Glass transition in polymers monitored by synchronous scan spectra

The synchronous scan spectra (SSS) technique was successfully applied to monitor the macromolecular chain motions near the glass transition temperature in polystyrene (PS) and poly (vinyl methyl ether) (PVME) films on a copper substrate. In SSS of PS and PVME films, two peaks at 467 nm and 473 nm, which correlated to the light source spectrum of the spectrofluorimeter, were used to characterize the glass transition of polymers. By monitoring the intensity of peaks at 467 and 473 nm in the spectra, the intensity-temperature curves exhibited kinks near the glass transition. The kinks have also been shown in plots of I_R473/I_R467 vs. temperature, which implies the distinct fluctuation of SSS intensity distribution at the glass transition temperature of the polymer. As a spectroscopy measurement method with simplicity, rapidity and sensitivity, the SSS method was proved to be able to monitor the glass transition in polymers, which has been commonly measured by differential scanning calorimetry (DSC).     

Ultrasensitive determination of serum albumin using resonance light scattering based on ZnS-polyacrylic acid nanoparticles

ZnS-polyacrylic acid (ZnS-PAA) was prepared by an in situ polymerization method using nano-ZnS as core in the presence of acrylic acid (AA), and ZnS-PAA nanoparticles was characterized by ultraviolet spectrometry (UV) and transmission electron microscopy (TEM). Based on the significant increase of the resonance light scattering (RLS) intensity with the interaction between nanoparticles and serum albumin, RLS method was developed for the sensitive determination of serum albumin (BSA and HSA). Under optimum conditions, the change of the intensity (ΔI) of the RLS spectra at λ = 392 nm was linearly proportional to the concentration of BSA and HSA. The linear range was 1–100 ng mL^?1 for HSA and 1–120 ng mL^?1 for BSA, and the limit of detection (LOD) was 0.4 ng mL^?1 for HSA and 0.5 ng mL^?1 for BSA. This method proved to be very sensitive, rapid, simple and tolerant of most interfering substances.     

Determination of nanograms of proteins based on the amplified resonance light scattering signals of Tichromine

A new high-sensitivity detection of protein assay at the nanogram level is developed based on the amplified resonance light scattering signals (RLS) of Tichromine (TCM). In Walpole (NaAc–HCl) buffer (pH 4.05), TCM reacts with proteins to form large particles, which results in remarkable enhanced RLS signals characterized by three peaks at 293 nm, 399 nm and 553 nm. Mechanistic studies showed that the enhanced RLS stems from a large complex of TCM–BSA formed for the electrostatic effect between TCM and BSA. With the enhanced RLS signals at the three wavelengths, the enhanced RLS intensity is proportional to the concentration of proteins in an appropriate range. The lowest limit of determination was 7.4 ng mL^?1. The proposed method was successfully applied to determine total protein in human serum samples.     

Size-controllable synthesis of spherical ZnO nanoparticles: Size- and concentration-dependent resonant light scattering

A new and simple direct precipitation method assisted with ultrasonic agitation was proposed for the preparation of spherical ZnO nanoparticles. The size of the ZnO nanoparticles, 10 nm to 85 nm, was tuned through controlling the calcination temperature and changing the ratio of the reactants. The resonant light scattering (RLS) of the ZnO nanoparticles dispersed/suspended in aqueous solution of Triton X-100 was studied under room temperature. It was found that the ZnO nanoparticles of different size or concentration all have a characteristic RLS peak at 387 nm. Under optimal conditions, the RLS intensity was proportional to the ZnO concentration in the range of 7.3 × 10^?8–1 × 10^?4 mol L^?1, while the cubic root of the RLS intensity was found to be proportional to the size of ZnO nanoparticles. Further, the quantitative relationship of the size of the ZnO nanoparticles versus the calcination temperature was derived, and this could be used to forecast/control the nano-size in the nano-ZnO preparation.     

