Assessment of nonrandom crosslinking in polymer networks by small‐angle light scattering

Abstract

SynopsisThe angle-dependent, isotropic light scattering exhibited by a diluent-swollen, ideal network is theoretically derived and compared with the light scattering exhibited experimentally by swollen real networks. I n good diluents the differepce is a measure of the spatial nonrandomness of the degree of crosslinking. A nonrandomness index (NRI) is introduced in terms of the Rayleigh ratios at zero scattering angle. A procedure is given for reliably obtaining the zero-angle Rayleigh ratio from experimental data a t finite angles (2-30"). Measurements are reported for a series of poly(2-hydroxyethyl methacrylate) (PHEMA) networks, prepared a t varying stages of dilution (in ethylene glycol, EG) and varying amounts of crosslinker (ethylene glycol dimethyacrylate, EGDMA). The theoretical Rayleigh ratios are calculated by employing the equilibrium degrees of swelling, refractive indices, and Young's moduli of the gels, measured in EG. The NRI is found to decrease upon decreasing the dilution during network formation and upon increasing the average crosslinking density. The NRI provides a probe of the network structure on a (sub)microscopic level. It is suggested that the NRI is closely correlated with the performance of elastomers under mechanical loading conditions.

Dynamic light scattering from swollen poly(dimethylsiloxane) networks

“…It should be noted that the scaling predictions derived by de Gennes for a good solvent are for the cooperative diffusion DcB using a fixed-solvent frame of reference. On the other hand, the D, obtained from a DLS experiment is based on a fixed-volume frame of referen~e.~~aO As shown by previous the two diffusion coefficients are related by D," = D,/ (1 -uZ) (16) The correction factor of (1 -up) is small for dilute systems as anticipated by de Gennes, but for the concentrations of the networks and solutions examined in this work, this factor is significant. illustrates that the (1 -up) factor has a significant effect on the scaling exponents.…”

Behavior of heterogeneous macromolecular structures Part I: Microgels and coated microgels

“…Dynamic light scattering allows calculation of an effective hydrodynamic radius Rh from the diffusion coefficient D by applying the Stokes-Einstein relationship: D = kT/(rmlo Rh) (1) where 1/0 is the solvent viscosity, k Boltzmann's constant and T the temperature in K [16]. Table 2.…”

“…In addition gels prepared from homopolymers sometimes show heterogeneities of not yet exactly known origin [1][2][3][4]. Deviations from theoretical prediction in elasto-mechanical measurements have for instance been attributed to such heterogeneities.…”

Estimation of the Generation and the Weight Fraction of Dense Polymer Regions in Heterogeneous Hydrogels

“…[1,2] For this reason, the structures of heterogeneous polymer gels are interesting and extensive studies have been made on the characterization of the gel heterogeneity. Various neutron, [3] X-ray and static light-scattering techniques [4][5][6][7][8] have shown the existence of concentration heterogeneities at sub-micrometer scales in gels.…”