Size Of Microdomains Research Articles

Micellar Morphology in Bulk Styrene-Core Ionic Diblock Copolymers

Diblock ionomers consisting of a short polystyrene block and a long ionic segment of poly-(4-vinylpyridinium methyl iodide) or poly(cesium methacrylate) have been investigated by SAXS in the solid state. The size of the spherical microdomains formed by the polystyrene blocks in the continuous ionic matrix has been measured and compared to that of the mirror system consisting of an ionic core in a nonionic matrix, previously investigated. Similar chain stretching of the core-forming block is observed for both systems, and it is concluded that the chain extension in the microdomains is due to the high surface energy between the ionic and the nonionic phases rather than to specific ionic interactions

Analysis of porous carbon with 129Xe, 1H NMR and N 2 porosimetry

Activated carbon materials are complex, noncrystalline solids that are difficult to characterize. In this work microstructure within the sample activated carbons has been elucidated by combining the results from 129Xe, 1H NMR spectroscopy and nitrogen porosimetry. Using the Horvath-Kawazoe model to transform nitrogen physiosorpdon data the micropore sizes of the carbons were found to be ~ 5.9Å. Evaluation of 129Xe and 1H NMR spectra of xenon and adsorbed methane, respectively, provided the chemical shift data necessary to calculate the lateral dimensions of the graphitic microdomains and, hence, those of the pores. By this method, the microdomain sizes were found to vary between 15 and 30Å. These values are in good agreement with the sizes of the microdomains expected based on earlier results provided in the literature that show a range from 15 to 60Å.

Scaling behavior of a model of block copolymers in three dimensions.

We have studied the dynamical and equilibrium scaling behaviors of a coarse-grained model for microphase separation of block copolymers. Our numerical study has been carried out in three dimensions. We compute the power-law exponent \ensuremath{\theta} characterizing the equilibrium microdomain size ${\mathit{R}}_{\mathrm{eq}}$ as a function of the molecular weight of the copolymers N as ${\mathit{R}}_{\mathrm{eq}}$\ensuremath{\sim}${\mathit{N}}^{\mathrm{\ensuremath{\theta}}}$, and conclude that we are able to study the weak-segregation regime, but not the true strong-segregation regime of the model. We have also tested scaling hypotheses connecting the microdomain size and the equilibrium structure factor of the block copolymers.

Use of Confocal Microscope for the Cellular Analysis of the Glycine Synaptic Receptor

The presence of glycine receptors was examined with a monoclonal antibody and indirect immunofluorescence on reticular neurons of the goldfish (Carassius auratus) brainstem. Images of thin (0.6 microns) optical sections were recorded from 80 microns thick specimen with a confocal microscope thus obviating the need for mechanical slicing. Due to the reduced out-of-focus noise, high resolution was obtained. Lookthrough projections were computer generated. Compared with classical methods involving serial sectioning, this approach allowed the analysis of the subcellular distribution of this receptor with a considerable gain of time and increased resolution. On the Mauthner cell, an identified reticulo-spinal neuron, we found, that the size of glycine receptor microdomains varies depending on the cellular localization, i.e. somatic or dendritic. Furthermore the intensity of fluorescence was uneven within individual clusters, probably reflecting differences in receptor concentration. These heterogeneities may influence the variance of synaptic inhibitory noise in different regions of the Mauthner cell.

Microstructure of silver superionic glasses

Raman spectroscopy, small angle neutron scattering (SANS) and neutron diffraction were performed on AgPO 3, AgPO 3-AgX and AgPO 3-MX 2 glasses ( X = I, Br or Cl; M = Pb or Hg). AgPO 3 glass is made up of long chains of PO 4 tetrahedra joined together by Ag atoms. Addition of AgX or PbX 2 does not modify the network forming unit and the radial distribution functions (RDF) of such glasses show a new large peak at 2.83 Å due to Ag-I interaction. The existence of AgI 4 units is confirmed by Raman investigation and analysis of the coordination numbers (c.n) of Ag-I pairs in RDF-differences. A rough estimation of the size of the AgI microdomains is given by SANS experiments. Not all the AgI pairs are involved in AgI cluster units. On the other hand, the situation is different for (1-x) AgPO 3-xHgX 2 glasses, no AgI peaks were identified by Raman or neutron techniques. HgX 2 molecular unit bands appear when x > 0.2 (Raman spectroscopy). The compatibility of the results obtained with recent structural investigations by non diffractometric techniques is discussed.

