Light scattering Rayleigh linewidth measurements on some dextran solutions

Light scattering Rayleigh linewidth measurements have been made upon eight fractions of dextran from Leuconostoc mesenteroides B512 with molecular weights ranging from 10 to 500 kg/mol and the relationship D₂₀ = 2.25 × 10^?4M^?0.45 (D in mm²/s, M in kg/mol) was established. No concentration dependence of diffusion constant was detected within experimental error (±3%). The measurements were corrected for the polydispersity of the fractions. The results are compared with diffusion constants obtained by conventional techniques and with viscosity data.     

Light scattering Rayleigh linewidth measurements on some solutions of cellulose trinitrate

Light scattering Rayleigh linewidth measurements have been made upon three cellulose trinitrate samples in ethyl acetate by obtaining the autocorrelation function of fluctuations in scattered intensity. The weight average degrees of polymerization (DP_w) were in the range 2400 to 3300 and $\text{DP}{}_{\mathrm{w}}\text{DP}{}_{\mathrm{n}}\text{～ 1.3}$. Measurements were made at concentrations below 2 × 10^?3 g/ml and no concentration dependence was detected within experimental error (±7%). No effects due to internal motion of the polymer chains were observed even though current theories predict that these effects should be quite large. Reasons for this are discussed and it is suggested that the effects of internal motion are diminished when the second virial coefficient is large and positive. Absolute values of translational diffusion constant calculated from the results lie well within the range of those obtained by other authors using conventional techniques. Over the limited range of degrees of polymerization investigated the equivalent hydrodynamic diameter per monomer unit was found to be $\text{0.45 ± 0.03}\text{A}\text{?}$. The effects of polydispersity on the results are discussed.     

Light scattering Rayleigh linewidth measurements upon solutions of globular proteins containing high molecular weight impurities

A theory is presented showing that the effect of a very small amount of high molecular weight impurity on a globular protein solution is to decrease the measured diffusion constant and increase the weight average molecular weight in equal proportions. This applies when the diffusion constant is determined by a light scattering Rayleigh linewidth measurement using the autocorrelation method. Experimental verification of this is provided by the results of measurements upon a solution of bovine plasma albumin containing a high molecular weight impurity. The effects of different amounts of impurity were simulated by making measurements at different angles of scatter. The limitations of the theory are discussed.     

Light scattering from polyethylene solutions

The technique of measurement of light scattering from dilute polyethylene (PE) solutions is reviewed. Conditions are discussed under which various PE samples can be characterized. The choice of the solvent affects the accuracy of molecular weight determination. It appears that measurement with thermodynamically poorer solvents yields results subjected to a smaller error. The interpretation of light scattering data is often disturbed by the presence of supermolecular structures in PE solutions. The effect of reprecipitation on the behavior of PE samples is described. The measurements were mostly performed on PE standards and on the Czechoslovak sample Liten Macro.     

Light scattering from dilute solutions of critically branched epoxy resins

Summary Critically branched polymers were prepared from the bifunctional 4,4-diglycidyl-2,2-diphenylpropane (diglycidyl ether of Bisphenol A) and tetrafunctional poly(oxypropylene)diamine (Jeffamine D-400) at different distances from the gel point. Solutions of these samples in dimethylformamide were studied by static and dynamic light scattering. The results are discussed in terms of the classical Flory-Stockmayer theory and the percolation theory of gelation. The experimental results were found to be in agreement with the classical theory. The distribution functions of relaxation times were experimentally determined by the analysis of time autocorrelation functions obtained by quasielastic light scattering measurements on critically branched polymer solutions.     

Light and neutron scattering studies of excess low-angle scattering in moderately concentrated polystyrene solutions

The light scattering (LS) and small-angle neutron scattering (SANS) behaviour of semi-dilute solutions of polystyrene has been determined in both ‘good’ and ‘theta’ solvents. Above a critical concentration related to chain overlap, an excess small-angle scattering component is in evidence for scattering vectors, q, such that qR_g < 1. Application of a number of recent solution scattering theories fails to account for the small-angle scattering observed. The inter- and intramolecular scattering functions are measured experimentally through characterization of the SANS behaviour of solutions containing mixtures of polystyrene and perdeuteropolystyrene. The resultant intermolecular scattering functions depend on the fraction of labelled chains, indicating clearly that the solutions contain large scale fluctuations. LS studies support this hypothesis and further show that the presence of these fluctuations is reproducible, yet dependent on the solution preparation procedure. Similar behaviour is observed in screening length measurements. The excess low-angle scattering is well characterized by the Debye—Bueche random two-phase model, which is subsequently used to estimate the characteristic dimensions of the long-range fluctuations.     

