Search

Poly(ether imide) (PEI) is a high-performance polymer with outstanding thermal stability, mechanical strength, and processability, but a critical drawback of poor solvent resistance. Exposure to solvents including chloroform, dimethylformamide, dichloromethane, and N-methyl pyrrolidone severely compromises the mechanical and thermal performances. Herein, we report a method for preparing thermally crosslinked PEI (X-PEI) from azide-terminated PEI (N₃–PEI–N₃) synthesized via a one-pot diazotization–azidation reaction. X-PEI affords unprecedented solvent resistance unpossessed by conventional PEIs, as well as solution processability unrivaled by counterpart high-performance polymers such as polyimide. The glass transition temperature, storage modulus, and swelling ratio correlate positively with crosslinking density, which is determined by the molar mass and azide concentration of N₃–PEI–N₃. This work advances the chemistry of high-performance polymers. The method is generic and applicable to other engineering polymers.

The implementation of the high-capacity Li metal anode in practical batteries has not been successful due to the short lifespan and severe safety concerns resulting primarily from low Coulombic efficiency and Li dendritic growth. Lightweight carbon skeletons are considered promising for hosting the lithium metal anode to overcome these limitations. Furthermore, the lithium metal loading must be minimized from the cost and safety standpoint, leading to the need of developing long cycle life “lean Li metal anodes”. Herein, we report a surface ozonolysis approach to homogenize Li nucleation sites and to guide the uniform Li metal deposition on flexible oxygen-enriched lignin-derived carbon membranes (OLCMs). The resulting lean OLCM@Li composite anode allows for stable Coulombic efficiency (>98% over 230 cycles), long cycle life (>1, 000 hr), and small voltage hysteresis (

Non-enzymatic degradation of wood via a chelator-mediated Fenton (CMF) system is the primary method for initial attack in brown rot fungal decomposition of wood, the most common type of fungal degradation of terrestrial carbon biomass on the planet. In this study, the degradation of thin films of cellulose and chitin by a CMF system was investigated and compared to enzymatic hydrolysis. The kinetics of the rapid cellulose and chitin deconstruction and the morphologies of the degraded cellulose and chitin surfaces were studied by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM), respectively. The QCM-D results quantitatively indicated that ~90 wt% of the regenerated cellulose or chitin was capable of being deconstructed by CMF action alone. While enzymatic degradation was consistent with stripping of layers from the surface of the cellulose or chitin films, the CMF process exhibited a pronounced two stage process with a rapid initial depolymerization throughout the films. The initial degradation rates for both model surfaces by the CMF system were faster than enzyme action. This research suggests that the CMF process should be applicable for the deconstruction of a wide variety of polysaccharides over Fenton chemistry alone.

Metal–organic frameworks (MOFs) have shown great promise as efficient CO2 adsorbents, as well as an emerging class of heterogeneous catalysts for conversion of CO2 to other useful chemicals. In this work, we synthesized and characterized two isostructural hafnium-based MOFs, denoted as Hf-VPI-100 (Cu) and Hf-VPI-100 (Ni). Both frameworks demonstrated high catalytic efficiency for cycloaddition of CO2 to epoxides under ambient pressure. In situ PXRD, QCM and DRIFTs have been used to probe the interaction between the guest molecules (CO2/epoxide) and Hf-VPI-100. The crystal structures of these frameworks were preserved during the exposure to CO2 atmosphere up to 20 bar. The epoxide uptake per unit cell of VPI-100 and diffusion coefficients have been calculated by QCM analysis. Comparison of catalytic efficiency between Hf-VPI-100 and the previously reported Zr-based VPI-100, aided by electronic structure calculations revealed that the open metal centers in the metallocyclam act as the primary Lewis acid sites to facilitate the catalytic conversion of CO2.

Residual lignin in pretreated biomass impedes enzymatic hydrolysis. Nonionic surfactants are known to enhance the enzymatic hydrolysis of lignocellulosic biomass but their mechanisms of action are incompletely understood. This study investigates the effect of a nonionic surfactant, Tween 80, on the adsorption of cellulases onto model lignin substrates. Lignin substrates were prepared by spin coating of flat substrates with three different types of lignin: organosolv lignin, kraft lignin, and milled wood lignin. The functional group distributions in the lignins were quantitatively analyzed by 31P NMR spectroscopy. The surface energies and surface roughnesses of the substrates were determined by contact angle measurements and atomic force microscopy, respectively. Tween 80 and cellulase adsorption onto the lignin substrates was analyzed with a quartz crystal microbalance with dissipation monitoring. Tween 80 adsorbed rapidly and primarily (≥85%) via dispersion interactions onto the lignin substrates and eff...

Chemical warfare agent (CWA) sorption into polymeric coatings is an important consideration for preventing human exposure to CWAs. The specific nature of CWA–polymer interactions greatly influences the degree of gas uptake into a polymeric coating. By uncovering the role the various functional groups in CWAs play during gas sorption, better films and coatings can be engineered. This study utilized a quartz crystal microbalance to measure sulfur mustard (HD) analog (simulant) and hexane vapor uptake into polyurethane films. Analysis of the uptake data with Flory–Huggins theory yielded interaction parameter values (χ) between 0.24 and 0.40 for each HD simulant-polyurethane system compared to 0.97 for hexane, revealing the importance of the chlorine and sulfur groups in gas uptake at the thin film interface. We predict similar uptake behavior for HD in polyurethane coatings due to structural similarities between HD and the simulants.

