A poly(glycerol monomethacrylate) (PGMA) macromolecular chain transfer agent has been utilized to polymerize benzyl methacrylate (BzMA) via reversible addition−fragmentation chain transfer (RAFT)-mediated aqueous emulsion polymerization. This formulation leads to the efficient formation of spherical diblock copolymer nanoparticles at up to 50% solids. The degree of polymerization (DP) of the core-forming PBzMA block has been systematically varied to control the mean particle diameter from 20 to 193 nm. Conversions of more than 99% were achieved for PGMA 51 −PBzMA 250 within 6 h at 70 °C using macro-CTA/initiator molar ratios ranging from 3.0 to 10.0. DMF GPC analyses confirmed that relatively low polydispersities (M w /M n < 1.30) and high blocking efficiencies could be achieved. These spherical nanoparticles are stable to both freeze−thaw cycles and the presence of added salt (up to 0.25 M MgSO 4 ). Three sets of PGMA 51 −PBzMA x spherical nanoparticles have been used to prepare stable Pickering emulsions at various copolymer concentrations in four model oils: sunflower oil, n-dodecane, nhexane, and isopropyl myristate. A reduction in mean droplet diameter was observed via laser diffraction on increasing the nanoparticle concentration. Finally, the cis diol functionality on the PGMA stabilizer chains has been exploited to demonstrate the selective adsorption of PGMA 51 −PBzMA 100 nanoparticles onto a micropatterned phenylboronic acid-functionalized planar surface. Formation of a cyclic boronate ester at pH 10 causes strong selective binding of the nanoparticles via the cis-diol groups in the PGMA stabilizer chains, as judged by AFM studies. Control experiments confirmed that minimal selective nanoparticle binding occurred at pH 4, or if the PGMA 51 stabilizer block was replaced with a poly(ethylene glycol) PEG 113 stabilizer block.

RAFT-mediated polymerisation-induced self-assembly (PISA) is used to prepare six types of amphiphilic block copolymer nanoparticles which were subsequently evaluated as putative Pickering emulsifiers for the stabilisation of n-dodecane-in-water emulsions. It was found that linear poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) diblock copolymer spheres and worms do not survive the high shear homogenisation conditions used for emulsification. Stable emulsions are obtained, but the copolymer acts as a polymeric surfactant; individual chains rather than particles are adsorbed at the oil-water interface. Particle dissociation during emulsification is attributed to the weakly hydrophobic character of the PHPMA block. Covalent stabilisation of these copolymer spheres or worms can be readily achieved by addition of ethylene glycol dimethacrylate (EGDMA) during the PISA synthesis. TEM studies confirm that the resulting cross-linked spherical or worm-like nanoparticles survive emulsification and produce genuine Pickering emulsions. Alternatively, stabilisation can be achieved by either replacing or supplementing the PHPMA block with the more hydrophobic poly(benzyl methacrylate) (PBzMA). The resulting linear spheres or worms also survive emulsification and produce stable n-dodecane-in-water Pickering emulsions. The intrinsic advantages of anisotropic worms over isotropic spheres for the preparation of Pickering emulsions are highlighted. The former particles are more strongly adsorbed at similar efficiencies compared to spheres and also enable smaller oil droplets to be produced for a given copolymer concentration. The scalable nature of PISA formulations augurs well for potential applications of anisotropic block copolymer nanoparticles as Pickering emulsifiers.

[1] New particle formation (NPF) occurs in various atmospheric environments, and these newly formed particles have the potential to grow to cloud condensation nuclei. But at present it is unclear which chemical species are involved in aerosol nucleation and growth, in part because there are only a limited number of simultaneous measurements of aerosol precursors and aerosol size distributions. Observations of ambient aerosol size distributions, sulfuric acid, and ammonia were made for over a year in Kent, Ohio, a relatively less polluted continental environment. Particle sizes in the diameter range from 3 to 1000 nm were measured continuously through the whole year, while sulfuric acid and ammonia were measured seasonally with two chemical ionization mass spectrometers. Strong NPF events were more frequently found during the spring and fall and less frequently during the summer and winter. The median of measured sulfuric acid was higher in spring (5.2 × 10 6 cm −3 ) and summer (2.9 × 10 6 cm −3 ) than in winter (6 × 10 5 cm −3 ) and fall (5 × 10 5 cm −3 ). We have used the inverse model Particle Growth and Nucleation to derive aerosol nucleation and growth rates from the measured aerosol size distributions. Nucleation rates derived during the NPF events ranged from 1.4 to 12.9 cm −3 s −1 and were proportional to the measured sulfuric acid concentration with a power of 0.6-2.3. Our results show that sulfuric acid is an important aerosol nucleation precursor, but only a small fraction of the aerosol growth rates could be explained by the condensation of sulfuric acid alone. Ammonia mixing ratios did not have a diurnal trend but had some seasonal variations, higher in spring than in fall and winter, typically at sub-ppbv level; aerosol nucleation rates did not show a clear correlation with ammonia at least at this sub-ppbv level, mostly because the ammonia mixing ratios were nearly constant. Our observations also indicate that the role that ammonia plays in aerosol nucleation is more complicated than is currently understood by the aerosol nucleation theories.Citation: Erupe, M. E., et al. (2010), Correlation of aerosol nucleation rate with sulfuric acid and ammonia in Kent, Ohio: An atmospheric observation,

