Perpendicular lamellar-in-lamellar and other planar morphologies in A-b-(B-b-A)2-b-C and (B-b-A)2-b-C ternary multiblock copolymer melts.

Ordered planar morphologies in A-b-(B-b-A)2-b-C and (B-b-A)2-b-C terpolymer melts are studied within the framework of the self-consistent field theory for volume fractions of components A, B, and C in the ratio 1:1:2 and the Flory-Huggins interaction parameters satisfying χ(AB) = 2χ(AC). The stable phases turn out to be the disordered, hexagonal, parallel lamellar-in-lamellar L∥ (including the simple lamellar) as well as non-shifted and shifted (L⊥ and SL⊥) perpendicular lamellar-in-lamellar morphologies. Depending on the value of the ratio r = Θ(AB)/Θ(BC), where Θ is a characteristic temperature of the units involved, different sequences of phase transitions are shown to occur. The hexagonal phase is characteristic for r ≅ 1. The L⊥ and SL⊥ morphologies occur at weak and intermediate segregations whereas the L∥ morphology appears for stronger degrees of segregation. For (B-b-A)2-b-C a reduction in r favors the shifted SL⊥ phase over the non-shifted L⊥ one, whereas for A-b-(B-b-A)2-b-C we find re-entrant phase transitions SL⊥ - L⊥. The physics determining the particular phase behavior is discussed.

Automated TIMI frame counting using 3-d modeling.

Three dimensional coronary modeling and reconstruction can assist in the quantitative analysis of coronary flow velocity from 2-d coronary images. In this paper a novel method to assess coronary flow velocity is proposed. First, 3-d models of the coronary arteries are estimated from bi-plane X-ray images using epipolar constraint energy minimization for the selected fiducial points like bifurcations, and subsequently 3-d B-spline energy minimization for the arterial segments. A 4-d model is assembled from a set of 3-d models representing different phases of the cardiac cycle. The 4-d model is fitted to the 2-d image sequences containing basal or hyperemic blood flow information. Then, by counting the frames in analogy with TIMI frame counting, an index of the mean coronary flow velocity can be estimated. Our experimental results show that the algorithm correlates with r=0.98 (P<0.0001, 95% CI 0.92-0.99) to the clinical measurements of the TFC.

Self-assembly of (A-comb-C)-b-(B-comb-C) diblock copolymer-based comb copolymers.

The phase behavior of (A-comb-C)-b-(B-comb-C) diblock copolymer melts is investigated using the strong segregation theory approach. Three different regimes are distinguished. In regime 1 both disordered comb blocks are microphase separated from each other, in regime 2 the side chains C are microphase separated from the disordered A-b-B diblock backbones, and, finally, in regime 3 all species A, B, and C are microphase separated. In the first regime the behavior is similar to that of a simple diblock copolymer melt with a renormalized Flory-Huggins interaction parameter. In regime 2 the region of stability of the different phases is significantly changed compared to simple diblocks due to the comb architecture. The fully microphase separated case, regime 3, is characterized by hierarchical structure formation. We restrict the analysis to systems where self-assembly results in the formation of alternating C layers and internally microphase separated AB layers. The latter consist of alternating A and B layers or disks of the minority component. In the former case, the A and B layers are generally perpendicular to the C layers. The parallel orientation is only possible for small grafting densities.

Parallel versus perpendicular lamellar-within-lamellar self-assembly of A-b-(B-b-A)(n)-b-C ternary multiblock copolymer melts.

Different types of lamellar-within-lamellar structure formations in A-b-(B-b-A)(n)-b-C terpolymer melts, with a volume fraction of components A, B, and C in the ratio of 1:1:2, are analyzed in the strong segregation limit using a simple theoretical approach. We consider the lamellar, parallel lamellar-within-lamellar, and perpendicular lamellar-within-lamellar self-assembled states. The influence of the copolymer chain length N, the value of the Flory-Huggins interaction parameters chi(AB), chi(AC), and chi(BC), and the number of blocks n in the AB multiblock chain on the phase behavior is discussed. We show that in the limiting case of n >> 1, the perpendicular lamellar-within-lamellar state becomes stable when the interaction parameters satisfy the relation 0 < chi(BC) < 0.22 chi(AC).

