Raman evaluation of the crystallinity degree and composition of poly(L-lactide-co-ε-caprolactone).

In this work, we study two series of the copolymers of L-lactide (LLA) and ε-caprolactone (CL) with the CL molar content of 5, 15, and 30 %. The first series was the commercial semicrystalline granules (Corbion, Netherlands), which we analyzed without any additional modification. The second series was amorphous films, prepared from the granules by hot pressing with the subsequent fast quenching in order to avoid the crystallization. We used Raman spectroscopy in conjunction with the quantum chemical modeling to evaluate the structure of the copolymers. As additional methods, we applied X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC). The main result of our study is the elaboration of the Raman methods of quantitative analysis of the relative contents of the comonomers and the crystallinity degree of the poly(L-lactide-co-ε-caprolactone). These methods are based on measurements of the ratios of the peak intensities of the poly(L-lactide) (PLLA) bands at 411 and 874 cm-1, the PLLA band at 2947 cm-1 and the poly(ε-caprolactone) band at 2914 cm-1. Raman study shows that growth of the CL content causes the monotonous decrease in the crystallinity degree of PLLA blocks. Density functional theory analysis of LLA decamer in the conformation of helix 103 allows us to assign the PLLA Raman bands. The Raman data on the composition and crystallinity degree of the copolymers correlate very well with the results of XRD and DSC studies, as well as with the information on the composition of the copolymers provided by manufacturer.

Enhanced electrorheological activity of porous chitosan particles.

Novel porous filler for electrorheological fluids was fabricated from chitosan via freeze drying technique. An exceptional electrorheological effect was discovered in suspensions of polydimethylsiloxane (silicone oil) filled by highly porous chitosan particles. The electrorheological activity was studied by rotational rheometry and visualized by optical microscopy. High porosity of the filler allows preparing highly efficient electrorheological fluids at rather low (< 1 wt%) concentration of dispersed phase. The mechanism of chain-like structure formation was considered. The electrorheological behavior of suspensions and the filler structural organization at different concentration were comprehended in terms of dielectric properties. The rheological data were approximated by Bingham and Cho-Choi-Jhon equations. The sedimentation stability of chitosan suspensions in polydimethylsiloxane was significantly affected by particles porosity.

Effect of exfoliating agent on rheological behavior of ß-chitin fibrils in aqueous suspensions and on mechanical properties of poly(acrylic acid)/ß-chitin composites.

Chitin whiskers are promising reinforcing filler for composites due to their mechanical properties, renewable nature and low cost. A new method for preparation of ß-chitin fibrils from squid pens in ascorbic acid aqueous solutions (AscA) was developed. Stirring of the solution with 2 g/l AscA for 2 h disperses the swollen chitin to individualized fibrils with an aspect ratio > 250. The optimal conditions of ß-chitin exfoliation in acrylic acid (AcrA) aqueous solution were found (0.75-2 g/l, 3-4 h). TEMPO-oxidized ß-chitin fibrils were chosen as a reference sample for comparison of different methods. 0.1% chitin suspensions exfoliated in AscA and AcrA solutions show similar gel-like behavior with a storage modulus (G') of 98 ±â€¯23 and 34 ±â€¯12 Pa, respectively, whereas G' of 0.1% dispersion of the TEMPO-oxidized ß-chitin fibrils was 0.015 ±â€¯0.005 Pa only. Composites based on poly(acrylic acid) comprising 1-3 wt% of ß-chitin fibrils were fabricated by polymerization filling. Mechanical properties of the composites were investigated in dry state in the temperature range of 25-250 °C and at controlled relative humidity in the range from 53.6% to 100%. It was revealed that the maximum reinforcing effect is achieved at high temperature (>120 °C) and high relative humidity (≥75.3%RH).

Rational Design of Hemicyanine Langmuir Monolayers by Cation-Induced Preorganization of Their Structure for Sensory Response Enhancement.

This study takes a novel approach to the enhancement of receptor properties of thin-film sensors based on hemicyanine dyes with dithia-aza-crown-ionophoric moiety. By means of in situ UV-vis and X-ray reflectivity (XRR) measurements, it was revealed that the introduction of up to 0.25 mmol of Hg2+ under a preliminarily compressed monolayer, formed on pure water, does not lead to cation binding. This is due to the formation of "head-to-tail" aggregates (H-type), in which ionophoric group is blocked by the neighboring molecule. However, the presence of barium cations in the subphase under the forming Langmuir monolayer of the mentioned compound causes codirectional (head-to-head) orientation of chromoionophore fragments. This provides preorganization of a monolayer structure that facilitates the binding of complementary mercury cations, even in a compressed state: asymmetric sandwich complexes containing two dye molecules coordinate a Hg2+ cation between them. This complex structure was confirmed by molecular modeling based on the electron density distribution calculated from XRR measurement data. Such preorganization of supramolecular ensembles induced by cations, which do not participate in the complex formation with macroheterocyclic receptors, may have applications in fields where strict control of molecular orientation at the interface is required, such as nanoelectronics, sensorics, catalysis, etc.

Heuristics for precise supramolecular control of soft matter structure and properties - 2,3,4-tris(dodecyloxy)benzenesulfonates with alkaline and organic cations.

Comprehensive analysis of the structure and phase behavior for a number of 2,3,4-tris(dodecyloxy)benzenesulfonates with alkali metal and organic focal groups revealed that the shape of the mesogenic group plays a decisive role in phase behavior of the material. Cubic and layered types of packing prevail when the size of the cation is small and, thus, the shape of the mesogenic molecule is close to conic one. With increasing cation size, the shape becomes more tapered, and columnar mesophases appear to be more stable. Interactions of the focal groups however determine the stability of mesophases. Comparatively strong interactions may, morever, provide substantial deviations from a phase diagram plotting the transition temperatures versus the radius of focal group, as in the case of pyridinium 2,3,4-tris(dodecyloxy)benzenesulfonate.

Cation-Controlled Excimer Packing in Langmuir-Blodgett Films of Hemicyanine Amphiphilic Chromoionophores.

Supramolecular structure of ultrathin films of hemicyanine dye bearing a crown ether group (CrHCR) was tuned by lateral pressure and investigated by means of compression isotherms, UV-vis and fluorescence spectroscopies, and X-ray reflectivity. Two different types of aggregation were revealed, depending on the absence or the presence of metal cations in the water subphase. While CrHCR forms at high surface pressures head-to-tail stacking aggregates on pure water, changing the subphase to a metal-cation-containing one leads to the appearance of well-defined excimers with head-to-head orientation. The structure of monolayers transferred onto solid supports by the Langmuir-Blodgett (LB) technique was examined by use of X-ray reflectivity measurements and molecular modeling. A model of cation-induced excimer formation in hemicyanine Langmuir monolayers is proposed. Finally, fluorescence emission properties of LB films of CrHCR can be managed by appropriate changes in the subphase composition, this last one determining the type of chromophore aggregation.