Ivan Šmit

Effect of the spacer length on the solid phase transitions of dissymmetric gemini surfactants

Three dissymmetric gemini surfactants (abbreviated as 12−s−14) in which n-dodecyldimethylammonium bromide and n-tetradecyldimethylammonium bromide are connected at the polar headgroups by a flexible −(CH2)s− spacer (s = 2, 6, or 10) have been synthesized. The influence of the spacer length on the structural and thermal properties of 12−s−14 surfactants was investigated by means of IR and NMR spectral analysis, X-ray diffraction, thermogravimetry, differential scanning calorimetry, and polarizing optical microscopy. Geminis with s = 2 or 10 form monolayers in which two alkyl chains are in the trans configuration, while the gemini with s = 6 forms interdigitated bilayers with two alkyl chains in the cis configuration with respect to the spacer. All compounds exhibited a complex polymorphism and thermotropic mesomorphism from the stable crystalline form to the liquid crystalline phases of smectic type. The number of thermal phase transitions and the sequence of phases are markedly affected by the spacer leng...

Polymorphism and mesomorphism of oligomeric surfactants: effect of the degree of oligomerization.

A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three, or four chains connected by an ethylene spacer at the headgroup level, abbreviated as dimer, trimer, and tetramer) were synthesized and characterized. The influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry, and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. The increase in the degree of oligomerization increases the interlayer distance and decreases the ordering in the solid phase; whereas the dimer sample is fully crystalline with well-developed 3D ordering and the trimer and tetramer crystallize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of the smectic type, with the exception of the tetramer that displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid-crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower temperatures and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.

Interfacial and mechanical properties of polypropylene/silica nano- and microcomposites

Various silica grades differing in particle size (micro- versus nanosilica) and surface modification (untreated versus modified surface) have affected interfacial and mechanical properties of compression-molded polypropylene composites with 2, 4, 6, 8 vol% of added silica. Mechanical properties have been influenced primarily by combination of stiff fillers and tough polypropylene matrix and additionally by restructured matrix. Namely, silica particles with different surface properties have influenced nucleation and spherulite growth differently affecting thus tensile properties of the composites. All composites exhibited best tensile strength in silica content range 2–6 vol%.

Morphology and Mechanical Properties of iPP/Silica Composites Modified with (Styrene-b-ethylene-co-butylene- b-styrene) Grafted with Maleic Anhydride

The effects of different silica grades and elastomer content on interfacial properties, morphology and mechanical properties of polypropylene/silica 96/4 composites modified with added 5, 10, 15, and 20% of poly(styrene-b-ethylene-co-butylene-b-styrene) grafted with maleic anhydride (SEBS-g-MA) were investigated. The iPP/silica/SEBS-g-MA composites were designed by adding four silica fillers differing in size (nano- vs. micro-) and in surface properties (hydrophilic vs. hydrophobic) and SEBS-g-MA that was used as a proven effective impact modifier and compatibilizer simultaneously. The morphology of every composite was a spectrum of several morphologies rather than one exclusive morphology. Good concordance between observed and predicted morphology indicated that the morphology of a particular composite was controlled primarily by interfacial properties. Tensile and impact properties were influenced primarily by competitive effects of a stiff filler and tough SEBS-g-MA elastomer. Increased impact strength and strain at break caused by adding SEBS-g-MA indicated a significant overcoming of the elastomeric toughening effect in relation to the filler’s stiffening effect. GRAPHICAL ABSTRACT

Lamellar to hexagonal columnar liquid crystalline phase transition in a catanionic surfactant mixture: dodecylammonium chloride–sodium bis(2-ethylhexyl) sulfosuccinate