Lamellar-in-lamellar structure of binary linear multiblock copolymers.

A theoretical description of the lamellar-in-lamellar self-assembly of binary A-b-(B-b-A)(m)-b-B-b-A multiblock copolymers in the strong segregation limit is presented. The essential difference between this binary multiblock system and the previously considered C-b-(B-b-A)(m)-b-B-b-C ternary multiblock copolymer system is discussed. Considering the situation with long end blocks, the free energy of the lamellar-in-lamellar self-assembled state is analyzed as a function of the number k of "thin" internal lamellar domains for different numbers m of repeating (B-b-A) units and different values of the Flory-Huggins chi(AB) interaction parameter. The theoretical predictions are in excellent agreement with the available experimental data.

Spontaneous bending of 2D molecular bottle-brush.

Using a scaling approach we consider a 2D comb copolymer brush under bending deformations. We show that the rectilinear brush is locally stable and can be characterized by a persistence length lambda increasing with the molecular weight of grafting side chains as lambda approximately M3. A bending instability due to redistribution of the side chains appears in the non-linear regime where bending is strong. Arguments are presented that the brush conformations consist of alternating rectilinear and bent sections corresponding to the different free-energy minima.

Chain elongation suppression of cyclic block copolymers in lamellar microphase-separated bulk.

Chain elongation suppression of cyclic block copolymers in microphase-separated bulk was determined quantitatively. Solvent-cast and annealed films are confirmed to show alternating lamellar structure and their microdomain spacing D increases with increasing total molecular weight M according to the relationship D proportional, variant M0.59, which agrees quite consistently with the theoretically predicted power law, i.e., D proportional, variant M3/5. This result is in contrast to the well-established issue for linear block copolymers, where the relationship D proportional, variant M2/3 has been confirmed to hold both experimentally and theoretically. This means that chain elongation of each component block is suppressed considerably, owing to their looped conformation in strongly segregated bulk.

Phase behavior and structure formation of hairy-rod supramolecules.

Phase behavior and microstructure formation of rod and coil molecules, which can associate to form hairy-rod polymeric supramolecules, are addressed theoretically. Association induces considerable compatibility enhancement between the rod and coil molecules and various microscopically ordered structures can appear in the compatibility region. The equilibria between microphase-separated states, the coil-rich isotropic liquid and the rod-rich nematic are discussed in detail. In the regime where hairy-rod supramolecules with a high grafting density appear as a result of the association, three phase diagram types are possible depending on the value of the association energy. In the low grafting density regime only the lamellar microstructure is proven to be stable.

One-dimensional optical reflectors based on self-organization of polymeric comb-shaped supramolecules.

We demonstrate that complexation of dodecylbenzenesulphonic acid, DBSA, to a diblock copolymer of polystyrene- block-poly(4-vinylpyridine), PS- block-P4VP, leads to polymeric supramolecules PS- block-P4VP(DBSA)y (y = 1.0, 1.5, and 2.0), which self-organize with a particularly large lamellar periodicity in excess of 1000 A. The structures consist of alternating PS and P4VP(DBSA)y layers, where the latter contains smaller internal structure, probably lamellar. The DBSA side chains are bonded to the pyridines by protonation and hydrogen bonding and they effectively plasticize the material. In this way relatively well-developed structures are obtained even without annealing or macroscopic alignment. Transmission and reflectance measurements show that a relatively narrow and incomplete bandgap exists for supramolecules of high molecular weight block copolymer at ca. 460 nm.

The influence of chain stretching on the phase behavior of multiblock copolymer and comb copolymer melts.