Conventional free radical polymerization and post-alkylation of 4-diphenylphosphino styrene (DPPS) generate a new class of high-molecular-weight phosphonium-containing homopolymers with tunable thermal, viscoelastic, and wetting properties. Post-alkylation and subsequent anion exchange provide an effective method for tuning Tg values and thermal stability as a function of alkyl chain length and counteranion selection (X(-) , BF4 (-) , TfO(-) , and Tf2 N(-) ). Rheological characterization facilitates the generation of time-temperature-superposition (TTS) pseudomaster curves and subsequent analysis of frequency sweeps at various temperatures reveals two relaxation modes corresponding to long-range segmental motion and the onset of viscous flow. Contact angle measurements reveal the influence of counteranion selection on wetting properties, revealing increased contact angles for homopolymers containing nucleophilic counteranions. These investigations provide fundamental insight into phosphonium-containing polymers, aiming to guide future research and applications involving electro-active polymeric devices.

Cationic derivatives of cellulose and other polysaccharides are attractive targets for biomedical applications due to their propensity for electrostatically binding with anionic biomolecules, such as nucleic acids and certain proteins. To date, however, relatively few practical synthetic methods have been described for their preparation. Herein, we report a useful and efficient strategy for cationic cellulose ester salt preparation by the reaction of 6-bromo-6-deoxycellulose acetate with pyridine or 1-methylimidazole. Dimethyl sulfoxide solvent favored this displacement reaction to produce cationic cellulose acetate derivatives, resulting in high degrees of substitution (DS) exclusively at the C-6 position. These cationic cellulose derivatives bearing substantial, permanent positive charge exhibit surprising thermal stability, dissolve readily in water, and bind strongly with a hydrophilic and anionic surface, supporting their potential for a variety of applications such as permeation enhancement, mucoadhesion, and gene or drug delivery. Expanding upon this chemistry, we reacted a 6-imidazolyl-6-deoxycellulose derivative with 1,3-propane sultone to demonstrate the potential for further elaboration to regioselectively substituted zwitterionic cellulose derivatives.

Hydroxypropyl-cellulose (HPC) is a surface-active, non-digestible polysaccharide, commonly used in food emulsions as thickener and/or emulsifier. Due to these dual characteristics, HPC is a potential ingredient to modulate lipid digestion. Since bile salts (BS) are key players during lipid digestion, the aim of this work was to investigate the impact that interactions of HPC with BS has on the digestion of emulsified lipids. We studied the effect of two BS species differing in bile-acid moiety, sodium-taurocholate (NaTC) and sodium-taurodeoxycholate (NaTDC). A Quartz-Crystal-Microbalance (QCM-D) was used to evaluate HPC-BS interfacial interactions during the sequential and simultaneous adsorption of both components at a hydrophobic surface, while microDifferential-Scanning-Calorimetry was used to examine bulk interactions. In vitro lipid digestion was studied by using a pH-stat method. Results showed that, under fed-state conditions, NaTDC micelles were more effective at displacing a pre-adsorbed HPC layer from the surface than NaTC monomers. Nevertheless, HPC was resistant to complete displacement by both BS. Additionally, HPC was more susceptible to interact with NaTDC in the bulk, compared to NaTC, which made the adsorption more competitive for NaTDC. The reduced amount of free NaTDC in solution could explain the delayed lipolysis shown by HPC-stabilized emulsions when NaTDC was used to simulate duodenal conditions. These findings show that the delay of lipid digestion by HPC is due to the combined effect of HPC-BS interfacial and bulk interactions, with BS-binding in solution mostly contributing to this effect, and the BS molecular and micellar structure playing essential roles on both situations. Virginia Agriculture Experiment Station; Hatch Program of the National Institute of Food and Agriculture (NIFA), USDA The authors acknowledge the financial support from the Virginia Agriculture Experiment Station and the Hatch Program of the National Institute of Food and Agriculture (NIFA), USDA.

Thermodynamic phase behavior of poly(e-caprolactone)-b-poly(tert-butyl acrylate) (PCL-b-PtBA) block copolymers at the Air/Water (A/W) interface was studied by analyzing surface pressure-area isotherms. Optical microscopy and atomic force microscopy were utilized to reveal the morphological features of three-dimensional domains grown in the Langmuir films. A series of PCL-b-PtBA block copolymers synthesized for this study share the same PCL block with molecular weight of Mn = 7.5 kg•mol−1, while the length of PtBA blocks varies. Homogeneous Langmuir monolayers were formed at the A/W interface before reaching the dynamic collapse pressure of PCL blocks. The growth of PCL flat-on crystalline domains predominately took place during the plateau regime after the collapse transition, though nucleation process occurred prior to the collapse transition. The tethered PtBA blocks remain as a monolayer at the A/W interface prior to the second collapse pressure at ∼ 24 mN•m−1, which is comparable to the collapse pressure of PtBA homopolymer monolayer. Depending on the length of PtBA blocks, the block copolymer crystals exhibit morphological features from distorted hexagonal shape, truncated parallelogram, dendrites with defects, stripes, and nano-scale domains, suggesting that the tethered amorphous PtBA block significantly reduced the mobility and packing efficiency of PCL blocks during the crystallization of PCL-b-PtBA copolymers at the A/W interface.

