Pascal Andre | RIKEN, Wako, Japan (original) (raw)

Papers by Pascal Andre

For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on... more For spintronic devices excited by a sudden magnetic or optical perturbation, the torque acting on the magnetization plays a key role in its precession and damping. However, the torque itself can be a dynamical quantity via the time-dependent anisotropies of the system. A challenging problem for applications is then to disentangle the relative importance of various sources of anisotropies in the dynamical torque, such as the dipolar field, the crystal structure or the shape of the particular interacting magnetic nanostructures. Here, we take advantage of a range of colloidal cobalt ferrite nanocubes assembled in 2D thin films under controlled magnetic fields to demonstrate that the phase, ϕ Prec , of the precession carries a strong signature of the dynamical anisotropies. Performing femtosecond magneto-optics, we show that ϕ Prec displays a π-shift for a particular angle θ H of an external static magnetic field, H. θ H is controlled with the cobalt concentration, the laser intensity, as well as the interparticle interactions. Importantly, it is shown that the shape anisotropy, which strongly departs from those of equivalent bulk thin films or individual noninteracting nanoparticles, reveals the essential role played by the interparticle collective effects. This work shows the reliability of a noninvasive optical approach to characterize the dynamical torque in high density magnetic recording media made of organized and interacting nanoparticles. D esigning complex nanostructures with controlled magnetic anisotropy is of utmost importance for innovative information processing technologies like spin-torque oscilla-tors, 1,2 as well as for medical applications such as cancer therapy. 3−5 For instance, the current data storage devices use highly anisotropic ferromagnetic nanostructures that provide large densities of information. Simultaneously, a faster manipulation of the magnetization is receiving lots of attention. In that context, emerging technologies aim at combining high temporal and spatial resolutions for the study of structures with reduced dimensionality. 6 This can be achieved using femto-second laser pulses to study and control the magnetization in a variety of nanosystems. 7−19 Among the possible colloidal magnetic nanoparticle model systems, 20−23 iron oxide nano-particles are attractive due to the possibility to readily tailor their composition, obtain well-defined shapes, and form superstructures. 24−28 In addition, their magneto-crystalline anisotropy can be tuned by metal doping with cobalt ions for example. 29−31 Here, considering the potentials associated with nanoparticle collective effects, we investigate ultrafast magnetization dynamics in concentrated nanoparticles assembled in two-dimensional (2D) thin films. We use the cobalt content to tune the anisotropy of ferrite nanocubes (Co x Fe 3−x O 4), and we explore the effect of interparticle interactions by magnetically " stamping " with an external field the films during their formation. We then evidence for the first time that the precession dynamics of the magnetization in single layer cobalt ferrite nanocubes is controlled by the interplay between the time dependent magneto-crystalline and shape anisotropies. We show that the precession can oscillate with opposite phase

RSC Advances 6, 57811 (2016)

The photophysical properties of donor–acceptor (D–A) and donor–acceptor–donor (D–A–D) liquid crys... more The photophysical properties of donor–acceptor (D–A) and donor–acceptor–donor (D–A–D) liquid crystalline dyads and triads based on two different discotic mesogens are examined in thin films by steady-state optical spectroscopy and subpicosecond transient absorption measurements. In these systems, triphenylene and perylene bisimide units are covalently linked by flexible decyloxy chain(s) and act as an electron donor (D) and acceptor (A), respectively. These discotic liquid-crystalline systems form well-separated D and A p-stacked columnar structures in thin films. The absorption spectra of the films indicate an aggregation of the perylene bisimide and triphenylene moieties along the columns. Steady-state photoluminescence measurements show a strong fluorescence quenching that is mainly attributed to a photo-induced charge transfer process taking place between the triphenylene and perylene bisimide units. Subpicosecond transient absorption measurements show that the photoinduced charge transfer (CT) states in the dyad and triad films are formed within 0.3 ps and recombine on a 150–360 ps time scale. In addition, a correlation between the dynamics of the charge recombination process and the spacing distances between D and A units can be established in the dyad and triad films. This study provides important information on the relationship between molecular packing and the charge transfer properties in such self-organized D and A columnar nanostructures.

