Specific Refractive Index Increment Research Articles

Specific refractive index increments of segmented polyurethanes

Specific refractive index increments ν of polyester-based segmented polyurethanes in N,N-dimethyl formamide have been determined, and the quotient dν/dfd has been evaluated (where fd is the weight fraction of hard-segment units). The results are in good agreement with the values calculated from group contributions to the molar refraction, using the Vogel or the Gladstone–Dale equations. The values calculated with the Lorenz–Lorentz equation are too low. A potential explanation of this fact is proposed. The same methods have been applied to reported ν values for polyether-based polyurethanes. An explanation is proposed for differences in dν/dfd for polyester- and polyether-based polyurethanes. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1917–1923, 1998

Some properties of poly(carbonates) and poly(thiocarbonates) from diphenols with methyl groups in the 3-position in the phenyl rings

Glass transition temperatures and the corresponding activation energies of poly(carbonates) and poly(thiocarbonates) with different side-chain substituents obtained from diphenols with methyl groups in the 3-position in the phenyl rings have been determined by differential scanning calorimetry at several scanning speeds. Partial specific volume and specific refractive index increments have also been obtained by densimetry and refractometry measurements in benzene at 25°C. The effect of the different substituents on these properties has been analysed. © 1998 SCI.

A general method for determining the micellar dissociation concentration of a surfactant using a differential refractometer

This paper describes a method for determining the micellar dissociation concentration (MDC) of a surfactant using a differential refractometer. This method can be generally applied to the MDC determination for anionic, cationic, zwitterionic and nonionic surfactants. The MDC values obtained by this method show good agreement with those given in the literature. The method described in this paper is very sensitive to small concentration changes around the MDC for all types of surfactants measured. The specific refractive index increment measured by the differential refractometer shows distinctly different values in the concentration regions below and above the MDC. The method described in this paper is potentially good for developing into an automatic measurement.

Determination of Specific Refractive Index Increments of Water Soluble Polymers by Quantitative Size Exclution Chromatography

Determination of Specific Refractive Index Increments of Water Soluble Polymers by Quantitative Size Exclution Chromatography

Determination of Specific Refractive Index Increments of Water Soluble Polymers by Quantitative Size Exclution Chromatography

Determination of Specific Refractive Index Increments of Water Soluble Polymers by Quantitative Size Exclution Chromatography

Studies on agaroses; 1. Specific refractive index increments in dimethyl sulfoxide and in water at various wavelengths and temperatures

Specific refractive index increments of three agarose samples in dimethyl sulfoxide and in water were measured at 436, 546 and 633 nm, and at several temperatures. The wavelength and temperature dependences of the increments were determined, simultaneously correlated using the surface regression method, and presented in a form suitable for tabulation. The influence of differences in the structure of agaroses from various algal sources on the specific refractive index increment is discussed.

Study of segmented ethylene terephthalate–caprolactone copolymer by differential refractometry and light scattering

AbstractA segmented ethylene terephthalate (ET)–caprolactone (CL) copolymer was characterized by light scattering in chloroform tetrahydrofuran and butanone. The flexibility of the copolymer chain is comparable with that of typical flexible chains, such as polystyrene. In the process of applying the Bushuk–Benoit light scattering theory to the segmented PET–PCL copolymer, we encountered not only the problem of finding three solvents with different refractive index but also the problem of determining the specific refractive index increments for the PET and PCL segments in the copolymer, i.e., νPET and νPCL. In principle, the approximate values of νPET and νPCL can be obtained from the PET and PCL homopolymers, respectively. In reality, it involves many practical problems, e.g., to find three solvents not only for copolymer but also for the PET and PCL homopolymers. In this study, a different method was used to find both νPET and νPCL, wherein the ν values of at least two segmented PET–PCL copolymers with different PET compositions were used. With νPET, νPCL, and ν, we characterized the absolute molecular weight. Further, we show that the composition of an unknown segmented PET–PCL copolymer can be estimated from νPET, νPCL, and ν. © 1994 John Wiley & Sons, Inc.

