Dynamical studies on low molecular weight polyacrylamide aqueous solution

From quasi elastic light scattering and viscosity measurements we deduce the unperturbed dimensions and dynamical power laws of low molecular weight polyacrylamide in 0.1 N NaCl aqueous solutions.     

Unperturbed dimensions and the theta temperature of dextran in aqueous solutions

Intrinsic viscosity measurements were carried out on dextran samples (of different molecular weights) in aqueous solutions at 25, 28, 31, 34, 37, 40, and 43°C. The extrapolation methods were used for the data; they gave unperturbed dimensions, K₀, of the chain. The unperturbed root‐mean‐square end‐to‐end distance 〈r²〉[STACK]^1/2₀[ENDSTACK] calculated for the polymer samples in water indicate that the polymer coils are slightly contracted in this solvent as the temperature is increased. The long‐range interaction parameter, B, was also determined. In aqueous dextran solutions, this showed a significant decrease in the long‐range interactions between 25 and 43°C. The values of Θ = 317.82 and 316.57 K were obtained from the temperature dependence of the interaction parameter B in the Kurata–Stockmayer–Fixman and Berry equations. Calculated values were interpreted mainly on the basis of hydrogen‐bond formation between polymer segments and dextran–water molecules in solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 871–876, 1999     

Effect of Side Groups on the Conformation of a Series of Polysiloxanes in Solution

The molecular conformation has been obtained for polysiloxane chains in which the pairs of substituents bonded at the silicon atom are CH₃, CH₃; C₂H₅, C₂H₅; CH₃, C₆H₁₃; CH₃, C₁₆H₃₃; and CH₃, C₆H₅. Polysiloxanes dissolved in toluene and benzene were studied using a coupled system: Gel Permeation Chromatography/Light Scattering (GPC/LS). Attention was focused on the influence in the molecular conformation of the quality of the solvent and the type of substituent on the main chain. The results obtained were strongly dependent on the side group size and flexibility. Poly(dimethylsiloxane) samples of 273,400 and 97,600 daltons showed a semi-flexible conformation, but the sample of relatively low molecular weight (36×10³ daltons) exhibited a slope of 0.6 in good solvents; i.e., demonstrated the behavior of dilute (non-overlapping) coils in a good solvent. With respect to the poly(diethylsiloxane), the source of the coil's expansion is the high mobility of the side chains. Poly(methylphenylsiloxane) exhibits a rigid rod conformation in both solvents. The orientation of the phenyl groups and the attractive interaction between these groups dominate the polysiloxane chain behavior in good solvents. For these polysiloxanes, the expansion factor value is analyzed and the influence of solvent on the polymer's unperturbed dimensions is discussed. Poly(methylhexylsiloxane) and poly(methylhexadecylsiloxane) show a spherical conformation in both solvents. This conformation may arise from strong interactions between the bulky side groups and the main chain.     

The θ-behaviour of heterogeneous macromolecules

A polymer chain consisting of N_r segments with a repulsive interaction (binary cluster integral β_r) and N_a ? N_r segments with a stronger, attractive and pairwise saturable interaction (β_a), which is at the averaged θ-point N²_rβ_r + N²_aβ_a = 0 deviations from the predictions of the two parameter theory: $\text{α}{}^2{}_{\mathrm{<mtext>R</mtext>}}\text{? 1 ～ δz}{}_{\mathrm{<mtext>r</mtext>}}\text{< 0}$ and A₂ ～ δz_r > 0 with $\text{δz}{}_{\mathrm{<mtext>r</mtext>}}\text{～ β}{}_{\mathrm{<mtext>r</mtext>}}\text{(}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. It is shown that the deviations from the universal behaviour are due to the existence of an intermediate length scale $\text{～}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}$.     

The unperturbed molecular dimensions of poly(ethylene oxide) in aqueous solutions from intrinsic viscosity measurements and the evaluation of the theta temperature

Intrinsic viscosity measurements were carried out on five well characterized fractions of poly(ethylene oxide) in aqueous solutions at 24.9°, 34.9°, and 45.5°C. The Stockmayer-Fixman extrapolation was applied to the data: it yields the unperturbed dimensions K₀ of the chain. The unperturbed root-mean-square end-to-end distance $\text{〈}\text{R}\text{?}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_0$ calculated for the polymer fractions in water indicate that the polymer molecules are expanded in this solvent as the temperature is raised. The temperature coefficient of unperturbed dimension, $\text{d In}\text{〈}\text{R}\text{?}{}^2\text{〉}{}_0\text{d}\text{t}\text{= 0.024}\text{K}{}^{\mathrm{?1}}$, calculated for poly(ethylene oxide) in water using the present data is about 100 times higher than the literature values of 0.23 (±0.02) × 10^?3 K^?1 and 0.2 (±0.2) × 10^?3 K^?1, respectively, obtained from force-temperature (‘thermoelastic’) measurements on elongated networks of the polymer in the amorphouse state and form viscosity measurements on this polymer in benzene. A value of θ=108.3°C was obtained from the temperature dependence of the interaction parameter B in the Stockmayer-Fixman equation.     