Journal of Magnetism and Magnetic Materials 417, 442 (2016)

Magnetic nanoparticles (MnPs) are relevant to a wide range of applications including high density... more Magnetic nanoparticles (MnPs) are relevant to a wide range of applications including high density information storage and magnetic resonance imaging to name but a few. Among the materials available to prepare MnPs, FePt is attracting growing attention. However, to harvest the strongest magnetic properties of FePt MnPs, a thermal annealing is often required to convert face-centered cubic as synthesized nPs into its tetragonal phase. Rarely addressed are the potential side effects of such treatments on the magnetic properties. In this study, we focus on the impact of silica shells often used in strategies aiming at overcoming MnP coalescence during the thermal annealing. While we show that this shell does prevent sintering, and that fcc-to-fct conversion does occur, we also reveal the formation of silicide, which can prevent the stronger magnetic properties of fct-FePt MnPs from being fully realised. This report therefore sheds lights on poorly investigated and understood interfacial phenomena occurring during the thermal annealing of MnPs and, by doing so, also highlights the benefits of developing new strategies to avoid silicide formation.

Journal of Material Chemistry A 4, 4252 (2016)

We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induc... more We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induces charge transfers which impact on both charge extraction and photogeneration within organic photovoltaic (OPV) devices. OPVs fabricated with modified HTL and two photoactive
polymer blends led systematically to power conversion efficiencies (PCE) increases, with PTB7:PC70BM blend exhibiting PCE of ~ 8.3 %, i.e. ~ 15 % increase compared to pristine HTL devices. A reduced device-to-device characteristics variations was also noticed when fluorinated additives were used to modify the PEDOT:PSS. Shading lights onto the effect of HTL fluorination, we show that the morphology of the polymer:PCBM blends remains surprisingly unaffected by the fluorinated HTL surface energy but that, instead, the OPVs are impacted not only by the HTL electronic properties (work function, dipole layer, open circuit voltage, charge transfer dynamic) but also by alteration of the complex refractive indices (photogeneration, short circuit current density, external quantum efficiencies, electro-optic modelling). Both mechanisms find their origin in fluorination induced charge transfers. This work points towards fluorination as a promising strategy toward combining both external quantum efficiency modulation and power conversion efficiency enhancement in OPVs. Charge transfers could also be used more broadly to tune the optical constants and electric field distribution, as well as to reduce interfacial charge recombinations within OPVs.

nanoScale 7, 11163 (2015)

Nanostructured composites of inorganic and organic materials are attracting extensive interest fo... more Nanostructured composites of inorganic and organic materials are attracting extensive interest for electronic and optoelectronic device applications. Here we report a novel method for the fabrication and patterning of metal selenide nanoparticles in organic semiconductor films that is compatible with solution processable large area device manufacturing. Our approach is based upon the controlled in-situ decomposition of cadmium selenide precursor complex in a film of the electron transporting material 1,3,5-tris(N-phenyl-benzimidazol-2-yl)-benzene (TPBI) by thermal and optical methods. Specifically we show that the photoluminescence quantum yield (PLQY) of the thermally converted CdSe quantum dots (QDs) in the TPBI film is up to 15%. We also show that laser illumination can form the QDs from the precursor. This is an important result as it enables direct laser patterning (DLP) of the QDs. DLP was performed on these nanocomposites using a picosecond laser. Confocal microscopy shows the formation of emissive QDs after laser irradiation. The optical and structural properties of the QDs were also analysed by means of UV-Vis, PL spectroscopy and transmission electron microscopy (TEM). The results show that the QDs are well distributed across the film and their emission can be tuned over a wide range by varying the temperature or irradiated laser power on the blend films. Our findings provide a route to the low cost patterning of hybrid electroluminescent devices.

Applied Physics Letter 106, 173301 (2015)

We demonstrate a static fabrication approach to make free-standing ordered arrays of fluorescent ... more We demonstrate a static fabrication approach to make free-standing ordered arrays of fluorescent nanofibres through control of the transverse electrospinning field. The alignment and the density of the nanofibre arrays are optimised by careful design of both the source and collector electrode geometries which can control the transverse electric field over the full path of the jet. In doing so, we fabricate suspended fluorescent nanofibres with an aspect ratio of 104, and with a substantially increased density and order parameter (by a factor of ∼10 compared to random deposition). Electrostatic modelling suggests that the field distribution of the component is the main contribution to the ordering between the plates. This method offers increased efficiency for the creation of ordered fibres collected over a small area and the characterisation of their photoluminescent properties.

