2017 Stephen P. Armes

From left: Jean-Christophe Castaing, Piotr Warszynski, and Steven P. Armes

Steven Armes was awarded the 2017 ECIS-Solvay Prize for his recent work on the rational design of tailored block copolymer nanoparticles via polymerization-induced self-assembly. Well-defined spheres, worm-like or vesicular particles were prepared by dispersion polymerization in either water, or polar solvents such as lower alcohols, or non-polar solvents such as n-alkanes.    

  1. Block copolymer worms have been shown to be thermoresponsive: worm-to-sphere order-order transitions can be induced by either cooling an aqueous dispersion of hydrophilic worms (JACS2012134, 9741) or heating an n-alkane dispersion of hydrophobic worms (JACS2014136, 5790). These observations have been rationalised in terms of surface plasticisation of the worms via solvent ingress. 
  2. Prof. Armes has shown that various block copolymer nanoparticles can be used as Pickering emulsifiers. In particular, worms have been shown to be more efficient than chemically identical spheres (Chemical Science20156, 4207). Framboidal vesicles (Chemical Science20156, 6179) have been demonstrated to be much more effective than smooth vesicles (JACS2012134, 12450). 
  3. He designed new cationic block copolymer worms to act as effective superflocculants for micrometer-sized silica particles. Such flocculation cannot be achieved using conventional water-soluble polymers because of the mismatch in length scales. Importantly, cross-linking of the worm cores was shown to be crucial for efficient flocculation (Chemical Science20167, 6853). 
  4. He has investigated also the vesicle growth mechanism during polymerisation-induced self-assembly (PISA) (JACS2015137, 1929). TEM, DLS and SAXS studies show that the overall vesicle dimensions are conserved as the vesicle membrane thickens, which leads to a gradual reduction in the vesicle lumen volume. This hitherto unknown growth mechanism places an intrinsic constraint on vesicle growth, since this phase eventually becomes unstable if a sufficiently thick membrane is targeted. In situ SAXS studies indicates that this vesicle growth mechanism is generic for all PISA formulations (Chemical Science20167, 5078). 
  5. Inspired by the observation of jellyfish intermediate morphologies, Prof. Armes has recently shown that silica nanoparticles can be encapsulated in situ within block copolymer vesicles as the latter are generated during PISA (JACS2015137, 16098). This model system has been rigorously characterised using TEM, SAXS, TGA and disc centrifuge photosedimentometry to determine the silica encapsulation efficiency; it was also shown that controlled release of the encapsulated silica nanoparticles occurs on cooling below 10 oC, since this induces a vesicle-to-sphere transition. 
  6. Aqueous block copolymer worms form soft, free-standing biocompatible hydrogels as a result of multiple inter-worm contacts. If human stem cells are immersed within such worm gels, they enter stasis (suspended animation) and no longer undergo proliferation. On removal from the worm gels, the stem cells “wake up” and begin proliferating again. This finding is important for the design of cost-effective hydrogels to enable cost-effective global transportation of stem cells (ACS Central Science20162, 65). 
  7. Prof. Armes has recently reported a new high temperature oil-thickening mechanism: diblock copolymer vesicles prepared directly in mineral oil using PISA are transformed into highly anisotropic worms on heating to 150 ℃ (Angewandte Chem.201755, 1746). This thermal transition leads to an increase in G’ by five orders of magnitude and potentially provides a new approach to lubrication for automotive engine oils.

    Prof. Armes is author of more than 570 publications in the field of polymer colloids with over 28,500 citations; h-index 99; > 2,000 citations per annum for the past nine years. His outstanding research has merited four Royal Society of Chemistry medals: the 2007 Macro Group medal, the 2010 Peter Day award, the 2013 Tilden medal and the 2014 Interdisciplinary medal. He also received the 2014 Thomas Graham Lectureship from the SCI/RSC Joint Colloid committee and the 2015 Colloid and Polymer Science Lectureship from the German Colloid Society. He was elected as a Fellow of the Royal Society of London in 2014.