Microwave-assisted organic functionalization of silica surfaces: Effect of selectively heating silylating agents

Microwave (MW)-assisted (2.45 GHz) organic functionalization of silica surfaces was investigated using (3-chloropropyl)dimethylsilanes with alkoxy, allyl, or aryl leaving groups in heptane or toluene at 80 °C. ²⁹Si and ¹³C CP/MAS spectroscopy confirmed the 3-chloropropyldimethylsilyl moiety was covalently grafted onto silica for all the samples. The effect of MW irradiation on the loading amount strongly depended on the leaving group as well as the solvent; using methoxysilane and p-anisylsilane in heptane caused a distinct acceleration. The correlation with the dielectric loss factors of the silylating agents suggested that the MW acceleration effect resulted from selectively heating the strongly MW-absorbing silylating agent. For the grafting reaction in toluene, the MW effect was not observed possibly because toluene masked the selective heating effect of the silylating agent.     

Effect of interfacial rheology on model emulsion coalescence I. Interfacial rheology

Interfacial elasticity and "dynamic" surface pressure isotherms were measured for interfaces between a dispersed water phase and a continuous phase of asphaltenes, toluene, and heptane. The interfacial modulus is a function of asphaltene concentration and in all cases reached a maximum at an asphaltene concentration of approximately 1 kg/m(3). The modulus increased significantly as the interface aged and slightly as the heptane content increased to a practical limit of 50 vol%. The modulus was approximately the same at 23 and 60 degrees C. The modulus correlated with the inverse of the initial compressibility determined from surface pressure isotherms. The surface pressure isotherms also indicated that a phase transition occurred as the interface was compressed leading to the formation of low compressibility films. Crumpling was observed upon further compression. The phase transition shifted to a higher film ratio with an increase in heptane content and interface age. Asphaltene concentration and temperature (23 and 60 degrees C) has little effect on the surface pressure isotherms. The surface pressure and elasticity measurements are consistent with the gradual formation of a cross-linked asphaltene network on the interface.     

Quartz Crystal Microbalance Monitoring of Asphaltene Adsorption/Deposition

Adsorption and deposition of asphaltenes onto differently coated (hydrophilic surfaces: silica, titanium, alumina, and a noncommercial tailor‐made FeO_x) quartz crystals from heptane/toluene (1∶1) and toluene solutions have been studied with the quartz crystal microbalance method with dissipation measurements (QCM‐D). The results show that the adsorbed mass is related to the solubility state of asphaltenes (aromaticity of the solvent), their origin (aggregate size in solution) and very little to the hydrophilicity of the investigated crystal. Adsorption/deposition of asphaltenes depends on their solubility. We found two cases: Either the asphaltenes are solubilized, or the asphaltenes are partly solubilized and partly precipitated. In the former case, asphaltenes are bounded very tightly to the surface and poorly for the latter. The change in solution composition due to decrease in asphaltene solvency causes formation of a variety of asphaltenes species. The results also were compared and discussed in relation to adsorption onto particles, determined with the UV depletion method. The study shows that QCM‐D method is a very useful tool to study the mechanisms and the effects of solvency of asphaltenes. We discuss and compare the different techniques.     

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) as a probe of macromolecule adsorption kinetics at functionalized interfaces

Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been employed to study the interfacial adsorption kinetics of coumarin-tagged macromolecules onto a range of functionalized planar surfaces. Such studies are valuable in designing polymers for complex systems where the degree of interaction between the polymer and surface needs to be tailored. Three tagged synthetic polymers with different functionalities are examined: poly(acrylic acid) (PAA), poly(3-sulfopropyl methacrylate, potassium salt) (PSPMA), and a mannose-modified glycopolymer. Adsorption transients at the silica/water interface are found to be characteristic for each polymer, and kinetics are deduced from the initial rates. The chemistry of the adsorption interfaces has been varied by, first, manipulation of silica surface chemistry via the bulk pH, followed by surfaces modified by poly(L-glutamic acid) (PGA) and cellulose, giving five chemically different surfaces. Complementary atomic force microscopy (AFM) imaging has been used for additional surface characterization of adsorbed layers and functionalized interfaces to allow adsorption rates to be interpreted more fully. Adsorption rates for PSPMA and the glycopolymer are seen to be highly surface sensitive, with significantly higher rates on cellulose-modified surfaces, whereas PAA shows a much smaller rate dependence on the nature of the adsorption surface.     

