文献类型：学位论文

中文题名：气/液界面含Gemini表面活性剂的混合单分子膜研究

英文题名：Study on the Mixed Monolayers Containing Gemini Surfactants at Air//Water Interface

作者：李蓉[1];

机构：[1]华东理工大学;

导师：胡英;华东理工大学

授予学位：博士

语种：中文

中文关键词：混合Langmuir单分子膜;LB膜;Gemini表面活性剂;DNA;两嵌段聚电解质

外文关键词：Mixed Langmuir monolayer; LB films; gemini surfactant; DNA; diblock polyelectrolyte

摘要：Gemini表面活性剂作为一种新型表面活性剂,与传统表面活性剂相比有许多优点,例如具有较低的临界胶束浓度、较高的表面活性、更好的润湿性和发泡能力等。本文主要利用LB膜技术、原子力显微镜、红外光谱、圆二色光谱等手段研究了gemini表面活性剂(m-s-m,其中m是尾链的长度,s指连接基团的长度；本论文中s指连接基团中亚甲基的个数)及其与阴离子表面活性剂、DNA(脱氧核糖核酸)在界面上的相互作用。此外,还考察了具有生物相容性的两嵌段共聚物在界面上的性质及其与gemini表面活性剂的相互作用。 研究发现,季钱盐阳离子型gemini表面活性剂在气/液界面上主要形成液态扩张膜,这表示它们在气/液界面上难以形成致密的单分子膜。此外,连接基团的性质在很大程度上影响着gemini表面活性剂在气/液界面上的性质。当连接基团为刚性时,连接基团平躺于气/液界面上,使得在表面压-分子面积(π-A)等温线中几个重要的参数,如极限分子面积、表面压起始增加值对应的分子面积等,随着连接基团的增长而呈线性增加；当连接基团为柔性时(s＞6),由于连接基团疏水性的增加,它们倾向于向空气一侧逃逸,在界面上形成拱桥形状,甚至呈倒U的构型。原子力显微镜的结果说明gemini表面活性剂在较高表面压下容易形成类似于表面胶束的聚集体,而很难形成致密的单分子膜。由等温线、LB膜接触角测定的结果可发现,尽管在较高表面压下gemini表面活性剂可形成表面聚集体,但是其大多数分子仍然平躺于气/液界面上 带正电荷的gemini表面活性剂与硬脂酸(SA)存在较强的静电吸引作用,因此它们之间的混合单分子膜表现为非理想性,整个混合体系为负偏差体系。研究发现,gemini表面活性剂中连接基团的长度会明显影响它与硬脂酸的相互作用。随着连接基团长度的增加,最大负偏差的位置向富含SA的方向移动(s=3时出现在XSA(硬脂酸摩尔分数)=0.67处,s=4时出现在XSA=0.7处,s=6、8和10时出现在XSA=0.8处,s=12时出现在XSA=0.75处),而且相应的混合单分子膜发生了相分离：当s≤8时,在整个SA组成范围内没有发生相分离；当连接基团s的长度增加到10时,在XSA=0.4-0.8之间出现了相分离；而当s=12时,甚至出现了两次相分离,第一次相分离出现XSA=0.4-0.75之间,第二次相分离出现在XSA=0.75-0.85之间。其LB膜的傅立叶红外光谱表明：尽管硬脂酸为弱酸,当XSA≤0.67时它是完全电离的,而XSA≥0.67时则是部分电离的。 DNA分子与表面活性剂在界面上的相互作用与在溶液中类似。在gemini/DNA复合物的LB膜中,DNA分子被压缩,其直径为1nm左右；导致DNA分子从天然的B-构型转变为高度致密的ψ-相。此外,gemini表面活性剂中连接基团长度的改变会影响它与DNA分子的相互作用方式,以至于形成不同的聚集体。当连接基团为刚性且两个头基之间的距离与DNA分子中磷酸根的距离或者大、小沟的宽度不匹配时,gemini表面活性剂中只有一个头基作用于一个DNA分子上,而另外一个头基则悬挂于该分子外。在提拉的过程中,悬挂于DNA分子外的表面活性剂头基可以在任意方向与另外的DNA分子相互作用。当s=6时,18-6-18的连接基团具有一定的柔性,其两个头基之间的距离可以与DNA分子中磷酸根的匹配,因此它的两个头基可以作用于DNA分子中的同一条聚核苷酸链上；而当s=8、10和12时,gemini表面活性剂的连接基团具有很好的柔性,两个头基之间的距离可以与DNA分子中小沟槽的宽度匹配,其两个头基则可以作用于同一DNA中的两条互补聚核苷酸链上。Gemini/DNA复合膜的原子力显微镜结果说明：当连接基团为刚性时gemini/DNA复合膜主要形成纤维结构,而当连接基团为柔性时则主要形成片状聚集体。 本文还研究了具有生物相容性的两嵌段聚电解质(PDMAEMAm-b-PAAn)在气/液界面上的性质及其与表面活性剂的相互作用。一方面,在碱性条件下,该聚电解质的PAA段电离而PDMAEMA段为疏水链,因此其表面活性随着DMAEMA链的增长而增大。另一方面,在酸性条件下,PDMAEMA段质子化而PAA成为相对疏水的部分。此时,PAA段的羧酸根具有一定的亲水性,因此对于同一种PDMAEMAm-b-PAAn聚电解质的表面活性随着pH值的降低而降低。另外,在酸性和碱性条件下PDMAEMAm-b-PAAn都能在界面上形成聚集体。在碱性条件下其主要形成核-壳结构,其中PDMAEMA段形成核部分而PAA段形成外壳部分,gemini表面活性剂可以将PDMAEMAm-b-PAAn球状聚集体连接成串珠结构,而传统表面活性剂却不能；在酸性条件下,主要由PAA段中的分子间或者分子内氢键作用而形成聚集体。
As a new class of surfactant, gemini surfactant greatly shows more enhanced properties compared with the conventional surfactant, such as much lower critical micelle concentration /(CMC/), high surface activity, better wetting and foaming behaviors. Therefore, the properties of cationic gemini surfactants /(m-s-m, m is the length of the hydrophobic chain, and s is the length of spacer, respectively; s represents the number of-CH2-in this dissertation/) and their interaction with different materials, including anionic surfactant and DNA /(deoxyribonucleic acid/), at the air//water interface have been investigated in this dissertation by means of LB technology, atom force microscope, FT-IR spectra and circular dichroism spectra etc. In addition, the properties of biocompatible amphiphilic copolymers and their complex monolayer composed of gemini surfactants have been investigated. It is shown that the liquid-expanded films are formed at the air//water interface for cationic gemini surfactant, which is suggest that the cationic gemini surfactants are difficult to form a compact film. At the same time, the spacer has a significant effect on the interfacial properties of gemini surfactants. The spacer lies on the air//water interface and induces the linear increase of the limiting area and lift-off area with its length when it is rigid, while when the spacer is flexible/(s> 6/), the increasing hydrophobility of spacer lead to the tendency to escape away from the aqueous side of the interface, so that the arc shape conformation of the spacer and even the reverse U-shape conformation are formed. The AFM image shows that the