Chemical Communication 51, 5836 (2015)

A simple and versatile solution-processing method based on molecular self-assembly is used to fab... more A simple and versatile solution-processing method based on molecular self-assembly is used to fabricate organic single crystal microwires of a low bandgap quinoidal oligothiophene derivative. Individual single crystal microwire transistors present well-balanced ambipolar behaviour with hole and electron mobilities as high as 0.4 and 0.5 cm2 V^-1 s^-1, respectively.

Nature Communication 5, 3583 (2014)

High-performance non-volatile memory that can operate under various mechanical deformations such ... more High-performance non-volatile memory that can operate under various mechanical deformations such as bending and folding is in great demand for the future smart wearable and foldable electronics. Here we demonstrate non-volatile solution-processed ferroelectric organic field-effect transistor memories operating in p- and n-type dual mode, with excellent mechanical flexibility. Our devices contain a ferroelectric poly(vinylidene fluoride-cotrifluoroethylene) thin insulator layer and use a quinoidal oligothiophene derivative (QQT(CN)4) as organic semiconductor. Our dual-mode field-effect devices are highly reliable with data retention and endurance of 46,000 s and 100 cycles, respectively, even after 1,000 bending cycles at both extreme bending radii as low as 500 mm and with sharp folding involving inelastic deformation of the device. Nano-indentation and nano scratch studies are performed to characterize the mechanical properties of organic layers and understand the crucial role played by QQT(CN)4 on the mechanical flexibility of our devices.

Medical Engineering & Physics 36, 11, 1521 (2014)

Feasibility studies are needed to demonstrate that safe and effective manipulation of bowel durin... more Feasibility studies are needed to demonstrate that safe and effective manipulation of bowel during Minimal Access Surgery (MAS) can be obtained by use of magnetic force. This paper characterises two classes of magnetic particles: stainless steel microparticles (SS-microPs) and iron oxide nanoparticles (IO-nPs) in terms of their magnetisation, chemical composition, crystallinity, morphology and size distribution. Both magnetic particles were dispersed in a high viscosity biological liquid for intraluminal injection of bowel. Ex vivo porcine bowel segments were then retracted by permanent magnetic probes of 5.0 and 10 mm diameter. Strong retraction forces reaching 6 N maximum were obtained by magnetic fluid based on dispersion of SS-microPs. In contrast, the IO-nP-based magnetic liquid generated less attraction force, due to both lower magnetic and solution properties of the IO-nPs. The comparison of the two particles allowed the identification of the rules to engineer the next generation of particles. The results with SS-microPs provide proof on concept that intraluminal injection of magnetic fluid can generate sufficient force for efficient bowel retraction. Thereafter we shall carry out in vivo animal studies for efficacy and safety of both types of ferrofluids.

Electronics Letters 50, 16, 1125 (2014)

Thiel-embalmed human cadaveric specimens are used widely for biomedical scientific investigation.... more Thiel-embalmed human cadaveric specimens are used widely for biomedical scientific investigation. This Letter reports electrical impedance measurements of Thiel-embalming solutions from 1 Hz to 32 MHz. Compared with other solutions studied, Thiel solution has the lowest impedance throughout the test spectrum. The electrical conductivity of a Thiel-embalmed liver sample exhibited a relatively flat frequency response from 100 to 500 kHz, which is the frequency range used for electro-surgery and radiofrequency tumour ablation (RFA). It measured 5 Sm−1 compared with 0.22 Sm−1 obtained from ex-vivo fresh pig liver. Using finite element modelling and experimental evaluation, the ablation zone obtained from the Thiel-embalmed liver sample was extremely small due to its much higher conductivity. Hence, it is concluded that Thiel-embalmed tissue cannot be used as a reliable model for RFA evaluation.

