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Membranes derived from self-assembled block polymers have shown promise as highly selective and highly permeable filters, but the complex synthetic routes and limited pore functionalities of existing systems need to be improved if these materials are to serve as a platform for the next generation of nanostructured membranes. Here, the facile synthesis of a polyisoprene- b -polystyrene- b -poly( N,N -dimethylacrylamide) (PI–PS–PDMA) triblock polymer using a controlled reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism is reported. This material is then processed into a membrane using a self-assembly and non-solvent induced phase separation (SNIPS) technique, which creates an asymmetric, porous structure consisting of a selective layer that contains a high density of PDMA-lined pores (9.4×10 13 pores m −2 ) with an average diameter of 8.1 nm, as determined using solute rejection tests. Solvent flow experiments demonstrate that the PI–PS–PDMA membrane has a pH-independent permeability of 6 L m −2 h −1 bar −1 . The PDMA moiety lining the pore walls is converted, through simple hydrolysis in the solid state, to yield a poly(acrylic acid)-lined (PAA-lined) structure. The permeability of the PI–PS–PAA membrane is pH-dependent, and ranges from 0.6 L m −2 h −1 bar −1 for solutions with a pH greater than 4 to 16 L m −2 h −1 bar −1 for a solution at pH 1. Solute rejection tests demonstrated a pore size of 3.4 nm for the PI–PS–PAA membrane, which is the smallest pore size reported to date for membranes fabricated from self-assembled block polymers. The facile synthesis of the PI–PS–PDMA material, the scalable SNIPS membrane fabrication protocol, and the simple conversion chemistry of the pore functionality demonstrate that these nanostructured membranes are a strong platform for applications within the range of water purification, pharmaceutical separations, sensors, and drug delivery.

Polymer electrolyte membranes with bicontinuous microphases comprising soft hydrated domains and mechanically robust hydrophobic domains are used in a wide range of electrochemical devices including fuel cells and electrolyzers. The self-assembly, water uptake, and proton conductivity of model block copolymer electrolytes with semicrystalline hydrophobic blocks were investigated. A series of sulfonated polystyrene-block-polyethylene (PSS–PE) copolymers were synthesized to probe the interplay between crystallization, morphology, hydration, and proton transport. In block copolymer systems with amorphous hydrophobic blocks, it has been shown that higher water update and proton conductivity are obtained in low molecular weight systems. However, crystallization is known to disrupt the self-assembly of low molecular weight block copolymers. We found that this disruption results in lower water uptake and proton conductivity. Increasing molecular weight results in less morphological disruption and improvement in ...

Electron correlation theories such as configuration interaction (CI), coupled-cluster theory (CC), and quadratic configuration interaction (QCI) are assessed by means of a Moller–Plesset perturbation expansion of the correlation energy up to fifth order. The computational efficiencies and relative merits of the different techniques are outlined. A new augmented version of coupled-cluster theory, denoted as CCSD (T), is proposed to remedy some of the deficiencies of previous augmented coupled-cluster models.

Polystyrene-block-polyethylene-block-polystyrene (SES) copolymers were blended with homopolymer polystyrene (PS), and films of the blend were solvent cast using a doctor blade. The nonporous SES and PS films were exposed to both tetrahydrofuran (THF) and methanol (MeOH) in an alternating fashion for 1 min intervals three times, without letting the films dry between solvent immersions. At this point, either the films were removed from MeOH and dried or the films were immersed in THF and then dried. THF is a nonsolvent for crystalline polyethylene (PE) but a good solvent for both amorphous PE and PS. Methanol is a nonsolvent for semicrystalline PE, amorphous PE, and PS. Films that were dried with MeOH as the final nonsolvent were highly porous and exhibited high conductivity when swollen in a liquid electrolyte. In contrast, films that were dried with THF as the final nonsolvent were nonporous and exhibited poor conductivity when swollen in a liquid electrolyte. We study the fundamental effect of nonsolvent...

The dynamics associated with magnetic field alignment of a model rod–coil block copolymer poly(2,5-di(2′-ethylhexyloxy)-1,4-phenylenevinylene)-b-polyisoprene (PPV–PI) have been investigated using a combination of time-resolved in situ small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Alignment is observed over a wide range of field strengths (0.2–7 T); however, the highest field strengths studied produce the highest degree of alignment. Experiments examining alignment of a disordered sample, cooled into the ordered state in the presence of a magnetic field, show that alignment mostly occurs during nucleation and growth of the block copolymer nanostructure. The slower secondary processes of defect annihilation and grain rotation progress are necessary in producing extremely highly aligned samples. At the highest field strength, due to the increased order–disorder transition temperature (TODT), selective ordering is likely observed at temperatures near the order–disorder transi...

