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In search of a new way to fabricate graphene-like materials, isostatic graphite targets were ablated using high peak power with a nanosecond-pulsed infrared laser. We conducted dry ablations in an argon atmosphere and liquid-phase ablations in the presence of a liquid medium (water or toluene). After the dry ablation, the SEM images of the target showed carbon in the form of a volcano-like grain structure, which seemed to be the result of liquid carbon ejected from the ablation center. No graphite exfoliation could be achieved using dry ablation. When using liquid phase ablation with water or toluene as a liquid medium, no traces of the formation of liquid carbon were found, but cleaner and deeper craters were observed. In particular, when using toluene as a liquid medium, typical graphite exfoliation was found. We believe that due to the extremely high pressure and high temperature induced by the laser pulses, toluene was able to intercalate into the graphite layers. Between the laser pulses, the intercalated toluene was able to flash evaporate and blow-up the graphite, which resulted in exfoliated graphite. Exfoliated graphite was found on the ablated graphite surface, as well as in the toluene medium. The ablation experiments with toluene undertaken in this study demonstrated an effective method of producing micrometer-sized graphene material. When using water as a liquid medium, no massive graphite exfoliation was observed. This meant that under the used laser conditions, toluene was a better intercalant for graphite exfoliation than water.

Recently, we reported the experimental tuning of the growth of freestanding SnO2 nanowires to a laterally aligned nanowire growth mode. Here, we present thermodynamic considerations taking into acc...

Upon immersion of a lithium (Li) anode into a diluted 0.05 to 0.20 M dimethoxyethanesolutionof the phosphoric acid derivative (CF 3 CH 2 O) 2 P(O)OH (HBFEP), anartificial solid electrolyte interphase (SEI) is generated on the Li-metal surface. Hence,HBFEP reacts on the surface to the corresponding Li salt (LiBFEP), which is a Li-ionconducting inorganic coordination polymer. This film exhibits -due to the reversiblybreaking ionic bonds- self-healing ability upon cycling-induced volume expansion of Li.The presence of LiBFEP as the major component in the artificial SEI is proven by ATRIRand XPS measurements. SEM characterization of HBFEP-treated Li samplesreveals porous layers on top of the Li surface with at least 3 μm thickness. Li-Lisymmetrical cells with HBFEP-modified Li electrodes show a three- to almost fourfoldcycle-lifetime increase at 0.1 mA·cm –2 in a demanding model electrolyte thatfacilitates fast battery failure (1 m LiOTf in TEGDME). Hence, the LiBFEP-enrichedlayer apparently acts as a Li-ion conducting protection barrier between Li and theelectrolyte, enhancing the rechargeability of Li electrodes.

Nacre-mimicking layered organic/inorganic hybrid materials exhibiting ultrahigh stiffness and strength frequently require multistep processing that is restricted to polar and even water-soluble polymers. Herein, nacre-mimetic hydrocarbon composites were fabricated by single-step injection molding. The key intermediates are organophilic ultrathin γ-Al(OH)3 (O-gibbsite) single-crystal nanoplatelets and all-hydrocarbon composites (All-PE) containing aligned, extended-chain ultrahigh-molecular-weight polyethylene (UHMWPE) as one-dimensional (1D) nanostructures embedded in a polyethylene (PE) matrix. This formation of flow-induced UHMWPE 1D nanostructures mimics chitin nanofibers in nacre and drives the alignment of O-gibbsite nanoplatelets to assemble bricks. Unprecedented high contents of up to 70 wt % O-gibbsite nanoplatelets are tolerated in injection molding. As verified by focused ion beam-scanning electron microscopy (FIB-SEM), the resulting brick-and-mortar architectures contain aligned O-gibbsite as b...

Porous membranes with special wetting properties have attracted great interest due to their various functions and wide applications, including water filtration, selective oil/water separation and oil skimming. Special wetting properties such as superhydrophobicity can be achieved by controlling the surface chemistry as well as the surface topography of a substrate. Three-dimensional (3D) printing is a promising method for the fast and easy generation of various structures. The most common method for 3D printing of superhydrophobic materials is a two-step fabrication process: 3D printing of user-defined topographies, such as surface structures or bulk porosity, followed by a chemical post-processing with low-surface energy chemicals such as fluorinated silanes. Another common method is using a hydrophobic polymer ink to print intricate surface structures. However, the resolution of most common printers is not sufficient to produce nano-/microstructured textures, moreover, the resulting delicate surface micro- or nanostructures are very prone to abrasion. Herein, we report a simple approach for 3D printing of superhydrophobic micro-/nanoporous membranes in a single step, combining the required topography and chemistry. The bulk porosity of this material, which we term “Fluoropor”, makes it insensitive to abrasion. To achieve this, a photocurable fluorinated resin is mixed with a porogen mixture and 3D printed using a stereolithography (SLA) printing process. This way, micro-/nanoporous membranes with superhydrophobic properties with static contact angles of 164° are fabricated. The pore size of the membranes can be adjusted from 30 nm to 300 nm by only changing the porogen ratio in the mixture. We show the applicability of the printed membranes for oil/water separation and the formation of Salvinia layers which are of great interest for drag reduction in maritime transportation and fouling prevention., 3D printed micro/-nanostructured thin membranes with inherent adjustable porosity in the submicron range for the use as water–oil separators.

