Using lattice simulations the effect of confinement on the size, orientation and elastic properties of athermal chains was investigated. For chains confined in a slit or in a “cylinder” with square profile a minimum was observed in the dependence of the mean‐square end‐to‐end distance 〈R2〉 on the plate distance D. However, the components of the mean chain dimensions perpendicular and parallel to the walls, 〈R2⟂〉 and 〈R2∥〉, steadily diverge with reduction of the pore size. In a slit the distribution functions of the chain vector perpendicular and parallel to the plates, W〈R2⟂ 〉 and W〈R2∥〉, respectively, were computed. The marked difference between these distribution functions is interpreted as a sign of enhanced alignment of chains of the shape of elongated ellipsoids along the pore walls. A major part of the free energy of confinement ΔAcf stems from this mechanism of pore‐induced macromolecular orientation. A striking anisotropy was observed in the elastic free energies Ael⟂ and Ael∥ of chains deformed in the direction perpendicular and parallel to the walls and in the corresponding force‐displacement functions. Finally, the relation between the elastic free energy Ael and the free energy of confinement ΔAcf and between the forces f and fsolv derived thereof is analysed. 相似文献
Summary: The morphologies and conformations of triblock copolymer (ABA and ABC) thin films confined between two identical walls were investigated by Monte Carlo simulation using bond length fluctuation and cavity diffusion algorithm on cubic lattice. Effects of the wall‐block interactions, copolymer chain composition and film thickness on morphologies, as well as on the fraction of chain “bridge” conformation fbridge are presented in detail. In ABA thin film, column, parallel, perforated and perpendicular lamellas were discriminated, furthermore, the transition of morphology and the variation of fbridge of ABA film along with the increase of thickness were revealed. In ABC thin film, lamella especially perpendicular lamella morphologies are predominant in varying the wall‐block interactions and the thickness. The results are consistent with some theoretical predictions such as DDFT and simulations reported in literature.
The Langmuir monolayer of carboxylic methyl ester Gemini surfactants with the azobenzene spacer, referred to as MCm(azo)MCm, was prepared and the π‐A isotherms were measured. The result revealed an orientational picture of the azobenzene spacer at the air/water interface. Before irradiation, the planar trans‐azobenzene group adopted an approximate configuration parallel to the interface and lay on the air/water interface. After UV‐light irradiation, the spacer became the twisted cis‐one. Because of the location of the polar headgroups at the air/water interface, the two phenyl rings were also forced to take a near‐parallel orientation with the interface to reduce the free energy. As a result, the spacer thin‐layer was "thickened", which caused an elevation in collapse pressure. 相似文献
Novel copolymers with controlled architectures can function as new building blocks for well‐defined nanostructures on the basis of microphase separation, unlike conventional ABA triblock copolymers. A series of well‐defined AxBAx‐type block–graft copolymers consisting of soft middle segments (dodecyl methacrylate (DMA)) and hard outer graft chains (styrene (St)) were synthesized by ruthenium‐catalyzed living radical block and graft polymerization. NMR spectroscopy and size‐exclusion chromatography combined with multiangle laser light scattering confirmed the well‐defined structure of the AxBAx block–graft copolymers with backbones and graft chains of controlled lengths. Transmission electron microscopy and transmission electron microtomography revealed a series of morphologies for the copolymers. Morphological changes were observed from PSt “honeycomb” cylinders to lamellae and poly(DMA) cylinders with increasing PSt‐graft content, whereby the phase diagram was shifted significantly to lower volume fractions of the larger‐number component (St) relative to those of the corresponding ABA triblock copolymers. More specifically, poly(DMA) cylinders were observed even before the St content reached 50 wt %. The AxBAx and ABA copolymers with 17–30 wt % of St exhibited characteristics of a thermoplastic elastomer with tensile strengths of 1–6 MPa and elongations at break of 70–300 %. These mechanical properties can be related well to the microphase structures of the AxBAx and ABA copolymers. 相似文献
