP) hybrid systems assembled by the Langmuir-Blodgett (LB) method. Regio-regular poly(3-(2-methoxyethoxy)ethoxymethyl)thiophene-2,5-diyl (PMEEMT) and poly(3-dodecylthiophene) (PDDT) were employed as the polymeric constituents. The presence of PDDT improved the amphiphilicity of PMEEMT by addressing the phase separation that occurred due to convective hydrodynamic instability on the substrate. 4 layer stacks of 90% and 99% PMEEMT films exhibited uniform film structure with a significant reduction in phase separation. A detailed mechanism for minimization of the surface effect has been proposed based on the interaction of polythiophenes with the substrate. For the first time, an ex situ approach has been adopted to incorporate AuNPs into LB films without affecting the film morphology and uniformity. The incorporation of AuNPs into the polythiophene matrix, aided by the affinity of sulphur for gold, was strongly dependent on the molecular arrangement of the matrix, which in turn depended on the composition of the matrix. The hybrid polythiophene films exhibited enhanced conductivity and can be applied in sensors, photovoltaics and memory devices.

Strands, networks, and continents from polystyrene dewetting at the air-water interface: implications for amphiphilic block copolymer self-assembly

We demonstrate that nanoscale aggregates similar to those formed via amphiphilic block copolymer self-assembly at the air-water interface, including strands, networks, and continents, can be generated by the simple spreading of PS homopolymer solutions on water. Two different PS homopolymers of different molecular weight (PS-405k, M(n) = 405 000 g mol(-1) and PS-33k, M(n) = 33 000 g mol(-1)) are spread at the air-water interface at various spreading concentrations ranging from 0.25 to 3.0 mg/mL. Aggregate formation is driven by PS dewetting from water as the spreading solvent evaporates. We propose that a high spreading concentration or a high molecular weight lead to chain entanglements that restrict macromolecular mobility in the solution, enabling the kinetic trapping of nanostructures associated with early and intermediate stages of PS dewetting. Comparison of PS-405k with a mainly hydrophobic PS-b-PEO block copolymer of similar molecular weight (PSEO-392k, M(n) = 392 000 g mol(-1), 2.0 wt % PEO) allows the effect of a relatively short surface active block on aggregate formation to be investigated. We show that whereas the PEO block is not a required component for the formation of strands and other nonglobular aggregates, it does increase the number of these aggregates at a given spreading concentration and decreases the minimum spreading concentration at which these aggregates are observed, along with decreasing the dimensions and polydispersity of specific surface features. The results provide supporting evidence for the role of PS dewetting in the generation of multiple PS-b-PEO aggregate morphologies at the air-water interface, as originally described in earlier paper from our group.

Nanostrand formation of block copolymers at the air/water interface

Langmuir-Blodgett monolayers consisting of a network of nanostrands have occasionally been reported in the literature, but are often coexistent with other morphologies, which is not useful for potential applications. With the use of PS-P4VP/PDP, a polystyrene-poly(4-vinyl pyridine) diblock copolymer of 12 mol % VP content mixed with 3-pentadecylphenol, it is shown that the disordered nanostrand network morphology can be obtained reproducibly and uniformly over large surface areas by spreading chloroform solutions of relatively high copolymer concentration. Use of a more slowly evaporating spreading solvent, 1,1,2,2-tetrachloroethane, and a low subphase temperature, 8-9 °C, results in much more densely aligned nanostrands. Poorly spreading solvents such as nitrobenzene produce the well-known fingerprint pattern often observed in spin- or dip-coated thin films of block copolymers. A mechanism for nanostrand network formation is proposed that involves the momentary formation of a fingerprint morphology in spreading drops followed by its breakup at the level of the mobile P4VP/PDP stripes as spreading continues, leaving P4VP-anchored PS nanostrands floating on the water surface.

Temperature tunable micellization of polystyrene-block-poly(2-vinylpyridine) at Si-ionic liquid interface

Highly ordered and stable micelles formed from both symmetric and asymmetric block copolymers of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) at the Si-ionic liquid (IL) interface have been investigated by scanning force microscopy (SFM) and transmission electron microscopy (TEM). The 1-butyl-3-methylimidazolium trifluoromethanesulfonate IL, a selective and temperature-tunable solvent for the P2VP block, was used and gave rise to block copolymer micelles having different morphologies that strongly depended on the annealing temperature. The effects of film thickness, molecular weight of block copolymers, and experimental conditions, such as preannealing, rinsing, and substrate properties, on the morphologies of block copolymer micelles were also studied. In addition, spherical micelles consisting of PS core and P2VP shell could also be obtained by core-corona inversion by annealing the as-coated micellar film in the IL at high temperatures. The possible mechanism for micelle formation is discussed.

Patterning block copolymer aggregates via Langmuir-Blodgett transfer to microcontact-printed substrates

We demonstrate a new strategy for producing hierarchical polymer nanostructures, which combines nanoscale self-assembly of amphiphilic block copolymers at the air-water interface with microscale templated assembly of the resulting aggregates on chemically patterned substrates. Aggregates are formed via interfacial self-assembly of 141k polystyrene-b-poly(ethylene oxide) (PS-b-PEO, MW = 141k, 11.4 wt % PEO) or a blend of 185k PS-b-PEO (MW = 185k, 18.9 wt % PEO) and PS-coated CdS nanoparticles to form strandlike copolymer or copolymer-nanoparticle aggregates. Using Langmuir-Blodgett (LB) techniques, the aggregates are then transferred to patterned substrates possessing alternating hydrophilic/hydrophobic stripes, obtained by microcontact printing octadecyltrichlorosilane (OTS) on glass. The aggregates are transferred under various conditions of surface pressure, orientation of the patterned substrate, and withdrawal speed. Templated assembly of aggregates into the hydrophilic substrate domains is achieved when the hydrophilic/hydrophobic stripes are oriented perpendicular to the water surface during LB transfer; this is explained by surface energy heterogeneities along the subphase-substrate contact line, which induce selective dewetting and concomitant monolayer rearrangement at the drying front. In contrast, parallel orientation of stripes results in nonselective transfer of the monolayer without registration to the underlying surface pattern. By studying the effect of surface pressure, we show that packing constraints imposed by compression of aggregates to high surface densities prevent the formation of patterned LB films that match the established periodicity of the OTS-patterned glass. As well, it is shown that efficient transfer of aggregates to the patterned glass requires slower substrate withdrawal speeds compared to transfer to unpatterned hydrophilic glass.