Spontaneous polymerization at the air-water interface: a Brewster angle microscopy study

When a dioctadecyldimethylammonium bromide (DODA) monolayer is spread onto a styrene sulfonate (SSt) aqueous solution, this monomer undergoes a spontaneous polymerization process [Fichet, O; Teyssié, D. Macromolecules 2002, 35, 5352]. However, the polymer synthesized in this monolayer cannot be investigated by classical characterization techniques. Brewster angle microscopy has thus been used as a complementary method in order to study this spontaneous polymerization. From these measurements, the threshold concentration above which the spontaneous polymerization occurs has been determined more precisely; the monomer adsorption under the DODA monolayer has been evidenced as being very fast, as supposed previously; moreover, sodium bicarbonate is confirmed as an inhibitor of the polymerization. Also, the replacement of SSt by toluene sulfonate (TSt) confirms the SSt spontaneous polymerization. Finally, the molecular weight and/or the structure of the polymer synthesized in the monolayer seems to be different from those synthesized in solution.     

Langmuir monolayers and Langmuir–Blodgett films of ferritin prepared by using a surfactant mixture of eicosylamine (EA) and methyl stearate (SME)

Magnetic Langmuir–Blodgett films of ferritin have been prepared by using the adsorption properties of a 1/4 mixed monolayer of eicosylamine (EA) and methyl stearate (SME). BAM images show that a more homogeneous distribution of ferritin at the air–water interface is achieved by using this mixture of surfactants instead of the DODA/SME mixed matrix of a previous work. Transfer of the monolayer onto different substrates allowed the preparation of multilayer LB films. Infrared and UV–Vis spectroscopies indicate that ferritin molecules are incorporated within the LB films. Furthermore, UV–Vis spectroscopy measurements reveal that the amount of ferritin incorporated into these LB film has been increased with respect to that in the DODA/SME LB films. Finally magnetic measurements confirm that the superparamagnetic properties of this molecule are preserved in the LB films.     

Surfactant-encapsulated clusters (SECs): (DODA)20(NH4)[H3Mo57V6(NO)6O183(H2O)18], a case study

We present a comprehensive study of the partially reduced polyoxomolybdate [H3-Mo57V6(NO)6O183(H2O)18]21-encapsulated in a shell of dimethyldioctadecylammonium (DODA) surfacmolecules. Treatment of an aqueous solution of (NH4)21[H3Mo57V6-(NO)6O183(H2O)18] . 65H2O (1a) with a trichloromethane solution of the surfactant leads to instant transfer of the encapsulated complex anion into the organic phase. Results from vibrational spectroscopy. analytical ultracentrifugation, small-angle X-ray scattering, transmission electron microscopy, elemental analysis, and Langmuir compression isotherms are consistent with a single polyoxometalate core encapsulated within a shell of 20 DODA molecules. The molar mass of the supramolecular assembly is 20249 gmol(-1) and the diameter is 3.5 nm. A material with the empirical formula (DODA)20(NH4)[H3-Mo57V6NO)6O183(H2O)18] (2) was isolated as a dark violet solid, which readily dissolves in organic solvents. Slow evaporation of solutions of 2 on solid substrates forces the hydrophobic particles to aggregate into a cubic lattice. Annealing these so-formed films at elevated temperature causes de-wetting with terrace formation similar to liquid crystals and block copolymers. Compound 2 forms a stable Langmuir monolayer at the air-water interface; Langmuir-Blodgett multilayers are readily prepared by repeated transfer of monolayers on solid substrates. The films were characterized by optical ellipsometry, Brewster angle microscopy, transmission electron microscopy, and X-ray reflectance.     

