Polymeric membranes microscopy

In addition to enzymatic hydrolysis of natural lipids in polymeric membranes as discussed in chapter 4.2.2., other methods have been applied to trigger the release of vesicle-entrapped compounds as depicted in Fig. 37. Based on the investigations of phase-separated and only partially polymerized mixed liposomes 101, methods to uncork polymeric vesicles have been developed. One specific approach makes use of cleavable lipids such as the cystine derivative (63). From this fluorocarbon lipid mixed liposomes with the polymerizable dienoic acid-containing sulfolipid (58) were prepared in a molar ratio of 1 9 101115>. After polymerization of the matrix forming sulfolipids, stable spherically shaped vesicles are obtained as demonstrated in Fig. 54 by scanning electron microscopy 114>. 

The first three methods involve the measurement of structural-related parameters while the last one is a typical permeation-related teclmique. Both electron microscopy and AFM can provide qualitative measurement of membrane materials. Figure 7 shows the top surface of porous polymeric membrane observed by scaiming electron microscopy (SEM). The bubble point method and permeation measurement, on the other hand, provide quantitative information of membrane materials. 

Fig. 7. Visualization of top surface of a porous polymeric membrane by scanning electron microscopy (10,000x).

Khulbe KC, Feng CY, Matsuura T (2007) Synthetic polymeric membranes, characterization by atomic force microscopy. Springer, pp 216, ISBN 3540739939... 

This book concentrates on atomic force microscopy (AFM), a method recently developed to study the surfaces of synthetic polymeric membranes. AFM is becoming a very important tool for the characterization of synthetic polymeric membranes. The development of membranes of improved performance depends on the exact knowledge of the morphology of a thin selective layer that exists at the surface of the membrane. The control of the morphology of the selective layer is crucial for the design of synthetic polymeric membranes. With a relatively short history of only twenty-five years, AFM has firmly established its position as a method to characterize the membrane surface. 

Many experimental techniques have been used to examine the detailed structure of perfluorinated polymeric membranes. These include transmission electron microscopy [23], small angle X-ray scattering [24], Infra Red spectroscopy [25,26], neutron diffraction [27], Nuclear Magnetic Resonance [26,28], mechanical and dielectric relaxation [25,29], X-ray diffraction, and transport measurements. All these methods show convincing evidence for the existence of two phases in the perfluorosulfonate and perfluorocarboxylate polymers. One phase has crystallinity and a structure close to that of polytetrafluoroethylene (PTFE), and the other is an aqueous phase containing ionic groups. 

Khulbe, K. C., C. Y. Feng, T. Matsuura, Synthetic Polymeric Membranes Characterization by Atomic Force Microscopy. 2007, Springer. 198. 

The hole formation in the liposomal membrane after treating the vesicles with reducing agents can be demonstrated by the fast and complete release of eosin, a fluorescent marker. Final proof that the polymeric backbone of the uncorked vesicles does not collapse comes from scanning electron microscopy. Fig. 56 shows the spherical structure of the liposomes with holes. 

CARS microscopy has emerged as a highly sensitive analytical tool for vibrational bioimaging, predominantly, of lipids in membrane model systems [69, 81-84], live unstained cells [85-95, 43], and both ex vivo and in vivo tissues [26, 96-103, 43]. Examples of CARS imaging applications in the physical and material sciences include the study of fracture dynamics in drying silica nanoparticle suspensions [104], patterned polymeric photoresist film [105], drug molecules in a polymer matrix [106], and liquid crystals [107, 108],... 

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