Influence of graft interface polarity on hydration/dehydration of grafted thermoresponsive polymer brushes and steroid separation using all-aqueous chromatography

We have prepared poly( N-isopropylacrylamide) (PIPAAm) brush-grafted surfaces with varied temperature-responsive hydrophobic properties through surface-initiated atom transfer radical polymerization (ATRP). These temperature-responsive surfaces were characterized by chromatographic analysis using modified silica beads as a chromatographic stationary phase in aqueous mobile phase. Mixed silane self-assembled monolayers (SAMs) comprising ATRP initiator and silanes with various terminal functional groups were formed on the silica bead surfaces. IPAAm was then polymerized by ATRP using the CuCl/CuCl2/Me6TREN catalyst system in 2-propanol at 25 degrees C for 16 h. The chromatographic retention behavior of steroids on the resulting PIPAAm brushes made on more polar silane components was distinct from that on more apolar silane interfaces. Retention times for steroids on PIPAAm mixed apolar silane graft interfaces were significantly longer than those on analogous polar silane interfaces due to enhanced dehydration of PIPAAm brushes on apolar silane-grafted surfaces. Changes in retention factor, k', on polar silane PIPAAm-grafted interfaces were relatively large compared to that on apolar PIPAAm grafted interfaces due to larger hydration/dehydration alterations of grafted PIPAAm brushes on the former surfaces. Applied step-temperature gradients from 50 to 10 degrees C show that PIPAAm brushes on polar silane interfaces tend to hydrate more, leading to shorter retention times. In conclusion, the polarity of the grafted interface significantly influences the grafted PIPAAm brush hydration/dehydration characteristics and subsequently also the temperature-modulated separation of bioactive compounds in all-aqueous chromatography.     

Lactone cleavage reaction kinetics of rhodamine dye at liquid/liquid interfaces studied by micro-two-phase sheath flow/two-photon excitation fluorescence microscopy

Two-photon excitation fluorescence microscopy was combined with the two-phase microflow system in order to measure the fast interfacial reaction rate at liquid/liquid interfaces. The lactone cleavage kinetics of octadecylrhodamine B (C(18)RB) at the toluene/water and heptane/water interfaces was studied by this new method. The organic solution containing the nonfluorescent lactone of C(18)RB was made to flow as an inner flow with an aqueous outer sheath flow. The diameter of the inner flow was <20 microm. A focused fundamental beam of a Ti:sapphire pulse laser of 780 nm was irradiated to the interface, and emitted fluorescence from the fluorescent product was detected by a charge-coupled device (CCD) camera or a streakscope. The increase in the concentration of the fluorescent form of C(18)RB was measured along the interface of the inner flow of the toluene/water and heptane/water systems for 80 micros just after the contact of two phases. The analysis made by the time-dependent Langmuir adsorption model with the aid of the digital simulation method gave the cleavage reaction rate constants of the lactone form of C(18)RB at the liquid/liquid interfaces.     

微量吸附热量计的检测和硅胶浸湿热的测量

微量量热法研究液固吸附正逐渐引起人们的兴趣。本实验室拟开展强化采油中表面活性剂在固体表面吸附机理的研究,装配了一台微量吸附热量计,并用标准化学反应检测其可靠性。研究表面活性剂的吸附规律,需要选用合适的吸附剂。硅胶的组份简单确定,不含干扰离子,表面积足够大,而且它就是油井矿物、粘土等的主要成份,被选为吸附剂样品。但硅胶的表面状态易受制备过程、热处理等因素影响,迄今尚无统一标准的硅胶表面,使用时应表征其表面状态。本文用热失重分析确定硅胶的活化温度、用微量吸附热量计测量了硅胶的浸湿热,并与文献数据进行比较。     

Swelling of <Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam-dodecyl methacrylate gel in {heptane + toluene} mixtures

A copolymer gel has been synthesized from N-vinylcaprolactam and dodecyl methacrylate in ethanol using the free radical cross-linking polymerization method. Characterizations of the gel were performed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA) techniques. Swelling behavior of the gel was investigated in heptane, toluene, and their binary mixtures with different compositions. Swelling value in toluene is higher than that in heptane and swelling value increases with the increasing initial content of toluene in the binary mixture with heptane. The swelling values are correlated by the first- and second-order differential equations, and the best model correlating the experimental results is a second-order one. Diffusion coefficients have also been calculated for heptane and toluene at each concentration by power-law and first-order equations. While the diffusion mechanism of the gel in heptane is a Fickian one, the gel swelled in toluene exhibits a non-Fickian character. Diffusion mechanisms of the gels in binary mixtures are much more complicated. Because of the higher swelling degree in toluene compared to that in heptane, selectivity of the gel in different {heptane + toluene} mixtures with selectivity close to 1 has also been taken into consideration.     

