Diversity of Nanostructured Self-Assemblies from a pH-Responsive ABC Terpolymer in Aqueous Media

Nanoscale polymer discs, toroids and platelets: a survey of their syntheses and potential applications

Polymer self-assembly has become a reliable and versatile workhorse to produce polymeric nanomaterials. With appropriate polymer design and monomer selection, polymers can assemble into shapes and morphologies beyond well-studied spherical and cylindrical micellar structures. Steadfast access to anisotropic polymer nanoparticles has meant that the fabrication and application of 2D soft matter has received increasing attention in recent years. In this review, we focus on nanoscale polymer discs, toroids, and platelets: three morphologies that are often interrelated and made from similar starting materials or common intermediates. For each morphology, we illustrate design rules, and group and discuss commonly used self-assembly strategies. We further highlight polymer compositions, fundamental principles and self-assembly conditions that enable precision in bottom-up fabrication strategies. Finally, we summarise potential applications of such nanomaterials, especially in the context of biomedical research and template chemistry and elaborate on future endeavours in this space.

Well-Defined Thermo- and pH-Responsive Double Hydrophilic Graft Copolymer Bearing a Pyridine-Containing Backbone

Graft copolymers have extensive applications in material science because of their tunable composition of backbone and side chains and diverse morphologies of aggregates. Recent studies mainly focused on the amphiphilic...

Recent trends in pH/thermo-responsive self-assembling hydrogels: from polyions to peptide-based polymeric gelators

In this article, we highlight some recent developments in "smart" physical hydrogels achieved by self-assembling of block type macromolecules. More precisely we focus on two interesting types of gelators namely conventional ionic (or ionogenic) block copolymers and peptide-based polymers having as a common feature their responsiveness to pH and/or temperature which are the main triggers used for potential biomedical applications. Taking advantage of the immense skills of conventional block copolymer hydrogelators, namely macromolecular design, self-assembling mechanism, gel rheological properties, responsiveness to various triggers and innovative applications, the development of novel self-assembling gelators, integrating the new knowledge emerging from the peptide-based systems, opens new horizons towards bio-inspired technologies.

Design of a C-b-(A-co-B)-b-C telechelic polyampholyte pH-responsive gelator

We report the synthesis and the pH dependent structural and rheological properties of a telechelic polyampholyte associative polymer, composed of a random polyampholyte central block, end-capped by shorter hydrophobic blocks [C-b-(A-co-B)-b-C block/random terpolymer type].

Diverse nanostructures and gel behaviours contained in a thermo- and dual-pH-sensitive ABC (PNIPAM–PAA–P4VP) terpolymer in an aqueous solution

PNIPAM-b-PAA-b-P4VP (NAV), a thermo- and dual-pH-sensitive ABC triblock copolymer, was synthesized via sequential reversible addition–fragmentation chain transfer (RAFT) polymerization and subsequent hydrolysis.

Asymmetric vesicle constructed by AB/CB diblock copolymer mixture and its behavior: a Monte Carlo study

Asymmetric vesicles constructed from AB/CB diblock copolymer mixture in a selective solvent for A and C blocks are studied using Monte Carlo simulation. The effects of the mixed ratio of the two diblock copolymers, the solution pH, and the hydrophilic chain length on the distributions of hydrophilic blocks on the surfaces of asymmetric vesicles are studied systematically. The simulation results show that asymmetric vesicle, in which the inner and outer surfaces are constructed from different hydrophilic blocks, can be obtained from AB/CB diblock copolymer mixture. The formation of ABC or CBA three-layer asymmetric vesicle depends on the composition of the mixture, the chain length of hydrophilic block, and the solution pH. The hydrophilic block with the same charge (induced by the solution pH), or longer chain length, or lower content in the mixture is more likely to distribute on the outer surface of the vesicle. Moreover, the transition from ABC to CBA three-layer asymmetric vesicle in which blocks C are charged can occur by adjusting the composition of the mixture. On the other hand, the investigations of the interfacial energy density of asymmetric vesicles elucidate the distribution regularity of hydrophilic blocks. When the hydrophilic chain lengths are equal, the difference between the outer and inner interfacial energies is the main factor that determines the asymmetric vesicle structures; that is, the distributions of different hydrophilic blocks on asymmetric vesicles always tend to gain the largest difference between the outer and inner interfacial energies. However, when the hydrophilic chain lengths are different, the chain conformational entropy becomes the main driving force for determining the distribution of hydrophilic blocks on asymmetric vesicles.

Supramolecular electron donor–acceptor complexes formed by perylene diimide derivative and conjugated phenazines

The nanostructure and binding mode of the perylene diimide–phenazine complex can be modulated by the phenazine derivative substituents.

Temperature-induced self-assembly of triple-responsive triblock copolymers in aqueous solutions

