Dynamic Response Studies on Aggregation and Breakage Dynamics of Colloidal Dispersions in Stirred Tanks

Aggregation and breakage of aggregates of fully destabilized polystyrene latex particles in turbulent flow was studied experimentally in both batch and continuous stirred tanks using small‐angle static light scattering. It was found that the steady‐state values of the root‐mean‐square radius of gyration are fully reversible upon changes of stirring speed as well as solid volume fraction. Steady‐state values of the root‐mean‐square radius of gyration were decreasing with decreasing solid volume fraction as well as with increasing stirring speed. Moreover, it was found that the steady‐state structure and shape of the aggregates is not influenced by the applied stirring speed.     

Gel effect in the bulk reversible addition–fragmentation chain transfer polymerization of methyl methacrylate: Modeling and experiments

A model for the evaluation of the kinetics and the chain length distribution in living/controlled radical polymerization mediated by reversible addition–fragmentation chain transfer (RAFT) in bulk is presented. Using the free volume theory, the model accounts for the diffusion limitations over both termination and RAFT exchange reactions. Model predictions are compared to experimental results of methyl methacrylate polymerization with cumyl dithiobenzoate as a RAFT agent. It is shown that the polymerization retardation observed in living systems at large conversions is well predicted. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1071–1085, 2006     

Experimental implementation of automatic ‘cycle to cycle’ control to a nonlinear chiral simulated moving bed separation

In order to better exploit the economic potential of the simulated moving bed chromatography a ‘cycle to cycle’ controller which only requires the information about the linear adsorption behavior and the overall average porosity of the columns has been proposed. Recently, an automated on-line HPLC monitoring system which determines the concentrations in the two product streams averaged over one cycle, and returns them as feedback information to the controller was implemented. The new system allows for an accurate determination of the average concentration of the product streams even if the plant is operated at high concentrations. This paper presents the experimental implementation of the ‘cycle to cycle’ control concept to the separation of guaifenesin enantiomers under nonlinear chromatographic conditions, i.e. at high feed concentrations. Different case studies have been carried out to challenge the controller under realistic operation conditions, e.g. introducing pump disturbances and changing the feed concentration during the operation. The experimental results clearly demonstrate that the controller can indeed deliver the specified purities and improve the process performance.     

Experimental verification of sample-solvent induced modifier-solute peak interactions in biochromatography

In a previous theoretical analysis based on equilibrium theory it has been shown how differences in the sample and elution modifier concentrations can lead to unexpected behavior of the solute eluted peaks such as retention time distortion, peak deformation and peak doubling. All these features are verified experimentally in this work using the polypeptide calcitonin and a variant of a specific monoclonal antibody as chromatographic model systems. For both experimental systems, the retention time distortion can be predicted with high accuracy by the solution of the equilibrium theory model. For the polypeptide, the predictions from the theory about the occurrence of peak deformation and double peaks has been successfully verified by a series of tailored experiments with positive as well as negative modifier perturbations.     

A global Inverse Map Theorem and biLipschitz maps in the Heisenberg group

Abstract We prove a global Inverse Map Theorem for a map f from the Heisenberg group into itself, provided the Pansu differential of f is continuous, non singular and satisfies some growth conditions at infinity. An estimate for the Lipschitz constant (with respect to the Carnot–Carathéodory distance in ) of a continuously Pansu differentiable map is included. This gives a characterization of (continuously Pansu differentiable) globally biLipscitz deformations of in term of a pointwise estimate of their differential. Keywords: Inverse problem, Heisenberg group     

Regular domains in homogeneous groups

We study John, uniform and non-tangentially accessible domains in homogeneous groups of steps 2 and 3. We show that domains in groups of step 2 are non-tangentially accessible and we give an explicit condition which ensures the John property in groups of step 3.

     

Experimental investigation of colloidal gel structures

We investigate experimentally the structural properties of colloidal gels, formed under both diffusion-limited and reaction-limited aggregation conditions, using light scattering measurements and compare the results with the literature Monte Carlo (MC) simulations. The scattering structure factors have been measured for the two classes of gels in the range of the particle volume fractions between 0.02 and 0.07. From these, the corresponding fractal dimension values have been estimated. These have been found to be in good agreement with those estimated from the structure factors computed from MC simulated gels. On the basis of our previous research (Lattuada et al. Langmuir 2003, 19, 6312), this confirms that the scattering structure factor of a gel provides erroneously a small fractal dimension value, which decreases as the particle volume fraction increases. Furthermore, it is observed that the average size of the fractal clusters is larger in real gels than in simulated gels.     

Scaling of the kinetics of slow aggregation and gel formation for a fluorinated polymer colloid

The aggregation and gelation kinetics in moderately concentrated (0.004 相似文献   

Enantiomer separation of alpha-ionone using gas chromatography with cyclodextrin derivatives as chiral stationary phases

The gas chromatographic enantiomer separation of alpha-ionone was studied with three different chiral stationary phases using as chiral selectors: (1) heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin, dissolved in polysiloxane PS-086, (2) octakis(2,6-di-O-pentyl-3-O-trifluoroacetyl)-gamma-cyclodextrin and (3) octakis(2,6-di-O-pentyl-3-O-butanoyl)-gamma-cyclodextrin, both dissolved in polysiloxane SE-54. The influence of the concentration of the chiral selector in the polysiloxane, coated on Chromosorb P AW-DMCS 80-100 mesh, is described and discussed, as well as the effect of Chromosorb loading. The feasibility of the preparative gas chromatographic separation of the enantiomers of alpha-ionone is considered; in order to provide a term of comparison, the estimated performances are compared with those achieved in the separation of the enantiomers of the inhalation anaesthetic enflurane.     

Solvent gradient operation of simulated moving beds. I. Linear isotherms

The simulated moving bed (SMB) is a multi-column chromatographic separation process, which--with respect to the single-column preparative batch process--allows for a continuous separation with larger productivity and smaller solvent consumption at the same time. The benefits of this process have been shown for several different applications in fine chemistry, particularly for the separation of enantiomers. In general, SMBs are operated under isocratic conditions. However, separation performance can be further improved by applying some sort of gradient mode operation, in order to optimize the operating conditions of each individual section of the unit. This can be achieved by tuning the retention behavior of the solutes to be separated along the unit, namely by enforcing weak adsorption conditions in sections 1 and 2, and strong adsorption conditions in sections 3 and 4. This can be achieved by applying a temperature gradient (high temperature in section 1, and low temperature in section 4), a pressure gradient (e.g. in the supercritical SMB, when pressure is high in section 1, and low in section 4), or a solvent gradient, which is the aim of this work. In the solvent gradient mode the mobile phase consists of a mixture of two or more solvents. To different mobile phase compositions corresponds a different retention behavior of the solutes, i.e. different adsorption isotherms. In this work we study a closed loop SMB unit with solvent mixtures of two different compositions entering the unit at the feed and desorbent inlet ports, respectively. Thereby two different mobile phase compositions are established in sections 1 and 2, and sections 3 and 4, respectively. To optimize this process the equilibrium theory design criteria for non-linear SMBs are extended to describe this operation mode. It is shown how the region of separation is derived and how the optimal operating conditions can be found. Finally the solvent gradient mode is compared with the isocratic mode in terms of productivity and solvent consumption.