The iso-concentration ordering kinetics of poly(styrene-b-butadiene) in a neutral solvent, toluene, at several concentrations along the solvent extraction path at room temperature were studied using dynamic mechanical rheological measurements and SAXS. These experiments are in contrast to more common studies of the ordering kinetics of block copolymers in which phase separation following temperature quenches is considered. Poly(styrene-b-butadiene) in toluene was found to order into hexagonally-packed cylinders beginning at a polymer concentration of 30 wt%. The half-time was found to be governed by a competition between thermodynamic and kinetic effects as concentration changes. An Avrami exponent of 1.0 was obtained at all concentrations and was correlated to two-dimensional diffusion-controlled growth or heterogeneous nucleation and linear growth at higher concentrations. A comparison of the rheological and SAXS data suggested that changes in the dynamic mechanical response during ordering were induced by the development of individual microstructures acting as physical crosslinks. A correlation between microstructure and the Avrami exponent was not found.

The ordering of a poly(styrene-b-butadiene) block copolymer solution into hexagonally packed cylinders during the extraction of a neutral solvent from a solution-cast film was studied in real time ...

Changes in the spacing of hexagonally packed cylinders in a poly(styrene-b-butadiene) copolymer film during the continual extraction of toluene under different solvent removal conditions were studied by in situ small-angle X-ray scattering (SAXS) measurements. As the solvent is removed from the film, the structure spacing increases due to increasing segregation power and then decreases as the polymer chains become kinetically trapped while microdomains continue to deswell. The structure spacing in the vertical film direction decreases more drastically due to compression of the domains as the film thickness decreases. The degree of compression increased with increased polymer concentration because of an increase in the chain relaxation time. Increasing the drying temperature resulted in more severe domain compression, which is ascribed to faster solvent removal. Removing solvent in the presence of a sweep gas further increased the domain compression as a result of the formation of a skin at the film surfac...

Nafion(117) membranes in contact with acidic solutions were characterized by small-angle X-ray scattering and by acid solution uptake measurements. The principle of Donnan equilibrium was used to o...

The atomization energies of the species AHn, where A is a first-row atom Li to F, are examined by Moller–Plesset theory. Direct application of fourth-order theory, together with the 6–311G basis is shown to be inadequate. Improvements introduced into the theory are (i) isogyric comparisons with the bond energy of the hydrogen molecule, (ii) extrapolation of the Moller–Plesset series to infinite order, and (iii) extension of the basis set by including diffuse sp-, extra d- and f-type Gaussian functions. Assuming additivity of these basis set extension effects, agreement with experiment to better than c2 kcal/mol is achieved for the total atomization energies of CH4, NH3, OH2, and FH. The experimental data for the remaining systems are reviewed in the light of application of this new theory.

A second-order (quadratically convergent) method is presented for simultaneously optimizing the molecular wavefunction and geometry within the finite basis Hartree–Fock model. Due to inclusion of exact second derivative information, its convergence properties are greatly superior to first-order optimization schemes, while its cost only scales as the fourth power of the molecular size, like conventional first-order optimizations. By contrast, a conventional second-order geometry optimization (in which the wavefunction is constrained to be optimal), involves a step scaling as the fifth power. The performance of the new method relative to a conventional geometry optimization is illustrated by calculations on (S)-α-formylaminopropanamide, CHO—NH—CHCH3—CO—NH2.

The interaction of a water molecule with a cluster of beryllium atoms [Ben … OH2, n = 1–5] has been examined by ab initio molecular orbital methods. The dependence of interaction energy and structure on the size of the cluster was investigated with a large basis set including polarization functions. The effects of electron correlation were considered by Moller-Plesset perturbation theory. A surprisingly large increase in the interaction energy from 5 kcal/mol to 23 kcal/mol occurs when the cluster size reaches three atoms with a decrease in the Be-O distance from 1.71 to 1.64 A. The dissociation energy shows no further large changes when the cluster size is increased to four and five atoms. The H2O is found to prefer corner binding sites significantly over edge or face sites on the clusters. The nature of the bonding between H2O and the Be clusters is discussed.

Molecular orbital techniques for the ab initio computation of harmonic force constants are reviewed. Extensive applications with the split-valence 3-21G basis are described and a systematic comparison between theoretical and experimental frequencies is undertaken. The 3-21G force constants are permanently stored on a disk file and may be used to predict frequencies for isotopically substituted species. Applications are made to some deuterated molecules.

We Present a preliminary report on the conformational and energetic analysis of the molecule (S)-2-acetylamino-N-methylpropanamide (alanine dipeptide) and an analog molecule, (S)-{alpha}-formylaminopropanamide, using high-quality ab initio methods. Alanine dipeptide and its analogs are of interest since they incorporate many of the structural features found in proteins, such as intramolecular hydrogen bonds, conformational flexibility, and a variety of chemical functionality. One purpose of this study is to provide a useful benchmark calculation, MP2/6-31+G{sup **}//HF/6-31+G{sup *}, for a number of conformations of the alanine system. Based on the comparison of these benchmark calculations with lower-level basis sets, HF/3-21G was chosen to generate a fully relaxed {phi}, {psi} dihedral map. These calculations are the first of their kind on systems of this size. Features of the {phi},{psi} alanine dipeptide map that are discussed include the energetically accessible conformations and possible pathways for their interconversion. In addition, we illustrate the importance of fully optimized geometries and the proper evaluation of correlation energies

