Search

Here, we report synergistic nanostructured surfaces combining bactericidal and bacteria-releasing properties. A polystyrene

The addition of nanofillers to rubber matrices is a powerful route to improve the mechanical properties. Here, we focus on a molecular understanding of basic mechanisms that are important for the r...

The addition of nanoparticles (NPs) to polymers is a powerful method to improve the mechanical and other properties of macromolecular materials. Such hybrid polymer-particle systems are also rich in fundamental soft matter physics. Among several factors contributing to mechanical reinforcement, a polymer-mediated NP network is considered to be the most important in polymer nanocomposites (PNCs). Here, we present an integrated experimental-theoretical study of the collective NP dynamics in model PNCs using X-ray photon correlation spectroscopy and microscopic statistical mechanics theory. Silica NPs dispersed in unentangled or entangled poly(2-vinylpyridine) matrices over a range of NP loadings are used. Static collective structure factors of the NP subsystems at temperatures above the bulk glass transition temperature reveal the formation of a network-like microstructure

A better understanding of the aggregation states of polymer chains in thin films is of pivotal importance for developing thin film polymer devices in addition to its inherent scientific interest. Here we report the preferential orientation of the crystalline lamellae for isotactic polypropylene (iPP) in spin-coated films by grazing incidence of wide-angle X-ray diffraction in conjunction with sum frequency generation vibrational spectroscopy, which provides information on the local conformation of chains at crystal/amorphous interfaces buried in a thin film. The crystalline orientation of iPP, which formed cross-hatched lamellae induced by lamellar branching, altered from a mixture of edge-on and face-on mother lamellae to preferential face-on mother lamellae with decreasing thickness. The orientation of methyl groups at the crystal/amorphous interfaces in the interior region of the iPP films changed, accompanied by a change in the lamellar orientation.

We have performed small-angle X-ray scattering (SAXS) measurements to study the evolution of length-scale-dependent nanoparticle (NP) correlations over a wide range of loadings in miscible silica–p...

Additive manufacturing (AM) is a promising technique to rapidly produce polymeric materials into complex 3-dimensional (3D) geometries. While AM is widespread and relevant for a range of applicatio...

Fouling is the undesirable accumulation of a material on a wide variety of objects and has now become a widespread global problem from land to ocean with both economic and environmental penalties. ...

Lignin, an abundant, naturally occurring biopolymer, is often considered "waste" and used as a simple fuel source in the paper-making process. However, lignin has emerged as a promising renewable resource for engineering materials, such as carbon fibers. Unfortunately, the molecular architecture of lignin (in vivo and extracted) is still elusive, with numerous conflicting reports in the literature, and knowledge of this structure is extremely important, not only for materials technologies, but also for production of biofuels such as cellulosic ethanol due to biomass recalcitrance. As such, the molecular structures of solvent-extracted (sulfur-free) lignins, which have been modified using various acyl chlorides, have been probed using small-angle X-ray (SAXS) and neutron (SANS) scattering in tetrahydrofuran (THF) solution along with hydrodynamic characterization using dilute solution viscometry and gel permeation chromatography (GPC) in THF. Mass spectrometry shows an absolute molecular weight ≈18-30 kDa (≈80-140 monomers), while GPC shows a relative molecular weight ∼3 kDa. A linear styrene oligomer (2.5 kDa) was also analyzed in THF using SANS. Results clearly show that lignin molecular architectures are somewhat rigid and complex, ranging from nanogels to hyperbranched macromolecules, not linear oligomers or physical assemblies of oligomers, which is consistent with previously proposed delignification (extraction) mechanisms. Future characterization using the methods discussed here can be used to guide extraction processes as well as genetic engineering technologies to convert lignin into value added materials with the potential for high positive impact on global sustainability.

We report in situ nanostructures and dynamics of polybutadiene (PB) chains bound to carbon black (CB) fillers (the so-called “bound polymer layer (BPL)”) in a good solvent. The BPL on the CB fillers was extracted by solvent leaching of a CB-filled PB compound and subsequently dispersed in deuterated toluene to label the BPL for small-angle neutron scattering and neutron spin echo techniques. The results demonstrate that the BPL is composed of two regions regardless of molecular weights of PB: the inner unswollen region of ≈ 0.5 nm thick and outer swollen region where the polymer chains display a parabolic profile with a diffuse tail. In addition, the results show that the dynamics of the swollen bound chains can be explained by the so-called “breathing mode” and is generalized with the thickness of the swollen BPL.

