Chain stiffening/stiffness

In Flory s original treatment, llmtra accounts for the increase of the chain stiffness when the temperature is lowered. Flory93 described this chain stiffening by... 

Glucose molecules can link together into chains, with each ring tethered to the next by a bridging oxygen atom. In one form, this is cellulose, the stiff material that gives the stalks of plants and the trunks of trees their structural strength. Chitin, a variation on cellulose, is an even stiffen material that forms the exoskeletons of crustaceans such as crabs and lobsters. 

Stiff polymers, such as polyphenylene, nylon 66, polyphenylene sulfone, and polyarylether ketone (PEEK), have relatively high Tg values because of the presence of phenylene and sulfone or carbonyl stiffening groups in the chain. 

The alternative method [46] of analyzing the data is based on the treatment by Odijk and Houwaart [36] of the excluded volume effect on the electrostatic stiffening of semi flexible chains. The total persistence length lt of a stiff polyelectrolyte is the sum of the intrinsic persistence length lp=hl2 and the electrostatic persistence length le,... 

An explanation for the poor movement in the absence of LC17 may be that the neck region of myosin is stiffened by the presence of the light chain and that a "stiff neck" is required for the generation of force and motion. 

Chain flexibility is determined by the ease with which rotation occurs about primary valence bonds. Polymers with low hindrance to internal rotation have low Tg values. Long-chain aliphatic groups — ether and ester linkages — enhance chain flexibility, while rigid groups like cyclic structures stiffen the backbone. These effects are illustrated in Table 4.1. Bulky side groups that are stiff and close to the backbone cause steric hindrance, decrease chain mobility, and hence raise Tg (Table 4.2). 

Chains of 8-AOB can be both stiffened and/or projected in off-angle directions when unsaturated groups are introduced. For example, a double bond places a stiff, bent segment along an alkyl chain. The liquid crystalline phase of 8-AOB is lost when an E or Z configuration double bond is placed near a chain middle (between C4 and C5 8(3)-D-AOB), but the clearing temperature - 356.SK for the E isomer and 354 K for the Z isomer, compared to 356.5 K for the saturated (parent) molecule - is affected only slightly [108]. By contrast, placement of the double bond at the ends of the alkanoyloxy chains (8(6)-D-AOB), stabilizes the columnar discotic phase which persists from 306 to 343 K [108]. 

We also note that the stiffness of our chains is lower by a factor of 15 compared to the theoretically predicted region. Some numerical discrepancy was expected due to the mean-field nature of the theory. May be, however, the theory also underestimates the stiffening the chains undergo upon ordering. When we measure the persistence length in the simulation defined by the decay of orientational correlation between... 

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