Molecular Aggregation Structure Research Articles

Studies on the effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped 2-perfluorooctylethyl methacrylate films

The effects of the alkyl group on the surface segregation of poly(n-alkyl methacrylate) end-capped with various numbers of units of 2-perfluorooctylethyl methacrylate (FMA) (PnAMA-ec-PFMA) were investigated by differential scanning calorimetry, angle-resolved XPS analysis, contact angle measurements, and X-ray diffraction (XRD). The results show that with similar numbers of FMA units at the polymer chain end the extent of fluorine segregation (Q) increased with increasing the number of carbon atoms in the side n-alkyl chains of poly(n-alkyl methacrylate). The surface fluorine content within 5nm deep of the film of poly(n-octadecyl methacrylate) end-capped with one FMA unit (PODMA160-ec-PFMA1.0) was 208-fold higher than that of the bulk level. These observed differences in Q values were found due to the aggregate structure of the end-capped polymers in the solution, the flexibility, and the crystallinity of the n-alkyl side chains. When the nonfluorinated block was completely amorphous, the molecular aggregate structure of the end-capped polymers in the solution played an important role in the surface segregation of the fluorinated moieties on the resulting film. However, when the nonfluorinated block was crystalline, crystallinity would enhance greatly the segregation of the fluorinated moieties.

Relationship between Molecular Aggregation Structures and Optical Properties of Polyimide Films Analyzed by Synchrotron Wide-Angle X-ray Diffraction, Infrared Absorption, and UV/Visible Absorption Spectroscopy at Very High Pressure

The relationship between the molecular aggregation structures and the optical properties of fully aromatic and semialiphatic polyimide (PI) films were analyzed by synchrotron wide-angle X-ray diffraction (WAXD), infrared absorption, and UV/visible absorption spectroscopy at very high pressures up to 8 GPa. The PIs showed significant reduction in the interchain distances in the first stage of compression up to 1 GPa, which resulted in an appreciable decrease in the interchain free volume. In addition, reduction in the C−C bond lengths of aromatic rings by ca. 0.7% was confirmed by the pressure-induced high wavenumber shift of the infrared stretching vibration of the PIs. Furthermore, pressure-induced bathochromic shifts were observed in the locally excited (LE) absorption band of PIs, which are related to the enhanced van der Waals interaction caused by the reduced interchain distances. The intensity of the charge transfer (CT) absorption band of s-BPDA/PDA poly(p-phenylene biphenyltetracarboximide) PI was...

A density matrix based approach for studying excitons in organic crystals

A theoretical analysis of molecular excitons in crystalline p-Nitro-Aniline (PNA) is presented. The approach is general and can be straightforwardly extended to the calculation of the exciton structure of other molecular crystals or aggregates. Based on the evaluation of transition density matrices (TDM), the method allows to easily classify the excited states of interacting molecules on the basis of those of the constituent molecules. Exciton couplings of selected dimers within the PNA crystal have been evaluated and the exciton dispersion has been determined. The experimental absorption spectrum of PNA powders can be analysed in details based on the exciton density of states.

Mutation-dependent Polymorphism of Cu,Zn-Superoxide Dismutase Aggregates in the Familial Form of Amyotrophic Lateral Sclerosis

More than 100 different mutations in Cu,Zn-superoxide dismutase (SOD1) are linked to a familial form of amyotrophic lateral sclerosis (fALS). Pathogenic mutations facilitate fibrillar aggregation of SOD1, upon which significant structural changes of SOD1 have been assumed; in general, however, a structure of protein aggregate remains obscure. Here, we have identified a protease-resistant core in wild-type as well as fALS-causing mutant SOD1 aggregates. Three different regions within an SOD1 sequence are found as building blocks for the formation of an aggregate core, and fALS-causing mutations modulate interactions among these three regions to form a distinct core, namely SOD1 aggregates exhibit mutation-dependent structural polymorphism, which further regulates biochemical properties of aggregates such as solubility. Based upon these results, we propose a new pathomechanism of fALS in which mutation-dependent structural polymorphism of SOD1 aggregates can affect disease phenotypes.

