Growth of silica nanoparticles in methylmethacrylate-based water-in-oil microemulsions

The mechanism of silica particle formation in monomer microemulsions is studied using dynamic light scattering (DLS), atomic force microscopy, small-angle X-ray scattering (SAXS), and conductivity measurements. The hydrolysis of tetraethylorthosilicate (TEOS) in methylmethacrylate (MMA) microemulsions (MMA = methylmethacrylate) is compared with the formation of SiO₂ particles in heptane microemulsions. Stable microemulsions without cosurfactant were found for MMA, the nonionic surfactant Marlophen NP10, and aqueous ammonia (0.75 wt%). In the one-phase region of the ternary phase diagram, the water/surfactant ratio (R _w) could be varied from 6 to 18. The DLS and SAXS measurements show that reverse micelles form in these water-in-oil (w/o) microemulsions. The minimum water-to-surfactant molar ratio required for micelle formation was determined. Particle formation is achieved from the base-catalyzed hydrolysis of TEOS. According to atomic force microscopy measurements of particles isolated from the emulsion, the particle size can be effectively tailored in between 20 and 60 nm by varying R _w from 2–6 in heptane w/o microemulsions. For MMA-based microemulsions, the particle diameter ranges from 25 to 50 nm, but the polydispersity is higher. Tailoring of the particle size is not achieved with R _w, but adjusting the particle growth period produces particles between 10 and 70 nm.     

The first 1,2-dibora-[2]ferrocenophane and its dynamic behaviour in solution

1,2-Bis(dimethylamino)-1,2-dibora-[2]ferrocenophane (1) was prepared by the reaction of 1,1′-dilithioferrocene with 1,2-dichlorobis(dimethylamino)diborane(4). In addition to hindered rotation about the B-N bond (ΔG^‡ > 80 kJ mol⁻¹), another dynamic process was revealed by ¹H and ¹³C NMR in solution at low temperature, and interpreted as motion of the cyclopentadienyl rings between staggered and eclipsed conformations (ΔG_{(233 K)}^‡ = 44 ± 1 kJ mol⁻¹).     

A MORPHOLOGICAL STUDY OF POLY（DIVINYLBENZENE-co-ACRYLIC ACID） IN CROSSLINKING PRECIPITATION POLYMERIZATION

Divinylbenzene-80 （DVB-80） and polar monomer acrylic acid （AA） having hydrogen bonding at a total monomer loading of 5 vol% were precipitated-copolymerized in a variety of organic solvents with 2,2＇-azobis（isobutyronitrile） （AIBN） as initiator. The experiments were investigated from a two-dimensional matrix, i.e., the actual crosslinking degree of DVB varying from 0 to 80% and the solvent composition varying from 0 to 100% of toluene mixture with acetonitrile, when the mixture of acetonitrile and toluene was used as the reaction solvent. Under various reaction conditions, six distinct morphologies including soluble polymers, swellable microgels, coagulum, irregular microparticles, and nano-/micrometer microspheres were formed and the structures of these polymer architectures were described. A morphological map was utilized to discuss the effects of both crosslinking degree of DVB and composition of solvent on the transitions between morphology domains. The results demonstrated that the microspheres are formed by an internal contraction due to the marginal solvency of the continuous phase and the crosslinking of the polymer network through the covalent bonding from DVB as well as the interchain hydrogen-bonding between the carboxylic acid units.     

Interactions between synthetic and indigenous naphthenic acids and divalent cations across oil–water interfaces: effects of addition of oil-soluble non-ionic surfactants

Interactions between naphthenic acids and divalent metal cations across model oil–alkaline water interfaces were investigated by correlating changes in dynamic interfacial tension (IFT), to plausible reaction mechanisms. The measurements were carried out by using a CAM 200 optical instrument, which is based on the pendant drop technique. The naphthenic acids used were synthesised model compounds as well as commercial acid mixtures from crude distillation and extracted acid fractions from a North Sea crude oil. The divalent cations involved Ca²⁺, Mg²⁺, Sr²⁺, and Ba²⁺, which are all common in co-produced formation water and naphthenate deposits. The results show that the dynamic IFT strongly depends on naphthenic acid structure, type of divalent cation, and the concentration of the compounds as well as the pH of the aqueous phase. Introducing divalent cations to systems involving saturated naphthenic acids caused mostly a permanent lowering of the IFT. The decline in IFT is due to electrostatic attraction forces across the interface between the cations in the aqueous phase and the carboxylic-groups at the o/w interface, which cause a higher interfacial density of naphthenic acid monomers. The permanent lowering in IFT is likely due to formation of positively charged monoacid complexes, which possess high interfacial activity. On the other hand, in the case of the aromatic model compounds, the cations affected the IFT differently. This is mainly discussed in light of degree of cation hydration and steric conditions. Various oil-soluble non-ionic surfactant mixtures were also introduced to systems involving a model naphthenic acid and Ca²⁺ in order to investigate how the interfacial competition affected the local interactions. Based on the behaviour of dynamic IFT, probable inhibition mechanisms are discussed.Electronic Supplementary Material Supplementary material is available for this article at     

Microchip electrophoretic protein separation using electroosmotic flow induced by dynamic sodium dodecyl sulfate-coating of uncoated plastic chips

Separation of sodium dodecyl sulfate (SDS)-protein complexes is difficult on plastic microchips due to protein adsorption onto the wall. In this paper, we elucidated the reasons for the difficulties in separating SDS-protein complexes on plastic microchips, and we then demonstrated an effective method for separating proteins using polymethyl methacrylate (PMMA) microchips. Separation difficulties were found to be dependent on adsorption of SDS onto the hydrophobic surface of the channel, by which cathodic electroosmotic flow (EOF; reversed flow) was generated. Our developed method effectively utilized the reversed flow from this cathodic EOF as a driving force for sample proteins using permanently uncoated but dynamic SDS-coated PMMA microchips. High-speed (6 s) separation of proteins and peptides up to 116 kDa was successfully achieved using this system.     