A synthesis of certain of the features of the recently developed HGP method of Head-Gordon and Pople with some of the constructs of the well-established McMurchie-Davidson (MD) scheme has led to the development of a new algorithm for the computation of the two-electron repulsion integrals which arise in conventional ab initio quantum chemical calculations using Gaussian basis sets. As in the MD scheme, derivatives of the two-electron integrals with respect to the nuclear coordinates are obtained very efficiently by the new algorithm. Moreover, in the spirit of the HGP approach, as much of the computational effort as possible is performed outside the contraction loops. This is achieved through the intermediacy of scaled, partially contracted integral sets and through the use of a near-optimal solution to the central tree-search problem. Explicit FLOP (floating point operation) counts suggest that the new algorithm is typically a factor of 2 cheaper than the HGP method for contracted basis sets.

Electronic structure calculations are performed using the coreless Hartree-Fock (CHF) effective potential scheme. Comparisons between all-electron and CHF valence electron energetic and structural results are made with a fixed all-electron basis set (6-31G). Also presented are the results of calculations using a split valence basis set that has been energetically optimized to the CHF local potential (CHF-LP-31G).

The complete spin-orbital formulation of the analytical first and second derivatives of the Hartree-Fock (HF) energy as well as the analytical first derivative of the correlated second-order Moller-Plesset perturbation energy (MP2) is presented. Some features of an efficient computational method to calculate these derivatives are described. The methods are applied to calculate the harmonic vibrational frequencies of ethylene, and the results are compared with experiment.

A simple two-electron, two-orbital model is used to discuss the electronic states and wave functions in molecules where orbital energies corresponding to different symmetries cross. According to this model, it is predicted that the triplet state has the lowest energy in the crossing region. If configuration interaction is used, the crossing of singlet total energy curves is avoided. It is also shown that the major features of the configuration interaction treatment can be reproduced by single-determinant wave functions provided that the molecular orbitals are permitted to be complex.

Some methods of describing electron correlation are compared from the point of view of requirements for theoretical chemical models. The perturbation approach originally introduced by Moller and Plesset, terminated at finite order, is found to satisfy most of these requirements. It is size consistent, that is, applicable to an ensemble of isolated systems in an additive manner. On the other hand, it does not provide an upper bound for the electronic energy. The independent electron-pair approximation is accurate to second order in a Moller-Plesset expansion, but inaccurate in third order. A series of variational methods is discussed which gives upper bounds for the energy, but which lacks size consistency. Finally, calculations on some small molecules using a moderately large Gaussian basis are presented to illustrate these points. Equilibrium geometries, dissociation energies, and energy separations between electronic states of different spin multiplicities are describe substantially better by Moller--Plesset theory to second or third order than by Hartree--Fock theory.