Molecular Aggregation Structures of Polyimide Films at Very High Pressure Analyzed by Synchrotron Wide-Angle X-ray Diffraction

Molecular Aggregation Structures of Polyimide Films at Very High Pressure Analyzed by Synchrotron Wide-Angle X-ray Diffraction

Analysis of Molecular Aggregation Structures of Fully Aromatic and Semialiphatic Polyimide Films with Synchrotron Grazing Incidence Wide-Angle X-ray Scattering

The intermolecular aggregation structures of fully aromatic polyimides (Ar-PIs) prepared from pyromillitic dianhydride (PMDA) and those of semialiphatic polyimides (Al-PIs) from 4,4′-diaminocyclohexylmethane (DCHM) were characterized by a grazing incidence wide-angle X-ray scattering (GIWAXS) technique. The aggregation structures of both Ar- and Al-PI thin films formed on Si substrates were identified as a mixture of a liquid-crystalline-like ordered domain and an amorphous matrix. For Ar-PIs whose glass transition temperatures (Tg) are higher than the imidization temperature (Ti), the aggregation structures are significantly influenced by the three-dimensional structures of the PI chain. Rodlike molecular structures with high planarity are prerequisites for the growth of ordered domains of Ar-PIs, whereas an Ar-PI having a bent and nonplanar structure displays the highest intensities of an amorphous halo. In addition, the bulky −CF3 groups in the diamine moiety increase the interchain distance in the ordered domains. On the other hand, for Al-PIs whose Tgs are lower than Ti, the degrees of interchain ordering in the ordered domains were higher than those of Ar-PIs, but the orientation of the ordered domains was decreased significantly by decreasing their Tgs. This is due to the vigorous motion of PI chains during thermal imidization.

液晶性セルロース誘導体の凝集状態制御について

We have designed a new material with stable cholesteric structure by blending a cellulose derivative, (acetoxypropyl)cellulose (APC), with a thermoplastic polymer, poly(viny acetate) (PVAc). In the material obtained from THF solution, the compatibility between APC and PVAc was confirmed by differential scanning calorimetry (DSC) and infrared spectroscopy (IR). The materials showed colors arising from the selective reflection of circular polarized light. The colors depended on the composition of the materials. The material obtained from acetone solution showed phase separation into an APC rich phase and a PVAc rich phase, respectively. This indicated that the aggregation structure of APC/PVAc blends was affected by the preparation condition for materials. The FT IR results supported that the molecular aggregation structure was controlled by the hydrogen bonds between APC and PVAc polymer chains.

Effect of block length on the self-assembly of end-capping perfluoroalkyl moieties on the polymer surface

Most research on copolymers with fluorinated monomers has focused on the relationship between fluorinated monomer content and the corresponding surface structure. However, the influence of the non-fluorinated block on the surface structure of the copolymer film is unknown. Various molecular weight poly(butyl methacrylates) (PBMA) end-capped with 2-perfluorooctylethyl methacrylate (FMA) units (PBMA-ec-FMA) have been synthesized by atom transfer radical polymerization (ATRP). The effect of the PBMA block length on the surface structure and properties of the polymers both in the solid state and in solution was investigated using various techniques. X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy and X-ray diffraction (XRD) analyses indicated that longer PBMA blocks enhanced both the enrichment of the fluorinated moieties and the order of the packing orientation of the perfluoroalkyl side chains on the surface. This enhancement was attributed mainly to the molecular aggregate structure of the end-capped polymers with long PBMA blocks in the solution and to the interfacial structure at the air/liquid interface, which favors the -(CF2)7CF3 moieties self-assembling on the polymer surface during film formation. This observation suggests that the polyacrylate block structure in fluorinated diblock copolymers, in addition to the fluorinated monomer content, plays an important role in structure formation on the solid surface.

Influence of α-methyl group on molecular aggregation structure and surface physicochemical properties of fluoroalkyl side chain polymers

Influence of α-methyl group on molecular aggregation states and surface physicochemical properties of poly(fluoroalkyl acrylate)s [PFA-Cy, where y is fluoromethylene number in Rf group] and poly(fluoroalkykl methacrylate)s [PFMA-Cy] thin films were systematically investigated. Spin-coated PFA-Cy and PFMA-Cy thin films were characterized by dynamic contact angle measurements and grazing-incidence wide-angle X-ray diffraction (GIWAXD) measurements. GIWAXD data revealed that fluoroalkyl side chains of PFA-Cy and PFMA-Cy with y≥8 formed regular structures in the surface region as well as bulk one. However, the degree of orientation and ordering of the Rf groups of PFMA-C8 thin films was low. Also, the receding contact angle (θr) of PFMA-C8 thin films was lower than that of PFA-C8 ones. By annealing treatment, the θr of PFMA-C8 was increased. These results suggest that the Rf groups of PFMA-C8 were disordered due to presence of the α-methyl group. The Rf groups became ordered to pack closely each other by annealing treatment, so that the water repellency was increased.