Sequential injection analysis with dynamic surface tension detection High throughput analysis of the interfacial properties of surface-active samples

A sequential injection analysis (SIA) system is coupled with dynamic surface tension detection (DSTD) for the purpose of studying the interfacial properties of surface-active samples. DSTD is a novel analyzer based upon a growing drop method, utilizing a pressure sensor measurement of drop pressure. The pressure signal depends on the surface tension properties of sample solution drops that grow and detach at the end of a capillary tip. In this work, SIA was used for creating a reagent concentration gradient, and for blending the reagent gradient with a steady-state sample. The sample, consisting of either sodium dodecyl sulfate (SDS) or poly(ethylene glycol) at 1470 g mol⁻¹ (PEG 1470), elutes with a steady-state concentration at the center of the sample plug. Reagents such as Brij®35, tetrabutylammonium (TBA) hydroxide and β-cyclodextrin were introduced as a concentration gradient that begins after the sample plug has reached the steady-state concentration. By blending the reagent concentration gradient with the sample plug using SIA/DSTD, the kinetic surface pressure signal of samples mixed with various reagent concentrations is observed and evaluated in a high throughput fashion. It was found that the SIA/DSTD method consumes lesser reagent and required significantly less analysis time than traditional FIA/DSTD. Four unique chemical systems were studied with regard to how surface activity is influenced, as observed through the surface tension signal: surface activity addition, surface activity reduction due to competition, surface activity enhancement due to ion-pair formation, and surface activity reduction due to bulk phase binding chemistry.     

THE CORRELATION EFFECT ON THE CHAIN MOTION CONTRIBUTION TO IONIC TRANSPORT IN POLYMER ELECTROLYTES

The ionic transport process in polymer electrolytes (such as polyethylene oxide) wassimulated numerically on a two dimensional square lattice where charge carriers areaccommodated by the lattice sites connected randomly with available bonds to represent theamorphous chain configuration. Following the dynamic bond percolation theory(DBPT),the chainmotion contribution to the ionic conduction was incorporated via periodical renewal of the randombond configuration. To check and extend the prediction made by DBPT employing global abruptbond renewal,spatial correlation of the bond reassignment was introduced to the system by: 1)regional bond renewal and 2) organized bond motion. It is found that the difference between thediffusivities simulated involving regional bond renewal and those of DBPT becomes negligiblewhen the bond renewal rate approaches the carrier hopping rate.     

An investigation of dynamic mechanical, thermal, and electrical properties of housing materials for outdoor polymeric insulators

The present paper reports the results about a study of mechanical, thermal, dynamic mechanical and electrical properties of housing (weather shed) materials for outdoor polymeric insulators. Silicone rubber, ethylene-propylene-diene monomer (EPDM) and alloys of silicon-EPDM are known polymers for use as housing in high voltage insulators. The result of dynamical mechanical measurement shows that the storage modulus of blends enhances with increase EPDM in formulation. It can be seen from the result of TGA measurement that initial thermal degradation of silicone rubber improves by the effect of EPDM in blends. The blends of silicone-EPDM show good breakdown voltage strength compared to silicone rubber. Surface and volume resistance of silicone rubber improve by EPDM content. The mechanical properties of EPDM such as strength, modulus and elongation at break improve by silicone.     

Manipulation of the Electroosmotic Flow in Glass und PMMA Microchips with Respect to Specific Enzymatic Glucose Determinations

The determination of glucose in microfluidic chips made of glass or PMMA was used as a model for the combination of an enzymatic reaction with the separation of compounds. It was based on the enzymatic oxidation of glucose and the amperometric detection of hydrogen peroxide. Real samples frequently contain compounds, such as ascorbic acid, which may interfere with quantitative glucose determinations. Thus, electrophoretic separation of specific from unspecific signals was envisaged by applying electric fields which are also used to control the flow of liquid via electroosmotic effects. Surface charge densities of the capillaries influence the electroosmotic flow (EOF). They are dependent on the chip material and on the adsorption of components from the background electrolyte. Reversal of the EOF after addition of cetyltrimethylammonium bromide (CTAB) and an increase in EOF after addition of sodium dodecylsulfate (SDS) were observed at lower surfactant concentrations with the PMMA chips rather than with the glass chips. For both chip materials these concentrations were below the critical micelle concentration. Effective separation of H₂O₂ and ascorbic acid was achieved with low CTAB concentrations, which lead to a reduction, but not to a reversal of the EOF. Reversal of the EOF by higher CTAB concentrations or the increase in cathodic EOF by SDS accelerated ascorbic acid transportation and reduced the differences in migration times. Thus, for the specific determination of glucose, glucose oxidase was added together with low CTAB concentrations to the background electrolyte. This avoided interference from ascorbic acid, and data obtained from the analysis of fruit juices showed a good correlation to data obtained from a reference method.     

新型含有机硅二元多嵌段共聚物的研究

报道了聚羟基醚（ＰＨＥ）、聚羟基醚砜（ＰＨＥＳ）、酚酞聚羟基醚（ＰＰＨＥ）和聚对羟基苯乙烯（ＰＨＳ）与端胺基聚二甲基硅氧烷（ＰＤＭＳ）通过羟胺缩合生成ＡＢｍｎ新型结构的可溶性含有机硅二元多嵌段共聚物，ｍ值在１～６之间，详细讨论了反应物浓度对共缩聚反应的影响，并通过分子量测定、红外光谱分析和动态力学分析（ＤＭＡ）技术初步确定了其反应机理、结构和动态力学性能．