Jaouad El harfi

Transport and encapsulation of gold nanoparticles in carbon nanotubes.

Nanoparticles confined in small volumes exhibit functional properties different from that of the bulk material. Furthermore, the smaller the volume available then the greater the effects of confinement are observed to be. Metallic nanoparticles encapsulated within carbon nanotubes have been proposed for many applications ranging from catalysis to quantum storage devices. In this study we examine encapsulation of discrete gold nanoparticles (AuNP) within multi-wall carbon nanotubes (MWNT), with internal diameter less than 10 nm. During the encapsulation process AuNP undergo Ostwald ripening allowing them to reach a diameter that precisely matches the internal diameter of MWNT (snug fit). The use of supercritical CO2 as a processing medium enables efficient transport and irreversible encapsulation of AuNP into narrow nanotubes. Once inside MWNT, the nanoparticles are unable to grow further and retain their spheroidal shape. This dynamic behaviour observed for AuNP differs significantly from the behaviour of molecular guest-species under similar conditions.

Controlled oligomerisation of isoprene-towards the synthesis of squalene analogues

Poly(isoprene) oligomers have been synthesised by the use of a range of controlled radical polymerisation techniques, including Catalytic Chain Transfer Polymerisation (CCTP), Reversible Addition Fragmentation Chain Transfer Polymerisation (RAFT), Atom Transfer Radical Polymerisation (ATRP) and Reverse Atom Transfer Radical Polymerisation (RATRP). The key molecular targets were (a) a low number average molecular weight equivalent to that of squalene and (b) a final backbone structure that contains a minimum of 75% of the 1,4 addition form of the isoprene monomer. These structural elements closely match those of the natural squalene which is the cosmetic/health care industry benchmark. CCTP and RAFT were successful in achieving the set targets via solution based polymerisation. The yields of oligomer from these techniques were approximately the same (∼42% from CCTP and ∼47% from RAFT), as were the Mns, (750 and 850 ± 220 g mol−1 respectively versus a GPC squalene target Mn of 570 g mol−1) and polydispersities (1.28 and 1.21 respectively versus a GPC squalene target of 1.02). The backbone structure of the materials produced by these techniques were shown to exceed the 75% 1,4 addition target. Therefore, both of these techniques have the potential to produce the target structures on a larger/commercial scale. However, the choice of initiator and/or RAFT agent was found to have a strong influence on the molecular weight obtained. The ATRP and RATRP techniques proved unable to demonstrate sufficient control over the polymerisation to produce the target oligomers under the reactions conditions applied whilst achieving acceptable yields (>40%).

Continuous direct on-line reaction monitoring of a controlled polymerisationvia dielectric measurement

This paper reports the application of an extremely facile methodology for monitoring the progress of chemical reactions. This has been exemplified by successfully following the progress of a controlled ring opening polymerisation of e-caprolactone which has been successfully monitored at high temperature (>100 °C), using a direct, on-line measurement of the system dielectric properties. The data was obtained via the use of a coaxial probe in a standard quick fit reaction flask. The on-line measurement has been related to a calibration curve and from this comparison it has been shown that dielectric data can be used to predict the molecular weight of the polymer at a particular point in the reaction. This in turn allowed isolation of a product with desired molecular weight and polydispersity index values, by enabling the reaction to be terminated prior to the point where reaction control is lost due to the appearance of side reactions. These on-line measurements were corroborated by comparison to conventional and accepted off-line measurement techniques.

Continuous and direct ‘in situ’ reaction monitoring of chemical reactions via dielectric property measurement: controlled polymerisation

This paper demonstrates that direct, “in situ” measurement of a reaction mixture using a coaxial probe technique can be used to accurately follow the progress of a chemical reaction. Such a system was shown to clearly indicate the presence/onset of and define the magnitude of key reaction parameters such as induction periods and end-points over a broad range of temperatures and viscosities. Thus it allowed the reaction to be conducted for the ideal time period, so maximising reactor through-put, energy efficiency and end product quality. Furthermore, by relating these ‘in situ’ measurements to a pre-prepared calibration curve, key experimentally achieved reaction rates could be determined. Finally, these continuously acquired, non-intrusive ‘in situ’ measurements were validated by comparison to conventional and industry accepted off-line measurement techniques.

Molecular Design of Squalene/Squalane Countertypes via the Controlled Oligomerization of Isoprene and Evaluation of Vaccine Adjuvant Applications

The potential to replace shark-derived squalene in vaccine adjuvant applications with synthetic squalene/poly(isoprene) oligomers, synthesized by the controlled oligomerization of isoprene is demonstrated. Following on from our previous work regarding the synthesis of poly(isoprene) oligomers, we demonstrate the ability to tune the molecular weight of the synthetic poly(isoprene) material beyond that of natural squalene, while retaining a final backbone structure that contained a minimum of 75% of 1,4 addition product and an acceptable polydispersity. The synthesis was successfully scaled from the 2 g to the 40 g scale both in the bulk (i.e., solvent free) and with the aid of additional solvent by utilizing catalytic chain transfer polymerization (CCTP) as the control method, such that the target molecular weight, acceptable dispersity levels, and the desired level of 1,4 addition in the backbone structure and an acceptable yield (∼60%) are achieved. Moreover, the stability and in vitro bioactivity of nanoemulsion adjuvant formulations manufactured with the synthetic poly(isoprene) material are evaluated in comparison to emulsions made with shark-derived squalene. Emulsions containing the synthetic poly(isoprene) achieved smaller particle size and equivalent or enhanced bioactivity (stimulation of cytokine production in human whole blood) compared to corresponding shark squalene emulsions. However, as opposed to the shark squalene-based emulsions, the poly(isoprene) emulsions demonstrated reduced long-term size stability and induced hemolysis at high concentrations. Finally, we demonstrate that the synthetic oligomeric poly(isoprene) material could successfully be hydrogenated such that >95% of the double bonds were successfully removed to give a representative poly(isoprene)-derived squalane mimic.