Understanding the binder–powder interaction and primitive formation is critical to advancing the binder jetting Additive Manufacturing process and improving the accuracy, precision, and mechanical properties of the printed parts. In this work, the authors propose an experimental approach based on sessile drop goniometry on a powder substrate to characterize the binder wetting powder process. As a binder drop penetrates into a prepared powder substrate, the dynamic contact angle formed in powder pores is calculated based on the measured binder penetration time, and the binder penetration depth is measured from the binder-powder granule retrieved from the powder substrate. Coupled with models of capillary flow, the technique provides a fundamental understanding of the binder–powder interaction that determines the material compatibility and printing parameters in binder jetting. Enabled by this gained understanding, it was determined that suspending nanoparticles in a binder could increase the capillary-driven penetration depth, which was then reduced by the further increase of the nanoparticle solid loading and resultant binder viscosity.

Surface-associated microbial communities, known as biofilms, pose significant challenges in clinical and industrial settings. Micro-/nanoscale substratum surface features have been shown to disrupt firm adhesion of planktonic microbes to surfaces, thereby interfering with the earliest stage of biofilm formation. However, the role of geometry and size of surface features in microbial retention is not completely understood. In this study, we developed a biophysical model that describes the changes in the total free energy (adhesion energy and stretching energy) of an adherent Candida albicans cell on nanofiber-coated surfaces as a function of the geometry (i.e., diameter) and configuration (i.e., interfiber spacing) of the surface features (i.e., nanofibers). We then introduced a new nondimensional parameter, Π, to represent the ratio of cell rigidity to cell-substratum interfacial energy. We show that the total free energy is a strong function of topographical feature size at higher Π and lower spacing values. To confirm our biophysical model predictions, we performed 24 h dynamic retention assays and quantified cell attachment number density on surfaces coated with highly ordered polystyrene nanofibers. We show that the total free energy of a single adherent cell on a patterned surface is a key determinant of microbial retention on that surface. The cell attachment density trend closely correlates with the predictions based on the adherent single-cell total energy. The nanofiber coating design (1.2 μm diameter, 2 μm spacing) that maximized the total energy of the adherent cell resulted in the lowest microbial retention. We further demonstrate the utility of our biophysical model by showing close correlation between the computed single-cell total free energy and biofilm nucleation on fiber-coated urinary and central venous catheters of different materials. This biophysical model could offer a powerful new paradigm in ab initio design of patterned surfaces for controlled biofilm growth for medical applications and beyond.

As a model system, thin films of trisilanolphenyl-POSS (TPP) and two different number average molar mass (5 and 23 kg mol−1) poly(t-butyl acrylate) (PtBA) were prepared as blends by Langmuir–Blodgett film deposition. Films were characterized by ellipsometry. For comparison, bulk blends are prepared by solution casting and the samples are characterized via differential scanning calorimetry. The increase in Tg as a function of TPP content for bulk high and low molar mass samples are in the order of ∼10 °C. Whereas bulk Tg shows comparable increases for both molar masses (∼10 °C), the increase in surface Tg for higher molar mass PtBA is greater than for low molar mass (∼22 °C vs. ∼10 °C). Nonetheless, the total enhancement of Tg is complete by the time 20 wt % TPP is added without further benefit at higher nanofiller loads. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 175–182

Single wavelength ellipsometry measurements at Brewster's angle and in multiple incident media provide a powerful technique for characterizing ultrathin (

(1,3)(1,4)-β-D-Glucan (mixed-linkage glucan or MLG), a characteristic hemicellulose in primary cell walls of grasses, was investigated to determine both its role in cell walls and its interaction with cellulose and other cell wall polysaccharides in vitro. Binding isotherms showed that MLG adsorption onto microcrystalline cellulose is slow, irreversible, and temperature-dependent. Measurements using quartz crystal microbalance with dissipation monitoring showed that MLG adsorbed irreversibly onto amorphous regenerated cellulose, forming a thick hydrogel. Oligosaccharide profiling using endo-(1,3)(1,4)-β-glucanase indicated that there was no difference in the frequency and distribution of (1,3) and (1,4) links in bound and unbound MLG. The binding of MLG to cellulose was reduced if the cellulose samples were first treated with certain cell wall polysaccharides, such as xyloglucan and glucuronoarabinoxylan. The tethering function of MLG in cell walls was tested by applying endo-(1,3)(1,4)-β-glucanase to wall samples in a constant force extensometer. Cell wall extension was not induced, which indicates that enzyme-accessible MLG does not tether cellulose fibrils into a load-bearing network.

Elucidating the interactions between crystalline chitin and various biomacromolecules is of fundamental importance for designing and fabricating chitin-based biomaterials. This work highlights a simple method to prepare ultrathin films of chitin nanocrystals (chitin NC) by spincoating chitin NCs from a colloidal suspension onto a gold surface modified by an amine-terminated self-assembled monolayer. Atomic force microscopy confirmed that chitin NC films are reasonably smooth and homogeneous, and quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments demonstrated that chitin NC films have twice as much water as amorphous regenerated chitin (RChitin) films of similar thickness. QCM-D data also showed that chitinase-catalyzed hydrolysis of chitin NC films was much slower than that of RChitin films. Chitinase not only degraded, but also caused the swelling of the chitin nanocrystals. BSA adsorption studies demonstrated that chitin NC films have high protein loading capacity, and thus show potential applications for enzyme immobilization.

