Hysteresis, adsorption energy

Hysteresis associated with item 3. Several possibilities a shift in adsorption energy, odd shaped pores, major and minor pores, distortion of the adsorbent... 

Block copol3nners form a new class of molecular composite materials by the phase separation of incompatible hard and soft segments which form their macro-molecular structure. Thermoplastic elastomers where the soft segments form the continuous phase have been extensively investigated by means of an adsorption-interdiffusion (A-I) model for the interfacial phase which bonds the hard and soft phases. The molecular structure and rheological activity of the interfacial phase in thermoplastic elastomer block copolymers is shown to play a dominant role in nonlinear viscoelastic response, mechanical hysteresis and energy absorption. Creation of elastomeric microphases in epoxy structural adhesives has been recently identified with in situ block copol3nnerization between carboxy terminated nitrile (CTBN) rubber and the diepoxide. 

Table 16-4 shows the IUPAC classification of pores by size. Micropores are small enough that a molecule is attracted to both of the opposing walls forming the pore. The potential energy functions for these walls superimpose to create a deep well, and strong adsorption results. Hysteresis is generally not observed. (However, water vapor adsorbed in the micropores of activated carbon shows a large hysteresis loop, and the desorption branch is sometimes used with the Kelvin equation to determine the pore size distribution.) Capillary condensation occurs in mesopores and a hysteresis loop is typically found. Macropores form important paths for molecules to diffuse into a par-... 

Clearly, proteins with a high concentration of binding sites on their surfaces may adsorb in the proper orientation, resulting in a multipoint attachment and high adsorption-free energy, even without any conformational adjustment. Thus, hysteresis can be present in some systems even at very short contact times. Proteins with very stable tertiary or quaternary structures may not show significant time-dependence due to the low probability for conformational change. 

Adsorption and desorption of liquid molecules at the spreading or receding liquid are accompanied by the dissipation of energy and are thus one source of hysteresis [254,255], At this point we would like to point out the similarity between contact angle and adhesion experiments. Adhesion is dominated by the solid-solid attraction, while contact angles reflect the solid-liquid attraction. 

As shown in Fig. 2, the hysteresis region enveloped by the adsorption and desorption curves in fact contain many local minima of free energy (Kierlik et al, 2001), which makes the nature of hysteresis in such systems fundamentally different from the van der Waals-type capillary condensations in simple pore systems (Kierlik et al, 2001 Woo et al, 2001). In contrast to the conventional first-order phase transitions where there exist two global minima... 

The comparison of the hysteresis behavior in simulation and experiment, shows that the hysteresis is mainly due to the existence of metastable states rather than due to kinetic effects. The asymmetry in the freezing and melting branches of the adsorption curve is explained based on the Landau free energy surfaces. The Landau free energy approach is a powerful tool in determining the freezing temperature, nature of the phase transition, structure of the confined phases, existence of metastable states and origin of the hysteresis behavior. 

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