Quasielastic light scattering studies of dynamics of polystyrene in cyclo-hexane
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Abstract The dynamics of concentration fluctuations of polystyrene (M W = 20,000) in cyclohexane is studied as a function of temperature and concentration using the photon correlation spectroscopic technique. Over a 60°C temperature range the translational diffusion coefficient D C changes by more than two orders of magnitude. At a given temperature, D C first decreases with increasing concentration until a critical concentration C* at 22% is reached, beyond which D C increases with increasing concentration, reaching a maximum at higher concentration. The critical concentration C* is insensitive to temperature variations and can be estimated according to the equation for overlap concentration. The scattering intensity measurement as a function of concentration also shows a maximum at C*, suggesting that the slow down of concentration fluctuations due to the decrease in(∂u/∂c)P.T. is responsible for the intensity maximum. It is concluded that the emergence of the cooperative motion of the entangled network at C* is closely related to the effects of critical phenomena observed at the cloud point and the slow-down of translational diffusion.Keywords:
Polystyrene
Intensity
Atmospheric temperature range
Critical point (mathematics)
List of contributors 1. Dynamic scattering from multicomponent polymer mixtures in solution and in bulk 2. Single photon correlation techniques 3. Noise on photon correlation functions and its effects on data reduction algorithms 4. Data analysis in dynamic light scattering 5. Dynamic light scattering and linear viscoelasticity of polymers in solution and in the bulk 6. Dynamic properties of polymer solutions 7. Application of dynamic light scattering to polyelectrolytes in solution 8. Simultaneous static and dynamic light scattering: application to polymer structure analysis 9. Dynamic light scattering from dense polymer systems 10. Dynamic light scattering from polymers in solution and in bulk 11. Dynamic light scattering from polymer gels 12. Dynamic light scattering from rigid and nearly rigid rods 13. Light scattering in micellar systems 14. Critical dynamics of binary liquid mixtures and simple fluids studied using dynamic light scattering 15. Application of dynamic light scattering to biological systems 16. Diffusing-wave spectroscopy Index
Electrophoretic light scattering
Static light scattering
Biological small-angle scattering
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Colloidal systems are a subject of great interest in soft condensed matter research as well as in industry. But the ability to characterize colloidal systems with dynamic light scattering (DLS) is in general limited to systems with negligible contributions from multiple scattering of light. Therefore a variety of systems is excluded from investigations with DLS at high concentration and therefore increased turbidity. Often these samples were investigated under high dilution with, at least for some systems, a high probability of measuring artefacts. A promising solution to this problem consists of suppressing multiple scattering in a DLS experiment with a cross-correlation technique. Therefore we developed a so-called 3d cross-correlation instrument which enables us to characterize extremely turbid suspensions. After having found that the instrument works very well with model systems, we now demonstrate that complex ‘real world’ systems can successfully be characterized using this technique. An investigation of milk shows a strong dependence of the measured particle size distribution upon dilution. With the 3d instrument, however, the undiluted milk can be measured and artificial changes of the sample properties can be excluded.
Dilution
Static light scattering
Turbidity
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Abstract Atactic polystyrene was hydrogenated under different conditions. At incomplete hydrogenation, a mixture of polystyrene and poly(vinyl cyclohexane) results. The glass temperatures were studied under different conditions by differential thermal analysis and found to be 100°C for polystyrene and 80°C for poly(vinyl cyclohexane). The solubility of poly(vinyl cyclohexane) is reported for different solvents. The influence of DTA evaluation techniques was studied.
Polystyrene
Differential thermal analysis
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In the scientific literature little attention has been given to the use of dynamic light scattering (DLS) as a tool for extracting the thermodynamic information contained in the absolute intensity of light scattered by gels. In this article we show that DLS yields reliable measurements of the intensity of light scattered by the thermodynamic fluctuations, not only in aqueous polymer solutions but also in hydrogels. In hydrogels, light scattered by osmotic fluctuations is heterodyned by that from static or slowly varying inhomogeneities. The two components are separable owing to their different time scales, giving good experimental agreement with macroscopic measurements of the osmotic pressure. DLS measurements in gels are, however, tributary to depolarized light scattering from the network as well as to multiple light scattering. The paper examines these effects as well as the instrumental corrections required to determine the osmotic modulus. For guest polymers trapped in a hydrogel the measured intensity, extrapolated to zero concentration, is identical to that found by static light scattering from the same polymers in solution. The gel environment modifies the second and third virial coefficients, providing a means of evaluating the interaction between the polymers and the gel.