Dynamic light scattering measurements of polystyrene in semidilute theta solutions

Measurements of the co-operative diffusion coefficient, D_c, and a centre of mass translational diffusion coefficient, D_s, have been made by dynamic light scattering for the polystyrene-cyclohexane theta system as a function of molecular weight and concentration. For semidilute solutions it is established that D_s∝N^?2c^?3 which is in agreement with the predictions from scaling arguments for the self-diffusion coefficient. However, if the co-operative mode is interpreted by D_c∝N^xc^y, the results of 0 < x < 0.7 and 0 < y < 0.5 are in disagreement with scaling predictions of D_c∝N⁰c¹. A discussion of the assumptions and potential shortcomings of the blob model which is used in the derivation of the power law predictions and the dynamic scattering equations is included. In addition, monomeric friction coefficients have been obtained from the D_s results within the framework of Doi-Edwards model. A comparison is made of the concentration dependence of the monomeric friction coefficient from the present data to that from similar experiments on a good solvent (tetrahydrofuran) system and from shear relaxation modulus measurements on the polystyrene in Aroclor 1248.     

A light scattering study of some solutions of triblock copolymers

Three samples of polystyrene-polybutadiene-polystyrene block copolymers have been studied by means of the light scattering technique in several solvents. The light scattering measurements indicate the degree of heterogeneity of the samples. Further measurements which were made on the least heterogeneous of the samples in a solvent closely matching the refractive index of the centre block suggest that the two types of polymer are largely separate. In this case the angular intensity variation of the light scattering can be interpreted in terms of the scattering obtained from a “dumb-bell” configuration.     

Light scattering and microcalorimetry studies on aqueous solutions of thermo-responsive PVCL-g-PEO copolymers

Dilute aqueous solutions of thermo-responsive poly(N-vinyl caprolactam)-graft-polyethylene oxide (PVCL-g-PEO) copolymers were studied by light scattering and high sensitivity differential scanning microcalorimetry. These copolymers are double hydrophilic at low temperatures, but become amphiphilic upon heating the solutions above the cloud point temperature of the PVCL segments (T_CP). The self-assembly properties of the copolymers are investigated by dynamic light scattering as a function of the temperature, degree of grafting and concentration. It was found that a certain critical polymer concentration is needed for the polymers to form stable aggregates. These structures are expected to consist of a hydrophobic PVCL core, stabilized by a hydrophilic PEO shell. The size of these aggregates increases with the degree of grafting. Microcalorimetry results revealed that the grafting of PVCL with hydrophilic PEO does not influence the phase transition enthalpy of PVCL.     

Light scattering evidence of selective protein fouling on biocompatible block copolymer micelles

Selective protein fouling on block copolymer micelles with well-known potential for tumour-targeting drug delivery was evidenced by using dynamic light scattering measurements. The stability and interaction of block copolymer micelles with model proteins (BSA, IgG, lysozyme and CytC) is reported for systems featuring a hydrophobic (poly[2-(diisopropylamino)-ethyl methacrylate]) (PDPA) core and hydrophilic coronas comprising poly(ethylene oxide)/poly(glycerol monomethacrylate) (PEO-b-PG2MA) or poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC). The results revealed that protein size and hydrophilic chain density play important roles in the observed interactions. The PEO(113)-b-PG2MA(30)-b-PDPA(50) nanoparticles are stable and protein adsorption is prevented at all investigated protein environments. The successful protein-repellent characteristic of these nanoparticles is attributed to a high hydrophilic surface chain density (>0.1 chains per nm(2)) and to the length of the hydrophilic chains. On the other hand, although PMPC also has protein-repellent characteristics, the low surface chain density of the hydrophilic shell is supposed to enable interactions with small proteins. The PMPC(40)-b-PDPA(70) micelles are stable in BSA and IgG environments due to weak repulsion forces between PMPC and the proteins, to the hydration layer, and particularly to a size-effect where the large BSA (R(H) = 4.2 nm) and IgG (R(H) = 7.0 nm) do not easily diffuse within the PMPC shell. Conversely, a clear interaction was observed with the 2.1 nm radius lysozyme. The lysozyme protein can diffuse within the PMPC micellar shell towards the PDPA hydrophobic core in a process favored by its smaller size and the low hydrophilic PMPC surface chain density (～0.049 chains per nm(2)) as compared to PEO-b-PG2MA (～0.110 chains per nm(2)). The same behavior was not evidenced with the 2.3 nm radius positively charged CytC, probably due to its higher surface hydrophilicity and the consequent chemical incompatibility with PDPA.     

Solution properties of xanthan. Light scattering and viscometry on dilute and moderately concentrated solutions

Elastic and quasi-elastic light-scattering, viscometric and rheological studies are given for solutions of the microbial polysaccharide Xanthomonas campestris (xanthan) in aqueous 0.62N NaCl for polymer concentrations from 0.03 to 2.2 g kg⁻¹. The observed negative ∂ln[η]/∂ln T is interpreted as a decrease of the persistence length with increasing T. The behaviour in moderately concentrated solutions (2<[η]c<25) reveals intermolecular association, leading to gel formation in the extreme case. The effect of the association on the viscometric and light-scattering data is discussed. It is concluded that the early stages of association involve structure with the chain axes nearly parallel, but that larger, particulate-like structures develop with increasing c, eventually leading to gel formation under certain conditions.     