Polycaprolactone‐based block copolymers. II. Morphology and crystallization of copolymers of styrene or butadiene and ε‐caprolactone

AbstractThree series of amorphous semicrystalline poly(styrene‐b‐ε‐caprolactone)s have been synthesized with polystyrene blocks of 6000 (series A), 40000 (series B), and 70000 (series C) molecular weight, respectively. In these materials, the polymer miscibility evolves from a situation where a diffuse interphase involves the major part of the volume of the copolymer (series A) to a sharp phase separation as observed for copolymers with the longest PS block (series C). The crystallization of PCL blocks is mainly governed by the phase morphology. In copolymers of series A, the crystallization rate of PCL blocks is slowed down the more as the miscibility with PS increases, and ultimately the degree of crystallinity Xc decreases significantly. When phase separation is sharp, Xc changes dramatically at the phase inversion and decreases when PS forms the continuous phase. At the inversion Xc depends on the mean size of the PCL microdomains as compared with the thickness of the crystalline lamellae. The periodicity of the phase morphology as observed by TEM is influenced by the solvent used in casting films, whereas monolamellar monocrystals can be obtained by a self‐seeding technique.

A theoretical study of micro-domain formation in mixed lipid membranes

Abstract The thermodynamic stability of micro-clusters in a membrane built-up by charged and uncharged lipid molecules is discussed. A simple variational function is proposed in order to describe the essential structure of such lipid domains. Solvent-screened electrostatic repulsion between the lipid ionic head groups, short-range forces between the lipid hydrophobic taisl and entropic effects are taken into account. The stability conditions as well as the composition and the size of the lipid micro-domains are calculated and expressed as a function of molecular parameters for the membrane and its environment (for example, short-range forces, surface charge density of the lipid bilayer, ion concentration of the electrolyte solution in contact with the lipid membrane and temperature). As an application, the effect of micro-domain formation on the number of adsorbed ions on a charged lipid membrane has been calculated.

Morphology of triblock copolymers in the presence of unbonded segments

AbstractThe morphology of ABA triblock copolymers [A: polystyrene, poly(α‐methylstyrene); B: polybutadine] containing unbonded A′ segments (free A chains) was studied using small‐angle X‐ray scattering and transmission electron microscopy. Experimental results indicate the formation of ‘mixed’ segregation microdomains containing both A and A′ segments. With the assumption that homopolymer molecules locate themselves in the central region of the microdomains, away from the interfacial regions — which sounds reasonable at least when the homopolymer concentration is not too high — simple equations were derived permitting the calculation of the microdomain size that would correspond to systems deprived of their parasitic homopolymer. Values obtained are in fairly good agreement with those predicted by Helfand's thermodynamic theory.

Uniformity of microdomain size of block polymers as compared with uniformity of their molecular weights

Analyse de l'uniformite de la taille des domaines des copolymeres bisequences styrene-isoprene, comparee a l'uniformite des distributions de masse moleculaire

Microdomain structure of poly(styrene‐4‐vinylpyridine) diblock copolymers

AbstractA series of AB and BAB type poly(styrene‐4‐vinylpyridine) diblock copolymers with a sharp distribution of molecular weights were synthesized to study relationships between the molecular weight and domain size of lamellar and spherical microdomains. The domain sizes of diblock copolymer specimens cast from chloroform or 1,1,2‐trichloroethane were estimated from transmission electron micrographs. As a result, the lameller domain spacings, predicted from Halfand's theory, agree well with the experimental results. The radius of spherical domains is far below the theoretical values predicted from Helfand's theory, though.

Characterization of the Microstructure of Poly(propylene oxide)–Segmented Polyamide and Its Suppression of Platelet Adhesion

The relationship between microphase-separated structures and antithrombogenicities of poly(propylene oxide) (PPO)–segmented polyamides of various polyamide segment lengths was studied. Transmission electron microscopic observation revealed fibrillar lamella structures to be present on the copolymer surfaces. Dynamic mechanical and thermal scanning measurements showed the existence of two mechanical relaxations attributable to micro-Brownian motions of the PPO and polyamide segments, indicating that the PPO and polyamide segments formed distinctly separated microdomain structures. Moreover, wide-angle X-ray diffraction and small-angle X-ray scattering measurements indicated these copolymers to be different in their microstructures with respect to size and distribution of crystalline and amorphous domains even though the crystalline structure was essentially the same as that of nylon 610. The degree of platelet adhesion and aggregation was significantly minimized on the surface of the copolymer, in which the average diameter of the crystalline and amorphous domains were 6.42 nm and 5.18 nm, respectively. This suggests that the size of segmented polyamide microdomains may be a determining factor in antithrombogenicity.