Molecular aggregation states of poly{2-(perfluorooctyl)ethyl acrylate} polymer brush thin film analyzed by grazing incidence X-ray diffraction

Fluoropolymer brush with crystalline side chains was prepared by surface-initiated atom transfer radical polymerization of 2-(perfluorooctyl)ethyl acrylate (FA-C8) from a flat silicon substrate. The crystallization and the molecular aggregation structures of polymer side chain at the outermost surface and internal region in the brush film were characterized by grazing incidence X-ray diffraction (GIXD) measurement using two different incident angles of X-ray. At the air interface of PFA-C8 brush film, the rod-like Rf group was oriented perpendicular to the surface forming a hexagonal packing structure to reduce surface energy. In contrast, the oriented Rf groups parallel to the substrate coexisted at the internal region in the brush. This unique depth dependence of crystalline state of the fluoropolymer brush was observed by surface-sensitive GIXD measurement.

Composition and solution properties of fluorinated block copolymers and their surface structures in the solid state

A series of diblock copolymers composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA144-b-PFMA n ) with various PFMA block lengths were prepared by atom transfer radical polymerization (ATRP). The surface structures and properties of these polymers in the solid state and in solution were investigated using contact angle measurement, X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, surface tension and dynamic laser light scattering (DLS). It was found that with increasing PFMA block length, water and oil repellency decreased, the ratio of F/C increased with increasing film depth, and the degree of ordered packing of the perfluoroalkyl side chains at the surface decreased. When the number of PFMA block units reached 10, PMMA segments were detected at the copolymer surface, which was attributed to the PFMA block length affecting molecular aggregation structure of the copolymer in the solution and the interfacial structure at the air/liquid interface, which in turn affects surface structure formation during solution solidification. The results suggest that copolymer solution properties play an important role in structure formation on the solid surface.

Relationship between Crystal Polymorphism and Solution Structure of an Imidazopyridine Derivative Developed as a Drug Substance for Osteoporosis

An imidazopyridine derivative developed for osteoporosis treatment (a bone proton pump inhibitor, abbreviated BPPI) was crystallized in two kinds of alcohol. Two crystal polymorphs appeared: an unstable B01 form and a stable B02 form. The B01 form was obtained only from an ethanol solution and was never obtained from a methanol solution. The B02 form was obtained from a methanol solution. In order to understand these different behaviors in the appearance of polymorphs from alcohol, the intra- and inter-molecular interactions of BPPI molecules in solution were analyzed by NMR. As a result, the conformation of BPPI molecules and the structure of molecular aggregates in solution were found to resemble those of the polymorphic crystals that appeared in each alcohol. This result suggests that the control of the conformation of solute molecules is important at first to control the appearing polymorph.

Molecular aggregation structure of exotic liquid crystals formed by thermotropic mesogen BABH(n)

Molecular aggregation structure of exotic liquid crystals formed by thermotropic mesogen BABH(<i>n</i>)

Surface molecular aggregation structure and surface physicochemical properties of poly(fluoroalkyl acrylate) thin films

Effect of side chain length on the molecular aggregation states and surface properties of poly(fluoroalkyl acrylate)s [PFA-Cy, where y is fluoromethylene number in Rf group] thin films were systematically investigated. Spin-coated PFA-Cy thin films were characterized by static and dynamic contact angle measurements, X-ray photoelectron spectroscopy (XPS), and grazing- incidence X-ray diffraction (GIXD). The receding contact angles showed small values for PFA-Cy with short side chain (y≤6) and increased above y≥8. GIXD revealed that fluoroalkyl side chain of PFA-Cy with y≥8 was crystallized and formed ordered structures at the surface region as well as bulk one. These results suggest that water repellent mechanism of PFA-Cy can be attributed to the presence of highly ordered fluoroalkyl side chains at the outermost surfaces. The results of XPS in the dry and hydrated states and contact angle measurement in water support the mechanism of lowering contact angle for water by exposure of carbonyl group to the water interface through reorientation of short fluoroalkyl chains. The surface nanotextured PFA-C8 through imprinting of anodic aluminum oxide mold showed extremely high hydrophobicity as well as high oleophobicity.

