preparation-hollow-polystyrene-particles-microcapsules-radical

Preparation of Hollow Polystyrene Particles and Microcapsules by Radical Polymerization of Janus Droplets Consisting of Hydrocarbon and Fluorocarbon Oils

In this article, we have demonstrated a method for producing hollow particles and microcapsules using oil droplets consisting of hydrocarbon oil (styrene) ...

Tokyo University of Science

Tokyo University of science

The azobenzene derivative 4,4'-bis{1-[2-(N,N-dimethylamino)]ethoxy}azobenzene has been found to form gold-colored plate-like crystals. The thin film obtained by accumulating the crystals has a maximum specular reflectance of ca. 15% for visible light. To investigate the structure of the gold-colored crystals, UV-vis, X-ray diffraction (XRD), and IR analyses were performed. UV-vis measurements show that the molecules in the crystal produce J-aggregates. Furthermore, XRD measurements estimated the long-range d-spacing for the crystal as 1.51 nm. These results indicate that the azobenzene moieties are oriented diagonally against the crystal surfaces. When the crystals are placed in a desiccator (humidity 40%) for 1 d, their color changes from gold to yellow. IR measurements show that the gold-colored crystals contain crystallized water, while there are no water molecules in the yellow crystals, in which the structure of the J-aggregates is disrupted. These results show that the crystallized water molecules are essential for the formation of the J-aggregates and the resultant gold luster.

Gold-colored organic crystals formed from an azobenzene derivative.

The morphologies of aggregates formed from a hybrid surfactant (F6H5OS) whose molecules have a hydrocarbon chain (pentyl group) and a fluorocarbon chain (perfluorohexyl group) were studied along with changes in the morphologies with time. F6H5OS exhibits a micelle-vesicle transition at a concentration of 5.5 mM in water. Cryo-TEM observation of 5 mM aqueous F6H5OS solution reveals the existence of only micelles with a diameter of ca. 6 nm, while the coexistence of micelles and vesicles is observed in 10 mM aqueous F6H5OS solution. When the 10 mM aqueous F6H5OS solution is aged, the micelles are transformed into vesicles. Further, the vesicles have different structures, namely, spherical and tubular structures. (1)H NMR, (1)H-(1)H NOESY, and FT-IR experiments suggest that upon aging, the conformation of hydrocarbon chains in F6H5OS changes, and the hydrocarbon chains are located close to the phenyl group in the surfactant molecules. At concentrations above 5.5 mM, small micelles are formed immediately after the preparation of the F6H5OS solutions; those micelles subsequently transform into vesicles. The hybridity of F6H5OS, i.e., having a fluorocarbon chain and a hydrocarbon chain in its molecule, plays an important role in the transformation of micelles into vesicles upon aging.

Self-assembly of a fluorocarbon-hydrocarbon hybrid surfactant: dependence of morphology on surfactant concentration and time.

Here, we report unusual behaviour of the viscoelasticity of surfactant aqueous solutions consisting of cationic cetyltrimethylammonium bromide (CTAB) and an anionic photoresponsive amphiphile, sodium [4-(4-butylphenylazo)phenoxy]acetate (C4AzoNa). When C4AzoNa molecules are trans-isomers, spheroidal micelles are formed in the surfactant solution, the viscosity of which is low. Irradiation of this solution by ultraviolet (UV) light yields an aqueous solution of CTAB/cis-C4AzoNa (cis-isomers of C4AzoNa), which is a highly viscous gel consisting of wormlike micelles. The drastic change in the surfactant solution viscosity is attributed to the formation and disruption of wormlike micelles. The geometrical structural transformation of the azobenzene groups in the C4AzoNa molecules of the CTAB/C4AzoNa mixture would lead to a change in the critical packing parameter of the mixture, thereby inducing the morphological transformation of the aggregates (spheroidal micelles to wormlike micelles). To our knowledge, this is the first report of a drastic increase in surfactant solution viscosity by UV light irradiation.

Unusual viscoelasticity behaviour in aqueous solutions containing a photoresponsive amphiphile.

