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.     

Polymer mixing in aqueous solution

The phase separation behaviour of two polymers (1 and 2) in organic solvents is relatively well understood and is usually due to repulsive interactions between 1 and 2 chain segments. In aqueous solutions, however, where the interaction of the polymer with the solvent is expected to be large, the behaviour is less well understood. In this paper the phase separation of polymers in aqueous solution has been studied and some of the factors which could control the phase separation have been investigated. The volumes of the separated phases were found to be related to the sizes of the polymer/solvent interactions. The polymer with the most positive second virial coefficent was found to occupy the phase with the largest volume. For both miscible and immiscible pairs the mixed second virial coefficients (A₁₂) was assessed from osmotic pressure measurements and was found to be an average of the individual second virial coeffients (A₁₁ and A₂₂). A few polymer pairs were found to mix and this was thought to be caused by hydrogen bonding between 1 and 2 chain segments. Mixtures of rod-like and coiled polymers were expected to phase separate to give a concentrated, ordered phase containing nearly all of the rod-like polymer and a larger phase containing the coiled polymer. However this behaviour was not found when a cellulose derivative (rod-like) was mixed with dextran (flexible).     

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.     

Properties of hydrophobically modified polyacrylamide with low molecular weight and interaction with surfactant in aqueous solution

Hydrophobically modified polyacrylamide (HMPAM), with a molecular weight of 10⁴ g/mol, was studied using a range of rheological methods and dynamic light scattering (DLS). DLS measurements indicate that the association of the modified polymer begins at low concentration. The modified polymer with high substitution forms transient networks below the critical concentration, but the networks are disrupted by the micelles formed by the polymer itself, and the networks do not contribute to viscosity enhancement. The modified polymers exhibited surface activity, and so they may be regarded as nonionic polymeric surfactants rather than thickeners. On the other hand, HMPAM is shown to interact with the surfactant SDS while PAM is inert to SDS. In the hydrophobic domains, it undergoes a surfactant‐induced association process; in the hydrophobe‐surfactant transition regions, the surfactant binds to the polymer in a noncooperative way and forms a polymer–surfactant complex. Contracted polymer chains begin to extend because of electrostatic repulsion, which can overcome the association at surfactant domains. The conformation of HMPAM polymer chains could be controlled by adding a specific amount of surfactant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4348–4360, 2006     

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.     

One‐ and two‐phase isochoric heat capacity measurements of aqueous solution of nacl near the critical point of pure water

Isochoric heat capacities of H₂O+NaCl solutions (0.0031 and 0.0063 mole fraction of NaCl) were measured with a high temperature and high pressure adiabatic calorimeter near the sub‐critical and near the supercritical point of pure water. Temperatures ranged from 361 to 677 K. Measurements were made at six densities, namely: 367.07 and 485.59 kg·m^?3 for x = 0.0031 mol fraction of NaCl and 388.65, 560.03, 607.05, and 973.70 kg·m^?3 for x = 0.0063 mol fraction of NaCl. Measurements were conducted in the two‐and one‐phase regions including near phase transition temperatures T_S(ρ). The phase transition temperatures T_S(ρ) and saturated isochoric heat capacity values C_VX have been determined for each isochore. The uncertainty in heat capacity measurements is estimated to be 3.5% to 4.5% near the phase transition and critical points. Present and previous results of heat capacity measurements were compared with predictions from the crossover (CREOS) and Pitzer—Tanger–Hovey equations of state (PTH EOS). Our previous heat capacity measurements were found to deviate systematically from crossover‐model predictions. The present results show good agreement with the crossover model for the composition x = 0.0031 mol fraction.     

有机硅表面活性剂对水体中多环芳烃的浊点萃取研究

Cloud point extraction （CPE） processes with two silicone surfactants, Dow Coming DC-190 and DC-193, were studied as preconcentration and treatment for the water polluted by three trace polycyclic aromatic hydrocarbons （PAHs）： anthracene, phenanthrene and pyrene. For all cases, the volumes of surfactant-rich phase obtained by two silicone surfactants were very small, i.e. a lower water content in the surfactant-rich phase was obtained. For example, less than 3% of the initial solution was obtained in a 1% （by mass） surfactant solution, which was much smaller than that of TX-114 in the same surfactant concentration. And TX-114 is known as a high compact surfactant-rich phase among most nonionic surfactants, thus the comparison showed that an excellent enrichment was ensured in the analysis application by the CPE process with the silicone surfactants, and the lower water content obtained in the surfactant-rich phase is also important in the large scale water treatment. The influences of additives and phase separation methodology on the recovery of PAHs were discussed. Comparing with DC-193, DC-190 has a lower cloud point and a higher recovery （near 100%） of all the three PAHs in same surfactant concentration, which was required for application as a preconcentration process prior to HPLC system. However the DC-190 solution is hard to be phase separated only by heating, whereas DC-193 has a relative higher phase separating speed by heating, but a high cloud point （around 360K） limits its application. Due to the phase separation by heating is the only method of CPE suitable to the large scale water treatment, the mixtures of two silicone surfacrants solutions were investigated in this study. A solution containing 1% of mixed DC-190 and DC-193 （in the ratio of 90 ： 10） removed anthracene, phenanthrene and pyrene near 100% with a relative low cloud point and quick phase separating speed.     