Manipulation of molecular aggregation and supramolecular structure using self-assembled lithium mixed-anion complexes

A set of zero-, one-, two-, and three-dimensional materials have been synthesized by systematically varying the stoichiometry of the two components 2,4,6-Me3-C6H2OLi (ArOLi) and Me2N(CH2)(2)OLi (ROLi) within single aggregates, while using 1,4-dioxane (diox) as a ditopic linker. The homoleptic complex [{(ArOLi)4 x (diox)2} superset3(diox)](infinity) 1 forms a 3D diamondoid extended structure, where Li4O4 cubanes act as tetrahedral nodes. Attempts to rationally alter the dimensionality of the network through the sequential replacement of ArOLi vertices by potentially chelating ROLi units have succeeded. The mixed-anion complexes [{(ROLi)(ArOLi)3 x (diox)(1.5)} superset1/2(C6H14)](infinity) 2 and [(ROLi)4(ArOLi)2 x (diox)](infinity) 4 , adopt 2D hexagonal net and 1D chain structures respectively. Furthermore, the two complexes [{(ROLi)3(ArOLi)3 x (diox)(0.5)}(C6H14)](infinity) 3 and [(ROLi) 5(ArOLi) x (diox)(0.5)](infinity) 5 both form unusual 0D molecular dumbbell structures in the solid state. Incorporation of multiple ROLi units in the mixed-anion complexes not only results in reducing the number of possible sites for polymer extension through chelation, but also changes the aggregation state of the building block from tetrametallic Li4O4 units to hexametallic Li6O6 units.

Comprehensive photoelectron spectroscopic study of anionic clusters of anthracene and its alkyl derivatives: Electronic structures bridging molecules to bulk

The evolution of the electronic structure of molecular aggregates is investigated using anion photoelectron (PE) spectroscopy for anionic clusters of anthracene (Ac) and its alkyl derivatives: 1-methylanthracene (1MA), 2-methylanthracene (2MA), 9-methylanthracene (9MA), 9,10-dimethylanthracene (DMA), and 2-tert-butylanthracene (2TBA). For their monomer anions (n=1), electron affinities are confined to the range from 0.47 to 0.59 eV and are well reproduced by density functional theory calculations, showing the isoelectronic character of these molecules. For cluster anions (n=2-100) of Ac and 2MA, two types of isomers I and II coexist over a wide size range: isomers I and II-1 (4< or =n<30) or isomers I and II-2 (n> or = approximately 40 for Ac and n> or = approximately 55 for 2MA). However, for the other alkyl-substituted Ac cluster anions (i.e., 1MA, 9MA, DMA, and 2TBA), only isomer I is exclusively formed, and neither isomer II-1 nor II-2 is observed. The vertical detachment energies (VDEs) of isomer I in all the anionic clusters depend almost linearly on n(-1/3). In contrast, the VDEs of isomers II-1 (n> or =14) and II-2 (n=40-100), appeared only in Ac and 2MA cluster anions, remain constant with n and are approximately 0.5 eV lower than those of isomer I. The PE spectra revealed the characteristics of each isomer: isomer I possesses a monomeric anion core that is gradually embedded into the interior of the cluster with increasing n. On the other hand, isomers II-1 and II-2 possess a multimeric (perhaps tetrameric) anion core, but they differ in the number of layers from which they are made up; monolayer (isomer II-1) and multilayers (isomer II-2) of a two-dimensionally ordered, finite herringbone-type structure, in which electron attachment produces only little geometrical rearrangement. Moreover, the agreement of the constant VDEs of isomer II-2 with the bulk data demonstrates the largely localized nature of the electronic polarization around the excess charge in a crystal-like environment, where about 50 molecules provide a charge stabilization energy comparable to the bulk.