Solution behavior of buckminsterfullerene (C60) in benzene

Solution characterization of buckminsterfullerene C60 in benzene was carried out by laser light scattering. Static and dynamic light scattering (SLS and DLS) experiments were accomplished by using an incident laser beam of 790 nm wavelength, and a fiber optic probe which was coupled to a RCA C31034 photomultiplier tube sensitive to the near ir wavelength. The effective hydrodynamic radius of C60 in benzene solution determined by using DLS was 6.4±0.1 Å, in close agreement with the distance measured from the center of the solvated benzene to the center of the benzene-solvated C60 (C60⋅4C6H6):6.7∼6.8 Å as evaluated from the single crystal structure by x-ray diffraction. C60 was found to aggregate slowly even in fairly dilute solution concentrations ranging from 0.78 to 1.39 mg/mL at temperatures 23∼27 °C. Based on the high specific refractive index increment of C60 in benzene, the molar mass of the C60 aggregates could be estimated. Together with the radius of gyration, the hydrodynamic radius, and its size distribution, the kinetics of the aggregation process was investigated. The aggregation of C60 in benzene solution was reversible, i.e., the C60 aggregates could be dispersed simply by hand shaking the solution. The light-scattering intensity results indicated that the structure of C60 aggregates could be described as a fractal with a dimension of 2.10 and the aggregation kinetics exhibited essentially an exponential behavior.

Incorporation of a differential refractometer into a laser light-scattering spectrometer

A new differential refractometer, which mainly consists of a laser light source, a position-sensitive detector, and a temperature-controlled refractometer cuvette has recently been developed. In comparison with a conventional differential refractometer, it has a different optical design so that the effect of laser beam drift can be greatly reduced. In our design, a very small pinhole is illuminated by the laser light and the illuminated pinhole is imaged to the detector by a lens located in the middle between the detector and the pinhole in a 2f-2f configuration. The cuvette is placed just before the lens. The pinhole, the cuvette, the lens, and the detector are mounted on a small optical rail. The refractometer can be easily incorporated into any laser light-scattering spectrometer, in which the laser, the thermostat, and the computer are shared. This not only reduces the total cost (at least ten times cheaper than a commercial differential refractometer), but also enables us to measure the specific refractive index increment and the scattered light intensity under the identical experimental conditions, such as wavelength and temperature. This novel refractometer has a wide linear detection range (±0.035 RI units) with a resolution of 10−6 RI units, which is sufficient for determining the specific refractive index increment of most polymer solutions.

Preferential adsorption and viscometric behaviour of poly(2-acrylamido-2-methyl propane sulphonamide) in formamide/water mixtures

Specific refractive index increments have been measured for solutions of a new, neutral, water-soluble polymer, poly(2-acrylamido-2-methyl propane sulphonamide) (PASAM), in binary solvents of formamide/water over the whole range of solvent composition. Comparison of these increments with those obtained at constant chemical potential of low molecular weight species yielded the coefficient of selective adsorption ( γ 1) of formamide by the polymer. Positive values of γ 1 were exhibited at solvent composition up to 65% (v/v) of the thermodynamically better solvent, formamide. At higher contents of formamide in the binary solvent, formamide is selectively desorbed. The intrinsic viscosities [η] of PASAM in formamide and in the binary solvents all exceed the value of [η] in water. The maximum value of [η] obtains when there is no selective adsorption, i.e. in the solvent containing ca 65% (v/v) of formamide. The validity of the very high value of the solubility parameter of PASAM estimated viscometrically is discussed.