This study reports polyhedral oligomeric silsesquioxane (POSS)-based hybrid fibers of architectural hierarchy and compositional heterogeneity. The kinetic arrest of substantial POSS content in the fibers was attributed to rapid solvent evaporation that retarded the phase separation of liquid jet. It provides new insight into the design of novel heterogeneous materials.

This work highlights a real-time and label-free method to monitor the dehydrogenative polymerization of monolignols initiated by horseradish peroxidase (HRP) physically immobilized on surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D). The dehydrogenative polymer (DHP) films are expected to provide good model substrates for studying ligninolytic enzymes. The HRP was adsorbed onto gold or silica surfaces or onto and within porous desulfated nanocrystalline cellulose films from an aqueous solution. Surface-immobilized HRP retained its activity and selectivity for monolignols as coniferyl and p-coumaryl alcohol underwent dehydrogenative polymerization in the presence of hydrogen peroxide, whereas sinapyl alcohol polymerization required the addition of a nucleophile. The morphologies of the DHP layers on the surfaces were investigated via atomic force microscopy (AFM). Data from QCM-D and AFM showed that the surface-immobilized HRP-initiated dehydrogenative polymerization of monolignols was greatly affected by the support surface, monolignol concentration, hydrogen peroxide concentration, and temperature.

Chitinases are widely distributed in nature and have wide-ranging pharmaceutical and biotechnological applications. This work highlights a real-time and label-free method to assay Chitinase activity via a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The chitin substrate was prepared by spincoating a trimethylsilyl chitin solution onto a silica substrate, followed by regeneration to amorphous chitin (RChi). The QCM-D and AFM results clearly showed that the hydrolysis rate of RChi films increased as Chitinase (from Streptomyces griseus) concentrations increased, and the optimal temperature and pH for Chitinase activity were around 37 °C and 6-8, respectively. The Chitinase showed greater activity on chitin substrates, having a high degree of acetylation, than on chitosan substrates, having a low degree of acetylation.

Pretreatment of lignocellulosic biomass with sulfuric acid may leave sulfate groups on its surface that may hinder its biochemical conversion. This study investigates the effects of sulfate groups on cellulase adsorption onto cellulose substrates and the enzymatic hydrolysis of these substrates. Substrates with different sulfate group densities were prepared from H2SO4- and HCl-hydrolyzed and partially and fully desulfated cellulose nanocrystals. Adsorption onto and hydrolysis of the substrates was analyzed by quartz crystal microbalance with dissipation monitoring (QCM-D). The surface roughness of the substrates, measured by atomic force microscopy, increased with decreasing sulfate group density, but their surface accessibilities, measured by QCM-D H2O/D2O exchange experiments, were similar. The adsorption of cellulose binding domains onto sulfated substrates decreased with increasing sulfate group density, but the adsorption of cellulases increased. The rate of hydrolysis of sulfated substrates decreased with increasing sulfate group density. The results indicated an inhibitory effect of sulfate groups on the enzymatic hydrolysis of cellulose, possibly due to nonproductive binding of the cellulases onto the substrates through electrostatic interactions instead of their cellulose binding domains.

Chitin is the second most abundant biopolymer and insight into its natural synthesis, enzymatic degradation, and chemical interactions with other biopolymers is important for bioengineering with this renewable resource. This work is the first report of smooth, homogeneous, ultrathin chitin films, opening the door to surface studies of binding interactions, adsorption kinetics, and enzymatic degradation. The chitin films were formed by spincoating trimethylsilyl chitin onto gold or silica substrates, followed by regeneration to a chitin film. Infrared and X-ray photoelectron spectroscopy, X-ray diffraction, ellipsometry, and atomic force microscopy were used to confirm the formation of smooth, homogeneous, and amorphous chitin thin films. Quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments showed these films swelled with 49% water by mass. The utility of these chitin films as biosensors was evident from QCM-D and surface plasmon resonance studies that revealed the adsorption of a bovine serum albumin monolayer.

Model cellulose surfaces have attracted increasing attention for studying interactions with cell wall matrix polymers and as substrates for enzymatic degradation studies. Quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange studies showed that the water content of regenerated cellulose (RC) films was proportional to the film thickness (d) and was consistent with about five water molecules per anhydroglucose unit. Sulfated nanocrystalline cellulose (SNC) and desulfated nanocrystalline cellulose (DNC) films had comparable water contents and contained about five times more water than RC films. A cellulase mixture served as a probe for studies of substrate accessibility and degradation. Cellulase adsorption onto RC films was independent of d, whereas degradation times increased with d. However, adsorption onto SNC and DNC films increased with d, whereas cellulase degradation times for DNC films were independent of studied d. Enhanced access to guest molecules for SNC and DNC films revealed they are more porous than RC films.

