Babak Valery G, Baros Francis, Boury Frank, Desbrières Jacques
DCPR, CNRS UMR 7630, 1 rue Grandville, BP 451, 54001 Nancy Cedex, France.
Colloids Surf B Biointerfaces. 2008 Aug 1;65(1):43-9. doi: 10.1016/j.colsurfb.2008.02.019. Epub 2008 Mar 4.
Strongly adsorbing hydrophobic cationic polyelectrolyte, Eudragit RS, containing approximately 2.5 mol% of pendent hydrophilic trimethylammonium (TMA) groups irreversibly adsorbs from its methylene chloride (MCl) solution at the MCl/water interface and forms solid-like adsorption layers (ALs). Submitted to periodic dilational deformations with the standard radial frequency omega(0)=0.63 rad/s, these ALs exhibit relatively high dilational storage modulus E' approximately 20 mN/m and practically zero loss modulus E'' at the bulk concentration C(Eud)=4 x 10(-3)g/L. The frequency scanning of these ALs in the diapason omega=0.01-0.63rad/s and the approximation of the experimental dependences E'(omega) and E''(omega) by two relaxation times rheological model makes it possible to estimate the crossing frequency of these ALs determined from the condition E'(omega(c))=E''(omega(c)) as omega(c) approximately 5 x 10(-4)rad/s. Upon dissolving the hydrophilic anionic polyelectrolyte, chitosan sulfate (ChS), in the water phase (C(ChS)=3 x 10(-2)g/L) the electrostatic interpolyelectrolyte complexes form at the MCl/water interface. The elasticity moduli E' and E'' of these mixed AL did not undergo remarkable variations, but the crossing frequency is sharply increased by approximately 10 times becoming equal to omega(c) congruent with 3 x 10(-3)rad/s. The increase of omega(c) certifies for the liquefaction of mixed Eudragit RS/ChS adsorption layers. A remarkable decrease of the storage modulus down to E'=8 mN/m and simultaneous increase of the crossing frequency up to omega(c) congruent with 10(-2)rad/s occurs upon increasing the concentrations of both components, Eudragit RS and ChS, up to 0.1g/L. The liquefaction effect in the mixed ALs of oppositely charged polyelectrolytes was explained on the basis of the proposed relaxation mechanism. The effect of the liquefaction of adsorption layers of strongly adsorbing hydrophobic polyelectrolytes by formation of interpolyelectrolyte complexes with hydrophilic polyelectrolytes must be taken into account in the production of nano-capsules and nano-fibers.
强吸附性疏水阳离子聚电解质Eudragit RS含有约2.5摩尔%的悬垂亲水性三甲基铵（TMA）基团，它从其二氯甲烷（MCl）溶液在MCl/水界面不可逆吸附，并形成类固态吸附层（ALs）。以标准径向频率ω(0)=0.63 rad/s进行周期性膨胀变形时，在本体浓度C(Eud)=4×10(-3)g/L下，这些吸附层表现出相对较高的膨胀储能模量E'约为20 mN/m，且损耗模量E''实际上为零。在ω=0.01 - 0.63rad/s范围内对这些吸附层进行频率扫描，并通过双弛豫时间流变模型对实验依赖关系E'(ω)和E''(ω)进行近似，使得能够根据E'(ω(c)) = E''(ω(c))的条件估计这些吸附层的交叉频率，约为ω(c)≈5×10(-4)rad/s。当在水相中溶解亲水性阴离子聚电解质壳聚糖硫酸盐（ChS）（C(ChS)=3×10(-2)g/L）时，在MCl/水界面形成静电聚电解质络合物。这些混合吸附层的弹性模量E'和E''没有明显变化，但交叉频率急剧增加约10倍，变为等于ω(c)≈3×10(-3)rad/s。ω(c)的增加证明了Eudragit RS/ChS混合吸附层的液化。当将Eudragit RS和ChS两种组分的浓度都增加到0.1g/L时，储能模量显著降低至E' = 8 mN/m，同时交叉频率增加到ω(c)≈10(-2)rad/s。基于所提出的弛豫机制解释了带相反电荷聚电解质混合吸附层中的液化效应。在纳米胶囊和纳米纤维的生产中，必须考虑通过与亲水性聚电解质形成聚电解质络合物来使强吸附性疏水聚电解质吸附层液化的效应。
