Flocculation by Cationic Polyelectrolytes: Relating Efficiency with Polyelectrolyte Characteristics

A series of acrylamide/dimethylaminoethylacrylate methyl chloride copolymers (AM-co-DMAEA) was evaluated as flocculants for model Precipitated Calcium Carbonate (FCC) in distilled water. These cationic polyelectrolytes (PEL) differed by their AM/DMAEA ratio, i.e., their charge density, chain architecture (linear and branched), their intrinsic viscosity (IV), and zeta potential of their aqueous solutions. The IV being directly related to the hydrodynamic volume of the PEL and the zeta potential reflecting the effective charges in suspension were selected for practically useful correlations with flocculation performance. The fractal dimension (d(F)) and the scattering exponent (SE) of the flocs, analyzed by the laser diffraction method, were taken as indication of primary particle and aggregate assembly. For the optimum PEL dosage, SE and d(F) varied with the IV and zeta potential. It was observable that floc size, floc resistance, and floc reorganization correlate with the PEL characteristics. Copolymers with lower IV, which is here associated with PEL of similar molar mass but lower charge density, yielded larger and less resistant flocs. Copolymers with higher IV originated smaller more compact flocs being more resistant. in high shear situations, where floc breakage should be avoided, as it is the case in papermaking, polymers with high IV yielding large SE are advantageous. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3603-3612,2010

An experimental design methodology to evaluate the importance of different parameters on flocculation by polyelectrolytes

Hamideh Ahmadloo, Ineide Cruz Pinheiro, David Hunkeler, Christine Wandrey

Aggregation of particles is fundamental for improving the performance of many solid/liquid processes. Aggregation can be induced by different means, and one of the most common is based on the addition of polymeric additives, namely polyelectrolytes. In this work we have studied the flocculation of precipitated calcium carbonate (PCC), which is used as a filler in papermaking, and is induced by a range of cationic polyacrylamides with different structures, varying in molar mass and degree of branching. The flocculation process was monitored continuously using the LDS technique (laser diffraction scattering), which provides information about the size distribution and structure (fractal dimension) of the aggregates, for each sampling instant and, thus, about the kinetic curve for the flocculation process. This information has then been used to produce a model, based on an experimental design strategy, which allows us to relate flocculation efficiency with the PEL characteristics and concentration. The Partial Least Squares (PLS) regression method was selected to perform the regression, given the significant co linearity among the input variables. The results obtained lead us to conclude that the polymer intrinsic viscosity (related with the PEL molar mass and charge density, and supplying information about the volume of the polymer molecule in the solution) and the degree of branching are the parameters with a stronger influence on flocculation efficiency. The PLS models developed were also successfully validated using an independent data set, which provides confidence on their consistency and prediction accuracy. (C) 2012 Elsevier B.V. All rights reserved.

Elsevier Science Sa2013

Functional polymer brushes via surface-initiated controlled radical polymerizations