We report that the nanometer-scale architecture of polymer chains plays a crucial role in its protein resistant property over surface chemistry. Protein-repellent (noncharged), few nanometer thick polymer layers were designed with homopolymer chains physisorbed on solids. We evaluated the antifouling property of the hydrophilic or hydrophobic adsorbed homopolymer chains against bovine serum albumin in water. Molecular dynamics simulations along with sum frequency generation spectroscopy data revealed the self-organized nanoarchitecture of the adsorbed chains composed of inner nematic-like ordered segments and outer brush-like segments across homopolymer systems with different interactions among a polymer, substrate, and interfacial water. We propose that this structure acts as a dual barrier against protein adsorption.

We here report that adsorbed chains composed of one of the constituent blocks can be used as a new surface modification approach to induce perpendicularly oriented lamellar microdomains in block copolymer thin films. A nearly symmetric polystyrene-block-poly(methyl methacrylate) (PS-block-PMMA) diblock copolymer was used as a model. Densely packed PS- or PMMA-adsorbed chains of about 2–3 nm in thickness (“polymer nanocoatings”) were deposited on silicon (Si) substrates using a solvent-rinsing approach. Spin-cast films of 40 or 60 nm-thick PS-block-PMMA (equivalent to two or three interdomain spacings) were subsequently deposited onto the PS or PMMA nanocoatings. Grazing incidence small-angle X-ray scattering experiments revealed the formation of perpendicularly oriented lamellar microdomains within the entire films at 200 °C, where balanced interfacial interactions at the polymer–air interface were achieved. Additionally, X-ray photon correlation spectroscopy studies demonstrated the dynamics of the fully...

Recently, the chain-folding structure of 13C-labeled poly(l-lactic acid) (PLLA) with different molecular weights (M) of 46K (small, s), 90K (middle, m), and 320K g/mol (large, l) in the solution-gr...

We here report the self-organization process of poly(styrene-b-ethylene/butadiene-b-styrene) (SEBS) triblock copolymer chains physically adsorbed on a non-neutral surface. Spin-cast SEBS thin films were prepared on silicon (Si) substrates and then annealed at a high temperature far above the bulk glass transition temperatures of the two constituent blocks. To reveal the buried interfacial structure, we utilized solvent rinsing processes and a suite of surface-sensitive techniques including ellipsometry, X-ray reflectivity, atomic force microscopy, and grazing incidence small angle X-ray scattering. We revealed that the SEBS chains form two different chain structures on the substrate simultaneously: (i) “flattened chains” with the average height of 2.5 nm but without forming microdomain structures; (ii) “loosely adsorbed chains” with the average height of 11.0 nm and the formation of perpendicularly oriented cylindrical microdomains to the substrate surface. In addition, the kinetics to form the perpendicular-oriented cylinder was sluggish (∼200 h) and proceeded via multistep processes toward the equilibrium state. We also found that the lateral microdomain structures were distorted, and the characteristic lengths of the microdomains were slightly different from the bulk even after reaching “quasiequilibrium” state within the observed time window. Furthermore, we highlight the vital role of the adsorbed chains in the self-assembling process of the entire SEBS thin film: a long-range perturbation associated with the adsorbed chains propagates into the film interior, overwhelming the free surface effect associated with surface segregation of the lower surface tension of polystyrene blocks.

We report the in situ structures and dynamics of hydrogenated polybutadiene (PB) chains bound to carbon black nanoparticle surfaces in polymer solutions composed of deuterated PB and deuterated toluene using small-angle neutron scattering and neutron spin-echo techniques together with molecular dynamics (MD) simulations. The experimental results showed that the swollen bound polymer chains exhibit the collective dynamics (the so-called breathing mode) at polymer concentrations (c) below and above the overlap polymer concentration (c*) (i.e., 0.61 < c/c* < 1.83), where the concentration profiles of the bound polymer remained unchanged with the different c values. Interestingly, the collective dynamics slowed down by a factor of 2 compared to that in pure d-toluene when the chain lengths of the bound polymer and matrix polymer were equal. However, when the free polymer chains were longer than the bound polymer chains, the decrease in collective dynamics was not as significant. MD simulations were performed ...

