Using light scattering to evaluate the separation of polydisperse nanoparticles

The analysis of natural and otherwise complex samples is challenging and yields uncertainty about the accuracy and precision of measurements. Here we present a practical tool to assess relative accuracy among separation protocols for techniques using light scattering detection. Due to the highly non-linear relationship between particle size and the intensity of scattered light, a few large particles may obfuscate greater numbers of small particles. Therefore, insufficiently separated mixtures may result in an overestimate of the average measured particle size. Complete separation of complex samples is needed to mitigate this challenge. A separation protocol can be considered improved if the average measured size is smaller than a previous separation protocol. Further, the protocol resulting in the smallest average measured particle size yields the best separation among those explored. If the differential in average measured size between protocols is less than the measurement uncertainty, then the selected protocols are of equivalent precision. As a demonstration, this assessment metric is applied to optimization of cross flow (V_x) protocols in asymmetric flow field flow fractionation (AF⁴) separation interfaced with online quasi-elastic light scattering (QELS) detection using mixtures of polystyrene beads spanning a large size range. Using this assessment metric, the V_x parameter was modulated to improve separation until the average measured size of the mixture was in statistical agreement with the calculated average size of particles in the mixture. While we demonstrate this metric by improving AF⁴V_x protocols, it can be applied to any given separation parameters for separation techniques that employ dynamic light scattering detectors.     

Melt transesterification and characterization of segmented block copolyesters containing 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol

Conventional melt transesterification successfully produced high‐molecular‐weight segmented copolyesters. A rigid, high‐T_g polyester precursor containing the cycloaliphatic monomers, 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol, and dimethyl‐1,4‐cyclohexane dicarboxylate allowed molecular weight control and hydroxyl difunctionality through monomer stoichiometric imbalance in the presence of a tin catalyst. Subsequent polymerization of a 4000 g/mol polyol with monomers comprising the low‐T_g block yielded high‐molecular‐weight polymers that exhibited enhanced mechanical properties compared to a nonsegmented copolyester controls and soft segment homopolymers. Reaction between the polyester polyol precursor and a primary or secondary alcohol at melt polymerization temperatures revealed reduced transesterification of the polyester hard segment because of enhanced steric hindrance adjacent to the ester linkages. Differential scanning calorimetry, dynamic mechanical analysis, and tensile testing of the copolyesters supported the formation of a segmented multiblock architecture. Further investigations with atomic force microscopy uncovered unique needle‐like, interconnected, microphase separated surface morphologies. Small‐angle X‐ray scattering confirmed the presence of microphase separation in the segmented copolyesters bulk morphology. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Morphology of a liquid-crystalline polyester film

Morphological studies are reported for a thermotropic liquid crystalline polyester. Small angle light scattering studies were carried out as a function of temperature using H_v and V_v polarization with photographic as well as photometric techniques. No scattering was observed from a thin film cast from a dilute solution of the polymer in a highly volatile solvent. When the film was heated, scattering of light was observed above the glass transition temperature of the polyester. The scattering was found to be azimuthally dependent with V_v intensities being much higher than the corresponding H_v intensities. The size of the morphological features responsible for SALS patterns were calculated and were found not to change significantly with temperature ranging from glass transition temperature to the solid-nematic transition temperature of the polyester. The WAXS pattern of solution cast polymer was representative of an amorphous structure. Solution cast films heat treated under various conditions (all above the T_g of the polymer) contained crystalline as well as amorphous structures. The maximum apparent crystallinity for annealed samples was of the order of 30%.     

Velocity dependence of the total cross section for helium-argon,neon-krypton and neon-xenon scattering

Velocity dependences of the total collision cross sections for scattering of helium by argon, neon by krypton and neon by xenon were measured using a time of flight method of velocity selection. For neon scattering glory oscillations were observed from which values of ?r_m (the product of the well depth and the internuclear separation at the minimum) were determined for various Lennard-Jones potentials. Comparison is made with the results from diffusion experiments and differential scattering measurements.     

Viscoelastic phase separation in polyethersulfone modified bismaleimide resin

The polymerization-induced phase separation process of polyethersulfone (PES) modified bismaleimide resin, 4,4′-bismaleimidodiphenylmethane (BDM), was investigated by time resolved light scattering (TRLS) and scanning electronic microscopes (SEM). At the blends with 10 wt% and 12.5 wt% PES, a phase inversion structure was found by SEM. TRLS results displayed clearly the spinodal decomposition (SD) mechanism and the exponential decay procedure of scattering vector q_m, which followed Maxwell-type relaxation equation. The characteristic relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in these PES modified bismaleimide blends were affected by viscoelastic effect.     