Homologous dicarboxyl dendritic amphiphiles-RCONHC(CH(3))(CH(2)CH(2)COOH)(2), 4(n); and ROCONHC(CH(3))(CH(2)CH(2)COOH)(2), 5(n), where R=n-C(n)H(2)(n)(+1) and n=13-22 carbon atoms-were synthesized. Critical micelle concentrations (CMCs) in aqueous triethanolamine solutions and at pH 7.4 were measured along with hemolytic activity (effective concentrations, EC(10)) in phosphate-buffered saline (PBS). LogCMC showed a linear dependence on chain length (n); the longest chain in each series had the lowest CMC-in triethanolamine: 4(21), 180μM and 5(22), 74μM and at pH 7.4: 4(21), 78μM and 5(22), 33μM. These two series, 4(n) and 5(n), and three series of homologous tricarboxyl dendritic amphiphiles-RCONHC(CH(2)CH(2)COOH)(3), 1(n); ROCONHC(CH(2)CH(2)COOH)(3), 2(n); RNHCONHC(CH(2)CH(2)COOH)(3), 3(n), where R=n-C(n)H(2)(n)(+1) and n=13-22 carbon atoms-were tested for growth inhibition of Staphylococcus aureus strain ATCC 6358 and methicillin-resistant S. aureus (MRSA) strain ATCC 43330 by microdilution in 0.1-strength brain heart infusion broth (BHIB). Amphiphiles 4(19), 4(21), 5(18), and 5(20) showed the strongest antibacterial activity (2.2-3.4μg/mL) against S. aureus (vancomycin, MIC=0.25μg/mL). These four plus 1(21), 2(20), 2(22), and 3(20) exhibited the strongest antibacterial activity (1.7-6.8μg/mL) against MRSA (vancomycin, MIC=0.25μg/mL). The MICs of these amphiphiles against six clinical MRSA were similar to those against the ATCC strain. In PBS, EC(10)s of the most active homologues ranged from 7 to 18μg/mL and 18 to 220μg/mL for di- and tricarboxyl dendritic amphiphiles, respectively. To assess the potential safety of using dendritic amphiphiles as drugs, measurements of micellar and hemolytic properties were conducted in the same medium (full-strength BHIB) that was used for antibacterial activity. The CMCs (9-36μg/mL, ∼18-72μM) of ten amphiphiles were measured by microdilution (log2 progression) with dye-covered beads. The EC(10)s were similar to those in PBS. The MICs of most amphiphiles (14-72μg/mL) and vancomycin (1.1-2.2μg/mL) against both S. aureus and MRSA increased significantly compared to the MICs measured in 0.1-strength BHIB. The one exception, 5(18), had an MIC against S. aureus of 1.1μg/mL compared to vancomycin (2.2μg/mL). With CMC (9-18μg/mL) and EC(10) (16μg/mL) values higher than the MIC, 5(18) was discovered as a lead for further development.

In this study, correlations between the charge density of adsorbed cationic xylans and the mechanical properties of selected pulps are discussed. Hand-sheet experiments were carried out using birch sulfate pulp and spruce sulfite pulp after the adsorption of 2-hydroxypropyl-trimethylammonium-4-O-methylglucuronoxylans (HPMAGXs) with different molar degrees of substitution (MS) in the range of 0.06–0.19. The charge density of the HPMAGX in water was determined by polyelectrolyte titration. Properties such as the tensile and burst index increased after HPMAGX addition and showed an optimum depending on the MS, which was 0.1 for both pulps. Other properties like the tear-index or the specific volume changed depending on the pulp. Beating experiments were also performed and showed an increasing tensile index of birch kraft pulp in the range of 53.7 to 85.7 N m g−1 for a beating time of 10 min. The adsorption of HPMAGXs with different MS onto thiol-based self-assembled monolayers (SAMs) on gold and regenerated cellulose surfaces were studied using surface plasmon resonance (SPR). Electrostatic interactions were found to be the most important factors affecting HPMAGX adsorption, and a strong correlation between HPMAGX adsorption onto carboxyl-terminated SAMs (SAM-COOH) and paper strength when HPMAGX was used as a papermaking additive was observed.

A high-speed vibration milling (HSVM) method was applied to synthesize water dispersible single-walled carbon nanohorns (SWNHs). Highly reactive free radicals (HOOCCH2CH2•) produced from an acyl peroxide under HSVM conditions react with hydrophobic SWNHs to produce a highly water dispersible derivative (f-SWNHs), which has been characterized in detail by spectroscopic and microscopic techniques together with thermogravimetric analysis (TGA) and dynamic light scattering (DLS). The carboxylic acid functionalized, water-dispersible SWNHs material are versatile precursors that have potential applications in the biomedical area.

Surface plasmon resonance studies showed pullulan cinnamates (PCs) with varying degrees of substitution (DS) adsorbed onto regenerated cellulose surfaces from aqueous solutions below their critical aggregation concentrations. Results on cellulose were compared to PC adsorption onto hydrophilic and hydrophobic self-assembled thiol monolayers (SAMs) on gold to probe how different interactions affected PC adsorption. PC adsorbed onto methyl-terminated SAMs (SAM-CH(3))cellulosehydroxyl-terminated SAMs (SAM-OH) for high DS and increased with DS for each surface. Data for PC adsorption onto cellulose and SAM-OH surfaces were effectively fit by Langmuir isotherms; however, Freundlich isotherms were required to fit PC adsorption isotherms for SAM-CH(3) surfaces. Atomic force microscopy images from the solid/liquid interfaces revealed PC coatings were uniform with surface roughnesses2 nm for all surfaces. This study revealed hydrogen bonding alone could not explain PC adsorption onto cellulose and hydrophobic modification of water-soluble polysaccharides was a facile strategy for their conversion into surface modifying agents.

