Templating of mesoporous molecular sieves by nonionic polyethylene oxide surfactants

Mesoporous silica molecular sieves have been prepared by the hydrolysis of tetraethylorthosilicate in the presence of low-cost, nontoxic, and biodegradable polyethylene oxide (PEO) surfactants, which act as the structure-directing (templating) agents. This nonionic, surfactant-neutral, inorganic-precursor templating pathway to mesostructures uses hydrogen bonding interactions between the hydrophilic surfaces of flexible rod- or worm-like micelles and Si(OC(2)H(5))(4-x)(OH)(x) hydrolysis products to assemble an inorganic oxide framework. Disordered channel structures with uniform diameters ranging from 2.0 to 5.8 nanometers have been obtained by varying the size and structure of the surfactant molecules. Metal-substituted silica and pure alumina mesostructures have also been prepared by the hydrolysis of the corresponding alkoxides in the presence of PEO surfactants. These results suggest that nonionic templating may provide a general pathway for the preparation of mesoporous oxides.     

Helical superstructures from charged Poly(styrene)-Poly(isocyanodipeptide) block copolymers

Amphiphilic block copolymers containing a poly(styrene) tail and a charged helical poly(isocyanide) headgroup derived from isocyano-L-alanine-L-alanine and isocyano-L-alanine-L-histidine were prepared. Analogous to low-molecular mass surfactants, these block copolymers self-assembled in aqueous systems to form micelles, vesicles, and bilayer aggregates. The morphology of these aggregates can be controlled by variation of the length of the poly(isocyanide) block, the pH, and the anion-headgroup interactions. The chirality of the macromolecules results in the formation of helical superstructures that have a helical sense opposite to that of the constituent block copolymers. The great variety of morphologies displayed by these block copolymers and the fact that they are easily accessible from poly(styrene) and different types of peptides open new opportunities for applications in the fields of life and materials sciences.     

Polystyrene-dendrimer amphiphilic block copolymers with a generation-dependent aggregation

A class of amphiphilic macromolecules has been synthesized by combining well-defined polystyrene (PS) with poly(propylene imine) dendrimers. Five different generations, from PS-dendr-NH(2) up to PS-dendr-(NH(2))(32), were prepared in yields of 70 to 90 percent. Dynamic light scattering, conductivity measurements, and transmission electron microscopy show that in aqueous phases, PS-dendr-(NH(2))(32) forms spherical micelles, PS-dendr-(NH(2))(16) forms micellar rods, and PS-dendr-(NH(2))(8) forms vesicular structures. The lower generations of this class of macromolecules show inverted micellar behavior. The observed effect of amphiphile geometry on aggregation behavior is in qualitative agreement with the theory of Israelachvili et al. The amphiphiles presented here are similar in shape but different in size as compared with traditional surfactants, whereas they are similar in size but different in shape as compared with traditional block copolymers.     

反胶束体系对姜黄素的增溶及其稳定性作用

以乙醇和2种非离子表面活性剂作增溶剂,制备了姜黄素反胶束体系,对姜黄素进行了增溶和稳定性试验.结果表明:在所考察的2种表面活性剂与乙醇的不同配比的反胶束中,对姜黄素增溶最佳配比都是1∶2(表面活性剂:乙醇),而在60℃时,EL-35与乙醇以1:2的配比形成的反胶束对姜黄素的增溶量达到了最大,最大值为34.198 mg·...     

Branched threadlike micelles in an aqueous solution of a trimeric surfactant

Very long threadlike micelles observed in aqueous solutions of some surfactants have attracted much attention because of the peculiar rheological properties of these systems. Molecular dynamics simulations have suggested that branched threadlike micelles should exist in concentrated solutions of dimeric surfactants. Here experimental evidence, obtained from transmission electron microscopy at cryogenic temperature, is presented of branched threadlike micelles in aqueous solutions of a triquaternary ammonium (trimeric) surfactant made up of three amphiphilic moieties connected at the level of the head-groups by two propanediyl spacers.     

Simulating the self-assembly of gemini (dimeric) surfactants

The morphologies and dynamics of aggregates formed by surfactant molecules are known to influence strongly performance properties spanning biology, household cleaning, and soil cleanup. Molecular dynamics simulations were used to investigate the morphology and dynamics of a class of surfactants, the gemini or dimeric surfactants, that are of potential importance in several industrial applications. Simulation results show that these surfactants form structures and have dynamic properties that are drastically different from those of single-chain surfactants. At the same weight fraction, single-chain surfactants form spherical micelles whereas gemini surfactants, whose two head groups are coupled by a short hydrophobic spacer, form thread-like micelles. Simulations at different surfactant concentrations indicate the formation of various structures, suggesting an alternative explanation for the unexpected viscosity behavior of gemini surfactants.     