Phase Behavior of Polystyrene-^/ocA:-poly(2-vinylpyridine) Copolymers in a Selective Ionic Liquid Solvent t4 s T tJ Justin M . Virgili, Alexander Hexemer, John A. Pople, Nitash P. Balsara,*' ' Rachel A. Segalman*^'* and t ^Department of Chemical Engineering, University of California, Berkeley, California 94720, Materials Sciences and^ Advanced Light Source and Energy and Environmental Technologies Divisions, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and Stanford Synchrotron Radiation Laboratory, Menlo Park, California 94025 n Received March 5, 2009; Revised Manuscript Received May A B S T R A C T : T h e phase behavior o f poly(styrene-Woc/c-2-vinylpyridine) c o p o l y m e r solutions i n an i m i d a - z o l i u m bis(trifluoromethane)sulfonamide ([Im][TFSI]) i o n i c l i q u i d has been studied using small-angle X - r a y scattering ( S A X S ) and optical transmission characterization. T h r o u g h scaling analysis o f S A X S data, we demonstrate that the [Im][TFSI] ionic liquid behaves as a selective solvent t o w a r d one o f the blocks. W e observe lyotropic a n d thermotropic phase transitions that correspond qualitatively to the phase behavior observed i n block c o p o l y m e r melts and block copolymer solutions i n molecular solvents. I n a d d i t i o n , we have studied the thermal properties o f block copolymer solutions i n the i o n i c liquid using differential scanning calorimetry a n d wide-angle X - r a y scattering. W e observe distinct c o m p o s i t i o n regimes corresponding to the change i n the block copolymer's glass transition temperature, T , with respect to the concentration o f polymer i n ionic l i q u i d . A t high block copolymer concentrations, a s a l t - l i k e regime corresponding to an increase i n the block copolymer T is observed, while at intermediate block copolymer concentrations, a solvent-like regime corresponding to a decrease i n the b l o c k c o p o l y m e r T is observed. A n unusual thermal transition consisting o f crystallization and subsequent melting o f the ionic l i q u i d is observed at the lowest block copolymer concentration characterized. g g s observed temperature-dependent scaling behavior o f the char- acteristic d o m a i n spacing i n polystyrene-Woc/c-poly(isoprene) (SI) copolymer solutions i n selective solvents. This observation was attributed to the temperature dependence o f the solvent/ block copolymer segment interaction parameter, leading to changes i n solvent partitioning between the polystyrene and poly(isoprene) microphases as temperature was varied. H a n l e y et al. have shown that thermotropic properties o f mixtures o f SI copolymers and diethyl phthalate arise from the tem- perature dependence o f solvent selectivity. Alexandridis et a l . have conducted a thorough investigation o f the phase behavior o f poly(ethylene oxide-Wocfc-propylene oxide-Woc/c-ethylene oxide) P E O copolymers (Pluronic) i n water, a solvent that is selective toward the poly(ethylene oxide) ( P E O ) b l o c k . One o f the observations of Alexandridis et al. was the strong temperature dependence o f micelle formation in dilute Pluronic/water mix- tures. The temperature dependence o f block copolymer/solvent interactions, however, is not universal across all systems. F o r example, Hadjuk et al. observed weak temperature dependence o f solvent/polymer interactions i n concentrated solutions o f an asymmetric PEO-Wocfc-poly(ethyl ethylene) copolymer i n water, despite strongly thermotropic interactions between P E O and w a t e r . These findings suggest that block copolymer composition and the local structure o f water molecules surround- ing the P E O segments play an important role i n determining the phase behavior o f copolymer solutions containing P E O blocks. Introduction Ionic liquids are a novel class o f solvents composed entirely o f ions which exhibit exceptional physiochemical properties, such as nonflammability, negligible vapor pressure, high ionic conductivity, and electrochemical stability. The outstanding electrochemical properties o f ionic liquids have led to studies involving their use i n lithium battery electrolytes, ' fuel c e l l s , and dye-sensitized solar c e l l s . While the need for introducing ionic liquids into a solid supporting matrix for these applications has been recognized, the combination o f block copolymers and ionic liquids results i n a new class o f functional materials with intricate structure o n the nanometer s c a l e . T h e structure is created by block copolymer self-assembly, while the functionality is obtained by exploiting the properties o f ionic liquids. Block copolymer/ionic liquid systems enable the design o f materials whose ion-conducting and mechanical properties can be sepa- rately optimized. Effects resulting from the addition o f both selective and , nonselective molecular solvents to block copolymers o n both the self-assembled nanostructure and the thermodynamic dri- ving forces affecting self-assembly have been extensively investi- gated using both e x p e r i m e n t s and t h e o r y . A t fixed temperature, the addition o f solvents to diblock copolymers results i n a rich variety o f lyotropic phase t r a n s i t i o n s . ' T h e temperature dependence o f interactions between the two blocks, and interactions between the blocks and the solvent, lead to an additional set o f thermotropic phase transitions. L a i et a l . Water-containing polyelectrolyte membranes are o f interest for fuel cell a p p l i c a t i o n s , ' and the incorporation o f nano- structure has recently been shown to significantly improve water uptake, while maintaining mechanical s t a b i l i t y . ' Incorpora- tion o f ionic liquids into polymer membranes is also o f interest Corresponding authors. E-mail: nbalsara@berkeley.edu (N.P.B.), segalman@berkeley.edu (R.A.S.).

The ionic conductivity, σ, of mixtures of nearly symmetric polystyrene-block-poly(ethylene oxide) copolymers and Li[N(SO2CF3)2] (LiTFSI) salt was measured as a function of molecular weight, salt concentration, and temperature. The molecular weight of the poly(ethylene oxide) block, MPEO, was varied from 7 to 98 kg/mol. The molar ratio of lithium to ethylene oxide, r, was varied from 0.02 to 0.10. In general, σ increases with increasing MPEO for all values of r. The data can be summarized by plots of normalized conductivity, σn, versus MPEO, where σn = σ/(fϕPEOσPEO), ϕPEO is the PEO volume fraction in the copolymer, σPEO is the conductivity of PEO homopolymer, and f is a morphology-dependent factor set equal to 2/3 for our lamellar samples. The temperature-dependent conductivity data at a given salt concentration collapse onto a single curve when plotted in this format. At r = 0.085, σn values reach a plateau in the vicinity of unity in the high MPEO limit. At other values of r, σn continues to increase wi...

Langmuir monolayers of straight-chain and branched hexadecanol and eicosanol mixtures were previously studied using surface pressure- area isotherms, Brewster angle microscopy, and interfacial rheology. In this paper, we investigate the structure of these fatty alcohol mixtures using these previous results together with X-ray diffraction and reflectivity measurements, which provide a better understanding of the structure of the monolayer in terms of the phase segregation and location of branched chains. For eicosanol below 25 mN/m, the branched chains are incorporated into the monolayer, yet they are phase-separated from the straight chains. At higher surface pressures, the branched chains are expelled from the monolayer and presumably form micelles or some other aggregate in the subphase. In contrast, the hexadecanol branched chains are not present in the monolayer at any surface pressure. These behaviors are interpreted with the help of the X-ray measurements and density profiles, and are explained in terms of straight-chain flexibility. We will discuss the effect of the monolayer structure on the surface shear viscosity. These studies provide a deeper understanding of the structure and behavior of amphiphilic mixtures, and will ultimately aid in developing models for lipids, micelle formation, and other important biological functions.

