Design and application of nanoscale actuators using block-copolymers

Block copolymers are versatile designer macromolecules where a “bottom-up” approach can be used to create tailored materials with unique properties. These simple building blocks allow us to create actuators that convert energy from a variety of sources (such as chemical, electrical and heat) into mechanical energy. In this review we will discuss the advantages and potential pitfalls of using block copolymers to create actuators, putting emphasis on the ways in which these materials can be synthesised and processed. Particular attention will be given to the theoretical background of microphase separation and how the phase diagram can be used during the design process of actuators. Different types of actuation will be discussed throughout

Diels–Alder cycloaddition and RAFT chain end functionality::an elegant route to fullerene end-capped polymers with control over molecular mass and architecture

Fullerene C60 functionalised polymers (FFPs) have found numerous applications from photovoltaic devices to materials for photodynamic therapy. Polymer end-capping is one way to fabricate FFPs since it provides enhanced control over the macromolecular architecture and composition. This paper reports, for the first time, a facile, metal catalyst-free approach to FFPs where polymers, generated by reversible-addition fragmentation chain transfer (RAFT) polymerisation, were coupled to a fullerene derivative through chain-end functionality, provided by the chain transfer agent without further modification. Two routes to a fullerene derivative were compared – based on the Prato reaction and Diels–Alder cycloaddition. The Diels–Alder route exclusively yielded the mono-addition product, whereas the Prato route resulted in a mixture of mono- and diadducts which required further separation. This elegant combination of well-defined RAFT polymerisation and precise Diels–Alder addition allowed one to obtain fullerene end-capped polymers within a wide range of molecular masses (from 5000 to 50 000 g mol−1)

Microporous frameworks based on adamantane building blocks:Synthesis, porosity, selective adsorption and functional application

Two microporous organic frameworks based on adamantane (hereafter denoted as MF-Ads) were fabricated through Sonogashira-Hagihara coupling polycondensation of aryl halides and alkynes. Results show that both types of MF-Ad networks had similar porous properties and exhibited excellent CO2 uptake capacity (72.5 cm3 g−1) and CO2/N2 selectivity (59.1) at 273 K and 1.0 bar. Taking advantage of the superhydrophobic wettability of the resulting MF-Ad networks, wire mesh scaffolds were used to fabricate superhydrophobic films with polydimethylsiloxane (PDMS) acting as a binder. These films displayed excellent instant hydrocarbon/water separation efficiency (up to 99.6%), which was maintained at a constant level after five repeated cycles. This work provides a novel insight into the fabrication of microporous organic frameworks and extends their applicability to carbon capture and absorption of hazardous organic pollutants

Binary shape-stabilized phase change materials based on poly(ethylene glycol)/polyurethane composite with dual-phase transition

Novel binary shape-stabilized composite phase change materials (CPCMs) have been successfully prepared using a crosslinked polyurethane (PU) copolymer with a solid–solid phase transition as the supporting framework for loading additional (‘free’) poly(ethylene glycol) (PEG). The PU copolymer was synthesized by a two-step method using 2-hydroxypropyl-β-cyclodextrin (Hp-β-CD) as a chain extender and PEG as a soft segment. The composition, morphology, phase transition behavior and thermal properties of the prepared CPCMs have been elucidated by a wide range of techniques. Investigation of FTIR spectra and SEM images reveal that the ‘free’ PEG and the PU copolymer network within the CPCMs have good compatibility and high affinity due to the noncovalent interactions. Polarized light optical microscopy shows that the CPCMs produce smaller spherulites than pristine PEG, and homogeneous nucleation was prevalent during the crystallization process. Due to the dual-phase transition of the CPCMs (the solid–liquid phase transition of ‘free’ PEG and solid–solid phase transition of the PU matrix) occurring within the same, narrow temperature window, the CPCMs have far higher heat storage density compared with that of traditional shape-stabilized PCMs with the same ‘free’ PEG content. Importantly, thermal cycling and thermogravimetric analyses show that the CPCMs have good reusability and excellent thermal stability for potential use in thermoregulation or energy storage applications