Data fitting in photon correlation spectroscopy studies of dilute polymer solutions

Two methods of processing data from photon correlation studies of polydisperse polymer samples in dilute theta solution have been compared using computer generated correlation functions. Force-fitting a single exponential to the data gives a value for the diffusion coefficient D only slightly less than D_z, the z-average value returned by the cumulants method. Both methods are shown to give the same concentration dependence for D.     

Cloud point phenomena in mixtures of anionic and cationic surfactants in aqueous solution

The interaction between anionic and cationic surfactants was investigated by means of surface tension, conductivity, and nuclear magnetic resonance. It was found that a strong interaction exists between anionic and cationic surfactants and the mixed surfactant has a hydrophobic property. The phase diagram has been determined as a function of temperature for the waterstearyltrimethylammonium chloride (STAC)-sodium laurate (NaL). The Krafft point rose remarkably in equimolar mixtures for this system. The phase diagram has been determined as a function of temperature for the STAC-sodium-N-lauroyl-N-methyl-β-alanine (NaLMA) system. The liquid-liquid phase separation phenomenon was observed around an equimolar mixture. It can be identified with the cloud point, which is shown by nonionic surfactants. This phenomenon seemed to be caused by the decreased solute-solvent interaction (i.e., dehydration of the amido group contained in NaLMA molecule) as the temperature is raised. The decreasing effect of protein (ovalbumin) denaturation was observed in the high area of the mole fraction of cationic surfactant in the cationic-anionic system. We believe that this is due to the remarkable lowering of the monomer concentration by the formation of a hydrophobic complex.     

Behaviour of methylmethacrylate-acrylonitrile random copolymers in dilute solution

Studies on the dilute solution properties of methylmethacrylate-acrylonitrile random copolymers of three different compositions, 0.236, 0.5 and 0.74 mole fraction (m.f.) of acrylonitrile (AN) designated as MAa, MAb and MAc, respectively, have been made in good solvents and theta solvents. MAa has been studied in benzene (Bz) and ethylacetate (EAc). MAb in acetonitrile (MeCN), dimethyl sulphoxide (DMSO) and a binary solvent mixture of Bz and dimentyl formamide (DMF) in the volume ratio 6.5:1 designated as BM1 and MAc in MeCN, DMSO and Bz + DMF in the volume ratio 1.667:1 designated as BM2. The Mark-Houwink exponent ‘a’ reveals that Bz is a theta solvent for MAa at 20°C. For MAb and MAc, BM1 and BM2, respectively have ‘a’ values of 0.5 at all three temperatures studied (30°, 40° and 50°C). It is not clear whether they represent theta states or preferential adsorption plays a role complicating the behaviour in solution. The values of A₂ are very low in MeCN considering that it is a very good solvent for the copolymer, ‘a’ values for MAb and MAc being 0.75 and 0.7, respectively.     

Beyond the aniline point: Critical solution point for the oil/aniline system as a measure of oil solubility

The present publication elaborates upon the possibility of using the critical solution point for the oil/aniline system instead of its aniline point in order to characterize oil solubility. From a theoretical point of view, the critical solution point should be a better indicator of the oil/aniline repellency, than the aniline point, because the former is directly proportional to the Flory interaction parameter and has a transparent thermodynamic meaning.     

Electrical conductivity and counterion association of cationic polyacrylamide derivatives in aqueous solution