Static light scattering
Intensity
Osmotic pressure
Light intensity
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This chapter provides a more detailed background to dynamic light scattering (DLS), starting with static light scattering (SLS), as the tools derived can be valuable for the subsequent derivation of the relevant electric field and intensity autocorrelation functions. The theoretical background is followed by a more detailed discussion of particle sizing and the evaluation of size distributions. The main section on DLS is followed by a description of new instrumental approaches to DLS based mainly on fibre optics, which allow DLS measurements to be made in more difficult environments. The chapter concludes with the introduction of a very new video-microscopy technique, namely differential dynamic microscopy (DDM). The two main applications of DLS in chemistry are particle sizing and the study of molecular aggregation and growth. A section discusses several practical examples, with particular focus on nanocolloids for their relevance in catalysis and self-assembled systems such as surfactants and block copolymers.
Particle (ecology)
Multiangle light scattering
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Abstract The turbidimetric titration method of determining theta conditions developed by Elias and modified by Cornet and van Ballegooijen has been extended and generalized for different types of polymer–solvent–nonsolvent systems. The modified procedures for the determination of theta compositions have been verified with the following systems: polystyrene–cyclohexane– n ‐hexane, polystyrene–cyclohexane– n ‐butanol, and polystyrene–toluene–nonsolvent.
Polystyrene
Hexane
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An aqueous suspension containing magnetic nanoparticles is not stable because the nanoparticles aggregate. As the aggregates size increases and the number of particles in suspension decreases, the rheological properties of the nanofluid, which are important for biomedical applications, change tremendously. Modified versions of the SLS and DLS experiments were used to monitor the nanoparticle aggregation and the results are presented in detail. Keywords: Fe3O4 nanoparticle synthesis, nanoparticle aggregation dynamics, static light scattering, dynamic light scattering
Suspension
Aqueous suspension
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Dynamic light scattering (DLS) has proven as a successful technique both for the determination of various thermophysical properties of fluids [1][2] and for particle size analysis [3][4]. A useful special application of characterising fluids by DLS is the measurement of the dynamic viscosity [5][6].
Static light scattering
Electrophoretic light scattering
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Abstract Dynamic light scattering is a new method for investigating macromolecular systems. The importance of the technique lies in its non-invasive character. It can be employed on extremely small fluid volumes, the instrumentation is relatively inexpensive and allows the rapid determination of diffusion coefficients as well as providing information on relaxation time distributions for the macromolecular components of complex systems. This volume is directed in part to the philosophy and current practice in dynamic light scattering: single photon correlation techniques are introduced, a discussion of noise on photon correlation functions is given and data analysis in dynamic light scattering to polymer structure analysis is presented and a comprehensive introduction to diffusing wave spectroscopy is given. Theoretical developments relating dynamic light scattering to the viscoelasticity of polymers in solution and in the bulk are described. The second aim is to illustrate the widely varying fields in which the technique finds application. Chapters are to be found on multicomponent mixtures, polyelectrolytes, dense polymer systems, gels, rigid rods, micellar systems and the application of dynamic light scattering to biological systems.
Electrophoretic light scattering
Static light scattering
Instrumentation
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The ability to characterize colloidal suspensions by means of dynamic light scattering is limited to systems with negligible contributions from multiple scattering. For larger particle sizes with high scattering contrast this immediately limits the technique to very low concentrations. A very interesting solution of this problem is to suppress multiple scattering in dynamic light scattering experiments using various cross-correlation schemes. Based on these considerations we have constructed a so-called 3D cross-correlation experiment with which we are able to characterize extremely turbid suspensions. We have tested the feasibility of these experiments with well defined model systems such as suspensions of monodisperse and bimodal latex particles with relatively high volume fractions. The results are very promising and demonstrate unambiguously that such systems can be quantitatively characterized by means of dynamic light scattering methods without having to resort to high dilution.
Dispersity
Particle (ecology)
Electrophoretic light scattering
Static light scattering
Dilution
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