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M Torkkeli

Publications and source records attributed to M Torkkeli.

6 recordsLinked to original sources
PubMed2005

Influence of molecular weight on the phase behavior and structure formation of branched side-chain hairy-rod polyfluorene in bulk phase.

We report on an experimental study of the self-organization and phase behavior of hairy-rod pi -conjugated branched side-chain polyfluorene, poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl]-i.e., poly[2,7-(9,9-bis(2-ethylhexyl)fluorene] (PF2/6) -as a function of molecular weight (M(n)) . The results have been compared to those of phenomenological theory. Samples for which M(n) =3-147 kg/mol were used. First, the stiffness of PF2/6 , the assumption of the theory, has been probed by small-angle neutron scattering in solution. Thermogravimetry has been used to show that PF2/6 is thermally stable over the conditions studied. Second, the existence of nematic and hexagonal phases has been phenomenologically identified for lower and higher M(n) (LMW, M(n) < M(*)(n) and HMW, M(n) > M(*)(n) ) regimes, respectively, based on free-energy argument of nematic and hexagonal hairy rods and found to correspond to the experimental x-ray diffraction (XRD) results for PF2/6 . By using the lattice parameters of PF2/6 as an experimental input, the nematic-hexagonal transition has been predicted in the vicinity of glassification temperature (T(g)) of PF2/6 . Then, by taking the orientation parts of the free energies into account the nematic-hexagonal transition has been calculated as a function of temperature and M(n) and a phase diagram has been formed. Below T(g) of 80 degrees C only (frozen) nematic phase is observed for M(n)< M(*)(n) = 10(4) g/mol and crystalline hexagonal phase for M(n) > M(*)(n) . The nematic-hexagonal transition upon heating is observed for the HMW regime depending weakly on M(n) , being at 140-165 degrees C for M(n) > M(*)(n). Third, the phase behavior and structure formation as a function of M(n) have been probed using powder and fiber XRD and differential scanning calorimetry and reasonable semiquantitative agreement with theory has been found for M(n) >or=3 kg/mol. Fourth, structural characteristics are widely discussed. The nematic phase of LMW materials has been observed to be denser than high-temperature nematic phase of HMW compounds. The hexagonal phase has been found to be paracrystalline in the (ab0) plane but a genuine crystal meridionally. We also find that all these materials including the shortest 10-mer possess the formerly observed rigid five-helix hairy-rod molecular structure.

Journal Article↗
PubMed2003

One-dimensional optical reflectors based on self-organization of polymeric comb-shaped supramolecules.

We demonstrate that complexation of dodecylbenzenesulphonic acid, DBSA, to a diblock copolymer of polystyrene- block-poly(4-vinylpyridine), PS- block-P4VP, leads to polymeric supramolecules PS- block-P4VP(DBSA)y (y = 1.0, 1.5, and 2.0), which self-organize with a particularly large lamellar periodicity in excess of 1000 A. The structures consist of alternating PS and P4VP(DBSA)y layers, where the latter contains smaller internal structure, probably lamellar. The DBSA side chains are bonded to the pyridines by protonation and hydrogen bonding and they effectively plasticize the material. In this way relatively well-developed structures are obtained even without annealing or macroscopic alignment. Transmission and reflectance measurements show that a relatively narrow and incomplete bandgap exists for supramolecules of high molecular weight block copolymer at ca. 460 nm.

Journal Article↗
PubMed2002

Small-angle x-ray scattering studies of human breast tissue samples.

Small-angle x-ray scattering (SAXS) patterns are recorded from thin breast tissue samples containing healthy and cancerous regions. The SAXS patterns are compared with histo-pathological observations. The information available from SAXS is reviewed, and a model for scattering from collagen is presented. Scattering patterns of collagen at regions far from the tumours are essentially different from those at tumours. The axial period of collagen fibrils is 65.0 +/- 0.1 nm in healthy regions, and 0.3 nm larger in cancer-invaded regions. The average intensity of scattering from cancerous regions is an order of magnitude higher than the intensity from healthy regions. This is interpreted to arise from an increase of the specific surface area of the scatterers, which is due to a disruption of the molecular and supra-molecular structures in cancerous regions and invasion of new types of cells. The differences of the SAXS patterns are large and distinctive enough to suggest that these phenomena may be utilized in mammography.

Breast↗
PubMed2001

Characterization of apo and partially saturated states of calerythrin, an EF-hand protein from S. erythraea: a molten globule when deprived of Ca(2+).

Calerythrin, a four-EF-hand calcium-binding protein from Saccharopolyspora erythraea, exists in an equilibrium between ordered and less ordered states with slow exchange kinetics when deprived of Ca(2+) and at low temperatures, as observed by NMR. As the temperature is raised, signal dispersion in NMR spectra reduces, and intensity of near-UV CD bands decreases. Yet far-UV CD spectra indicate only a small decrease in the amount of secondary structure, and SAXS data show that no significant change occurs in the overall size and shape of the protein. Thus, at elevated temperatures, the equilibrium is shifted toward a state with characteristics of a molten globule. The fully structured state is reached by Ca(2+)-titration. Calcium first binds cooperatively to the C-terminal sites 3 and 4 and then to the N-terminal site 1, which is paired with an atypical, nonbinding site 2. EF-hand 2 still folds together with the C-terminal half of the protein, as deduced from the order of appearance of backbone amide cross peaks in the NMR spectra of partially Ca(2+)-saturated states.

Bacterial Proteins↗
PubMed1998

Switching supramolecular polymeric materials with multiple length scales

It was demonstrated that polymeric supramolecular nanostructures with several length scales allow straightforward tailoring of hierarchical order-disorder and order-order transitions and the concurrent switching of functional properties. Poly(4-vinyl pyridine) (P4VP) was stoichiometrically protonated with methane sulfonic acid (MSA) to form P4VP(MSA)1.0, which was then hydrogen-bonded to pentadecylphenol. Microphase separation, re-entrant closed-loop macrophase separation, and high-temperature macrophase separation were observed. When MSA and pentadecylphenol were complexed to the P4VP block of a microphase-separated diblock copolymer poly[styrene-block-(4-vinyl pyridine)], self-organized structures-in-structures were obtained whose hierarchical phase transitions can be controlled systematically. This microstructural control on two different length scales (in the present case, at 48 and 350 angstroms) was then used to introduce temperature-dependent transitions in electrical conductivity.

Journal Article↗