Thomas Hobbes, war and ‘the natural condition of man’: plus ca change

It is customary in any commentary on Thomas Hobbes (1588–1679) and his best-known work, Leviathan, to emphasise the influence on him of the pre-eminent thinkers of his time, men with whom he had personal dealings (such as Bacon, Descartes and Galileo), forerunners of the Age of Enlightenment. It is also well recognised that Hobbes was much influenced by the civil disorders in England during his own time. However, the influence on him of the great writers and thinkers of ancient Greece has been less well recognised.&nbsp

RAFT Dispersion Alternating Copolymerization of Styrene with N-Phenylmaleimide: Morphology Control and Application as an Aqueous Foam Stabilizer

We report a new nonaqueous polymerization-induced self-assembly (PISA) formulation based on the reversible addition−fragmentation chain transfer (RAFT) dispersion alternating copolymerization of styrene with N-phenylmaleimide using a nonionic poly(N,N-dimethylacrylamide) stabilizer in a 50/50 w/w ethanol/methyl ethyl ketone (MEK) mixture. The MEK cosolvent is significantly less toxic than the 1,4-dioxane cosolvent reported previously [Yang, P.; et al. Macromolecules 2013, 46, 8545−8556]. The core-forming alternating copolymer block has a relatively high glass transition temperature (Tg), which leads to vesicular morphologies being observed during PISA, as well as the more typical sphere and worm phases. Each of these copolymer morphologies has been characterized by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies. TEM studies reveal micrometer-sized elliptical particles with internal structure, with SAXS analysis suggesting an oligolamellar vesicle morphology. This structure differs from that previously reported for a closely related PISA formulation utilizing a poly(methacrylic acid) stabilizer block for which unilamellar platelet-like particles are observed by TEM and SAXS. This suggests that interlamellar interactions are governed by the nature of the steric stabilizer layer. Moreover, using the MEK cosolvent also enables access to a unilamellar vesicular morphology, despite the high Tg of the alternating copolymer coreforming block. This was achieved by simply conducting the PISA synthesis at a higher temperature for a longer reaction time (80 °C for 24 h). Presumably, MEK solvates the core-forming block more than the previously utilized 1,4-dioxane cosolvent, which leads to greater chain mobility. Finally, preliminary experiments indicate that the worms are much more efficient stabilizers for aqueous foams than either the spheres or the oligolamellar elliptical vesicles

Addition of water to an alcoholic RAFT PISA formulation leads to faster kinetics but limits the evolution of copolymer morphology

RAFT dispersion polymerization of benzyl methacrylate (BzMA) has been used previously (E. R. Jones, et al., Macromolecules, 2012, 45, 5091) to prepare poly(2-(dimethylamino)ethyl methacrylate)-poly- (benzyl methacrylate) (PDMA–PBzMA) diblock copolymer nanoparticles in ethanol via polymerizationinduced self-assembly (PISA). However, the rate of polymerization was relatively slow, with incomplete monomer conversions being obtained when targeting higher mean degrees of polymerization (DP) even after 24 h at 70 °C. Herein we examine the effect of the addition of up to 20% w/w water co-solvent on the kinetics of BzMA polymerization for this PISA formulation. Significantly faster polymerizations were observed: for a target DP of 200, 90% BzMA conversion was achieved within just 6 h in the presence of 20% w/w water, compared to only 35% conversion in anhydrous ethanol under the same conditions. This rate enhancement enables much higher mean DPs to be obtained for the core-forming PBzMA and is attributed to greater partitioning of the BzMA monomer within the particles, which increases the local monomer concentration. However, the presence of water adversely affected the evolution of copolymer morphology from spheres to worms to vesicles when employing a relatively short PDMA chain transfer agent, with only kinetically-trapped spheres being obtained at higher levels of added water. Aqueous electrophoresis studies indicate that the PDMA stabilizer chains acquired partial cationic charge in the presence of water. This leads to more efficient inter-particle repulsion, thus preventing the sphere-sphere fusion events required for an evolution in morphology. In summary, the addition of water to such PISA formulations allows the more efficient synthesis of spherical nanoparticles, but should be used with caution if either diblock copolymer worms or vesicles are desired

Stimulus-responsive block copolymer nano-objects and hydrogels via dynamic covalent chemistry

Herein we demonstrate that dynamic covalent chemistry can be used to induce reversible morphological transitions in block copolymer nano-objects and hydrogels. Poly(glycerol monomethacrylate)–poly(2- hydroxypropyl methacrylate) (PGMA–PHPMA) diblock copolymer nano-objects (vesicles or worms) were prepared via polymerization-induced self-assembly. Addition of 4-carboxyphenylboronic acid (CPBA) leads to the formation of phenylboronate ester bonds with the 1,2-diol pendent groups on the hydrophilic PGMA stabilizer chains; such binding causes a subtle reduction in the packing parameter, which in turn induces either vesicle-to-worm or worm-to-sphere transitions. Moreover, CPBA binding is pH-dependent, so reversible transitions can be achieved by switching the solution pH, with relatively high copolymer concentrations leading to associated (de)gelation. This distinguishes these new physical hydrogels from the covalently cross-linked gels prepared using dynamic covalent chemistry reported in the literature