Theory of spontaneous vesicle formation in surfactant mixtures

The curvature elastic energy of bilayer vesicles formed by a mixture of two surfactants, which individually form either micelles or lamellar bilayer phases is described theoretically. In the limit of large bending elastic modulus K being much greater than the temperature T, the free energy is minimized by vesicles with different concentrations of the two surfactants in each monolayer of the bilayer. Vesicles are more stable than lameliar structures only when interactions or complexing of the two surfactants is taken into account.     

Non-centrosymmetric cylindrical micelles by unidirectional growth

Although solution self-assembly of block copolymers (BCPs) represents one of the most promising approaches to the creation of nanoparticles from soft matter, the formation of non-centrosymmetric nanostructures with shape anisotropy remains a major challenge. Through a combination of crystallization-driven self-assembly of crystalline-coil BCPs in solution and selective micelle corona cross-linking, we have created short (about 130 nanometers), monodisperse cylindrical seed micelles that grow unidirectionally. These nanostructures grow to form long, non-centrosymmetric cylindrical A-B and A-B-C block co-micelles upon the addition of further BCPs. We also illustrate the formation of amphiphilic cylindrical A-B-C block co-micelles, which spontaneously self-assemble into hierarchical star-shaped supermicelle architectures with a diameter of about 3 micrometers. The method described enables the rational creation of non-centrosymmetric, high aspect ratio, colloidally stable core-shell nanoparticles in a manner that until now has been restricted to the biological domain.     

Self-assembly of ordered, robust, three-dimensional gold nanocrystal/silica arrays

We report the synthesis of a new nanocrystal (NC) mesophase through self-assembly of water-soluble NC micelles with soluble silica. The mesophase comprises gold nanocrystals arranged within a silica matrix in a face-centered cubic lattice with cell dimensions that are adjustable through control of the nanocrystal diameter and/or the alkane chain lengths of the primary alkanethiol stabilizing ligands or the surrounding secondary surfactants. Under kinetically controlled silica polymerization conditions, evaporation drives self-assembly of NC micelles into ordered NC/silica thin-film mesophases during spin coating. The intermediate NC micelles are water soluble and of interest for biolabeling. Initial experiments on a metal-insulator-metal capacitor fabricated with an ordered three-dimensional gold nanocrystal/silica array as the "insulator" demonstrated collective Coulomb blockade behavior below 100 kelvin and established the current-voltage scaling relationship for a well-defined three-dimensional array of Coulomb islands.     

Self-assembled aggregates of rod-coil block copolymers and their solubilization and encapsulation of fullerenes

Amphiphilic poly(phenylquinoline)-block-polystyrene rod-coil diblock copolymers were observed to self-organize into robust, micrometer-scale, spherical, vesicular, cylindrical, and lamellar aggregates from solution. These diverse aggregate morphologies were seen at each composition, but their size scale decreased with a decreasing fraction of the rigid-rod block. Compared to coil-coil block copolymer micelles, the present aggregates are larger by about two orders of magnitude and have aggregation numbers of over 10(8). The spherical and cylindrical aggregates have large hollow cavities. Only spherical aggregates with aggregation numbers in excess of 10(9) were formed in the presence of fullerenes (C60, C70) in solution, resulting in the solubilization and encapsulation of over 10(10) fullerene molecules per aggregate.     

土壤环境中粘粒的分散-凝聚行为及其影响因素

本文研究了一般无机离子,重金属离子,表面活性剂和高分子化合物对土壤粘粒分散凝聚行为的影响,以期为土壤环境的保护与管理提供理论依据。结果表明i:)一般无机离子可通过对粘粒表面扩散双电层的压缩作用导致粘粒凝聚,且离子价数越高压缩作用越强i;i)重金属离子在粘粒上的专性吸附,导致其对扩散双电层的压缩作用更强i;ii)阳离子表面活性剂在较低浓度时可形成粒间疏水性表面胶束使粘粒凝聚,而在较高浓度时可形成粒内亲水性表面胶束使粘粒分散i;v)阳离子型高分子化合物在较低浓度时对粘粒的架桥作用可使粘粒凝聚,而在较高浓度时的静电斥力可使粘粒分散;v)随着pH的升高,粘粒由于表面负电荷的增加而趋于分散。以上说明:双电层的压缩、专性吸附、粒间疏水性表面胶束和架桥作用等均可使土壤粘粒凝聚,降低其稳定性。     

On the origins of morphological complexity in block copolymer surfactants

Amphiphilic compounds such as lipids and surfactants are fundamental building blocks of soft matter. We describe experiments with poly(1,2-butadiene-b-ethylene oxide) (PB-PEO) diblock copolymers, which form Y-junctions and three-dimensional networks in water at weight fractions of PEOintermediate to those associated with vesicle and wormlike micelle morphologies. Fragmentation of the network produces a nonergodic array of complex reticulated particles that have been imaged by cryogenic transmission electron microscopy. Data obtained with two sets of PB-PEOcompounds indicate that this type of self-assembly appears above a critical molecular weight. These block copolymers represent versatile amphiphiles, mimicking certain low molecular weight three-component (surfactant/water/oil) microemulsions, without addition of a separate hydrophobe.     