The subject of this paper is inspired by microphase-separated copolymer melts in which a small-scale structure is present inside one of the phases of a large-scale structure. Such a situation can arise in a diblock copolymer melt, if one of the blocks of the diblock is in itself a multiblock copolymer or a comb copolymer. Due to the presence of the large-scale structure, the chains are stretched. The aim of this paper is to investigate the influence of this chain stretching on the formation of the small-scale structure. To gain insight we study infinite melts of infinitely long copolymer chains that are subjected to a stretching force. For melts of monodisperse multiblock copolymers we find that the stretching destabilizes the homogeneous phase. If the stretching is strong, the lamellar structure is the only stable structure. The periodicity increases with the degree of stretching. For melts of monodisperse comb copolymers the chain stretching has no influence on the stability of the homogeneous phase. If the stretching is strong, the lamellar structure and the hexagonal structure are the only stable structures. The periodicity is independent of the degree of stretching. For the multiblock copolymer we investigated the influence of block length polydispersity. For small polydispersity the period of the structure increases monotonically with the degree of stretching. For intermediate polydispersity, the period initially decreases before it starts to increase. For large polydispersity, the mean-field period at the spinodal is infinite, becoming finite once the stretching force exceeds some critical value. For very large polydispersity the mean-field period at the spinodal remains infinite for any value of the stretching force.

Molecular shape of the cationic lipid controls the structure of cationic lipid/dioleylphosphatidylethanolamine-DNA complexes and the efficiency of gene delivery.

Pyridinium amphiphiles, abbreviated as SAINT, are highly efficient vectors for delivery of DNA into cells. Within a group of structurally related compounds that differ in transfection capacity, we have investigated the role of the shape and structure of the pyridinium molecule on the stability of bilayers formed from a given SAINT and dioleoylphosphatidylethanolamine (DOPE) and on the polymorphism of SAINT/DOPE-DNA complexes. Using electron microscopy and small angle x-ray scattering, a relationship was established between the structure, stability, and morphology of the lipoplexes and their transfection efficiency. The structure with the lowest ratio of the cross-sectional area occupied by polar over hydrophobic domains (SAINT-2) formed the most unstable bilayers when mixed with DOPE and tended to convert into the hexagonal structure. In SAINT-2-containing lipoplexes, a hexagonal topology was apparent, provided that DOPE was present and complex assembly occurred in 150 mm NaCl. If not, a lamellar phase was obtained, as for lipoplexes prepared from geometrically more balanced SAINT structures. The hexagonal topology strongly promotes transfection efficiency, whereas a strongly reduced activity is seen for complexes displaying the lamellar topology. We conclude that in the DOPE-containing complexes the molecular shape and the nonbilayer preferences of the cationic lipid control the topology of the lipoplex and thereby the transfection efficiency.

Strongly adsorbed comb copolymers with rigid side chains.

We study the conformational behavior in a plane of a comb copolymer molecule, consisting of a semiflexible backbone and rigid side chains interacting via a van der Waals potential. Using a mean-field approach, two different regimes are distinguished depending on the strength of the attraction between the side chains. In the weak attraction limit the side chains are oriented preferably perpendicular to the backbone. The persistence length lambda of the comb copolymer molecule scales as the second power of the length of the side chain L: lambda is proportional to L2. In the strong attraction limit all side chains become strongly tilted and the persistence length scales as lambda is proportional to L4. The nonlinear bending regime is also studied and characterized by a change in structure and a decreasing moment of bending force as a function of curvature, i.e., bending becomes easier.

Switching supramolecular polymeric materials with multiple length scales

It was demonstrated that polymeric supramolecular nanostructures with several length scales allow straightforward tailoring of hierarchical order-disorder and order-order transitions and the concurrent switching of functional properties. Poly(4-vinyl pyridine) (P4VP) was stoichiometrically protonated with methane sulfonic acid (MSA) to form P4VP(MSA)1.0, which was then hydrogen-bonded to pentadecylphenol. Microphase separation, re-entrant closed-loop macrophase separation, and high-temperature macrophase separation were observed. When MSA and pentadecylphenol were complexed to the P4VP block of a microphase-separated diblock copolymer poly[styrene-block-(4-vinyl pyridine)], self-organized structures-in-structures were obtained whose hierarchical phase transitions can be controlled systematically. This microstructural control on two different length scales (in the present case, at 48 and 350 angstroms) was then used to introduce temperature-dependent transitions in electrical conductivity.

[Ultrasound tissue emulsification of brain tumors]. / Die Ultraschallgewebeemulgierung von Hirntumoren.

A report is given on the design of an equipment combination developed in co-operation with the Central Institute for Welding Technology of the GDR, by means of which cerebral tumour tissue can be emulsified and sucked off. The suitability of the equipment was tested experimentally and confirmed in clinical application.