CTAB 용액의 미세구조와 유변학적 물성에 대한 첨가제의 영향Effects of Solubilized Additives on the Microstructure and Its Rheological Properties of CTAB Solutions
계면활성제(Cetyltrimethylammonium Bromide) 용액에 서로 다른 기능을 하는 두 종류의 첨 가제를 투입하여 미셀의 미세구조 전이현상을 규명하였다. 양이온 계면활성제는 CMC 이상의 농도에서 2단계의 미세구조 전이거동을 나타낸다. 우선 구형 미셀은 첨가제의 투입에 의하여 표면에서의 친수성기 간의 반발력이 감소됨으로써 실린더형 또는 디스크형 미셀로 전이가 일어난다. 더욱 농도가 증가하면 이방성을 가지는 실린더형 미셀간의 중첩 또는 hooking 현상에 의한 두번째 전이가 일어난다. 이때 미셀용액은 흔히 점탄성을 나타내거나 확연한 비뉴톤성 유체거동을 나타낸다. 본 연구에서는 heptanol의 화학 구조적 차이가 물성에 나타내는 효과를 규명하고, wormlike 미셀을 형성하는 NaSal에 의한 점탄성 거동을 살펴보았다. Heptanol의 화학구조의 영향을 보면, 약친수성기인 OH기가 알킬그룹과 나란하게 존재하여 밀집된 구조를 가지기 쉬운 primary heptanol이 가장 효과적으로 미세구조 전이를 유도함을 관찰하였다. 다른 이성질 heptanol의 경우 secondary heptanol이 tertiary heptanol에 비하여 효과적임을 보이지만 화학적 구조의 유사성으로 인하여 유변학적 물성에는 큰 차이를 나타내지 않았다. 첨가제로 NaSal이 첨가된 용액은 선형 점탄성 거동을 보이며, 몰비 가 증가함에 따라 scission 과정이 관찰되었다. 또한 몰농도비에 따라 항복응력과 shear thickening 특징을 보이는데, 이는 흐름장의 세기에 따라 미세구조 변화가 일어나기 때문이다.
The effect of cosurfactant and NaSal additives on the evolution of microstructure in micellar solution are investigated. The microstructure is developed via two-step shape transitions in micellar solution when the surfactant concentration exceeds a CMC. First, the initial spherical micelles undergo shape transition to rodlike or disclike micelles because the surface characteristics of micelle demand the compact packing as the surfactant concentration increases. The packing density strongly depends on the rate of decrease in the repulsions between micelleheadgroups as well as on temperature. Further increment in the surfactant concentation makes the anisotropic rodlike micelles overlapped one anther. Solutions in these states exhibit non-Newtonian behaviors such as shear thinning. Addition of solubilized additives enhances the transitions which are affected by the concentration and chemical structure of the additive. Presence of cosurfactants with long alkyl chains reduces the repulsion by forming surfactant-alcohol mixed micelles.In the present study, we examine the effects of chemical structure of alcoholic additives which possess a very weakly hydrophilic hydroxyl group. The primary heptanol can be easily penetrated into the micelles and aligned parallel to the surfactant molecules, and thus it enhances the two-step shape evolutions.On the other hand, the secondary and tertiary heptanols retard the shape transition since the compact packing of surfactant molecules is suppressed. NaSal added solutions have a sufficiently narrow concentration range in which rodlike micelles exist. That is, the solutions exhibit the linear viscoelastic properties in the entrire range of CTAB concentration. As the molar ratio increases, the solutions possess the shear thickening behavior aand the yield stress, which indicates that the microstructure is induced by the flow.
The effect of cosurfactant and NaSal additives on the evolution of microstructure in micellar solution are investigated. The microstructure is developed via two-step shape transitions in micellar solution when the surfactant concentration exceeds a CMC. First, the initial spherical micelles undergo shape transition to rodlike or disclike micelles because the surface characteristics of micelle demand the compact packing as the surfactant concentration increases. The packing density strongly depends on the rate of decrease in the repulsions between micelleheadgroups as well as on temperature. Further increment in the surfactant concentation makes the anisotropic rodlike micelles overlapped one anther. Solutions in these states exhibit non-Newtonian behaviors such as shear thinning. Addition of solubilized additives enhances the transitions which are affected by the concentration and chemical structure of the additive. Presence of cosurfactants with long alkyl chains reduces the repulsion by forming surfactant-alcohol mixed micelles.In the present study, we examine the effects of chemical structure of alcoholic additives which possess a very weakly hydrophilic hydroxyl group. The primary heptanol can be easily penetrated into the micelles and aligned parallel to the surfactant molecules, and thus it enhances the two-step shape evolutions.On the other hand, the secondary and tertiary heptanols retard the shape transition since the compact packing of surfactant molecules is suppressed. NaSal added solutions have a sufficiently narrow concentration range in which rodlike micelles exist. That is, the solutions exhibit the linear viscoelastic properties in the entrire range of CTAB concentration. As the molar ratio increases, the solutions possess the shear thickening behavior aand the yield stress, which indicates that the microstructure is induced by the flow.
- Publisher
- 한국유변학회
- Issue Date
- 1997-03
- Keywords
surfactant solution; micelle microstructure evolution; shear viscosity; flow birefringence; yield stress; shear thickening; relaxation behavior; viscoelasticity
- Citation
The Korean Journal of Rheology, Vol.9, No.1, pp.6-15
- Appears in Collection
- CBE-Journal Papers(저널논문)
- Files in This Item
- 02.pdf(615.59 kB)Download
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