Dr Oleksandr O. Mykhaylyk

Scattering methods

Much of my research focuses on the structural analysis of soft matter materials and in particular polymers. We live in a Golden age of Materials Science and Biology, based on a solid underpinning from Chemistry and Physics. One of the keys to this success is recent progress in structural characterization techniques where scattering methods, giving access to structural organization of matter from atomic scales to microns, occupy a dominating role. Experimental data obtained by scattering methods (SAXS, WAXS, XRD, SANS and SLS) provide structural information associated with Fourier space.

My research investigates how this information can be transformed into real space, convenient for our understanding. This involves structural modelling, Monte-Carlo simulations and Fourier transformation techniques. An advantage of scattering methods is that they can be used for kinetic studies of materials in-situ in different environments. Therefore, an other aspect of my work is design of dedicated experimental set-ups for studying materials under external impact such as shear flow or extensional flow, temperature or pH changes.

I have a continuous interest in fat crystallization, colloids and nanoparticles structure, in particular core-shell systems (examples of my research are nanodiamonds to carbon onions transition, a phase separation of polyurethane confined by a nanosized spherical shell). My current research is on thermo-responsive block-copolymer micelles and vesicles.

Mechano-optical Rheology

Rheology is widely recognized as a basic method in processing of polymers, food and cosmetics. In addition, visualization can be used as an effective tool for studying phenomena taking place in fluids. Since soft matter materials subjected to flow often demonstrate a related anisotropy in their refractive index and stress, this causes birefringence visualizing the flow. I have recently developed a new combinatorial technique, shear-induced polarized light imaging (SIPLI), for rheo-optical measurements of polymeric liquids.

The SIPLI technique has already been successfully used for studying shear-induced nucleation and crystallization of polyolefins (see the figure), fibrillation in natural silks and flow alignment of block-copolymer self-assembled structures. My present research focuses on further development of SIPLI for in-situ studies of shear-induced phenomena such as stress, orientation and structural transitions taking place in gels, polymers, copolymers, liquid crystals and colloids.

Polymer Crystallization

Microstructure of solidified polymers depends on thermo-mechanical process history. In general, processed thermoplastics are composed of two structural morphologies: spherulitic (isotropic) and shish-kebab (anisotropic). Ratio of these morphologies in the end-product controls its mechanical properties and material performance.

While spherulitic structure is reasonably understood there is still no a reliable theory for structural formation of shear-induced shish-kebabs. My work is on physical understanding of how the formation of shear-induced morphologies is related to polymer polydispersity, thermodynamics and flow conditions. Based on our research we have proposed a four-stage model for shish-kebab formation including stretching of molecules, nucleation, aggregation and fibrillation.