Phase Separation,Wetting and Dewetting in PS/PVME Blend Thin Films: Dependence on Film Thickness and Composition Ratio

The effects of film thickness and composition ratio on the morphology evolution of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend thin films were investigated. Diverse morphology evolutions including droplet-matrix structure, hole emergence, bicontinuous structure formation, percolation-to-droplet transition could be observed under annealing in two-phase region, depending on film thickness and composition ratio. The mechanism for these morphology variations was related to the complex effects of phase separation, dewetting and preferential wetting. The comparison between the thickness of bottom PVME layer and the twice of gyration radius 2R_g(PVME) played a dominant role in morphology control. Only when the PS/PVME film had specific film thickness and compositional symmetry, phase separation and dewetting could happen in sequence.     

Self-assembly via a complex phase transition in mixtures of polystyrene-block -polybutadiene block copolymer and poly(methyl vinyl ether)

The self-assembly of a binary mixture of polystyreneblock-polybutadiene (SB) and poly(methyl vinyl ether) (PVME) was studied by transmission electron microscopy and time-resolved light scattering. The self-assembly studied involved first microphase separation, in which a microdomain structure composed of polybutadiene block chains (PB) was formed in a matrix composed of polystyrene block chains (PS) and PVME homopolymers, and subsequently macrophase separation of the PVME from the microdomain phase of SB. The microphase separation was induced in a film preparation process using a solution cast method at room temperature. The macrophase separation was induced by rapidly heating the film specimens to above a critical temperature where PVME and PS undergo spinodal decomposition (SD). This complex phase transition, involving microphase separation followed by macrophase separation, was found to generate a superlattice structure (or a modulated structure) with two characteristic spacings: A_macro associated with the SD and A_micro associated with the microphase separation, both being generally time-dependent. The growth of the “macrodomains” was found to be pinned at A_macro ˜ 840 nm due to the elastic effect of the microdomain structure. The microdomain structure with A_micro ˜ 57 nm was found to undergo a morphological transition (a transition between two ordered phases of block copolymers) as a consequence of the local composition change of the two polymers induced by the SD.     

3D FT-IR imaging spectroscopy of phase-separation in a poly(3-hydroxybutyrate)/poly(l-lactic acid) blend

In the present study, 3D FT-IR spectroscopic imaging measurements were applied to study the phase separation of a poly(3-hydroxybutyrate) (PHB)/poly(l-lactic acid) (PLA) (50:50 wt.%) polymer blend film. While in 2D projection imaging the z-dependent information is overlapped, thereby complicating the analysis, FT-IR spectro-micro-tomography, obtained from computed tomographic back projection calculations, results in distinct 3D chemical images that provide detailed information of phase separation of the two polymer components that are well separated.     

Resonance light scattering spectroscopy study of interaction between gold colloid and thiamazole and its analytical application

In this paper, we used resonance light scattering (RLS) spectroscopy to study the interaction between thiol-containing pharmaceutical-thiamazole and gold colloid. At pH 5.2, the resonance light scattering spectrum of gold nanoparticles has a maximum peak at 555 nm and the RLS intensity is enhanced by trace amount of thiamazole due to the interaction between thiamazole and gold colloid. The binding of colloidal gold to thiamazole results in ligand-induced aggregation of colloidal gold, which was characterized by RLS spectrum, ultraviolet-visible (UV-Vis) spectrum, and transmission electron microscopy (TEM). Based upon the study, we proposed a highly sensitive, gold colloid-based assay using RLS spectrum to detect pharmaceuticals for the first time. The mechanism of binding interaction between Au colloid and thiamazole was also discussed.     

