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.     

Incompatibility of polymer solutions. III. Critical opalescence in the system polystyrene + polyisobutylene + toluene

The angular dependence of light scattering from the homogeneous ternary system polystyrene + polyisobutylene + toluene was measured at a fixed (critical) concentration as a function of temperature. On approaching the critical temperature the scattering becomes very large and strongly angle-dependent. The experiments show that the interaction range r_G is of the same order of magnitude as the molecular radius of gyration of the polymer, but cannot be set equal to it as in the case of a binary system of one polymer in a single solvent. The temperature dependence of the various interaction parameters does not depend on the molecular weights of the polymers.     

THE OBSERVATION OF INTERNAL MOTION OF LINEAR POLYSTYRENE CHAINS IN CYCLOHEXANE AROUND θ TEMPERATURE

 A high molecular weight (Mw = 1.85 × 10⁷) polystyrene (PS) with narrow distribution was prepared by high vacuum anionic polymerization in tetrahydrofuran. By use of dynamic light scattering, the dynamics of PS chains in cyclohexane was studied around the θ temperature. For the first time, we have observed the internal motion of polymer chains in solutions below the θ temperature by using dynamic light scattering at smaller angles (even qR_g < 1).     

THE OBSERVATION OF INTERNAL MOTION OF LINEAR POLYSTYRENE CHAINS IN CYCLOHEXANE AROUND 0 TEMPERATURE

A high molecular weight (M_w=1.85×10~7) polystyrene (PS) with narrow distribution was prepared by high vacuum anionic polymerization in tetrahydrofuran.By use of dynamic light scattering,the dynamics of PS chains in cyclohexane was studied around theθtemperature.For the first time,we have observed the internal motion of polymer chains in solutions below theθtemperature by using dynamic light scattering at smaller angles (even qR_g<1).     

Star‐shaped nanomicelles of polyisobutylene‐polystyrene diblock copolymers. New stabilizer for living dispersion polymerization of styrene

Formation of star‐shaped nanomicelles of polyisobutylene‐polystyrene (PIB‐PS) diblock copolymers in hexane solution is reported. The length of the polystyrene segments were varied in the M_n range of 4000‐13000 g/mol at approximately constant polyisobutylene segments length. The size and the size distribution of the nanomicelles were investigated by dynamic light scattering. Based on static light scattering measurements the mass‐average molecular mass of the micelles and the number of arms were also determined. The synthesized diblock‐copolymers were demonstrated to be capable of stabilizing the growing particles which were formed in the living anionic dispersion polymerization of styrene in hexane.     

Statistical thermodynamics of polymer solutions. VIII. Effect of intermolecular correlations on rayleigh scattering

The effect of intermolecular correlations on the angular dependence of the intensity of Rayleigh scattering from a dilute solution of a flexible-chain polymer in a good solvent is studied for an approximate model that retains the random-flight intramolecular segment-pair correlation while probabilities of multiple intermolecular contacts are simplified as products of probabilities of single contacts, all conditional on a common “initial” contact. This model, unlike one in which a polymer chain is represented as a spherically symmetrical cloud of segments, gives very little deviation from Zimm's “single-contact” approximation in light scattering: i.e., the initial concentration dependence of the concentration/intensity ratio is almost the same at all scattering angles. This behavior, which appears to underestimate the intermolecular correlations, can be accounted for by the symmetry of the bimolecular cluster as represented by the model.     

The impact of water and hydrocarbon concentration on the sensitivity of a polymer-based quartz crystal microbalance sensor for organic compounds

Long-term environmental monitoring of organic compounds in natural waters requires sensors that respond reproducibly and linearly over a wide concentration range, and do not degrade with time. Although polymer coated piezoelectric based sensors have been widely used to detect hydrocarbons in aqueous solution, very little information exists regarding their stability and suitability over extended periods in water. In this investigation, the influence of water aging on the response of various polymer membranes [polybutadiene (PB), polyisobutylene (PIB), polystyrene (PS), polystyrene-co-butadiene (PSB)] was studied using the quartz crystal microbalance (QCM). QCM measurements revealed a modest increase in sensitivity towards toluene for PB and PIB membranes at concentrations above 90 ppm after aging in water for 4 days. In contrast, the sensitivity of PS and PSB coated QCM sensors depended significantly on the toluene concentration and increased considerably at concentrations above 90 ppm after aging in water for 4 days. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR–FTIR) showed that there is a change in the sorption mechanism at higher toluene levels for PS and PSB. Positron annihilation lifetime spectroscopy (PALS) studies were performed to investigate the free volume properties of all polymers and to monitor any changes in the free volume size and distribution due to water and toluene exposure. The PALS did not detect any considerable variation in the free volume properties of the polymer films as a function of solution composition and soaking time, implying that viscoelastic and/or interfacial processes (i.e. surface area changes) are probably responsible for variations in the QCM sensitivity at high hydrocarbon concentrations. The results suggest that polymer membrane conditioning in water is an issue that needs to be considered when performing QCM measurements in the aqueous phase. In addition, the study shows that the hydrocarbon response is concentration dependant for polymers with a high glass transition temperature, and this feature is often neglected when comparing sensor sensitivity in the literature.     

