Simon J. Holder

Mechanochromic systems for the detection of stress, strain and deformation in polymeric materials

The detection of stress in polymeric materials such as plastics, elastomers, composites and coatings is critical in the monitoring of material failure including stress fractures, fatigue and hysteresis. Mechanochromic systems that utilise a change in fluorescent output as a result of the mechanical deformation of a polymer have only been actively investigated relatively recently and whilst the field is still relatively small a considerable number of examples of such systems now exist. This article will discuss the principles behind such systems and review examples in the literature and survey the most common fluorophores used in such systems including phenylene vinylene oligomeric derivatives, polycyclic aromatic compounds, carbazole derivatives and conjugated polymers.

Temperature-Responsive Nanospheres with Bicontinuous Internal Structures from a Semicrystalline Amphiphilic Block Copolymer

Internally structured self-assembled nanospheres, cubosomes, are formed from a semicrystalline block copolymer, poly(ethylene oxide)-block-poly(octadecyl methacrylate) (PEO(39)-b-PODMA(17)), in aqueous dispersion. The PODMA block provides them with a temperature-responsive structure and morphology. Using cryo-electron tomography, we show that at room temperature these internally bicontinuous aggregates undergo an unprecedented order-disorder transition of the microphase-separated domains that is accompanied by a change in the overall aggregate morphology. This allows switching between spheres with ordered bicontinuous internal structures at temperatures below the transition temperature and more planar oblate spheroids with a disordered microphase-separated state above the transition temperature. The bicontinuous structures offer a number of possibilities for application as templates, e.g., for biomimetic mineralization or polymerization. Furthermore, the unique nature of the thermal transition observed for this system offers up considerable possibilities for their application as temperature-controlled release vessels.

Cryo electron tomography reveals confined complex morphologies of tripeptide-containing amphiphilic double-comb diblock copolymers.

(Chemical Equation Presented) Sequence sets structure: Amphiphilic norbornene-based double-comb diblock polymers with peptide and oligo(ethylene oxide) side chains aggregate in water to form unprecedented complex morphologies depending on the amino acid sequence of the peptide. The internal structures of the aggregates observed by cryo electron tomography show densely folded and highly branched wormlike micelles (left) and spherical aggregates with a bicontinuous architecture (right).

The detection of phenols in water using a surface plasmon resonance system with specific receptors

A number of receptor molecules designed to bind phenols selectively have been synthesised and evaluated for use in a surface plasmon resonance (SPR) optical sensing system. To optimise sensitivity, films of the receptors entrapped in sol-gel and polymer matrices have been prepared. The most promising receptor systems are shown to give high sensitivity to phenols, together with SPR responses whose characteristics depend on the particular phenol present. These systems offer the promise of identification and quantification of phenol pollutants in water.

ABA triblock copolymers : from controlled synthesis to controlled function

The ABA amphiphilic block copolymers, poly(hydroxyethyl methacrylate-block-methylphenylsilane-block-hydroxyethyl methacrylate) (PHEMA–PMPS–PHEMA) and poly[oligo(ethylene glycol) methyl ether methacrylate-block-methylphenylsilane-block-oligo(ethylene glycol) methyl ether methacrylate] (POEGMA–PMPS–POEGMA) were successfully synthesised via atom transfer radical polymerisation (ATRP). Macroinitiators suitable for the ATRP of oligo(ethylene glycol) methyl ether methacrylate and 2-hydroxyethyl methacrylate were synthesised from the condensation reaction of α,ω-dihalopolymethylphenylsilane and 2′-hydroxyethyl 2-bromo-2-methylpropanoate. The copolymers were characterised using 1H NMR and 13C NMR spectroscopy and molecular weight characteristics were determined using size exclusion chromatography and 1H NMR. The aggregation behaviour of some of the copolymers in water was studied using transmission and scanning electron microscopy and dynamic light scattering. These revealed the prevalent aggregate species to be micelles. Larger aggregates of 300–1000 nm diameter were also observed. The UV induced degradation of the aggregates was studied by UV-Vis spectroscopy. The thermal behaviour of selected copolymers was studied by differential scanning calorimetry and microphase separation of the two components was demonstrated.

Induction of preferential helical screw senses in optically inactive polysilanes via chiral solvation

Communication: Two optically active solvents were synthesised, (S)-(-)-2-methyl-1-propoxybutane and (S)-(-)-(2-methylbutoxymethyl)benzene. The main chain conformations of poly(methylphenylsilane) and poly(hexylmethylsilane) in these solvents were investigated using optical UV-visible and circular dichroism spectroscopy. It was observed that dissolving these inherently achiral polysilanes in optically active solvent induces the polymer chains to adopt preferred helical screw senses. This is the first example of induction of optical activity in conjugated polymers through chiral solvation.

Controlling Internal Pore Sizes in Bicontinuous Polymeric Nanospheres

Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17 kDa and hydrophilic weight fractions of ≤0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460 nm. Significantly, altering the block copolymer hydrophilic–hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19 nm.

Plastic- and liquid-crystalline architectures from dendritic receptor molecules

Host molecules with U-shaped receptor cavities have been derivatized at their convex side with two n-hydrocarbon tails (1), two first-generation (2), and two second-generation (3) monodendritic hydrocarbon tails. Although hosts 1 and 2 display plastic-crystalline behavior, evidence suggests that host 3 forms a cubic liquid-crystalline phase. In this phase, molecules of 3 are arranged in spherical supramacromolecular assemblies, in which the receptor cavities are situated in the core and the hydrocarbon tails at the periphery. The 1:1 host-guest complex of 3 with methyl 3,5dihydroxybenzoate forms a similar liquid-crystalline phase, with the guest included in the core of the assemblies.

Epidermal Passive RFID Strain Sensor for Assisted Technologies

An epidermal passive wireless strain sensor using radio frequency identification (RFID) tags is presented. The tag is intended to detect eyebrow or neck skin stretch where paraplegic patients have the capability to tweak facial muscles. The tag is designed on a barium-titanate-loaded polydimethylsiloxane (PDMS) substrate and is assessed to demonstrate the strain gauge sensitivity and repeatability as a function of skin stretch.

Silane-based hybrids for biomedical applications *

In this paper, the preparation of different hybrid silane materials is presented and their possible use in biomedical applications is discussed. The first example describes the development of biocompatible coatings based on sol-gel silicates, which can be used as a protective coating for implantable glucose sensors. Blending the silica with different organic polymers modified the properties of the resulting sol-gel materials. Their biocompatibility, both in vivo and in vitro, and their applications on biosensors were investigated. In the second example, an amphiphilic block copolymer comprising hydrophilic poly(ethylene oxide) blocks and hydrophobic poly(methylphenylsilane) segments is presented. In aqueous medium, this polymer forms vesicles in which a fluorescent dye is encapsulated. It was demonstrated that the vesicle aggregates could be broken up using UV irradiation, indicating that these vesicles were potentially interesting as controlled release systems. Monolayer studies confirmed that after photolytic cleavage of the poly(methylphenylsilane) segments, no organized structures were formed from the remaining material.