Characterization of phase separation of polystyrene/poly(vinyl methyl ether) blends using fluorescence

We have investigated the fluorescence emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The specific chemical structure of the fluorescent labels is found to affect the measured phase separation temperature T_S, with fluorophores covalently attached in closer proximity to the PS backbone identifying phase separation a few degrees earlier. The sharp increase in fluorescence intensity upon phase separation that occurs for all fluorophores with little change in spectral shape is consistent with a mechanism of static fluorescence quenching resulting from the specific interaction with a nearby quenching molecular unit. Based on recent work that has identified a weak hydrogen bond occurring between the aromatic hydrogens of PS and the ether oxygen of PVME, we believe a similar weak hydrogen bond is likely occurring between the PVME oxygen and the aromatic dyes providing a local (few nanometer) sensitivity to phase separation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

The Interaction between Propranolol and Gold Nanoparticles and its Analytical Application

The addition of propranolol induced the aggregation of gold nanoparticles, and increased Rayleigh light scattering (RLS) intensity greatly. The interaction between them was studied by RLS spectrum, UV-Vis spectrum and transmission electron microscopy (TEM). Based on these results, a novel method was proposed for propranolol assay. With the combination of solid phase microextraction (SPME), the proposed method was successfully applied to determine propranolol in urine.     

An investigation of the effect of microwave treatment on the structure and unfolding pathways of β-lactoglobulin using FTIR spectroscopy with the application of two-dimensional correlation spectroscopy (2D-COS)

Microwave treatment of β-lactoglobulin (β-Lg) in D₂O solution under various conditions was monitored by Fourier transform mid infrared (mid-FTIR) spectroscopy. At sub-ambient temperatures, no microwave-induced changes in the conformation of the protein were detected. Microwave heating of the β-Lg solutions to temperatures in the range of 40–60 °C resulted in a marked increase in the rate of hydrogen–deuterium (H–D) exchange as compared to conventional heating at the same temperature. At heating temperatures in the range of 70–90 °C, the microwave-heated solutions exhibited more extensive protein aggregation than conventionally heated solutions. Application of two-dimensional (2D) correlation analysis to the Fourier self-deconvolved FTIR spectra recorded as a function of number of cycles of microwave or conventional heating revealed that the unfolding pathway of β-Lg was different in these two temperature ranges (40–60 °C versus 70–90 °C) but was similar in both microwave – treated and conventionally heated samples. Nevertheless, within the temperature range of 70–90 °C microwave treatment accelerated the unfolding of β-lactoglobulin.     

Determination of neomycin in water samples by high performance anion chromatography with pulsed amperometric detection

A simple, fast and reliable method, using high performance anion chromatography with pulsed amperometric detection, had been developed for the analysis of neomycin in water samples. The elution and separation were carried out with an isocratic mobile phase, containing 10 mmol/L NaOH. The influence of the concentration and pH of the mobile phase on the separation and detection was investigated. A quadruple-potential waveform used for the detection was optimized. The detection limit of neomycin was down to 0.027μg/mL. The linearity of neomycin calibration curve ranged from 0.050 to 0.505μg/mL with correlation coefficient of 0.9997. R.S.D. (n = 11) was 4.0%.     

Static structure factor and chain dimensions in polymer blends with non-local mixing entropy

It is suggested that the non-locality of the entropy part of the interaction parameter in partially miscible blends can be measured directly by scattering experiments. The structure factor computed in the random phase approximation is compared with experiments on weakly crosslinked polystyrene (PS) polyvinylmethylether (PVME) blends. These polymers have significantly different monomer units to form ‘smooth’ (PVME) and ‘rough’ (PS) polymers. An excess scattering is observed and related to the non-locality. It is further shown that these effects are significant near the glass transition of the blend. In particular, the influence of the non-local mixing entropy on the single chain behaviour close to the onset of the microphase separation is studied quantitatively.     