Equivalent electrical conductivity (Λ) is reported for three series of cationic quaternary ammonium polyacrylamide derivatives with $\hbox{MeSO}_{4}ˆ{‐}$ , Cl⁻, Br⁻ and I⁻ as counterions at 25 °C, the polyion equivalent concentration C ranging from 5.3 × 10⁻⁴ to 6.4 × 10⁻³ N and from 1.0 × 10⁻³ to 1.4 × 10⁻² N. Equivalent electrical conductivity increases with decreasing polyion equivalent concentration, and the sequence of equivalent electrical conductivity Λ of polyelectrolytes for the same series with different counterions in the range of concentration investigated is: $\hbox{MeSO}_{4}ˆ{‐} &#62; \hbox{Cl}ˆ{‐} &#62; \hbox{Br}ˆ{‐} &#62; \hbox{I}ˆ{‐}$ . The plots of the counterion–polyion interaction parameter f and degree of dissociation α of polyelectrolyte versus the polyion equivalent concentration C show that the order of counterion associating or binding to polyions for the same polyelectrolyte series in the range of concentration studied is $\hbox{MeSO}_{4}ˆ{‐} &#60; \hbox{Cl}ˆ{‐} &#60; \hbox{Br}ˆ{‐} &#60; \hbox{I}ˆ{‐}$ . The chemical structures of the polyion have much influence on the Λ, f and α values of the polyelectrolytes. © 1999 Society of Chemical Industry     

氨基酸在水溶液中扩散系数的预测

以F ick定律和不可逆过程热力学为基础,结合文献中对扩散系数预测模型的分析,提出了一个氨基酸在水溶液中扩散系数预测的半经验模型。用实验测定的7种氨基酸在水溶液中的扩散系数和一些文献中的扩散系数数据对模型参数进行了拟和。利用该模型对多种氨基酸及尿素在水溶液中的扩散系数进行了计算,计算值与实验值的平均相对误差均小于0.6%。     

Potential dependence of normalized friction coefficient of passive iron surface evaluated by nano-scratching in solution

Nano-scratching in solution was performed to the single-crystal iron (1 0 0) surface passivated at 0.0-1.0 V (SHE) in pH 8.4 borate buffer solution to evaluate the friction coefficient of the iron (1 0 0) surface kept in the passive state and its potential dependence. The friction coefficient obtained with nano-scratching for the passive iron surface depended on normal force, i.e., normal displacement, which resulted mainly from the geometry of the diamond tip. In order to avoid the effect of the tip geometry on friction coefficient, the normalized friction coefficient was newly defined with dividing friction coefficient by geometrical factor. The normalized friction coefficient obtained with nano-scratching in solution for the iron (1 0 0) surface kept in the passive sate was significantly larger than those obtained with nano-scratching in air after passivation. The normalized friction coefficient obtained with nano-scratching in air after passivation was almost independent of potential in the passive region. On the other hand, the normalized friction coefficient obtained with nano-scratching in solution increased with increasing potential in the passive region.The difference between normalized friction coefficients obtained with nano-scratching in solution and in air was discussed by taking into account a series of mechano-electrochemical reaction (film rupture, active dissolution and repassivation) which would take place at the moving front of the diamond tip during nano-scratching in solution. The large potential dependence of the normalized friction coefficient obtained with nano-scratching in solution was explained in terms of the increase in repassivation rate at the film rupture sites with increasing potential in the passive region.     

碳纤维在水溶液中的分散性研究

本文研究了不同长度、不同基质的碳纤维在水溶液中的分散性,以及不同分散剂的分散效果。     

Effect of different additives on the cloud point of a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer in aqueous solution

Cloud point studies on aqueous solutions of a polyethylene oxide (PEO)-polypropylene oxide-PEO triblock copolymer (Pluronic^® L64: EO₁₃PO₃₀EO₁₃, total m.w.=2900, PEO=40%; EO=ethylene oxide; PO=propylene oxide) in the presence of different additives show some interesting features. The effect of various inorganic salts was an increase or decrease in cloud point based on their salting in and salting out action and followed the Hofmeister lyotropic series. Nonelectrolytes and hydrotropes increased the cloud point by influencing water structure. Hydrotropes altered the cloud point of the copolymer at much lower concentrations than inorganic salts. Ionic surfactants produced a marked increase in the cloud point of copolymer solutions. The effect was greater for surfactants with greater hydrophobicity. Alcohols and other organic liquid additives that are infinitely miscible with water increase the cloud point of the copolymer, whereas additives that are partially miscible in water decrease the cloud point.     

水溶液中硼氧配阴离子的存在形式及影响因素

综述了硼酸盐水溶液中硼氧配阴离子的存在形式、振动光谱研究结果及影响其变化的因素.硼酸盐水溶液中,硼氧配阴离子除了常见的[B(OH)4]-,B(OH)3,[B3O3(OH)4],[B4O5(OH)4]2-,[B5O6(OH)4]-,[B6O7(OH)6]2-以外,还存在着[B2O(OH)6]-2,[B3O3(OH)5]2-等,各种硼氧配阴离子相互作用、相互影响.FT-IR和Raman光谱研究结果进一步明确了硼氧配阴离子的存在形式及相互作用.同时指出了各种硼氧配阴离子的存在形式及相互作用与溶液总硼浓度、pH、金属阳离子、温度及水热条件等有关,且主要依赖于溶液总硼浓度和pH.高的总硼浓度和较低的pH有利于高聚合度的硼氧配阴离子的存在,反之则利于低聚合度的硼氧配阴离子的存在.     