Behavior of thermosensitive graft copolymer with aromatic polyester backbone and poly-2-ethyl-2-oxazoline side chains in aqueous solutions

Thermoresponsive graft copolymers with alkylene-aromatic polyester main chain and poly-2-ethyl-2-oxazoline side chains were synthesized. Two copolymer samples which differed in grafting density (0.5 and 0.7) were studied using dynamic and static light scattering and turbidimetry in aqueous solutions at concentration 0.0053?g?cm^?3. Hydrodynamic radii of scattering objects and their contribution to light scattering were obtained as a function of temperature in a wide temperature interval. Temperatures of phase separation were found out. Effect of grafting density on the copolymer behavior in aqueous solutions upon heating was determined. In particular, the phase separation temperature reduces with the decreasing grafting density.     

Incompatibility of polymer solutions. I. Binodals and spinodals in the system polystyrene + polyisobutylene + toluene

The incompatibility of polystyrene (PS) and polyisobutylene (PIB) in toluene is characterized by binodals obtained from phase separation and spinodals obtained from light scattering at zero scattering angle. From these the interaction parameter χ₂₃, between unlike polymer segments was calculated. It appears to be dependent on molecular weight and composition. The nature of χ₂₃, especially its low value, is discussed.     

Chitosan/N-methylol nylon 6 blend membranes for the pervaporation separation of ethanol–water mixtures

Blend membranes of chitosan and N-methylol nylon 6 were prepared by solution blending. Their pervaporation performances for the separation of ethanol–water mixtures were investigated in terms of acid (H₂SO₄) post-treatment, feed concentration, blend ratio and temperature. The pervaporation performance of the blend membranes was significantly improved by ionizing with H₂SO₄. The blend ratio of chitosan and N-methylol nylon 6 plays a different role at feed solutions of low and high water content. At a feed solution having low water content, an increase in chitosan content caused a decrease in permeability and an increase in separation factor. At a feed solution having high water content, the permeability increases with an increase in chitosan content, while the separation factor shows a maximum value around 60 wt% chitosan. It is proposed that extra permeation channels generated from the phase separation boundary between ionized chitosan and N-methylol nylon 6 account for the abnormal temperature dependence of pervaporation performance of the blend membranes.     

Ionization of water clusters by collision with surface

New results of the investigations of the phenomenon of the ion formation and separation at the neutral water cluster scattering by solid surface are reported. First, molecular dynamics simulation has shown the possibility of polar dissociation of water molecules in (H ₂ O)_n cluster with n = 34 and 64 during their impact with a rigid surface. Second, the current of ions rebound from target and the current to the target at scattering of (H2O)_n clusters (up to n = 50000) by various targets are measured. Third, we have measured the water-cluster-induced electrification of the electric field mill sensor, which has been used for the rocket measurement of mesospheric electric field structure in the vicinity of noctilucent clouds (NLC). A comparison between these and rocket measurements shows that the fluctuations of the field mill signal detected when a rocket was passing the NLC layer is a result of the impact of NLC particles on the field mill electrodes.     

pH-thermosensitive behavior of N,N-dimethylaminoethyl methacrylate (Co)polymers with N-vinylcaprolactam

The effect of acidity of a medium on the phase separation temperature and the intensity of light scattering for dispersions produced by heating of aqueous solutions of N,N-dimethylaminoethyl methacrylate, N-vinylcaprolactam, and their copolymers has been studied. It has been demonstrated that the phase separation temperature and the turbidity of polyvinylcaprolactam (and vinylcaprolactam-enriched copolymers) solutions are pH-independent. Poly(N,N-dimethylaminoethyl methacrylate) (and N,N-dimethylaminoethyl methacrylateenriched copolymers) exhibits temperature sensitivity only in the alkaline region, and the phase separation temperature and turbidity versus pH plots are described by curves with maxima. The addition of sodium dodecyl sulfate to polymer solutions in the general case causes an increase in the phase separation temperature. However, if positive charges occur on macromolecules (in initial solutions of poly(N,N-dimethylaminoethyl methacrylate) or acidified solutions of polyvinylcaprolactam), the increase in the phase separation temperature is preceded by its decrease owing to the electrostatic interaction of surfactant anions with cationic centers. As acid is introduced into the H₂O-sodium dodecyl sulfate-polyvinylcaprolactam ternary system, the phase separation temperature of the polyvinylcaprolactam-dodecyl sulfate complex is decreased.     

Liquefaction of corn stover and preparation of polyester from the liquefied polyol

This research investigated a novel process to prepare polyester from corn stover through liquefaction and crosslinking processes. First, corn stover was liquefied in organic solvents (90 wt% ethylene glycol and 10 wt% ethylene carbonate) with catalysts at moderate temperature under atmospheric pressure. The effect of liquefaction temperature, biomass content, and type of catalyst, such H₂SO₄, HCl, H₃PO₄, and ZnCl₂, was evaluated. Higher liquefaction yield was achieved in 2 wt% sulfuric acid, 1/4 (w/w) stover to liquefying reagent ratio; 160°C temperature, in 2h. The liquefied corn stover was rich in polyols, which can be directly used as feedstock for making polymers without further separation or purification. Second, polyester was made from the liquefied corn stover by crosslinking with multifunctional carboxylic acids and/or cyclic acid anhydrides. The tensile strength of polyester is about 5 MPa and the elongation is around 35%. The polyester is stable in cold water and organic solvents and readily biodegradable as indicated by 82% weight loss when buried in damp soil for 10 mo. The results indicate that this novel polyester could be used for the biodegradable garden mulch film production.     