Self-assembly of block copolymers (BCPs) into arrays of well-defined nanoscopic structures has attracted extensive academic and industrial interests over the past several decades. In contrast to the bulk where phase behavior is controlled by the segmental interaction parameter, the total number of segments in BCPs and volume fraction, the morphologies and orientations of BCP thin films can also be strongly influenced by the substrate surface energy/chemistry effect (considered as a “substrate field”). Here, we report the formation of locally favored structures where all constituent blocks coexist side-by-side on nonneutral solid surfaces irrespective of their chain architectures, microdomain structures, and interfacial energetics. The experimental results using a suite of surface-sensitive techniques intriguingly demonstrate that individual preferred blocks and nonpreferred blocks lie flat on the substrate surface and form a two-dimensional percolating network structure as a whole. The large numbers of so...

Here we report a link between the interfacial structure and adhesive property of homopolymer chains physically adsorbed (i.e., via physisorption) onto solids. Polyethylene oxide (PEO) was used as a model and two different chain conformations of the adsorbed polymer were created on silicon substrates via the well-established Guiselin's approach: "flattened chains" which lie flat on the solid and are densely packed, and "loosely adsorbed polymer chains" which form bridges jointing up nearby empty sites on the solid surface and cover the flattened chains. We investigated the adhesion properties of the two different adsorbed chains using a custom-built adhesion testing device. Bilayers of a thick PEO overlayer on top of the flattened chains or loosely adsorbed chains were subjected to the adhesion test. The results revealed that the flattened chains do not show any adhesion even with the chemically identical free polymer on top, while the loosely adsorbed chains exhibit adhesion. Neutron reflectivity experiments corroborated that the difference in the interfacial adhesion is not attributed to the interfacial brodening at the free polymer-adsorbed polymer interface. Instead, coarse-grained molecular dynamics simulation results suggest that the tail parts of the loosely adsorbed chains act as "connector molecules", bridging the free chains and substrate surface and improving the interfacial adhesion. These findings not only shed light on the structure-property relationship at the interface, but also provide a novel approach for developing sticking/anti-sticking technologies through precise control of the interfacial polymer nanostructures.

Combining monodisperse building blocks that have distinct folding properties serves as a modular strategy for controlling structural complexity in hierarchically organized materials. We combine an α-helical bundle-forming peptide with self-assembling dendrons to better control the arrangement of functional groups within cylindrical nanostructures. Site-specific grafting of dendrons to amino acid residues on the exterior of the α-helical bundle yields monodisperse macromolecules with programmable folding and self-assembly properties. The resulting hybrid biomaterials form thermotropic columnar hexagonal mesophases in which the peptides adopt an α-helical conformation. Bundling of the α-helical peptides accompanies self-assembly of the peptide-dendron hybrids into cylindrical nanostructures. The bundle stoichiometry in the mesophase agrees well with the size found in solution for α-helical bundles of peptides with a similar amino acid sequence.

It is known that when nanoparticles are added to polymer thin films, they often migrate to the film–substrate interface and form an “immobile interfacial layer”, which is believed to be the mechanism behind dewetting suppression. We here report a new mechanism of dewetting suppression from the structural aspect of polymer chains accommodated at the film–substrate interface. Dodecanethiol-functionalized gold (Au) nanoparticles embedded in relatively low molecular weight PS thin films prepared on silicon (Si) substrates were used as a model. We mimicked the previously reported conditions, where the nanoparticles preferentially migrate to the substrate, and successfully stabilized the PS thin films via thermal annealing. A suite of surface-sensitive techniques including atomic force microscopy, grazing incidence small-angle X-ray scattering, X-ray/neutron reflectivity, and sum frequency generation spectroscopy in conjunction with the established solvent leaching process enabled us to unveil the polymer chain...