A new magnetic resonance imaging (MRI) contrast agent based on the trimetallic nitride templated (TNT) metallofullerene Gd(3)N@C(80) was synthesized by a facile method in high yield. The observed longitudinal and transverse relaxivities r(1) and r(2) for water hydrogens in the presence of the water-soluble gadofullerene 2 Gd(3)N@C(80)(OH)(approximately 26)(CH(2)CH(2)COOM)(approximately 16) (M = Na or H) are 207 and 282 mM(-1) s(-1) (per C(80) cage) at 2.4 T, respectively; these values are 50 times larger than those of Gd(3+) poly(aminocarboxylate) complexes, such as commercial Omniscan and Magnevist. This high (1)H relaxivity for this new hydroxylated and carboxylated gadofullerene derivative provides high signal enhancement at significantly lower Gd concentration as demonstrated by in vitro and in vivo MRI studies. Dynamic light scattering data reveal a unimodal size distribution with an average hydrodynamic radius of ca. 78 nm in pure water (pH = 7), which is significantly different from other hydroxylated or carboxylated fullerene and metallofullerene derivatives reported to date. Agarose gel infusion results indicate that the gadofullerene 2 displayed diffusion properties different from those of commercial Omniscan and those of PEG5000 modified Gd(3)N@C(80). The reactive carboxyl functionality present on this highly efficient contrast agent may also serve as a precursor for biomarker tissue-targeting purposes.

Phase separation in thin film blends of poly(tert-butyl acrylate) (PtBA) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP), is studied as functions of annealing temperature and time, using reflected light optical microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The results demonstrate that the PtBA/TPP blend system confined to thin films ( approximately 90 nm) exhibits lower critical solution temperature (LCST) behavior with a critical temperature of approximately 70 degrees C and a critical composition of 60 wt % PtBA with insignificant dewetting at the phase boundary. Off-critical spinodal behavior is observed for 58 and 62 wt % PtBA blend films. Phase separation by nucleation and growth is observed for all compositions outside the window between 58 and 62 wt % PtBA. The temporal evolution of spinodal decomposition in 60 wt % PtBA blend films is explored at annealing temperatures of 75, 85, 95, and 105 degrees C. The morphological evolution in 60 wt % PtBA blend films is similar for all experimental temperatures (75, 85, 95, and 105 degrees C) with the expected shorter time scales for phase evolution at higher annealing temperatures. Fast Fourier transforms of optical micrographs reveal that these blend films immediately undergo phase separation by spinodal decomposition during temperature jump experiments. Power law scaling for the characteristic wavevector with time (q approximately t(n) with n approximately -1/4 to -1/3) for domain growth during the early stages of phase separation yields to domain pinning at the later stages for 60 wt % PtBA blend films annealed at 75, 85, and 95 degrees C. In contrast, domain growth is pinned over the entire experimental time scale for 60 wt % PtBA blend films annealed at 105 degrees C.

Poly(epsilon-caprolactone) (PCL) samples with number average molar masses (Mn) ranging from 3.5 to 36 kg.mol-1 exhibit molar mass dependent nucleation and growth of crystals, crystal morphologies, and melting properties at a temperature of 22.5 degrees C in Langmuir films at the air/water (A/W) interface. At surface area per monomer, A, greater than approximately 0.37 nm2.monomer-1, surface pressure, Pi, and surface elasticity exhibit molar mass independent behavior that is consistent with a semidilute PCL monolayer. In this regime, the scaling exponent indicates that the A/W interface is a good solvent for the liquid-expanded PCL monolayers. Pi-A isotherms show molar mass dependent behavior in the vicinity of the collapse transition, i.e., the supersaturated monolayer state, corresponding to the onset of the nucleation of crystals. Molar mass dependent morphological features for PCL crystals and their subsequent crystal melting are studied by in situ Brewster angle microscopy during hysteresis experiments. The competition between lower segmental mobility and a greater degree of undercooling with increasing molar mass produces a maximum average growth rate at intermediate molar mass. This behavior is analogous to spherulitic growth in bulk PCL melts. The plateau regions in the expansion isotherms represent the melting process, where the polymer chains continuously return to the monolayer state. The magnitude of Pi for the plateau during expansion decreases with increasing molar mass, indicating that the melting process is strongly molar mass dependent.

Combining two non-surface-active building blocks, oligomeric poly(ethylene glycol) (PEG) and a completely hydrophobic polyhedral oligomeric silsesquioxane (POSS) cage, creates amphiphilic telechelic polymers (POSS−PEG−POSS), which exhibit surface activity at the air/water (A/W) interface. POSS moieties serve as the hydrophobic groups for hydrophilic PEG chains of different number-average molar mass (1, 2, 3.4, 8, and 10 kg mol-1). For short PEG chains (1, 2, and 3.4 kg mol-1), insoluble monolayers form, whereas POSS end groups were not sufficiently hydrophobic to keep higher molar mass hydrophilic PEG blocks (8 and 10 kg mol-1) at the A/W interface. Thermodynamic analyses of the 1, 2, and 3.4 kg mol-1 POSS−PEG−POSS via surface pressure−area per monomer isotherms indicate that the POSS end groups reside at the A/W interface and that the PEG chains are squeezed into the subphase with increasing surface pressure. This conclusion is supported by X-ray reflectivity studies on Y-type Langmuir−Blodgett multilaye...