The glass transition temperature (Tg) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect, i.e., the Fox&ndash, Flory relationship between Tg and the average molecular weight between crosslinking points (Mc), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) conetworks was prepared and investigated. Two Tgs were found for the conetworks by DSC. Fox&ndash, Flory type dependence between Tg and Mc of the PMMA component (Tg = Tg,&infin, &minus, K/Mc) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5&ndash, 20 nm, but the correlation between Tg and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors (scissors effect), and the Tg of PMMA depend exclusively on the Mc in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials.

The glass transition temperature (Tg) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect, i.e., the Fox–Flory relationship between Tg and the average molecular weight between crosslinking points (Mc), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) conetworks was prepared and investigated. Two Tgs were found for the conetworks by DSC. Fox–Flory type dependence between Tg and Mc of the PMMA component (Tg = Tg,∞ − K/Mc) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5–20 nm, but the correlation between Tg and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors (scissors effect), and the Tg of PMMA depend exclusively on the Mc in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials.

Despite the great interest in nanoconfined materials nowadays, nanocompartmentalized poly(ionic liquid)s (PILs) have been rarely investigated so far. Herein, we report on the successful alkylation of poly(1-vinylimidazole) with methyl iodide in bicontinuous nanophasic poly(1-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) to obtain nanoconfined methylated PVImMe-l-PTHF poly(ionic liquid) conetworks (PIL-CNs). A high extent of alkylation (~95%) was achieved via a simple alkylation process with MeI at room temperature. This does not destroy the bicontinuous nanophasic morphology as proved by SAXS and AFM, and PIL-CNs with 15&ndash, 20 nm d-spacing and poly(3-methyl-1-vinylimidazolium iodide) PIL nanophases with average domain sizes of 8.2&ndash, 8.4 nm are formed. Unexpectedly, while the swelling capacity of the PIL-CN dramatically increases in aprotic polar solvents, such as DMF, NMP, and DMSO, reaching higher than 1000% superabsorbent swelling degrees, the equilibrium swelling degrees decrease in even highly polar protic (hydrophilic) solvents, like water and methanol. An unprecedented Gaussian-type relationship was found between the ratios of the swelling degrees versus the polarity index, indicating increased swelling for the nanoconfined PVImMe-l-PTHF PIL-CNs in solvents with a polarity index between ~6 and 9.5. In addition to the nanoconfined structural features, the unique selective superabsorbent swelling behavior of the PIL-CNs can also be utilized in various application fields.

Despite the great interest in nanoconfined materials nowadays, nanocompartmentalized poly(ionic liquid)s (PILs) have been rarely investigated so far. Herein, we report on the successful alkylation of poly(1-vinylimidazole) with methyl iodide in bicontinuous nanophasic poly(1-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) to obtain nanoconfined methylated PVImMe-l-PTHF poly(ionic liquid) conetworks (PIL-CNs). A high extent of alkylation (~95%) was achieved via a simple alkylation process with MeI at room temperature. This does not destroy the bicontinuous nanophasic morphology as proved by SAXS and AFM, and PIL-CNs with 15–20 nm d-spacing and poly(3-methyl-1-vinylimidazolium iodide) PIL nanophases with average domain sizes of 8.2–8.4 nm are formed. Unexpectedly, while the swelling capacity of the PIL-CN dramatically increases in aprotic polar solvents, such as DMF, NMP, and DMSO, reaching higher than 1000% superabsorbent swelling degrees, the equilibrium swelling degrees decrease in even highly polar protic (hydrophilic) solvents, like water and methanol. An unprecedented Gaussian-type relationship was found between the ratios of the swelling degrees versus the polarity index, indicating increased swelling for the nanoconfined PVImMe-l-PTHF PIL-CNs in solvents with a polarity index between ~6 and 9.5. In addition to the nanoconfined structural features, the unique selective superabsorbent swelling behavior of the PIL-CNs can also be utilized in various application fields.

Macroscopically homogeneous poly(N-vinylimidazole)-linked by-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) were investigated to reveal the effect of conetwork composition in a broad composition range between 25–91 wt% PTHF content and the molecular weight of the components on phase separation and the formation of different morphological features. No macroscopic phase separation was found in these conetworks with semicrystalline PTHF phase, but the segregation of the various covalently connected phases occurs in the nanoscale. The nanophase separated APCNs possess compositionally asymmetric morphology with spherical and elongated domains together with a bicontinuous (cocontinuous) domain structure having ∼7–19 nm average domain sizes. The molecular weight of the PTHFDMA cross-linker, varying between 2170 and 10 030 g mol−1, also influences the size and distance between the phases. Moreover, morphology dependent interactions with polar and non-polar solvents, as well as amphiphilic swelling behavior were found. These nanostructured materials, due to their unique nanophasic morphology and swelling properties possess significant importance and have numerous potential applications in various fields from medicine to material science and engineering.