Generalized view of molecular weight dependence of microdomain size of block polymers. Appraisal of Hadziioannou-Skoulios' data on binary mixtures of block polymers

Generalized view of molecular weight dependence of microdomain size of block polymers. Appraisal of Hadziioannou-Skoulios' data on binary mixtures of block polymers

Theory of inhomogeneous polymers in presence of solvent

Abstract A theory is developed to predict the free energy and microdomain size of block copolymer systems, taking into account solvent-polymer interactions. The mean-field equations for the polymer probability densities are derived from fundamental statistical mechanics, starting from the total interaction energy of the system, and making use of functional integral techniques. We introduce the constraint of no volume change upon mixing directly into the derivation of the mean-field equations, and thereby eliminate the need to add an indeterminate function to the free energy density to suppress density fluctuations for systems with small compressibility. We solve the mean-field equations numerically for the lamellar block copolymer microdomain structure, and we investigate the effec of the solvent on the size of the microdomains. For the Polystyrene-polyisoprene toluene system we find a first-order “melting” transition for the periodic structure when the block copolymer becomes saturated with solvent.

Microdomain size of styrene-lsoprene block copolymers and unperturbed chain dimension of polyisoprene having high 1,2-and 3,4-linkages

Abstract Sizes of the microdomain structures for a series of styrene-isoprene A-B type block copolymer having approximately equal weight fractions of A and B blocks (and thus having alternating lamellar microdomains) were measured by the small-angle x-ray technique as a function of molecular weight. The unperturbed chain dimension of a polyisoprene homopolymer having the same microstructure as the poly-isoprene sequence of the block copolymer was measured by viscometry. For a polyisoprene microstructure of 38 wt % 1, 2-addition, 59 wt % 3, 4-addition, and 3 wt % 1, 4-addition, it was found that nm or nm at the temperature of 57.1°C. The observed domain size was shown to be predictable by the equilibrium theories of Meier and Helfand based upon random-flight chain statistics in the domain space.

The ordering transition in Ni 3Al alloys

The ordering of nickel rich non-stoichiometrico Ni 3Al alloys has been examined by transmission electron microscopy. Utilizing superlattice dark-field microscopy and diffraction, it has been possible to observe an earlier stage of ordering than heretofore reported, as a result of very rapid helium quenching. Alloys of over about 17 at.% Al undergo ordering almost completely throughout the lattice if allowed to reside perhaps a few hundred ths of a sec in the region of most rapid reaction, which is roughly 1000°–1100°C. Subsequent phase separation and coarsening occur much more slowly. Alloys of less than about 16 at.% Al exhibit SRO domains on quenching which are unstable and disappear in the presence of quenched in vacancies at 270°C. These two compositions thus appear to be separated by a spinodal curve. The results substantiate the concept that SRO microdomain size increases with ordering energy, V( S). It would appear that ordering by a second order transition ( ∂ 2G ∂T 2 discontinuous through T c ) is possible in A 3 B-f.c.c. alloys, and that such a transition can be distinguished by its mechanism. The mechanism of such an ordering transition must involve diffusion, not down a chemical gradient, but rather that resulting from individual biased vacancy jumps. The vacancy-atom interchanges of greatest probability will be those which result in the formation of the greatest number of “right” bonds.

Zur Struktur des γ‐MnO2

AbstractBy treating Mn3O4 of a specific surface of about 30 m2/g with hot diluted nitric acid, a relatively well crystallised γ‐MnO2 has been obtained. It consists of flat needles of approximately 40,000 × 2000 × 500 Å. Selected area electron diffraction patterns from such single crystals give the (b c) zone of Ramsdellite with c as needle axis. The reflections are broadened in the b‐direction, which is consistent with the shift and broadening of the X‐ray reflections of similar type. The X‐ray Guinier pattern is consistent with the postulated intergrowth structure, proposed by BYSTRÖM and later by de Wolff. Hence the present product consists of a Ramsdellite matrix with statistically distributed Pyrolusite microdomains. The domains are supposed to have the size of one cell only in the b‐direction and of a few cells in the a‐direction, and to be present in relatively small concentrations. From the absence of satellites in the electron diffraction pattern it follows that the domains are disordered and do not form a super‐lattice with giant periods as might be supposed. There is no need to distinguish between η‐ and γ‐MnO2 (GLEMSER [2]); the whole group of varieties, hitherto distinguished by Glemser as «η‐ and γ‐MnO2», have the same lattice and differ only by crystallite size and concentration of microdomains.

Perfectness of Macrodomains of BaTiO3 Crystals

Statistico-thermodynamical investigation is made on the size and density of reversely-polarized microdomains contained within a unidomain c -plate (or a macrodomain of a multidomain c -plate) of BaTiO 3 in thermal equilibrium at room temperature, with or without constant electric field applied. Microdomains treated here are confined to ones running through the crystal plate from the surface on the one side to the surface on the other side. It is found that a thinner crystal plate contains more reversely-polarized microdomains, and a plate thicker than about 2×10 -6 cm contains practically no reversely-polarized microdomains. Reversely-polarized microdomains tend to disperse rather than coalesce, and can hardly be depressed by electric field. Just below the Curie temperature, it is expected that the critical thickness is considerably larger than the above value, since the domain-wall energy per unit area is fairly small.