Change in oligomeric structure of solubilized Na + /K +-ATPase induced by octaethylene glycol dodecyl ether, phosphatidylserine and ATP

Membrane-bound Na + /K +-ATPase purified from dog kidney was solubilized with octaethylene glycol dodecyl ether (C 12E 8), and the resultant solubilized enzyme was chromatographed on a TSKgel G4000SW XL or G3000SW XL column equilibrated with elution buffers containing various ligands affecting oligomerization of the enzyme. Weight-averaged molecular weight ( M w ) values for the main protein components eluted were estimated by low-angle laser light-scattering photometry. With increasing concentration of C 12E 8 included in the elution buffer from 0.1 to 5 mg/ml, the M w decreased from 230 000 to 153 000, indicating that C 12E 8 induced dissociation of the enzyme. In contrast, the M w of the protein component increased up to 1.44 · 10 6 as the concentration of phosphatidylserine (PS) added to the elution buffer containing a fixed concentration of 0.3 mg/ml C 12E 8 was increased to 120 μg/ml. The association and/or aggregation were reversible by removal of the PS by rechromatography. Addition of PS to the elution buffer also allowed the solubilized enzyme to exhibit ATPase activity comparable to that of the membrane-bound enzyme during passage through the column. This was also the case with phosphatidylglycerol (PG) and phosphatidylinositol, but not with phosphatidylcholine or phosphatidylethanolamine. The specific refractive index increment d n / d c p ) of the solubilized enzyme was increased by addition of exogenous PG or PS, strongly suggesting that the phospolipid became bound to the enzyme, and that it induced association of the enzyme. The association induced by PS was inhibited by ATP and ADP, but not AMP. The concentrations for half-maximal inhibition were 0.44 mM for ATP and 0.88 mM for ADP. The PS-induced associated enzyme isolated by chromatography in the presence of 120 μg/ml PS was dissociated by ATP with K 0.5 of 0.16 mM. The dissociating effect of C 12E 8, ATP and ADP and the associating effect of PS on the solubilized enzyme are consistent with the reports that C 12E 8 mimics the effect of regulatory ATP at the low-affinity site on the conformationl transition from E 2 to E 1, and that phospholipids are essential for the reverse transition from E 1 to E 2. The results can be explained by assuming that the enzyme takes the form of a loosely associated diprotomer in the E 1 state and a tightly associated one in the E 2 state.

Solution properties of poly(fluorostyrene‐co‐chlorostyrene) copolymers. I. Light scattering, differential refractometry and viscometry

AbstractThe weight‐average molecular weights (M̄w) of nominally random, unfractionated copolymers of ortho‐ and para‐fluorostyrene and ortho‐ and para‐chlorostyrene were determined by light scattering measurements in tetrahydro‐furan, toluene, carbon tetrachloride and chloroform. It was shown that there is no significant variation in measured M̄w in the various solvents, a finding indicating that the copolymers are not compositionally heterogeneous. Intrinsic viscosity measurements in the same solvents established a consistent relationship between [n] and M̄w despite the differences in copolymer compositions. It was not possible to establish a similar relationship between the second virial coefficient A2 and M̄w. It was concluded that measurements of the specific refractive index increment could be used for determining copolymer composition if the measurements were performed in thermodynamically poorer solvents. The results established for the Mark‐Houwink constant α, intrinsic viscosity, and A2 values indicated that these solvated copolymer molecules are in a less expanded conformation than are polystyrene molecules of similar molecular weights in a given solvent.

Molecular weight characterization of polyacrylamide‐CO‐sodium acrylate. II. Light scattering