Study of pH-sensitive copolymer/phospholipid complexes using the langmuir balance technique: effect of anchoring sequence and copolymer molecular weight

The behavior of three copolymers of N-isopropylacrylamide (NIPAM), methacrylic acid (MAA), and hydrophobic moiety was studied at phospholipid monolayer/subphase interfaces. The hydrophobic moieties, N-terminal dioctadecylamine (DODA) and random octadecylacrylate (ODA), were used as anchoring groups. The interactions between a 1,2-distearoyl-sn-glycero-3-phosphatidylcholine (DSPC) monolayer and the copolymers were studied using the Langmuir balance technique. The effect of subphase pH, distribution of anchors along the copolymer chain, and copolymer molecular weight on the nature of the interactions between the copolymer chains and the DSPC monolayer were investigated. A first-order kinetics model was used to analyze the copolymers adsorption at the DSPC monolayer/subphase interface and allowed the interaction area between the copolymer chains and the DSPC monolayer, A(x), to be determined. The interaction area appears to depend on the subphase pH and the copolymer molecular weight. On decreasing pH, the interaction area of high molecular weight copolymers increases significantly; this is consistent with the copolymer chain phase transition from an extended coil to a collapsed globule while pH is lowered. In the latter conformation, strong hydrophobic attractive interactions between the copolymer chains and the hydrophobic part of the DSPC monolayer favor the copolymer intercalation, which could eventually provoke the phospholipidic layer destabilization or rupture.     

Magnetic Langmuir-Blodgett films of ferritin with different iron contents

Magnetic Langmuir-Blodgett films of four ferritin derivatives with different iron contents containing 4220, 3062, 2200, and 1200 iron atoms, respectively, have been prepared by using the adsorption properties of a 6/1 mixed monolayer of methyl stearate (SME) and dioctadecyldimethylammonium bromide (DODA). The molecular organization of the mixed SME/DODA monolayer is strongly affected by the presence of the water-soluble protein in the subphase as shown by pi-A isotherms, BAM images, and imaging ellipsometry at the water-air interface. BAM images reveal the heterogeneity of this mixed monolayer at the air-water interface. We propose that the ferritin is located under the mixed matrix in those regions where the reflectivity is higher whereas the dark regions correspond to the matrix. Ellipsometric angle measurements performed in zones of different brightness of the mixed monolayer confirm such a heterogeneous distribution of the protein under the lipid matrix. Transfer of the monolayer onto different substrates allowed the preparation of multilayer LB films of ferritin. Both infrared and UV-vis spectroscopy indicate that ferritin molecules are incorporated within the LB films. AFM measurements show that the heterogeneous distribution of the ferritin at the water-air interface is maintained when it is transferred onto solid substrates. Magnetic measurements show that the superparamagnetic properties of these molecules are preserved. Thus, marked hysteresis loops of magnetization are obtained below 20 K with coercive fields that depend on the number of iron atoms of the ferritin derivative.     

Polyoxometalates matrixed into surfactants: synthesis, characterizations, and conformations of surfactants

We synthesized two surfactant-encapsulated polyoxometalate (POM) clusters (SECs), (DODA)(15)[H(3)Mo(57)V(6)(NO)(6)O(189)(H(2)O)(12)(VO)(6)].13H(2)O (SEC-2, DODA: dimethyldioctadecyl ammonium) and (DODA)(12)[Eu(H(2)O)P(5)W(30)O(110)].28H(2)O (SEC-3). SECs were characterized in detail by elemental analysis, UV-Vis absorption spectroscopy, FTIR, 1H NMR, thermogravimetric analysis, Langmuir isotherms, and powdered X-ray diffractions. SEC-2 can form a stable monolayer at the air-water interface. SEC-2 and SEC-3 possess a layered structure with periodicities of 3.8 and 5.05 nm, respectively. Alkyl chains in SEC-2 are disordered, but SEC-3 is indicative of well-ordered alkyl chains. According to the simplified structural analysis for SEC-2 and SEC-3, DODAs occupy areas of 1.12 and 0.589 nm(2) on the surface of the POMs, which are characteristic of the liquid-like and crystalline-like phases for DODA, respectively. The different conformations of DODAs then lead to the different packing structures of SECs. This work is aiming to control the organizational structures of the POM-based materials by selecting the appropriate POMs.     