This Article reports on the influence of light irradiation on the stability of emulsions prepared using a photoresponsive gemini surfactant (C7-azo-C7) having an azobenzene skeleton as a spacer. When mixtures of trans C7-azo-C7 aqueous solution and n-octane are homogenized, stable emulsions are obtained in a specific region of weight fraction and surfactant concentration. Fluorescence microscopy observations using a small amount of fluorescent probes show that the stable emulsions are oil-in-water (O/W)-type. UV irradiation of stable O/W emulsions promotes the cis isomerization of trans C7-azo-C7 and leads to the coalescence of the oil (octane) droplets in the emulsions, that is, demulsification. While the equilibrated interfacial tension (IFT) between aqueous trans C7-azo-C7 solution and octane is almost the same as that between aqueous cis C7-azo-C7 and octane, the occupied area per molecule for C7-azo-C7 at octane/water interface decreases with the cis photoisomerization of trans isomer. Dynamic IFT measurement shows that UV irradiation to the interface between aqueous trans C7-azo-C7 solution and octane brings about an increase in the interfacial tension, indicating that the Gibbs free energy at the interface increases. From these results, the cis isomerization of trans C7-azo-C7 molecules at the O/W interface due to UV irradiation leads to direct contact between the water and octane phases, because of the reduction of molecular area at the interface, and subsequently makes the emulsions demulsified.

Photoinduced demulsification of emulsions using a photoresponsive gemini surfactant.

This paper reports a method to control the formation and disruption of vesicles from a novel single-tailed surfactant (11-ferrocenylundecylammonium bromide, 11-FAB), which contains two stimuli-responsive groups corresponding to pH variation and redox reaction conditions, by external stimuli. Although 11-FAB is a single-tailed surfactant, pure 11-FAB spontaneously forms vesicles in water. Microscopic observations of 2.5 mM aqueous solutions of pure 11-FAB (pH = 5.2) show that a number of 11-FAB vesicles are giant, with diameters of 10-30 μm. The disruption of vesicles is observed in aqueous 11-FAB solutions under basic conditions. The vesicles are then reformed under acidic conditions. Reduced 11-FAB also forms large vesicles in electrolyte solutions. These vesicles are disrupted by electrochemical oxidation and reformed by subsequent chemical reduction. This reversible disruption and reformation of vesicles is attributed to the drastic change in the molecular structure of 11-FAB. To our knowledge, this is the first report of control over the formation and disruption of vesicles using two stimuli responses.

Control of dual stimuli-responsive vesicle formation in aqueous solutions of single-tailed ferrocenyl surfactant by varying pH and redox conditions.

A new azobenzene derivative, bis[4-(3-methylbutoxy)phenyl]diazene (DC-azo), was synthesized as yellow powder through a three-step reaction. DC-azo was crystallized from a mixture of acetone/water in the form of highly insulating gold-colored crystals with a specular reflectance of 21% over the wavelength range of 520-800 nm. The CIELAB color space of the crystals indicated that the crystals were slightly more reddish and less yellowish than metallic Au. The crystals retained their gold coloration under dry conditions and were stable up to 383 K. The X-ray diffraction (XRD) measurements estimated the long-range periodical thickness in the crystal to be 1.12 nm, thereby indicating that the DC-azo molecules were oriented such that the azobenzene moieties showed a tilt angle of 32.2° against the crystal surface. The gold-colored crystals of DC-azo could be a potential substitute for the conventional metallic paints.

Gold-colored organic crystals of an azobenzene derivative.

The influence of ultraviolet (UV) light irradiation on the emulsification properties of mixtures of an anionic surfactant, sodium dodecyl sulfate (SDS), and a photoresponsive cationic surfactant, 2-(4-(4-butylphenyl)diazenylphenoxy)ethyltrimethylammonium bromide (C4AzoTAB), containing an azobenzene group has been investigated. When mixtures of n-octane and aqueous SDS/trans-C4AzoTAB solution are homogenized, stable emulsions are obtained in regions of specific surfactant concentrations and molar ratios of the mixed surfactants. The stable emulsions are stable for over a week and found to be of the oil-in-water (O/W) type. UV light irradiation of the stable O/W emulsions leads to the coalescence of smaller oil droplets into larger ones in the emulsions, i.e., demulsification. As a result, the oil and aqueous surfactant solution phases are fully separated by UV light irradiation for 90 min, even shorter than our previous result (6 h; Langmuir 2014 , 30 , 41 - 47 ). The use of a microreactor shortens the time required for the photoinduced demulsification into 3.5 min. When mixtures of octane and aqueous SDS/cis-C4AzoTAB solution are homogenized, no emulsions are obtained. The interfacial tension (IFT) between octane and aqueous SDS/cis-C4AzoTAB solution is higher than that between octane and aqueous SDS/trans-C4AzoTAB solution, indicating that the IFT of SDS/trans-C4AzoTAB mixtures increases with the cis photoisomerization of the trans isomer. These results suggest that cis isomerization of the SDS/trans-C4AzoTAB mixtures due to UV light irradiation causes Ostwald ripening of the octane droplets in the emulsions, thereby reducing the interfacial area between the octane and water phases as the IFT between octane and the aqueous surfactant solution increases. Subsequently, the octane and aqueous solution phases separate.

