Gelation of amphiphilic lipopolymers at the air-water interface: 2D analogue to 3D gelation of colloidal systems with grafted polymer chains?
Gelation of amphiphilic lipopolymers at the air-water interface: 2D analogue to 3D gelation of colloidal systems with grafted polymer chains?
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DOI：
10.1021/la0261390
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发表时间：
2003-01-21
期刊：
影响因子：
3.9
通讯作者：
Naumann, CA
中科院分区：
文献类型：
--
作者：
Foreman, MB;Coffman, JP;Naumann, CA
已知两亲性脂质聚合物在空气-水界面处形成2D热可逆凝胶。最近，我们已经报道了不同分子量的聚（乙二醇）（PEG）脂聚合物的表面流变学和膜平衡实验，这表明聚合物和脂质部分之间足够的横截面积失配对于形成稳定的2D凝胶是必要的（J. Coffman和C.瑙曼Macromolecules 2002，35，1835）。在目前的研究中，我们已经通过表面流变学和膜平衡技术研究了疏水锚对凝胶化性质的影响，PEG脂质聚合物的实验，带有饱和和部分不饱和烷基链的聚[（2-正壬基-2-恶唑啉）（x）-B-（2-甲基-或2-乙基-2-恶唑啉）（y）]（NxMy或NxEy）不同嵌段长度的二嵌段共聚物表明，凝胶的形成不仅仅是亲水性和疏水性之间面积失配的结果两亲物的非线性（锥形），但是疏水部分内足够强度的货车德瓦尔斯相互作用对于形成2D凝胶是必需的，因此验证了Carlier预测，即所有烷基链缩合是发生凝胶化过程的必要前体。我们还提出了以上和以下的烷基链缩合和凝胶化转变，这与以前的中子和X-射线散射实验，表明这两个转变后发生的表面胶束oflipopolymers形成在空气-水界面上的PEG脂聚合物的中子反射数据。基于这些研究结果，我们假设脂聚合物在空气-水界面处的凝胶化过程是由脂聚合物的表面胶束化Mused的，这可以被看作是具有接枝聚合物链的聚合物胶体（如共聚物和星星聚合物）观察到的3D凝胶形成的2D模拟。
Amphiphilic lipopolymers are known to form 2D thermoreversible gels at the air- water interface. Recently, we have reported surface rheology and film balance experiments on poly(ethylene glycol) (PEG) lipopolymers of different molecular weights, which indicated that a sufficient cross-sectional area mismatch between polymer and lipid moieties is necessary to form stable 2D gels (J. Coffman and C. Naumann. Macromolecules 2002, 35, 1835). In the current studies, we have investigated the influence of the hydrophobic anchor on the gelation properties by surface rheology and film balance technique, Experiments on PEG lipopolymers, carrying saturated and partially unsaturated alkyl chains and on poly [(2-n-nonyl -2-oxazoline)(x)-b-(2-methyl-or 2-ethyl-2-oxazoline)(y)] (NxMy or NxEy) diblock copolymers of different block length show that the gel formation is not merely the result of the area mismatch between hydrophilic and hydropliobic Illoieties of the amphiphile (cone shape), but that a sufficient strength of van der Waals interaction within the hydrophobic moiety is necessary for the 2D gel to form, thus verifying carlier predictions that all alkyl chain condensation is a necessary precursor for the gelation process to occur. We also present neutron reflectometry data on PEG lipopolymers above and below the alkyl chain condensation and gelation transitions, which, in agreement to previous neutron and X-ray scattering experiments, reveal that both transitions occur after surface micelles oflipopolymers are formed at the air-water interface. On the basis of these findings, we assume that the gelation process of lipopolymers at the air-water interface is Mused by a surface micellization of lipopolymers, which can be seen as the 2D analogue to the 3D gel formation observed for polymeric colloids with grafted polymer chains, such as, copolymers and star polymers.