Contact angles of colloid silica and gold particles at air-water and oil-water interfaces determined with the gel trapping technique

We have used the recently developed gel trapping technique (GTT) to determine the three-phase contact angles of submicrometer silica particles partially coated with octadecyl groups. The particles were spread at air-water and decane-water surfaces, and the aqueous phase was subsequently gelled with a nonadsorbing polysaccharide. The particles trapped at the surface of the aqueous gel were lifted by molding with curable poly(dimethylsiloxane) and imaged with scanning electron microscopy (SEM) to determine the particle contact line diameter which allows their contact angle at the original air-water or oil-water interface to be estimated. We report for the first time the use of the GTT for characterizing the contact angle of individual submicrometer particles adsorbed at liquid interfaces. The SEM images also reveal the structure of the particle monolayer at the interface and the structure of adsorbed particle aggregates. We have also determined the contact angles of agglomerated gold powder microparticles at the air-water and the decane-water interfaces. It was found that agglomerated gold particles demonstrate considerably higher contact angles than those on flat gold-coated surfaces.     

Segmental dynamics of interfacial poly(methyl acrylate)-d(3) in composites by deuterium NMR spectroscopy.

The interface in composite materials containing an ultrathin layer of poly(methyl acrylate)-d(3) (PMA-d(3)) on silica was studied using deuterium NMR. PMA-d(3) was deposited from solution at saturation coverage from toluene onto silica. The samples were dried and composite samples made by hot pressing the PMA-d(3)/silica samples with hydrogenated polystyrene (PS) and high (HMW) and low (LMW) molecular weight hydrogenated poly(methyl acrylate) (PMA) as the overlayer. The interfacial layers of PMA-d(3) were studied at the air-polymer-silica and polymer-polymer-silica interfaces using deuterium solid-state quadrupole-echo NMR and the results compared to those for the bulk polymer. It was found that for samples at the air-polymer-silica interface, some of the polymer segments in the surface sample had segmental mobility higher than that of the corresponding bulk PMA-d(3) sample at the same temperature. When overcoated with unlabeled polymer, the interfacial polymer at the polymer-polymer-silica interface showed reduced mobility due to the presence of the overlayer. The adsorbed PMA-d(3), in the composite samples, decreased in mobility in the order of LMW-PMA > HMW-PMA > PS. The PS sample caused the greatest reduction in the PMA-d(3) interfacial mobility. The order was consistent with the segmental mobilities of the polymers used for the overlayers. The lower the mobility of the polymer used for the overlayer, the more restricted were the polymer segments in the adsorbed PMA-d(3) layer.     

Investigation of the interfacial properties of water-in-diluted-bitumen emulsions using micropipette techniques

The interfacial properties of water-in-diluted bitumen emulsions were studied using micropipette techniques. It was observed that, as bitumen concentration in the bulk phase (C0) increased, the interfacial tension on the water droplet surfaces decreased. In addition, there was a small effect on the interfacial tension when different solvent mixtures were used. Mixtures of toluene and heptane in different ratios were used as solvents for bitumen dilution. Crumpling of the interface was influenced by bitumen concentration and type of solvent. No crumpling was found for bitumen content less than 0.01% for all solvents used. Crumpling was observed at higher bitumen concentrations when deionized water (pH 5.4-5.6) was used. Setting "heptol[A]" to be the mixture of toluene and heptane, with the volume percent of toluene being A, the following were concluded. Crumpling disappeared at C0 > 1% and when heptol[100] was used, and also at C0 > 10% and when heptol[30] was used. Crumpling was strongly affected by the water pH. In the case of heptol[50], at a higher pH, the crumpling region that normally occurred at C0 > 0.01% disappeared. The micropipette technique proved to be useful in studying the interfacial properties of micrometer-sized emulsion drops.     