Phase transitions from a dispersed lamellar to hexagonal liquid crystalline phase have been investigated in a catanionic surfactant mixture formed by mixing a single tailed cationic surfactant, dodecylammonium chloride, with a double tailed anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate. Depending on the bulk composition and total surfactant concentration, mixed micelles, vesicles, lamellar and hexagonal columnar liquid crystalline phases have been identified. Differences in the geometry of the two hydrophobic chains stabilize vesicles of different shapes (spherical, tubular and pearled) relative to the liquid crystalline phase even in stoichiometric mixtures. At higher surfactant concentrations the phase transition from a dispersed lamellar to hexagonal columnar liquid crystalline phase proceeds continuously, with both phases coexisting over a range of concentrations. The transition proceeds through processes of vesicle aggregation, reorganization into multilayer sheets rolled-up into tubules, and formation of a hexagonal columnar liquid crystalline phase.

Influence of Dodecylammonium Chloride on the Properties of Carrageenan Gels

Rheological measurements, confocal laser scanning microscopy, and x-ray diffraction were used to study the influence of dodecylammonium chloride (DDACl) on the gelation of κ- and ι-carrageenans. The increase of DDACl concentration led to the changes of gel structure from nano to macro-scale. At the macroscopic level, two phase regions have been differentiated; one below the surfactant micellar region containing turbid gel and the other in the micellar region characterized by gel collapsing. The effect of monomer DDACl concentration on gel structure at the nano level was detected by rheological measurements. All gel samples exhibited shear thinning behavior, well fitted by power law equation, indicating that they maintain mainly carrageenan rheological properties. The change of flow behavior parameters with increasing DDACl concentration might be ascribed to the formation of surfactant domains inside gel networks. Progressive increase of surfactant concentration caused gradual break down of the gel structure and enhanced ordering of surfactant molecules. In the vicinity of the critical micelle concentration, the appearance of microphase separated domains, visualized by confocal laser scanning microscopy indicated pronounced structural changes of both, κ- and ι-carrageenan gels. X-ray diffraction of collapsed gels revealed the formation of a bilayered surfactant structures in conjunction with the carrageenan chains. The increase of DDACl concentration enhanced ordering and growth of mesostructural domains consisting of stacked bilayers. Both, local ordering of bilayers and regular stacking of lamellae revealed stronger electrostatic interactions between surfactant and carrageenan with higher charge density on chains.

Polypropylene Blends with m-EPR Copolymers: Structure, Morphology and Thermal Properties

ABSTRACT The effects of different contents of two metallocene propylene-based m-EPR elastomers on structure, morphology, thermal, and dynamic mechanical properties of the isotactic polypropylene/m-EPR blends were investigated. The both m-EPR copolymers have been built in isotactic polypropylene matrix as amorphous phase. However, the nucleation effect at lowest addition (2.5 vol%) and the solidification effect along with increased m-EPR’s additions have caused changes of the crystallinity degree and the size of spherulites in the isotactic polypropylene matrix. Higher degree of miscibility/compatibility of the isotactic polypropylene/m-EPR2, with lower viscosity has been observed. Homogeneous dispersion of m-EPR particles as well as their radial distribution has been observed. GRAPHICAL ABSTRACT

Polypropylene Blends with m-EPR Copolymers: Mechanical and Rheological Properties

The effects of two metallocene ethylene-propylene-based elastomers (m-EPR1 and m-EPR2) differing in molecular mass and viscosity on mechanical, rheological and interfacial properties were compared. The m-EPR elastomers were added to iPP in 2.5, 5, 10, 15, and 20 vol.%. Torque values, elongation at break and impact strength measured of the iPP/m-EPR1 blends were higher than the iPP/m-EPR2 blends due to higher molten viscosity of m-EPR1 than m-EPR2 copolymer. Slight differences in Young moduli as well as in tensile strength at yield and at break might indicate that tensile properties of iPP/m-EPR blends were not significantly affected by difference in viscosity or molecular mass, miscibility and spherulite size. Optimization diagrams indicated the metallocene m-EPR copolymers are efficient impact modifiers for polypropylene and showed good balancing of mechanical properties in iPP/m-EPR blends.