Eight 6FDA-TFDB polyimide(PI)samples with absolute molecular weights ranging from 1.25 × 10^5 g mol^-1 to 3.11 × 10^5 g mol^-1 are obtained by precipitation fractionation.Rheological experiments are conducte...Eight 6FDA-TFDB polyimide(PI)samples with absolute molecular weights ranging from 1.25 × 10^5 g mol^-1 to 3.11 × 10^5 g mol^-1 are obtained by precipitation fractionation.Rheological experiments are conducted to determine the influence of molecular weight on the associating behavior of PI in A/X-dimethylformamide(DMF)solutions in a broad volume fraction,including abnormal steady shear flow,solution heterogeneity,and scaling behavior.Abnormal flow behaviors,i.e.,multi-region shear thinning and weak shear thickening,are studied,and these behaviors have not been reported in literature.The heterogeneity of PI/DMF solutions is examined by dynamic rheological test.By plotting qsp versus four concentration regions of l-IV can be distinguished for all PI samples with various molecular weights.The scaling results in different concentration regions are in good agreement with the associative polymer theory proposed by Rubinstein and Semenov.The scaling exponents do not show molecular weight dependence in concentration regions I and II.In concentration regions Ⅲ and Ⅳ,the scaling exponents change little when the molecular weight is below 242 k but increase when the molecular weight increases from 242 k to 311 k.This work can help us to understand polyimide solution properties from dilute to semidilute entangled solutions,and will guide the polyimide solution preparation for different processing.展开更多
In this paper,a semi-analytical calculation model for the coefficient of friction(COF)of single spherical protrusions is presented.It allows the prediction of the deformative friction part(μ_(def))and adhesive fricti...In this paper,a semi-analytical calculation model for the coefficient of friction(COF)of single spherical protrusions is presented.It allows the prediction of the deformative friction part(μ_(def))and adhesive friction part(μ_(def))of the friction pairings steel|polyethylene with ultra-high molecular weight(PE-UHMW)and polyoxymethylene(POM)|PE-UHMW.The experimental studies included unlubricated friction tests,which served to determine the total COF(μ_(def)),as well as tests being lubricated with silicone oil,from whichμ_(def)is obtained.Based on the verification tests,it could be shown that both states of lubrication result in the same deformation and that the relationship between the rear angle(w)andμ_(def)postulated in the calculation model is valid.Therefore,friction tests with segmented spheres were carried out,which allow a specific variation of thew.It can be concluded that for both pairings theμ_(def)is generally of minor significance(approx.1/3μ_(tot))and the influence of theμ_(adh)predominates(approx.2/3μ_(tot))the friction process.Furthermore themtot decreases with increasing contact pressure especially in the low pressure range and depends on the form of motion(continuous and discontinuous).展开更多
三次采油技术中使用的部分水解聚丙烯酰胺(HPAM)在高温高盐条件下会发生明显的水解和降解反应,抗温抗盐性能较差。疏水缔合聚合物凭借聚合物分子间缔合作用形成的大分子网状结构使其抗盐性有所改善,从而弥补了HPAM抗盐性差的缺陷。然而...三次采油技术中使用的部分水解聚丙烯酰胺(HPAM)在高温高盐条件下会发生明显的水解和降解反应,抗温抗盐性能较差。疏水缔合聚合物凭借聚合物分子间缔合作用形成的大分子网状结构使其抗盐性有所改善,从而弥补了HPAM抗盐性差的缺陷。然而,疏水缔合聚合物存在其分子线团尺寸与油藏多孔介质孔隙尺寸间适应性差的问题,导致疏水缔合聚合物注入困难。针对疏水缔合聚合物与油藏适应性较差的问题,采用β-环糊精(β-CD)为疏水缔合聚合物缔合程度调节剂,通过室内岩心驱替实验方法,开展了β-CD对疏水缔合聚合物传输运移特性影响的研究。结果表明,β-CD可以改变AP-P4的缔合作用及在多孔介质中的行为。在浓度为1 g/L的疏水缔合聚合物AP-P4溶液中加入β-CD后,溶液黏度随β-CD加量的增加而减小,当β-CD加量达到0.07%时,AP-P4溶液黏度最低(26.2 m Pa·s),为本体黏度,难以发生缔合作用。同时,随着β-CD加量的增大,AP-P4分子链间缔合作用减弱,聚合物分子线团尺寸减小。随着β-CD加量的增大,在岩心渗透率相同(相近)条件下,AP-P4溶液的阻力系数和残余阻力系数减小,疏水缔合聚合物溶液在岩心内的传输运移能力增强。展开更多
基金the National Basic Research Program of China(No.2014CB643604)the National Natural Science Foundation of China(No.51173178).