A series of triple-thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (PNPAM, A), poly(methoxydiethylene glycol acrylate) (PMDEGA, B), and poly(N-ethylacrylamide) (PNEAM, C) was synthesized by sequential reversible addition-fragmentation chain transfer polymerizations. Polymers of differing block sequences, ABC, BAC, and ACB, with increasing phase transition temperatures in the order A < B < C were prepared. Their aggregation behavior in dilute aqueous solution was investigated using dynamic light scattering, turbidimetry, and NMR spectroscopy. The self-organization of such polymers was found to dependent strongly on the block sequence. While polymers with a terminal low-LCST (lower critical solution temperature) block undergo aggregation above the first phase transition temperature at 20-25 °C, triblock copolymers with the low-LCST block in the middle show aggregation only above the second phase transition. The collapse of the middle block is not sufficient to induce aggregation but produces instead stable, unimolecular micelles with a collapsed middle block, as supported by NMR and fluorescence probe data. Continued heating of all copolymers led to two additional thermal transitions at 40-55 and 70-80 °C, which could be correlated to the phase transitions of the B and C blocks, respectively. All polymers show a high tendency for cluster formation, once aggregation is induced. The carrier abilities of the triple responsive triblock copolymers for hydrophobic agents were probed with the solvatochromic fluorescence dye Nile Red. With passing through the first thermal transition, the block copolymers are capable of solubilizing Nile Red. In the case of block copolymers with sequences ABC or ACB, which bear the low-LCST block at one terminus, notable amounts of dye are solubilized already at this stage. In contrast, the hydrophobic probe is much less efficiently incorporated by the BAC triblock copolymer, which forms unimolecular micelles. Only after the collapse of the B block, when reaching the second phase transition at about 45 °C, does aggregation occur and solubilization becomes efficient. In the case of ABC and ACB polymers, the hydrophobic probe seems to partition between the originally collapsed A chains and the additional hydrophobic chains formed after the collapse of the less hydrophobic B block.

pH responsive self assemblies from an A(n)-core-(B-b-C)n heteroarm star block terpolymer bearing oppositely charged segments

We report on the association capability of a novel multisegmented, multiarm star terpolymer to form a diversity of pH-responsive amphoteric micellar nanostructured self-assemblies.

Designing a thermo-switchable channel for nanofluidic controllable transportation

Owing to the important roles of chemical gates in biological systems, the biomimetic design of artificial switchable nanodevices has been attracting tremendous interest. Here, we design a cylindrical thermo-sensitive channel, in which nanofliudic transport properties can be controlled by manipulating environmental temperature. The switchable channel is formed by a polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS)-like triblock copolymer brush whose conformation and phase behavior are dependent on temperature. With the increase of temperature, the designed channel exhibits "close→open→close" behavior, which can serve as a kind of excellent switchable nanodevice for nanofluidic controllable transportation.

Dynamic assembly of block-copolymers

Block copolymers (BCs) are well-known building blocks for the creation of a large variety of nanostructured materials or objects through a dynamic assembly stage which can be either autonomous or guided by an external force. Today's nanotechnologies require sharp control of the overall architecture from the nanoscale to the macroscale. BCs enable this dynamic assembly through all the scales, from few aggregated polymer chains to large bulk polymer materials. Since the discovery of controlled methods to polymerize monomers with different functionalities, a broad diversity of BCs exists, giving rise to many different nanoobjects and nanostructured materials. This chapter will explore the potentialities of block copolymer chains to be assembled through dynamic interactions either in solution or in bulk.

New micellar morphologies from amphiphilic block copolymers: disks, toroids and bicontinuous micelles

This review discusses recent advances of the self-assembly of amphiphilic block copolymers into novel micellar architectures in dilute solutions. The formation of multi-compartment, disk-like, toroidal and bicontinuous micelles and the macromolecular architectures that give rise to these morphologies are reviewed and discussed.

Dynamic multicompartment-core micelles in aqueous media

We investigate micellar aggregates of amphiphilic block terpolymers, polybutadiene-block-poly(2-vinyl pyridine)-block-poly(methacrylic acid) (PB800P2VP190PMAA550) and their quaternized analogues polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB800P2VPq190PMAA550) in aqueous solution using light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM). At high pH, PB800P2VP190PMAA550 forms core--shell--corona micelles with a hydrodynamic radius Rh approximately 100 nm and a continuous shell of P2VP. However, at pH 4 partial intramicellar interpolyelectrolyte complex (im-IPEC) formation between P2VP and PMAA results in a patchy, collapsed shell. This is far more pronounced for the quaternized analogue, PB800P2VPq190PMAA550, which forms aggregates of similar size, also exhibiting a noncontinuous, patchy shell. Here, these im-IPECs of the positively charged P2VPq and the partially negatively charged PMAA are present over the whole investigated pH range (4-10). We further demonstrate that size and charge of the corona can be tuned through the block terpolymer composition, in particular, the ratio between P2VPq and PMAA. These micelles are dynamic and able to react to changes in pH or salinity in terms of corona diameter and aggregation number.

pH-triggered block copolymer micelle-to-micelle phase transition

We present a first experimental observation and provide a theoretical interpretation of a pH-induced micelle-to-micelle phase transition in aqueous solutions of spherical block copolymer micelles with polybasic coronas. Dynamic light scattering, static light scattering, and atomic force microscopy confirm sharp changes in micellar hydrodynamic size and aggregation number occurring in a narrow pH range, DeltapH<0.1. In agreement with theory, zeta potential measurements indicated an abrupt change in ionization of polymer chains in the micellar corona at the transition pH.

Responsive brush layers: from tailored gradients to reversibly assembled nanoparticles

We present a condensed overview of the recent developments of novel responsive thin polymer films from end-tethered chains (polymer brushes), which are different from conventional, uniform, and planar brush layers. For this discussion, we selected two types of recently introduced surface layers: binary brush layers with variable chemical composition forming a controllable gradient of composition and properties in a selected direction and brush layers either grafted directly to inorganic nanoparticles to form hybrid core-shell structures or combined with inorganic nanoparticles embedded into this layer. Unlike traditional brush layers, such a design brings a novel set of responsive surface properties allowing for capillary-driven microfluidic motion, combinatorial-like multiplexing response, reversible aggregation and dis-assembly of nanoparticles, fabrication of ultrahydrophobic coatings, and switchable mass transport across interfaces.