Thermodynamic analyses of surface pressure-area (P-A) isotherms and Brewster angle microscopy (BAM) reveal that poly(e-caprolactone) (PCL) with a weight average molar mass of Mw ¼ 10 kg mol � 1 and polydispersity index of Mw/Mn ¼ 1.25 and poly(t-butyl acrylate) (PtBA, Mw ¼ 25.7 kg mol � 1 ; Mw/Mn ¼ 1.07) form compatible blends as Langmuir films below the dynamic collapse transition for PCL at P ¼ 11 mN m � 1 . For PCL-rich blends, in situ BAM studies reveal growth of PCL crystals for compression past the PCL collapse transition. PCL crystals grown in the plateau regime of the P-A isotherm exhibit a dendritic morphology presumably resulting from the rejection of PtBA from the growing PCL crystals and hindered dif- fusion of PCL from the surrounding monolayer to the crystal growth fronts. The abil- ity to transfer the PCL dendrites as Langmuir-Schaefer films onto silicon substrates spincoated with a polystyrene layer facilitates detailed morphological characterization by optical and atomic force microscopy (AFM). AFM reveals that the dendritic branching occurs along the {100} and {110} sector boundaries and is essentially inde- pendent of composition. AFM also reveals that the average thickness of PCL den- drites formed at room temperature (22.5 8C), � 7-8 nm, is comparable with that of PCL crystals grown from single-component PCL Langmuir films and spincoated thin films. In contrast, for PtBA-rich blend films PCL crystallization is suppressed. These findings establish PCL blends as an ideal system for exploring the interplay between chain diffusion and crystal growth in a two-dimensional confined geometry. V C 2007

The surface viscoelasticity of poly(1-alkylene-co-maleic acid) (PXcMA) with side chains varying from C4 to C16 was investigated at the air/water interface using the technique of surface light scatt...

Atomic force microscopy, reflection absorption infrared spectroscopy, and X-ray reflectivity studies reveal that poly(L-lactic acid) molecules in Langmuir-Blodgett (LB) films exist as 10(3) helices over nearly the entire length of the polymer chain. This feature gives rise to LB films with highly ordered nanoscale smectic liquid crystalline-like surface patterns with low surface roughness and lamellar spacings that scale with molar mass. These studies provide a new approach for controlling surface morphology with a biodegradable polymer commonly used for drug delivery and tissue engineering.

Surface pressure-induced crystallization of poly(epsilon-caprolactone) (PCL) from a metastable region of the surface pressure-area per monomer (Pi-A) isotherm in Langmuir monolayers at the air/water (A/W) interface has been captured in real time by Brewster angle microscopy (BAM). Morphological features of PCL crystals grown in Langmuir films during the compression process exhibit four fully developed faces and two distorted faces. During expansion of the crystallized film, polymer chains slowly detach from the crystalline domains and diffuse back into the monolayer as the crystals "melt". Typical diffusion-controlled morphologies are revealed by BAM during the melting process as the secondary dendrites melt away faster, that is, at a higher surface pressure than the principal axes. Electron diffraction on Langmuir-Schaefer films suggests that the lamellar crystals are oriented with the polymer chain axes perpendicular to the substrate surface, while atomic force microscopy reveals a crystal thickness of approximately 7.6 nm.

A trisilanol polyhedral oligomeric silsesquioxane (POSS), trisilanolcyclohexyl-POSS (TCyP), has recently been reported to undergo a series of phase transitions from traditional Langmuir monolayers to unique rodlike hydrophobic aggregates in multilayer films that are different from "collapsed" morphologies seen in other systems at the air/water interface. This paper focuses on the phase transitions and morphology of films varying in average thickness from monolayers to trilayers and the corresponding viscoelastic properties of trisilanolcyclohexyl-POSS molecules at the air/water interface by means of surface pressure-area per molecule (Pi-A) isotherms, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) measurements. The morphology studies by BAM reveal that the TCyP monolayer can collapse into different 3D structures by homogeneous or heterogeneous nucleation mechanisms. For homogeneous nucleation, analysis by Vollhardt et al.'s nucleation and growth model reveals that TCyP collapse is consistent with instantaneous nucleation with hemispherical edge growth at Pi = 3.7 mN.m(-1). Both surface storage (Gs') and loss (Gs") moduli obtained by ISR reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms: (A) A viscous liquidlike "monolayer"; (B) a "biphasic regime"between a liquidlike viscous monolayer and a more rigid trilayer; and (C) an elastic solidlike "trilayer". These observations provide interesting insights into collapse mechanisms and structures in Langmuir films.