Evolution of concentration fluctuation during phase separation of polystyrene/poly(vinyl methyl ether) blend in the presence of nanosilica

The influence of nanosilica on the concentration fluctuation of polystyrene/poly (vinyl methyl ether) (PS/PVME) mixtures was investigated during phase separation. The amplitude of concentration fluctuation was quantified by dielectric spectrums based on the idea of Lodge–Mcleish model and the linearized Cahn–Hilliard theory could describe the amplitude evolution of concentration fluctuation at the early stage of phase separation. Hydrophilic nanosilica A200 dispersed in PVME‐rich phase behaved an obvious inhibition effect on the concentration fluctuation of blend matrix, while hydrophobic nanosilica R974 dispersed in PS‐rich phase had little effect on the concentration fluctuation. The kinetics and amplitude evolution of concentration fluctuation during phase separation for PS/PVME/A200 nanocomposites were remarkably restrained due to the surface adsorption of PVME on A200. As the segmental dynamics of PVME and PS in homogeneous matrix was hardly influenced by A200 and R974, the enhanced miscibility and the significantly constrained flow relaxation of PVME chains might contribute to the retarded concentration fluctuation of PS/PVME/A200 nanocomposites. While the weak interaction between R974 and components of blend matrix and little effect of R974 on the molecular dynamics of PS chains may result in the weak retardation of concentration fluctuation for blend matrix. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1337–1349     

Tracer diffusion of star-branched polystyrenes in poly(vinyl methyl ether) gels

The tracer diffusion of 3-, 4-, and 12-arm polystyrene (PS) stars in poly(vinyl methyl ether) (PVME) gels has been measured by dynamic light scattering (DLS). The intensity correlation functions were analyzed by two methods. One was that employed previously in a DLS study of linear PS diffusion in PVME gels [N. A. Rotstein and T. P. Lodge, Macromolecules, Vol. 24. p. 1316 (1992)], and the other was based on consideration of possible nonergodicity effects [P. N. Pusey and W. van Megen, Physica A, Vol. 157, p. 705 (1990)]. Both methods gave equivalent results, suggesting that nonergodicity plays a small role in this system. This conclusion is not unreasonable, given that the PVME gels are almost isorefractive with the solvent (toluene), and that the signal is dominated by scattering from the PS chains. The resulting star diffusivities are consistently less than or equal to those for linear probes of comparable size, with the difference increasing with molecular weight. The diffusivities are also less than or equal to those obtained for the same stars in PVME solutions. A weak dependence on the number of arms is also observed. Finally, the mobility of a given star in a gel is much more sensitive to variations in the average molecular weight between cross-links than is the mobility of a linear chain. All of these features in the data are broadly consistent with the reptation hypothesis. © 1993 John Wiley & Sons, Inc.     

Cloud-point measurements of the {H2O + poly(ethylene glycol) + NaNO3} system

The cloud-point (CP) temperatures and phase separation of {H₂O + poly(ethylene glycol) + NaNO₃} ternary system is studied by the turbidimetry method using a reaction calorimeter. The phase separation was also observed by visual inspection. Differences between the CP measured using the turbidimetry method and visual inspection, was up ±0.5 K. The Flory–Huggins model with a temperature and concentration-dependent interaction parameter was employed to correlate the phase diagram of the system. As a result of the correlation an average absolute deviation of 0.002 is obtained.     

The investigation of the interactions between CdSe quantum dots and human serum albumin by resonance Rayleigh scattering and second-order scattering spectra

Human serum albumin (HSA) was the most abundant protein in human plasma and has significant physiological function. In Tris–HCl buffer solution (pH 7.4), water-soluble semiconductor CdSe quantum dots (QDs) reacted with HSA and the products resulted in a great enhancement of the intensity of resonance Rayleigh scattering (RRS) and second-order scattering (SOS). Based on this, a new method was developed to investigate the interactions between QDs and HSA. The parameters with regard to determination were optimized, and the reaction mechanism was discussed. Under optimal conditions, the increments of scattering intensity (ΔI) were directly proportional to the concentrations of HSA in the range of 0.4–48.0 μmol L^?1. The detection limits were 0.10 μmol L^?1 for RRS method and 0.25 μmol L^?1 for SOS method. The proposed method was sensitive, simple and rapid. It has been successfully applied to the determination of HSA in human urine samples. Analytical results obtained with this novel assay were satisfactory.     