We employ dissipative particle dynamics (DPD) to examine the self‐assembly behavior of A2‐star‐(B‐alt‐C) molecules. We successfully observe various types of hierarchical structure‐within‐structures, such as A‐formed spheres in the matrix formed by B and C alternating layers, hexagonally packed A‐formed cylinders in the matrix with B and C segregated layers, B and C alternating layers‐within‐lamellae, coaxial B and C alternating domains within hexagonally packed BC‐formed cylinders in the A‐matrix, and co‐centric BC‐alternating domains within BC‐formed spheres in the A‐matrix, by increasing the A composition. Generally speaking, the small length‐scale B and C segregated domains are in parallel to the large length‐scale structures. This hierarchical periodicity along the same axis as well as the various characteristic structures, that the A2‐star‐(B‐alt‐C) copolymers display, are quite different from those in A‐block‐(B‐graft‐C) coil‐comb copolymers. Moreover, it is interesting to find that when the copolymer chain length increases, though the hierarchical structure type is maintained, the number of small length‐scale lamellae that can form within the large length‐scale structure increases. These hierarchical structures under various compositions are reported theoretically for the first time in the copolymer systems consisting of the alternating blocks, and are in good agreement with the most recent experimental work by Matsushita and co‐workers (Macromolecules 2007 , 40, 4023).相似文献
The silver bismuth tridecasulfide Ag3.5Bi7.5S13 crystallizes in the monoclinic space group C2/m. Its structure is built up of two alternating kinds of layered modules parallel to (001). In the module denoted A, octahedra around the metal positions (M = Ag/Bi, M2 and an S atom on 2/m, other atoms on m) alternate with paired monocapped trigonal prisms around Bi. The NaCl‐type module B is composed of parallel eight‐membered chains of edge‐sharing octahedra running diagonally across it. Ag3.5Bi7.5S13 is the member with N = 8 of the pavonite homologous series NP of ternary compounds with the general formula [Bi2S3]2·[AgBiS2](N−1)/2. 相似文献
Single crystals of the new Zintl phases AIn2P2 [A = Ca (calcium indium phosphide), Sr (strontium indium phosphide) and Ba (barium indium phosphide)] have been synthesized from a reactive indium flux. CaIn2P2 and SrIn2P2 are isostructural with EuIn2P2 and crystallize in the space group P63/mmc. The alkaline earth cations A are located at a site with m symmetry; In and P are located at sites with 3m symmetry. The structure type consists of layers of A2+ cations separated by [In2P2]2− anions that contain [In2P6] eclipsed ethane‐like units that are further connected by shared P atoms. This yields a double layer of six‐membered rings in which the In—In bonds are parallel to the c axis and to one another. BaIn2P2 crystallizes in a new structure type in the space group P21/m with Z = 4, with all atoms residing on sites of mirror symmetry. The structure contains layers of Ba2+ cations separated by [In2P2]2− layers of staggered [In2P6] units that form a mixture of four‐, five‐ and six‐membered rings. As a consequence of this more complicated layered structure, both the steric and electronic requirements of the large Ba2+ cation are met. 相似文献
Three alkali metal acetylides, namely KNaC2, KRbC2, and NaRbC2, were synthesized and characterized by means of X‐ray powder diffraction. KNaC2 and KRbC2 crystallize as a variant of the anti‐PbCl2‐type structure (Pnma, Z = 4), whereas NaRbC2 crystallizes as a variant of the anti‐PbFCl‐type structure (Pmmn, Z = 2). Based on a simple systematic approach developed by Sabrowsky et al. for inter‐alkali metal chalcogenides all known inter‐alkali metal acetylides can be classified into two classes: variants of the anti‐PbCl2 type structure and variants of the anti‐PbFCl type structure. Acetylides with Q(ABC2) ≤ 1.45 crystallize in the anti‐PbCl2‐type structure, whereas for Q(ABC2) > 1.45 the anti‐PbFCl‐type structure is found (Q(ABC2) = Vm(A2C2)/Vm(B2C2) with Vm(A2C2) > Vm(B2C2); Vm: molar volume, A, B = alkali metals). 相似文献
Summary: We used the dissipative particle dynamics method to simulate the self‐assembly of symmetric triblock copolymers of the type ABA. Depending on the volume fraction of the end blocks fA, several mesophases including lamellar, perforated lamellar, gyroid, hexagonal cylinders and bcc spherical micelles were obtained. The order‐disorder transition (ODT) at fA = 0.5 was found to be about χN = 19.8. The ODT for the cylindrical mesophase at symmetrical points on the phase diagram had different values, indicating asymmetry in the phase diagram. We were also able to estimate the bridge fraction in the different mesophases. They range from about 0.44 for the lamellar mesophase to about 0.75 for the spherical micelles. Our simulation results are in good agreement with previously reported theoretical calculations and experimental observations.