We report the effects of compressed CO, molecules as a novel plasticization agent for poly(3-hexylthiophene) (P3HT)-conjugated polymer thin films. In situ neutron reflectivity experiments demonstrated the excess sorption of CO, molecules in the P3HT thin films (about 40 nm in thickness) at low pressure (P = 8.2 MPa) under the isothermal condition of T = 36 degrees C, which is far below the polymer bulk melting point. The results proved that these CO2, molecules accelerated the crystallization process of the polymer on the basis of ex situ grazing incidence X-ray diffraction measurements after drying the films-via rapid depressurization to atmospheric pressure: both the out-of-plane lamellar ordering of the backbone chains and the intraplane pi-pi stacking of the side chains were significantly improved, when compared with those in the control P3HT films subjected to conventional thermal annealing (at T = 170 degrees C). Electrical measurements elucidated that the CO2-annealed P3HT thin films exhibited enhanced charge carrier mobility along with decreased background charge carrier concentration and trap density compared with those in the thermally annealed counterpart. This is attributed to the CO2-induced increase in polymer chain mobility that can drive the detrapping of molecular oxygen and healing of conformational defects in the polymer thin film. Given the universality of the excess sorption of CO2 regardless of the type of polymers, the present findings suggest that CO2 annealing near the critical point can be useful as a robust processing strategy for improving the structural and electrical characteristics of other semiconducting conjugated polymers and related systems such as polymer:fullerene bulk heterojunction films.

The temperature dependence of structural development in a self-exfoliating nano-composite system has been studied utilizing time resolved small angle x-ray scattering (SAXS) and time resolved mechanical spectroscopy (TRMS) employing small amplitude oscillatory shear (SAOS). This system consists of a montmorillonite organoclay and end-functionalized polybutadiene. Self-exfoliation refers to a system where a layered component, in this case clay, breaks into individual sheets randomly distributed throughout the matrix without any shear, sonication, or other external input. With SAOS, a maximum rate of modulus growth was found at intermediate temperatures. With SAXS complete exfoliation was found to occur fastest at intermediate temperatures. A comparison between SAXS and SAOS showed that the early rapid change in rheological properties results from the expansion of the clay stacks and intercalation. Alternative exfoliation mechanisms are hypothesized to fully explain the new SAOS and SAXS findings along with several other inconsistencies with this system's previously proposed mechanism.

We investigated the effect of density fluctuation of supercritical carbon dioxide (scCO2) on anomalous swelling of multilayer polymer thin films on the ridge in the pressure–temperature phase diagram of CO2. In order to measure the swelling ratio along the film depth, we alternately deposited hydrogenated poly(methyl methacrylate) (PMMA) and deuterated polystyrene (dPS) thin films and performed the neutron reflectivity measurements as a function of CO2 pressure at 36 °C. The results showed that, in contrast to previous studies, CO2 was to penetrate deeply throughout the multilayer thin film where the magnitude of swelling along the density fluctuation ridge of CO2 was independent of film thickness. Block copolymer thin films of dPS-b-PMMA with a parallel lamellar orientation also showed similar swelling behavior in scCO2. However, it is well-known that single-layer polymer thin films exhibit anomalous swelling behavior only near the film surface. This difference is probably due to the fact that the multil...

We report the structural relaxation process of irreversibly adsorbed polymer chains via thermal annealing that lie flat on a solid (“flattened chains”). Amorphous polystyrene and quartz, which together constitute a weakly attractive system, was used as a model where the local chain conformations of the flattened chains were investigated by sum frequency generation spectroscopy (SFG). Two different film preparation processes (i.e., spin coating and dip coating methods) were utilized to create different initial chain conformations. The spin-coated and dip-coated PS thin films were annealed at a temperature far above the bulk glass transition temperature to reach the “quasiequilibrium” state and subsequently rinsed with chloroform to uncover the buried flattened chains. The SFG results revealed that the backbone chains (constituted of CH and CH2 groups) of the flattened PS chains preferentially orient to the weakly interactive substrate surface via thermal annealing regardless of the initial chain conformati...

The evolution of nanoscale properties is measured during the thermally triggered curing of an industrial epoxy adhesive. We use x-ray photon correlation spectroscopy (XPCS) to track the progression of the curing reaction through the local dynamics of filler particles that reflect the formation of a thermoset network. Out-of-equilibrium dynamics are resolved through identification and analysis of the intensity–intensity autocorrelation functions obtained from XPCS. The characteristic time scale and local velocity of the filler is calculated as functions of time and temperature. We find that the dynamics speed up when approaching the curing temperature (Tcure), and decay rapidly once Tcure is reached. We compare the results from XPCS to conventional macroscale characterization by differential scanning calorimetry (DSC). The demonstration and implementation of nanoscale characterization of curing reactions by XPCS proves useful for future development and optimization of epoxy thermoset materials and other industrial adhesive systems.