Mechano‐Responsive,Thermo‐Reversible,Luminescent Organogels Derived from a Long‐Chained,Naturally Occurring Fatty Acid

The gelating ability of an α‐diketo derivative of oleic acid, 9,10‐dioxooctadecanoic acid ( DODA ), is investigated. DODA can gelate aromatic liquids and many other organic liquids. By contrast, none of the liquids examined can be gelated by the methyl ester of DODA. DODA is a more efficient gelator than stearic acid and the monoketo derivative due to its more extensive intermolecular dipole–dipole interactions. Formation of organogels of DODA can be induced by both thermal and mechanical stimuli, during which the luminescent and mechanical properties can be modulated significantly. The emission from DODA in 1‐octanol exhibits a large, reversible, hypsochromic shift (≈25 nm) between its thermally cycled gel and sol states. The emission changes have been exploited to probe the kinetics of the aggregation and deaggregation processes. DODA is the simplest gelator of which we are aware that exhibits a reversible shift in the emission. Although the self‐assembled fibrillar networks of the DODA gels in 1‐octanol, benzonitrile, or silicone oil are crystalline, isothermal mechanical cycling between the gel and the sol states is rapid and can be repeated several times (i.e., they are thixotropic). The single‐crystal structure of DODA indicates that extended intermolecular dipole–dipole interactions are crucial to the thermal and mechanical formation of DODA gels and the consequential changes in emissive and mechanical properties. From analyses of structural information, gelator packing, and morphology differences, we hypothesize that the mechanical destruction and reformation of the gel networks involves interconversion between the 3D networks and 1D fiber bundles. The thermal processes allow the fibrillar 3D networks and their 0D components (i.e., isolated molecules or small aggregates of DODA ) to be interconverted. These results describe a facile approach to the design of mechano‐responsive, thermo‐reversible gels with control over their emission wavelengths.     

Langmuir-Blodgett films of a Mo-blue nanoring [Mo(142)O(429)H(10)(H(2)O)(49)(CH(3)CO(2))(5)(CH(3)CH(2)CO(2))](30)(-) (Mo(142)) by the semiamphiphilic method

Langmuir monolayers and LB films of the ring-shaped mixed-valence polyoxomolybdate [Mo142O429H10(H2O)49(CH3CO2)5(CH3CH2CO2)](30-) (Mo142) dissolved in the aqueous subphase have been successfully fabricated by using the adsorption properties of a DODA monolayer. Infrared and ultraviolet-visible spectroscopy of the LB films indicates that Mo142 and DODA molecules are incorporated within these LB films. X-ray reflectivity experiments indicate that the LB films exhibit a well-defined lamellar structure formed by bilayers of DODA molecules alternating with monolayers of Mo142. Using behenic acid-modified hydrophobic quartz substrate is critical for the formation of the well-defined lamellar structure. From the values of the periodicity obtained by these experiments it is clear that the Mo142 clusters lie flat along the charged organic layers. AFM images also showed the flat and homogeneous films on the quartz substrates treated with behenic acid. Cyclic voltammograms of Mo142-LB films deposited on ITO substrates showed quasi-reversible oxidation/reduction waves with positive shift of the potential compared to the case of solution.     

Study on water evaporation through 1-alkanol monolayers by the thermogravimetry method

The influence of 1-alkanol monolayers on the rate of water evaporation has been studied by measuring water loss per unit time using thermogravimetry. The evaporation rate of water from the surface covered by an insoluble monolayer for each of four saturated 1-alkanols (C(13)OH, C(15)OH, C(17)OH, and C(19)OH) was measured as a function of temperature and alkyl chain length, where the monolayer was under equilibrium spreading pressure. The evaporation rate decreased with increasing alkyl chain length or increasing molecular interaction among 1-alkanol molecules in the insoluble monolayer. Using the Arrhenius equation, the activation energy for the water evaporation was calculated from the temperature dependence of the evaporation rate, which showed that the activation energy decreased with increasing temperature. On the other hand, the activation energy increased with increasing alkyl chain length, which indicates that the activation energy includes the energy to cross the insoluble monolayer at the air/water interface. This energy increased almost linearly with alkyl chain length, when the length is longer than a dodecyl group. This means that water molecules need more energy to escape from the liquid to the gaseous phase across a membrane of longer 1-alkanols, which becomes more evident at lower temperatures. The temperature dependence of the activation energy was slightly larger for longer 1-alkanols than for shorter ones.     