Carbon Dioxide Transport by Ocean Currents at 25{degrees}N Latitude in the Atlantic Ocean

Measured concentrations of CO(2), O(2), and related chemical species in a section across the Florida Straits and in the open Atlantic Ocean at approximately 25 degrees N, have been combined with estimates of oceanic mass transport to estimate both the gross transport of CO(2) by the ocean at this latitude and the net CO(2) flux from exchange with the atmosphere. The northward flux was 63.9 x 10(6) moles per second(mol/s); the southward flux was 64.6 x 10(6) mol/s. These values yield a net CO(2) flux of 0.7 x 10(6) mol/s (0.26 +/- 0.03 gigaton of C per year) southward. The North Atlantic Ocean has been considered to be a strong sink for atmospheric CO(2), yet these results show that the net flux in 1988 across 25 degrees N was small. For O(2) the equivalent signal is 4.89 x 10(6) mol/s northward and 6.97 x 10(6) mol/s southward, and the net transport is 2.08 x 10(6) mol/s or three times the net CO(2) flux. These data suggest that the North Atlantic Ocean is today a relatively small sink for atmospheric CO(2), in spite of its large heat loss, but a larger sink for O(2) because of the additive effects of chemical and thermal pumping on the CO(2) cycle but their near equal and opposite effects on the CO(2) cycle.     

Atmospheric carbon dioxide and carbon reservoir changes

The net release of CO(2) from the biosphere to the atmosphere between 1850 and 1950 is estimated to amount to 1.2 x 10(9) tons of carbon per year. During this interval, changes in land use reduced the total terrestrial biomass by 7 percent. There has been a smaller reduction in biomass over the last few decades. In the middle 19th century the air had a CO(2) content of approximately 268 parts per millon, and the total increase in atmospheric CO(2) content since 1850 has been 18 percent. Major sinks for fossil fuel CO(2) are the thermocline regions of large oceanic gyres. About 34 percent of the excess CO(2) generated so far is stored in surface and thermocline gyre waters, and 13 percent has been advected into the deep sea. This leaves an airborne fraction of 53 percent.     

The hydroperoxyl radical in atmospheric chemical dynamics: reaction with carbon monoxide

From measurements of the photochemical rate of production of CO(2)(16,18) and CO(2)(16,16), produced from the low intensity photolysis of mixtures of CO, H(2)O, Ar, and O(2)(18,18), the rate constant for the reaction HO(2) + CO --> CO(2) + OH has been determined at 300 degrees K to be less than or equal to 10(-20) cubic centimeter per molecule per second. These measurements indicate that the reaction of thermalized HO(2) is of negligible importance as a sink mechanism for converting CO to CO(2) in either the troposphere or the stratosphere.     

Polar Volatiles on Mars--Theory versus Observation: Excess solid carbon dioxide is probably present in the north residual cap