Tailoring trimodal polyethylene (PE) molar mass distributions by means of ethylene polymerization on three-site catalysts, supported on functionalized graphene (FG), enables nanophase separation during polymerization and melt processing, paralleled by PE self-reinforcement. Typically, FG/MAO-supported three-site catalysts combine bis(iminopyridyl)chromium trichloride (CrBIP), producing PE wax having high crystallization rate, and quinolylcyclopentadienylchromium dichloride (CrQCp), forming in situ ultrahigh molecular weight PE (UHMWPE) nanostructures, with bis(iminopyridyl)iron dichloride (FeBIP) or bis(tert-butyl cyclopentadienyl)zirconium (ZrCp), respectively, producing HDPE with variable intermediate molar mass. During injection molding, the formation of shish-kebab fiber-like extended-chain UHMWPE structures, as verified by SEM, AFM, and DSC, account for effective self-reinforcement. Only in the presence of high UHMWPE content, PE wax, usually an unwanted byproduct in HDPE synthesis, functions as a bu...

The design of supported two- and three-site catalysts for ethylene polymerization and tailoring nanophase-separated polyethylene reactor blends represents the key to the development of advanced all-polyethylene nanocomposite materials exhibiting substantially improved performance and high resource-, eco- and energy efficiency. Two or three different single-site catalysts independently produce high density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE) and PE wax on the same catalyst support. Since this catalyst-mediated nanophase separation prevents UHMWPE entanglement, typical for conventional homogeneous reactor blends, much higher UHMWPE content up to 30 wt % is incorporated in the presence of PE wax without impairing injection molding. During melt processing the shear-induced oriented UHMWPE crystallization affords shish-kebab-fiber-like nanostructures. This accounts for effective PE self-reinforcement paralleled by simultaneous improvement of stiffness, strength and toughness. Hence, this strategy holds great promise for converting commodity PE into high performance plastics and single component PE composites, entering the performance range currently claimed by glass fiber reinforced PE.

A series of macroscopically homogeneous poly(N-vinylimidazole)-l-poly(propylene glycol) (PVIm-l-PPG) (“l” stands for “linked by”) amphiphilic conetworks (APCNs) composed of otherwise incompatible polymers were successfully synthesized in a broad composition range (34–88 wt% PPG) by free radical copolymerization of hydrophilic N-vinylimidazole (VIm) and hydrophobic poly(propylene glycol) dimethacrylate (PPGDMA) macromolecular cross-linkers. Strikingly, while PVIm and PPGDMA homopolymers are immiscible and their blends have two distinct glass transition temperatures (Tg), the PVIm-l-PPG conetworks possess only one Tg indicating the absence of considerable phase separation in the conetworks, which was also confirmed by AFM measurements. This is in sharp contrast to the two Tgs of APCNs reported so far in the literature, on the one hand. On the other hand, the Tg values do not follow known correlations between Tg and composition, like the Fox equation or additive rule, widely applied for compatible polymers. These results indicate a strong interpolymer interaction on the molecular level between the PVIm and PPG chains in these new APCNs resulting in single Tg. Thermogravimetric analysis (TGA) shows that degradation of the conetworks occurs at high temperatures in two stages without sharp changes, but with a transition period in between. The DTG curves indicate that the components retain their chemical integrity to certain extent in these APCNs. The amphiphilic nature of the PVIm-l-PPG conetworks was confirmed by their composition dependent swelling in both polar (water, ethanol) and nonpolar (THF) solvents, that is in spite of the lack of phase separation, these new materials behave as either hydrogels or hydrophobic gels (organogels) depending on the swelling medium in a broad composition range.

Multicellular spheroids represent a well-established 3D model to study healthy and diseased cells in vitro. The use of conventional 3D cell culture platforms for the generation of multicellular spheroids is limited to cell types that easily self-assemble into spheroids because less adhesive cells fail to form stable aggregates. A high-precision micromoulding technique developed in our laboratory produces deep conical agarose microwell arrays that allow the cultivation of uniform multicellular aggregates, irrespective of the spheroid formation capacity of the cells. Such hydrogel arrays warrant a steady nutrient supply for several weeks, permit live volumetric measurements to monitor cell growth, enable immunohistochemical staining, fluorescence-based microscopy, and facilitate immediate harvesting of cell aggregates. This system also allows co-cultures of two distinct cell types either in direct cell-cell contact or at a distance as the hydrogel permits diffusion of soluble compounds. Notably, we show that co-culture of a breast cancer cell line with bone marrow stromal cells enhances 3D growth of the cancer cells in this system.

A versatile gas phase mineralization process affords nanosheets containing a functionalized graphene (FG) core and a thin silica shell. The number of cycles, exposing FG to sequenced tetrachlorosilane and water vapors, controls the silica content and the silica shell thickness. The resulting high surface area core/shell nanosheets, containing 22 to 34 wt.-% silica, are used to immobilize single-site catalysts. During polymerization, the FG/silica nanosheets are uniformly dispersed in ultrahigh molecular weight polyethylene. This catalytic polymerization filling process, exploiting the encapsulation of graphene in a silica shell, is of interest to prepare electrically insulating carbon/polyolefin composite materials with high thermal conductivity useful in lightweight engineering.