Rational design rules for programming hierarchical organization and function through mutations of monomers in sequence-defined polymers can accelerate the development of novel polymeric and supramolecular materials. Our strategy for designing peptide–dendron hybrids that adopt predictable secondary and quaternary structures in bulk is based on patterning the sites at which dendrons are conjugated to short peptides. To validate this approach, we have designed and characterized a series of β-sheet-forming peptide–dendron hybrids. Spectroscopic studies of the hybrids in films reveal that the peptide portion of the hybrids adopts the intended secondary structure.

The glass transition of supported polystyrene (PS) and poly(2-vinylpyridine) (P2VP) thin films in the vicinity of the substrate interface was studied by using a nanoplasmonic sensing (NPS) method. This “nanocalorimetric” approach utilizes localized surface plasmon resonance from two-dimensional arrangements of sensor nanoparticles deposited on SiO2-coated glass substrates. The NPS results demonstrated the existence of a high glass transition temperature (Tg,high) along with the bulk glass transition temperature (Tg,bulk ≈ 100 °C for PS and P2VP) within the thin films: Tg,high ≈ 160 °C for PS and Tg,high ≈ 200 °C for P2VP. To understand the origin of the Tg,high, we also studied the thermal transitions of lone polymer chains strongly adsorbed onto the substrate surface using solvent rinsing. Interestingly, the NPS data indicated that the Tg,high is attributed to the adsorbed polymer chains. To provide a better understanding of the mechanism of the Tg,high, molecular dynamics simulations were performed on a...

A series of polystyrene-block-poly(4-(phenylethynyl)styrene) (PS-b-PPES) diblock copolymers with a range of compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. Block copolymer/cobalt carbonyl adducts (PSx-PPESy[Co2(CO)6]n) were subsequently prepared by reaction of Co2(CO)8 with the alkyne groups of the PPES block. Phase behavior of the block copolymer/cobalt carbonyl adducts (PSx-PPESy[Co2(CO)6]n, 8% ≤ wt % PS ≤ 68%) was studied by small-angle X-ray scattering and transmission electron microscopy (TEM). As the composition of PSx-PPESy[Co2(CO)6]n copolymers was shifted from PS as the majority block to PPESy[Co2(CO)6]n as the majority block, the morphology was observed to shift from lamellar with larger PS domains to cylindrical with PS as the minority component and then to spherical with PS as the minority component. These observations have been used to map out a partial phase diagram for PSx-PPESy[Co2(CO)6]n diblock copolymers. Heating of PSx-PPESy[Co2(CO)...

Membrane thickness fluctuations have been associated with a variety of critical membrane phenomena, such as cellular exchange, pore formation, and protein binding, which are intimately related to cell functionality and effective pharmaceuticals. Therefore, understanding how these fluctuations are controlled can remarkably impact medical applications involving selective macromolecule binding and efficient cellular drug intake. Interestingly, previous reports on single-component bilayers show almost identical thickness fluctuation patterns for all investigated lipid tail-lengths, with similar temperature-independent membrane thickness fluctuation amplitude in the fluid phase and a rapid suppression of fluctuations upon transition to the gel phase. Presumably, in vivo functions require a tunability of these parameters, suggesting that more complex model systems are necessary. In this study, we explore lipid tail-length mismatch as a regulator for membrane fluctuations. Unilamellar vesicles of an equimolar mixture of dimyristoylphosphatidylcholine and distearoylphosphatidylcholine molecules, with different tail-lengths and melting transition temperatures, are used as a model system for this next level of complexity. Indeed, this binary system exhibits a significant response of membrane dynamics to thermal variations. The system also suggests a decoupling of the amplitude and the relaxation time of the membrane thickness fluctuations, implying a potential for independent control of these two key parameters.

The re-entrance sites, successive chain-folding number ⟨n⟩, and chain-folding fraction ⟨F⟩ of the chain-folding (CF) structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) with an weight-averaged molecular weight (⟨Mw⟩ = 37 K g/mol) in solution- and melt-grown crystals as a function of crystallization temperature (Tc) were determined using solid-state (SS) NMR. The solution- and melt-grown crystals possessed adjacent re-entry structures between the right- and left-handed stems along the (100) and (010) planes, which were invariant as a function of Tc. The adjacent re-entry structures in the former exhibited long-range order (⟨n⟩ ≥ 8) compared with that in the latter (⟨n⟩ ≥ 1.7–2). These results indicated that the concentration and entanglement of polymers play significant roles in the CF process and structural formation during the initial stage of crystallization, whereas kinetics does not. Transmission electron microscopy (TEM) revealed well-defined hexagonal and circular crystals grown from the so...