双分布聚乙二醇接枝纳米二氧化硅的高效可控制备

在混合溶剂中通过"grafting to"的方法将2种分子量不同的聚乙二醇单甲醚(MPEG M_w=750,4000)接枝到氨基修饰的St?ber法二氧化硅(SiO_2-NH_2)表面,制备双分布纳米接枝复合物.采用二步法,先将带环氧端基的低分子量聚乙二醇单甲醚(MPEG-EO)与SiO_2-NH_2在甲苯溶剂中充分反应后,与高分子量的MPEG-EO在甲苯和正癸烷的混合溶剂中使用相同的反应条件和后处理方法,能便捷制备出具有双分布接枝的纳米复合物.在接枝反应体系中,分子链的链段尺寸和接枝密度之间存在着密切关系.一定的范围内,接枝密度随链段尺寸减小而增大.通过改变混合溶剂比例来调控接枝链段的尺寸,可以很好控制聚合物的接枝密度.在双分布接枝的纳米复合物中,低分子量的接枝密度为0.85 chains/nm~2,高分子量的接枝密度能达到0.40 chains/nm~2,体现出了简单、高效、可控的特点,与聚环氧乙烷(PEO)共混后分散良好,对于制备出均匀分散的纳米复合材料起到了一定的指导作用.     

In situ polymerization of molecular macroclusters on a silica surface: poly(N-isopropylacrylamide) nanofilms

We have found that alcohols, carboxylic acids, and amides self-assemble into a unique molecular architecture, a hydrogen-bonded molecular macrocluster, when they are selectively adsorbed onto silica (glass and oxidized silicon) surfaces in nonpolar solvents such as cyclohexane. In our previous study, this phenomenon could be successfully applied to fabricate molecularly flat and defect-free nanofilms of several tens of nanometers thickness. In this study, we prepared a poly(N-isopropylacrylamide) [poly(NIPAAm)] film on the basis of in situ polymerization of a monomer macrocluster layer formed on silica surfaces and investigated how the molecular arrangement of the adsorbed NIPAAm monomers affects the efficiency of the polymerization of them. Poly(NIPAAm) films were prepared by the following two methods: (1) the one-solution method, the in situ photopolymerization of an NIPAAm monomer adsorption layer on silica in one solution (chloroform, cyclohexane, and toluene), and (2) the solution exchange method, adsorption of NIPAAm monomers onto a silica surface from NIPAAm (0.1 mol %) in chloroform, exhange of the solution to 0.005 mol % NIPAAm in cyclohexane, and then polymerization by UV irradiation. By the solution exchange method, molecularly flat, defect-free, and thermoresponsive films were obtained and the thickness could be controlled by the irradiation time, while only several nanometers thickness could be attained by the one-solution method. The structure of NIPAAm adsorption layers formed in each solution condition was characterized by attenuated total reflection Fourier transform infrared spectroscopy. It was revealed that only the solution exchange procedure induced the beta-sheet-like adsorbed structure of NIPAAm in which the double bonds of neighboring NIPAAm monomers were closely located, which should have resulted in effective polymerization.     

Control of carboxylic acid and ester groups on chromium (VI) binding to functionalized silica/water interfaces studied by second harmonic generation

Resonantly enhanced surface second harmonic generation (SHG) measurements carried out at pH 7 and room temperature were performed to study how surface-bound carboxylic acid and methyl ester functional groups control the interaction of chromate ions with fused silica/water interfaces. These functional groups were chosen because of their high abundance in humic and fulvic acids and related biopolymers commonly found in soils. They were anchored to the silica surface using organosilane chemistry to avoid competing complexation processes in the aqueous solution as well as competitive adsorption of the organic compounds and chromate. The SHG experiments were carried out at room temperature and pH 7 while using environmentally representative chromate concentrations ranging from 1 x10(-6) to 2 x 10(-4) M. Chromate is found to bind to the acid- and ester-functionalized silica/water interfaces in a reversible fashion. In contrast to the plain silica/water interface, chromate binding studies performed on the functionalized silica/water interfaces show S-shaped adsorption isotherms that can be modeled using the Frumkin-Fowler-Guggenheim (FFG) model. This model predicts a coverage-dependent binding constant of K(ads) x exp(gtheta). Values for g are found to be 3.2(2), 2.1(2), and 1.3(2) for the carboxylic acid-, the ester-, and the nonfunctionalized silica/water interfaces, respectively, and are consistent with stabilizing lateral adsorbate-adsorbate interactions among the Cr(VI) species adsorbed to the functionalized surfaces. The FFG model allows for the parametrization of the solid-liquid partition coefficient and chromate retardation factors in silica-rich soil particles whose surfaces contain organic adlayers rich in carboxylic acid and methyl ester groups. The straightforward model presented here predicts that chromate retardation increases by up to 200% when carboxylic acid functional groups are present at the silica/water interface. Increases up to 50% are predicted for methyl ester-containing organic adlayers, and the retardation factor remains effectively near unity for the plain silica/water interface (no siloxanes present).     