The catalytic ethylene polymerization on dual-site catalysts, supported on functionalized graphene, enables nanostructure formation in polyethylene reactor blends by in situ formation of uniformly dispersed ultrahigh molecular weight polyethylene (UHMWPE) nanoplatelets and in situ formed aligned UHMWPE shish-kebab nanofibers. For tailoring bimodal molar mass distributions, the quinolylsilylcyclopentadienylchromium(III) complex (Cr-1), producing UHMWPE with Mw > 3 × 106 g mol–1, is blended together with bisiminopyridine complexes of either chromium(III) (CrBIP), producing polyethylene (PE) wax (2 × 103 g mol–1), or iron(II) (FeBIP), producing PE with Mw = 2.0 × 105 g mol–1. Hence, the FeBIP/Cr-1 and CrBIP/Cr-1 molar ratios govern the PE/UHMWPE weight ratio without affecting the average molar mass of the individual PE fractions. In sharp contrast to conventional UHMWPE/PE reactor blends, the UHMWPE content is substantially increased up to 17 wt % without impairing melt processing. In the case of graphene-su...

Multifunctional isocyanurates are tailored as new additives for improving POM melt flow (“High Speed POM”). In a versatile one-pot synthesis, reacting trimerized hexamethylene diisocyanate with various alcohols and amines, functionalities, branching, and n-alkyl chain length are readily varied. The influence of substitution patterns on POM rheology is investigated. Adding 3 wt% isocyanurate urethane (I3O) together with 0.33 wt% nanosilica increases POM melt flow path by 60%. Large POM stacking boxes are molded at temperatures lowered by 40 K. This markedly enhances cooling and reduces cycle times. Isocyanurate urea (I3N) does not require nanosilica addition. Lubrication mechanisms and the role of in situ gradient formation, as measured by AFM, are studied.

Novel families of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites, containing uniformly dispersed, functionalized graphene (FG) nanosheets, were prepared by means of the polymerization filling technique (PFT). Unparalleled by any other carbon and boehmite nanocomposites, FG/UHMWPE exhibited an unusual simultaneous improvement in stiffness, elongation at break, and effective nucleation of polyethylene crystallization at only 1 wt % FG content. FG nanosheets are ultrathin—with a thickness of only one carbon atom and lateral dimensions of several micrometers. Owing to the presence of surface hydroxyl groups on the FG, single FG/methylaluminoxane (MAO) nanosheets can be effectively dispersed in n-heptane, thus enabling immobilization of an MAO-activated chromium (Cr1) single-site catalyst on FG. In contrast to nanometer-scale carbon black (CB), multiwall carbon nanotubes (CNT), graphite, and nanoboehmite, which failed to form stable dispersions, FG/MAO/Cr1 afforded the highest catalyst activit...

It could be an unintentional effect to deposit metal nanoparticles on a simple Teflon-coated magnetic stirring bar. Rhodium nanoparticles, as an example, were reproducibly deposited onto a standard, commercial Teflon-coated magnetic stirring bar by easy and rapid microwave-assisted decomposition of the metal carbonyl precursor Rh 6 (CO) 16 in the ionic liquid 1- n -butyl-3-methyl-imidazolium tetrafluoroborate. Such metal nanoparticle deposits are not easy to remove from the Teflon surface by simple washing procedures and present active catalysts which one is not necessarily aware of. Barely visible metal-nanoparticle deposits on a stirring bar can act as trace metal impurities in catalytic reactions. As a proof-of-principle the rhodium-nanoparticle deposits of 32 μg or less Rh metal on a 20 mm × 6 mm magnetic stirring bar were shown to catalyze the hydrogenation reaction of neat cyclohexene or benzene to cyclohexane with quantitative conversion. Rhodium-nanoparticle-coated stirring bars were easily handable, separable and re-usable catalyst system for the heterogeneous hydrogenation with quantitative conversion and very high turnover frequencies of up to 32,800 mol cyclohexene × (mol Rh) −1 × h −1 under organic-solvent-free conditions.

There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly(( R ),( S )- N -(1-hydroxy-butan-2-yl)acrylamide) (P-( R ),( S )-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n -heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases.

A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase.

Amphiphilic polymer conetworks (APCN) combine the properties of different polymers on the nanoscale affording advanced materials with unique properties. Here, we present the first APCN with a chiral hydrophilic phase. The conetworks were prepared by copolymerizing the tailored chiral monomer (R)-N-(1-hydroxybutan-2-yl)acrylamide (R-HBA) with two different crosslinkers that consist of bitelechelic methacrylate-terminated poly(dimethylsiloxane) (PDMS) of a molecular weight of 1100 g/mol and 5620 g/mol, respectively. The resulting polymer conetworks P-R-HBA-l-PDMS exhibited both two different Tg values, indicating nanophase separation. However, the conetwork with PDMS1.1 did not show nanophases in the AFM and did not swell the phases separately in orthogonal solvents. On the other hand the materials with PDMS5.6 acted like a typical APCN. The APCN P-R-HBA-l-PDMS5.6 was found to be temperature sensitive in water, decreasing its degree of swelling linearly with increasing temperature. Additionally, the conetwork is increasing its degree of swelling in n-heptane in the region of the Tg of the P-R-HBA phase. The impact of the chiral polymer on the release of cinchona alkaloids was examined. For example, (−)-cinchonine diffuses four times faster off the P-R-HBA-l-PDMS networks than off the P-S-HBA-l-PDMS conetworks.

