X-ray reflectivity and diffraction studies on lipid and lipopolymer Langmuir-Blodgett films under controlled humidity

湿度制御下における脂質・脂質高分子LB膜のX線反射率及びX線回折による研究

Bolze, J.*; 高橋 正光; 水木 純一郎; Baumgart, T.*; Knoll, W.*

Bolze, J.*; Takahashi, Masamitsu; Mizuki, Junichiro; Baumgart, T.*; Knoll, W.*

放射光を用いたX線反射率測定及び微小角入射X線回折法を用いて、湿度を制御した環境下における脂質及び脂質高分子LB膜の構造を調べた。試料には、DSPE及びPEO分子鎖の長さがn=8,17,45のDSPE-PEO脂質高分子からなる膜を用いた。DSPEのみの膜の場合、雰囲気中の相対湿度を2%以下から97%に変化させると、DSPEが水を含み、膜厚が増加する。これは可逆な変化であり、これにより膜のラフネスは変化しない。 DSPEの膜厚は、試料作製時の面内の圧力のかけ方によって、多少違いが見られる。また、湿度が増えると、DSPE膜の面内の配向性が著しく増加した。PEO分子鎖の長さがn=8のDSPE-PEOの場合も、膜の膨潤は可逆であることが見い出された。水の取込み量はDSPE膜に比べると多い。

Synchrotron X-ray reflectivity and grazing incidence diffraction were applied to study the structures of phospholipid Langmuir-Blodgett films under controlled humidity. DSPE and DSPE-PEO lipopolymers, in which a PEO chain with n= 8, 17, or 45 EO units is covalently linked to the polar headgroup of DSPE, were used. When the relative humidity was changed from below 2 to 97%, the phosphate headgroup in a DSPE film was hydrated with a concomitant thickness increase of 0.42 nm. The swelling of the monolayer was found to be a reversible process without any significant roughening of the film. Subtle differences in the film thickness could be detected for DSPE monolayers transferred under various lateral pressures. The degree of lateral ordering of the alkyl chains in DSPE monolayers increased considerably when the humidity was raised. In the case of DSPE-PEO with eight EO units, the hydration of the monolayer was also found to be reversible, but the water uptake was larger due to the presence of the hydrophilic polymer interlayer.