Design, synthesis and RAFT polymerisation of a quinoline-based monomer for use in metal-binding composite microfibres

Metal-binding polymer fibres have attracted major attention for diverse applications in membranes for metal sequestration from waste waters, non-woven wound dressings, matrices for photocatalysis, and many more. This paper reports the design and synthesis of an 8-hydroxyquinoline-based zinc-binding styrenic monomer, QuiBoc. Its subsequent polymerisation by reversible addition–fragmentation chain transfer (RAFT) yielded well-defined polymers, PQuiBoc, of controllable molar masses (6 and 12 kg mol−1) with low dispersities (Đ, Mw/Mn < 1.3). Protected (PQuiBoc) and deprotected (PQuiOH) derivatives of the polymer exhibited a high zinc-binding capacity, as determined by semi-quantitative SEM/EDXA analyses, allowing the electrospinning of microfibres from a PQuiBoc/polystyrene (PS) blend without the need for removal of the protecting group. Simple “dip-coating” of the fibrous mats into ZnO suspensions showed that PQuiBoc/PS microfibres with only 20% PQuiBoc content had almost three-fold higher loadings of ZnO (29%) in comparison to neat PS microfibres (11%)

Ternary blend nanofibres of poly(lactic acid), polycaprolactone and cellulose acetate butyrate for skin tissue scaffolds:influence of blend ratio and polycaprolactone molecular mass on miscibility, morphology, crystallinity and thermal properties

Ternary blends of poly(lactic acid) (PLA), polycaprolactone (PCL) and cellulose acetate butyrate (CAB) were fabricated into the form of electrospun nanofibres targeted for skin tissue scaffolds. The effects of blend ratio and molecular mass of PCL (PCL1 and PCL2) on morphology, miscibility, crystallinity, thermal properties, surface hydrophilicity and cell culture of the nanofibres were investigated. Blends with high PLA loading (80/10/10 PLA/PCL/CAB) gave fibres with a smooth surface, owing to the enhanced miscibility between the polymer chains from the presence of CAB, which acts as compatibilizer. In contrast, blends with high PCL loading were immiscible, which led to beads during the electrospinning process. The increased molecular mass of PCL2 produced smoother fibres than low-molecular-mass PCL1. The XRD patterns of blends of PLA/PCL1/CAB and PLA/PCL2/CAB were similar to one another, in which the high-crystallinity peaks of PCL seen for 20/70/10 blends were very small for 50/40/10 blends and much less prevalent for 80/10/10 blends. Better fibre formation (80/10/10>50/40/10>20/70/10) with less crystallinity occurs in well-formed fibres. Selected blends of PLA/PCL/CAB promoted growth of NIH/3T3 fibroblast cells, demonstrating that our novel biocompatible ternary blend nanofibrous scaffolds have potential in skin tissue repair applications. In addition, this work helps in the design and understanding of the factors that control the properties of nanofibrous PLA/PCL/CAB scaffolds

Tuneable denture adhesives using biomimetic principles for enhanced tissue adhesion in moist environments

Nature provides many interesting examples of adhesive strategies. Of particular note, the protein glue secreted by marine mussels delivers high adhesion in wet and dynamic environments owing to existence of catechol moieties. As such, this study focuses on denture fixatives, where a non-zinc-containing commercial-based formulation has been judiciously modified by a biomimetic catechol-inspired polymer, poly(3,4-dihydroxystyrene/styrene-alt-maleic acid) in a quest to modulate adhesive performance. In vitro studies, in a lap-shear configuration, revealed that the catechol-modified components were able to enhance adhesion to both the denture base and hydrated, functional oral tissue mimic, with the resulting mode of failure prominently being adhesive rather than cohesive. These characteristics are desirable in prosthodontic fixative applications, for which temporary adhesion must be maintained, with ultimately an adhesive failure from the mucosal tissue surface preferred. These insights provide an experimental platform in the design of future biomimetic adhesive systems. Statement of Significance: Mussel adhesive proteins have proven to be promising biomimetic adhesive candidates for soft tissues and here for the first time we have adapted marine adhesive technology into a denture fixative application. Importantly, we have incorporated a soft tissue mimic in our in vitro adhesion technique that more closely resembles the oral mucosa than previously studied substrates. The novel biomimetic-modified adhesives showed the ability to score the highest adhesive bonding out of all the formulations included in this study, across all moisture levels.This paper will be of major interest to the Acta Biomaterialia readership since the study has illustrated the potential of biomimetic principles in the design of effective prosthodontic tissue adhesives in a series of purpose-designed in vitro experiments in the context of the challenging features of the oral environment

