Size-selective separation

We have summarized our experimental and theoretical work in the study of pH, temperature and pressure dependent phase transitions in hydrogels. Our focus, on the mechanisms of swelling and collapse, suggests using the gels for size-selective separations. An application of poly(N-isopro-pylacrylamide) to produce soy protein isolate is described in detail. 

A possible separation protocol for a complex polymer mixture is presented in Fig. 4. The sample under investigation comprises molecules of different chemical compositions (different colors) and different sizes. In a first separation step this mixture is separated according to composition yielding fractions which are chemically homogeneous. These fractions are transferred to a size-selective separation method and analyzed with respect to molar mass. As a result of this two-... 

In general, metal colloid sols are referred to as monodisperse when the particle size deviates by less than 15% from the average value, and histograms with a standard deviation a from the mean particle size of approximately 20% are described as showing a narrow size distribution. The kinetics of the particle nucleation from atomic units and of the subsequent growth process cannot be observed directly by current physical methods. The tools of the preparative chemist to control the particle size in practice are size-selective separation [50c,52] and size-selective synthesis [42,12a,50,53]. 

Microporous membranes are often used in many processes to remove impurities or contaminants through size-selective filtration. The breath figures method also finds application in this field, specially the approaches that facilitate the easy transfer to other supports. Another prerequisite is the formation of through pores that penetrate from the top of the layer to the bottom and the use of ice support favors this fact. For example, highly uniform membranes of PS-h-PDMAEMA have been prepared with pores on the micrometer scale for size-selective separation. The films were prepared by casting at an air-ice interface and easily transferred onto other supports [219]. Miktoarm star copolymers with proper water wettability and mechanical stability have been used to fabricate separation membranes also using ice substrate [131]. Moreover, the breath figures approach has been employed to build polymer membranes on structured substrates in order to obtain hierarchically structured microsieves [208]. 

There is cimently a renewed interest in that field partly because of the nano-technologies emergence. Actirally the design of nano-porous open frameworks is a factor of this revival (Yaghi et al., 1996, 2004 Serpaggi et al., 1999) because these compormds are anticipated to exhibit good efficiency as far as size selective separation, catalysis and gas storage are concerned (Eddaoudi et al., 2002). 

Size-selective separation Controlled permeation of membranes—chemical valve 14, 29, 56... 

We investigated the deposited material using cryo-SEM to reveal the formation of a porous gel-like layer with relatively uniform pores (Fig. 13c-e). The structure was strikingly reminiscent of that of filtration membranes, motivating us to investigate the system as a size-selective separation membrane. Assuming that it possesses... 

Addressing the viability and versatility of water-based noncovalent polymeric materials, we have shown that hydrophobic interactions are adequate for creating noncovalent membranes for size-selective separation of nanoparticles and proteins. These membranes exhibit separation properties similar to their covalent counterparts. Unlike cOTiventional membranes, our systems are fuUy recyclable and more versatile, shaping a paradigm of water-based materials as a viable alternative to covalent systems. 

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