Kinetics of epoxidation of poly(trans-1,4-butadiene) crystals in suspension

The kinetics of the epoxidation reaction between metachloroperbenzoic acid (MCPBA) and poly-(trans-1,4-butadiene), (PTBD), crystals in toluene suspension was investigated in the 6–21°C range using infrared spectroscopy. Crystals of PTBD with M?_n = 36,000 grown from heptane and from toluene solutions and crystals of PTBD with M?_n = 5500 grown from heptane were studied. For toluene-grown crystals the total number of double bonds available for reaction increases with reaction temperature. For all preparations studied the epoxidation reaction is initially second-order—first-order with respect to [MCPBA] and first-order with respect to the concentration of the available double bonds. The second-order rate constant is found to be dependent on temperature, on molecular weight, and also on the crystal preparation conditions. The bromination of PTBD crystals was studied in CCl₄ suspension at 0°C; this reaction was found to be complete within 1 hr with the fraction of double bonds brominated consistent with the epoxidation results. The IR spectra for dried mats of brominated and of epoxidized PTBD crystals were obtained: Changes in the amorphous band at 1335 cm^?1 due to reaction of double bonds at crystal surfaces were observed. The results of this investigation are discussed in terms of the amorphous content of the PTBD lamellas.     

A quartz crystal microbalance study of the adsorption of asphaltenes and resins onto a hydrophilic surface

The adsorption of extracted and purified samples of asphaltenes and resins onto gold surfaces has been studied as a function of bulk concentration using a quartz crystal microbalance with dissipation measurements (QCM-D). With this device, which works equally well in transparent, opaque, and nontransparent samples, the adsorbed amount is measured through a change in resonant frequency of the quartz oscillator. The measured change in dissipation reports on changes in layer viscoelasticity and slip of the solvent at the surface. The results show that the adsorbed amount for resins from heptane corresponds to a rigidly attached monolayer. The adsorbed amount decreases with increasing amount of toluene in the solvent and is virtually zero in pure toluene. Asphaltenes, on the other hand, adsorb in large quantities and the mass and dissipation data demonstrate the presence of aggregates on the surface. The aggregates are firmly attached and cannot be removed by addition of resins. On the other hand, resins and asphaltenes associate in bulk liquid and the adsorption from mixtures containing both resins and asphaltenes is markedly different from that obtained from the pure components. Hence, we conclude that preformed resin aggregates adsorb to the surface. These results are compared and discussed in relation to adsorption from crude oil diluted in heptane/toluene mixtures.     

Effects of graft densities and chain lengths on separation of bioactive compounds by nanolayered thermoresponsive polymer brush surfaces

