Synthesis and characteristics of microcapsules containing electrophoretic particle suspensions

A microcapsule containing titanium dioxide (TiO₂) and halocarbon oil was synthesized via an in situ polymerization using urea, melamine, and formaldehyde (UM/F) as a wall material to examine its potential application as a microcapsule-based electronic ink display technique. Poly(sodium styrene sulfonate) was used as an anionic polymeric surfactant to stabilize a droplet of the suspension, and easily combined with the UM/F prepolymer through ionic adsorption. The microcapsules obtained had an average diameter and wall thickness of approximately 50 μm and 500 nm, respectively. The electrophoretic TiO₂ particles in the microcapsules responded to electric fields with a response time of few seconds.     

Effect of electric fields on the surface profiles of electrorheological suspensions

The surface deformation induced in electric fields is studied on the comb pattern electrodes for silica suspensions. On the application of electric fields, a fine pattern with a waveform is developed from the smooth surface. The surface profiles can be approximated by single sinusoidal waves or their superposition depending on the sample thickness. In electric fields, the silica suspensions shows the viscosity decrease in steady shear and yield stress in the limit of zero shear rates. The viscosity decrease can be attributed to electrophoretic migration of particles to one electrode and the development of yield stress to eletrorheological effects due to chain formation of particles between electrodes. In thick liquid films, the dielectric polarization forces are predominant and the sinusoidal profiles with a wavelength of pitch of electrodes are formed. In thin films, the electrophoretic forces are predominant and the wavelength coincides with twice the pitch of electrodes. At intermediate thicknesses, the surface profiles can be expressed by a superposition of two sinusoidal waves.     

Quasi-static electrorheological properties of hematite/silicone oil suspensions under DC electric fields

In this work, a modified rheometer has been used to gain information on the "start-up" of the shear flow of an electrorheological (ER) fluid consisting of hematite particles dispersed in silicone oil. The results show that unelectrified suspensions behave essentially as fluids, continuously deforming upon application of shear. However, this behavior changes in the presence of an electric field. For low fields and low volume fractions of solids, a solidlike (drastic increase in shear stress after the strain is applied) behavior is observed for small deformations. If the strain is increased, the yield starts and a transition to a viscoelastic-plastic nature is observed. Finally, a plastic behavior is characteristic of the post-yield regime. If the field strength and solids content are high, a discontinuous flow profile develops. These results, together with direct structural observations, suggest that the observed behavior is compatible with the formation of layers of particles electrophoretically deposited on the electrodes; the layers turn into rings when the shear field is applied. It is the slip of the fluid between these rings that can be considered responsible for the ER effect in these suspensions.     

Two-dimensional colloidal structures responsive to external fields

Recently advances in the area of ordering phenomena of colloidal suspensions under the combined action of external fields and spatial confinement have taken place. Colloidal systems confined to an interface are ideal models for the two-dimensional melting transition or light-induced crystallization and re-entrant melting. © 1999 Elsevier Science Ltd.     

The early stages of Saccharomyces cerevisiae yeast suspensions damage in moderate pulsed electric fields

The objectives of this study were to investigate the effects of pulsed electric fields (PEF) application to colloidal suspension of Saccharomyces cerevisiae. The electrical conductivity measurements during the PEF-treatment of S. cerevisiae suspensions were used to monitor the extent of cell damages in the intervals of electric field strength E = 3–15 kV/cm and time of PEF treatment t_PEF = 10⁻⁴ to 1 s. At relatively small fields (E < 7.5 kV/cm) the early stages of yeast cells damages were observed. At such treatment conditions, the damage was incomplete and developed at long time of PEF treatment, below the value of E = 7.5 kV/cm which is commonly referred in literature as a threshold for this culture. Data obtained for the disintegration in conductivity experiments were found in good correlation with direct counting of yeast lethality using light microscopy. The PEF-induced lethality of the yeast cells and size flocs increased with the mixing of suspensions and the increase of temperature.     

