Change in Free Volume Parameters of Poly(vinyl alcohol) Gels Studied by Positron Annihilation Lifetime Measurement

Positron annihilation studies on radiation-crosslinked poly(N-isopropylacrylamide) hydrogels

“…This shows that water molecules occupy the free volume and that Ps annihilation takes place mainly in free water. A similar observation has been made by Ito et al in poly(vinyl alcohol) gels 23. The result therefore shows that incorporation of water alters the free‐volume structure because of a possible change in the conformational state of the polymer.…”

Ortho-positronium annihilation parameters in polyvinyl alcohol films with various degrees of polymerization, saponification and crystallinity

“…Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 5/28/15 2:03 PM mental result by Ito et al [6]. This fact certifies that our samples are prepared almost free from water.…”

“…4, this equation gives a free-volume radius ranging from 0.2 to 0.3 nm, depending on the degree of saponification, and the size of the freevolume is then estimated to be 0.033-0.113 nm 3 . The freevolume radius for the fully saponificated PVA (bulk PVA) was estimated to be 0.21 nm, which was in good agreement with those in the previous works [2,6]. It should especially be noted that this value corresponds to the value of the PVA gel having 0 wt % water content, according to the experi- Fig.…”

“…After saponification, the sample solution was purified by dialysis using a cellulose tubing, and transparent films were made using a casting method. Since it has already been known that the water content affects on the o-Ps parameters [6], the sample films thus prepared were dried for 400 hours until the weight reduction becomes negligibly small. In order to estimate the degree of crystallinity, X-ray powder diffraction was also undertaken with the film samples according to the procedure by Hermans et al [7,8], which consists of measuring integrated intensities of the crystalline peaks and that of the diffuse background.…”

Free-volume change in volume phase transition of polyacrylamide gel as studied by positron annihilation: Salt dependence

“…Later, the present authors revealed that the number concentration of the free-volume significantly correlated with an enthalpy of the hydrogen bond in the PVA gel. 26 We previously dealt with solvent composition dependence of the free-volume size of the PNIPA gel during a volume phase transition (VPT) in a methanol-water mixed solvent 27 ; and found that the free-volume size of the collapsed PNIPA gel is close to the corresponding mixed solvent. The evidence strongly suggests that a balance of an interaction strength among the solvent molecules and the polymer chain affects the aggregation of a gel network of the PNIPA gel, i.e., the macroscopic volume shrinkage.…”