Effects of aggregation structure on rheological properties of thermoplastic polyurethanes

The effects of the molecular aggregation structure on the rheological properties of thermoplastic polyurethane (TPU) were investigated. The TPU was composed of poly{(tetramethylene adipate)- co-(hexamethylene adipate)} glycol as the soft segments, 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segments. The TPU sheets prepared by injection molding were annealed at various temperatures from 23 to 120 °C to vary the molecular aggregation structure. Glass transition temperature of the soft segment and melting points of the hard segment domains of the TPUs decreased and increased, respectively, with increasing annealing temperature. The results of DSC, solid-state NMR spectroscopy and dynamic viscoelastic measurements revealed that the degree of micro-phase separation of the TPUs becomes stronger with increasing annealing temperature due to the progress of formation of well-organized hard segment domains. The dynamic temperature sweep experiments for molten TPUs revealed that the temperature at critical gel point, which is defined as the temperature at which the dynamic storage modulus coincides with the loss storage modulus, in the cooling process increased with the progress of aggregation of the hard segments in the TPUs observed in the solid state. The uniaxial elongational viscosity measurements showed that TPUs exhibited an obvious strain hardening behavior with strain rate owing to residual hard segment domains at an operating temperature. It was revealed that the formation of well-organized hard segment domains had a profound effect on the rheological properties of TPUs, in particular on their elongational viscosity.

Effects of polymerization method on structure and properties of thermoplastic polyurethanes

AbstractThe effects of the dynamic polymerization method and temperature on the molecular aggregation structure and the mechanical and melting properties of thermoplastic polyurethanes (TPUs) were successfully clarified. TPUs were prepared from poly (ethylene adipate) glycol (Mn = 2074), 4,4′‐diphenylmethane diisocyanate and 1,4‐butanediol by the one‐shot (OS) and the prepolymer (PP) methods in bulk at dynamic polymerization temperatures ranging from 140 to 230 °C. Glass‐transition temperatures (Tgs) of the soft segment and melting points (Tms) of the hard segment domains of OS‐TPUs increased and decreased, respectively, with increasing polymerization temperatures, but those of PP‐TPUs were almost independent of the polymerization temperature. Tgs of the soft segment and Tms of the hard segment domains of these TPUs polymerized above 190 °C were almost the same regardless of the polymerization method. Solid‐state nuclear magnetic resonance spectroscopy (NMR) analyses of OS‐ and PP‐TPUs showed that the relative proton content of fast decay components, which corresponds to the hard segment domains, in these TPUs decreased with increasing polymerization temperatures. These results clearly show that the degree of microphase separation becomes weaker with increasing polymerization temperatures. The temperature dependence of dynamic storage modulus and loss tangent of OS‐TPUs coincided with those of PP‐TPUs at polymerization temperature above 190 °C. The apparent shear viscosity for OS‐ and PP‐TPUs polymerized above 190 °C approached a Newtonian behavior at low shear rates regardless of the polymerization method. These results indicate that TPUs polymerized at higher temperatures form almost the same molecular aggregation structures irrespective of the dynamic polymerization method. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 800–814, 2007

Surface Molecular Aggregation Structure of Poly(fluoroalkyl acrylate) Thin Films

Surface Molecular Aggregation Structure of Poly(fluoroalkyl acrylate) Thin Films

Penning ionization electron and ultraviolet photoelectron spectroscopy of ultrathin bis(l,2-benzoquinonedioximato)platinum(II) films

Penning ionization electron spectra (PIES) and ultraviolet photoelectron spectra (UPS) have been measured for ultrathin (3–10 Å) bis(1,2-benzoquinonedioximato)platinum(II) (Pt(bqd) 2) films to investigate the molecular aggregation and electronic structure. Upon vapor deposition onto a cooled graphite (0 0 0 1) surface, Pt(bqd) 2 forms either of two films A and B with completely different spectra. The PIES of film A exhibits enhanced bands due to π and platinum 5d ⊥ (d xz , d yz or d z 2 )-derived MOs while that of film B is characterized by overwhelming bands due to oxygen nonbonding MOs, which indicates that the molecule lies flat in film A but the molecular short axis stands in film B. Moreover, the UPS features of film A do not correspond to those of film B and are essentially the same as those of an amorphous film prepared on a cooled metal surface. Nevertheless, films A and B afford almost the same features in both PIES and UPS when annealed to room temperature: the PIES become rather smooth to provide somewhat enhanced π and d ⊥-derived bands whereas the UPS obtain an increased number of distinct bands. From these observations, it is considered that the electronic structure of a Pt(bqd) 2 molecule is modified through the intermolecular interactions of the d ⊥-derived MOs, which operate differently depending on the molecular aggregation.