The hexagonal cylinders generated with the A6B4A6 copolymer. 相似文献
A nanocylindrical wall structure was obtained by layer‐by‐layer (LbL) assembly of poly‐L ‐arginine (PLA) and human serum albumin (HSA) and characterized by scanning electron microscopy (SEM), scanning force microscopy (SFM), and cryogenic transmission electron microscopy (cryo‐TEM). SEM and SFM measurements of a lyophilized powder of (PLA/HSA)3 nanotubes yielded images of round, chimney‐like architectures with approximately 100 nm wall thickness. Cryo‐TEM images of the hydrated sample revealed that the tube walls are composed of densely packed HSA molecules. Moreover, when small‐angle X‐ray scattering was used to characterize the individual PLA and HSA components in aqueous solutions, maximum diameters of approximately 28 nm and 8 nm were obtained, respectively. These values indicate the minimum thickness of wall layers consisting of PLA and HSA. It can also be concluded from SEM as well as from cryo‐TEM images that the protein cylinders are considerably swollen in the presence of water. Furthermore, HSA retains esterase activity if assembled in nanotubes, as indicated by measurements of para‐nitrophenyl acetate hydrolysis under semi‐physiological conditions (pH 7.4, 22 °C). The enzyme activity parameters (Michaelis constant, Km, and catalytic constant, kcat) were comparable to those of free HSA. 相似文献
Given some lattice, the number ZHP of Hamiltonian paths and also the number ZN of N‐step shorter self‐avoiding walks on the surface of cylinders, cones, tori, and spheres has been Monte Carlo estimated. The procedure is an extension of the technique used in a previous paper for plane squares and rectangles, which is based on the Rosenbluth‐Rosenbluth chain‐generation procedure. Starting from a rectangle having m lines and n columns, and thus m×n lattice sites, one may obtain cylindrical, conical, toroidal and spherical surfaces through continuous deformations, which respect the topology. Then a correspondence is established between a plane figure of the ‘polar’ coordinates kind and the topology of the above surfaces. Using this topological equivalence, and thus operating exclusively on the plane ‘polar’ figure, Monte Carlo simulations show that for given m and n, ZHP and ZN increase when going from the plane rectangle to the cylinder and then to the cone and the torus. The number ZNC of N‐step cycles (closed configurations) has also been Monte Carlo estimated. The Monte Carlo results for the surfaces studied here have been condensed in fifth degree polynomials in Φ, where Φ is the fraction of available lattice sites on the surface which are occupied by the N‐step self‐avoiding walk. The variation of the ratio ZNC /ZN with m and n has been estimated for cylindrical and conical surfaces. Finally, an effective coordination number qeff has been introduced for finite surfaces, and its variation with Φ studied. 相似文献
The structure of a new layered oxyfluoride, viz. potassium strontium diniobium hexaoxide fluoride, KSrNb2O6F, was refined from powder neutron diffraction data in the orthorhombic space group Immm. The oxyfluoride compound is an n = 2 member of the Dion–Jacobson‐type family of general formula A[A′n−1BnX3n+1], which consists of double layered perovskite slabs, [SrNb2O6F]−, between which K+ ions are located. Within the perovskite slabs, the NbO5F octahedra are significantly distorted and tilted about the a axis. A bond‐valence‐sum calculation gives evidence for O/F ordering in KSrNb2O6F, with the F− ions located in the central sites of the corner‐sharing NbO5F octahedra along the b axis. All atoms lie on special positions, namely Nb on m, Sr on mmm, K on m2m, F on mm2, and O on sites of symmetry m and m2m. 相似文献
Monte Carlo simulations for the adsorption of symmetric triblock copolymers from a nonselective solvent at a solid-liquid interface have been performed on a lattice model. In simulations, triblock copolymer molecules are modeled as self-avoiding linear chains composed of m segments of A and n segments of B arranged as Am/2BnAm/2. Either segment A or segment B is attractive, while the other is non-attractive to the surface. The microstructure of the adsorbed layers, including the segment-density profiles and the size distribution of loops, tails and trains are presented. The effect of the adsorption energy, the bulk concentration, the chain composition, as well as the chain length on various adsorption properties has been studied. The results have shown that the size distribution