Carbon backbone hydrophobic properties

One of the oldest and well-known thermosensitive polymers is poly(N-isopropyl acrylamide) (PNIPAm), consisting of hydrophilic (amide) and hydrophobic (isopropyl) groups on an aliphatic carbon backbone. PNIPAm has well-investigated LCST properties [154] and has been proposed for a host of applications, including its use in biomedicine [155]. Another commonly used group include pluronics [156], also known under the nonproprietary name poloxamers , which commonly consist of triblock copolymers of PEO and PPO, the ratio of which determines the HLB. 

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

In this type of membrane, as well as in similar products made by other manufacturers, the Teflon-like backbone is responsible of very high chemical resistance (due to the strong bond between carbon and fluorine), high hydrophobic characteristics, and good mechanical properties. The hydrophobic feature is useful to favor the expulsion of product water out of the cell, in order to prevent flooding phenomena, while the mechanical strength permit the production of very thin films (down to 50 pm). 

Snapshots of the final microstructure were analyzed in terms of density map profiles, radial distribution functions (RDFs), pore size distributions, and pore shapes. Figure 8.6 shows a snapshot of the carbon-Nafion-water-solvent (CNWS) blend. The interaction parameters of the carbon particles are selected to mimic the properties of Vulcan-type C/Pt particles. They are hydrophobic, with a repulsive interaction with water and Nafion sidechains, and semi-attractive interactions with other carbon particles as well as with Nafion backbones. 

Final microstructures obtained reveal a high sensitivity of carbon agglomeration and ionomer structure formation to the wetting properties of carbon particles and the strength of ionomer-carbon interactions. While ionomer sidechains are confined in hydrophilic domains, with a weak contact to carbon domains, ionomer backbones are preferentially attached to the surface of carbon agglomerates for the given hydrophobic type of C. As expected, the correlation between hydrophilic species... 

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