Methylene Blue Adsorption on a DMPA Lipid Langmuir Monolayer

Adsorption of methylene blue (MB) onto a dimyristoylphosphatidic acid (DMPA) Langmuir air/water monolayer is studied by molecular dynamics (MD) simulations, UV reflection spectroscopy and surface potential measurements. The free‐energy profile associated with MB transfer from water to the lipid monolayer shows two minima of ?66 and ?60 kJ mol^?1 for its solid and gas phase, respectively, corresponding to a spontaneous thermodynamic process. From the position of the free‐energy minima, it is possible to predict the precise location of MB in the interior of the DMPA monolayer. Thus, MB is accommodated in the phosphoryl or carbonyl region of the DMPA Langmuir air/water interface, depending on the isomorphic state (solid or gas phase, respectively). Reorientation of MB, measured from the bulk solution to the interior of the lipid monolayer, passes from a random orientation in bulk solution to an orientation parallel to the surface of the lipid monolayer when MB is absorbed.     

Image formation by dyeing of copolymers bearing photogenerated acid and base groups with dye bath containing acid and basic dyes

Copolymers bearing photoacid generating groups and/or photobase generating groups were dyed after UV irradiation with a dye bath containing both an acid dye and a basic dye. Acetophenone O‐acryloyloxime (AAPO) was used as a monomer bearing acyloxyimino (AOI) group that generates a primary amino group upon irradiation, which is followed by hydrolysis. Phenacylsulfonylstyrene (PSSt) and 1,2,3,4‐tetrahydronaphthylideneamino p‐styrenesulfonate (NISS) were chosen as monomers having β‐keto sulfone (β‐KS) and iminosulfonate (IS) groups, respectively, which yielded acid groups when irradiated. Copolymers of AAPO and methyl methacrylate (MMA) were dyed with only the acid dye, and those of PSSt or NISS were dyed with only the basic dye after irradiation. AAPO‐PSSt‐MMA films became dyeable with the acid dye when irradiated for a short time and with the basic dye with further irradiation. However, AAPO‐NISS‐MMA copolymers showed the reverse dyeing behavior. IR spectra revealed that AOI groups were photochemically decomposed prior to the β‐KS groups for AAPO‐PSSt‐MMA, and AOI and IS groups decomposed simultaneously for AAPO‐NISS‐MMA. These results suggested the possibility of adsorption of different ionic dyes on the films by a change of irradiation time; in fact, color patterns could be obtained in a single staining process using the dye bath. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3043–3051, 2000     

Regular two-dimensional molecular array of photoluminescent Anderson-type polyoxometalate constructed by Langmuir-Blodgett technique

A regular two-dimensional photoluminescent array of Anderson-type polyoxometalates (POMs) was constructed as built-up Langmuir-Blodgett (LB) films. LB films of hexatungstoantimonate (SbW(6)) and -manganate (MnW(6)) were successfully fabricated by using dimethyldioctadecylammonium (DODA) as cationic partner, while hexamolybdochromate (CrMo(6)) was unsuccessful. Specular X-ray reflectivity (SXR) and grazing incidence X-ray diffraction (GIXD) measurements revealed that both SbW(6)/DODA and MnW(6)/DODA LB films exhibited well-ordered layers consisting of periodic arrangement of the planar-structured Anderson-type molecules. Surprising periodicity was observed in SbW(6)/DODA LB film, in which the distance between SbW(6) and DODA layers was 4.40 nm, and SbW(6) anions would form a two-dimensional square lattice with a length of 1.4 nm. SbW(6)/DODA LB films exhibited photoluminescence at 77 K, while emission spectra were observed at room temperature for SbW(6) solid.     