of various configurations is dependent of the adsorption energy, the chain composition and the chain length. The mean length of the loops, trains and tails is insensitive to the bulk concentration. The mean length of the trains increases and that of the tails decreases as the adsorption energy and the length of the attractive segments increase. The mean length of the loops for the end-adsorbed copolymers appears a maximum and that for middle-adsorbed copolymers appears a minimum as the length of attractive segments increases. The length of the non-attractive segments affects mostly the size distribution of the tails. The longer the chain is, the larger the tail appears. The mean length of the tails and loops increases linearly as the length of the non-attractive segments increases, but that of the trains approximately is unchanged. 相似文献
The first three representatives of the new family of oxacyclophanes incorporating two 2,7‐dioxyfluorenone fragments, connected by [‐CH2CH2O‐]m spacers (m=2–4), have been synthesized. The yield of the smallest oxacyclophane (m=2) is considerably higher with respect to the larger ones (m=3 and m=4), which are formed in comparable yields. Molecular modeling and NMR spectra analysis of the model compounds suggest that an essential difference in oxacyclophanes yields is caused by formation of quasi‐cyclic intermediates, which are preorganized for macrocyclization owing to intramolecular π–π stacking interactions between the fluorenone units. The solid‐state structures of these oxacyclophanes exhibit intra‐ and intermolecular π–π stacking interactions that dictate their rectangular shape in the fluorenone backbone and crystal packing of the molecules with the parallel or T‐shape arrangement. The crystal packing in all cases is also sustained by weak C? H ??? O hydrogen bonds. FAB mass spectral analysis of mixtures of the larger oxacyclophanes (m=3 and m=4) and a paraquat moiety revealed peaks corresponding to the loss of one and two PF6? counterions from the 1:1 complexes formed. However, no signals were observed for complexes of the paraquat moiety with the smaller oxacyclophane (m=2). Computer molecular modeling of complexes revealed a pseudorotaxane‐like incorporation of the paraquat unit, sandwiched within a macrocyclic cavity between the almost parallel‐aligned fluorenone rings of the larger oxacyclophanes (m=3 and m=4). In contrast to this, only external complexes of the smallest oxacyclophane (m=2) with a paraquat unit have been found in the energy window of 10 kcal mol?1. 相似文献
A series of newly synthesized 1,3‐purinodiones with potential anticonvulsant activity, exhibiting affinity to adenosine A1 and/or A2A receptors, were subjected to micellar LC (MLC) with SDS as micelle‐forming agent and n‐propanol as organic modifier. Two C18 silica‐based columns were employed in MLC: a particle one and a monolithic. In parallel, those derivatives were also analyzed in RP‐LC on four silica‐based columns and on an immobilized artificial membrane column. The correlations between the relevant logarithms of the retention factors of analytes obtained in MLC, immobilized artificial membrane and RP‐LC systems on the one hand, and the calculated log P (clog P) and log D values (clog D) on the other, were examined. The level of the correlations of retention data from MLC and RP‐LC systems with clog P and clog D obtained is similar but it could be stressed that MLC allows increasing the speed of analysis and using only one mobile phase. Moreover, there is no need of applying an extrapolation procedure in lipophilicity determination. Therefore, the MLC systems, providing chromatographic data in a fast and efficient manner, were demonstrated as promising alternatives to the classical RP‐LC systems to estimate the lipophilicity of drugs and drug candidates. 相似文献
Two aggregation‐induced emission active luminogens (TPE–pTPA and TPE–mTPA) were successfully synthesized. For comparison, another six similar compounds were prepared. Because of the introduced hole‐dominated triphenylamine (TPA), fluorene groups with high luminous efficiency, and unconjugated linkages, the π conjugation length of the obtained luminogens is effectively restricted to ensure their blue emission. The undoped organic light‐emitting diodes based on TPE–pTPA and TPE–mTPA exhibited blue or deep‐blue emissions, low turn‐on voltages (3 V), and high electroluminescence efficiencies with Lmax, ηC,max, and ηP,max values of up to 26 697 cd m?2, 3.37 cd A?1, and 2.40 Lm W?1. 相似文献