Jacques Joosten

Inversion of static light scattering measurements for particle size distributions

Abstract The inversion of static light scattering measurements (SLS) for the evaluation of particle size distributions is reported. The performances of two inversiion methods, i.e., the maximum entropy method and a constrained regularization method (Contin), are illustrated with simulated data and experiments on samples with unimodal, bimodal, and trimodal distributions of spherical particles and on a sample with a broad size distribution. Some experimental results are compared to assessments by photon correlation spectroscopy (PCS) and electron microscopy (EM). It appears that a significantly better resolution in particle size is obtained by SLS than by PCS. However, for a sample with a broad distribution in particle sizes, not all details of the distribution observed by EM were resolved.

MAXIMUM ENTROPY INVERSION OF STATIC LIGHT SCATTERING DATA FOR THE PARTICLE SIZE DISTRIBUTION BY NUMBER AND VOLUME

The application of Maximum Entropy analysis of static light scattering data for the evaluation of particle size distributions by number and by volume in the submicron size ranges is reported. The practical performances for homogeneous spheres are illustrated with simulated data and experiments on unimodal, bimodal and trimodal distributions of monodisperse latices. Accurate reconstructions by number are observed. The reconstructions by volume lead to somewhat broadened distributions. The method also allows the resolution of closely spaced distributions of particle sizes.

Competing reactions in anionic gel-poly(propylene imine) dendrimer-surfactant ternary systems

Competitive interactions in ternary systems including a lightly crosslinked polyanionic hydrogel, a protonated Astramol™ poly(propylene imine) dendrimer (of first to fifth generation), and an ionic surfactant were studied. It was found that the direction of the substitution reactions in systems containing cationic surfactants depends on the length of the aliphatic radical in the surfactant molecule as well as on the dendrimer generation number. Depending on these parameters, the interpolyelectrolyte complex formed by the network polyanion and the cationic dendrimer is either capable or incapable of sorbing surfactant cations from aqueous solutions, thereby transforming into the network polyanion-cationic surfactant complex with the release of dendrimers to the surrounding solution. It was shown that the substitution reaction in systems containing anionic surfactants leads to the formation of a polyanionic gel reinforced by particles of the dendrimer-anionic surfactant complex.

Interaction of ampholyte dendrimers with network polycations and polyanions

The interaction of polyampholyte propylenimine dendrimers of five generations containing peripheral carboxyl and inner tertiary amino groups with lightly crosslinked highly swelling polyelectrolyte gels has been studied. It has been shown that the polyampholyte dendrimers of all five generations are efficiently sorbed by a polyanion sulfur-containing hydrogel (below the isoelectric point) and a polyamine hydrogel (above the isoelectric point) to give rise to interpolyelectrolyte complexes. The composition of interpolyelectrolyte complexes and the equilibrium concentration of the dendrimer in the surrounding solution are appreciably affected by the pH of the medium. Amount of zwitterion pairs in a dendrimer molecule significantly influence the formation of interpolymer salt bonds. The polyampholyte dendrimer can pass from an anionic hydrogel to a cationic one upon a small change in pH near the isoelectric point.

Interaction of ampholyte dendrimers with linear polyelectrolytes

The interaction of ampholyte propylenimine dendrimers containing peripheral carboxyl groups and inner tertiary amino groups with linear polyelectrolytes has been studied. Both in acidic and alkaline media up to pH ∼ pI, dendritic polyampholytes can form interpolyelectrolyte complexes with flexible linear polyanions and polycations. A variation in the composition of complexes with a change in pH is associated with the formation of intramolecular zwitterion pairs in a dendrimer molecule. The ability of interpolyelectrolyte complexes to dissolve in water is shown to be determined by the degree of dissociation of ionogenic groups of the dendrimer not directly involved in the formation of interpolyelectrolyte salt bonds stabilizing the complex. It has been demonstrated that the territorial separation of carboxyl and tertiary amino groups in the polyampholyte dendrimers is reflected in different structures of interpolyelectrolyte complexes formed by dendrimers with oppositely charged linear polyions.

Blends of Fatty-Acid-Modified Dendrimers With Polyolefins

Blends were made by solution and melt-mixing fatty-acid-modified dendrimers with various polyolefins. Small-angle neutron scattering (SANS) was used to determine the miscibility of the blends. Poly(propylene imine) (PPI) dendrimers G1, G3, and G5 [DAB-dendr-(NH2)y] with y = 4, 16, and 64, were reacted with stearic acid or stearic acid-d35 forming amide bonds. The modified dendrimers were then blended with high-density polyethylene (HDPE), high-density polyethylene-d4 (HDPE-d4), low-density polyethylene (LDPE), amorphous polypropylene (PP), or an ethylene–butylene copolymer (E-co-B). Limiting power law behavior shows that all of the blends are immiscible. It is likely that the dendrimers form a second phase, being finely dispersed, but thermodynamically immiscible.

Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.