Dimitri Ivanov

Microfluidics in biotechnology

Microfluidics enables biotechnological processes to proceed on a scale (microns) at which physical processes such as osmotic movement, electrophoretic-motility and surface interactions become enhanced. At the microscale sample volumes and assay times are reduced, and procedural costs are lowered. The versatility of microfluidic devices allows interfacing with current methods and technologies. Microfluidics has been applied to DNA analysis methods and shown to accelerate DNA microarray assay hybridisation times. The linking of microfluidics to protein analysis techologies, e.g. mass spectrometry, enables picomole amounts of peptide to be analysed within a controlled micro-environment. The flexibility of microfluidics will facilitate its exploitation in assay development across multiple biotechnological disciplines.

Nano-structured polymer blends: phase structure, crystallisation behaviour and semi-crystalline morphology of phase separated binary blends of poly(ethylene oxide) and poly(ether sulphone)

The crystallisation behaviour and morphology of binary phase separated crystalline/amorphous blends of poly(ethylene oxide) (PEO) and poly(ether sulphone) (PES) are investigated. The crystallisation behaviour of the PEO/PES blends changes strongly with demixing time and temperature. A method is proposed to determine the composition and amount of PEO-rich phase in the partially demixed blend systems from the dynamic crystallisation behaviour. The results are in agreement with the structure development as predicted for spinodal decomposition that proves the validity of this method. The phase and semi-crystalline morphologies are visualised by scanning electron microscopy and atomic force microscopy. The semi-crystalline morphology is also studied by real-time small angle and wide angle X-ray scattering. It is shown that, depending on the blend composition, a spherulitic or isolated lamellar crystalline morphology is formed in the demixed PEO/PES blends.

New Star-shaped Mesogens with Three Different Arms on a 1,3,5-Benzene Core

The convergent synthesis of new symmetrical and non-symmetrical star-shaped mesogens based on a phloroglucinol core is presented. Molecules with three different arms were derived via esterification of various 4-benzoylbenzoic acid derivatives, substituted with polar groups and n alkoxy chains (n = 1–3), by using a combination of protecting group techniques and stoichiometric reactions. The thermotropic properties were investigated by differential scanning calorimetry, polarised optical microscopy and synchrotron X-ray diffraction. It is found that molecules with more than seven lateral chains form mesophases. The presence of strong polar groups (−NO2) enlarges the temperature range of the liquid crystal phase. For all studied materials the diffractograms can be indexed according to a two-dimensional hexagonal lattice. The lattice parameters indicate that the flexible chains are interdigitated.

Discotic liquid crystals as electron carrier materials

A series of five new hexaalkylthiohexaazatriphenylenes 2a-e has been synthesized. Their thermotropic behaviour has been investigated and compared with the corresponding series of hexaalkylthiotriphenylenes 1a-e and hexaalkylthiohexaazatrinaphthylenes 3a-e . Unexpectedly, hexaalkylthiohexaazatriphenylenes 2a-e , hexaalkylthiotriphenylenes 1d-e and hexaalkylthiohexaazatrinaphthylenes 3e , do not form columnar liquid crystalline mesophases.

The crystallization of poly(aryl-ether-ether-ketone) (PEEK): reorganization processes during gradual reheating of cold-crystallized samples

We have studied by means of X-ray scattering, DMA and densitometry the evolution of the semi-crystalline structure of poly(aryl-ether-ether-ketone) (PEEK) upon reheating specimens initially crystallized isothermally near T-g. Two regimes of reorganization behavior were evidenced. In the low-temperature interval (temperatures below T-g + similar to 50 degrees C), the slow dynamics of amorphous segments prevents large-scale rearrangements, strongly limiting the process of reorganization. Only lamellar-scale reorganization occurs, resulting in a slight increase of the crystal thickness and perfection, and in an increase of the constraints in amorphous regions, reflected by an increase of T-g. At higher temperatures, however, a larger-scale melting/recrystallization mechanism sets in. It consists in the recrystallization of whole lamellar stacks to give a state of overall lower free energy, with much thicker and dense crystals separated by larger and less constrained amorphous regions of lower T-g

Atomic Force Microscopy Studies of Semicrystalline Polymers at Variable Temperature

The capabilities of Atomic Force Microscopy, AFM, in studies of polymer phase transitions and, more generally, the semicrystalline polymer morphology are described. It is shown how variable temperature AFM can provide unique information on the organization of semicrystalline polymers at the nanometer scale and its evolution in the course of crystallization. The practical examples selected for this work illustrate applications of AFM to structural studies of homopolymers and polymer blends crystallized in the bulk, in thin films and in solutions. The investigated systems include solution grown single crystals of polyethylene, cold-crystallized poly(ether ether ketone), as well as melt-crystallized poly(ethylene terephthalate), poly(trimethylene terephthalate), syndiotactic polystyrene, poly(e-caprolactone), isotactic and syndiotactic polypropylene. The issues related to AFM image analysis and its quantitative comparison with the results of complementary techniques such as small-angle X-ray scattering (SAXS) are addressed. More specifically, it is shown how AFM can provide statistically meaningful parameters for the semicrystalline structure and an accurate choice of a structural model for the interpretation of SAXS data.

Discotic mesogens with potential electron carrier properties

A new family of discotic liquid crystals, potentially electron carriers, has been synthesised, some members of which exhibit a particularly rich thermotropic behaviour.

Variable‐Temperature Atomic Force Microscopy

Atomic Force Microscopy (AFM) is a well-established surface characterisation technique initially introduced for high-resolution surface profiling. Fast development of AFM instrumentation has significantly extended its capabilities, which now also include measurements of local mechanical, adhesive, magnetic, electric and thermal properties.