Conformation of polyacrylamide in aqueous solution with interactive additives and cosolvents

The viscosity of polyacrylamide (PAM) dilute aqueous solutions with NaCl, glucose, and SDS as additives was measured by Ubbelohde viscometry. There was linear relationship between reduced viscosity vs. PAM concentration in aqueous solutions. The Huggins constant k and intrinsic viscosity [η] were used to study the conformation of the polymer chains and the degree of polymer–solvent interaction. In addition, the viscosity of diluted PAM solutions in water with acetone, ethanol, DMF, and ethylene glycol as cosolvent was measured. It was found that the polymer chain conformation contracted as the acetone, ethanol, and DMF cosolvent composition ratio increased, but there was no distinguishing difference between water–ethylene glycol compositions. The solution properties of PAM were used to estimate the swelling properties of PAM gel in the same external conditions, as gel is formed by crosslinking of linear polymer. In good solvent the polymer chain should be expanded, and gel is expected to have large swelling ratio. In water cosolvent systems, when the linear polymer chain underwent coil–globule transition, PAM gel should have volume phase transition under corresponding external conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3122–3129, 2003     

Influence of temperature and concentration on tribological properties of silicon nitride in glycerol aqueous solution

Friction and wear behaviors of self-mated Si₃N₄ in glycerol aqueous were investigated by varying the temperature (30 °C, 50 °C, and 70 °C) and concentration (pure water, 5 vol%, 20 vol%, and 50 vol%) of glycerol aqueous solution. Friction tests were conducted on a ball-on-disk apparatus. Normal load and sliding velocity were fixed at 30 N and 0.5 m/s, separately. After each tests, friction coefficients and wear rates were measured to evaluate friction and wear behavior. The results showed that the period of running-in process reduces with the increase of concentration and decrease of temperature. Increase of temperature could intensify wear behavior, and when concentration is larger than 20 vol%, wear rate of glycerol aqueous solution is one order less than that of pure water. Our findings could also guide for the use of glycerol aqueous solution as lubricant at different temperature. At 30 °C, the higher the concentration was, the smaller wear volume and total wear rate were. However, at 50 °C and 70 °C, total wear rates of disk were the largest when concentration is 5 vol%, a concentration of glycerol larger than 20 vol% must be added into water to reduce the wear rate. Wear regimes at different conditions were also given in this paper based on lubrication state number.     

纳米微粒及其分散剂对溴化锂溶液表面张力和沸腾温度的影响

在纯溴化锂溶液中加入纳米微粒或分散剂,对比测试其与纯溴化锂溶液的表面张力和沸腾温度的数据,并从所用分散剂的分子结构和纳米微粒的尺寸及外部轮廓的角度出发,定性推测不同种类分散剂及纳米微粒对溴化锂溶液表面张力和沸腾温度的影响.试验发现,添加分散剂溶液的表面张力明显降低,其沸腾温度也相应减小;固体纳米微粒因其填充加热表面凹坑使溶液的沸腾温度有所升高.对于加入纳米微粒及其分散剂的溴化锂溶液,溶液表面张力衰减的正效应因素和纳米微粒填充凹坑的负效应因素的耦合影响将对其沸腾温度产生重要影响.     

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.     

Flash point and fire hazard analysis of three organic fuels and their aqueous solutions at low pressures

To study the low pressure influence on the flash point and fire hazard of organic fuels and their aqueous solutions, a series of experiments has been conducted to measure the open‐cup and closed‐cup flash points of methanol, ethanol, and n‐decane aqueous solutions including different mole fractions under different static pressures ranging from 35 to 101 kPa. The results show that both the pressure and fuel mole fraction have a nonlinear correlation with the flash point of the miscible fuel specimens like the correlation provided in this paper. For the partially miscible fuel specimens with a lower density than water, the water content has almost no influence on the flash point. The fire risks of the experimental results were analysed based on the standard GB50160‐2008, which shows that the fire risk becomes higher at low pressures, and there is a critical pressure at the turning point of the change in fire classification. A method to achieve the critical low pressure of different fuels or aqueous solutions from the fire hazard classification is derived in this paper.