Bio-Medical Materials and Engineering 24, 1, 445 (2014)

Safe and effective manipulation of soft tissue during laparoscopic procedures can be achieved by ... more Safe and effective manipulation of soft tissue during laparoscopic procedures can be achieved by the use of mucoadhesive polymer films. A series of novel adhesive polymer films were formulated in house based on either Carbopol or Chitosan modified systems. The mechanical properties of the polymers and their adherence to bowel were evaluated using exvivo pig bowel immersed in 37 °C water bath and connected to an Instron tensiometer. Young’s modulus was 300 kPa for the Carbopol-polymer and 5 kPa for the Chitosan-polymer. The Chitosan-polymer exhibited much larger shear adhesion than its tensile adhesion: 3.4 N vs. 1.2. Both tensile and shear adhesions contributed to the large retraction force (2.6 N) obtained during l polymer-bowel retraction testing. Work of adhesion at the polymer/serosa interface, defined as the area under the force curve, was 64 mJ, which is appreciably larger than that reported with existing polymers. In conclusion, adhesive polymers can stick to the serosal side of the bowel with an adhesive force, which is sufficient to lift the bowel, providing a lower retraction stress than that caused by laparoscopic grasping which induces high localized pressures on the tissue.

BioMedical Research International # 526512+8 (2013)

Magnetic retraction offers advantages over physical retraction by graspers because of reduced tis... more Magnetic retraction offers advantages over physical retraction by graspers because of reduced tissue trauma. The objectives of this study are to investigate a novel method of magnetisation of bowel segments by intraluminal injection of magnetic glue and to demonstrate the feasibility ofmagnetic retraction of bowel with sufficient force during minimal access surgery. Following an initial materials characterisation study, selected microparticles of stainless steel (SS410-𝜇Ps) were mixed with chosen cyanoacrylate glue (Loctite 4014). During intraluminal injection of the magnetic glue using ex vivo porcine colonic segments, a magnetic probe placed at the injected site ensured that the SS410-𝜇Ps aggregated during glue polymerisation to form an intraluminal mucosally adherent coagulum. The magnetised colonic segments were retracted by magnetic probes (5 and 10 mm) placed external to the bowel wall.
A tensiometer was used to record the retraction force.With an injected volume of 2mL in a particle concentration of 1 g/mL, this technique produced maximalmagnetic retraction forces of 2.24 ± 0.23Nand 5.11 ± 0.34N(𝑛 = 20), with use of 5 and 10mmprobes, respectively. The results indicate that the formation of an intraluminal coagulum based on SS410-𝜇Ps and Loctite 4014 produces sufficient magnetic retraction for bowel retraction.

Chemical Communication 48, 19, 2501 (2012)

This communication demonstrates that hybrid nanocolloids can be designed and used to create nanop... more This communication demonstrates that hybrid nanocolloids can be designed and used to create nanoprobes for remotely sensing the temperature of aqueous media. Such multi-modal nanocolloids combine development opportunities not only for multimodal magnetic-optical imaging but also for non-invasive and remote absolute temperature optical monitoring suitable for hyperthermia treatments and cell poration.

International Journal of nanoTechnology 9, 1-2, 39 (2012)

Over the past few years FePt nanoparticles (nPs) have become key-candidates for the development ... more Over the past few years FePt nanoparticles (nPs) have become
key-candidates for the development of platforms for data storage, catalysis and a wide range of biomedical applications. While fairly young in regards of other magnetic nPs, the synthesis of FePt nPs has certainly reached a maturity which makes it timely to briefly review the main colloidal chemistry pathways used to obtain them. With a biased interest towards direct face centred tetragonal (fct) crystalline phase formation, we then present a short review aiming at introducing the readers to the syntheses of FePt nPs. We then take advantage of this snapshot to comment on advantages and drawbacks of each approach together with highlighting the potential directions the field might evolve towards in the near future to form full chemically organised FePt nPs.

