Claudia Sayer

BSA Adsorption on Differently Charged Polystyrene Nanoparticles using Isothermal Titration Calorimetry and the Influence on Cellular Uptake

BSA adsorption onto negatively and positively charged polystyrene nanoparticles was investigated. The nanoparticles were characterized in terms of particle size, zeta potential, surface group density, and morphology. The adsorption behavior of BSA on the particle surface, as a function of pH and overall charge of the particle, was studied using ITC. Different thermodynamic data such as enthalpy changes upon binding and stoichiometry of the systems were determined and discussed. The degree of surface coverage with BSA was calculated using the thermodynamic data. The cellular uptake of particles before and after BSA adsorption was studied using HeLa cells in the presence and absence of supplemented FCS in the cell culture medium.

Dynamic optimization of semicontinuous emulsion copolymerization reactions: composition and molecular weight distribution

Abstract Iterative dynamic programming (IDP) is used to compute optimal monomer and chain transfer agent feed profiles to produce polymer with specified copolymer composition and molecular weight distribution. The approach used allows the implementation of constrained optimization procedures for systems described by complex mathematical models, as those needed for proper description of emulsion copolymerization reactors, especially when the computation of the whole molecular weight distribution is desired. The proposed approach is applied to the semicontinuous methyl methacrylate (MMA)/butyl acrylate (BuA) emulsion copolymerization in stirred tank reactors, using dodecanethiol as chain transfer agent (CTA). It is shown that this technique allows the effective computation of feed policies for the production of copolymers with constant composition and well-defined molecular weight distributions.

Dynamic optimization of non-linear emulsion copolymerization systems: Open-loop control of composition and molecular weight distribution

Time optimal monomer and chain-transfer agent feed profiles were computed and implemented experimentally for the simultaneous control of copolymer composition and molecular weight distribution in non-linear emulsion copolymerization systems. Iterative dynamic programming was used for the off-line calculation of the optimal feed policies. This approach can deal with constrained optimization of systems described by complex mathematical models, as those needed for the emulsion copolymerization kinetics, especially when the computation of the whole molecular weight distribution is included. The proposed approach was applied to the semibatch methylmethacrylate (MMA)/n-butylacrylate (n-BA) emulsion copolymerization, using n-dodecanethiol as chain-transfer agent, and allowed the production of copolymers with constant composition and with well-defined molecular weight distributions.

Computation of molecular weight distributions by polynomial approximation with complete adaptation procedures

The choice of appropriate reference functions is still the major drawback for collocation techniques to be used during the computation of molecular weight distributions (MWDs) in polymerization reactions and other problems constituted by systems of differential-difference equations. Complete adaptation procedures provide significant improvement of numerical approximations obtained, but convergence to the real solution is not assured and oscillatory numerical approximations may be obtained when the actual solution experiences large variations during time integration. An alternative method to compute the reference function in an adaptative manner, called here the integration of the reference function procedure, is presented. The technique is used to allow the computation of MWDs in two polymerization problems: the metallocene-based propene polymerization and the methyl methacrylate/butyl acrylate emulsion polymerization. The integration of the reference function procedure allowed the proper computation of broad, bimodal and fast changing distributions with polynomials of very low order (below 4), where other approximation techniques failed. The method may be easily implemented and does not require any pre-processing before implementation.

Molecular weight distribution in composition controlled emulsion copolymerization

The effect of different strategies for copolymer composition control on the molecular weight distribution (MWD) and gel fraction in the emulsion copolymerization of methyl methacrylate and butyl acrylate was investigated. Starved and semistarved processes for copolymer composition control were both considered. For gel-forming systems it was found that the starved process gave more gel and lower molecular weights than the semistarved process. The feasibility of simultaneous control of the copolymer composition and the MWD was assessed.

Evidences of correlation between polymer particle size and Raman scattering

This work describes evidences of correlation between polymer particle size and Raman scattering and shows that it is possible to use Raman scattering to monitor the evolution of average particle size during emulsion polymerization reactions. The main focus is the estimation of the average polymer particle diameter from spectra collected in a short acquisition time and consequently low signal-to-noise ratio. Finally, a multivariate linear model, (Partial Least Square-PLS), is fitted from the reaction data and a good linearity between spectra and average polymer particle diameter is found. It is shown that despite varying monomer and polymer concentrations it is possible to monitor average particle sizes during emulsion polymerization reactions using Raman spectroscopy.

Dynamic optimization of semicontinuous emulsion copolymerization reactions: Composition and molecular weight distribution

Iterative dynamic programming is used to compute optimal monomer and CTA feed profiles to produce polymer with pre-specified copolymer composition and MWD. This approach can deal with constrained optimizations of systems described by complex mathematical models, as those needed for the emulsion copolymerization kinetics, especially when the computation of the whole MWD is included. The proposed approach is applied to the semicontinuous MMA/BuA emulsion copolymerization, using dodecanethiol as CTA, allowing the effective computation of feed policies for the production of constant composition copolymer with well-defined MWDs.

Control strategies for complex chemical processes. Applications in polymerization processes

The proper implementation of advanced control schemes for complex chemical processes heavily rely on the availability of appropriate mathematical models. The main objective of this paper is to show through examples how process models can be inserted into advanced controllers to allow the successful control of the process when the controlled variables are not measured or are measured infrequently. The control strategies are illustrated with actual data obtained for two typical polymerization processes. In the first example, a control algorithm is designed and implemented experimentally for the simultaneous closed-loop control of composition and average molecular weight of a copolymer latex. In the second case, a control scheme is designed for the simultaneous control of polymer production, polymer composition and melting index (MI) in a solution ethylene Ziegler-Natta polymerization process.

Detection of monomer droplets in a polymer latex by near-infrared spectroscopy

It is shown here that near-infrared spectroscopy (NIRS) may be used to detect the presence of monomer droplets in polymer lattices directly from spectra, without any kind of previous calibration. Experiments involving the addition of methyl methacrylate (MMA) and butyl acrylate (BuA) to monomer-free lattices indicated that there exists a specific wavelength (1620 nm) where, at some instant of the addition process, spectra are subject to a marked change. It is shown that this abrupt spectral change is caused by the formation of monomer droplets in the reaction medium. This finding may significantly improve the controllability of emulsion polymerization processes and the quality of its products, as shown by actual MMA/BuA emulsion polymerization experiments, which reinforces the potential of NIRS as a multipurpose analytic tool for in-line and in-situ simultaneous monitoring of different properties in emulsion polymerizations.

Monitoring emulsion homopolymerization reactions using FT-Raman spectroscopy

The present work describes a methodology for estimation of monomer concentration during homopolymerization reactions by Raman spectroscopy. The estimation is done using linear models based on two different approaches: a univariate approach and a multivariate approach (with principal component regression, PCR, or partial least squares regression, PLS). The linear models are fitted with data from spectra collected from synthetic samples, i.e., samples prepared by dispersing a known concentration of monomer in polymer emulsions. Homopolymerizations of butyl acrylate and of vinyl acetate were monitored by collecting samples from the reactor, and results show that the methodology is efficient for the model fitting and that Raman spectroscopy is a promising technique for on-line monitoring of the emulsion polymerization process.