AbstractThe first large‐scale fractionation method for polyacrylamides is reported. This has been optimized to prepare a series of narrowly distributed polymer standards with molecular weights between 10,000 and 1,000,000. These were subsequently hydrolyzed to between 5 and 35% sodium acrylate content through a saponification reaction. It has been found that the classical light‐scattering theory, derived for nonionic scattering bodies, can be applied to polyelectrolytes provided the specific refractive index increment (∂n/∂c) is evaluated at constant electrochemical potential (μ). This is obtained by dialyzing the polymer solution against the dialysate (0.2MNa2SO4 for polyacrylamide‐co‐sodium acrylate) for a predetermined equilibrium period, specific to the pore size of the membrane used. From such measurements at various copolymer compositions (F), the following empirical relationship is established: where a was found to be −0.076. The validity of the specific refractive index increment at constant chemical potential is established through light‐scattering measurements of the weight‐average chain length of the hydrolyzed polyacrylamides. These were then compared with the chain lengths of the parent nonionic polymers from which they were derived. Excellent agreement is observed, implying the polyelectrolyte characterization method developed, and specifically the (∂n/∂c)μ's, are accurate and reliable.

The synthesis of poly‐L‐amino acids and their characterization by size exclusion chromatography with low‐angle laser light scattering (SEC‐LALLS/UV/DRI)

AbstractThe synthesis and characterization of polyamino acids are described in this paper. Detailed polymerization descriptions of newly synthesized polyamino acids are discussed. The final polyamino acids were characterized by elemental analysis, infrared (IR) spectroscopy, mass spectra, and low‐angle laser light scattering (LALLS). LALLS was used to determine the weight average molecular weight (MW) indicating the extent of the polymerization procedure. Isocratic size exclusion chromatography (SEC) coupled to a tri‐detection system consisting of a LALLS, ultraviolet/visible detector (UV/VIS), and a modified differential refractive index detector (DRI) was used to calculate on‐line specific refractive index increment (dn/dc), MW, percent recovery, and polydispersity, all in one injection once one determines the on‐line molar absorptivity value of the synthesized polyamino acid. © 1992 John Wiley & Sons, Inc.

Light scattering by solutions of associating polymers at equilibrium

The intensity of zero-angle static Rayleigh light scattering by a polymer solution containing associated species, all in equilibrium with each other, can be calculated by introducing the thermodynamic condition for equilibrium either at the start or at the end of the calculation. Provided all species have the same value of the specific refractive index increment, it is shown for Flory-Huggins systems that the same formula is obtained by both routes. 9 refs.

Interfacing gradient elution ion-exchange chromatography and low-angle laser light-scattering photometry for analysis of proteins

Molecular weights (MWs) of different proteins were determined by interfacing gradient elution ion-exchange chromatography and low-angle laser light-scattering photometry (IEC-LALLS). A high-performance strong cation-exchange column was used to elute proteins using fast (5 min) and conventional (15-30 min) gradients. The eluted proteins were characterized on-line by determining their MWs using LALLS. The specific refractive index (RI) increment (d n/d c) and the RI of the solvent used over the gradient range were determined off-line and used to calculate the absolute weight-average MWs. Four proteins, ribonuclease A, α-chymotrypsinogen A, trypsinogen and β-lactoglobulin A (β-LACT) were studied. Accurate MWs were obtained for all the proteins using fast and conventional gradients, except for β-LACT, which aggregated as a function of the gradient employed. The degree of aggregation of β-LACT increased as the rapidity of the gradient was increased over a fixed gradient range. This study indicated that it is possible to separate and characterize proteins rapidly using IEC-LALLS.

024 Size-exclusion chromatography with simultaneous low-angle laser light scattering, ultraviolet and refractive index detection: absolute molecular mass determination with online determination of the specific refractive index increment

024 Size-exclusion chromatography with simultaneous low-angle laser light scattering, ultraviolet and refractive index detection: absolute molecular mass determination with online determination of the specific refractive index increment

Determination of pituitary and recombinant human growth hormone molecular weights by modern high-performance liquid chromatography with low angle laser light scattering detection

