Langmuir-Blodgett films of polymers with fluorocarbon side chains as gas separation membranes

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منو

" Langmuir-Blodgett films of polymers with fluorocarbon side chains as gas separation membranes "
L. S. Song J. B. R. Lando, Charles E.

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1112543
Doc. No	:	TLpq303829391
Main Entry	:	J. B. R. Lando, Charles E.
	:	L. S. Song
Title & Author	:	Langmuir-Blodgett films of polymers with fluorocarbon side chains as gas separation membranes\ L. S. SongJ. B. R. Lando, Charles E.
College	:	Case Western Reserve University
Date	:	1990
student score	:	1990
Degree	:	Ph.D.
Page No	:	165
Abstract	:	Ultrathin Langmuir-Blodgett (LB) films were prepared using amphiphiles containing fluorocarbon side chains and hydrophilic spacer groups in the main chain to demonstrate their applicabilities as gas separation membranes. The solid substrates used for support included silicon wafers, hydrophobic microporous polypropylene films (Celgard 2400), and silicone rubber films. The pressure-area isotherms indicated that all the amphiphiles were able to self-organize into densely packed monolayers. The stability of the monolayer was evident by the lack of appreciable creep. The layer spacings of the fluorocarbon amphiphiles were determined by X-ray diffraction and Ellipsometry. The layer spacing increased with the copolymer concentration. The tilt of the fluorocarbon side chain was also evident in the measurements. The SEM photographs showed that the LB films of the fluorocarbon amphiphiles could bridge the pores of the Celgard 2400 support if the number of the LB layers was adequately high. A 50:50 mixture of CH4/CO2 was used for permeation experiments. While the homopolymers with no hydrophilic main chain showed no reduction in gas permeabilities, the copolymers with high monomer concentrations showed a good barrier ability due to the increase in interactions both between and within layers. A decrease in gas permeation with increasing number of the LB layers was observed. The gas permeability ratio of CO2 to CH4 was improved by coating the Celgard 2400 supported amphiphilic LB film with a layer of highly permeable but non-selective silicone rubber. The improvement in gas separation was attributed to the effective coverage of the micropores on the LB film by the silicone rubber coating. A model was developed to predict the permeation performance of the LB membranes with a laminated structure. The model correlated with gas permeability to the number, the thickness, and the porosity of the LB monolayers and the thickness of the coating material. The model predictions for CO2/CH4 separation agreed well with the experimental results obtained for silicone rubber coated LB membranes. On the other hand, the observed CO2/CH4 separation factors for the LB membranes without silicone rubber coating matched the square root of CH4 to CO2 molecular weight ratio, implying the dominance of the Knudsen mechanism during permeation.
Subject	:	Polymers
	:	Pure sciences