Periodic patterns resembling spirals were observed to form spontaneously upon unassisted cooling of d-glucaric acid- and d-galactaric acid-based polyamide solutions in N-methyl-N-morpholine oxide (NMMO) monohydrate. Similar observations were made in d-galactaric acid-based polyamide/ionic liquid (IL) solutions. The morphologies were investigated by optical, polarized light and confocal microscopy assays to reveal pattern details. Differential scanning calorimetry was used to monitor solution thermal behavior. Small- and wide-angle X-ray scattering data reflected the complex and heterogeneous nature of the self-organized patterns. Factors such as concentration and temperature were found to influence spiral dimensions and geometry. The distance between rings followed a first-order exponential decay as a function of polymer concentration. Fourier-Transform Infrared Microspectroscopy analysis of spirals pointed to H-bonding between the solvent and the pendant hydroxyl groups of the glucose units from the polymer backbone. Tests on self-organization into spirals of ketal-protected d-galactaric acid polyamides in NMMO monohydrate confirmed the importance of the monosaccharide's pendant free hydroxyl groups on the formation of these patterns. Rheology performed on d-galactaric-based polyamides at high concentration in NMMO monohydrate solution revealed the optimum conditions necessary to process these materials as fibers by spinning. The self-organization of these sugar-based polyamides mimics certain biological materials.

A new method for determining molecular weight distributions is explored. Matrix fluorescence photobleaching recovery (MFPR) requires dye attachment to the polymer analyte. No physical separation of macromolecules is accomplished, as in the predominant gel permeation chromatography technique. Rather, the distribution of diffusion coefficients is determined by inverse Laplace transformation of fluorescence photobleaching recovery decay profiles, and the diffusion data are then mapped onto molecular weight using a measured calibration. Resolution is enhanced by forcing the labeled polymer analyte to diffuse through a solution that contains unlabeled matrix, which can even be the same type of polymer. Relative to free diffusion, this increases the dependence of diffusion on molecular weight, making it easier to differentiate components having similar mass. Simulated, noise-corrupted data for molecules diffusing by reptation suggest that excellent resolution may be achieved. Empirical tests were conducted usin...

Small-angle X-ray scattering, depolarized light scattering, and transmission electron microscopy were used to study the dependence of structure and thermodynamics on cross-linking of a symmetric poly(styrene-block-isoprene) copolymer. The polyisoprene block was cross-linked well above the order−disorder transition (ODT) temperature of the un-cross-linked block copolymer. A mean-field theory based on a coarse grained free energy and an RPA-like formulation was developed to predict the dependence of the ODT temperature on cross-linking density. Our theory is limited to cross-linking densities below the gel point. In both experiments and theory the ODT temperature increases as the number of junctions is increased for cross-linking densities below the gelation point. We show that reversible order−disorder transitions are obtained in these materials even when the cross-linking density is larger than that required to obtain a gel. At cross-linking densities near the gel point, the depolarized light scattering s...

Many fractures occur in teeth that have been altered, for example restored or endodontically repaired. It is therefore essential to evaluate the structure and mechanical properties of these altered dentins. One such altered form of dentin is transparent (sometimes called sclerotic) dentin, which forms gradually with aging. The present study focuses on differences in the structure and mechanical properties of normal versus transparent dentin. The mineral concentration, as measured by X-ray computed microtomography, was significantly higher in transparent dentin, the elevated concentration being consistent with the closure of the tubule lumens. Crystallite size, as measured by small angle X-ray scattering, was slightly smaller in transparent dentin, although the importance of this finding requires further study. The elastic properties were unchanged by transparency; however, transparent dentin, unlike normal dentin, exhibited almost no yielding before failure. In addition, the fracture toughness was lowered by roughly 20% while the fatigue lifetime was deleteriously affected at high stress levels. These results are discussed in terms of the altered microstructure of transparent dentin.

Development of synchrotron techniques for the determination of the structure of disordered, amorphous and surface materials has exploded over the past 20 years owing to the increasing availability of high-flux synchrotron radiation and the continuing development of increasingly powerful synchrotron techniques. These techniques are available to materials scientists who are not necessarily synchrotron scientists through interaction with effective user communities that exist at synchrotrons such as the Stanford Synchrotron Radiation Laboratory. In this article the application of multiple synchrotron characterization techniques to two classes of materials defined as 'surface compounds' is reviewed. One class of surface compounds are materials like MoS(2-x)C(x) that are widely used petroleum catalysts, used to improve the environmental properties of transportation fuels. These compounds may be viewed as 'sulfide-supported carbides' in their catalytically active states. The second class of 'surface compounds' are the 'Maya blue' pigments that are based on technology created by the ancient Maya. These compounds are organic/inorganic 'surface complexes' consisting of the dye indigo and palygorskite, common clay. The identification of both surface compounds relies on the application of synchrotron techniques as described here.