A series of model sterically stabilized diblock copolymer nanoparticles has been designed to aid the development of analytical protocols in order to determine two key parameters: the effective particle density and the steric stabilizer layer thickness. The former parameter is essential for high resolution particle size analysis based on analytical (ultra)centrifugation techniques (e.g., disk centrifuge photosedimentometry, DCP), whereas the latter parameter is of fundamental importance in determining the effectiveness of steric stabilization as a colloid stability mechanism. The diblock copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using RAFT aqueous emulsion polymerization: this approach affords relatively narrow particle size distributions and enables the mean particle diameter and the stabilizer layer thickness to be adjusted independently via systematic variation of the mean degree of polymerization of the hydrophobic and hydrophilic blocks, respectively. The hydrophobic core-forming block was poly(2,2,2-trifluoroethyl methacrylate) [PTFEMA], which was selected for its relatively high density. The hydrophilic stabilizer block was poly(glycerol monomethacrylate) [PGMA], which is a well-known non-ionic polymer that remains water-soluble over a wide range of temperatures. Four series of PGMAx–PTFEMAy nanoparticles were prepared (x = 28, 43, 63, and 98, y = 100–1400) and characterized via transmission electron microscopy (TEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). It was found that the degree of polymerization of both the PGMA stabilizer and core-forming PTFEMA had a strong influence on the mean particle diameter, which ranged from 20 to 250 nm. Furthermore, SAXS was used to determine radii of gyration of 1.46 to 2.69 nm for the solvated PGMA stabilizer blocks. Thus, the mean effective density of these sterically stabilized particles was calculated and determined to lie between 1.19 g cm–3 for the smaller particles and 1.41 g cm–3 for the larger particles; these values are significantly lower than the solid-state density of PTFEMA (1.47 g cm–3). Since analytical centrifugation requires the density difference between the particles and the aqueous phase, determining the effective particle density is clearly vital for obtaining reliable particle size distributions. Furthermore, selected DCP data were recalculated by taking into account the inherent density distribution superimposed on the particle size distribution. Consequently, the true particle size distributions were found to be somewhat narrower than those calculated using an erroneous single density value, with smaller particles being particularly sensitive to this artifact.

Abstract. Amphiphilic diblock copolymer nano-objects can be readily prepared using reversible addition-fragmentation chain transfer (RAFT) polymerization. For example, poly(glycerol monomethacrylate) (PGMA) chain transfer agents (CTA) can be chain-extended using 2-hydroxypropyl methacrylate (HPMA) via RAFT aqueous dispersion polymerization to form welldefined spheres, worms or vesicles at up to 25% solids. The worm morphology is of particular interest, since multiple inter-worm contacts lead to the formation of soft free-standing gels, which undergo reversible degelation on cooling to sub-ambient temperatures. However, the critical gelation temperature (CGT) for such thermo-responsive gels is < 20C, which is relatively low for certain biomedical applications. In this work, a series of new amphiphilic diblock copolymers are prepared in which the core-forming block comprises a statistical mixture of HPMA and di(ethylene glycol) methyl ether methacrylate (DEGMA), which is a more hydrophilic monomer than HPMA.Statistical copolymerizations proceeded to high conversion and low polydispersities were achieved in all cases (Mw/Mn < 1.20). The resulting PGMA-P(HPMA-stat-DEGMA) diblock copolymers undergo polymerization-induced self-assembly at 10% w/w solids to form free-standing worm gels. SAXS studies indicate that reversible (de)gelation occurs below the CGT as a result of a worm-to-sphere transition, with further cooling to 5 °C affording weakly interacting copolymer chains with a mean aggregation number of approximately four. This corresponds to almost molecular dissolution of the copolymer spheres. The CGT can be readily tuned by varying the mean degree of polymerization and the DEGMA content of the core-forming statistical block. For example, a CGT of 31°C was obtained for PGMA59-P(HPMA91-stat-DEGMA39). This is sufficiently close to physiological temperature (37°C) to suggest that these new copolymer gels may offer biomedical applications as readily-sterilizable scaffolds for mammalian cells, since facile cell harvesting can be achieved after a single thermal cycle.