Mechanical behavior of polyester polymer concrete under low strain rate loading conditions

Polymer concrete (PC) has superior mechanical properties in comparison with cement concrete. In this research, the mechanical behavior of polyester polymer concrete (PPC) and its polyester resin were studied at different loading rates. Special specimens for testing the PPC and the polyester resin under low strain rate loading conditions were fabricated. Experiments were performed under different strain rates, from 0.00033 to 0.15 s⁻¹, and results for the PPC and the polyester resin were compared. Furthermore, the influence of strain rate on the mechanical response of the neat polyester and the PPC was investigated. The results show a maximum 40% increase in tensile strength of the neat polyester, while the elastic modulus does not change significantly. The compressive strength of the PPC increases by 25%. These results show that the mechanical behavior of the polyester resin and its PC is extremely sensitive to the strain rate.     

AB3 building blocks for the synthesis of polyester dendrimers

Syntheses of several examples of a new type of trivalent building blocks for the preparation of aliphatic polyester dendrimers are presented. Starting from the well-known mono-O-benzylidenepentaerythritol, AB₃ type acid dendrons can be obtained in high yield in only two steps. Other triprotected bis-2,2-(hydroxymethyl)-3-hydroxypropanoic acid derivatives with varying protecting groups were also synthesized readily. This type of dendron was used in combination with 2,2′-bis(hydroxymethyl) propanoic acid (bis-HMPA) divalent dendrons to produce low generation mixed polyester dendrimers with increased number of branching points.     

Facile creation of superoleophobic and superhydrophilic surface by using perfluoropolyether dicarboxylic acid/silica nanocomposites

Perfluoropolyether dicarboxylic acid [HO(O?)CCF(CF₃){OCF₂CF(CF₃)}_nO(CF₂)₅O{CF(CF₃)CF₂O}_m―CF(CF₃)C(?O)OH; n + m = 6–12; PFPE‐DAcD] was applied to the preparation of PFPE‐DAcD/SiO₂ nanocomposites by the sol–gel reactions of the corresponding diacid with tetraethoxysilane in the presence of silica nanoparticles under alkaline conditions. PFPE‐DAcD/SiO₂ nanocomposites thus obtained were found to exhibit a good dispersibility and stability in not only water but also the traditional organic solvents such as methanol, ethanol, 2‐propanol, tetrahydrofuran, and 1,2‐dichloroethane. Field emission scanning electron micrograph (FE‐SEM) and dynamic light‐scattering (DLS) measurements show that these fluorinated composites are nanometer size‐controlled very fine particles. Dodecane and water contact angle measurements on the modified glass, filter paper, and polyester fabric surfaces treated with these fluorinated nanocomposites were found to exhibit the superoleophobicity and superhydrophilicity. Especially, the modified polyester fabric swatch was applied to the oil/water separation to give the high separation efficiency. Copyright © 2015 John Wiley & Sons, Ltd.     

Micro- and mesoscopic structure of poly(vinyl alcohol) gels determined by neutron and light scattering

We studied the structure of poly(vinyl alcohol) (PVA) gels formed in mixtures of dimethyl sulfoxide (DMSO) and water using several scattering techniques such as wide-angle neutron scattering (WANS), small-angle neutron scattering (SANS), ultra-small-angle neutron scattering (U-SANS) and light scattering (LS) to cover a very wide Q range from 10^-4 to 10 Å^-1. The WANS measurements have revealed that the cross-linking points of the gels are crystallites, and the size and its distribution have been evaluated by the SANS measurements. The SANS results have also shown that the structure observed in the low Q range below 10^-2 Å^-1 is dominated by a liquid–liquid-phase separation. The early stage of the phase separation has been studied in detail using the time-resolved LS technique, while the late stage has been investigated by the U-SANS technique because the LS measurements cannot access the opaque samples. On the basis of the results, we present a quantitative sketch of the structure of the PVA gel.     