Active Demulsification of Photoresponsive Emulsions Using Cationic-Anionic Surfactant Mixtures.

This study examined the influence of ultraviolet (UV) irradiation on aqueous surfactant solutions containing an anionic stilbene derivative (sodium [4-[(E)-2-(4-butylphenyl)ethenyl]phenoxy]acetate; C4StilNa) as a photoresponsive skeleton. Prior to UV irradiation, an aqueous solution of cetyltrimethylammonium bromide (CTAB) and C4StilNa was a low-viscosity fluid forming spheroidal micelles. Exposure of the low-viscosity fluid to UV light resulted in the formation of threadlike micelles and an increase in the viscosity of the aqueous CTAB/C4StilNa solution. (1)H nuclear magnetic resonance spectroscopy indicated that the photochemically induced isomerization and dimerization reactions of C4StilNa molecules had occurred in the aggregates due to UV irradiation. Overall, the structural transformation of the stilbene groups in the C4StilNa molecules with the photochemical reactions leads to an increase in the critical packing parameter and consequently a photoinduced transition of spheroidal micelles to threadlike micelles.

Photoinduced formation of threadlike micelles from mixtures of a cationic surfactant and a stilbene amphiphile.

This article reports the influence of redox reactions on emulsions of n-octane and an aqueous solution of a ferrocene-containing surfactant (FTMA; (11-ferrocenylundecyl)trimethylammonium bromide). Above a certain surfactant concentration, stable O/W emulsions were formed from an aqueous solution of reduced FTMA; in contrast, mixtures of n-octane and an aqueous solution of oxidized FTMA did not form emulsions at any surfactant concentration. Furthermore, adding an oxidant to the stable O/W emulsions of reduced FTMA led to coalescence of the oil (octane) droplets in the emulsions, and subsequently, the oil and water (aqueous FTMA solution) phases fully separated from the emulsions, i.e., demulsification occurred. Equilibrated interfacial tension measurements indicate that oxidation of the ferrocenyl group in FTMA brings about an increase in the interfacial tension between the octane and aqueous surfactant solution phases. From these results, we concluded that the oxidation of reduced FTMA to oxidized FTMA led to the desorption of surfactant molecules adsorbed at the interface of the octane/aqueous surfactant solution, leading to demulsification.

Article	Year
Gold-colored organic crystals formed from an azobenzene derivative. Journal of oleo science\| PubMed ID: 20124757	2010
Self-assembly of a fluorocarbon-hydrocarbon hybrid surfactant: dependence of morphology on surfactant concentration and time. The journal of physical chemistry. B\| PubMed ID: 20882953	2010
Unusual viscoelasticity behaviour in aqueous solutions containing a photoresponsive amphiphile. Journal of colloid and interface science\| PubMed ID: 23838330	2013
Photoinduced demulsification of emulsions using a photoresponsive gemini surfactant. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 24354334	2014
Control of dual stimuli-responsive vesicle formation in aqueous solutions of single-tailed ferrocenyl surfactant by varying pH and redox conditions. Journal of oleo science\| PubMed ID: 24492378	2014
Gold-colored organic crystals of an azobenzene derivative. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 24690083	2014
Active Demulsification of Photoresponsive Emulsions Using Cationic-Anionic Surfactant Mixtures. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 26731043	2016
Photoinduced formation of threadlike micelles from mixtures of a cationic surfactant and a stilbene amphiphile. Journal of colloid and interface science\| PubMed ID: 26967168	2016
Demulsification of Redox-Active Emulsions by Chemical Oxidation. Langmuir : the ACS journal of surfaces and colloids\| PubMed ID: 27402350	2016

Yutaka Takahashi

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