A SLOW RELAXATION MODE OF POLYMER CHAINS IN A SEMIDILUTE SOLUTION

Dust-free semidilute and concentrated polystyrene(PS)solutions in different solvents were prepared by slow evaporation and in situ anionic polymerization,which removes the effects of troublesome artifacts such as dust contamination and concentration gradient.The dynamics was reexamined by a combination of static and dynamic laser light scattering.In benzene and toluene(good solvents for PS),only one fast diffusive mode of polymer chains can be observed when the concentration(c)is up to 20%,which is attri...     

Angular-ratiometric plasmon-resonance based light scattering for bioaffinity sensing

We describe an exciting opportunity for affinity biosensing using a ratiometric approach to the angular-dependent light scattering from bioactivated and subsequently aggregated noble metal colloids. This new model sensing platform utilizes the changes in particle scattering from very small colloids, which scatter light according to traditional Rayleigh theory, as compared to the changes in scattering observed by much larger colloidal aggregates, formed due to a bioaffinity reaction. These larger aggregates no longer scatter incident light in a Cos(2) theta dependence, as is the case for Rayleigh scattering, but instead scatter light in an increased forward direction as compared to the incident geometry. By subsequently taking the ratio of the scattered intensity at two angles, namely 90 degrees and 140 degrees , relative to the incident light, we can follow the association of biotinylated bovine serum albumin-coated 20 nm gold colloids, cross-linked by additions of streptavidin. This new model system can be potentially applied to many other nanoparticle assays and has many advantages over traditional fluorescence sensing and indeed light-scattering approaches. For example, a single nanoparticle can have the equivalent scattered intensity as 10(5) fluorescing fluorescein molecules substantially increasing detection; the angular distribution of scattered light from noble metal colloids is substantially easier to predict as compared to fluorescence; the scattered light is not quenched by biospecies; the ratiometric measurements described here are not dependent on colloid concentration as are other scattering techniques; and finally, the noble metal colloids are not prone to photodestruction, as is the case with organic fluorophores.     

Properties of cellulose acetate in solution. II. Light scattering and elasticity measurements on gels in benzyl alcohol

Kinetic studies are reported for the light scattering and elasticity of thermally reversible gels of cellulose acetate in benzyl alcohol over a range of temperature and polymer concentration. The small-angle light scattering data are found to be described by exponential correlation functions, and it is concluded that the scattering has its origin in the nonrandom character of the crosslinking in the gels studied. The elasticity is discussed in terms of the density of crosslinks in the gels. Thus, the kinetics studied by light scattering and elasticity measurements are independently related to temperature and polymer concentration.     

On the structure of glassy polymers. I. Small-angle X-ray scattering from polycarbonate

The small-angle x-ray scattering (SAXS) from glassy bisphenol-A polycarbonate has been measured using a Bonse–Hart system. The data cover the angular range (2θ) between 20 sec and 2 deg. After correcting for absorption, background, and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a standard silica suspension. The corrected absolute intensity decreases strongly with increasing angle over the range between 20 sec and 30 min, and is nearly constant between 30 min and 2 deg. The magnitude of the scattering in the constant range, 0.44 (electrons)² Å^?3, is well represented by the thermodynamic theory for fluids applied at the glass-transition temperature. The increase in intensity at smaller angles cannot be described by structures on the scale of the nodules reported in this material (50–200 Å), but can be well represented by a small concentration of heterogeneities (0.04% by volume or less), several thousand angstrom units in size, superimposed on the thermal density fluctuations frozen in at the glass transition. It is suggested that the nodular features reported for this material are not representative of bulk material but should be associated with surface effects. The bulk structure can—as far as the SAXS is concerned—be well described as a random amorphous solid, containing simple thermal fluctuations and a small concentration of relatively large heterogeneities.     