Organic Electronics 12, 11, 1800 (2011)

We demonstrate the realization of the first liquid nonvolatile rewritable memories relying on a b... more We demonstrate the realization of the first liquid nonvolatile rewritable memories relying on a blend of liquid carbazole and silver nanoparticles. When an external bias voltage is applied across this single active layer based structure, a bistable current with an ON/OFF ratio of about 2 x 10^2 is observed. Write–read–erase cycles and recorded information stability are also demonstrated. This study provides evidence that hybrid materials hold unexplored promises for original nonvolatile flash memories and should stimulate strong interest in the area of low-cost, large area, flexible data storage devices.

Organic Electronics 12, 11, 1800 (2011)

Chemical Physics Letters 509, 4-6,158 (2011)

Structures of Fe3Pt3(CO)15 (1), Fe2Pt5(CO)12(COD)2 (2), Fe2Pt(CO)8(COD) (3) and Fe2Pt2(CO)10 (4),... more Structures of Fe3Pt3(CO)15 (1), Fe2Pt5(CO)12(COD)2 (2), Fe2Pt(CO)8(COD) (3) and Fe2Pt2(CO)10 (4), as well as the driving forces for their formation from Fe(CO)5 and Pt(COD)2 (COD = 1,5-cyclooctadiene) have been computed at the PBE0-D3 level of density functional theory. Judged from a comparison of computation vs. experiment, this level should be well suited to study structures and thermochemistry of mixed Fe–Pt clusters, which may occur at the early stages of FePt nanoparticle synthesis.

Crystal Engineering Communication 13, 10, 3330 (2011)

This communication demonstrates that ionic liquids can alter the crystallinity and chemical order... more This communication demonstrates that ionic liquids can alter the crystallinity and chemical ordering of nanocolloids synthesized in solution.

Journal of Material Chemistry 21, 3646 (2011)

Aqueous low temperature pathways are attractive for synthesizing colloidal iron–platinum nanopart... more Aqueous low temperature pathways are attractive for synthesizing colloidal iron–platinum nanoparticles, which are promising candidates for applications ranging from data storage to biomedicine. Identifying the inhomogeneous composition of the products as the major hurdle of such syntheses, we present and discuss data including synthesis time, iron precursors and reducing agent aiming at quantifying and understanding the effect of the ionic precursor and the reducing agent on the composition of alloyed nanomaterials. We demonstrate that the nanoparticle composition could be modulated by using faster reducing agents as well as iron(II) salts which are less susceptible to base hydrolysis than iron(III) salts. The strategy we highlight here should be applicable to other alloy nPs fabricated by low temperature co-reduction in aqueous solution.

Organic & Biomolecular Chemistry 9, 4, 1189 (2011)

A range of dendritic molecules was made using the monodentate SEMI-ESPHOS phosphine oxide ligand,... more A range of dendritic molecules was made using the monodentate SEMI-ESPHOS phosphine oxide ligand, which was derivatised with a series of functional groups including bromide, vinyl, allyl and terminal alkyne. Several methods to attach the resulting precursors onto octavinylsilsesquioxane (OVS), ranging from hydrosilylation, Suzuki, Heck, Grubbs or Sonogashira coupling reactions, have been investigated. Cross-metathesis of SEMI-ESPHOS oxide dendrons containing vinyl end groups with OVS catalyzed by Grubbs’ catalyst was proven to be effective in the formation of precursors for dendritic molecules based on OVS.

Journal of the American Chemical Society 132, 42, 15022 (2010)

Iron-platinum alloy nanoparticles (FePt NPs) are extremely promising candidates for the next gene... more Iron-platinum alloy nanoparticles (FePt NPs) are extremely promising candidates for the next generation of contrast agents for magnetic resonance (MR) diagnostic imaging and MR-guided interventions, including hyperthermic ablation of solid cancers. FePt has high Curie temperature, saturation magnetic moment, magneto-crystalline anisotropy, and chemical stability. We describe the synthesis and characterization of a family of biocompatible FePt NPs suitable for biomedical applications, showing and discussing that FePt NPs can exhibit low cytotoxicity. The importance of engineering the interface of strongly magnetic NPs using a coating allowing free aqueous permeation is demonstrated to be an essential parameter in the design of new generations of diagnostic and therapeutic MRI contrast agents. We report effective cell internalization of FePt NPs and demonstrate that they can be used for cellular imaging and in vivo MRI applications. This opens the way for several future applications of FePt NPs, including regenerative medicine and stem cell therapy in addition to enhanced MR diagnostic imaging.