Temperature and salt-induced micellization of some block copolymers in aqueous solution

Micellization of three commercial samples of ethylene oxide (EO)-propylene oxide (PO) (PEO-PPO-PEO) triblock copolymers (pluronics) P65 (EO₂₅PO₃₀EO₂₅, mw PPO=1750, %PEO=50), P85 (EO₂₅PO₄₀EO₂₅, mw PPO=2250, %PEO=50), and F88 (EO₁₀₂PO₄₀EO₁₀₂, mw PPO=2250, %PEO=80) in aqueous sodium chloride solution (0–3 M) was examined by cloud point, surface tension, dye spectral change, fluorescence, and viscosity measurements over a temperature range of 25–50°C. Salt-induced micellization and micelle growth were observed. The presence of sodium chloride enhanced hydrophobicity in the PPO moiety and reduced hydrophilicity of PEO moieties, favoring micellization at relatively lower concentrations than in water at ambient temperature. The effect of salt on micellization is similar to that of increasing temperature. The critical micelle concentrations (CMC) and critical micelle temperatures showed a marked decrease in the presence of added salt. CMC obtained by different methods were in good agreement.     

Moisture-sorption properties and studies on the dilute solution behavior of epoxidized natural rubber ENR 50

Studies of the dilute solution capillary viscosity and moisture sorption of commercial samples of epoxidized natural rubber (ENR 50) were carried out. Dilute solution viscometry of ENR 50 solutions was conducted in xylene, tetrahydrofuran, and methyl ethyl ketone solvents and the degradation due to shearing and oxidation for this rubber was followed. At average elevated temperatures and high relative humidities, epoxidized natural rubber ENR 50 shows high moisture sorption. Moisture sorption measurements at 100% RH and 34°C followed by desorption show near equilibrium moisture intake of 3.402–3.661 g H₂O/100 g rubber, which agrees reasonably well with the estimated value of 4.108 g H₂O/100 g ENR 50. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1633–1644, 1999     

Improved accuracy and precision in the light-scattering characterization of homo- and copolymers in THF

A one-point method was developed for the estimation of weight-averaged molecular weights from light-scattering data. The method is based on the calculation of the second virial coefficient from theoretical predictions of the dependence of A₂ on the molecular weight. The second virial coefficient is then regressed for a particular polymer—solvent combination from a series of preexisting measurements over a range of molecular weights. The one-point method is found to yield as accurate molecular weight estimates as obtained from a Debye plot using the conventional dilution technique. The variance in the estimation of the Rayleigh factor has also been found to be highly dependent on the measurement concentration. Therefore, the precision in the estimation of molecular weight can be improved by calculating molecular weights at or near the optimal concentration, which is itself molecular weight-dependent. The one-point method is demonstrated for poly(methyl methacrylate)s of various polydispersities in tetrahydrofuran. The molecular weight of polystyrene and polystyrene-co-acrylic acid were also estimated by the one-point method in THF. In the case of the polystyrene-co-acrylic acid, THF becomes a poorer solvent with increasing levels of acrylic acid in the copolymer, and the parameter (A₂M^0.5) is found to vary with the copolymer composition, as is theoretically predicted. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1303–1316, 1997     

Interpretation of intrinsic viscosity/temperature data for solutions of poly(phenyl acrylate) and poly(ethylene oxide)

Measured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase with T for solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] with T was observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata-Stockmayer-Roig, Fixman, and Stockmayer (Padé). These yielded values of ?3.4 × 10^?3 to ?4.7 × 10^?3 deg^?1 and ?0.9 × 10^?3 to ?2.4 × 10^?3 deg^?1 for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ-temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critical solution temperature for aqueous PEO.     

分子结构和温度对油基氧乙烯醚水溶液表面吸附动力学的影响

使用最大气泡法测定了油基十氧乙烯基醚C18H35O（CH2CH2O）10H（Brij97,C18EO10OH）,油基二十氧乙烯基醚C18H35O（CH2CH2O）20H（C18EO20OH）水溶液的动态表面张力（DST）,考察了结构及温度对DST的影响,详细表征了DST随时间的变化过程,计算了动态表面张力的参数（n,t^n,γm）,结合Word—Tordai方程计算了表观扩散系数（Da）和吸附势垒（Ea）。探讨了上述参数的变化规律。