Electrical conductivity of graphite suspensions in potassium chloride solutions in direct- and alternating-current electric fields

Electrical conductivity of graphite dispersions in aqueous KCl solutions has been measured. The measurements have been performed in alternating- (1000 Hz) and direct-current electric fields. In an alternating-current electric field, at electrolyte concentrations of 0.0005–0.01 М, the conductivity increases as depending on the mass fraction of the dispersed phase. In 0.1 М solutions, a decrease in the conductivity of the suspension is followed by an increase at dispersed phase contents of higher than 15 wt %. In a direct-current electric field, the conductivity of graphite suspensions (0.001–0.01 М KCl) varies slightly and increases at dispersed phase contents of higher than 15 wt %. In 0.1 М solutions, the specific conductivity of the suspension initially decreases and, then, increases at dispersed phase concentrations above 15 wt %. The unusual electrical properties of the suspensions have been explained as being results of variations in the capacitive and active components of the conductivity of graphite dispersions in electrolytes within the framework of a topological model. Particle polarization and a relatively high capacitive component of the conductivity mainly contribute to an increase in the conductivity of the suspensions in 0.0005–0.01 М electrolytes in the alternating-current electric field. A decrease in the conductivity of suspensions in 0.1 М electrolytes is due to a negative difference between the capacitive and active components of the specific conductivity. It has been assumed that the aggregation of graphite particles yields conducting structures at dispersed phase concentrations above 15 wt %.     

Synthesis,characterization, and controlled release study of polyurea microcapsules containing metribuzin herbicide

Russian Journal of Applied Chemistry - Controlled release herbicide formulation was prepared by microencapsulation using interfacial polymerization technique. Methylene bisdiphenyl diisocynate...     

Synthesis and characterization of a Gd(III) based contrast agent responsive to thiol containing compounds

A novel Gd(III) complex with a modified DO3A-like chelating cage has been synthesized and characterized as a candidate contrast agent responsive to the concentration of free thiols in tissues (essentially represented by reduced glutathione, GSH). The novel compound (called Gd-DO3AS-Act) bears a flexible linker ending with a 2-pyridyl-dithio group, that can promptly react with free thiols (XSH) to form mixed disulfides of the form Gd-DO3AS-SX. Compound Gd-DO3AS-Act is characterized by a millimolar relaxivity as high as 8.1 mM(-1) s(-1) (at 20 MHz, 25 degrees C and pH 7.4). Upon reaction with GSH, the Gd-DO3AS-SG covalent adduct is formed and the millimolar relaxivity drops to 4.1 mM(-1) s(-1). Such a decrease in relaxivity is explained on the basis of the formation of an intramolecular coordinative bond between one of the glutathionyl carboxyl groups and the Gd(III) centre, lowering the hydration state of the paramagnetic centre. (1)H-NMR dispersion profiles together with (17)O-NMR transverse relaxation time versus temperature profiles confirm that the hydration of the Gd(III) centre is strongly reduced ongoing from Gd-DO3AS-Act to the Gd-DO3AS-SG adduct. The relaxivity difference brought about by the reaction of Gd-DO3AS-Act with GSH can be enhanced up to 60% in the presence of poly-beta-cyclodextrin.     

Preparation of microcapsules containing two-phase core materials

Urea-formaldehyde (UF) microcapsules containing two-phase core materials in which phthalocyanine blue BGS (beta-CuPc) particles were homodispersed in tetrachloroethylene (TCE) were prepared by in situ polymerization. The effects of the various process parameters, including the type of surface modifier, the viscosity of UF prepolymer, the type of water-soluble surfactant, and the concentration of oil-soluble surfactant in the capsule core on the dispersity of beta-CuPc particles in TCE and the properties of the capsule wall and the adsorption of beta-CuPc particles on the internal surface of capsule wall were experimentally investigated. It was shown that using octadecylamine (ODA) to modify beta-CuPc particles resulted in a significant increase of the dispersing extent (DE) and the electrophoresis velocity of the particles in TCE (about 4 and 20 times more than that of unmodified). In addition, the optimal reaction conditions of the synthesis UF prepolymer were obtained by the orthogonal test. On the other hand, as the oil/water interfacial tension of emulsion was big enough, the microcapsule formed. The concentration of Span-80 in TCE was no less than 0.062 mM; the adsorption of beta-CuPc particles on internal surface of wall were restrained. Finally, the microcapsules in which beta-CuPc particles possess reversible response to dc electric field were obtained.     