Investigation on the toxic interaction of chrysoidine hydrochloride–CTMAB combined contamination with calf thymus DNA

The toxic interaction of the azo dye-chrysoidine hydrochloride combined with cetyltrimethyl ammonium bromide (CTMAB) in living tissue was studied in vitro. The absorption spectrum, resonance light scattering (RLS), circular dichroism (CD) and transmission electron microscopy (TEM) results showed that the toxicity of chrysoidine hydrochloride itself to calf thymus DNA (ct-DNA) is weak, while the chrysoidine hydrochloride–CTMAB combined pollution showed obvious toxic interaction with ct-DNA. The chrysoidine hydrochloride–CTMAB combined contamination can interact with ct-DNA to form an ion-associated complex through electrostatic and hydrophobic forces. The conformation of DNA was changed in the interaction process to show toxic. The experimental results showed that the combination of chrysoidine hydrochloride–CTMAB has higher toxicity to ct-DNA than either chrysoidine hydrochloride or CTMAB individually, and the combined pollution showed a strong toxic co-effect at a dose of 3.0 × 10^?4 mol L^?1 chrysoidine hydrochloride and 1.6 × 10^?5 mol L^?1 CTMAB.     

The effect of phase‐separated morphology on the rheological properties of polystyrene/poly(vinyl methyl ether) blend

The effect of phase‐separated morphology on the rheological properties of polystyrene/poly(vinyl methyl ether) (PS/PVME) blend was investigated by optical microscopy (OM), light scattering (LS) method, and rheology. The blend had a lower critical solution temperature (LCST) of 112°C obtained by turbidity experiment using LS at a heating rate of 1°C/h. Three different blend compositions (critical 30/70 PS/PVME by weight) and two off‐critical (50/50 and 10/90)) were prepared. The rheological properties of each composition were monitored with phase‐separation time after a temperature jump from a homogeneous state to the preset phase‐separation temperature. For the 30/70 and 50/50 blends, it was found that with phase‐separation time, the storage and loss moduli (G′ and G″) increased at shorter times due to the formation of co‐continuous structures resulting from spinodal decomposition. Under small oscillatory shearing, shear moduli gradually decreased with time at longer phase‐separation times due to the alignment of co‐continuous structures toward the flow direction, as verified by scanning electron microscopy. However, for the 10/90 PS/PVME blend, the rheological properties did not change with phase‐separation times. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 889–906, 1999     

The buffering-out effect and phase separation in aqueous solutions of EPPS buffer with 1-propanol, 2-propanol,or 2-methyl-2-propanol at T = 298.15 K

Buffering-out is a new liquid–liquid phase separation phenomenon observed in mixtures containing a buffer as a mass separating agent. The (liquid + liquid) equilibrium (LLE) and (solid + liquid + liquid) equilibrium (SLLE) data were measured for the ternary systems {3-[4-(2-hydroxyethyl)piperazin-1-yl]propanesulfonic acid (EPPS) buffer + 1-propanol, 2-propanol, or 2-methyl-2-propanol + water} at T = 298.15 K under atmospheric pressure. The phase boundary data were fitted to an empirical equation relating to the concentrations of organic solvent and buffer. The effective excluded volume (EEV) values of EPPS were obtained from the phase boundary data. The phase-separation abilities of the investigated aliphatic alcohols were discussed. The reliability of the experimental tie-lines was satisfactorily confirmed by the Othmer–Tobias correlation. The experimental tie-lines data for the ternary systems have been correlated using the NRTL activity coefficient model. The separation of these aliphatic alcohols from their azeotropic aqueous mixtures is of particular interest to industrial process. The addition of the EPPS as an auxiliary agent breaks the (1-propanol + water) and (2-methyl-2-propanol + water) azeotropes. The possibility of using the new phase separation systems in the extraction process is demonstrated by using different dyestuffs.