Light scattering studies of poly(γ-benzyl L-glutamate) solutions and films

Summary Concentrated solutions (>20 wt%) of poly ( -benzyl L-glutamate) (PBLG) were investigated using small angle light scattering (SALS). The gels and cholesteric liquid crystals formed in PBLG concentrated solutions, were analyzed in terms of theories previously developed for SALS from crystalline polymers. It was found that there are two types of the fibrillar aggregation of -helices in gels and furthermore, two types of the orientation correlation of -helices in cholesteric liquid crystals.     

Multiple scattering in small-angle neutron scattering measurements on polymers

Multiple scattering corrections in small-angle neutron scattering experiments on polymers have been examined. Numerical calculations show that, for typical experimental conditions, the second-order scattering is less than 2% of the first-order scattering for QR_g up to 10.0. An approximate expression is also given for obtaining a rough estimate of the second-order scattering without numerical calculation.     

Light scattering study of stereocomplex behaviour in solutions of poly(methyl methacrylate)

The behaviour of mixtures of iso- and syndiotactic poly(methyl methacrylate) (PMMA) as a function of time and polymer whole concentration in several solvents has been studied by light scattering and laser light scattering. The different solvents investigated in this study are acetonitrile, ethyl acetate, dimethylformamide (DMF), tetrahydrofuran (THF) and 1,4-dioxane. We have found that the last one behaves as a weakly complexing solvent, while the others show a complexing power decreasing from acetonitrile to THF.An increase in polymer whole concentration induces a higher aggregation of the macromolecular coil, while the compaction process of stereocomplex particles is not strongly influenced. The influence of time in stereocomplex behaviour depends on the nature of the solvent employed. In strongly complexing solvents there is initially a strong increase in the aggregation process and a decrease in compaction. However, in weakly complexing solvents these kinetic processes are less important.     

Low-angle laser light scattering from polystyrene solutions: intensity measurements and photon correlation spectroscopy

Light scattering measurements have been made on polystyrenes with a range of molecular weights in toluene and for one polystyrene with a range of molecular weights in toluene and for one polystyrene in a range of solvents including a theta solvent. Intensity data were used to calculate second virial coefficients and molecular weights, whilst photon correlation spectroscopy was used to calculate diffusion coefficients. All measurements were made at 30°C and at a scattering angle of ca.4°. The data were used to examine current theories of polymer diffusion and the relation between hydrodynamic radius (R_H) and radius of gyrations ($\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$). The results support accepted theories of polymer diffusion, but suggest that the relation between R_H and $\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ requires further analysis.     

Solution properties of polyacrylic esters. I. Light scattering and viscosity measurements in tetrahydrofuran

Dilute THF-solutions of different fractions of polymers of methyl, ethyl, n-propyl, n-, i- and t-butyl, n-hexyl, 2-ethylhexyl, and lauryl acrylate, prepared by solution polymerization in benzene, were studied by light scattering and viscosity methods. Poly(acrylic acid) was examined in dioxane. For the different polyacrylic esters the [η]-M_w-relations were established and the dependence of the radius of gyration <r²_w> on the molecular weight was determined.     

Polymers bearing intramolecular photodimerizable probes for mass diffusion measurements by the forced Rayleigh scattering technique: synthesis and characterization

A new photochromic probe, bis(9-anthryl methyl) ether (BAME) derivative, was synthesized and introduced as an effective probe for forced Rayleigh scattering (FRS) measurement. It is shown that BAME and polystyrene labelled with BAME exhibit a large change in refractive index under irradiation of u.v. light (363.8 nm). The self-diffusion of BAME and polystyrene labelled with BAME (PSA) were measured in various solvents. Results of PSA in good, marginal and poor solvents are consistent with those obtained from quasi-elastic light scattering (QELS). Since the photodimerization reaction of anthracene has been extensively studied in solution and crystal as well as in polymer matrix, unfavourable multistep photochemical reactions can be avoided. One such unfavourable case, which involves a fluorescence quenching solvent CCl₄, is demonstrated. A temperature dependence study of polystyrene in semi-dilute theta solution by FRS has suggested that the non-exponential intensity decay is due to large concentration fluctuations in the solution. The well known photochemistry, large refractive index change and temperature stability have made BAME a very promising probe for FRS measurements.     

Light scattering studies of aqueous solutions of a new flocculation agent from polyacrylonitrile and dicyandiamide

The molecular parameters of the flocculation agent from polyacrylonitrile and dicyandiamide (PAN-DCD) were determined in dimethylsulfoxide. In acidic and alkaline aqueous solutions (0.1 N) PAN-DCD is weakly aggregated, additionally a small fraction of polymer exists as highly aggregated particle component. A shift of the pH-value in direction to the neutral range leads immediately to particle growth, which is finished at pH 3, coming from the acidic range and pH 10, coming from the alkaline one. After the passage of the neutral range disaggregation occurs. Flocculation can also be induced by addition of salt. The structural parameters of the particles were determined by a detailed analysis of the light scattering curves. Results obtained give information about the flocculation mechanism.