Christos Mantzaridis

Complexes between High Charge Density Cationic Polyelectrolytes and Anionic Single- and Double-Tail Surfactants

Polyelectrolyte/surfactant complexes formed between well-defined linear flexible polyelectrolytes, namely, quaternized poly[3,5-bis(dimethylaminomethylene)hydroxystyrene] (Q-N-PHOS), bearing two cationic sites on each repeating unit, and two different anionic surfactants, namely, sodium dodecyl sulfate (SDS) with one hydrocarbon tail and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) with two hydrocarbon chains, are studied by means of fluorescence spectroscopy, electrophoretic, dynamic and static light scattering, and atomic force microscopy. Depending on the surfactant state in initial solutions (i.e., below or above nominal critical micelle concentration, cmc) and final (-/+) charge ratio, self-assembly in nanoparticles of variable size, stability, and effective charge is possible. Spherical, rather polydispserse complexes are formed in all cases. Critical aggregation concentrations (cac) depend on the surfactant type, while hydrophobicity of the main polyelectrolyte chain plays a role in colloidal stability of the complex nanoparticles.

Association of Poly(4-hydroxystyrene)-block-Poly(Ethylene oxide) in Aqueous Solutions: Block Copolymer Nanoparticles with Intermixed Blocks

Association behavior of diblock copolymer poly(4-hydroxystyrene)-block-poly(ethylene oxide) (PHOS-PEO) in aqueous solutions and solutions in water/tetrahydrofuran mixtures was studied by static, dynamic, and electrophoretic light scattering, (1)H NMR spectroscopy, transmission electron microscopy, and cryogenic field-emission scanning electron microscopy. It was found that, in alkaline aqueous solutions, PHOS-PEO can form compact spherical nanoparticles whose size depends on the preparation protocol. Instead of a core/shell structure with segregated blocks, the PHOS-PEO nanoparticles have intermixed PHOS and PEO blocks due to hydrogen bond interaction between -OH groups of PHOS and oxygen atoms of PEO and are stabilized electrostatically by a fraction of ionized PHOS units on the surface.

Wormlike core–shell nanoparticles formed by co-assembly of double hydrophilic block polyelectrolyte with oppositely charged fluorosurfactant

Formation of polyelectrolyte–surfactant complexes (PE–S) between an anionic polyelectrolyte, poly(sodium 2-sulfamate-3-carboxylate isoprene)-block-poly(ethylene oxide) (PSCI-PEO) and a cationic fluorosurfactant, N-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl) pyridinium chloride (HFDPCl) was studied in alkaline aqueous solutions by static, dynamic and electrophoretic light scattering. The structure of the formed PE–S nanoparticles was investigated by SAXS, cryogenic transmission electron microscopy and atomic force microscopy. The results show that the tendency of the fluorosurfactant to form elongated threadlike micelles drives the PE–S co-assembly to a flexible core–shell cylindrical morphology with the core of the PE–S and the shell of the PEO blocks. Unlike other PE–S systems involving double hydrophilic polyelectrolytes, well-defined core–shell particles exist only in the narrow range of HFDPCl-to-PSCI unit stoichiometric ratios corresponding to zero ζ-potential of the aggregates.

Experimental investigation of long time irradiation in polydiene solutions: reversibility and instabilities

Polydiene solutions have recently been shown to possess a refractive index/concentration optical nonlinearity upon irradiation by CW-laser of a power as low as a few mW with typical timescales for solitonic formation in the order of seconds. Here we report on the effects of longer time laser irradiations which unveiled a variety of light-induced patterns. At extended irradiation times, rather than saturation or steady state of the single-filament pattern initially formed, the formation of more complex structures was systematically observed. The reversibility of the laser-induced concentration increase was shown to depend on irradiation time. Whereas exposures of the order of the inverse of the rate of formation resulted in reversible patterns, prolonged irradiation led to surprisingly long lasting irreversible structures that even resisted dissolution in a pure solvent. An intermediate case of semi-reversible patterns was observed giving rise to a pearl-necklace formation. Despite the as yet unidentified coupling, polydiene solutions offer a rich playground for soft matter nonlinear optics and potentially provide a readily available system for micro-patterning in a lithographic-like manner.

Micro-fabrication by laser radiation forces: a direct route to reversible free-standing three-dimensional structures.

The origins and first demonstration of structurally stable solids formed by use of radiation forces are presented. By experimentally proving that radiation forces can indeed produce stable solid material forms, a novel method enabling two- and three-dimensional (2d and 3d) microfabrication is introduced: An optical, non-contact single-step physical operation, reversible with respect to materials nature, based on the sole use of radiation forces. The present innovation is elucidated by the formation of polyisoprene and polybutadiene micro-solids, as well as plasmonic and fluorescent hybrids, respectively comprising Au nanoparticles and CdS quantum dots, together with novel concepts of polymeric fiber-drawing by radiation forces.

Self-induced transparency in diblock copolymer dispersions.

We report on the versatile effect of weak red laser light impinging on diblock copolymer [poly(isoprene-b-styrene)] dispersions in two selective solvents for each block. In the strongly scattering but transparent micellar solutions in hexane (a good solvent for polyisoprene), higher refractive index copolymer-rich fibers were formed. In the turbid dispersions of the same copolymer in ethyl acetate (a good solvent for polystyrene), the effect of self-induced transparency was observed. A two-step patterning mechanism caused the generation of a transparent microchannel, increasing light transmission. The analogy between the current effect and that observed in homopolymer polyisoprene solutions in different solvents is discussed toward an understanding of the unanticipated light-soft-matter interaction.

Kinetics of Light-Induced Concentration Patterns in Transparent Polymer Solutions

When exposed to weak visible laser light, solutions of common polymers like poly(isoprene) and poly(butadiene) respond by local concentration variations, which in turn lead to refractive index changes. Various micropatterns have been recently reported, depending mostly on the solvent environment and the irradiation conditions. Here, we focused on the simpler case of single polymer-rich filaments and we employed phase contrast microscopy to systematically investigate the influence of laser illumination and material parameters on the kinetics of the optically induced local concentration increase in the polydiene solutions. The refractive index contrast of the formed filaments increased exponentially with the laser illumination time. The growth rate exhibited linear dependence on the laser power and increased with polymer chain length in semidilute solutions in good solvents. On the contrary, the kinetics of the formed filaments appeared to be rather insensitive to the polymer concentration. Albeit the origin of the peculiar light field-polymer concentration coupling remains yet elusive, the new phenomenology is considered necessary for the elucidation of its mechanism.

Polydiene Solutions: A Surprising Versatile Non Linear Optics Material

The astonishing non linear optical properties of solutions of polyisoprene and polybutadiene in various organic solvents are reviewed: When irradiated with mild laser light, the non absorbing solutions respond by a change of the local polymer concentration inducing a local variation of the refractive index that alters the light propagation. Observed formations include optical spatial soliton‐like filaments, multi‐filaments arrays resulting from modulational instabilities, multi‐filament holographic gratings or even more complex structures.