The determination of molecular weight for pituitary and recombinant human growth hormone (p-hGH/Crescormon and r-hGH/Protropin) has been performed. This has involved on-line coupling of size-exclusion chromatography (SEC) and gradient elution, reversed-phase high-performance liquid chromatography (RP-HPLC) with low-angle laser light scattering (LALLS) detection. A 5-μm, 300 Å, Delta-bond octyl column was used. Traditional specific refractive index increment (d n/d c) and refractive index ( n) measurements have been performed in order to derive absolute weight-average molecular weight ( M w) information for p-hGH and r-hGH. Known concentrations of each protein have been separated using reversed-phase gradients utilizing acetonitrile with on-line LALLS determination of excess Rayleigh scattering factors. Accurate M w data has been obtained for both proteins under conventional RP-HPLC gradient elution conditions. SEC data of both hGHs were found to be concentration, mobile phase, and column dependent for the particular analyses. Both medium- and high-resolution SEC—LALLS studies were performed, and all of these determinations further confirmed our RP-HPLC results. On-line LALLS provides certain advantages in identifying aggregates that may be present, even in medium-resolution SEC, where incomplete resolution occurs. The on-line coupling of modern RP-HPLC for biopolymers with LALLS detection represents a major step forward in the ability of bioanalytical chemists to determine the nature (monomer versus higher-order aggregate) of such materials. Other classes of biopolymers should prove suitable for studies with the same RP-HPLC—LALLS—UV approaches.

Complete on-line determination of biopolymer molecular weight via high-performance liquid chromatography coupled to low-angle laser light scattering, ultraviolet, and differential refractive index detection

An optically modified high-performance liquid chromatography refractive index detector was developed to allow complete on-line determinations for biopolymer molecular weights. On-line concentration, refractive index, specific refractive index increment (dn/dc2)mu, and Rayleigh factor were determined under flow injection analysis (FIA) and size exclusion chromatography (SEC) conditions using low-angle laser light scattering, ultraviolet, and modified refractive index detection. This instrumental system is capable of determining absolute on-line molecular weights. The error and time requirements involved in conventional methodologies for proteins have been reduced. Sample quantities have been reduced from 150 to 200 mg, in conventional off-line methods, to less than 2 mg for on-line FIA and 0.5 mg for on-line SEC, if mass absorptivities (a) are known. Otherwise, the determination of a will be the most sample-demanding step, requiring about 3 mg of the pure protein. On-line measurements of (dn/dc2)mu are in good agreement with traditional off-line values established at Donnan equilibrium (usually within 5%). In addition, this technique provides true injected mass as determined by the UV detector, after chromatographic exposure where losses may occur, which is then used in the calculation of biopolymer molecular weight.

Determination of biopolymer (protein) molecular weights by gradient elution, reversed-phase high-performance liquid chromatography with low-angle laser light scattering detection

The determination of molecular weights for certain proteins haas been performed. This was involved the on-line coupling of gradient elution, reversed-phase high-performance liquid chromatography (RP-HPLC) with low-angle laser light scattering (LALLS) detection. A new 1.5-μm, non-porous, Monosphere RP-C 8 column has been used in order to perform fast and conventional RP-HPLC gradients (5–45 min). Traditional specific refractive index increment (d n/d c) and refractive index ( n) measurements have been performed in order to derive absolute weight-average molecular weight ( M w) information for ribonuclease A, lysozyme, and bovine serume albumin. Standard mixtures of known concentrations of each protein have been separated using reversed-phase gradients utilizing acetonitrile with on-line LALLS determination of excess Rayleigh scattering factors. Accurate M w data have been obtained for all three proteins, but only under certain, conventional reversed-phase gradient elution conditions. Between 5–10 min of fast gradient elution, each protein appears to exhibit unusual M w values, suggestive of aggregate formations. Methods have been developed to define the nature of such aggregates. The on-line coupling of modern RP-HPLC for biopolymers with LALLS represents a major step forward in the ability of bioanalytical chemists to determine the nature (monomer versus aggregate) of such materials. Other classes of biopolymers should prove suitable for studies with the same RP-HPLC—LALLS—UV approaches.