We report a mobility gradient of polymer chains in close proximity of a planar solid substrate in compressed carbon dioxide (CO2) gas. A series of bilayers composed of bottom hydrogenated polystyrene (h-PS) and top deuterated PS (d-PS) layers were prepared on Si substrates. A high-pressure neutron reflectivity (NR) technique was used to study the diffusive motion at the h-PS/d-PS interface as a function of the distance from the substrate interface. The results reveal that the interdiffusive chain dynamics gets strongly hindered compared to the bulk when the distance from the substrate is less than 3R(g) (R-g is the radius of polymer gyration of the h-PS). At the same time, by utilizing rapid quench of CO2 and subsequent solvent leaching, we reveal the presence of the CO2-induced polymer adsorbed layer on the substrate. We postulate that loop components in the adsorbed polymer chains provide a structure that can trap the neighboring polymer chains effectively, hence reducing the chain mobility in the close vicinity of the solid substrate even in the presence of the effective plasticizer.

Attaching dendritically branched side chains to each repeat unit of a linear polymer produces molecular building blocks of nanometer-sized dimensions called dendronized polymers. The structure of these complex molecular architectures is highly tunable and, therefore, of interest for a wide range of potential applications. The first examples of dendronized polymers prepared by living ring-opening metathesis polymerization of oxanorbornenedicarboximide macromonomers with poly(alkyl ether) dendrons are reported. Small-angle X-ray scattering experiments on bulk samples confirm that the diameter of the individual cylindrical polymers can be tailored by the choice of dendron generation or the length of the hydrocarbon peripheral group. Analysis of the SAXS data based on a core-shell model indicates that although the diameter of the cylinder increases with generation, the size of the core does not change; this suggests that these dendrons only loosely encapsulate the polymer backbone. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3221–3239

Recently, nanoconfined poly(vinylidene fluoride) (PVDF) and its random copolymers have attracted substantial attention in research. In addition to the drastic change in crystallization kinetics, major interest lies in crystal orientation and polymorphism in order to understand whether enhanced piezoelectric and ferroelectric properties can be achieved. For example, PVDF has been two-dimensionally (2D) confined in cylindrical nanopores of anodic aluminum oxide (AAO) with various pore diameters. The crystal c-axis becomes perpendicular to the cylinder axes, which favors dipole switching in the impregnated AAO membrane. However, no polar phases have been obtained from 2D confinement even down to 35 nm pores after melt recrystallization. In this work, we realized three-dimensionally (3D) confined crystallization of PVDF in 180 nm nanospheres by employing a facile emulsifier-free batch seeded emulsion polymerization to prepare PVDF@polystyrene (PS) core–shell particles. Influences of polymerization temperature...

Thermal annealing is one of the most indispensable polymer fabrication processes and plays essential roles in controlling morphologies and properties of polymeric materials. We here report that thermal annealing also facilitates polymer adsorption from the melt on planar silicon (Si) substrates, resulting in the formation of a high-density polymer nanolayer with flattened chain confirmations. Three different homopolymers (polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate)), which have similar inherent stiffness and bulk glass transition temperature (Tg), but have different affinities with Si substrates, were chosen as models. Spin-cast films (∼50 nm in thickness) with the three polymers were prepared on cleaned Si substrates and then placed in a vacuum oven set at a temperature far above the bulk Tg. In order to monitor the polymer adsorption process at the solid-polymer melt interface during thermal annealing, we used the protocol that combines vitrification of the annealed films (via rapi...

The orientation changes of perpendicular cylindrical microdomains in polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) thin films upon annealing in different solvent vapors were investigated by in situ grazing incidence small-angle X-ray scattering (GISAXS) and ex situ scanning force microscopy (SFM). The swelling of P4VP perpendicular cylinders (C⊥) in chloroform, a non-selective solvent vapor, leads to the reorientation to in-plane cylinders through a disordered state in a particular kinetic pathway in the phase diagram upon drying. On the other hand, the swelling of the P4VP perpendicular cylinders in a selective solvent vapor (i.e., 1,4-dioxane) induces a morphological transition from cylindrical to ellipsoidal as a transient structure to spherical microdomains; subsequent solvent evaporation resulted in shrinkage of the matrix in the vertical direction, merging the ellipsoidal domains into the perpendicularly aligned cylinders. In this paper, we have discussed the mechanism based on the selectivity of the solvent to the constituting blocks that is mainly responsible for the orientation changes.