The scattering of light from thin polymer films: Multiple scattering. II. Effect of depolarization

A procedure is described to include the effect of depolarization of the originally plane-polarized incident light beam as it passes through a thin polymer sample on the intensity of multiple light scattering. The multiple scattering gives rise to “polarization scrambling” in which, for example, H_v scattering measurements involve multiple scattered rays which may have undergone some V_v scattering. These phenomena reduce the angular dependence of scattering since large intensities originally occurring at small values of θ are rescattered so as to enhance intensities at other angles. Correction factors for both H_v and V_v scattering are presented.     

Synthesis and characterization of multi-arm star-branched polyisobutylenes

Multi-arm star-branched polyisobutylenes were synthesized by the “arm-first, core-last” method using the 2-chloro-2,4,4-trimethylpentane/pyridine/TiCl₄ initiating system and the reactive core-forming comonomers 1,3-diisopropenylbenzene (DIPB) and divinylbenzene (DVB). Star formation was confirmed by RI and UV GPC and static light-scattering analyses. It was determined that DVB was significantly superior to DIPB. Using DVB, star polymers formed more rapidly and contained a much lower amount of residual PIB arms. Increasing the concentration of the reactive comonomer from 1 to 10 times the concentration of chain ends, [CE], increased the efficiency of the star-forming reaction substantially. Modest increases in the fraction of PIB arms incorporated into the star could be obtained by increasing the duration of the star-forming reaction. The timing of addition of the reactive comonomer to the PIB arms seems to be the process parameter most critical to the star development, since early addition at excessively low IB conversion hinders star formation by causing a copolymerization between IB and the core-forming comonomer. Late addition risks loss of a significant fraction of PIB chains due to spontaneous β-proton expulsion. A fully developed multi-arm star-branched PIB was synthesized by utilizing 10:1 [DVB]:[CE], 24 h star-forming reaction time, 14,000 g/mol target arm M_n, and addition of DVB at 99% IB conversion. The resultant star polymer contained only 4% unreacted PIB arms and possessed M_w = 345,000 g/mol by light scattering. The weight-average number of arms per star polymer was calculated to be 23. © 1996 John Wiley & Sons, Inc.     

Confinement effect of polystyrene on the relaxation behavior of polyisobutylene

The dynamic mechanical loss tangent (tan δ) peak of polyisobutylene (PIB) reveals an asymmetrical broad structure with a maximum on the high‐temperature side and a shoulder on the low‐temperature side. By comparing with the literature results, it is suggested that the shoulder and the maximum originate from local segmental motion and Rouse modes, respectively. Blending polystyrene (PS) with PIB has two effects on the relaxation behavior of PIB. One effect is that the maximum and the shoulder are both suppressed, but the maximum is suppressed to a higher extent. After PS forms the continuous phase, the maximum becomes lower than the shoulder, and even almost disappears when the weight ratio of PIB/PS is under 20/80. The other effect is that, before PS forms the continuous phase, the temperature position of the maximum (T_s) and that of the shoulder (T_α) remains constant, but after PS forms the continuous phase, both of them are reduced with decreasing particle size of the PIB phase, in a way similar to nano‐confinement effect on the depression of glass transition temperature. The depression amplitude of T_s is larger than that of T_α. The aforementioned two effects can be interpreted in terms of the limited expansion of free volume of the PIB phase exerted by the PS phase, which affects the maximum to a higher extent than the shoulder because Rouse modes are more sensitive to the free volume than local segments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

On the origin of the forward peak and backward oscillations in the F + H(2)(v = 0) --> HF(v' = 2) + H reaction

We present a semiclassical complex angular momentum (CAM) analysis of the forward scattering peak which occurs at a translational collision energy around 32 meV in the quantum mechanical calculations for the F + H(2)(v = 0, j = 0) --> HF(v' = 2, j' = 0) + H reaction on the Stark-Werner potential energy surface. The semiclassical CAM theory is modified to cover the forward and backward scattering angles. The peak is shown to result from constructive/destructive interference of the two Regge states associated with two resonances, one in the transition state region and the other in the exit channel van der Waals well. In addition, we demonstrate that the oscillations in the energy dependence of the backward differential cross section are caused by the interference between the direct backward scattering and the decay of the two resonance complexes returning to the backward direction after one full rotation.     