RSC Advances 6, 57811 (2016)

Journal of Magnetism and Magnetic Materials 417, 442 (2016)

Journal of Material Chemistry A 4, 4252 (2016)

nanoScale 7, 11163 (2015)

Applied Physics Letter 106, 173301 (2015)

Chemical Communication 51, 5836 (2015)

Nature Communication 5, 3583 (2014)

Medical Engineering & Physics 36, 11, 1521 (2014)

Electronics Letters 50, 16, 1125 (2014)

Bio-Medical Materials and Engineering 24, 1, 445 (2014)

BioMedical Research International # 526512+8 (2013)

Chemical Communication 48, 19, 2501 (2012)

International Journal of nanoTechnology 9, 1-2, 39 (2012)

Organic Electronics 12, 11, 1800 (2011)

Chemical Physics Letters 509, 4-6,158 (2011)

Crystal Engineering Communication 13, 10, 3330 (2011)

Journal of Material Chemistry 21, 3646 (2011)

Organic & Biomolecular Chemistry 9, 4, 1189 (2011)

Journal of the American Chemical Society 132, 42, 15022 (2010)

Mucoadhesive polymeric films have been developed with an aim to minimise trauma caused to tissue ... more Mucoadhesive polymeric films have been developed with an aim to minimise trauma caused to tissue during minimal access (laparoscopic) surgery; as the retraction of organs and tissues to allow manipulations without causing damage is a major challenge. The films are designed to adhere to the outer serosal surface (in the abdominal cavity) of the organ or tissue and have been developed based on blends of chitosan and Carbopol 971.

Biomedical Engineering / Biomedizinische Technik, 2012

Journal of the American Chemical Society, 2004

Here, we report the first example of transition metal-catalyzed one-pot synthesis of water-solubl... more Here, we report the first example of transition metal-catalyzed one-pot synthesis of water-soluble dendritic molecular nanocarriers behaving like unimolecular micelles. Using the palladium-alpha-diimine chain walking catalyst, copolymerization of ethylene and comonomer 3 afforded, in one step, amphiphilic copolymer 1 having a hydrophobic core and a hydrophilic shell. A much larger amphiphilic core-shell copolymer 2 was synthesized by a two-step approach: a copolymer having many free hydroxyl groups was first prepared, which was subsequently coupled to poly(ethylene glycol) (PEG) to afford the copolymer 2. Light-scattering, fluorescence, and UV/vis spectroscopic studies with Nile Red in aqueous solution showed unimolecular micellar properties for both copolymers 1 and 2. The dye encapsulation capacity for the core-shell copolymers is nearly proportional to the molecular weight of the hydrophobic core. The unimolecular micellar properties coupled with the good water solubility and biocompatibility of the PEG moieties make these molecular nanocarriers promising candidates for many applications including drug delivery and controlled drug release.

The Journal of Supercritical Fluids, 2006

Nitroxide-mediated radical polymerization was used to synthesize poly(1,1,2,2-tetrahydroperfluoro... more Nitroxide-mediated radical polymerization was used to synthesize poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) homopolymer, PFDA, and to tailor the synthesis of semifluorinated polystyrene-b-PFDA block copolymer, PS-b-PFDA. The solubility of the polymers was investigated in the solvent carbon dioxide (CO 2 ) using cloud point and light scattering techniques. The solvent quality of CO 2 for PFDA homopolymer was shown to increase with CO 2 pressure and this information coupled with the size of the block copolymer species indicated the formation of PS-b-PFDA micelles. Residual PS homopolymer remained soluble in PS-b-PFDA micelles at low pressure and induced the formation of a second population of larger aggregates when the solvent quality was tuned.