surface micelles and the multilayer aggregates appear at the air//water interface, whereas it is also difficult to form homogenous monolayers at higher surface pressure. According to the results ofπ-A isotherms and contact angle of LB film, it is found that although the surface micelles and the multilayer aggregates appear at higher surface pressure, the major molecules lie nearly flat on the water surface. Gemini//SA /(stearic acid/) mixed monolayers exhibits negative deviation from ideal nmixing because of the electrostatic attractive interaction between gemini surfactant and stearic acid. It shows that the length of spacer group plays an important role in determining the surface properties of gemini//SA mixed monolayers. The most negative deviation shift to SA rich component with the spacer increase /(XSA /(the mole fraction of SA/)=0.67 for s=3, XSA= 0.7 for s=4, XSA=0.8 for s=6-10, and XSA=0.75 for s=12/). Furthermore, phase separation is observed in corresponding mixed monolayers:when s≤8, no phase separation is observed at all SA composition; when the spacer group increases up to 10, phase separation appears at XSA= 0.4-0.8. In particular, for s=12, phase separation appears in two composition regions of XSA= .4-0.75 and XSA= 0.75-0.85, respectively. The result of FT-IR spectra of LB films show that although SA is a weak acid, it ionizes completely when XSA≤0.67, while ionizes partially when XSA＞0.67. The interaction between DNA and surfactant at the air-water interface is the same as that of in solution. It is found that DNA molecule is condensed to-1 nm in gemini//DNA complex LB film, inducing the conformation of DNA changes from B-form conformation to aψ-phase. In addition, the length of spacers has a significant effect on the binding site between gemini surfactant and DNA, so that different aggregates are formed. When the spacer is rigid, and the intramolecular distance of N+-N+ of gemini mismatches that of P- - P- or the width of minor groove and major groove, only one ammonium group in a gemini surfactants can bind on one phosphate group in a DNA molecule, while the other one stretches out of this DNA. The later can easily interact with other DNA molecules at a random orientation during the deposition process. When s=6, the flexibility of the spacer in 18-6-18 lead to the match between the N+-N+ and P- - P- distance, which results in that 18-6-18 could anchor on one backbone in a DNA molecule. As s increases up to s＞6, the flexibility of the spacers increase, which makes N+-N+ distances match the width of minor groove in DNA molecule, so that gemini surfactants can interact on the complementary double strands in a DNA molecule. The results of AFM indicate that when spacer is rigid, the main morphology of gemini//DNA complex is fibril, while the main morphology is plate structure when spacer is flexible. Finally, the properties of biocompatible amphiphilic polyelectrolyte /(PDMAEMAm-b-PAAn/) and their complex with surfactants have been investigated at the air//water interface. PAA segment is ionized at basic condition, and PDMAEMA segment is hydrophobic chains, so that its surface activity increases with the increase of PDMAEMA segment. On the contrary, PDMAEMA segment is protonated, and PAA segment is relatively hydrophobic chains at acid condition. However, - COOH is a hydrophilic functional group in PAA segment. Thus, the surface activity decreases with the decrease of pH for PDMAEMAm-b-PAAn. In addition, surface aggregates are formed both at the basic and acid condition. Spherical aggregates are formed at basic condition, which is consisted of a PDMAEMA core surrounded by a water-soluble ionized PAA corona, and gemini surfactant can connect these spherical aggregates together to form necklace-like structure, while the traditional surfactant does not. On the contrary, random aggregates are formed by means of the hydrogen bond of intermolecular or intramolecular of PAA segment at acid condition.