Blends of amphiphilic poly(dimethylsiloxane) (PDMS) and a model polyhedral oligomeric silsesquioxane (POSS) nanofiller, trisilanolisobutyl-POSS, form homogeneous monolayers at the air/water interface. At high POSS content (>80 wt %), a thermodynamic analysis of surface pressure−area per monomer (Π−A) isotherm data suggests possible phase separation prior to collapse of the PDMS component. PDMS bilayer formation that normally occurs around Π ≈ 8 mN m-1 shifts to higher surface pressures with increasing trisilanolisobutyl-POSS content, indicating compatibility between the two materials in the monolayer state that is analogous to a positive deviation binary liquid mixture. Further compression leads to the collapse of the POSS component into multilayer domains around Π ≈ 17.5 mN m-1. Brewster angle microscopy shows the amount of PDMS in the blend alters the aggregation state of the nonequilibrium solidlike trisilanolisobutyl-POSS domains. These results provide insight into POSS aggregation mechanisms that may...

A trisilanol derivative of polyhedral oligomeric silsesquioxane (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. This paper explores the mono- and multilayer properties of another POSS derivative, trisilanolcyclohexyl-POSS, with pi-A isotherm and Brewster angle microscopy measurements. Results show that with continuously increasing surface concentration via symmetrical compression, trisilanolcyclohexyl-POSS amphiphiles at the air/water interface undergo a series of phase transitions from traditional Langmuir monolayers (one-POSS-molecule thick) to unique rodlike hydrophobic aggregates in multilayer films (approximately eight-POSS-molecules thick) that are dramatically different from "collapsed" morphologies seen in other systems. Stable and hydrophobic rodlike structure formation on water is presumably due to trisilanolcyclohexyl-POSS' unique molecular structure and strong tendency to form intermolecular hydrogen bonds in the solid state. This result is consistent with existing POSS/polymer composite research, which shows that POSS molecules tend to aggregate and crystallize into lamellar nanocrystals.

Using surface quasi-elastic light scattering (SLS), we have studied the monolayer behavior of diblock copolymers A−B, where the A block is polystyrene (PS, surface inactive and water insoluble) and the B block is poly(methyl methacrylate) (PMMA, surface active but water insoluble), at the air/water interface (two-dimensional domain) in terms of the power spectra and the surface viscoelasticity. The polystyrene blocks of the diblock copolymers have similar molecular weights, but the molecular weights of the poly(methyl methacrylate) blocks vary. Substantial changes in viscoelastic behavior accompany changes in surface concentration and can be attributed to differences in molecular packing resulting from micelle formation and surface phase behavior, which are consistent with atomic force microscope (AFM) images of monolayer films transferred from air/water interfaces to solid substrates. The state change is similar to previous results obtained using the dynamic (stepwise compression) method. At submonolayer...

Stable suspensions of superparamagnetic cobalt nanoparticles have been prepared in poly(dimethysiloxane) (PDMS) carrier fluids in the presence of poly[dimethylsiloxane- b -(3-cyanopropyl)methylsiloxane- b -dimethylsiloxane] (PDMS–PCPMS–PDMS) triblock copolymers as steric stabilizers. A series of the polysiloxane triblock copolymers with systematically varied molecular weights were prepared via anionic polymerization using LiOH as an initiator. These copolymers formed micelles in toluene and served as ‘nanoreactors’ for thermal decomposition of the Co 2 (CO) 8 precursor. The nitrile groups on the PCPMS central blocks are thought to adsorb onto the particle surface, while the PDMS endblocks protrude into the reaction medium to provide steric stability. The particle size can be controlled by adjusting the cobalt to copolymer ratio. TEM shows non-aggregated cobalt nanoparticles with narrow size distributions which are evenly surrounded with copolymer sheaths. However, some degree of surface oxidation was observed over time, resulting in a decrease in magnetic susceptibility.

Chemical incompatibility and relatively weak interaction between lignocellulosic fibers and synthetic polymers have made studies of wood fiber-thermoplastic composite more challenging. In this study, adsorption of 2-hydroxypropyltrimethylammonium xylans onto rod-like cellulose nanocrystals are investigated by zeta-potential measurements, and polarized and depolarized dynamic light scattering as a factor for better understanding of lignocellulosic fibers and cellulose nanocrystals. Zeta-potential measurements show xylan derivative adsorption onto cellulose nanocrystals. Decay time distributions of the ternary system and binary system from dynamic light scattering show that aggregates exist in the binary system and they disappear in the ternary system. At low 2-hydroxypropyltrimethylammonium xylan concentrations relative to that of cellulose nanocrystal, xylan derivatives adsorbed onto some of the cellulose nanocrystal. Hence, more xylan derivatives adsorbed onto cellulose nanocrystal increased with increasing xylan derivative concentration. Also, the concentration dependence of the ratio of the rotational diffusion coefficient to the translational diffusion coefficient revealed a strong adsorptive interaction between xylan derivatives and the cellulose nanocrystals.

Magnetic cobalt nanoparticle dispersions in biocompatible poly(dimethylsiloxane) fluids were studied for treating retinal detachments. Dispersions were prepared in toluene with triblock poly(dimethylsiloxane-b-(3-cyanopropyl)methylsiloxane-b-dimethylsiloxane) stabilizers where anchor blocks adsorbed onto the particles and tail blocks provided steric stability. These copolymers formed micelles in toluene with aggregation dependent on block lengths, and dispersion formation also depended on block lengths. The stabilizers could also function as the carrier fluids.