Journal of Polymer Science Part A: Polymer Chemistry, 2004

Poly(perfluorooctyl-ethylenoxymethylstyrene) (PFDS) and poly(1,1,2,2-tetrahydroperfluorodecyl acr... more Poly(perfluorooctyl-ethylenoxymethylstyrene) (PFDS) and poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) (PFDA) homopolymers as well as poly(styrene)-bpoly(perfluorooctyl-ethylenoxymethylstyrene) (PS-b-PFDS) and poly(styrene)-bpoly(1,1,2,2-tetrahydroperfluorodecyl acrylate) acrylate) (PS-b-PFDA) block copolymers of various chain lengths were synthesized by nitroxide-mediated radical polymerization in the presence of either 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) in the case of FDS monomer or N-tert-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (DEPN) in the case of the FDA monomer. The molar composition of the block copolymers was determined by elemental analysis and proton NMR while the blocky structure was checked by SEC analysis in trifluorotoluene. Block copolymers PS-b-PFDS (3.6K/60K) and PS-b-PFDA (3.7K/43K) were soluble in neat CO 2 at moderate pressure and temperature, indicating the formation of micelles. Similar block copolymers with a longer PS block such as PS-b-PFDA (9.5K/49K), corresponding to a lower CO 2 -philic/CO 2 -phobic balance, were insoluble in neat CO 2 but could be solubilized in the presence of styrene as a cosolvent. Additionally, surface and bulk properties of PS-b-PFDA were investigated, indicating the same surface tension as for the PFDA homopolymer (␥ LV ϭ 10.3 mN/m) and a bulk nanostructured morphology.

Physical Chemistry of Interfaces and Nanomaterials VIII, 2009

Phone +44 (0) 1334 463036; fax +44 (0) 1334 463104 ABSTRACT An inorganic silsesquioxane and organ... more Phone +44 (0) 1334 463036; fax +44 (0) 1334 463104 ABSTRACT An inorganic silsesquioxane and organic 4-vinyl biphenyl chromophore based dendrimer was synthesized and the steric hindrance of the dendrons was used as a trigger to control the photophysical properties in the near-UV and blue spectral ranges. Consistent photoluminescence quantum yields and time resolved fluorescence were measured in solution, confirming that molecular engineering of the dendrons together with confinement around the inorganic core allows the design of more efficient photoluminescent dendrimers. Low temperature photoluminescent studies were completed to demonstrate the stability of the dendrimer photophysical properties. A very general strategy is then presented which uses stable chemistry to control the emission spectral range by changing the chromophore, and gives control of photoluminescence efficiency by grafting side-groups onto the chromophores.

physica status solidi (c), 2014

Optical Trapping and Optical Micromanipulation VI, 2009

Engineering semiconductor nanostructures has immense potential for applications pertaining to nan... more Engineering semiconductor nanostructures has immense potential for applications pertaining to nanophotonics especially due to their optical properties. Nanostructures can come in various forms i.e. tubes, rods and dots. Each presents themselves as a possible candidate for creating larger photonics structures. In this paper, we describe the optical trapping characteristic of dielectric enhanced nanoparticles. Two techniques of dielectric enhancements are employed: silica coating and microsphere tagging, for the efficient manipulation of nanoparticles.

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 2007

The synthesis of polymer nanoparticle composites consisting of CdSe or CdS with a polymer contain... more The synthesis of polymer nanoparticle composites consisting of CdSe or CdS with a polymer containing pendant phosphine group, prepared by modification of polybutadiene, is reviewed. The CdSe composites give near band edge emission for larger particles, but white light emission, apparently from energy transfer into an emitting state of the polymer for smaller particles. Blue emission is obtained from CdS within the same polymer, provided it is kept under an inert atmosphere. The synthesis of InN nanoparticles from the co-decomposition of [InCl 2 N 3 ] 2 with Li[NSiMe 3 ] in diisopropylbenzene is also described. The as-prepared particles are mixed with In metal, which is in turn removed by washing with dilute HCl followed by I 2 /THF to give hexagonal or cubic InN particles with average diameters of 20 -30 nm. Addition of iodine gives smaller (7 nm) more uniform particles mainly of hexagonal InN. Using Li 3 N as an additional source leads to In/InN core shell fibers by a solution-liquid-solid growth mechanism, from which the indium cores can be removed by washing with dilute HCl followed by I 2 /THF to give thick walled InN nanotubes ca. 15 nm in diameter with a wall thickness of 5 nm.