A high performance liquid chromatography column (HPLC) Hypercarb ® packed with porous graphite has proven to discriminate polyolefin molecules due to differences in their adsorption and desorption behaviour. While linear polyethylene (PE) and syndiotactic polypropylene (sPP) are adsorbed on the graphite packing, isotactic polypropylene (iPP) is not adsorbed. The column operates at 160 °C with 1-decanol as sample solvent and mobile phase. We have now tested this HPLC system for separations of random propene/1-alkene and ethylene/1-hexene copolymers: While copolymers of propene with 1-butene, 1-hexene and 1-octene copolymers eluted in size exclusion mode without adsorption, propene/1-octadecene and ethylene/1-hexene copolymers are strongly retained and eluted only after application of a linear gradient starting from 1-decanol and ending with pure 1,2,4-trichlorobenzene. The retention of propene/1-alkene (>11 carbons in the side chain) copolymers increases with the concentration of comonomer, making this HPLC system suitable to separate these copolymers according to their chemical composition. In contrast, the retention of ethylene/1-hexene samples decreases with increasing 1-hexene content. Branching in this case shortens the length of continuous methylene sequences of the polymer backbone, which are expected to adsorb in a planar conformation to the graphite layers. This is the first report on the separation of short chain branched polyolefins by high-temperature adsorption liquid chromatography.

The formation of gradient interfaces between PS- and PB-rich microphases in SBS block copolymers was investigated by means of solid-state NMR and solution NMR as well as TEM, AFM, and SAXS as a fun...

Amphiphilic conetworks based on end-linked copolymers of the hydrophilic ionizable 2-(dimethylamino)ethyl methacrylate and the hydrophobic n-butyl methacrylate bearing 3, 5, 7, and 9 blocks were synthesized using group transfer polymerization, and employing a bifunctional initiator and sequential addition of monomers and ethylene glycol dimethacrylate cross-linker. All the linear precursors to the conetworks had the same molecular weight and composition, and differed only in their number of blocks. The aqueous degrees of swelling of the ionized conetworks increased with the number of blocks, manifesting the reduction of the driving force for nanophase separation, resulting from the reduction of the length of the hydrophobic segments. Reduction in the tendency for nanophase separation with increasing block number was also supported by atomic force microscopy on bulk conetworks, which indicated a decrease in the domain size as the number of blocks increased.

The present paper aims to study the possibility to modify the properties of poly(vinyl alcohol) (PVA) hydrogels prepared in the presence of different salt types (Na2SO4, NaCl and NaNO3) in order to extend the nature of the salts already used in obtaining films or gels, to expand their concentration domains and to explain the increase of film strain, concomi- tantly with the increase of their crystallinity. The morphology of the PVA based hydrogels has been studied by Scanning Electronic Microscopy (SEM), the interaction between the PVA macromolecular chains and salts has been determined by Fourier Transform Infrared Spectroscopy (FTIR), while the mechanical properties of the cryogels have been investigated by oscillatory dynamic mechanical measurements. The gels swelling in water have been monitored by gravimetric method in order to evidence the alteration of the PVA cryogel properties such as crystallinity and porosity determined by the salt addition to the initial PVA aqueous solution. The data reported show that the ions present in the PVA solution influence the interaction between PVA-water and PVA-PVA chains; their influence on the salt-based PVA hydrogels follow the Hofmeister lyotropic series.

We demonstrate the fast, direct, and quantitative observation of temperature- and comonomer- induced changes in the interfacial size and composition in phase-separated styrene-butadiene-styrene block copolymers by double-quantum-filtered proton spin-diffusion NMR experiments performed under high-resolution magic-angle spinning conditions. The experiment is based on the dipolar-mediated diffusion of spin magnetization from the (styrenic) rigid phase through a more mobile interphase of variable size and composition into the soft (polybutadiene) domain. The experiment spectroscopically distinguishes between mobilized styrene segments located in the interphase and those mixed (dissolved) in the bulk of the mobile domain. The results indicate that temperature-induced softening due to mobilization of styrene units at the interface and the tendency to become part of an extended interphase is stronger for systems with a lower segregation strength, having statistically distributed styrene comonomers in the soft domain.

A novel family of optically transparent acrylic nanocomposites containing up to 30 wt % silica nanoparticles with an average diameter of 20 nm was developed for application in structural light modulation (SLM) and stereolithography (SL) technologies. The uniform dispersion of nanoparticles affords a significantly improved toughness/stiffness-balance of the photopolymerized and postcured nanocomposites. It is possible to increase stiffness, as expressed by Young's modulus, from 1290 to 1700 MPa without encountering the embrittlement typical for many other conventional filled polymers. Fracture behaviour is examined by means of fracture mechanics investigation and SEM analyses of fracture surfaces. According to TEM analyses and measurement of optical transmittance remarkable uniform dispersion of silica nanoparticles was achieved. The silica nanoparticle concentrations up to 17 wt % give only marginally higher viscosities and do not affect transmittance, while slightly increasing the exposure times needed in photopolymerization. Moreover, the silica nanoparticles afford materials with reduced shrinkage and improved properties. The green effective ankle splay out (EASO) measured on H-shaped diagnostic specimens, is significantly reduced for the nanocomposite materials from 1.38 mm for the unfilled material to 0.82 mm for nanocomposites containing 30 wt % nanosilica. The building accuracy is increased significantly with increasing content of silica nanofillers.