The residual frost caps of Mars are probably water-ice. They may be the source of the water vapor associated with seasonal polar hoods. A permanent reservoir of solid CO(2) is also probably present within the north residual cap and may comprise a mass of CO(2) some two to five times that of the present atmosphere of Mars. The martian atmospheric pressure is probably regulated by the temperature of the reservoir and not by the annual heat balance of exposed solid CO(2) (37). The present reservoir temperature presumably reflects a long-term average of the polar heat balance. The question of a large permanent north polar cap is reexamined in light of the Mariner 9 data. The lower general elevation of the north polar region compared to the south and the resulting occurrence in the north of a permanent CO(2) deposit are probably responsible for the differences in size and shape of the two residual caps. The details of the processes involved are less apparent, however. It might be argued that the stability of water-ice deposits depends on both insolation and altitude. The present north and south residual caps should be symmetrically located with respect to such a hypothetical stability field. However, the offset of the south cap from the geometrical pole, the non-symmetrical outline of the north cap, and the apparently uniform thickness of the thin, widespread water-ice all argue against control by simple solid-vapor equilibrium of water under present environmental conditions. We think that the present location of the water-ice may reflect, in part, the past location of the permanent CO(2) reservoir. The extreme stability of polar water-ice deposits increases the likelihood that past environmental conditions may be recorded there. Detailed information on elevations in the vicinity of the residual caps is needed before we can further elucidate the nature and history of the residual caps. This, along with measurements of polar infrared emission, should be given high priority in future missions to Mars. Two conclusions follow from the limitation of the mass of solid CO(2) on Mars at present to two to five times the mass of CO(2) in the atmosphere. If all of this CO(2) was entirely sublimated into the atmosphere as a result of hypothetical astronomical or geophysical effects, the average surface pressure would increase to 15 to 30 mbar. Although such a change would have considerable significance for eolian erosion and transportation, there seems to be little possibility that a sufficiently earthlike atmosphere could result for liquid water to become an active erosional agent, as postulated by Milton (38). The pressure broadening required for a green-house effect requires at least 10 to 20 times more pressure (39). If liquid water was ever active in modifying the martian surface, it must have been at an earlier epoch, before the present, very stable CO(2)/H(2)O system developed. There can be no intermittent earthlike episodes now. Furthermore, the present abundance of CO(2) on Mars may be an indicator of the cumulative evolution of volatiles to the surface of the planet (40). Thus, even the possibility of an earlier earth-like episode is dimmed. On Mars, the total CO(2) definitely outgassed has evidently been about 60 +/- 20 g/cm(2). On the earth, about 70 +/- 30 kg/cm(2) of CO(2) have been released to the surface (41). Hence, the total CO(2) devolved by Mars per unit area is about 0.1 percent of that evolved by the earth. Thus, the observational limits we place on solid CO(2) presently located under the north residual cap also may constitute considerable constraints on the total differentiation and devolatilization of the planet. If they are valid, it would seem unlikely that Mars has devolatilized at all like the earth, or ever experienced an earthlike environment on its surface.     

Toroidal triblock copolymer assemblies

A stable phase of toroidal, or ringlike, supramolecular assemblies was formed by combining dilute solution characteristics critical for both bundling of like-charged biopolymers and block copolymer micelle formation. The key to toroid versus classic cylinder micelle formation is the interaction of the negatively charged hydrophilic block of an amphiphilic triblock copolymer with a positively charged divalent organic counterion. This produces a self-attraction of cylindrical micelles that leads to toroid formation, a mechanism akin to the toroidal bundling of semiflexible charged biopolymers such as DNA. The toroids can be kinetically trapped or chemically cross-linked. Insight into the mechanism of toroid formation can be gained by observation of intermediate structures kinetically trapped during film casting.     

Multicompartment micelles from ABC miktoarm stars in water

By combining three mutually immiscible polymeric components in a mixed-arm star block terpolymer architecture, we have observed the formation of a previously unknown class of multicompartment micelles in dilute aqueous solution. Connection of water-soluble poly(ethylene oxide) and two hydrophobic but immiscible components (a polymeric hydrocarbon and a perfluorinated polyether) at a common junction leads to molecular frustration when dispersed in aqueous solution. The incompatible hydrophobic blocks form cores that are protected from the water by the poly(ethylene oxide) blocks, but both are forced to make contact with the poly(ethylene oxide) by virtue of the chain architecture. The structures that emerge depend on the relative lengths of the blocks and can be tuned from discrete multicompartment micelles to extended wormlike structures with segmented cores.     

Cylindrical block copolymer micelles and co-micelles of controlled length and architecture

Block copolymers consist of two or more chemically different polymers connected by covalent linkages. In solution, repulsion between the blocks leads to a variety of morphologies, which are thermodynamically driven. Polyferrocenyldimethylsilane block copolymers show an unusual propensity to forming cylindrical micelles in solution. We found that the micelle structure grows epitaxially through the addition of more polymer, producing micelles with a narrow size dispersity, in a process analogous to the growth of living polymer. By adding a different block copolymer, we could form co-micelles. We were also able to selectively functionalize different parts of the micelle. Potential applications for these materials include their use in lithographic etch resists, in redox-active templates, and as catalytically active metal nanoparticle precursors.     

植物叶面铺展剂复配规律 Ⅵ.SDS和DTAB混合水溶液体相和表面层行为

ＳＤＳ／ＤＴＡＢ复配体系在体相及气／液表面层中相互作用行为研究表明,添加适量ＤＴＡＢ,混合溶液的胶束生成、表面张力降低能力和表面张力降低效率均得到明显改善,这３项指标均在较大浓度比例范围内产生增效效应．分子相互作用理论计算结果显示,ＳＤＳ和ＤＴＡＢ不论在混合胶束还是在混合表面层中均产生强烈相互作用．两亲分子碳氢链之间的疏水相互作用和相反电性离子头基之间的库仑引力是混合体系产生高表面活性的主要原因,等链长的正／负离子铺展剂复配为较大浓度范围内的表面张力降低能力增效提供了条件．