文摘Eight 6FDA-TFDB polyimide(PI)samples with absolute molecular weights ranging from 1.25 × 10^5 g mol^-1 to 3.11 × 10^5 g mol^-1 are obtained by precipitation fractionation.Rheological experiments are conducted to determine the influence of molecular weight on the associating behavior of PI in A/X-dimethylformamide(DMF)solutions in a broad volume fraction,including abnormal steady shear flow,solution heterogeneity,and scaling behavior.Abnormal flow behaviors,i.e.,multi-region shear thinning and weak shear thickening,are studied,and these behaviors have not been reported in literature.The heterogeneity of PI/DMF solutions is examined by dynamic rheological test.By plotting qsp versus four concentration regions of l-IV can be distinguished for all PI samples with various molecular weights.The scaling results in different concentration regions are in good agreement with the associative polymer theory proposed by Rubinstein and Semenov.The scaling exponents do not show molecular weight dependence in concentration regions I and II.In concentration regions Ⅲ and Ⅳ,the scaling exponents change little when the molecular weight is below 242 k but increase when the molecular weight increases from 242 k to 311 k.This work can help us to understand polyimide solution properties from dilute to semidilute entangled solutions,and will guide the polyimide solution preparation for different processing.
基金funded by the Federal Ministry of Economic Affairs and Energy(BMWi)through the“Otto von Guericke”German Federation of Industrial Research Associations(AiF)on the basis of a resolution of the German Bundestag as part of the programme to promote joint industrial research(IGF No.20967 BG).
文摘In this paper,a semi-analytical calculation model for the coefficient of friction(COF)of single spherical protrusions is presented.It allows the prediction of the deformative friction part(μ_(def))and adhesive friction part(μ_(def))of the friction pairings steel|polyethylene with ultra-high molecular weight(PE-UHMW)and polyoxymethylene(POM)|PE-UHMW.The experimental studies included unlubricated friction tests,which served to determine the total COF(μ_(def)),as well as tests being lubricated with silicone oil,from whichμ_(def)is obtained.Based on the verification tests,it could be shown that both states of lubrication result in the same deformation and that the relationship between the rear angle(w)andμ_(def)postulated in the calculation model is valid.Therefore,friction tests with segmented spheres were carried out,which allow a specific variation of thew.It can be concluded that for both pairings theμ_(def)is generally of minor significance(approx.1/3μ_(tot))and the influence of theμ_(adh)predominates(approx.2/3μ_(tot))the friction process.Furthermore themtot decreases with increasing contact pressure especially in the low pressure range and depends on the form of motion(continuous and discontinuous).
文摘三次采油技术中使用的部分水解聚丙烯酰胺(HPAM)在高温高盐条件下会发生明显的水解和降解反应,抗温抗盐性能较差。疏水缔合聚合物凭借聚合物分子间缔合作用形成的大分子网状结构使其抗盐性有所改善,从而弥补了HPAM抗盐性差的缺陷。然而,疏水缔合聚合物存在其分子线团尺寸与油藏多孔介质孔隙尺寸间适应性差的问题,导致疏水缔合聚合物注入困难。针对疏水缔合聚合物与油藏适应性较差的问题,采用β-环糊精(β-CD)为疏水缔合聚合物缔合程度调节剂,通过室内岩心驱替实验方法,开展了β-CD对疏水缔合聚合物传输运移特性影响的研究。结果表明,β-CD可以改变AP-P4的缔合作用及在多孔介质中的行为。在浓度为1 g/L的疏水缔合聚合物AP-P4溶液中加入β-CD后,溶液黏度随β-CD加量的增加而减小,当β-CD加量达到0.07%时,AP-P4溶液黏度最低(26.2 m Pa·s),为本体黏度,难以发生缔合作用。同时,随着β-CD加量的增大,AP-P4分子链间缔合作用减弱,聚合物分子线团尺寸减小。随着β-CD加量的增大,在岩心渗透率相同(相近)条件下,AP-P4溶液的阻力系数和残余阻力系数减小,疏水缔合聚合物溶液在岩心内的传输运移能力增强。
