【正文】 體積為最大值 [19]。 3. Results and discussion . The surface activity . Effect of hydrophobic chain length (nonpolar chain) Fig. 1 represents the relation between the surface tension and ?log concentration of the synthesized nonionic Schiff base amphiphiles containing similar polyethylene glycol content (n=45 EO units) at 25 ?C. It is clear that the surface tension profile has the characteristics of the nonionic surfactants. That appeared in the relatively higher surface tension values. Also, it could be observed that increasing the number of methylene groups along the hydrophobic chains from 10 to 18 units decreases the critical micelle concentrations gradually [17]. That effect was explained in a previous work [20,21] due to the repulsion occurred between the hydrophobic chains (nonpolar phase) and the water phase (polar phase), which forced the molecules to adsorb at the air– water interface and to micellize in the bulk of their solutions in order to decrease that repulsion. While, the lowest critical micelle concentration was found at base containing PEO2020 and the hydrophobic chains is oleate (Table 2), which referred to the above reasons and also to the unsaturation sites in the oleate chain which increases the repulsion extent. The effectiveness (π cmc) values showed gradual decrease by increasing the hydrophobic chain length indicating the increasing of accumulated surfactant molecules at the interface. The maximum accumulation was indicated by the lowest surface tension depression at the critical micelle concentration and was recorded for SB2020oleate molecules at 44 mN/m . The effectiveness values as well as the maximum surface excess considered as a clear description for the accumulation extent of amphiphiles molecules at the air– water interface. The calculated values of the maximum surface excess showed increasing trend from SB2020decanoate to SB2020oleate as represented from the slope of preCMC region of surface tension profile (Fig. 1). The maximum surface excess values were increased from decanoate to oleate derivatives indicating higher surface concentration and increasing number of surfactant molecules at the interface. Values of the minimum surface area occupied by the nonionic Schiff base amphiphiles at the interface (Amin) were calculated according to the equation: where, Γ max and NAV are the maximum surface excess and Avogadro’ s number, respectively. Increasing the maximum surface excess values indicates the increasing of adsorbed molecules at the interface, hence the area available for eachmolecule will decrease. That causes the pacting of surfactant molecules at the interface to form denser layer. The values of critical micelle concentration, effectiveness, maximum surface excess and minimum surface area of the Schiff base nonionic amphiphiles were listed in Table 2. . 表面活性 . 疏水鏈 （非極性鏈） 長(zhǎng)度的影響 Fig. 1表示表面張力與合成的包含相同分子量聚乙二醇 (n=45 EO 單元 )的非離子型兩親席夫堿濃度直接的聯(lián)系。 隨著從 10到 18增加疏水鏈上的亞甲基數(shù)， 臨界膠束濃度逐漸 降低 [17]。含 有 PEO2020和油酸做疏水鏈的席夫堿 (Table 2) 最低臨界膠束濃度 為 ， 其中提到的上述原因，也是為了在油酸鏈 增加 不飽和點(diǎn)的排斥程度。最大累積值是 臨界膠束濃度 下的最低表面張力，最大值為 SB2020oleate 的 分子數(shù)在 44 mN/m時(shí)的值 。最大 剩余面積值的計(jì)算表明，從 SB2020decanoate 到 SB2020oleate 增加趨勢(shì)，表示表面張力前臨界膠束濃度區(qū)域的斜率范圍。 非離子 型 希夫 堿 兩親分子在界面 所占最小表面積值（ Amin） 計(jì)算 公式 如下： 式中Γ max表示最大 剩余 面積， NAV 表示阿伏伽德羅數(shù) 。表面活性劑分子間的壓迫 力使得在相界面形成致密的膜層。 . Effect of polyethylene oxide content (polar chains) Fig. 2 represents the effect of ethylene oxide contents on the surface activities of the synthesized nonionic Schiff base amphiphiles at constant hydrophobic chain length (16 methylene groups). It is clear that increasing the number of ethylene oxide units within the nonionic moiety from 9 to 45 and 68 EO units increases the hydrophilic characters of these molecules, which increases their critical micelle concentrations and also their surface tension values. Increasing of the CMC values can be referred to the formation of hydrogen bonds (HBs) between amphiphiles and water molecules. HBs increase the adsorption of these amphiphiles at the air– water interface, which increases the CMC values gradually. The maximum CMC value was observed for the longest polyethylene oxide chain (n = 68) at mM/L. On the other hand, the effectiveness (π CMC) values of the synthesized Schiff base nonionic amphiphiles SBn 16 were increased gradually by decreasing the length (n) of the nonionic moiety (where n = 9, 45 and 68) [22,23]. The effectiveness (π CMC) and the efficiency (pC20) values showed an increasing trend by increasing the hydrophobic chain length. The maximum lowering in the surface tension values was corresponded to the SB400palmitate. The maximum surface excess (Γ max) values showed lower surface concentration for the Schiff base amphiphiles which have the higher ethylene oxide content. The highest value of the maximum surface excess was observed for SB40016 (Table 2). On contrarily, the minimum surface area (A min) values