Comparison of pseudo-living character of RAFT polymerizations conducted under homogeneous and heterogeneous conditions

RAFT dispersion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is conducted in ethanol at 70 �C using either poly(2-(dimethylamino)ethyl methacrylate) or poly(methacrylic acid) as a macromolecular chain transfer agent. If the diblock copolymer nanoparticles are not too large, the small refractive index difference between the PTFEMA cores and ethanol leads to minimal light scattering. This enables the pseudo-living character of RAFT formulations conducted under solution and dispersion polymerization conditions to be compared by monitoring the loss of RAFT chain-ends via UV-visible absorption spectroscopy. Significantly fewer chain-ends are lost during RAFT dispersion polymerization, suggesting that such heterogeneous formulations have greater pseudo-living character. Moreover, 19F NMR spectroscopy provides the first direct experimental evidence that RAFT dispersion polymerization proceeds via monomer-swollen block copolymer micelles. The relatively low refractive index of PTFEMA complicates GPC analysis, leading to apparent contamination of the diblock copolymer and erroneously high polydispersities. However, this artefact can be corrected by deconvolution of the GPC curves, followed by their reconstruction using appropriate refractive indices

Would Functional Agricultural Foods Improve Human Health?

Concern over diet-health relationships has moved to the forefront of public health concerns in the UK and much of the developed world. It has been estimated, for example, that obesity costs the UK National Health Service up to £6b per year (Rayner and Scarborough, 2005), but if all consumers were to follow recommended healthy eating guidelines there would be major implications for food consumption, land use and international trade (Srinivasan et al, 2006). This is unlikely to happen, at least in the short term, but it is realistic to anticipate some dietary adjustment toward the recommendations, resulting in an improvement in diet quality (Mazzocchi et al, 2007). Although consumers are reluctant to make major changes to their diets, they may be prepared to substitute existing foods for healthier alternatives. Three of the most prominent nutritional recommendations are to consume more fruit and vegetables, which contain phytochemicals beneficial to health, reduce consumption of saturated fatty acids (SFA) and increase intake of long-chain n-3 fatty acids (FA). In the first case, consumption of fruit and vegetables has been stable at around three 80 g portions per person per day according to the Health Survey for England. It is estimated that 42,200 deaths per year could be avoided in England and 411,000 Quality Adjusted Life Years (QALYs) could be saved if fruit and vegetable consumption were increased to the recommended 5 portions per day (Ofcom 2006). As well as continuing to encourage people to eat more, it could be desirable to ‘intensify’ the beneficial phytochemical content of existing fruit and vegetables.Agribusiness, Agricultural and Food Policy, Farm Management, Food Consumption/Nutrition/Food Safety, Industrial Organization,

A hybrid multiagent approach for global trajectory optimization

In this paper we consider a global optimization method for space trajectory design problems. The method, which actually aims at finding not only the global minimizer but a whole set of low-lying local minimizers(corresponding to a set of different design options), is based on a domain decomposition technique where each subdomain is evaluated through a procedure based on the evolution of a population of agents. The method is applied to two space trajectory design problems and compared with existing deterministic and stochastic global optimization methods

Preparation of non-aqueous Pickering emulsions using anisotropic block copolymer nanoparticles

In this work, we show that amphiphilic diblock copolymer worms prepared via alcoholic RAFT dispersion polymerization can be used to stabilize non-aqueous Pickering emulsions. A previously reported synthesis protocol based on polymerization-induced self-assembly (PISA) was modified to enable the preparation of poly(2-(dimethylamino)ethyl methacrylate)-poly(benzyl methacrylate) (PDMA-PBzMA) worm-like particles directly in methanol at relatively high solids. A dilute dispersion of these highly anisotropic nanoparticles was then homogenized with sunflower oil to produce sunflower oil-in-methanol emulsions. The mean droplet diameter ranged from 9 to 104 μm, depending on the nanoparticle concentration and the stirring rate used for homogenization. The sunflower oil content was increased systematically, with stable emulsions being obtained up to a volume fraction of 0.60. In all cases, the sunflower oil droplets gradually increase in size on ageing for up to 4 days. However, stable emulsions were obtained after this time period, with no further change in the mean droplet diameter for at least 2 months on standing at ambient temperature. Turbidimetry studies of the continuous phase after sedimentation of the relatively dense emulsion droplets indicated that the initial adsorption efficiency of the PDMA-PBzMA worms is very high, but this is reduced significantly as the droplet diameter gradually increases during ageing. There is a concomitant increase in fractional surface coverage over the same time period, suggesting that the increase in droplet diameter is the result of limited coalescence, rather than an Ostwald ripening mechanism

Synthesis of diblock copolymer spheres, worms and vesicles via RAFT aqueous emulsion polymerization of hydroxybutyl methacrylate

RAFT aqueous emulsion polymerization of hydroxybutyl methacrylate using a poly(glycerol monomethacrylate) precursor leads to diblock copolymer spheres, worms or vesicles. A pseudo-phase diagram is constructed and the vesicles are briefly evaluated as a Pickering emulsifier