Bulk and microscopic properties of copolymer networks in mixed aqueous solvents

Abstract

Amphiphilic films and hydrogels have been prepared from ethanol/water solutions containing a hydrocarbon‐grafted water‐soluble cellulose ether. These materials are characterized by dispersed hydrophobic microdomains which form spontaneously in the solvent due to the inherent incompatibility of the side chains with water. At low applied shear stress, the microdomains behave as temporary linkages of finite lifetimes, imparting viscoelastic properties to the networks. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel, and the number of linkages per backbone ranges from 22.8 ± 1.3 to 26.2 ± 1.5 over the frequency range 30–50 rad/s. The behavior of the solutions and gels was characterized using fluorescence and dynamic rheological measurements. It was demonstrated that the microdomains are capable of sequestering water‐insoluble solutes. © 1992 John Wiley & Sons, Inc.

Physical Gelation of Hydrophobically Modified Polyelectrolytes. 1. Homogeneous Gelation of Alkylated Poly[acrylamide-co-sodium acrylate]

“…In common with simple surfactant micelles, the aggregates of C 10 side chains probably have a higher aggregation number than those of C 8 chains, a factor that would contribute to a higher G ‘ as well. In addition, on the basis of earlier studies, we expect that a only a fraction (∼30% for HMHEC) of the side chains are incorporated into these assemblies. Thus it is possible that there is a higher total number of aggregates in the C 10 system as well, given that the longer hydrophobes are more driven to aggregate in solution.…”

“…19 The disparate phase behavior in the presence of surfactants (see ref 16 vs 17 and 18) has been attributed to different degrees of water solubility as measured by different hydroxyethyl molar substitution levels on the polymer backbones. 16 Water-insoluble HMHECs undergo exclusively heterogeneous gelation in anionic surfactant solutions below the cmc [20][21][22] and in ethanol/water mixtures 23,24 and exhibit a peak in dynamic storage modulus (G′) with temperature occurring at ∼50 °C, coinciding with the collapse of the already precipitated gel phase. 25 Hydrophobically modified (R) polyacrylamide (AM), or RAM, forms homogeneous non-Newtonian solutions or gels containing hydrophobic aggregates in both water 26,27 and sodium dodecyl sulfate (SDS) solutions below the cmc.…”

Mathematical model of mass transport through dispersed‐phase polymer networks

“…This permits control over both the relative solubility of the solute in the domains, a , and their geometry (hence h,) and interfacial area, Ai. The total concentration of polymer in the gel governs the volume fraction of microdomains, 4 (Varelas and Steiner, 1991). We have also learned (Wu et al, 1995) that the porosity of the interface, and hence h,, is a function of the processing temperature of the gel.…”

Effects of Temperature and Shear History on the Network Properties of Amphiphilic Hydrogels

“…Our group has been investigating viscoelastic hydrogels made from a water-insoluble hydrophobically modified (hydroxyethyl)cellulose (HMHEC) in aqueous systems. − The hydrogels precipitate out of solution and form a separate phase in equilibrium with a Newtonian supernatant containing little or no polymer. They are physical gels, in that the cross-linking interactions that define the three-dimensional network structure (i.e., the hydrophobic clusters) are physical, rather than chemical, in nature.…”

“…Thus, the strength of the gel will depend on the number and composition of the microdomains. The hydrogels may be dried into films and reswollen to a constant volume without dispersing …”