The nature of order−disorder transitions in cross-linked diblock copolymer melts was studied using small-angle X-ray scattering (SAXS) and birefringence measurements. Experiments were conducted on cross-linked polystyrene-block-polyisoprene copolymer samples wherein the polyisoprene block was selectively cross-linked at a temperature well above the order−disorder transition temperature of the pure block copolymer. We find a reversible transition from a disordered gel to an ordered gel when the cross-linking density is below a critical value. The rheological properties of disordered block copolymer gels are very different from that of cross-linked homopolymer gels.

We present a small-angle neutron scattering study of a series of isomeric dendrimer-like star copolymers investigated in solution. Each copolymer consists of a highly branched core with linear partially deuterated polymer chains emanating from the outermost generation to create a starlike copolymer. By studying the copolymers in solvents contrast matched to the outer starlike chains, we focus our study on the effects of the core branching architecture. In our dilute solution data analysis we use models to obtain analytical expressions for the form factor of the copolymer cores. We find the core radius of gyration and fractal dimension depend on the core branching architecture. From our semidilute data we obtain experimental structure factors and see evidence of liquidlike structuring in some copolymers. Thus, the architectural features of these isomeric copolymers have an impact on both the conformation of and interactions between these molecules in solution.

Diblock copolymers with extreme architectural asymmetry, namely dendritic-linear coil molecules, have recently been exploited in the construction of well-defined Langmuir-Blodgett monolayers1 and the chemical alteration of bulk material surfaces via adsorption. Others have studied the assembly of dendritic-linear hybrid blocks in aqueous solution for solute encapsulation. These studies of supramolecular assembly and surface adsorption/assembly exploit the high density of chemical functionality on the periphery of dendritic molecules and the disparate chemical nature inherent in block copolymers for structure formation via self-assembly from solution. To understand the effects of the architectural asymmetry present in dendritic-linear coil block copolymers on supramolecular self-assembly and structure formation, the bulk phase behavior of two series of benzyl ether dendrimer-polystyrene (PS) linear coil diblocks was characterized.

We characterize the structures of various polyelectrolyte block copolymer micelles in dilute aqueous solution as a function of pH and ionic strength. The block copolymers carry a common core block, 2-(diethylamino)ethyl methacrylate (DEAEMA), and one of three coronal blocks, 2-(dimethylamino)ethyl methacrylate (DMAEMA), poly(ethylene oxide) (PEO), and DMAEMA, whose side chain amine groups are selectively quaternized with benzyl chloride (Q-DMAEMA). The PEO−DEAEMA, DMAEMA−DEAEMA, and Q-DMAEMA−DEAEMA copolymers form micelles with electrostatically neutral, weakly charged, and highly charged coronae, respectively. We adjust the fractional charge α on the DEAEMA and DMAEMA blocks by adjusting the solution pH. For DMAEMA−DEAEMA micelles increasing the fractional charge α swells the micelle corona while decreasing the aggregation number due to electrostatic repulsions. The decrease in aggregation number is also observed with increasing α for the PEO−DEAEMA and Q-DMAEMA−DEAEMA micelles, due to electrostatic repu...

The dynamic response of elastomeric polypropylene (ePP) prepared by metallocene 2-arylindene hafnium catalyst was investigated by rheo-optical birefringence as well as wide- and small-angle X-ray scattering (WAXS and SAXS). Solvent extraction of ePP ([mmmm] = 34%) results in three fractions with increasing tacticity, crystallinity, and molecular weight in the following order: ether soluble ([mmmm] = 21%), heptane soluble (44%), and heptane insoluble (76%). Unstretched ePP reveals a crystalline phase of the {alpha}-form isotactic polypropylene (i-PP). Tensile stretching of ePP yields three sets of scatterings (equatorial, off-axis diagonal, and meridional arc). High-tacticity fractions contribute to the equatorial and off-axis diagonal scatterings, revealing molecular-scale orientation parallel to the strain axis and crystalline phase transformation from the {alpha}-form to the mesomorphic form. The meridional arc is contributed by the low-tacticity ether-soluble fraction with crystalline chains oriented with a preferred direction orthogonal relative to the strain direction. SAXS, which probes long-range ordering, exhibits broad and diffuse meridional peak for the intermediate-tacticity fraction. This implies that lamellae are oriented orthogonal to the strain direction upon stretching. Permanent deformation of ePP after stretching, as measured by the residual strain (tensile set), originates from permanently oriented crystallites and chains pinned within crystalline networks.

A combination of tensile stress, rheooptical birefringence, and wide-angle X-ray scattering (WAXS) was used to probe the dynamic response of the low-tacticity ether-soluble (ES) fraction of elastomeric polypropylene (ePP) derived from metallocene 2-arylindene hafnium catalyst. The ES fraction has isotactic pentad distribution [mmmm] = 21% and a very low amount of crystallinity (≤2% by differential scanning calorimetry and WAXS). In tensile stretching and step-strain shearing, ES exhibits unusual deformation behavior of crystalline chains preferentially oriented orthogonal relative to the deformation axis. Under deformation, WAXS shows arcing along the meridian axis at a scattering angle 2θ = 16.0° (d = 0.551 ± 0.002 nm) which coincides with one of the characteristic reflections of the β-form, but the higher order reflection for the β-form at 2θ = 21.3° is not observed. The meridional arcing, which signifies crystallization of the low-tacticity fraction of ePP, is also observed when ES is blended with high...