Information Coding in a Reconfigurable DNA Origami Domino Array

DNA nanostructures with programmable nanoscale patterns has been achieved in the past decades, and molecular information coding (MIC) on those designed nanostructures has gained increasing attention for information security. However, achieving steganography and cryptography synchronously on DNA nanostructures remains a challenge. Herein, we demonstrated MIC in a reconfigurable DNA origami domino array (DODA), which can reconfigure intrinsic patterns but keep the DODA outline the same for steganography. When a set of keys (DNA strands) are added, the cryptographic data can be translated into visible patterns within DODA. More complex cryptography with the ASCII code within a programmable 6×6 lattice is demonstrated to demosntrate the versatility of MIC in the DODA. Furthermore, an anti‐counterfeiting approach based on conformational transformation‐mediated toehold strand displacement reaction is designed to protect MIC from decoding and falsification.     

Surfactant-Induced Trans-Interface Transportation and Complex Formation of Giant Polyoxomolybdate-Based Clusters

The interaction and complex formation between cationic surfactants dimethyldioctadecylammonium Bromide (DODA-Br) and a polyoxomolybdate (POM)-based giant cluster {Mo₇₂Fe₃₀}, in its both single cluster (in aqueous solution, these clusters exist as anions) format and supramolecular format in aqueous solution, are studies by using laser light scattering (LLS) techniques. DODA/{Mo₇₂Fe₃₀} complexes containing basically single {Mo₇₂Fe₃₀} clusters are observed when the {Mo₇₂Fe₃₀} aqueous solution is freshly prepared and contains mainly unimer or oligmer {Mo₇₂Fe₃₀} anions. The {Mo₇₂Fe₃₀} clusters tend to form supramolecular vesicle structures slowly in solution. At high surfactant concentrations, the DODA cationic surfactants can break the vesicle structure and form single {Mo₇₂Fe₃₀}/DODA complexes. At low surfactant concentrations, complexes containing the whole vesicles coated by a layer of DODA is formed and transferred into the organic phase. For the surfactant concentrations in between, the vesicles are partially destroyed, leading to the formation of complexes with large size distribution. Studying the behaviors of the interaction between DODA and {Mo₇₂Fe₃₀} anionic structures will help to further explore the complicated mechanism of the POM vesicle formation, which was recently discovered but still not fully understood. Such unique complex structures may also have potential applications as nanoreactors or nanocontainers.     

Configuration and photochemical reaction of a bolaamphiphilic diacid with a diazo resin in monolayers and Langmuir-Blodgett films

The monolayer formation of a bolaamphiphile, 1,18-octadecanedicarboxylic acid (ODA), on pure water and the subphase containing a positively charged photoactive 2-nitro-N-methyldiphenylamine-4-diazoniumformaldehyde resin (NDR) have been investigated by pi-A isotherms, pi-t curves, and Brewster angle microscopy (BAM) measurements. It has been revealed that although an unstable monolayer was formed by ODA alone, a stable complex monolayer between ODA and NDR could be formed at the interface through electrostatic adsorption and hydrogen bonding. It has been shown that the ODA formed a U-shaped monolayer at a lower pressure and was converted to a stretched configuration upon compression to a higher surface pressure on the subphase containing NDR. Under UV irradiation at the interface photoreaction can occur in the complex monolayer, which causes shrinkage of the monolayer. Photochemical reactions can also occur in deposited Langmuir-Blodgett films. In reactions occurring at the air/water interface, the two ends of ODA can react with NDR to form an ester containing aromatic rings. This makes the compound more hydrophobic and can easily be stretched without any phase transition upon compression. When the film with U-shaped configuration was deposited onto solid substrates, the configuration could be kept even upon photoirradiation.     

双长链烷基稀土杂多酸化合物LB膜的制备、结构及性质研究

制备了三种新型双窗长链烷基稀土杂多酸化合物langmuir和langmuir-blodgett膜：DODA/Ln(PW~1~1)~2(Ln=La,Sm,Eu)。用π-A等温线,IR,UV,小角X射线衍射,荧光光谱,光电压谱对其进行了表征。结果表明：它们在空气-水界面有良好的成膜性能,这些单层在表面压为零时,表观单分子占有面积为0.45～0.50nm^2。LB膜有良好的层间有序性,稀土杂多酸阴离子是作为一无机层夹在两个双长链烷基层之间。DODA/Ln(PW)~1~1)~2LB膜具有Sm,Eu的特征荧光,其光电压谱亦有较强的光电响应。     

