Association, chain-micelle

Block or graft copolymers in a selective solvent can form structures due to their amphiphilic nature. Above the critical micelle concentration (CMC), the free energy of the system is lower if the block copolymers associate into micelles rather than remain dispersed as single chains. Often the micelles are spherical, with a compact core of insoluble polymer chains surrounded by a corona of soluble chains (blocks) [56]. Addition of a solvent compatible with the insoluble blocks (chains) and immiscible with the continuous phase leads to the formation of swollen micelles or polymeric micro emulsion. The presence of insoluble polymer can be responsible for anomalous micelles. 

The strong cooperativity of amphiphile association into micelles is well established and for long-chain surfactants it is often a good approximation to consider micelle formation as analogous to a phase separation. Even if the concentration dependence of many physico-chemical properties, within experimental accuracy, is in concor-... 

Some clear solutions of cellulose, however, are in fact micellar. Clear, apparently purely physical solutions of cellulose are formed in 7V-methyl-morpholine A -oxide (NMNO) and anhydrous dimethylacetamide-LiCl, but they can give rise to anomalously high DP values, because of association of the glucan chains in so-called fringe micelles , in which a group of chains associate chain-to-chain but the ends are largely random chain (Figure 4.34b and c). 

Since the chain length of tallow components is essentially between C14 and Cis, the total number of different structures in the softener active exceeds 15 [26], The raw material also contains mono- and usually tri-tallow derivatives. Most of those molecules are not water soluble and do not associate into micelles, but form stable colloidal dispersions in water. Maltese crosses can be observed using an optical microscope under polarized light (Figure 12.7), revealing the presence of strongly birefringent particles, typical of liquid crystalline phases [88,89],... 

STRONG ASSOCIATION AND MICELLIZATION EQUILIBRIA OF LONG-CHAIN SURFACTANTS... 

Strong association and micellization equilibria of long-chain surfactants... 

In order to calculate the free energy of micellization accurately, one needs to take into account the enthalpic terms describing the interactions between the block copolymer and solvent, the free energy of the micelle (Fniiceiie), the mixing free energy (Fniix), as well as the translational entropy associated with micelles and free chains (5ni). 

Assuming that the differences between the interactions of the headgroups of amphiphiles with water in the monomeric and micellar forms are smaller than those between the respective interactions of the hydrophobic chains, it follows that the overall heat associated with micelle formation can be treated similarly to the solubility of hydrocarbons, i.e., in terms of the interplay between three major contributing stabilizing interactions,... 

Let us consider the formation of a micelle of volume v and surface area s by association. A micelle contains p molecules of the polymer composed of n segments. In the micelle the polymer chain is elongated by a as the diameter of a micelle increases, but the specific surface of dispersion is decreased. The free-energy change AG becomes... 

Vanin et al. studied order proflles of the perdeuterated laurate chain in chiral and achiral phases by means of deuterium NMR. The quadrupole splittings measured for the sequence of CD2 moieties are all quite similar for the nematic and chiral nematic phase the conclusion was that chiral distortions of the micellar shape must be very small. Their proposal for the mechanism behind the phase chirality is analogous to the one for polypeptides an asymmetric point charge distribution which in this case was speculated to be created by the chiral dopant on the micellar surface [19]. Radley and Tracey prepared samples from a racemic detergent and observed high fluidity, whereas those consisting of some enantiomeric excess showed a significantly increased viscosity [30]. But this is no proof for the association of micelles to necklaces. 

We have so far used two approaches to prepare architectural polymers from block copolymer precursors. Both approaches involved block copolymer assembly in the first step and chemical locking of the assembled structure in the second step. In Approach 1, the block copolymer undergoes intramolecular assembly in a block-selective solvent to yield single-chain micelles. In Approach 2, two block copolymers are used. Both of these copolymers that are used possess a short block that can associate with a corresponding short block in the other copolymer. The associated blocks are then stitched together chemically, in order to yield an architectural polymer. We will use two examples in this section to illustrate these two approaches. 

More recently, it was reported (29) that a graft copolymer carrying a donor fluorophore in the chain backbone and acceptor groups at the end of the side chains exhibited sharply increased energy tranfer when the polymer associated to micelles. 

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