The use of spin-diffusion NMR for the measurement of domain sizes in multiphase materials is becoming increasingly popular, in particular for the study of heterogeneous polymers. Under conditions where T1 relaxation can be neglected, which is mostly the case at high field, analytical and approximate solutions to the evolution of spin diffusion are available. In order to extend the technique to more general conditions, we performed a comprehensive study of the diffusion of magnetization in a model copolymer at low field, where T1 tends to be of the same order of magnitude as the typical spin-diffusion time. In order to study the effects of T1 and to delineate the optimal T1 values for back correction prior to applying the initial-rate approximation, we developed a numerical simulation based on the diffusion equation and including longitudinal relaxation. We present and discuss the limits of simple correction strategies for initial-slope analysis based on apparent relaxation times from saturation-recovery experiments or the spin-diffusion experiments themselves. Our best strategy faithfully reproduces domain sizes obtained by both TEM investigations and full simultaneous fitting of spin-diffusion and saturation-recovery curves. Full fitting of such independent data sets not only yields correct domain sizes, but also the true longitudinal relaxation times, as well as spin-diffusion coefficients. Effects of interphases with distinct mobility on spin-diffusion curves, as well as practical hints concerning the reliable component decomposition of the detected low-resolution FID signal by help of different magnetization filters are also discussed in detail. © 2008 Elsevier Inc. All rights reserved.

Brilliant and angle-dependent iridescent colors were obtained from polymer films produced via colloidal crystallization of monodisperse core-shell particles by drying aqueous dispersions. By variation of the particle size, the brilliant color could be varied throughout the visible spectrum. The color effects of the smooth thin films exhibit excellent thermal and water stability. The morphology of the core-shell particles and the properties of the corresponding films were characterized by dynamic light scattering (DLS), atomic force microscopy (AFM), differential scanning calorimetry (DSC), and reflection spectrum measurements. The results indicate that the brilliance of the film is strongly dependent on size and quality of the crystalline domains.

The phenoxyimine catalyst (bis-(N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride) was tailored to enable random and block copolymerisation of propylene and ethylene with compositions covering the entire feasible composition range. Well-defined high molecular weight diblock copolymers of the type PE-block-P(E-co-P), consisting of a semi-crystalline polyethylene and a soft P(E-co-P) block, were prepared and evaluated with respect to propylene content and the block lengths. The characterisation by means of AFM, CRYSTAF data and high temperature chromatographic elution provided the experimental evidence that no homo-polyethylene and less than 5% of the random copolymer are formed as by-products.

Epoxy-layered silicates nanocomposites based on diglycidyl ether of bisphenol A and an anhydride-curing agent have been successfully synthesised. A manufacturing process using hand lay-up, vacuum bagging, and hot pressing techniques was developed to produce glass fibre-reinforced laminates with this nanocomposite matrix. Transmission electron microscopy indicated that silicate layers dispersed in the epoxy matrix present a long-range order with an interlamellar spacing of about 9 nm. X-ray diffraction analysis confirmed this nanostructure both in the nanocomposites and in the fibre-reinforced composite based on the same matrix. Scanning electron micrographs of the laminate with a nanocomposite matrix showed that nanolayers are apparently sticking at the surface of the glass fibre, improving possibly in this manner the interfacial properties of the fibres. Flexural testing of the laminates showed that the nanolayers improve the modulus and the strength, respectively, by 6% and 27%. Dynamic mechanical analyses of the epoxy and nanocomposite plates and their corresponding laminates showed a systematic glass transition temperature decrease of the nanocomposite based materials. This explains probably the larger water uptake observed at 50 °C in the plate and the laminate based on a nanocomposite matrix as compared with those based on the pristine epoxy.

The reaction of hydrazine with ethyl glycolate results in 1,2-bisglycoylhydrazine, a monomer that was used for the lipase-catalyzed synthesis of biodegradable poly(ester hydrazide)s. The polymers derived from the hydrazide-containing monomer and vinyl-activated adipic, suberic, and sebacic acid, respectively, showed low melting temperatures of 136 to 141 °C and are thermally stable up to 300 °C. The aliphatic poly(ester hydrazide)s (PEHs) are highly crystalline, as proven by polarization microscopy and atomic force microscopy. Further, the PEHs represent the first described biodegradable poly(hydrazide)s. They degrade in the presence of lipase at 37 °C within a few weeks.