Infrared imaging of a solid phase surfactant monolayer

A new method for visualizing solid phase surfactant monolayers is presented. This method utilizes infrared (IR) imaging of the surface of a warm subphase covered by the monolayer. When the subphase is deep, natural convection occurs, resulting in a complex surface temperature field that is easily visualized using an IR camera. The presence of a surfactant monolayer changes the hydrodynamic boundary condition at the interface, dramatically altering the surface temperature field, and permitting the differentiation of surfactant-covered and surfactant-free regions. In this work, solid phase monolayers are imaged using this IR method. Fractures in the monolayer are dramatically visualized because of the sudden elimination of surfactant in the region opened up by the crack. The method is demonstrated in a wind/water tunnel, where a stearic acid monolayer is deposited and a crack is created through shear on the surfactant surface, created by suddenly increasing the velocity of the air over the water.     

Dynamic viscoelastic properties of spread monostearin monolayer in the presence of glycine

The monostearin monolayer at the air-aqueous interface is more expanded in presence of glycine and at higher temperature from both the surface pressure-area per molecule (pi-A) isotherms and static elasticity-surface pressure (E(s)-pi) curves. The dilational viscoelastic properties of monostearin monolayer spread on the subphase of glycine solution have been determined by the dynamic oscillation method and discussed as a function of surface pressure, temperature, and frequency. At the frequency of 50 mHz, the monostearin monolayer on pure water shows negative dilational viscosity and is viscoelastic at some surface pressures, while the monostearin monolayer in the presence of glycine is nearly elastic over a wide range of surface pressure, especially at 25 degrees C. Both positive and negative loss angle tangent can be deduced as a function of surface pressure. The negative dilational viscosity can be attributed to the phase transitions induced by the propagation of the surface waves during the dynamic oscillation. It can be convinced that the interactions between monostearin and glycine play an important role in the formation and rheological behavior of the monolayer. On the other hand, temperature has effect on the dilational elasticity and the dilational viscosity of the monostearin monolayer in different extents. Furthermore, at the surface pressure of 20 mN/m, the monostearin monolayer on the glycine solution at 18 degrees C is essentially elastic at lower frequency (<100 MHz) and shows viscoelastic behavior at higher frequency. These phenomena should be associated with the complicated monolayer structure and structural reorganization due to the interactions between monostearin and glycine in presence of glycine.     

Preparation of chiral polystyrene monoliths by utilizing W/O emulsion polymerization and their optical resolution ability

We synthesized two kinds of chiral polystyrene‐based monoliths, which are macroporous gel with continuous open‐celled monolith structure. Thus, two chiral styrene monomers, (–)‐p‐[dimethyl(10‐pinanyl)silyl]styrene ((–)‐PSSt) and (–)‐p‐(menthoxycarbonyl)styrene ((–)‐MtSt]), were prepared and subjected to water‐in‐oil emulsion polymerization in the presence of divinylbenzene and AIBN. The macroporous structure of the obtained monoliths was directly confirmed by SEM observation. The obtained monoliths showed an optical resolution ability. That is, in the enantioselective adsorption using trans‐stilbene oxide, poly[(–)‐PSSt] monolith and poly[(–)‐MtSt] monoliths preferentially adsorbed (S,S)‐isomer [poly[(–)‐PSSt] monolith: α^(S,S) = 1.49 (0.25 wt % acetone solution); poly[(–)‐MtSt] monolith: α^(S,S) = 1.39 (0.25 wt % toluene solution)]. Depinanylsilylation of the poly[(?)‐PSSt] monolith and removal of menthyl groups from the poly[(–)‐MtSt] monolith were achieved by acid‐catalyzed scission of the Si? C bond and base‐catalyzed hydrolysis, respectively. In addition, de‐poly[(–)‐PSSt] and de‐poly[(–)‐MtSt] showed enantioselectivity ((S,S)‐isomer preferentially absorbed) in adsorption using trans‐stilbene oxide in spite of the absence of chiral substituents in the monoliths. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2348–2357, 2005