Controlled synthesis of poly(neopentyl p-styrene sulfonate) via reversible addition-fragmentation chain transfer polymerisation

The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using RAFT polymerisation has been studied. Selected experimental conditions led to the production of PNSS with variable molecular weights and low dispersities (D{stroke}≤1.50). The controlled synthesis of poly(neopentyl p-styrene sulfonate) (PNSS) using reversible addition-fragmentation chain transfer polymerisation has been studied under a wide range of experimental conditions. PNSS can be used as an organic-soluble, thermally labile precursor for industrially valuable poly(p-styrene sulfonate), widely employed in technologies such as ionic exchange membranes and organic electronics. The suitability of two different chain transfer agents, three solvents, three different monomer concentrations and two different temperatures for the polymerisation of neopentyl p-styrene sulfonate is discussed in terms of the kinetics of the process and characteristics of the final polymer. Production of PNSS with systematically variable molecular weights and low dispersities (D{stroke} ≤1.50 in all cases) has been achieved using 2-azidoethyl 2-(dodecylthiocarbonothioylthio)-2-methylpropionate in anisole at 75°C, with an initial monomer concentration of 4.0molL-1. Finally, a poly(neopentyl p-styrene sulfonate)-b-polybutadiene-b-poly(neopentyl p-styrene sulfonate) (PNSS-b-PBD-b-PNSS) triblock copolymer has been synthesised via azide-alkyne click chemistry. Moreover, subsequent thermolysis of the PNSS moieties generated poly(p-styrene sulfonate) end blocks. This strategy allows the fabrication of amphiphilic copolymer films from single organic solvents without the need for post-deposition chemical treatment

Hydrogen Bonding Aggregation in Acrylamide: Theory and Experiment

Hydrogen bonding plays a role in the microphase separation behavior of many block copolymers, such as those used in lithography, where the stronger interactions due to hydrogen bonding can lead to a smaller period for the self-assembled structures, allowing the production of higher resolution templates. However, current statistical thermodynamic models used in descriptions of microphase separation, such as the Flory–Huggins approach, do not take into account some important properties of hydrogen bonding, such as site specificity and cooperativity. In this combined theoretical and experimental study, a step is taken toward the development of a more complete theory of hydrogen bonding in polymers, using polyacrylamide as a model system. We begin by developing a set of association models to describe hydrogen bonding in amides. Both models with one association constant and two association constants are considered. This theory is used to fit IR spectroscopy data from acrylamide solutions in chloroform, thereby determining the model parameters. We find that models with two constants give better predictions of bond energy in the acrylamide dimer and more realistic asymptotic behavior of the association constants in the limit of high temperatures. At the end of the paper, we briefly discuss the question of the determination of the Flory–Huggins parameter for a diblock copolymer with one self-associating hydrogen bonding block and one non-hydrogen bonding block by means of fitting the scattering function in a disordered state

Microporous frameworks with conjugated π-electron skeletons for enhanced gas and organic vapor capture

Novel conjugated microporous frameworks based on adamantane (CMF-Ads) have been successfully synthesized under mild conditions. Eight-arm tetraphenyl “knots” and a conjugated π-electron skeleton endowed the target CMF-Ads with ultra-high thermal stability (up to 500 °C), high surface area (up to 907 m2 g−1), excellent CO2 uptake capacity of 15.13 wt % at 273 K and 1 bar, as well as superior organic vapor (benzene, hexane) adsorption. The ultra-high gas uptake capacity and selectivity of these CMF-Ads herein exceeds most conjugated microporous frameworks reported to date, highlighting their potential as materials for clean energy application