Preparation of new membranes by complex formation of itaconic acid–acrylamide copolymer with polyvinylpyrrolidone: studies on gelation mechanism by light scattering

Mechanism of membrane formation by dipping a 10 wt% aqueous homogeneous polymer solution of poly(itaconic acid–co-acrylamide) (75:25 molar ratio)/polyvinylpyrrolidone (50/50) into acid solution was investigated by time-resolved light scattering and the pH effect of the acid solution to gelation mechanism during membrane formation was discussed. In the pH range 1.58–1.25, the gelation was governed by phase separation mechanism via the spinodal decomposition and then a membrane with regular pore size was obtained. The phase separation was caused by polymer–polymer complex formation between polymers. From an analysis based on Cahn's linearized theory of the spinodal decomposition, the apparent diffusion coefficient D_app of phase separation was smaller for lower pH. Because, at low pH there exists a lot of complex which dramatically reduces the chain mobility. The average pore size of membrane also depends on pH. When the pH was lower than 1.25, the liquid–liquid phase separation did not occur but the solution gelled homogeneously and a wrinkle-like morphology without pore was observed. FTIR analysis of the dried membranes showed that the complex formation had occurred by hydrogen bonding between the component polymers and its extent increased linearly with decreasing pH.     

Effects of Pluronics surfactants on morphology and porosity of hematite particles produced from forced hydrolysis reaction

The shape and porosity of hematite particles, produced from a forced hydrolysis reaction of acidic FeCl₃ solution, were controlled by using Pluronics as nonionic surfactants (0–4 wt.%). Pluronics possess a nominal formula of (PEO) _x –(PPO) _y –(PEO) _x . The effect of Pluronics with low hydrophilicity (PEO contents were less than 50 mol%) was small and provided spherical particles the same as that of the system without Pluronics (control system). However, Pluronics with higher hydrophilicity (PEO contents were over 50 mol%) gave ellipsoidal hematite particles. This effect on the particle morphology was enhanced by an increase in their molecular weight. On the other hand, the Pluronics possessing an opposite nominal formula [(PPO) _x –(PEO) _y –(PPO) _x ] exhibited no effect on the particle shape; it only depressed phase transformation from ?-FeOOH to hematite. Not only the morphology but also the pore size of hematite particles was controlled from nonporous to mesoporous by using Pluronics. The N₂ adsorption experiment and t-plot curve analysis revealed that the hematite particles changed from mesoporous to microporous by an increase in the concentration of Pluronics. On the other hand, in the presence of very low amounts of Pluronics molecules (0.1 wt.%), nonporous hematite particles were produced via strong aggregation of PN particles by their hydrogen bonding between hydroxyl and PEO or PPO groups. The dynamic light scattering measurement for the system with Pluronics clarified the existence of polynuclear (PN) particles with a hydrodynamic particle diameter (D _a) of ca. 40 nm after these were aged for 6 h. The size of PN particles remained constant at ca. 40 nm during aging time of 12 h～3 days, but the scattering intensity was decreased. This decrease in the scattering intensity reveals that the number of PN particles is reduced by aggregation. The transmission electron microscope, inductively coupled plasma atomic emission spectroscopy, and total organic carbon analysis measurements employed on the systems produced for ellipsoidal particles elucidated that the formation of ellipsoidal hematite particles is attributed to the adsorption of Pluronics on the surfaces of PN and growing hematite particles.     

Morphology of polyurethanes with triol monomer crosslinked on hard segments

Polyester‐based polyurethanes containing ≈60 wt % of polyester were synthesized from low molecular weight polyester (M_n ≈2000) and 4,4′‐methylene bis(phenyl isocyanate) (MDI), with butanediol as a chain extender and glycerol as a crosslinker. The triol crosslinker was used in substitution for the 1,4‐butanediol chain extender; thus, the crosslinker was chemical bonded to the hard segments of polyurethane. The morphologies of these polyurethanes were studied by differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), TMA (thermal mechanical analysis), and FTIR (Fourier transform infrared spectroscopy). Owing to the highly steric hindrance, the presence of triol crosslinker in the hard segments resulted in a decrease in the aggregation of hard segments through hydrogen bonding. The experimental results revealed that the degree of phase segregation of soft and hard segments decreased with increasing the triol crosslinker content in the hard segments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2673–2681, 1999     

Hydrophobic properties of plasma polymerized thin film gas selective membranes

Hydrophobic gas separation membranes were prepared by a plasma polymerization process. Thin films of about 400–500 nm thickness deposited on porous Al₂O₃ substrates represent the composite membranes investigated. The permeation properties of the composites were examined by the pressure increase and an isobar method. Depending on the precursor composition and the plasma polymerization parameters, it is possible to prepare membranes with Knudsen-like or solution-diffusion controlled separation factors. Low plasma polymerization energy densities and a mixture of silico- and fluoro-organic precursors result in water/methane separation factors as low as α_CH4^H₂O = 0.3 and high membrane permeabilities. Infrared analysis yields that the structure of the films is mainly determined by the silico-organic component. The fluoro-organic coprecursor causes a fluorination of methyl groups of the films as manifested by an infrared absorption band at 900-880 cm⁻¹.