The thermodynamic interactions in anionically synthesized poly(styrene-block-ferrocenyldimethylsilane) (SF) copolymers were examined using birefringence, small-angle X-ray and neutron scattering (S...

Variations of Gaussian-3X (G3X) theory are presented having the quadratic configuration interaction (QCISD(T)) energy calculation replaced by either a coupled cluster (CCSD(T)) or Brueckner (BD(T)) energy. This modification is reported for several G3X methods including G3X, G3X(MP3), G3X(MP2), G3SX, and G3SX(MP3). In most cases the replacement of the QCISD(T) energy by one of these alternative energies results in a slight improvement in the accuracy of these methods as assessed on the G3/99 test set of molecules. These new G3X methods are useful alternatives to the G3X methods based on quadratic configuration interaction.

The traditional separation of electrons in molecules into core and valence types is often based on molecular orbital energies. This method is known to lead in some cases to large relative errors in correlated calculations. Instead, we propose a method based on the definition of molecular core character using separation of basis functions into core and valence types. This gives size-consistency to separation of electrons in molecules into core and valence types.

Item does not contain fulltext High-resolution synchrotron radiation computed tomography (SRCT) and small-angle x-ray scattering (SAXS) were performed on normal and dentinogenesis imperfecta type II (DI-II) teeth. The SRCT showed that the mineral concentration was 33% lower on average in the DI-II dentin with respect to normal dentin. The SAXS spectra from normal dentin exhibited low-angle diffraction peaks at harmonics of 67.6 nm, consistent with nucleation and growth of the apatite phase within gaps in the collagen fibrils (intrafibrillar mineralization). In contrast, the low-angle peaks were almost non-existent in the DI-II dentin. Crystallite thickness was independent of location in both DI-II and normal dentin, although the crystallites were significantly thicker in DI-II dentin (6.8 nm [SD = 0.5] vs. 5.1 nm [SD = 0.6]). The shape factor of the crystallites, as determined by SAXS, showed a continuous progression in normal dentin from roughly one-dimensional (needle-like) near the pulp to two-dimensional (plate-like) near the dentin-enamel junction. The crystallites in DI-II dentin, on the other hand, remained needle-like throughout. The above observations are consistent with an absence of intrafibrillar mineral in DI-II dentin.

We develop a simple semiempirical Pariser–Parr–Pople-type model of a metal. It can be used for studies of adsorption and of the interactions between the metal surface and external charges, and is compatible with ab initio description of the molecules outside the metal. We investigate the dependence of the image-type field on the few parameters that control the model behavior, and develop a simple direct minimization self-consistent field technique that is useful for convergence in nearly degenerate cases.

Medium basis sets based upon contractions of Gaussian primitives are developed for the third-row elements Ga through Kr. The basis functions generalize the 6-31G and 6-31G* sets commonly used for atoms up to Ar. A reexamination of the 6-31G* basis set for K and Ca developed earlier leads to the inclusion of 3d orbitals into the valence space for these atoms. Now the 6-31G basis for the whole third-row K through Kr has six primitive Gaussians for 1s, 2s, 2p, 3s, and 3p orbitals, and a split-valence pair of three and one primitives for valence orbitals, which are 4s, 4p, and 3d. The nature of the polarization functions for third-row atoms is reexamined as well. The polarization functions for K, Ca, and Ga through Kr are single set of Cartesian d-type primitives. The polarization functions for transition metals are defined to be a single 7f set of uncontracted primitives. Comparison with experimental data shows good agreement with bond lengths and angles for representative vapor-phase metal complexes. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 976–984, 2001

The design, synthesis, and solution properties of six constitutional isomers of dendrimer-like star polymers is described. Each of the polymers have comparable molecular weights (∼80 000), narrow polydispersities (

We present a description of a short-range high-density hole in a polarized electron gas. Two leading derivatives of the same-spin correlation hole in a dense electron gas near the origin are derived analytically. They agree well with published numerical results, provided that they are renormalized appropriately. Combined with the two leading derivatives of the opposite-spin correlation hole calculated earlier, they give a complete description of the correlation hole in a dense electron gas near the origin. The spin resolution of the correlation hole in the dense gas is also discussed.

The G2/97 test set [J. Chem. Phys. 106, 1063 (1997)] for assessing quantum chemical methods used to predict thermochemical data is expanded to include 75 additional enthalpies of formation of larger molecules. This new set, referred to as the G3/99 test set, includes enthalpies of formation, ionization potentials, electron affinities, and proton affinities in the G2/97 set and 75 new enthalpies of formation. The total number of energies in the G3/99 set is 376. Overall, G3 theory has a mean absolute deviation of 1.07 kcal/mol for the G3/99 test set and does about as well for the new hydrocarbons and substituted hydrocarbons as it does for those in the G2/97 test. However, G3 theory has large deviations for several of the new nonhydrogen systems in the G3/99 test set such as SF6 and PF5. Part of the source of error is traced to the inadequate geometries used in G3 theory for these molecules. Other variations of G3 theory are also assessed such as G3(MP2), G3(MP3), and the versions of G3 theory using scaled...