Nanostructured poly(methyl methacrylate) (PMMA) gradient materials with in situ nanocoating were obtained via self-assembly of semifluorinated hyperbranched polyglycerol amphiphiles (FPG) at the PMMA surface during free-radical MMA bulk polymerisation. The FPG was designed as novel nanoadditive and prepared by etherification of the hydrophilic hyperbranched polyglycerol core with allylether and subsequent quantitative addition of the hydroand oleophobic 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octane-1-thiol to the double bond end groups. As a result of the FPG self-assembly, a fluorine-containing nanocoating, with an average thickness of 150 to 200 nm at the PMMA surface, was detected by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) of an 4 He + beam. The resulting nanocoating formation was driven by the interactions of the perfluorohexyl end groups and the in situ phase separation with increasing conversion of the MMA polymerisation. The FPG nanocoating consisted of a nanolayered substructure composed of alternating fluorine-containing and fluorine-free layers with an average thickness of 3-5 nm, which was evidenced by atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). Very small amounts of the FPG amphiphile, typically less than 3 wt.-% added to PMMA, were found to be sufficient to achieve the in situ nanocoating formation at the PMMA surface. The surfaces of the PMMA/FPG surface gradient materials were water and oil repellent.

The microstructure and morphology of stereoblock polypropylenes containing sequences of isotactic (i) and syndiotactic (s) polypropylene (PP) were studied by 13C NMR spectroscopy, wide angle x-ray scattering (WAXS), size exclusion chromatography (SEC) combined with FT-IR analysis of the fractions, and atomic force microscopy. The 13C NMR spectra show the presence of long stereoregular sequences in the respective stereoblock polypropylene which are able to form the crystal modification known from the respective stereoregular homopolymers as revealed by WAXS measurements. A bimodal molar-mass distribution is detected by SEC. All SEC fractions contain i-PP and s-PP sequences, proven by FT-IR spectroscopy. It is shown by atomic-force microscopy that the stereoblock polypropylene, synthesized by homopolymerization of propylene using iso- and syndiotactic catalysts, form a microphase-separated morphology. The microphase separation is preserved also after treatment with hot toluene. A parallel investigation was ...

The melt miscibility of stereoregular polypropene with branched ethene homopolymers, prepared by Ni- and Pd-based catalysts, was investigated by means of transmission electron microscopy, atomic force microscopy, and differential scanning calorimetry. The number of branched C atoms per 1000 C atoms, referred to as degree of branching (DB), was varied from 6 to 112. Miscibility increases with increasing DB. Blends of branched ethene homopolymers and poly(ethene-co-1-octene) with isotactic (i-PP) and syndiotactic polypropylene (s-PP) were compared and show slightly improved miscibility for s-PP. For DBs of 98 and 112 partial miscibility with polypropene was found. The miscibility of polyethenes with longer branches resemble that of polyethene/1-octene copolymers, whereas short branched polyethenes behave more like polyethene/1-butene copolymers.

The crystallization behavior of poly(1-butene) (P1b) was investigated by polarized light microscopy (PLM), atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS), dilatometry, and also by time- and temperature-resolved small-angle X-ray scattering experiments (SAXS). Observations in the PLM indicate a temperature-dependent change in the mechanism of crystallization. When crossing a certain critical crystallization temperature, the morphology changes from spherulites to quadratic, platelike single crystals. Investigations of samples with different molar mass show that the transition temperature is molar mass-dependent; on decreasing the molar mass the transition shifts to lower temperatures. As proved by WAXS, both the spherulites and the single crystals are of the metastable form II. The morphological change is also observed in AFM images obtained after a rapid cooling of the samples to room temperature; the difference in the morphological appearance is preserved through the transformation from...

New acrylic nanocomposites consisting of methyl methacrylate (MMA)/n-dodecylmethacrylate (LMA) copolymers and intercalated layered silicates were prepared. The silicates were based upon bentonite which was rendered organophilic by ion exchange with N,N,N,N,-dioctadecyl dimethyl ammonium ions. Morphological, thermal, mechanical, and optical properties were examined as a function of both organophilic bentonite and LMA content. Addition of LMA improved the compatibility between the layered silicate and the acrylic matrix, thus promoting bentonite intercalation and formation of anisotropic laminated silicate nanoparticles of an average diameter of 18 nm, average length of 450 nm, and interlayer distance of 4.8 nm, as determined by WAXS, TEM, and AFM. Addition of 2–10 wt % of intercalated layered silicate accounted for improved stiffness/toughness balance, higher glass temperature, and enhanced thermal stability, with respect to the properties of the corresponding MMA/LMA copolymer. As a result of the addition of LMA, translucent acrylic nanocomposites were obtained. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 396–405, 2000

Blends of isotactic polypropene (i-PP) with random ethene/1-butene (EB) copolymers containing 10, 24, 48, 58, 62, 82, and 90 wt % 1-butene were prepared in order to examine the influence of the EB molecular architecture on the morphology development as well as on the thermal and mechanical properties. Compatibility between i-PP and EB increased with increasing 1-butene content in EB to afford single-phase blends at a 1-butene content exceeding 82 wt %. The morphology was investigated using AFM and TEM. Improved compatibility accounted for enhanced EB dispersion and interfacial adhesion. Highly flexible as well as stiff blends with improved toughness were obtained. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 838–848, 1999

50/50 wt % blends of isotactic polypropene (i-PP) with metallocene-based random poly(ethene-co-1-butene) (PEB) were prepared with 1-butene content varied from 52 to 100 wt %. The melt miscibility of the i-PP/PEB blends as a function of 1-butene content was studied by investigating the morphologies of the blends in the solid state by phase-imaging tapping mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). It was found that i-PP is melt miscible with PEB for 1-butene contents of ≈88 wt % (miscibility window). Differential scanning calorimetry (DSC) analysis showed a slower and hindered i-PP crystallization in the miscible or partially miscible blends. Intensive investigations on the apparently one-phase blend were performed by optical microscopy, small-angle X-ray scattering and dynamic mechanical analysis.