Stefano Tugulu

The term polymer brush refers to a well defined arrangement of polymer chains, which are tethered with one end to an interface and usually the surface of a solid substrate. Due to steric repulsion the polymer chains furthermore adopt a defined, stretched chain conformation, which significantly differs from the random walk conformation of free polymer chains in solution or in conventionally solution casted polymer coatings. From a structural point of view polymer brushes can therefore be regarded as the most defined type of polymer coating that can currently be realized. Especially the combination of surface-initiated polymerizations (SIP) with modern, controlled polymerization methods thereby allows tailoring the structure of the polymer brushes almost on the molecular level. Specifically precise control over the thickness, composition, chain architecture, grafting density and via the use of lithographic techniques also over the topography of the brushes can be achieved. This high degree of control over the structural and implicated (physico-)chemical properties of the brush allows at the same time tailoring and fine tuning the interfacial properties of the brush. This thesis describes the systematic exploitation of well-defined polymer brushes as functional coatings with fine-tuned physicochemical properties to direct and control the interaction with and the response of specific biological, bioanalytical and even reactive chemical environments. In detail the use of surface-initiated atom transfer radical polymerization (SI-ATRP) for the fabrication of functional polymer brushes will be presented. These brushes were used as highly defined coatings in various applications ranging from biomedical and bioanalytical applications to biomimetic materials fabrication (Figure 1). Figure 1 Numerous synthetic approaches for the preparation of polymer brushes have been described in the literature. Chapter 2 will therefore present a summary of the most important types of surface-initiated polymerizations, focusing especially on controlled SIP methods and SI-ATRP. Chapter 3 describes a chemoselective and specific immobilization strategy to decorate intrinsically bioinert polymer brushes with proteins of interest in a defined orientation and density. Specifically the resulting substrates represent attractive candidates for the realization of protein microarrays. In view of this application protein-small molecule and protein-protein interactions as well as posttranslational modifications were analyzed within a feasibility study. Due to their well-defined structure polymer brushes represent also attractive candidates for the realization of molecularly defined cell adhesion substrates for tissue engineering or as highly defined biophysical model system to analyze cell adhesion and mechanics. Chapter 4 describes the decoration of intrinsically bioinert polymer brushes with small peptide ligands with defined density to induce integrin specific cell adhesion on the brushes. Peptide functionalized polymer brushes could be readily endothelialized and adhering cell layers have shown to preserve their homeostatic ability to respond to an applied mechanical stimulus in a physiological manner. In Chapter 5 the limitations of high density polymer brushes in biomedical applications were assessed by analyzing their stability under in vitro cell culture conditions. Intrinsically bioinert high density polymer brushes were found to degraft from glass or silicon substrates upon swelling in good solvents, which lead to deterioration of the bioinert properties of the substrate. The degrafting of the brushes might be connected to swelling induced mechanical activation of chemical bonds, which link the brushes to the substrate. Chapter 6 describes the transfer of the developed SIP approach onto flexible PDMS substrates by exploiting the formation of interpenetrating networks of ATRP-initiator siloxane and PDMS. The modification of the PDMS substrates with hydrophilic brushes effectively reduces the unspecific protein adsorption on the substrates. This approach might therefore represent an attractive and facile route for the surface modification of miniaturized PDMS devices for biomedical or bioanalytical applications. In Chapter 7 the systematic development of a reliable and robust protocol for the aqueous SI-ATRP of sodium methacrylate is presented, which gives access to poly(methacrylic acid) (PMAA) brushes with defined molecular weight and grafting density. The resulting brushes were assessed for their ability to direct the mineralization of calcium carbonate. Chapter 8 describes the use of photolithographically patterned poly(methacrylic acid) brushes as biomimetic, acidic macromolecular matrix to fabricate microstructured calcite thin films that are an exact 3D replica of the PMAA brush. The presented strategy relies on three key elements: (i) the use of photolithographic techniques to prepare microstructured PMAA brushes; (ii) the ability of PMAA brushes to stabilize amorphous calcium carbonate (ACC) and (iii) the possibility to convert the metastable ACC phase into a polycrystalline calcite film via a thermal treatment.

EPFL2007

Correlation between flocculation and adsorption of cationic polyacrylamides on precipitated calcium carbonate

Hamideh Ahmadloo, Ineide Cruz Pinheiro, David Hunkeler, Christine Wandrey

The study of each stage of the flocculation process is essential to better understand and predict flocculation mechanisms. The adsorption of cationic polyacrylamide derivatives (C-PAM) onto precipitated calcium carbonate (PCC) has been investigated systematically as a function of the C-PAM characteristics including molar mass, chain architecture, and charge density. The adsorption results show that, for C-PAM of similar molar mass, highly branched architectures reach the equilibrium faster than linear C-PAM. Similarly, the flocculation rate is higher for the branched C-PAM, which may be indicative of the predominance of the bridging mechanism. In terms of the molar mass, lower molar mass leads to lower adsorption rates and slower flocculation. Adsorption isotherms of C-PAM onto precipitated calcium carbonate could be described by the Langmuir isotherm model. The maximum amount of C-PAM that adsorbs on the particle surface as a monolayer, obtained from adsorption tests through the Langmuir isotherm linear fit, could be correlated with the structure of the aggregates, obtained from flocculation experiments. Moreover, a good correlation was obtained between the adsorption results and the kinetics of the first stage of the flocculation process dominated by particle aggregation. (c) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Inst Chemical Engineers2015

Functional polymer brushes via surface-initiated controlled radical polymerizations

Stefano Tugulu

EPFL2007