We study the correlation energy in the H2 molecule as a function of bond distance and the electron coupling parameter that modifies the strength of electron–electron repulsion. For the unscaled electron repulsion we find an unusual complexity of the correlation energy dependence on the bond distance. This complexity remains if the electron repulsion is scaled down. We pay particular attention to the range of bond distances near the H2 equilibrium geometry. We confirm that good performance of the modern exchange–correlation functionals in molecular geometry optimization is due to the cancellation of errors between the exchange and correlation components. These components have different functional dependence on the electron coupling parameter, so the cancellation of errors no longer occurs when the electron repulsion is scaled down. This observation is important if the adiabatic connection theorem is used to construct the exchange–correlation functionals. It is also relevant for the performance of exchange–...

The design, synthesis and solution properties of dendritic-linear hybrid macromolecules is described. The synthetic strategy employs living ring-opening polymerization in combination with selective and quantitative organic transformations for the preparation of new molecular architectures similar to classical star polymers and dendrimers. The polymers were constructed from high molecular weight poly(e-caprolactone) initiated from the surface hydroxyl groups of dendrimers derived from bis(hydroxymethyl) propionic acid (bis-MPA) in the presence of stannous 2-ethyl hexanoate (Sn(Oct)2). In this way, star and hyperstar poly(e-caprolactones) were elaborated depending on the generation of dendrimer employed. The ROP from these hydroxy groups was found to be a facile process leading to controlled molecular weight, low dispersity products (Mw/Mn) < 1.15. In addition to the use of dendrimers as building blocks to star polymers, functional dendrons derived from bis-MPA were attached to chain ends of the star polymers, yielding structures that closely resemble that of the most advanced dendrimers. Measurements of the solution properties (hydrodynamic volume vs. molecular weight) on the dendritic-linear hybrids show a deviation from linearity, with a lower than expected hydrodynamic volume, analogous to the solution properties of dendrimers of high generation number. The onset of the deviation begins with the polymers initiated from the secondmore » generation dendrimer of bis-MPA and becomes more exaggerated with the higher generations. It was found that polymerization amplifies the nonlinear solution behavior of dendrimers. Small angle neutron scattering (SANS) measurements revealed that the radius of gyration scaled with arm functionality (f) as f 2/3, in accordance with the Daoud-Cotton model for many arm star polymer.« less

A modification of Guassian-3 (G3) theory using multiplicative scale factors, instead of the additive higher level correction, is presented. In this method, referred to as G3S, the correlation energy is scaled by five parameters and the Hartree–Fock energy by one parameter. The six parameters are fitted to the G2/97 test set of 299 energies and the resulting mean absolute deviation from experiment is 0.99 kcal/mol compared to 1.01 kcal/mol for G3 theory. The G3S method has the advantage compared to G3 theory in that it can be used for studying potential energy surfaces where the products and reactants have a different number of paired electrons. In addition, versions of the computationally less intensive G3(MP3) and G3(MP2) methods that use scaled energies are also presented. These methods, referred to as G3S(MP3) and G3S(MP2), have mean absolute deviations of 1.16 and 1.35 kcal/mol, respectively.

Q-Chem 2.0 is a new release of an electronic structure programpackage, capable of performing first principles calculations on the ground andexcited states of molecules using both density functional theory and wavefunction-based methods. A review of the technical features contained withinQ-Chem 2.0 is presented. This article contains brief descriptive discussions of thekey physical features of all new algorithms and theoretical models, together withsample calculations that illustrate their performance. c 2000 John Wiley S electronic structure; density functional theory;computer program; computational chemistry Introduction A reader glancing casually at this article mightsuspect on the basis of its title that it is a thinlydisguised piece of marketing for a program pack-age. This is not the case. Rather, it is an attemptto document the key methodologies and algorithmsof our electronic structure program package, Q-Chem 2.0, in a complete and scientifically accurateway, with full references to the original literature.This is important for two principal reasons. First,while the use of electronic structure programs isburgeoning, many users of such programs do nothave much feel for the underlying algorithms thatmake large-scale calculations routine even on suchreadily available hardware as personal computers.Therefore, a link between the program package andthe original literature that is written at the level ofan introductory overview can be a useful bridge.Second, while citations of large-scale commercialprograms in published applications are tradition-ally part of the conditions of use of such codes, they

Variations of Gaussian-3 (G3) theory are presented in which the quadratic configuration interaction (QCISD(T)) energy calculation is replaced by a coupled cluster (CCSD(T)) energy calculation. This modification is made to four G3 methods that have been previously introduced. The replacement of the QCISD(T) energy by the CCSD(T) energy results in little change in the accuracy of the methods as assessed on the G2/97 test set, although the maximum deviations decrease slightly. These new G3 methods based on the coupled cluster technique are a useful alternative to the G3 methods based on quadratic configuration interaction.