R/S analysis of earthquake time interval

Liu, Changhai; Yi-gao, Liu; Jun, Zhang

doi:10.1007/bf02650577

Cited by 22 publications

(32 citation statements)

References 3 publications

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“…This increase of G′ is most certainly due to the gradual increase of the inter‐ and intra‐chain hydrogen bonding and hence the increase in interactions and entanglements between the PVA chains. It is generally agreed that the formation of a physical gel from a polymer solution is the result of physical crosslinking of the intermolecules in solution and it is presupposed to be a contact or collision of polymer chains 6, 23. The PVA‐24 solution shows very complicated and unusual behavior.…”

Section: Resultsmentioning

confidence: 99%

“…It is generally agreed that the formation of a physical gel from a polymer solution is the result of physical crosslinking of the intermolecules in solution and it is presupposed to be a contact or collision of polymer chains. 6,23 The PVA-24 solution shows very complicated and unusual behavior. In the low-frequency range, the G 0 of PVA-24 is only little higher than PVA-13, but becomes the highest in the highfrequency range.…”

Section: Resultsmentioning

confidence: 99%

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Characteristic rheological features of high concentration PVA solutions in water with different degrees of polymerization

Gao

Yang

et al. 2010

J of Applied Polymer Sci

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This work aims to study the impact of the degree of polymerization (Pn) on the rheological behavior of PVA solutions (15 wt %) under steady and oscillatory shear conditions. The values of Pn range from 1300 to 2400. The results show that PVA-13 solution exhibits almost Newtonian flow behavior, whereas high Pn PVA solutions exhibit shear thinning behavior, for which the complex viscosity increases with Pn. However, the shear viscosity of PVA-24 is lower than that of PVA-20 at low shear rate (<1 s À1 ). In addition, the storage modulus of PVA solutions increases with increasing degree of polymerization from 1300 to 2000. There is a sharp increase at degrees of polymerization higher than 1300. However, the storage modulus of PVA-24 is lower than that of PVA-17 and PVA-20 at low shear rate (<1 rad/s). The viscoelastic exponent of the PVA solutions shows a minimum value at degree of polymerization 2000. Thixotropy is detected by a hysteresis loop of the flow curves. The creep response of PVA solutions has also been investigated, with PVA-24 showing negligible compliance recovery. These facts indicate that increasing Pn produces a corresponding effect in varying the molecular structure and types of hydrogen bonding, including intra-and inter-chain, and polymer-water hydrogen bonding. Rheological parameters (G 0 , n, tand, J, and so on) can be used to evaluate the change in the molecular structure and type of hydrogen bonding.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Characteristic rheological features of high concentration PVA solutions in water with different degrees of polymerization

Gao

Yang

et al. 2010

J of Applied Polymer Sci

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“…The high swelling rate of the hydrogels may be attributed to their microporous structure as shown in Figure 3, which increases surface area of the composite hydrogel and facilitates the penetration of water into the network. If the swelling of a polymeric hydrogel fits the process of first dynamics, the relationship between swelling rate and swelling time at a certain temperature is as follows:38 where t is the swelling time; Q t is the water absorbency at the corresponding time; Q e is the equilibrium water absorbency; Q 0 is the water absorbency when t = 0.…”

Section: Resultsmentioning

confidence: 99%

A Novel N‐Succinylchitosan‐graft‐Polyacrylamide/Attapulgite Composite Hydrogel Prepared through Inverse Suspension Polymerization

Zhang

Wang

2007

Macro Materials & Eng

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A novel N‐succinylchitosan‐graft‐polyacrylamide/attapulgite composite hydrogel was prepared by using N‐succinylchitosan, acrylamide and attapulgite through inverse suspension polymerization. The result from FTIR spectra showed that OH of attapulgite, OH and NHCO of N‐succinylchitosan participated in graft polymerization with acrylamide. The introduced attapulgite could enhance thermal stability of the hydrogel. Scanning electron microscopy observation indicates that the composite hydrogel has a microporous surface. The volume ratio of heptane to water, weight ratio of acrylamide to N‐succinylchitosan and attapulgite content have great influence on swelling ability of the composite hydrogel. The composite hydrogel shows higher swelling rate and pH‐sensitivity compared to that of without attapulgite.magnified image

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“…On the assumption that the swelling of the polymer fits a first‐order process,24 the swelling rate at a given temperature is: Where t is the swelling time, Q t is the swelling ratio at that time, Q e is the equilibrium swelling ratio. eq.…”

Section: Resultsmentioning

confidence: 99%

Hydroxyethyl chitosan‐g‐poly(acrylic acid‐co‐sodium acrylate) superabsorbent polymers

Chen

Liu

Hui‐min

2010

J of Applied Polymer Sci

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A novel hydroxyethyl chitosan-g-poly (acrylic acid-co-Sodium Acrylate) (HECTS-g-(PAA-co-PSA)) superabsorbent polymer was prepared through graft copolymerization of acrylic acid and sodium acrylate onto the chain of hydroxyethyl chitosan. The structure of the polymer was characterized by FTIR. By studying the water absorption of the polymer synthesized under different conditions, the optimal conditions for synthesizing the polymer with the highest swelling ratio was defined. This superabsorbent polymer was further treated by the solvent precipitation method and by the freeze-drying method. We found that the water absorption rate of the treated polymer was greatly increased and the microstructure of the treated polymer was changed from small pores to loose macro pores. The swelling processes of the polymers before and after modification fit first-order dynamic processes. The amount of the residual acrylic acid was greatly decreased after treatments.

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R/S analysis of earthquake time interval

Cited by 22 publications

References 3 publications

Characteristic rheological features of high concentration PVA solutions in water with different degrees of polymerization

Characteristic rheological features of high concentration PVA solutions in water with different degrees of polymerization

A Novel N‐Succinylchitosan‐graft‐Polyacrylamide/Attapulgite Composite Hydrogel Prepared through Inverse Suspension Polymerization

Hydroxyethyl chitosan‐g‐poly(acrylic acid‐co‐sodium acrylate) superabsorbent polymers

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