The equilibrium swelling of the system Polystyrene (PS) (M = 1.7 × 10s, monodisperse)/diethyl ether at 30 °C and 35 °C has been studied in detail in quiescent state for a time span over 150 d. Arguments...The equilibrium swelling of the system Polystyrene (PS) (M = 1.7 × 10s, monodisperse)/diethyl ether at 30 °C and 35 °C has been studied in detail in quiescent state for a time span over 150 d. Arguments are given to show that the swelling process in a “non-solvent” is a network swelling rather than a phase separation process. It is different from the cloud point curve (CPC) experiment studied in literature, where the experiment starts from a one-phase solution, so that the cohesional entanglement present in the solid polymer is disrupted by dissolution. The cohesional entanglement structure of the solid polymer, on the contrary, is retained in the concentrated phase on swelling, at least in the initial stage. The course of swelling as presented by the curve Va(t) was found to proceed in three stages, where Va is the volume of the concentrated phase. In the first and third stages of Va(t), the curve goes up smoothly, while in the second stage the curve Va(t) shows large up and down jumps, indicating probably a readjustment in the network structure. Some results on a monodisperse PS sample of M = 5.8 × 105 and a polydisperse sample of M = 2.0 × 105 are also given. The values of Va observed at swelling equilibrium are not in accord with the expected cloud point temperature. The cloud point curve represents a phase separation process occurring in local regions (space limited to μm) and in time scale of the order of minute, while the process Va(t) occurred in the whole space of the concentrated phase, in time scale of days. For quantitative characterization of the network present in the concentrated phase, a precise value of the polymer-solvent interaction parameter x is needed.展开更多
Poly(acrylic acid) (PAA) gel network with only chemical crosslinking and hydrophobically modified PAA (HM-PAA) gels with both chemical and physical crosslinking were synthesized by radical polymerization in tert-butan...Poly(acrylic acid) (PAA) gel network with only chemical crosslinking and hydrophobically modified PAA (HM-PAA) gels with both chemical and physical crosslinking were synthesized by radical polymerization in tert-butanol, using ethylene glycol dimethacrylate (EGDMA) as crosslinker, and 2-(N-ethylperfluorooctanesulfoamido)ethyl methacrylate (FMA), stearyl acrylate (SA) or lauryl acrylate (LA) as hydrophobic comonomer respectively. The effect of the fractions and the species of the hydrophobes on swelling properties of HM-PAA gels and the interaction of gels and surfactants were studied. The results showed that the swelling ratio of HM-PAA gels exhibited a sharp decrease with increasing hydrophobic comonomer concentration, which could be ascribed to the formation of strong hydrophobic association among hydrophobic groups. It was proved that two kinds of binding mechanisms of surfactant/gel and different kinds of hydrophobic clusters existed in gels containing both physical and chemical networks.展开更多
文摘The equilibrium swelling of the system Polystyrene (PS) (M = 1.7 × 10s, monodisperse)/diethyl ether at 30 °C and 35 °C has been studied in detail in quiescent state for a time span over 150 d. Arguments are given to show that the swelling process in a “non-solvent” is a network swelling rather than a phase separation process. It is different from the cloud point curve (CPC) experiment studied in literature, where the experiment starts from a one-phase solution, so that the cohesional entanglement present in the solid polymer is disrupted by dissolution. The cohesional entanglement structure of the solid polymer, on the contrary, is retained in the concentrated phase on swelling, at least in the initial stage. The course of swelling as presented by the curve Va(t) was found to proceed in three stages, where Va is the volume of the concentrated phase. In the first and third stages of Va(t), the curve goes up smoothly, while in the second stage the curve Va(t) shows large up and down jumps, indicating probably a readjustment in the network structure. Some results on a monodisperse PS sample of M = 5.8 × 105 and a polydisperse sample of M = 2.0 × 105 are also given. The values of Va observed at swelling equilibrium are not in accord with the expected cloud point temperature. The cloud point curve represents a phase separation process occurring in local regions (space limited to μm) and in time scale of the order of minute, while the process Va(t) occurred in the whole space of the concentrated phase, in time scale of days. For quantitative characterization of the network present in the concentrated phase, a precise value of the polymer-solvent interaction parameter x is needed.
文摘Poly(acrylic acid) (PAA) gel network with only chemical crosslinking and hydrophobically modified PAA (HM-PAA) gels with both chemical and physical crosslinking were synthesized by radical polymerization in tert-butanol, using ethylene glycol dimethacrylate (EGDMA) as crosslinker, and 2-(N-ethylperfluorooctanesulfoamido)ethyl methacrylate (FMA), stearyl acrylate (SA) or lauryl acrylate (LA) as hydrophobic comonomer respectively. The effect of the fractions and the species of the hydrophobes on swelling properties of HM-PAA gels and the interaction of gels and surfactants were studied. The results showed that the swelling ratio of HM-PAA gels exhibited a sharp decrease with increasing hydrophobic comonomer concentration, which could be ascribed to the formation of strong hydrophobic association among hydrophobic groups. It was proved that two kinds of binding mechanisms of surfactant/gel and different kinds of hydrophobic clusters existed in gels containing both physical and chemical networks.