We have prepared various poly(N-isopropylacrylamide) (PIPAAm)-grafted silica bead surfaces through surface-initiated atom transfer radical polymerization (ATRP) by changing graft densities and brush chain lengths. The prepared surfaces were characterized by chromatographic analysis using the modified silica beads as chromatographic stationary phases. ATRP initiator (2-(m,p-chloromethylphenyl)ethyltrichlorosilane) density on silica bead surfaces was modulated by changing the feed composition of the self-assembled monolayers (SAMs) of mixed silane coupling agents consisting of ATRP initiator and phenethyltrichlorosilane on the surfaces. IPAAm was then polymerized on SAM-modified silica bead surfaces by ATRP in 2-propanol at 25 degrees C. The chain length of the grafted PIPAAm was controlled by simply changing the ATRP reaction time at constant catalyst concentration. The thermoresponsive surface properties of the PIPAAm-grafted silica beads were investigated by temperature-dependent elution behavior of hydrophobic steroids from the surfaces using Milli-Q water as a mobile phase. On the surfaces grafted with shorter PIPAAm chains, longer retention times for steroids were observed on sparsely grafted PIPAAm surfaces compared to dense PIPAAm brushes at low temperature, because of hydrophobic interactions between the exposed phenethyl groups of SAMs on silica surfaces and steroid molecules. Retention times for steroids on dilute PIPAAm chain columns decreased with temperature similarly to conventional reverse-phase chromatographic modes on octadecyl columns. This effect was due to limited interaction of solutes with the PIPAAm-grafted surfaces. Retention times for steroids on dilute PIPAAm brush surfaces with longer PIPAAm chains became greater above the PIPAAm transition temperature. At low-temperature regions, hydrated and expanded PIPAAm at low temperatures prevented hydrophobic interactions between the phenethyl group of SAMs on the silica bead surfaces and steroid molecules. Retention times for steroids on a dense PIPAAm brush column increased with temperature since solvated polymer segments within the dense brush layer undergo dehydration over a broad range of temperatures. In conclusion, PIPAAm graft density has a crucial influence on the elution behavior of steroids because of the interaction of analytes with silica bead interfaces, and because of the characteristic dehydration of PIPAAm in dense-pack brush surfaces.     

How to prevent the loss of surface functionality derived from aminosilanes

Aminosilanes are common coupling agents used to functionalize silica surfaces. A major problem in applications of 3-aminopropylsilane-functionalized silica surfaces in aqueous media was encountered: the loss of covalently attached silane layers upon exposure to water at 40 degrees C. This is attributed to siloxane bond hydrolysis catalyzed by the amine functionality. To address the issue of loss of surface functionality and to find conditions where hydrolytically stable amine-functionalized surfaces can be prepared, silanization with different types of aminosilanes was carried out. Hydrolytic stability of the resulting silane-derived layers was examined as a function of reaction conditions and the structural features of the aminosilanes. Silane layers prepared in anhydrous toluene at elevated temperature are denser and exhibit greater hydrolytic stability than those prepared in the vapor phase at elevated temperature or in toluene at room temperature. Extensive loss of surface functionality was observed in all 3-aminopropylalkoxysilane-derived layers, independent of the number and the nature of the alkoxy groups. The hydrolytic stability of aminosilane monolayers derived from N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES) indicates that the amine-catalyzed detachment can be minimized by controlling the length of the alkyl linker in aminosilanes.     

Preparation and characterization of nanocomposite polyurethane

Polyurethane/nanosilica composites were prepared using polyester polyol/nanosilica composite resins obtained from in situ polymerization or blending methods and investigated by Fourier transform infrared spectra (FTIR), dynamical mechanical analysis (DMA), transmittance electron microscopy (TEM), contact angle measurement, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM), respectively. It was found that more polyester segments had chemically bonded with silica particles during in situ polymerization than during blending, introducing nanosilica increased the Tgs of polyurethanes, and different preparation methods and different particle sizes caused various impact on Tg. Contact angle measurement and XPS analyses indicated that nanosilica tended to move towards the surfaces and interfaces of polyurethane coats, decreasing the free energies of the surfaces and interfaces, but the nanosilica particles were just observed at interfaces not surfaces by AFM.     

Tuning aggregation of microemulsion droplets and silica nanoparticles using solvent mixtures

The effect of solvent on stability of water-in-oil microemulsions has been studied with AOT (sodium bis(2-ethylhexyl)sulfosuccinate) and different solvent mixtures of n-heptane, toluene and dodecane. Dynamic light scattering DLS was used to monitor the apparent diffusion coefficient D(A) and effective microemulsion droplet diameter on changing composition of the solvent. Interdroplet attractive interactions, as indicated by variations in D(A), can be tuned by formulation of appropriate solvent mixtures using heptane, toluene, and dodecane. In extreme cases, solvent mixtures can be used to induce phase transitions in the microemulsions. Aggregation and stability of model AOT-stabilized silica nanoparticles in different solvents were also investigated to explore further these solvent effects. For both systems the state of aggregation can be correlated with the effective molecular volume of the solvent V(mol)(eff) mixture.