Synthesis and some reactions of oxazolidines containing functional groups

A number of hitherto unknown 2-substituted 3-furfuryloxazolidines and 2-substituted 3-tetrahydrofurfuryloxazolidines are synthesized. The reaction of hydroxyethyloxazolidine with esters, and of 5-(phenylaminomethyl)-3-phenyloxazolidine with ethylene chlorohydrin are investigated.     

Synthesis and some reactions of oxazolidines containing functional groups

A number of hitherto unknown 2-substituted 3-furfuryloxazolidines and 2-substituted 3-tetrahydrofurfuryloxazolidines are synthesized. The reaction of hydroxyethyloxazolidine with esters, and of 5-(phenylaminomethyl)-3-phenyloxazolidine with ethylene chlorohydrin are investigated.     

Synthesis and cationic photopolymerization of electroactive monomers containing functional groups

The synthesis and cationic photopolymerization of different cationically polymerizable monomers containing electroactive groups are reviewed with 98 references. The preparation of various compounds containing electron‐donor or electron‐acceptor moieties and photopolymerizable functional groups is described. After a short discussion of basic principles of cationic polymerization, photoinduced cationic polymerizations of various cationically polymerizable monomers containing both electron‐donor or electron‐acceptor chromophores and the functional groups such as epoxy, vinyl, thiiranyl, oxetanyl and others are reviewed. Copyright © 2005 John Wiley & Sons, Ltd.     

Conductivity of flowing polyaniline suspensions in electric field

The formation of chain structures by polarized polyaniline (PANI) particles suspended in silicone oil in the electric field has been monitored by recording suspension conductivity in the course of time. For that purpose, three types of PANI particles differing in the conductivity (3.1 × 10⁻³, 1.7 × 10⁻¹, and 2.0 × 10⁻¹ S cm⁻¹) have been chosen out of a series of nine samples prepared by controlled protonation of PANI base in orthophosphoric acid solutions. Relaxation times reflecting this process and characterizing the rate of the response to the electric field decreased with particle conductivity, indicating a higher polarizability of particles. At the same time, the maximum conductivity of suspension increased as a consequence of the electric and shear forces acting on the particles. In the shear fields, shorter relaxation times appeared than at rest. The simultaneous measurement of the shear stress confirmed that the conductivity investigation can reliably characterize the development of electrorheological structures.     

Stable fluoroaliphatic radicals containing functional groups: Synthesis and reactivity

β-Fluorosulphatoperfluoroalkyl radicals (3, 7 and 8) are obtained by the reaction of fluoroolefins (HFP trimer and dimer, and perfluoro4 4-dimethylpent-2-ene, respectively) with (FSO₃)₂. The pure β-fluorosulphatotetrafluoroethylperfluorodiisopropylmethyl radical (3) has been isolated and converted to the perfluoroacetyldiisopropylmethyl radical (4) under the action of CsF. The reaction of radicals 3,7 and 8 with SbF₅ leads to the replacement of the FSO₃ group by a fluorine atom. The ability of the FSO₃ group in β-fluorosulphatoperfluoroalkyl radicals to play the role of a leaving group is explained by the stabilizing effect of the unshared electron on the adjacent carbocation centre.     

Synthesis of functional block copolymers and terpolymers containing polyglycidyl methacrylate blocks

Here, the synthesis of triblock terpolymers using tert‐butyl acrylate, glycidyl methacrylate, and methyl methacrylate was studied in detail using atom transfer radical polymerization. Those polymers are promising candidates for irreversible linked microstructured layers on surfaces. The experiments showed that the polymerization has to be started with the acrylate and can be extended with the methacrylates. The first two steps can be done in a one pot procedure employing the method of halogen exchange. With optimized reaction conditions in the last step, the obtained terpolymers show narrow molecular weight distributions and the polymerization process is well controlled. Conducting the synthesis in the opposite direction mostly a nonuniform product was obtained as the GPC analysis showed. Further characterization was done with ¹H NMR spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, the latter showing different glass points for the single blocks in the terpolymers if they are not too short. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 675–684