Phase separation and permeability in polyisobutylene‐based miktoarm star polymers

The phase behavior of (PS‐PIB)₂‐s‐PAA miktoarm star terpolymers with varying volume fractions of PAA was investigated directly by transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering, and indirectly by thermogravimetric analysis and degree of water sorption. The microdomains of (PS‐PIB)₂‐s‐PAA demonstrate a unique and unexpected progression from highly ordered cylinders, to lower ordered spheres, to gyroid structures with increasing PAA content from 6.6 to 47 wt %. Interestingly, the phase behavior in the miktoarm star polymer system is significantly different from that reported previously for the linear counterpart of similar composition (PAA‐PS‐PIB‐PS‐PAA), where a steady progression from cylindrical to lamellar morphology was observed with increasing PAA content. At low PAA concentrations, the morphology is driven primarily by the relative solubility of the components, while at high PAA content the molecular architecture dominates. Thermal annealing demonstrated the thermodynamic stability of the morphologies, indicating the potential for design of novel microstructures for specific applications through precise control of architecture, composition, and interaction parameters of the components. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 916–925     

Covalently closed microemulsions in presence of triblock terpolymers

This paper is focused on the influence of polystyrene (PS)-poly(1,4-butadiene) (PB)-poly(ethylene oxide) (PEO) triblock terpolymers on the w/o microemulsion of the pseudo-ternary system water/sodium dodecylsulfate (SDS)/xylene-pentanol. Despite the insolubility of the copolymer in water as well as in the xylene-pentanol mixture, it can be incorporated into the w/o microemulsion and interactions between the triblock terpolymer molecules and the anionic surfactant headgroups can be detected by differential scanning calorimetry (DSC) measurements. Furthermore, dynamic light scattering measurements were used to determine the aggregate diameter of the modified microemulsions. For lower polymer concentrations large aggregates between 100 and 500 nm can be observed. Surprisingly, at a higher terpolymer concentration of 5 wt%, significant smaller aggregate diameters can be identified by dynamic light scattering and Cryo-SEM. One can conclude that the copolymers are incorporated in the inverse microemulsion droplets, where the PB blocks cover the water droplets. The thermally induced radical cross-linking of the butadiene units in the presence of azobisisobutyronitrile (AIBN) leads then to covalently closed nanocapsules with an average size of 10 nm.     

Wetting by simple room-temperature polymer melts: deviations from Newtonian behavior

The hydrodynamics near moving contact lines of two room-temperature polymer melts, polyisobutylene (PIB) and polystyrene (PS), are different from those of a third polymer melt, polydimethylsiloxane (PDMS). While all three fluids exhibit Newtonian behavior in rotational rheological measurements, a model of the hydrodynamics near moving contact lines which assumes Newtonian behavior of the fluid accurately describes the interface shape of a variety of PDMS fluids but fails to describe the interface deformation by viscous forces in PIB and PS. The magnitude of the deviations from the model and the distance along the liquid-vapor interface over which they are seen increase with increasing capillary number. We conclude that the wetting behaviors of PIB and PS are influenced by weak elasticity in these low molecular weight melts and that dynamic wetting is more sensitive to this elasticity than standard rheometric techniques.     

Analysis of the structure of very large bacterial aggregates by small-angle multiple light scattering and confocal image analysis

This work aims at developing a more accurate measurement of the physical parameters of fractal dimension and the size distribution of large fractal aggregates by small-angle light scattering. The theory of multiple scattering has been of particular interest in the case of fractal aggregates for which Rayleigh theory is no longer valid. The introduction of multiple scattering theory into the interpretation of scattering by large bacterial aggregates has been used to calculate the fractal dimension and size distribution. The fractal dimension is calculated from the form factor F(q) at large scattering angles. At large angles the fractal dimension can also be computed by considering only the influence of the very local environment on the optical contrast around a subunit. The fractal dimensions of E. coli strains flocculated with two different cationic polymers have been computed by two techniques: static light scattering and confocal image analysis. The fractal dimensions calculated with both techniques at different flocculation times are very similar: between 1.90 and 2.19. The comparison between two completely independent techniques confirms the theoretical approach of multiple scattering of large flocs using the Mie theory. Size distributions have been calculated from light-scattering data taking into account the linear independence of the structure factor S(q) relative to each size class and using the fractal dimension measured from F(q) in the large-angle range or from confocal image analysis. The results are very different from calculations made using hard-sphere particle models. The size distribution is displaced toward the larger sizes when multiple scattering is considered. Using this new approach to the analysis of very large fractal aggregates by static light multiple scattering, the fractal dimension and size distribution can be calculated using two independent parts of the scattering curve.