Applied Chemistry for Engineering (공업화학)

The Korean Society of Industrial and Engineering Chemistry (한국공업화학회)
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Studies on the Micelle Formation of Nonionic Surfactant(1) -1NMR Self-Diffusion and Proton Relaxation of Polyoxyethylene Alkyl Ether-

계면활성제 수용액의 미셀형성(제1보) - Polyoxyethylene Alkyl Ether의 자기확산과 프로톤 이완 -

  • Choi, Seung-Ok (Department of Industrial and Engineering Chemistry, Chungbuk National University) ;
  • Jeong, Hwan-Kyeong (Department of Chemical Science and Technology, Faculty of Engineering, Kyushu University) ;
  • Lee, Jin-Hee (Department of Industrial and Engineering Chemistry, Chungbuk National University) ;
  • Nam, Ki-Dae (Department of Industrial and Engineering Chemistry, Chungbuk National University)
  • 최성옥 (충북대학교 공과대학 공업화학과) ;
  • 정환경 (일본 규수대학 물질응용 공학과) ;
  • 이진희 (충북대학교 공과대학 공업화학과) ;
  • 남기대 (충북대학교 공과대학 공업화학과)
  • Received : 1998.03.24
  • Accepted : 1998.07.24
  • Published : 1998.11.10

Abstract

Binary system of water and polyoxyethylene dodecyl ether, $C_{12}H_{25}(OCH_2CH_2)nOH$, have been studied by $^1H$ NMR techniques. For n=5($C_{12}EO_5$) and n=8($C_{12}EO_8$), the self-diffusion coefficients of nonionic surfactants in the isotropic phase($L_1$) have been measured by using pulsed field gradient technique for a range of temperature and concentrations. In addition the line widths of the different proton signals have been monitored, and samples of some liquid crystalline characteristic were also studied. Dramatic Broadening of the methylene signals of the alkyl($C_{12}H_{25}$) chain is observed as the hexagonal liquid crystalline phase is approached in the $C_{12}EO_5-$water system, while only small broadening is observed in the $C_{12}EO_8-$water system. It was shown that there was a growth of $C_{12}EO_5$ micelles to rods with increasing concentrations, while the $C_{12}EO_8-$ micelles at low temperature remain small in the concentration range. The self-diffusion coefficients of the surfactants decrease rapidly with increasing concentration until a minimum is reached after which there is slow increase. The location of the minimum point occurs at lower concentrations the temperature is close to the cloud point, where the system separate into two isotropic phase. In the line width studies, broadening is found at a certain temperature interval when the concentration is increased in the $C_{12}EO_5$ system. The results indicate that the surfactant aggregates grow in size at the cloud point is approached. The aggregates seem to be flexible and probably not to be of a definite shape close to the cloud point. In the $C_{12}EO_8$ system, the micelles are much less affected by an increase in temperature and micellar growth can't be unambiguously established. The methylene signals of the ethylene oxide moieties consistantly show narrower $^1H$ signals, showing that in the aggregates they are less ordered than the chain methylenes. The various changes in aggregate size and shape are correlated with the stability ranges of the isotropic and liquid crystalline phases according to phase diagrams from the literature. Both aggregate size and phase structure are in qualitative agreement with concentration based on the effective shape of the molecules at different temperature and concentration.

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