The mechanism and process of the thermally induced order−order transition (OOT) of a polystyrene-block- polyisoprene diblock copolymer from cylinders on a hexagonal symmetry (hex-cyl) to spheres on a body-centered cubic symmetry (bcc-sphere) were investigated by means of time- resolved observation of high-resolution small-angle X-ray scattering (hr-SAXS) profiles obtained with a Bonse-Hart type USAXS apparatus. The USAXS apparatus enabled us to precisely study changes in the scattering peak profiles with time induced by the OOT between the two equilibrium morphologies of hex-cyl and bcc-sphere with a high resolution with respect to magnitude of scattering vector q. The peaks due to hex-cyl and bcc-sphere, which are closely located and hence overlapped one another in q-space when they are observed with conventional SAXS apparatuses, are well resolved into separated peaks with the hr-SAXS, which gave a new insight into the OOT process and mechanism as elucidated in the text.

Numerous studies have shown that the glass transition temperature, Tg, of polymers may change visibly upon addition of even small amounts of nanoparticles. In this study, we examine the effect of polymer–nanoparticle interfacial energy on this phenomenon in nanocomposite films containing polystyrene-grafted nanoparticles mixed with polystyrene homopolymer at low particle loadings. A previous experiment showed that the interfacial energy of this system modulates with the grafting density of the grafted polymer and the molecular weight ratio of the matrix and grafted polymers. We find that the changes in Tg vary with both parameters in manners that quantitatively agree with the interfacial energy.

We report the effects of compressed CO

Various properties of ultrathin polymer films differ substantially from their bulk values. However, the critical question is whether the unusual properties are uniform throughout the films. To explore the presence of heterogeneous viscosity distributions, we have established grazing-incidence X-ray photon correlation spectroscopy for single polymer films with embedded metal nanoparticles that act as markers. In addition, the combined use of resonance enhanced X-ray scattering enables us to intensify the probing electrical field in the regions of interest within a single polymer film.

We report the structural heterogeneity of recrystallized linear low-density polyethylene (LLDPE) films (25, 50, and 100 rim in thickness) in the direction normal to the surface, based on in situ grazing incidence small-angle X-ray scattering (GISAXS) and X-ray diffraction (GID) measurements. The GID results have clarified the presence of the edge-on lamellae at the surfaces and in the interior of the LLDPE films prepared on Si substrates as thin as 25 nm in thickness. However, the degree of the crystallinity for the 25 nm thick film was almost half of those for the SO and 100 nm thick films, while the melting temperature (T-m) for all the films remained unchanged relative to the bulk (T-m = 117 degrees C). Moreover, the GISAXS results for the 25 nm thick film indicate the structural heterogeneity in the direction normal to the surface: (i) At the polymer/air interface, the presence of the disordered edge-on lamellae which lack well-defined long periods even at T << T-m; (ii) At the polymer/substrate interface, the persistence of a substrate-bound edge-on lamellar layer even at T >> T-m; (iii) In between the two interfacial layers, the existence of the well-ordered edge-on lamellae with the long periods. These heterogeneous structures can be explained as a consequence of the nucleation initiated at the topmost surface of the substrate-bound lamellar layer.

Polymer properties, such as their mechanical strength, barrier properties, and dielectric response, can be dramatically improved by the addition of nanoparticles. This improvement is thought to be because the surface area per unit mass of particles increases with decreasing particle size, R, as 1/R. This favorable effect has to be reconciled with the expectation that at small enough R the nanoparticles must behave akin to a solvent and cause a deterioration of properties. How does this transition in behavior from large solutes to the solvent limit occur? We conjecture that for small enough particles the layer of polymer affected by the particles (“bound” polymer layer) must be much smaller than that for large particles: the favorable effect of increasing particle surface area can thus be overcome and lead to the small solvent limit with unfavorable mechanical properties, for example. To substantiate this picture requires that we measure and compare the “bound polymer layer” formed on nanoparticles with th...