J. Jakeš

Semidilute solutions of poly(methacrylic acid) in the absence of salt: Dynamic light-scattering study

Abstract Water solutions of poly(methacrylic acid) of molecular weight Mw = 3.0 × 104 and Mw = 4.0 × 105, neutralized with NaOH, were investigated by photon correlation spectroscopy. At a low degree of neutralization α, the short-time decay only is observed. When α > 0, a second, much slower, process becomes noticeable. It gains quickly in influence when α increases. The reciprocal values of characteristic relaxation times for both dynamic processes were found to decrease linearly with the square of the scattering vector, showing that both processes are diffusive. The following interpretation of these processes founded on the concentration and angle dependences of the corresponding diffusion coefficients and scattering amplitudes is given: (1) for the low-molecular-weight sample (Mw = 3.0 × 104), D∫ (fast process) and be attributed to the Nernst-Hartley diffusion coefficient of polyions, and Ds (slow process) to a diffusion of interchain domains (clusters) with a radius of gyration RG ≈ 50 nm; (2) for the high-molecular-weight sample (Mw = 4.0 × 105), where an overlap of polymer chains occurs, Df can be attributed to a cooperative diffusion coefficient reflecting the concentration fluctuations due to the polyions and counterions, and Ds to slow concentration fluctuations having a large correlation length (≈ 100 nm). The existence of two diffusive modes in salt-free solutions of polyelectrolytes cannot be explained within the framework of the scaling approach as proposed by de Gennes and Odijk.

Determination of the activation energy of chlorocyclohexane conformational transitions by infrared spectra

Abstract Chlorocyclohexane is used to demonstrate that it is possible to determine the height of the barrier between conformational isomers by following the kinetics of conformational transitions by infrared spectra. For this, crystallization of the sample has to be prevented by a suitable solvent.

Quasielastic light scattering from semidilute solutions in θ-solvent: Distribution functions of decay times

SummaryMeasurements of composite autocorrelation functions extending over a broad time range on semidilute theta solutions of polystyrene in cyclohexane are reported. Three mathematical methods were used to obtain the corresponding distribution functions of decay times, F(τ). Results of the different methods are in mutual agreement. It is found that F(τ) consists of several separated bands. The shortest and longest decay times have been extracted from F(τ) and, on the basis of their concentration and angular dependences, attributed to the gel mode and reptation process, respectively.

Influence of temperature on polyelectrolyte dynamics : partially neutralized solutions of poly (methacrylic acid)

The influence of temperature on the dynamics of partially neutralized solutions of poly(methacrylic acid) was investigated by photon correlation spectroscopy. A pronounced effect of aggregation above T ⋍ 70°C is observed. The aggregation process is accompanied by a rapid increase of the relative scattering amplitude of the slow diffusive mode occurring in strongly interacting polyelectrolyte systems, by a decrease of the corrected slow diffusion coefficient, and by an increase of the total scattered light intensity. The process is not fully reversible. The aggregation tendency strongly depends on the degree of neutralization α of the sample. In the interval α=0 to α=1 it reaches a maximum at α⋍0.4. An aggregation mechanism based on intermolecular hydrogen bonding between carboxyl groups is proposed.

Dynamic structure of swollen crosslinked poly(ethylene oxide) gels from n.m.r. line-shape analysis and magic angle rotation n.m.r.

Abstract Chemically crosslinked poly(ethylene oxide) gels swollen to equilibrium in CDCl 3 (22.3 w/w% of polymer) and CCl 4 (77.5 w/w% of polymer) were characterized by combination of the results of 1 H n.m.r. spectra measured with magic angle rotation ( MAR -n.m.r.) and numerical analysis of static 1 H n.m.r. line shapes. From MAR -n.m.r., activation energies of rapid segmental motions were found to be 1.7 ± 0.3 kcal mol −1 in CDCl 3 and 9.4 ± 0.6 kcal mol −1 in CCl 4 . Static line-shape analysis yields a parameter which characterizes the deviation of segmental motions from isotropy in space. This parameter was found to be independent of temperature and equal in both systems.

Effect of multiple light scattering on transmitted and scattered light

Photocount distributions have been calculated and experimentally determined for light transmitted through a dispersion of particles of varying density. From these the coherent and incoherent components of the transmitted light intensity could be determined. The coherent intensity was shown to obey the Lambert-Beer law. Autocorrelation functions of light scattered in the presence of multiple light scattering were measured and inverted by using an inverse Laplace transform technique. The single-scattering and multiple-scattering contributions can be distinguished in the corresponding spectra of decay times. The amount of multiple light scattering increases with increasing concentration of scatterers and reaches the limit of strong multiple light scattering when the transport of light through the dispersion becomes diffusive.

Dynamic light scattering from polymer solutions and gels at the gelation threshold

Abstract The purpose of this communication is to report relaxation time distributions derived from dynamic light scattering measurements, close to the gelation threshold, for PMMA gels swollen in butylacetate. The distributions are composed of contributions from two diffusive (K2-dependent) modes corresponding to collective diffusion of the gel matrix and the interdiffusive modes of sol components inside the gel matrix. While the collective diffusion is typified by a unique value of the correlation length, the latter are described by a very broad distribution due to substantial polydispersity. K-independent structural relaxations, which are usually present in semidilute solutions in poor solvents, are not present.

Dynamic light scattering measurements on the polystyrene/ethyl acetate system at semi-dilute concentrations as a function of temperature

SummaryMeasurements of autocorrelation functions extending over a broad time range are reported for a sample of polystyrene in ethyl acetate as a function of temperature between −44°C (θ-temperature) and 70°C. The corresponding spectra of decay times are obtained by two mathematical methods. The existence of three dynamic processes is shown and their temperature and angular behaviour is studied.

Structure of amorphous polyethylene from n.m.r. line shape analysis and MAR-n.m.r.

Abstract Based on results of proton nuclear magnetic resonance measurements with magic angle rotation (MAR n.m.r.), the line of amorphous polyethylene in conventionally measured proton n.m.r. spectra is described as a convolution of a basic narrow line-shape function S(v) with an orientation-dependent dipolar broadening function G(v). With this approach it is possible to describle to describe the broadline n.m.r. spectrum of polyethylene as a superposition of the crystalline component and of a single amorphous phase. The fit of experimental and computed spectra, and the parameters obtained by this type of line-shape analysis are discussed for a series of polyethylene samples of different crystallinity.

Light scattering from dilute solutions of critically branched epoxy resins

SummaryCritically 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.