Isotactic polypropylene blends with 0–20 vol % thermoplastic elastomers were prepared to study the influence of elastomer particle size on mechanical properties. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene (SEBS) was used as thermoplastic elastomer. SEBS particle size, determined by means of transmission electron and atomic force microscopy, was varied by using polypropylene and SEBS of different molecular weight. With increasing polypropylene molecular weight and, consequently, melt viscosity and decreasing SEBS molecular weight, SEBS particle size decreases. Impact strength of pure polypropylene is almost independent of molecular weight, whereas impact strength of polypropylene blends increases strongly with increasing polypropylene molecular weight. The observed sharp brittle–tough transition is caused by micromechanical processes, mostly shear yielding, especially occurring below a critical interparticle distance. The interparticle distance is decreasing with decreasing SEBS particle size and increasing volume fraction. If the polypropylene matrix ligament between the SEBS particles is thinner than 0.27 μm, the blends become ductile. Stiffness and yield stress of polypropylene and polypropylene blends increase with increasing polypropylene molecular weight in the same extent, and are consequently only dependent on matrix properties and not on SEBS particle size. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1891–1901, 1998

The vapor induced modification of bulk samples of syndiotactic random copolymers of styrene and p-n-butylstyrene is studied by wide-angle X-ray scattering and light microscopy. Two samples with p-n-butylstyrene contents of 4 and 11 mol% are compared. It is shown that treatment with CHCl3 leads to the formation of a clathrate modification similar to that of neat syndiotactic polystyrene. The change of the surface topography of the copolymers as a result of CHCl3 vapor exposition is studied by tapping-mode/height-mode atomic force microscopy.

Superstructure formation during crystallization has been examined as a function of isotactic poly(propene) and poly(ethene) molecular architectures, tailored by means of metallocene catalyzed propene polymerization, metallocene catalyzed ethene/alk-1-ene copolymerization, and nickel-catalyzed migratory insertion polymerization of ethene to afford methyl-branched poly(ethene) without using comonomers. The role of steric irregularities in the chain resulting from false insertion in stereoselective polymerization or from short chain branching, respectively, was investigated. Randomly distributed regio- and stereo-regularities in isotactic poly(propene) chains and variation of crystallization temperature were the key to controlled poly(propene) crystallization and predominant formation of the γ-modification. Poly(propene) melting temperature increased with increasing isotactic segment length between stereo- and regio-irregularities. Superstructures of isotactic γ-poly(propene) were analyzed by means of light and atomic force microscopy. Both types of short-chain branched poly(ethene)s, prepared by ethene/oct-1-ene copolymerization and migratory insertion homopolymerization, showed similar dependence of melting temperature on the degree of branching, calculated as the number of branching carbon atoms per 1000 carbon atoms. Phase transitions were monitored by means of wide angle X-ray scattering and pressure–volume–temperature measurements. Atomic force microscopy was applied to image both lamella- and fringed micelle-type superstructures as a function of the degree of branching.

The occurrence of banded spherulites in blends of poly(epsilon-caprolactone) with poly(styrene-ran-acrylonitrile) is studied by means of optical-, scanning electron-, environmental scanning electron-, and atomic force-microscopy as well as small-angle X-ray scattering. The measurements reveal that lamellae are confined in fibrils that bend periodically from the center of spherulites in a radial direction. The fibrils show also a regular spacing in the lateral direction. Single bent lamellae can be observed by atomic force microscopy after permanganic etching. The enrichment of amorphous material near to the growth front of the spherulites can be directly observed by polarized light microscopy after temperature jump experiments. The excluded amorphous material on the surface of the growing spherulites has the shape of droplets. This might be the main reason for the initiation of the bending process because the result is a non-uniform stress distribution acting on the growing lamellae at the interface between spherulites and the surrounding melt. The amorphous material of the blends can be found in three areas as observed by small-angle X-ray scattering experiments and microscopical methods: i) between the lamellae, ii) excluded from the interlamellar region but within the spherulite, and iii) for high contents of non-crystallizable material, it can be excluded from the spherulite. The banding periodicity of spherulites as a function of the crystallization temperature can be described in terms of two models, based either i) on the inherent twisting of lamellae perpendicular to the axis of a screw dislocation or ii) on the dependence of the diffusion of amorphous material away from the growth front of lamellae and the temperature dependence of the rate of crystallization Both models fail at very low supercoolings near to temperatures where the banding disappears completely.